U67 Cylinder Head Valves

Engine, Transmission and related drivetrain.
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D52E
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U67 Cylinder Head Valves

Post by D52E » 08 Feb 2019 14:32

I need some advice for a U67/L20B (0.5 mm to 1mm over-bore). The intent of this request is to decide on the best valve size option for the head.

The head will be used with a small Garrett GT2256 turbo. The head appears to have the original brass intake valve seats so I was thinking of getting new seats added. Since I was going to get this done I decided to get new valves. SI has intake valves in 43 mm, 44 mm and 46 mm. They also have exhaust valves in 35 mm and 38 mm.


What valve sizes would be best for this combination? Keeping in mind that I plan to bore the L20B to 0.5 mm or 1.0 mm at this time and I'm not sure what the requirements would be for un-shrouding the valves in the combustion chambers. I'm also not sure if going for the largest valves is the best move.
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abisel
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Re: U67 Cylinder Head Valves

Post by abisel » 08 Feb 2019 20:00

When I had my U67 head rebuilt:
  • Replaced all valve seats with steel 'cause one of the brass seats had come out.
  • Replaced the 43mm intake valves with 44mm.
  • Left the exhaust valves stock at 35mm. There isn't very much room to up-size the exhaust valve, but you can ask the folks rebuilding the head.
  • Ported the intake and exhaust runners to match the intake/exhaust gasket dimensions.
  • Installed a WebCam 91 camshaft with all new valve train components including new lash pads to match the new cam.
I have a pair of Weber 40DCOE carbs that needed new jetting to go with the modifications to the head. Took some trial and error to get the right jet sizes. And advanced the timing to 10 Degree.

Have a stock exhaust manifold and 2.5" exhaust.

Car runs like a stripped butt ape.

iceman510
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Re: U67 Cylinder Head Valves

Post by iceman510 » 08 Feb 2019 21:03

If I recall correctly without consulting the book, sizes 44 In and 38 Ex are considered typical upgrades, which I also believe are the 280 engine valve sizes.

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D52E
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Re: U67 Cylinder Head Valves

Post by D52E » 11 Feb 2019 07:06

So far I’m leaning towards 44 mm intake due to bore size creating shrouding. I’m still debating about 35 mm or 38 mm exhaust.

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abisel
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Re: U67 Cylinder Head Valves

Post by abisel » 11 Feb 2019 07:48

A couple more things to consider with your U67 head rebuild.

Don't forget to install bronze valve guides. Get rid of the old steel guides. https://www.ebay.com/itm/Valve-Guides-I ... 2435299451

Get ARP head studs to replace the stock head bolts. For my L20B engine, the part number for the ARP studs is 202-4201. They will torque down better than the long OE head bolts. Be sure to clean out the threaded holes in the block to get rid of any crap that may be at the bottom of the holes. Use a tap if necessary to chase the threads.

Depending on the mating surfaces of the block and head, you may want to consider the K&W Copper Coat spray copper head gasket sealer (old-school gasket sealer that still performs well). I had a minor water leak the first time I did a head gasket that was fixed by using an ITM head gasket (p/n 09-40520 for the L20B) along with the Copper Coat. But first, I removed the coating on the new head gasket with lacquer thinner and then applied a light coating of the copper spray to both sides. Waited for the copper spray to become tacky before assembly. No leaks at all.

Also depending on how much material was removed from the top and/or bottom surfaces of the head during the rebuild, you may need to install shims under the cam towers. https://zcardepot.com/products/cylinder ... ISDfD_BwE#

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