TURBO Q & A FORUM
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///FiveOneOh
- Posts: 2136
- Joined: 23 Jun 2003 00:21
- Location: Abbotsford
I'm going with 7:1 just because I think if I try 10:1 I'm sure I'll blow soemthign up. least thats with the L
as for my KA. I've have been told that you can safly run 7 pounds of boost on a stock KA24E with a VG Gerrat T3. what do you guys think? should I risk this? I was going throw a Nismo head gasket on there just to add a little more strength. The stock KA isn;t fast enough. after watching Keith blow past the Ka cars on the track day videos I'm not impressed.
as for my KA. I've have been told that you can safly run 7 pounds of boost on a stock KA24E with a VG Gerrat T3. what do you guys think? should I risk this? I was going throw a Nismo head gasket on there just to add a little more strength. The stock KA isn;t fast enough. after watching Keith blow past the Ka cars on the track day videos I'm not impressed.
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turbo510sss
turbo Q and Q forum
510rob wrote:hmmm, lots of questions need lots of answers... in no particular order, here we go...
MOTORS
In a nutshell, L-series engines have REALLY strong cranks and blocks with REALLY shitty exhaust ports in the heads sitting on top of them (unless you were lucky enough to get the FP head kit, or an FIA head kit). They were built in the era PREDATING Finite Element Analysis (FEM), which basically makes everything as light and cheap as they can possibly get away with making it, which also means it breaks when you try to hot-rod the shit out of it... so they have heavy, over-built parts everywhere, and most importantly, A GOOD OILING SYSTEM... (the oil system has nothing to do with FEM either way)
with all of that said...
The L18 is same bore as a L20, but has a shorter stroke. So the L18 will theoretically rev higher than an L20, but it is a largely academic argument will little quantatative basis in the real world... so go for the L20 if you have both of them (L18 & L20) sitting in front of you.
I have seen L16 motors running up to 9500-10000 on a dyno (that sounded COOL!!!), and they were making just short of 200HP - that is a far cry from the new generation of 4-valve engines like the Toyota 4AG series that are making around 245HP in the Atlantic series formula cars... BUT!!! The toyota Atlantic motors only have three true stock Toyota parts - the block casting, the head casting and the valve cover casting, EVERYTHING else is aftermarket, and the cost is frightening ($15000US for a motor) On the other hand, those Datsun L-16s had lots of modified stock parts in them, and did a remarkably good job with those pieces... (and cost at least a little bit less, and lasted longer) (another side note, I had a chat with an Atlantic engine builder once, who told me a GOOD Altantic motor will make 245HP at the start of the race, and will be down to about 220-215HP at the end of the race, which is only about 30 minutes long, so think about that kind of durability...not very good if there's no prize money or sponsorship involved!)
I remember another old full-tilt dry-sumped "L-series" motor built around a Z24 block, Z22 crank, and fully modified and welded up U67 head. This motor ran to 8000rpm, with about 14:1 compression, and Ti valves and everything else (for those that ever saw one, it had that CRAZY old Electramotive L3 cam in it) - the lifespan of the crank was only about 12 hours at best before the fatigue cycling would get to it and it would start to crack from the inside out... this motor made somewhere between 215-235HP, and had HUGE torque output...
I know of a turbo L20 that had 13 YEARS on it before being rebuilt (Bert Vorgon's contraption) - depending on it's different configurations over the years, it was always making well over 250HP... and approaching 300HP by the end of the 13 years - THIS MOTOR NEVER REVVED OVER 8000RPM, AND ONLY EVER DID THAT HIGH RPM FOR A FEW SPURTS... it mostly stayed around 7000-7500 rpm... and lasted and lasted and lasted...whilst making very high torque numbers
Think about these facts...
raising RPM will kill the motor faster (exponential increase in mechanical stress loads with rpm change)
bigger motors make more power (yahoo!!!)
if the rpm increase of a smaller motor doesn't offset the increased displacement of the bigger motor, it's a waste of time...
So, with that said, run a big motor, and forget about RPM unless you are stuck by the rule book and you have to run a certain volume of motor...then you worry about running in the expensive RPM range (making decent torque/horsepower at over 8000rpm can get expensive very quickly!!!)
TURBOS AND COMPRESSION RATIO SUBJECT
Lowering your static compression ratio will let you run at a slightly higher turbo pressure ratio before the onset of detonation for your particular setup, but you will sacrifice throttle response below turbine range if you do it (drop the static compression a point or two)
Conversely, if you bump up the static compression, the motor will be more snappy off boost, and you will gain horsepower on boost; as the static compression drops, the unswept volume increases... take a 2000cc motor for this example
2000cc, 14:1 compression = 143cc unswept volume
2000cc, 10:1 compression = 200cc unswept volume
2000cc, 8:1 compression = 250cc unswept volume
2000cc, 7:1 compression = 286cc unswept volume
If you take the turbo into consideration, as soon as the valve opens, the turbo blows charge into the chamber and cylinder, so if you have a bigger unswept volume, it kind of adds to the displacement of the motor... so the 2.0L 7:1 motor is actually a 2286cc equivalent displacement, and the 2.0L 10:1 motor is a 2200cc motor... (remember - bigger motors make more power) Where's the trade off? You need to get the turbine turning and the compressor spinning before it will be a 2286cc motor system; until the turbo is making decent boost, the motor is only a 7:1 2.0L over-cammed wimp!!! On the other hand, if you had picked 10:1 compression, it would be a tough street motor until the turbo kicked in, then it would be an even tougher motor with the turbo...
The Porsche turbo cars from the late 70's would typically run around 7:1 compression, and lots of boost - that was their preference, and they won lots of races that way...
The first production turbo passenger car was the 1962 Oldsmobile F-85 with the optional Jetfire motor - 215ci (3500cc) all aluminum motor, 10.5:1 compression and about 5psi of boost...(read http://www.442.com/oldsfaq/ofjet.htm if you want more info)
Once again, it really depends on what you actually plan to do with the motor...and your personal taste...
EFI SUBJECT
Lots of people make good EFI computers - look for a management system that does away with the lousy distributor timing while you are at it because usually it doesn't cost much more with than without...
If you are trying to impress BMW and Porsche techies, buy a Motec system and hire them to come to your dyno site to tune it for you.
If you are on a budget, and at all sensible, seriously consider the SDS system - we've had great success with it on a maximum effort turbocharged SPM race car; we are totally satisfied with their system and their service, and I personally think they offer unbeatable value - all of the parts used in the system are top quality, and their service is unbelievebly good - they should be a model for other companies on how to keep customers happy, and keep customers...
TWM sells a complete intake setup to convert to EFI if you want to bolt straight money onto your motor with no fabrication time or work...
As far as an actual injector flow rate, that is really based on your planned HP output; 550cc injectors on a 300HP 4 cylinder motor are a good match for gasoline flow rates - alcohol applications will require about double the flow rate of gasoline applications.
Robert F.
Thanks for the info I will now be able to build my motor and now what i need to do for the most part on the turbo set up I might have more questions later as the build comes along. I called TWm inductions and they are going to be gewtting me a set up for my L series motor I am going to go with the L 18 since I have the block and maybe Just sell the L20 block I am going to be getting soon. well thanks for the info again and I will hit you up for more answers as I build the motor. thanks again Billy.
Turbo510SSS - glad to help where I can - any more questions, fire away...
Cam, as to your comment about a head gasket making a motor stronger: it doesn't work that way... the gasket has to seal two mating surfaces together primarily to hold cylinder pressure, and in no way can that piece make the two mating surfaces any stronger - the best way to allow ANY head gasket to do its job under increased pressure (i.e. any hot-rod conditions) is to o-ring either the block or head surfaces. If you've o-ring'd the block, the head gasket is not going to go anywhere, even if it's a cheapie - the expensive head gasket fad is just stupid in my opinion - you shouldn't be shimming up the head to drop the compression, especially with a shim that costs something stupid like $250 - put the money into the pistons or cams or something that actually can make a difference - besides, by shimming up the head a bit to drop the compression, you're decreasing the quench/squish band distance that will give you chamber turbulence, and more power, and more stable burning, and all the other associated goodness... (its all these little things that make up the difference between a winning motor and a losing motor...)
The weak point of the KA motors for high power applications is NOT the head gasket; it is the pistons and connecting rods... the connecting rod center to center distance is up around 6.5 inches long, and it does not have a very thick beam section. They look kind of like a little drinking straw with a piston hanging off one end, which is not what you want if you are going to make over 300HP.
For any high output motor, you have to start thinking about things in a HP per hole sense... if you want 300HP out of a 4 cylinder, each hole has to do make/take/endure a continuous 75HP... now look at the parts in front of you like the crank mass, bearing size, rod section, piston strength, yada yada yada, and ask yourself if they look like they will be able to withstand the loads associated with 75HP per hole...
150HP = 38 per...
200HP = 50 per...
250HP = 63 per... (now we are at 2 times the original designed output for an L20B, which is a pre-F.E.A. era motor)
300HP = 75 per... (now we are at 2 times the designed output of the KA24, which is a F.E.A. era motor!!!)
350HP = 88 per... (now we start getting close to 3 times the original designed output requirement of an L20B)
400HP = 100 per... (how long do you think stock parts will last at this point?)
The really crazy motor to think about it the old BMW M12/M13 F1 motor from 1980's turbo era... it was a 1500cc 4 cylinder making over 1100HP on a dyno!!! shoosh!!! That's 275HP per hole!!! Yeowch!!!
Robert F.
Cam, as to your comment about a head gasket making a motor stronger: it doesn't work that way... the gasket has to seal two mating surfaces together primarily to hold cylinder pressure, and in no way can that piece make the two mating surfaces any stronger - the best way to allow ANY head gasket to do its job under increased pressure (i.e. any hot-rod conditions) is to o-ring either the block or head surfaces. If you've o-ring'd the block, the head gasket is not going to go anywhere, even if it's a cheapie - the expensive head gasket fad is just stupid in my opinion - you shouldn't be shimming up the head to drop the compression, especially with a shim that costs something stupid like $250 - put the money into the pistons or cams or something that actually can make a difference - besides, by shimming up the head a bit to drop the compression, you're decreasing the quench/squish band distance that will give you chamber turbulence, and more power, and more stable burning, and all the other associated goodness... (its all these little things that make up the difference between a winning motor and a losing motor...)
The weak point of the KA motors for high power applications is NOT the head gasket; it is the pistons and connecting rods... the connecting rod center to center distance is up around 6.5 inches long, and it does not have a very thick beam section. They look kind of like a little drinking straw with a piston hanging off one end, which is not what you want if you are going to make over 300HP.
For any high output motor, you have to start thinking about things in a HP per hole sense... if you want 300HP out of a 4 cylinder, each hole has to do make/take/endure a continuous 75HP... now look at the parts in front of you like the crank mass, bearing size, rod section, piston strength, yada yada yada, and ask yourself if they look like they will be able to withstand the loads associated with 75HP per hole...
150HP = 38 per...
200HP = 50 per...
250HP = 63 per... (now we are at 2 times the original designed output for an L20B, which is a pre-F.E.A. era motor)
300HP = 75 per... (now we are at 2 times the designed output of the KA24, which is a F.E.A. era motor!!!)
350HP = 88 per... (now we start getting close to 3 times the original designed output requirement of an L20B)
400HP = 100 per... (how long do you think stock parts will last at this point?)
The really crazy motor to think about it the old BMW M12/M13 F1 motor from 1980's turbo era... it was a 1500cc 4 cylinder making over 1100HP on a dyno!!! shoosh!!! That's 275HP per hole!!! Yeowch!!!
Robert F.
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turbo510sss
engine componets?????
Hey I was wondering where and what companys sell Cranks, Rods, Pistons, Cams, Rocker arms, Ect. for the L18 motor 
Whats a good companys to look for I was also wondering what a good compresion ratio would be to run on the L18 with a turbo I am also windering if I can stroke and bore the block or should I stick with stock specs for better horsepower with a turbo I would like to know bec I want the block to handle about 10-15 pounds of boost for when I am at the track and be able to set it to about 7-9 pounds of boost for around town and not have to rebuild the motor every other month. Thanks again Billy. Also chekc out my web site as the project comes along.
Whats a good companys to look for I was also wondering what a good compresion ratio would be to run on the L18 with a turbo I am also windering if I can stroke and bore the block or should I stick with stock specs for better horsepower with a turbo I would like to know bec I want the block to handle about 10-15 pounds of boost for when I am at the track and be able to set it to about 7-9 pounds of boost for around town and not have to rebuild the motor every other month. Thanks again Billy. Also chekc out my web site as the project comes along.
Hey Rob,
Still have that 1800 of yours?
richard
Still have that 1800 of yours?
richard
richard norrish
'68 'goon resto / '71 ice racer / '72 'goon project / '70 4-door rust pile / '67 520 project
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'68 'goon resto / '71 ice racer / '72 'goon project / '70 4-door rust pile / '67 520 project
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shardik wrote: My swap will be made of solid gold and it will run on puppy farts.
