Picked up my P90 yesterday! I am still thinking a mild shave, flat top pistons, stock cam and ecu. 10:1 compression with a 1mm gasket. Port and polish while I'm at it.

Thoughts? Not worth it?

Sent from Canadia

Hi!

 

I am going to be rebuilding my 76 L28 this year and would like to know what pitfalls to be aware of in the process. I am planning on using a P90 solid lifter cylinder head and flat top pistons. I would like to end up with between 10:1 - 11:1 compression. We have 94 octane fuel in my area.

 

 

Picked up my P90 yesterday! I am still thinking a mild shave, flat top pistons, stock cam and ecu. 10:1 compression with a 1mm gasket. Port and polish while I'm at it.

Thoughts? Not worth it?

Pretty clear that you've already decided...

 

You haven't said if you've even driven the stock N42/N42 engine with dished pistons and 8.3 CR using the 1976 EFI system.  So if it doesn't run right you won't know if the EFI system is out of whack or if it's the modifications you're making.  You're going to end up with many unknowns on a primitive EFI system.  Could be fun if you like solving problems, not so much if you like bolt on and go projects.  I'd be interested in how the stock EFI system handles those changes but it will be hard to tell what's causing what.  Good luck.

Pretty clear that you've already decided...

I guess so. I'll get the head shaved and do the porting and polishing first. I plan on doing the body restoration first so I have about a year before I need to worry about the motor. With two complete motors, I can play around a bit.

Sent from Canadia

Well everyone has pretty much told you that the stock ECU will probably not handle this combo-but-good luck trying it.

By the way ,that combo yields 8.63:1 , so a mild shave probably won't be 10:1

Maybe you should find a local Z club and buy someones gas and dinner for a ride in a stock Z and make your decision then.

It might be tunable with some tricks, and timing adjustments.  Just be ready to make some changes.  And don't forget that noise and power might not offset gassy smell and dead spots in throttle action, for your wife, like they might for you.  Should be interesting.  

From another head thread...

I expect the same compression with a head shave.

WHAT DOES THIS RAISE THE COMPRESSION TO?

After running it for a year, I had the machine shop CC it when I had it off for my newest engine mod. They got exactly 46cc. That equates to 10.06:1 on a L28 with flattop pistons. At 500 miles my new motor showed 210-215 psi on each cylinder(!) But remember... this P79/P90 head mod is meant for flattop piston L28 motors only. If you use a dished L28, the compression will only be in the low 9s which won't be worth the trouble.

Sent from Canadia

As for the stock ecu, I agree I may have to stay with the stock motor config for now, but with two motors I may be able to source a triple weber carb setup for the P90 head combo.

Again I appreciate all the feedback guys. I am a member of the local z car club and have a lot of experience with 370's. The long winter an short driving season here have prevented me from taking advantage of a ride along in another members 280.

Sent from Canadia

I have driven old Z's and the newer 350z's. They really have very different driving experiences. I like the older feel of the early Z cars but I am sort of "Vintage" too. I would image a 280Z making reasonable numbers is gonna feel slow and unrefined against a 300+ hp tweaked 370z... my 2 cents

Charles

I have driven old Z's and the newer 350z's. They really have very different driving experiences. I like the older feel of the early Z cars but I am sort of "Vintage" too. I would image a 280Z making reasonable numbers is gonna feel slow and unrefined against a 300+ hp tweaked 370z... my 2 cents

Charles

 

I agree, it would be an unfair comparison. I really don't want to replicate the beast that is my 370.... I want something fun and spirited with a feel of history and authenticity. I also want to have a hand in the resurrection of this car and making it better than new.

I may have missed it, but I didn't see any mention of what you are planning to bore out the cylinders to in order to get the compression ratio you want. You have to bore it, Mill the p90, or use a different head, even with the flat tops, or find the unobtainable Datsun performance domed Pistons if you want the kind of compression you're talking about.

I'm doing a p90 / F54 with SUs and I think I'll be able to get mid to high 9s with .5mm over.

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Sorry I missed this post.... Been busy!

I think I will be using the stock N42 head on the stock build. The P90 will be a project for the performance block later. Needs more research.