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Discussion Starter · #1 ·
What kind of power will I get by bolting on and retuning for a stock p90 head with 10: 5: 1 ratio to my mostly stock 73 240z block? I have Ztherepy SUs with SM needles, and 6 to 2 headers with a 2 1/4" exaust system, also a zx distributer with a blaster 2 coil. Do I have to run premium gas?

What power gain, should I say..

just curious....
 

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Thats a hard thing to say. In my experience I saw only a 5-10hp gain from going from stock 8.3:1 compression vs 10:1. Actually what happened is it was my 280z set up vs a friends 240z with L28 set up. Our engines were very similar except for the compression and he had dual SU's compared to my EFI. Others will argue that higher compression will give more power but I have no basis for saying so. All I can say is what I saw that day at the dyno shop when both of us went. Both of our cars were dyno tunned to reach max hp while using the best hp and torque curves for it. I would say low end would be a 5hp gain and high end would be 20hp. Of course this relies on many factors such as other mods. Being that this is on a mostly stock car I would say you'll probably be in the lower range of the gains. On the other hand if you were to add a cam while doing the higher compression it would make a much better set up than just the high compression alone. See what other more experienced guys say like Tony D, Norm the 12 sec dude, Steves280, Pallnet, and a few others. In short I would do it as it can only help and set the engine up for more mods later. As for the gas issue with 10.5:1 chances you are going to need to run premium gas, especially once you tune the car which will require playing with the timing. Small price to pay for a better ride.
 

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http://www.bgsoflex.com/crchange.html

Looks like about 10HP if you don't change anything else. Might not -sound- like much but that's a bunch more than a header is likely to give you. And yes you will be using premium fuel, that's why they sell it, for high compression engines.


If you have a hot cam, it can be the difference in good performance and the car being a dog. BTW a P90 head isn't going to raise the compression on your engine, it's going to lower it. You'd be WAY better off getting a 2.8L flat top piston bottom end than trying to make power out of a 2.4L
 

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I have an f54 with flat tops and an n42 head, this is apparenty 10 compression and its not that fast at all... i have never dyno tuned it but i have set the timing to the book and all other bits and pieces mentioned in the haynes manual.

So yeah i probly wouldnt get to excited.

Mat.
 

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You're going to have a VERY hard time getting to 10.5:1 CR with a P90 head on an L24. Stock P90 on L24 => 7.6:1, and the "standard" .080" shaved P90 only gets you to 8.6:1 on the L24. You might consider the head from an earlier 240Z (E31, '71 E88, '72 E88) or a 280Z N42 head to boost your compression. Or you might just save your money and effort for an L28.
 

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Discussion Starter · #7 ·
Hmmm,
So an N42 will give me higher compression?
And the 73-74 E88 is lower compression?
I'm planning on getting a cam in the future as well, so I want a head with bigger valves.
The # 1 reason I was looking for a P90 is because they have hardend steel seats and guides. And I was hoping to find a head that had these so I could buy it used for relitively cheap and bolt it up without too much expence. Hmmmm, I can't afford to pay the cost of upgrading to hardened steel parts, typical machine shops charge 150 for installing seats and 250 for valve job. plus parts.
 

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Ive said it before and Ill say it again, go get yourself a Maxima L24E N47 head. it has chambers about the size of the E31 head, but they are the same shape as the P90 and P79 chambers. will give about 9:1 on a stock flat top L24. It will have the hardened steel valve seats, but it will also have exhaust liners, which arent all that bad. It will have bigger exhaust valves, but you will need bigger intakes. any N47 or N42 intake valves will work.

McAdam
 

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Discussion Starter · #9 ·
yes, that would be a good setup, but I need square exaust ports for my headers. hmmm,
 

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Screw the square port headers. Go get an L28 with round ports, they will have steel seats and it's going to make much more power than the L24 will, even without headers. If you get an F54 block version, it will have flat top pistons which will make later modifications easier. The round ports flow just as well as square unless you port the crap out of the square port head.

There is no replacement for displacement. IMHO you're wasting your time hotroding an L24.
 

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A square port exhaust manifold or header will work on a round port head.

I would use a 1981 to 1983 L28 engine (F54 block and a P79 or P90 head) with a 260 or 270 degree cam (with the proper springs/ retainers/lash pads and resurfaced rocker arms). Call Delta Cams.

later up grade to a R200 3.90 gear and a 1981 to 1983 5 spd. A 2+2 flywheel/clutch would also be nice.

This will get your 240 deep into the 14's in the 1/4 mile.
 
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