Richard,
I still have the L-18; why? (hint hint hint)
Billy,
here's how to do it with an L-18 (or at least what I did)
MAGNAFLUX ALL PARTS BEFORE SPENDING ANY MONEY OR TIME ON THEM...
BLOCK - bore out the #2 & #4 oil passages in the block between the main gallery and the crank seats, as well as boring out the #2 and #4 bearing insert oil holes to match, otherwise the crank will not be happy, and the motor will not last as long... deburr the block, o-ring the deck, and lightly chamfer all the thread holes, polish and deburr the caps if you have time, and use ARP studs (because if nothing else, they just plain look nice!)
CRANK - take an angle grinder to the crank (yep, a big old nasty weld-grinding beast) and remove as much unnecessary forging shit and crap from the crank as you can (don't overheat the metal though), then start in with a die grinder, and smooth any and all sharp edges, and all rough machining marks - 4 cylinder cranks balance without bob weight, so try to keep the material removal even off opposing sides... take out the soft plugs, and CAREFULLY tap the gallery ends with a 1/16" NPT tap, and plug them with appropriate 1/16"NPT plugs. Have the crank balanced, and micropolished... WRAP THE JOURNALS WITH LOTS OF TAPE BEFORE YOU START ON THE GRINDING SO YOU DON'T SLIP AND FUCK UP THE JOURNAL SURFACES.
PISTONS/RODS - What I did is this... I bought CIMA/Mahle 85.5mm forged piston kit for VW type 1 motor, EMPI Teflon wrist pin buttons, and VW bronze rod bushing inserts... the stock Datsun pins are 21mm, the VW bushings are 24mm o.d., 22mm i.d., so I had the rods offset machined to bring the center to center down from 130.2mm to 129mm at the same time they were being opened up from 21mm to 24mm for the bushing inserts. The Mahle piston height is 39.6mm or something, (it was a while ago, and anyone with measuring instruments can easily repeat this...), so I decked the piston crowns by about .5 mm, for numbers like this...
130.2 + 38.1 = 168.3mm
129 + 39.6 - 0.5 = 168.1mm
DON'T QUOTE THE NUMBERS BECAUSE THEY ARE FROM 5-YEARS PAST MEMORY, NOT FROM RECENT MEASUREMENTS...
So, with the cam I have, I ended up with a assembly-using-modelling-clay measured 0.1" clearance between valves and pistons (that's about twice as much as a hype aspirated race motor should have)
The rods should be polished/deburred, and you might as well throw in some ARP rod bolts, and have them shot peened for sure, and all the regular stuff, or go big bucks and order up a set of Cunningham billet rods of you feel rich that day
CAM - Don't run much more than about 270 degrees exhaust, or you'll kill all the turbine's energy everytime the cam has it's overlap period and the intake side blows cold intake charge right through to the exhaust side. Once you max out the cam profile for a turbo motor, you have to start tuning it with the actual turbo... the cam gets more lift and duration as usual until you max the exhaust duration and the overlap period, but for a turbo motor if you need more rpm, you need tighter valve springs, lighter valves, and a higher flow turbocompressor, and a bigger intercooler, and and and...
My present cam is something like this...
Intake Profile
Duration: 280 degrees
Lift: 0.338” at the cam = 0.507” at the valve (1.5 rocker ratio)
Exhaust Profile
Duration: 256 degrees
Lift: 0.328” at the cam = 0.492” at the valve (1.5 rocker ratio)
Total Overlap : 48 degrees (low overlap)
Lash: 0.008” Intake, 0.012” Exhaust
(there is not much growth in those motors (L-series), maybe 0.001”...Give it 0.009” & 0.013” respective & then check it when it has warmed up...
...has very low overlap, early exhaust opening and intake closing...
(I'm going to bed... this took too bloody long to write)
I still have the L-18; why? (hint hint hint)
Billy,
here's how to do it with an L-18 (or at least what I did)
MAGNAFLUX ALL PARTS BEFORE SPENDING ANY MONEY OR TIME ON THEM...
BLOCK - bore out the #2 & #4 oil passages in the block between the main gallery and the crank seats, as well as boring out the #2 and #4 bearing insert oil holes to match, otherwise the crank will not be happy, and the motor will not last as long... deburr the block, o-ring the deck, and lightly chamfer all the thread holes, polish and deburr the caps if you have time, and use ARP studs (because if nothing else, they just plain look nice!)
