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Randalla

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A few years ago I bought an extra L28 engine that had just been completely rebuilt by Jasper, but never fired. The engine sat in storage with my cars for the last four years and I've finally decided to do something with it. The block is an F54, with dished pistons, and the head that came on it is a P79. This combination provides a very low compression engine. The engine will eventually be transplanted into my 72 240Z. My goals are to increase performance over my tired stock L24, be able to run on premium fuel without detonation and to have the engine run equally well (relatively speaking) with my stock SU's or 40mm tripple Webers. I'm not touching the bottom end of the motor at all at this point, so the options are with the top end (head choice and upgrades). I'm well aware that the dished pistons may not be ideal for power but I'm trying to do this on a budget, while keeping this car very driveable. The head will receive a mild cam (approximately 270 lift) and no matter what head I end up choosing, ports will be polished and the valves will be unshrouded.

 

I have three heads, an E31, E88 and the P79 currently on the engine. With the dished pistons I know I need the E31 or E88 to up compression where I want to be, somewhere around 9.5 : 1. It seems the two heads each have pluses and minuses. The E31 has a smaller quench area, will provide slightly higher compression than the E88, but has small exhaust valves, which I'm assuming may be a detriment with the larger displacement L28. I've been told I can swap in L28 intake valves on this head but this would require cutting some of the combustion chamber away to accomodate them. This would also seem to compound the smaller exhaust valve issue.

 

The E88 head, with larger quench area can more easily be refitted with L28 intake valves and already has larger exhaust valves stock. It will however produce a bit lower compression motor than with the E31 head. I've been told there are two versions of the E88 head (an emission version and a higher compression version) but don't know what I have or how to tell them apart.

 

So, my question is what way would you go, and why, given my goals and pocketbook, Would appreciate any and all advice. Again, I'm not touching the bottom end, so please don't suggest replacing the pistons with flat tops. Thank you.   

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Have you looked around for an N42 or N47 head?  Might be the quickest, easiest way to get to the 75-79 L28 performance level.  Someone might trade you for one of those other three heads.

Edited by Zed Head
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I think you have your quench definition backwards. The 31 head will have more quench thus higher CR.

Popping on any early head (31 or 88) without having it rebuilt would be risky. Might as well have the larger valve on the exhaust done on the 31.

The 79 would be terrible compression like said.

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I'm doing an E31 now, or a machinest is.  They need the bronze intake vale seats replaced with steel, very basic start.  I am going with the big valves like your P79 has.  If you wanted to you could have the bottom of the P79 cut to raise the compression but you'd have to raise the height of the cam with shims to compensate.  Member "Dizeased" has done a few and loves them but he goes all the way with his, all new cam and valve train componets.  One day I'll hopefully be able to try his build.  :)

 

Here's a picture of one of his.

 

post-23570-0-26220800-1427544569_thumb.p

 

 

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I've looked at the write ups on using the P79 and modifying the cam towers and shaving the head but decided not to go that way for a variety of reasons. Madkaw, I should have also said that if the E88 or E31 are used they would be completely rebuilt, not simply bolted on. Siteunseen, will your E31 go on an L24 or L 28 block? Are you leavng the exhaust valves alone and only adding the larger intakes, or making  other changes as well?

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It has both of the larger valves.  It would bolt right onto a 2.8 block without any work but I'm putting it on the 2.4 block which requires some extra grinding so they won't hit the smaller bore of the 2.4.  Bore releifs, notching the block and valve releifs are some of the terms I've heard so far.  As for other changes I'm adding a better breathing cam coupled with it's accompanying componets.

 

I should add that a smaller cam isn't necessary, I'm just bored.  It's been a long winter.  :)

post-23570-0-29443500-1427061294_thumb.j
post-23570-0-60292400-1427061269_thumb.j
Edited by siteunseen
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A few years ago I bought an extra L28 engine that had just been completely rebuilt by Jasper, but never fired. The engine sat in storage with my cars for the last four years and I've finally decided to do something with it. The block is an F54, with dished pistons, and the head that came on it is a P79. This combination provides a very low compression engine. 

Who is Jasper, and why was the engine built this way?  Who made these choices?

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I wonder if it might not really have flat-top pistons.  That would change everything.  The dished pistons came with the turbo engines and P90 heads, so unless Jasper was mixing engine parts, the stock P79 configuration would be flat-tops.

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Yes, Jasper is a large national engine re-builder. And yes, the head is now off and the engine does indeed have dished pistons. I have no idea why the engine was built this way, but that's what I'm working with and why the question. No idea who made those choices. So...given all that, E31 or E88, with what modifications? Thanks guys.

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