Randalla Posted March 28, 2015 Share Posted March 28, 2015 (edited) 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. Edited March 28, 2015 by Randalla Vague title edit Quote Link to comment Share on other sites More sharing options...
steve260z Posted March 28, 2015 Share Posted March 28, 2015 (edited) using the engine calculator I show just 8.7 compression ratio with the E31...unless I plugged something in wrong. Sorry..Had the head gasket in mm not inches. Are your headers/manifold square or round? That would impact your budget Edited March 28, 2015 by steve260z Quote Link to comment Share on other sites More sharing options...
Randalla Posted March 28, 2015 Author Share Posted March 28, 2015 (edited) Don't yet have the headers I will be using, but they will likely be jet hotted square port MSA headers. Edited March 28, 2015 by Randalla Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 29, 2015 Share Posted March 29, 2015 "Quench Area" exists in no L-Series with dished pistons unless the dish mirrors the combustion chamber...so there goes that rationale! The boom mom end having Flat-Tops...you could have this discussion. With dished Pistons you may as well just run what you got...the P79 flows well...and you won't have any problem with gas anywhere. Quote Link to comment Share on other sites More sharing options...
cgsheen Posted March 29, 2015 Share Posted March 29, 2015 Tony, - assuming there was an actual rationale for this engine builder - Why use dished pistons with this block / head combo? Building a turbo engine? Plus, will you guys that know these engines help get Randalla the information he needs. He's resistant to having anything done to the bottom end - IDK why... A few of us here in town have been telling him to swap the pistons for flat-tops. I'm sure he'd listen to someone who actually knows the "whys and wherefores" (not me...) and explains the course-of-action and benefits. Or, at least the difference between what he has and what he could have... Don't hate me Randy, I'm just trying to help! Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 29, 2015 Share Posted March 29, 2015 (edited) 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. You might measure the head height just to know more about what you have. Seems odd that a well-known engine builder would build an odd engine like what you describe. Could be that the heads been milled and everything is actually as it should be. And, as Tony D says, even if it is the low CR blend, it will run. Someone did that on another forum just to get a usable engine so that they could sell a car. Same combination, except it was the stock N42 block and dished pistons. Said it ran great, although they'd never had a good-running engine before so may not know "great", using the stock 280Z EFI system. You can always swap it later if it's a dog. Your real decision looks to be between money spent on pistons and rings, or milling the P79 and replacing valves, or buying another head. Edited March 29, 2015 by NewZed Quote Link to comment Share on other sites More sharing options...
DAW Posted April 26, 2015 Share Posted April 26, 2015 There would be one solution if it were me. Although the P79 exhaust ports don't match the L28ET manifold ports as they do on the P90 head, with the combination you have there (which by the way is terrible. the c.r. is only suitable for turbo or super charging). I'd port match the best I could and run a medium boost conservative turbo with an intercooler. Bear in mind that the 280ZXT did not have an intercooler. But you have to run the turbo (brown-top) injectors and ECCS for the turbo; or else you need mega squirt-type support. Or, you could adapt a fuel ignition mgmt. from a late model I6 type engine, like BMW por ejamplo. Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 26, 2015 Share Posted April 26, 2015 It's JSper Engines...right across from the Hiloday Inn... Been there... This is a commercial rebuilder, not necessarily a specialist builder of L-Engines. It's a typical domestic commercial rebuilder throwing what they had together with what fits. The O79 came with flat-tops for NA. The P90 came with dish tops for Turbo. If this isn't forecast to be a Turbo Application, you have the wrong bottom end for the application and it needs to be changed, period. Unless the trip is to Mexico and you plan on running 80 octane Pemex strained through your hat. He never states if it's a long black or short block he has...the head really is irrelevant until he accepts he has to strap a turbo on it to get anything out of what he has. In over a month since posting no re visitation has occurred by the OP...I doubt we will see much at this point. If it's a budget build forget the cam, forget the port and polish...it's all wasted money on the combination you have. Quote Link to comment Share on other sites More sharing options...
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