CRANK - take an angle grinder to the crank (yep, a big old nasty weld-grinding beast) and remove as much unnecessary forging shit and crap from the crank as you can (don't overheat the metal though), then start in with a die grinder, and smooth any and all sharp edges, and all rough machining marks - 4 cylinder cranks balance without bob weight, so try to keep the material removal even off opposing sides... take out the soft plugs, and CAREFULLY tap the gallery ends with a 1/16" NPT tap, and plug them with appropriate 1/16"NPT plugs. Have the crank balanced, and micropolished... WRAP THE JOURNALS WITH LOTS OF TAPE BEFORE YOU START ON THE GRINDING SO YOU DON'T SLIP AND FUCK UP THE JOURNAL SURFACES.
PISTONS/RODS - What I did is this... I bought CIMA/Mahle 85.5mm forged piston kit for VW type 1 motor, EMPI Teflon wrist pin buttons, and VW bronze rod bushing inserts... the stock Datsun pins are 21mm, the VW bushings are 24mm o.d., 22mm i.d., so I had the rods offset machined to bring the center to center down from 130.2mm to 129mm at the same time they were being opened up from 21mm to 24mm for the bushing inserts. The Mahle piston height is 39.6mm or something, (it was a while ago, and anyone with measuring instruments can easily repeat this...), so I decked the piston crowns by about .5 mm, for numbers like this...
130.2 + 38.1 = 168.3mm
129 + 39.6 - 0.5 = 168.1mm
DON'T QUOTE THE NUMBERS BECAUSE THEY ARE FROM 5-YEARS PAST MEMORY, NOT FROM RECENT MEASUREMENTS...
So, with the cam I have, I ended up with a assembly-using-modelling-clay measured 0.1" clearance between valves and pistons (that's about twice as much as a hype aspirated race motor should have)
The rods should be polished/deburred, and you might as well throw in some ARP rod bolts, and have them shot peened for sure, and all the regular stuff, or go big bucks and order up a set of Cunningham billet rods of you feel rich that day
CAM - Don't run much more than about 270 degrees exhaust, or you'll kill all the turbine's energy everytime the cam has it's overlap period and the intake side blows cold intake charge right through to the exhaust side. Once you max out the cam profile for a turbo motor, you have to start tuning it with the actual turbo... the cam gets more lift and duration as usual until you max the exhaust duration and the overlap period, but for a turbo motor if you need more rpm, you need tighter valve springs, lighter valves, and a higher flow turbocompressor, and a bigger intercooler, and and and...
My present cam is something like this...
Intake Profile
Duration: 280 degrees
Lift: 0.338” at the cam = 0.507” at the valve (1.5 rocker ratio)
Exhaust Profile
Duration: 256 degrees
Lift: 0.328” at the cam = 0.492” at the valve (1.5 rocker ratio)
Total Overlap : 48 degrees (low overlap)
Lash: 0.008” Intake, 0.012” Exhaust
(there is not much growth in those motors (L-series), maybe 0.001”...Give it 0.009” & 0.013” respective & then check it when it has warmed up...
...has very low overlap, early exhaust opening and intake closing...
(I'm going to bed... this took too bloody long to write)
Hehe, I wish I knew what you were talking about.
Somebody needs to make a complete, yes, complete L-motor turbocharging kit... I think that would be pretty neat, and I'm sure there would be some good money involved for the one that decides to build up these kits.
Personally I'd love to have an L18 turbocharged over a newer, bigger motor.. keeps the 510-vintageness in tact, and the motor's are so damned easy to work on.
A question for somebody...
I was told that turbochargin a carburetated motor was pointless.. is this true? How does one go about doing this? I can understand how it works for SFI motors, but how about carbs? How the carb compensate for the added O2? Would it lean out as the boost goes up, or would you have to re-jet so you'd have a richer mixture at full boost, and a flood-type mixture for idle? How does that work?! I don't get it..
Can somebody shine some light on that for me? Thanks!
Somebody needs to make a complete, yes, complete L-motor turbocharging kit... I think that would be pretty neat, and I'm sure there would be some good money involved for the one that decides to build up these kits.
Personally I'd love to have an L18 turbocharged over a newer, bigger motor.. keeps the 510-vintageness in tact, and the motor's are so damned easy to work on.
A question for somebody...
