what performance mods for a n42 L28??

[datfreak]

What to do?

I'd like to knock the compression up to around 10:1 and I know flattop pistons will do this but they are very expensive- Ive also heard of people welding up the standard head and making the chambers smaller but that also sounds very expensive.

The other option is to use a 2.4l head- but then its got smaller inlets valves and it doesnt raise the compression much(not enough to be worth it).

Also what cam is everyone using? Ive read that anything bigger then a 280 degree cam on the street is a real bitch- I'd love to hear what everyone else has and how well it drives.(in a prev zcar I had a 284 degree cam and I thought it was really easy to drive but maybe it wasnt as big as the seller said it was).

Does any one have pics of the limits of porting a n42 head? Anyone done it DIY in this forum..please share info if you have.

Ive bought a l24 electronic dizzy of a skyline.. Ive still got to set it up.

Any other performance ideas??

[TKR514]

If you are worried about cost, realize that you will be stuck with "Premium Only" gas if you go to 10:1 or more.

A fun site on what to do is located at:

http://www.geocities.com/zgarage2001/z.html

Look under Performance Tips and it walks through engine, carbs, differential choices, etc.

Sounds like a fun project you're working on!

[texasz]

Just curious, but what would happen if you didn't run premium gas in a 10:1 ratio car?

[TKR514]

My guess would be pre-ignition when you get up to 10:1 or above.

My lowly 8.3:1 L28E recommends 91 RON. Upping the compression to 10:1 should require at least 93 pump octane(premium) to run whithout problems. That's what all the street strokers around here have to run..

[datfreak]

I was going to run it on optimax or BP 98- both of which are 98 octane(I have to run that on my turbo capri now anyway)

[Gav240z]

Basically the best way to get good compression from factory parts is to use the F54 engine block and the N42 head it gives you 10:1 compression roughly and you get the bigger valves and ports etc..

There is an engine calculator on this website under the download section if you can't find it I'll email it to you.

My car is running early E88 head off a 72 240z and F54 block get's 10:1 compression and has had a mild cam installed with ZX valves etc.. It goes pretty well in tune previous owner claims it had over 200HP but he was running tripple mikuni's I'm planning on setting up mine on the SU's and having the car get onto a dyno at a fuel systems place to get it running just right.

At the moment I get detonation on premium depending on if I open it up WOT and I try to avoid driving it in such a way that it will ping. Until i get her adjusted properly carbies wise anyway I believe it's running too lean.

Anyway an electronic dizzy does wonders to the way the car drives trust me it's bliss.

TexasZ if you don't run premium you will get pre-ignition as TKR mentioned which is basically when the spark is fired before the piston reaches TDC or just after. To get a car to fire on TDC is very hard btw, anyway this causes the car to basically work against itself and loose power not to mention it will destroy the pistons and could even put a hole in them.

If anything I've said is incorrect don't hesitate to correct me guys.

:classic:

[texasz]

Ok, you say that the F54 block is the block to have as many others have also said (seems to be an agreement on this)...good, I got one in the garage. You then say that the N42 head is the head to have, others have said this as well. However, I have also read that the P90 (NOT the P90a) head is the one to have. What's the difference? Why does there seem to be a debate on this? Which one REALLY is the better one to have? I do still want to be able to drive my car on the street, but want the best performance I can reasonably get without spending a fortune.

[Gav240z]

From what I gather the P90(I have one aswell) is the best engine head in terms of the way the combustion chamber is designed and it flows the best. This is because it was the Turbo head apparently I've heard the P79 head is identical but the non turbo head.

The P90A is the oddball because of the Hydraulic lifters that bleed and become useless because finding replacement through Nissan is near impossible especially here in AUS as we never got a Turbo ZX.

The reason we recommend the N42 F54 combo is budget. Basically you can mod most of the L series heads and get great results but it all comes down to how much you spend on the head.

The P90 is the best for turbo but it's hard to get higher compression without spending the big $$$.

:classic:

[texasz]

Yes, I have read that the P90 and P79 are almost identical except for the exhaust ports, on the P79 they are round with those little sleeves in them and on the P90 they are square. The other difference that I remember reading is one you already sighted about the P90 breathing the best of all the heads.

What mods would have to be made to the P90 head to make it better? You said big $$$, I will have to contact someone locally to see how much it would cost but have to know what to ask to have done first.

[Gav240z]

Alot of people don't actually want to change the head because they feel Nissan did alot of research on getting it right.

You could increase the size of the exhaust ports give them a polish etc.. but the main problem is it's difficult to get the higher compression ratio as it was designed the be a low compression engine for the turbo.

I'm hoping my P90 wasn't shaved to raise compression and that only the pistons were changed but even so it would only result in about 8:1 compression which I would believe as my high comp E88 feels alot different very torquey nice to rev.

Anyway I'm not an expert on the science of Engine heads still a learner hopefully someone else can chime in and give you a bit more detail on the subject.:classic:

[Brett240]

the get compression out of a p90 you need to shave the head at least 80thou i think it results in around 10 to 1 with flatops (if im wrong one of you guys knows the excact figures) i had my P90 ported and polished at the same time as i had it shaved for compression so im not sure of the cost of shaving the head but this would be the only cost in getting the needed compression. i wouldnt say its big bucks to get the performance from a p90, the hardest thing would be to find one (in Aus anyway).

[Gav240z]

Thanks Brett I was trying to answer questions where I wasn't 100% sure but looks as though I was nearly correct which is good :classic: . I have an early E88 on my car currently and I am pretty happy with it because there supposed to be almost indentical to the early E31's which had the high compression and good non emission controlled design that the later 260z especially heads had.

The E31 is a great head once you mod it a bit it suffers from small valves and ports but my engine has had the larger ZX valves installed and been ported etc.. to suit the L28 bottom end.

I would use my P90 for an N/A application but I would rather save it for a later Turbo project. It's a bit of an Um and ah decision to turbo my Z but the way I'm going I'll probably own 2 Z's again (Note I said again :classic: .) I currently only have 1 however and the spare engine isn't really in my way in the garage.

I suggest TexasZ that if you really want to learn about the L-Engine you have a read of the site posted above and go through a book called "How To modify your L engine" forgot exact title and don't have book with me but it talks about the things you can do to the L engine heads and I for one haven't read the whole thing just bits and pieces.

I've seen many different heads used for turbo Z applications even the E88 has been used with good results. I know of one Z putting out around 500HP with an E88 on it. What it really comes down to is budget. This owner decided to go with the E88 because he could get away with no emission controls in his state in the US if he had of used the P90 he would have to comply with the rules of that year of engine.

Anyway I'll leave it there if you have any more questions I can answer by all means ask.

:classic: