Need Experienced Opinions ??

[Sboxin]

Its time to refresh our 3.8L 964 race engine. Here are a few photos of valves, spark plugs and heads. We have about 70 hours of run time but some are warmup time - the rest are race time 5000 to 6500rpm and a bit to 7200rpm

Do the plugs and valves look like a lean running condition - we are using a SW dyno tuned Motronic chip/ECU at a level 13 AFR - stock intake and custom exhaust headers ?

We seem to have a head lifting condition showing exhaust head leakage - what do you think. Some think this is from an overheated combustion chamber caused by a lean fuel condition - What do you think? We are using Supertec head studs and none were loose. We have sent the stock 964 fuel injectors out to be tested and cleaned thinking this may cause a lean condition - and will add an O2 sensor/gauge data logging system when putting the engine back into the car. Some racers have upgraded the injectors to a Lucas 24# that may run a bit rich at high RPM - what do you think ??

Also, the engine has JE 12.5CR pistons and Webcams 20/21 cams running on 100octane unleaded race fuel (to try and cool the combustion chamber/heads)

The crank, rods, heads and pistons are at Ollies with flywheel for testing, cleaning and balancing and new exhaust valves.

The rod bearings need to be replaced because of minor damage - the crank bearings are fine but will be replaced anyhow. We will also replace the piston rings.

Our engine builder is Don Jackson Enterprise here in Phoenix - they built this engine in 2012 and refreshed in 2016. My son drives about 6 races a year now that he has young children :-)) He plans to drive at NASA Nationals at Laguna this September.

Thank you for input to my questions.

Regards,
Roy T

[r lane]

I think 100 octane is not enough for 12.5 to 1. I also think that with that compression, the heads wil l bow. The stud spacing compared to a 3.0 or 3.2 is greater. Don't know what you can do about that other than lowering the compression.

[Sboxin]

Originally Posted by r lane

I think 100 octane is not enough for 12.5 to 1. I also think that with that compression, the heads wil l bow. The stud spacing compared to a 3.0 or 3.2 is greater. Don't know what you can do about that other than lowering the compression.

r lane - -
Thank you for your response. I agree that the 964 heads are a weak link in these race engines and Steve Wong said so before he started the Dyno tune process - that's why he tuned for a lower HP than the engine could produce at max power settings - - we dyno at max 277 RWHP and 255ftlbs RWT and have had the same set up for 10 years running this engine with no head damage. The 100 oct fuel is more to cool the heads than to get max HP from the 12.5CR pistons.

We will know more after getting the fuel injectors tested and cleaned - - and when our engine builder talks to Henry about the heads lifting with the Supertec head studs.

Regards,
Roy T

[Mixed76]

Better pictures of your heads, their corresponding cylinders, and what you are interpreting as signs of the heads lifting would help.

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[Sboxin]

Originally Posted by Mixed76

Better pictures of your heads, their corresponding cylinders, and what you are interpreting as signs of the heads lifting would help.

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Mixed76 - -

Sorry, these are the only photos I have - the heads and pistons are at Ollie's in Lake Havasu, AZ . . .

the engine builder is the person saying the heads are lifting but not sure why . . .
but suspect over heating due to lean fuel condition at high end RPM . . .

Regards,
Roy T

[Sboxin]

Thanks Ian, ( icarp ) for a great phone discussion about our race engine . . .

I'll post an update when we have more information about the heads, fuel injectors and measured combustion compression...

Regards,
Roy T

[winders]

If the engine really does have 12.5:1 compression, I don't see how 100 octane race fuel is enough even if you limit the revs to 7200 RPM or so. I would expect you to need at least 110 octane fuel.

Heads can "lift" due to detonation which is a likely outcome if you are not running a high enough octane fuel.

[Sboxin]

Originally Posted by winders

If the engine really does have 12.5:1 compression, I don't see how 100 octane race fuel is enough even if you limit the revs to 7200 RPM or so. I would expect you to need at least 110 octane fuel.

Heads can "lift" due to detonation which is a likely outcome if you are not running a high enough octane fuel.

Scott,
Thanks for your response. I responded to your PM - thank you your added information - we will be following up on your suggestions.

Regards,
Roy T

[Sboxin]

Finally - - engine going back together . . .

A few photos of assembly by Don Jackson Enterprise - Phoenix, AZ
Regards,
Roy T

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