Why Am I Getting Such Terrrible MPG?

[okayfine]

For all intents, the 510 fuel tank if run dead empty is 10 gallons ( depending on what manual you look at )

And the manual says the 510 tank is 11.9 gallons. If the OP's tank was "bone dry" when he put gas into it, then drove it until it started to sputter, there's could be ~2 gallons in the tank, affecting mileage calcs.

Keith's method for calculating mileage above is sound. Only better thing is to run the same loop multiple times to get a more accurate average.

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Also keep in mind that real, actual winter conditions increases gas use, especially with an engine build like you have. Winter gas also hits mileage.

[bertvorgon]

that's 10 gallons IMPERIAL.

http://www.convertunits.com/from/Imperi ... US+gallons
+ or minus a hair depending on if you fill RIGHT to the lip of the gas cap.

[okayfine]

Right, dead is dead, but gallons aren't necessarily gallons. Oy!

Datzenmike's 4mpg calculation is actually 3.3US?

[datzenmike]

Empty or not to begin with, he said $40 of gas. (tank could have been empty or several gallons left in it?) I guesstimate $1.20 a liter (could be less) but that's 33.3 liters or 7.32 Imp gallons to go 50Kn or 30 miles.... 4.091 PMG

In us measure that's 3.408 US MPG. That's off the scale bad or the gauge is reading low and there is more left in the tank than fumes.


If the mileage was out by double that's still 8 MPG
If the gas used was half that, that's still 8 MPG.

[McShagger510]

Hey 30something, when did Paul tune your car? If it sat for a bit, maybe the float in the carb(s) is hanging up. A light tap with a small hammer could feel it up. Also what do the plugs look like - wet, dry, tan, black???

I have run a similar engine setup (same M780 cam, high compression, dual 40 Webers, etc.) on a razoo L16 and got bad gas milage too. All depends on what you want: go fast and drink gas or tame it down & put around town. That cam is way too big for the street in my opinion. I remember the power coming on at 3500 rpm and going to 7000 rpm in my old engine. Below that it was a slug. My suggestion would be to install a 445 cam (from Colt Cams) and then have Paul re-jet the carbs. The car would be waaaaay more fun to drive, have nice bottom end torque and get better gas milage.

On the flip side, having an EFI 2.4 dual cam engine (KA24) in a 510 is nothing short of pure bliss ………….. from what I hear.

James

[30something]

Loving all the replies for my troubles. Thank you all. I truly want to get into this car every day going to work or what have you but this engine is going to put me in the poor house trying to keep fuel in it. Trying to put a smaller cam in this motor I don't think is the solution. As I put in my profile, I have done a total ground up restoration of a 1981 Toyota 4x4 pickup. No engine modification scares me. Wiring, engines, paint, fabrication bring it on! For the past week I have been on Youtube, Google, Wikipedia, the510realm researching everything. More info for me the better. would love to do a KA or SR swap. Not concerned over the extra weight, just want to get something that is more fuel efficient and still fun to drive. Here is the next set of questions:

1- How much is my motor worth?

2- How much should I expect to pay for a KA or SR motor an trans?

3- Are they easy to get or does anyone know of 1 for sale?

I even went to Pick and Pull today for their 50% off sale and the 92 280sx was looking a little pillaged.

Thank you for more answers and help.

[James]

Even with your motor, your mileage doesn't seem right. You didn't answer any of the questions in regards to spark plugs timing etc……..
Also - I would try the filling up method as well just to verify where things are really out.

[okayfine]

I truly want to get into this car every day going to work or what have you but this engine is going to put me in the poor house trying to keep fuel in it.

Then FIX IT! If you've read the replies here in this thread of yours, you should understand that the fuel economy you're reportedly getting is so far out of the range that we might expect - we think there's some serious errors in your data-gathering methodology. We can not conceive of an L-series engine built like yours that gets such terrible mileage. There is something wrong. It can be fixed.

People here in this thread have asked you repeatedly to gather more and better data to help us help you. You have not done so. There's nothing else we can do for you until you do so.

Seems it is time to link you to this:
viewtopic.php?f=1&t=16460

Here is the next set of questions:

All your new questions can relatively easily be answered by searching. Even a cheap (?!) KA swap will buy many, many gallons of gas for you to run in your current car.

[JordanTr]

1- How much is my motor worth?

2- How much should I expect to pay for a KA or SR motor an trans?

3- Are they easy to get or does anyone know of 1 for sale?

I even went to Pick and Pull today for their 50% off sale and the 92 280sx was looking a little pillaged.

Thank you for more answers and help.

2. Depends what you get. Piecemeal you will be around 4-600 for a KA and around thrice that for an SR motorset. If you get a 240sx parts car for the KA, the swap will be cost you -400 to -600 since you can make money parting out all the bits. Buying a PnP motor would be expensive methinks if you wanted all the little bits.

[McShagger510]

*ahem*

Hey 30something,

When did Paul tune your car?

If it sat for a bit, maybe the float in the carb(s) is hanging up. A light tap with a small hammer could feel it up.

What is the oil like??
Does it feel thin & smell like gasoline?

Also what do the plugs look like - wet, dry, tan, black???


Cheers, James

[okayfine]

FWIW, this blown big-block, 650HP-making monster got 9mpg US over an 1100 mile road trip:

[datzenmike]

The cam is a bit hairy to expect any good mileage. What differential ratio? 4.11 or 4.375 because these are bad for mileage too.

You don't quite say it but $40 to go 50Km??? That's about 7.3 gallons @ 1.20 / L so 4 MPG? Even if misreading the gauge by double 8 MPG is seriously bad. Check the plugs. If dry and sooty the carb(s) are flooding. Maybe fuel pressure is too high. Gas tank or gas line leak??? take a look.

What do the plugs look like. At 4 MPG they should be black.


If over 7 gallons was put in what did the gauge read? Did it drop steadily over the trip. Could the gauge be wrong? Maybe there's almost 6 gallons still in the tank.

In us measure that's 3.408 US MPG. That's off the scale bad or the gauge is reading low and there is more left in the tank than fumes.

This is so out to lunch that....

If the mileage was out by double that's still 8 MPG
If the gas used was half that, that's still 8 MPG.

Either the data is wrong or it's mechanical and can be fixed.

[McWicked]

I don't see anyway that the OP's car could be burning the equivalent of 4 MPG of gasoline. Either the calculations are off, or he's dumping a bunch of gas (either overboard or down the cylinder walls into the oil pan).

-McWicked

[upsman24]

Put a locking gas cap on it...... Your friendly neighbor is sucking your tank dry. There is no way in hell that motor is running good and getting 4 MPG. It would not run at idle. This is not a variable lift motor. Stop waisting everyones time. Fill the tank, drive the piss out it, log mileage and then calculate. Its that simple. Like someone else has said "JUST FIX IT".

[dp61]

Sell that useless motor! I'll buy it as a spare! Name your price!