port and polished head?
 

I have an 83 280zx with a p79 head and I was wondering how much porting and polishing should be done to the head and intake to get the most performance. Any information would be great.

Thanks

If you just polish surface would be better than nothing, You have to be careful when removeing materail so you dont remove to much. I dont know of any spec's you could follow and not sure that there are any. I plan on a rebuild for my 83ZXT this winter and I plan on porting and polishing my head and intake as well. I would have head rebuilt then remove valves and polish away. Would only remove enough under valve seat area to make it smooth. On the port side I have heard people using the gasket as a guide, only open port as large as gasket opening I would go through the archives to check for other posts on this. Just remember this when you grind it out you cant put it back. I did find a good site that has kits to polish and port. Its at Ameduri Racing Products its www.fastpts.com. Good luck and let me know how yours comes out or if you find any more info on it............


Jimmys83ZXT

I was planning on taking it in to a machine shop and having it done but I just wanted to get a little more info before taking it in. Thanks for the help and I'll check out the website.

Hey guys. I normally stick to the early z section, but I thought I'd participate. My question is, is the P79 head the best one to start with? I'd think a p90, which comes with square ports on an NA motor would be better. It has the same combustion camber volume, so you'd still pass smog. I had this head with flat top pistons on my '77 and it was nice!

As for the porting, its been my understanding that the best thing to do is merely unshroud the valves and port match the ports. This does enlage the chamber a bit, put the compromise is worth it.

True. The P79 is not the best, but the P90 is hard to find and getting more expensive. P79 isn't all that bad. I think its better to have a closed chamber head with round exhaust ports than an open chambered head with larger square exhaust ports! (ok, the P90 is not open chambered, but the earlier Z heads were)

Power is found mainly on the intake anyway. Since you've got steel liners in the exhaust ports, just unshroud the exhaust valves and do your port matching on the intake. You'll be good. Shave the head, performance cam, advance cam to #2 position with a new timing set, and you're good to go.

I'm a bit confused. By closed or open chamber, do you mean volume? Unless its a typo, the P79 has the same camber volume as the P90, at 53.6 cc's, and the earlier castings, E88 and N42, have a smaller 44.6 cc volume, but compensated with a dished piston.

I have heard of guys removing the steel insterts, any truth to that? Difficulty?

http://www.zcluboftexas.org/128combo.html

The open or closed chamber is the shape and design of the chamber but not the size. The open chamber is a round dome shape. The closed chamber is a peanut shape with one side having a flat surface that will come very close to the piston on the compression stroke. This forces all the air and fuel mixture over to one side of the chamber (close to the spark plug). This allows for better combusion.

The web page below outlines the open and closed chambered heads of the 4-cyl L-series engines. They look the same on the six.

http://www.worldaccessnet.com/~dcmur.../head_ID_2.htm

Thanks for the info. I doesn't happen too much anymore with the Z's, but I learned something new! What you say makes sense, but from you've said, and what I've read, the P90 is still the way to go.

All right, I spun a rod bearing, so I have new rings, bearings(rod and main),and new crank allready in the block. What should I do now to get more power? Which head? What should I do to the head and intake? Most power I could get without nitrous or turbo. Any help would be great.

True, if you want to do it right get the P90 to start with.

With your block, FastZ, make sure you're running flat top pistons still. Use a P79 or P90 head (which will be closed chambered) and shave the head 0.08 inches. Which is 80 thousanths.

Put in a mild performance cam, stage 1 or 2. With new timing components (new chain, tensioners, sprockets, ect) set the timing chain at the #2 position. This advance will correct some of the slack caused by shaving the head.

Do what you want with your intake and exhaust. Don't open up your exhaust too much. 2.25" is what I recommend.

I agree. If the fuel injection is being retained, only a mild cam is recommended. Also, I can't preach enough, use a single 2 1/4" pipe for street applications.

So are the heads basically the same? As in enough difference to make a difference?

i had thought that the best was to have a 82-83 block with an n42 head. is that right or should i now go find a p90? thay is for an n/a motor.

You heard the N42 was good because those heads have a smaller combustion chamber. They originally came with dished pistons in the older blocks so putting that head on the 81-83 block (with flat top pistons) will yield high compression without having to shave the head. I think about 10:1 compression.

...but they are open chambered and more prone to pinging. You may end up running high octain fuel all the time at that compression ratio just to fight pinging.

P90 is a better head in design, but when used without modifications it still has 8.8:1 compression on the 81-83 block. Shaving the head is the only way to increase compression ratio. well, besides doing other things more drastic.

ok, thanks.

i have a n42 head ready to swap into my zx. i guess i'll go ahead and use it. i don't mind using high octane fuel...i already try to anyway.
should i use 108 octane additives?
thanks.

only use the additives if you need to. Put high octaine in it and drive it hard and see how the engine sounds. Hopefully you won't need anything more.

arizona gas sucks. i can only find 92 octane here.
hope that is enough.
thanks for sharing your knowledge.

Oh well, we have 91/92 here in Washington too. I've seen higher octane in Canada but they pay for it!

Anyone now where I can get a good cam and timing gears mentioned in this thread. Got some money coming in going to start working on it again.:D

msa or stillen

If your looking for compression and resistance to pinging, get yourself a maxima N47 head. It came in 1981 to 1984 maximas and has the same cumbustion chamber shape as the P79 and P90, but the combustion chamber is only 40cc's. If you put this head on a flat top block, your compression ratio is going to be about 10.7:1. only things you need to do to it are put larger intake valves in it and I cleaned up the exhaust valve bowls a bit.

It does have the "evil Exhaust liners", but on an NA motor they are actually better than the square ports! this page will explain. I plan on running this set-up on my motor and I may get a mild cam to go with it. coltcams.com makes a nice grind for the FI 280's, its a 256 degree cam with almost half an inch of lift! that won't come til later.

hey speedgato! where in AZ can you find 92? all I have found is 91, I am in phoenix, by the way....

McAdam

i just kept digging and digging and digging and diging at the local scrap yards.

i'm in tucson

the yards in phx, out by the airport, are usually pretty well stocked, they don't have any there?

can you recommend any good body shops in your part of the state?

i want to get the msa II body kit put on.

thanks

hey mac
i just saw your post on clubs in az.
i go to phx a lot, are the people pretty cool.
ie. helpful with questions and recommendations?

thanks

thats a good question.....
Most of the poeple in the Desert Z Association are older. there are a few young people in there and there are a few guru's that know quite a bit, but for the most part, its old farts in thier Z's, lol.

I haven't met a lot of people from Datsun NIssan Drivers yet, but there are a few people on that board that know their stuff. If you have any questions, feel free to ask me, i know quite a bit, but I don;t think I have acheived "guru" status, lol!

McAdam

great.

thanks mac.