I was told that turbochargin a carburetated motor was pointless.. is this true? How does one go about doing this? I can understand how it works for SFI motors, but how about carbs? How the carb compensate for the added O2? Would it lean out as the boost goes up, or would you have to re-jet so you'd have a richer mixture at full boost, and a flood-type mixture for idle? How does that work?! I don't get it..
Can somebody shine some light on that for me? Thanks!
Steve Boatman
Grants Pass, OR
1971 510 2DR | KA24DE
Grants Pass, OR
1971 510 2DR | KA24DE
How would a turbo kit solve the knowledge issue??
If you can't understand the previous posts, then maybe the turbocharger isn't the right thing for you. Turbo's might make a more efficient motor, but if you don't understand the mechanics of it all, you'll have a melted pile of junk, to say the least. And it will happen, under boost, faster that you know what hit you.
If you can't understand the previous posts, then maybe the turbocharger isn't the right thing for you. Turbo's might make a more efficient motor, but if you don't understand the mechanics of it all, you'll have a melted pile of junk, to say the least. And it will happen, under boost, faster that you know what hit you.
Love people and use things,
because the opposite never works.
because the opposite never works.
No no no.. you don't get it. Bleah.
I meant, what is the downfall of using a turbocharger, when using carbs? I know EFI is easy, the O2 sensor will pick up the added amount of air availiable in the engine, and it will automatically increase the amount of fuel, thus far making it so it won't lean out and you'd get maximum (or near) efficiency out of the charge.
I know how a turbo works, I just don't quite grasp how a carburetor can supply enough fuel at high-boost levels.. how does that work? EFI will automatically adjust to the amount of air and manifold pressure, etc, but how does it work with a carburetor? There is no computer there to do the math...
So, would it be a matter of re-jetting to a richer mixture, and run a slightly faster idle to keep it from flooding out?
I meant, what is the downfall of using a turbocharger, when using carbs? I know EFI is easy, the O2 sensor will pick up the added amount of air availiable in the engine, and it will automatically increase the amount of fuel, thus far making it so it won't lean out and you'd get maximum (or near) efficiency out of the charge.
I know how a turbo works, I just don't quite grasp how a carburetor can supply enough fuel at high-boost levels.. how does that work? EFI will automatically adjust to the amount of air and manifold pressure, etc, but how does it work with a carburetor? There is no computer there to do the math...
So, would it be a matter of re-jetting to a richer mixture, and run a slightly faster idle to keep it from flooding out?
Steve Boatman
Grants Pass, OR
1971 510 2DR | KA24DE
Grants Pass, OR
1971 510 2DR | KA24DE
Yes, I agree with Byron - turbochargers are not exactly a complicated device - automotive turbos only have about three moving parts for God's sake!!! BUT... if you have something set up wrong and hit the gas, they can fry a motor faster than you can say "WHAT THE F_ _C JUST HAPPENED?!?". So, once again, knowledge is the key to everything...
Now, as Steve requested, it's time to talk low-tech... carbs & turbos...
Remember these things...
internal combustion engines are glorified air pumps
air needs fuel to burn, and each fuel burns at peak efficiency with a specific mixture
if you put more air in, you gotta put in an appropriate amount of fuel to match
When things heat up, they expand
OK, great, easy, no problem, super duper...
So, a carb is a metering device that relies on venturi effect to develop a high enough gas velocity to cause a drop in pressure across the main "venturi", which causes a pressure gradient across the jet, which allows fuel to flow from high pressure side (float bowl exposed to atmpshperic air) to low pressure (intake vacuum + venturi vacuum caused by mass flow across small diameter section).
As you rev the motor up, it moves more air, and the vacuum across the jet is stronger... more fuel flows through the jet... at a non-linear rate...
If you turbo the motor, you can either set it up for "draw through" or "blow through"
Draw through puts the carb on the low pressure side of the turbo - in this case, you'll have worse response time, but a simpler setup for fabricating the intake system and fuel system... when the motor is running under boost, the turbo is an intermediate device between the motor and the carb, and it sucks air through the carb just like the engine would have done if there were no turbo there
Blow through puts the carb on the high pressure side of the turbo - better response time, but more complicated intake because you have to seal the carb from the regular atmosphere and expose it to an artificial atmosphere fed by the turbocharger... and the fuel system is more complicated because it has to keep ahead of the turbo intake pressure by whatever your fuel desired pressure is (for a Weber it's about 3psi, so if you want to run 15psi intake, you'll need 18psi at the carb - it's quite simple really)
Those are greatly simplified examples for this discussion, but they should serve to get anyone interested going in the right direction for their taste.
