Building A L28 (Na)

[TheCrazySwede]

Keep up the good work. I'm doing a oem rebuild/refresh to a l26. My first full engine build ever.

Glad to hear! We're on the same boat on this one, haha.

[siteunseen]

So I visited the lads over at Rebello, and they advised against going for the P90, for a couple of reasons.

To start off, he mentioned how the quench pads in the P90 wouldn't leave much piston clearance if I went to flat-tops, and Dave had no idea how these motors made it out the factory.

He also mentioned how building a P90 head is not cost efficient at all, because you end up doing more work for not so much more performance.

What I was recommended was to stick with my N42, use flat-tops, and just compensate with a thicker gasket. I know there are some 2mm gaskets out there, but I can't seem to find one...according to OZDAT, it will give me a compression of 9.1:1.

I'm still debating if that's cutting it too close, running on Cali's pump gas. Would I have to run octane boosters? Do those things even work? Also, if anyone knows where I can find a good 2mm head gasket (getting the block bored .20 over, so I don't know if these things have to be retro-fitted after wards) I'd really appreciate it.

You've saved me a lot of reading/time/money! I'm keeping the one and only N42 head that I have.

[madkaw]

Wow- Rebello can't believe these engines made it out of the factory with the close piston/head clearance . Just having a hard time believing this.

I guess the extra clearance would be the safe route.

And I am not questioning Rebello s engine building capability, but to prefer an open chambered design head for piston clearance doesn't quite make sense.

[mdec]

"I'm still debating if that's cutting it too close, running on Cali's pump gas. Would I have to run octane boosters? Do those things even work? ..."

From my experience w/o question Octane Boosters do work if your select the correct brand. I have good luck with both NOS & AMSOIL.

I was interesting to hear what dave said about going with the N42 head & a thicker gasket. Is there some calculation/model around that can calculate how gasket thk varies the CR ?

[Diseazd]

Ditto that Steve! Are you sure you heard Dave right? Just by the fact that the head is shaved, assures you that you've got head gasket clearance at the least. My guess is he'd rather not go to the trouble to measure, shave .080 inches, then shim the springs and towers if he could avoid it by using the N42 head. Many, many people are using the stock and shaved P90 and P79 heads. I'm running four right now......absolutely love the combo.....no ping at any RPM either.

[TheCrazySwede]

Ditto that Steve! Are you sure you heard Dave right? Just by the fact that the head is shaved, assures you that you've got head gasket clearance at the least. My guess is he'd rather not go to the trouble to measure, shave .080 inches, then shim the springs and towers if he could avoid it by using the N42 head. Many, many people are using the stock and shaved P90 and P79 heads. I'm running four right now......absolutely love the combo.....no ping at any RPM either.

From what I understand, that's I was told. As many of you know, and I've addressed this in my post, I'm not very experienced in these matters, so whatever advice I get from people who know what they are doing, I tend to blindly accept it.

Maybe he told me about these things because he figured I wouldn't know too much about these things in order to work out a good combo, and he figured he'd save me a lot of trouble (and money) going with my own head, which I appreciate.

He did, in fact, address his concern about clearance level. There might have been a few details here and there that I didn't understand (too many numbers for me to follow!) so I might not be telling you guys all of what he said, only what I remember.

[TheCrazySwede]

"I'm still debating if that's cutting it too close, running on Cali's pump gas. Would I have to run octane boosters? Do those things even work? ..."

From my experience w/o question Octane Boosters do work if your select the correct brand. I have good luck with both NOS & AMSOIL.

I was interesting to hear what dave said about going with the N42 head & a thicker gasket. Is there some calculation/model around that can calculate how gasket thk varies the CR ?

Cool, glad to hear! I'll be sure to check those out.

The site I used for my compression calculations is this: OZDAT.com Engine Design Utility

Play around with the gasket height on that one.

[240260280z]

Wow- Rebello can't believe these engines made it out of the factory with the close piston/head clearance . Just having a hard time believing this.

I guess the extra clearance would be the safe route.

And I am not questioning Rebello s engine building capability, but to prefer an open chambered design head for piston clearance doesn't quite make sense.

Ditto for me. All of the E31 performance heads were welded and shaped like peanuts. (Have a look at Frank Honsowetz's Book). It was an evolved shape that was apparently adapted by the 280ZX P79 & P90 (and other Nissan products I assume) as well as on the Maxima N47 heads.

Edited June 18, 2014 by Blue

[TheCrazySwede]

So according to my calculations @ OZDAT,

If I grab my N42, have it bored .20", install flat-tops and a high lift cam and use a 2mm head gasket, I'll end up with 9.1 compression. (A 1.5mm gasket gets me 9.6 compression)

Now, a P90 head with the same layout (except with a 1mm gasket) gets me 8.7 compression. Without flat-tops, I get 7.5

That being said, on paper at least, doesn't the N42 head sound like a solid build? Many of you here have a lot of experience with these builds, so I'd really like to know what you guys think. Rebello suggested the N42 route, but I want you guy's opinions on the matter.

Again, I really appreciate all the help. As I've mentioned before, this is my first motor and my first "hands-on" experience with these things, so all of your help means a lot.

Thank you.

[Jeff G 78]

I have two flat top L28 engines. One has an N47 with 9.83:1 and the second is a P79 with 9.3:1. When I built the second engine, I skipped the N42/N47 heads I have and bought a P79. I think it's a better head that handles high compression better. Either head will work fine, but I chose the safe route and went with the more robust chamber design for my race engine.

[Diseazd]

I agree with Jeff.....Many have ping problems with the N42/N47....."0" problems with the modern chambered P79/P90 head.....even when running as high as 10:1 CR......but, it does cost more to mod up the P79/P90.

Edited June 23, 2014 by Diseazd

[TheCrazySwede]

Thanks for the input, guys.

Yeah, pinging is something I'd rather avoid. I'm just curious, but how are you guys getting such high static compression ratios with your P90/P79 heads? Would it require major work to get those numbers? I'm just using calculation tools, so they might not be 100% accurate, but I'm not getting past 8.8:1 with either one of those heads.

Would you guys mind sharing your secrets? I've looked around threads (and other forums) for builds with those, but every single one of them involves the builder knowing what he's doing, so they aren't asking the questions that I would be asking. Does anyone know a good build that wouldn't be too difficulty (although I am up for a challenge if needed) for a newbie to follow?