Now, why not turbo a carb motor? I don't know; why not? Bert Vorgon's car is carb's and turbo'd, and it has a long list of victories (some pretty prestigious ones to boot!) - it is blow through, and has been tuned over about 25 years to be at its current state of operation = lots of trial and error, and lots of work, and I'm sure lots of head scratching, but lots of smiles too!!!
Turbo Tom's famous turbo 510 was draw through, and he has lots of trophies for that car too
you tell me which one is better... they are neither better or worse, only different, like apples and oranges...
Oh yeah, the early Lotus Esprit Turbo cars are a twin side draft Dell'Orto 45mm DHLA carb blow through system on a 4 cylinder, and they were sold as a prestigious high performance car, so would you say it is not worth doing? Those are some friggin' quick cars too!!! BUT they were known for melting pistons at full throttle (and about 150-160MPH)
The problem with blow through is this (and I think this is what you were digging at Steve) - compression of air is a non-linear relationship as fas as density and temperature go. As you run higher boost (not even considering the non linearity of the actual turbocompressor itself), the air temperature, and therefore the charge density changes; the carb DOES NOT COMPENSATE FOR CHANGES IN CHARGE DENSITY - uh oh...that is bad (at least in a text book it is - the real world is like this - gasoline is quite tolerant of a wide range of charge mixtures, and the motor can take a pretty rich mixture, so give it a go becaue what have you got to lose?).
Steve, ask lots of questions
Now, as Steve requested, it's time to talk low-tech... carbs & turbos...
Remember these things...
internal combustion engines are glorified air pumps
air needs fuel to burn, and each fuel burns at peak efficiency with a specific mixture
if you put more air in, you gotta put in an appropriate amount of fuel to match
When things heat up, they expand
OK, great, easy, no problem, super duper...
So, a carb is a metering device that relies on venturi effect to develop a high enough gas velocity to cause a drop in pressure across the main "venturi", which causes a pressure gradient across the jet, which allows fuel to flow from high pressure side (float bowl exposed to atmpshperic air) to low pressure (intake vacuum + venturi vacuum caused by mass flow across small diameter section).
As you rev the motor up, it moves more air, and the vacuum across the jet is stronger... more fuel flows through the jet... at a non-linear rate...
If you turbo the motor, you can either set it up for "draw through" or "blow through"
Draw through puts the carb on the low pressure side of the turbo - in this case, you'll have worse response time, but a simpler setup for fabricating the intake system and fuel system... when the motor is running under boost, the turbo is an intermediate device between the motor and the carb, and it sucks air through the carb just like the engine would have done if there were no turbo there
Blow through puts the carb on the high pressure side of the turbo - better response time, but more complicated intake because you have to seal the carb from the regular atmosphere and expose it to an artificial atmosphere fed by the turbocharger... and the fuel system is more complicated because it has to keep ahead of the turbo intake pressure by whatever your fuel desired pressure is (for a Weber it's about 3psi, so if you want to run 15psi intake, you'll need 18psi at the carb - it's quite simple really)
Those are greatly simplified examples for this discussion, but they should serve to get anyone interested going in the right direction for their taste.
Now, why not turbo a carb motor? I don't know; why not? Bert Vorgon's car is carb's and turbo'd, and it has a long list of victories (some pretty prestigious ones to boot!) - it is blow through, and has been tuned over about 25 years to be at its current state of operation = lots of trial and error, and lots of work, and I'm sure lots of head scratching, but lots of smiles too!!!
Turbo Tom's famous turbo 510 was draw through, and he has lots of trophies for that car too
you tell me which one is better... they are neither better or worse, only different, like apples and oranges...
Oh yeah, the early Lotus Esprit Turbo cars are a twin side draft Dell'Orto 45mm DHLA carb blow through system on a 4 cylinder, and they were sold as a prestigious high performance car, so would you say it is not worth doing? Those are some friggin' quick cars too!!! BUT they were known for melting pistons at full throttle (and about 150-160MPH)
The problem with blow through is this (and I think this is what you were digging at Steve) - compression of air is a non-linear relationship as fas as density and temperature go. As you run higher boost (not even considering the non linearity of the actual turbocompressor itself), the air temperature, and therefore the charge density changes; the carb DOES NOT COMPENSATE FOR CHANGES IN CHARGE DENSITY - uh oh...that is bad (at least in a text book it is - the real world is like this - gasoline is quite tolerant of a wide range of charge mixtures, and the motor can take a pretty rich mixture, so give it a go becaue what have you got to lose?).
Steve, ask lots of questions
Yes, Keith's fuel pressure tracks the boost pressure - it is set for 3-3.5psi at idle, and then it follows whatever boost he's running as "boost psi + 3.5 psi". In amongst all of those little hoses, wires and doo-dads, there is an air pressure line connecting the "airbox surrounding the carb" to the "fuel pressure regulator". Keith's boost knob regulates air pressure, and the air pressure slaves the fuel pressure through the reference line ...the knee-bone's connected to the ...leg-bone ...the leg-bone's connected to the ... thigh bone ...the thigh-bone's connected to the ... you get the picture
It's a simple system really, at least until you start to screw around with the pressure over such a wide range; 3 psi is pretty low pressure, but once you start to get up around 20psi fuel pressure to run around 16-17psi boost (or whatever you are running +3psi), it is not exactly low pressure anymore, so there is a huge dynamic element there... some fuel pumps crap out at anything over 7psi, some pumps are unhappy below 10psi. On the far side of things, I've had a fuel pump literally balloon low cost rubber fuel lines and split them it in half (that was an observed and quantified 64psi at the pump, which was waaaaaaay too much). A little piece of advice for everyone who decides to start screwing around with turbos in any way, shape, or form; NEVER cheap out on any of the fuel lines in your car because the pressure become dynamic once you are running boost, and you've just introduced fatigue cycling to the tubing/hoses, so cheap hose will fail - and it's not a matter of if it will fail, its a matter of WHEN it is going to fail, because it inevitably will... and a pump capable of 64psi, blowing fuel everywhere is something the firemen might give you a knock in the head for when no one is looking, after they've had to douse your pride and joy with some of that nasty aluminum-etching dry chemical in their extinguishers...
I'm sure Keith would agree that one of the biggest key's to the success of his car has been getting the fuel system dialed in to perfection over the years - if your fuel pressure is all over the place, there's no point in trying to jet the carb, or adjust the timing in any scientific or logical manner... A GOOD FUEL SYSTEM IS THE FOUNDATION FOR A SUCCESSFUL TURBO INSTALLATION WITH A CARB
It's a simple system really, at least until you start to screw around with the pressure over such a wide range; 3 psi is pretty low pressure, but once you start to get up around 20psi fuel pressure to run around 16-17psi boost (or whatever you are running +3psi), it is not exactly low pressure anymore, so there is a huge dynamic element there... some fuel pumps crap out at anything over 7psi, some pumps are unhappy below 10psi. On the far side of things, I've had a fuel pump literally balloon low cost rubber fuel lines and split them it in half (that was an observed and quantified 64psi at the pump, which was waaaaaaay too much). A little piece of advice for everyone who decides to start screwing around with turbos in any way, shape, or form; NEVER cheap out on any of the fuel lines in your car because the pressure become dynamic once you are running boost, and you've just introduced fatigue cycling to the tubing/hoses, so cheap hose will fail - and it's not a matter of if it will fail, its a matter of WHEN it is going to fail, because it inevitably will... and a pump capable of 64psi, blowing fuel everywhere is something the firemen might give you a knock in the head for when no one is looking, after they've had to douse your pride and joy with some of that nasty aluminum-etching dry chemical in their extinguishers...
I'm sure Keith would agree that one of the biggest key's to the success of his car has been getting the fuel system dialed in to perfection over the years - if your fuel pressure is all over the place, there's no point in trying to jet the carb, or adjust the timing in any scientific or logical manner... A GOOD FUEL SYSTEM IS THE FOUNDATION FOR A SUCCESSFUL TURBO INSTALLATION WITH A CARB
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turbo510sss
Hey 510rob I was wondering can I use a electronic tuebo boost controller If I don't have a computer on my 510 since I am goingt o run a L18 or do I have to go with a manual boost controller? I was also wondering if Garrett turbos are any good? I am looking at a Garrett 60 trim turbo for $540 bucks here is the link Garrett 60 trim turbo. I also want to know what would be better the .63 or .48 A/R 4Bolt Rear Housing? Also whats a good wastegate and blow off valvue to run for a L18 turbo motor Whats a good set up to run for that aplication. Let me know what you thinkThanks again Billy.