DoTheDrew888

I am planning on doing a full rebuild on my engine. While I am in there replacing the timing chain and all that crap I want to put in a performance cam and get the head ported and polished. I have two questions 1) Can I use my P79 head on the N47 block with the dished pistons? 2) I have an engine out of a 1980 ZX in my car right now so I am going to need to buy the engine overhual kit from MSA for the '80 ZX. Will that cause any trouble when putting on the P79? One more thing, if anyone has bought the engine overhual kit from MSA can you tell me what all is included in it? Thanks a lot guys.

DoTheDrew888

I decided not to use the P79 and just use the N47 head. One thing I was worried about tho was whether a stock head gasket can handle an aftermarket cam. Is there anything I should be aware of before I put this cam in? Does anyone have expirience with aftermarket cams?

s/cL3.0

I have seen people use stock turbo head gaskets and push upwards of 300 HP on a turbo motor..I would assume a cam would not affect the head fasket.

lww

Due to the larger capacity of the P79 chambers (53.6cc's), you would have been running about a 7.3:1 compression ratio with dished pistons.

The N47 head will bring your compression back up to 8.3:1 with it's smaller combustion chambers (44.6cc's).

If you went to flat top pistons on the P79 you'd get 8.5:1 compression.

With the N47 head and flat top pistons, you'll get a 9.8:1 compression. This is what I ran on my 1980 SCCA Club Racer.

DoTheDrew888

Would I be able to run that high of compression on pump gas?? If so I might consider switching to flat tops while I have the whole thing torn apart. I think I have 3 or 4 flat top pistons from my old engine that didn't get damaged. If anyone has 2 or 3 flat tops they would be willing to sell I would be interested.

EatmyDust

Ok here is the deal you can run up to 11:1 on good pump gas, but not higher. I am sure youve herd of detnation. well the gas will start to ignight befor the spark plugs go off, wich will blow hols in your pistons. Yes your head gasket is fine with the performance cam I boght the stage three and did all the port and polish on my head as well, only I used an N42 of a 1976 280z wich gave me better exaoust releas. I allso put the performanc 3 in 2 headers, and this machine rors man. Make sure you do a good job at cleaning your head, and do a good valve job to. but remeber somtimes when you do a valve job a car might start to smoke.

DoTheDrew888

That is a very similar setup to the one I am going to have on my car. Do you have any performance info about that setup? Dyno numbers? I would be really interested in knowing what to expect out of this engine.

Also, I have decided to go with the flattop pistons to raise my compression and hopefully save some of the low-end torque I will lose with the cam. I have 5 flattops that are still in useable condition. Anyone got one flattop they would be willing to sell me?

DoTheDrew888

Also, I know when I replace the pistons I will need to use new piston rings, oil rings, and connecting rod bearings. Will i need to buy new main bearings also? Anything else I should consider when putting in new pistons?

Thanks a lot.

EatmyDust

Yes you have to change all your rings. that is standerd for piston replacement never use old rings on a new piston. and yes change all your bearings as well rod and mains. it will only be about $62. Make sure to keep the back of the bearings dry going in, and put some asembly lub on the babit when you put the crank and cam in. I would probably put a dial indacater on your crank befor istalation, jost to make sure it dosn't woble. torque to specs, and presureize your lubricationn sytem befor start up, unhook your coil surn over for 10 secounds to make sure the oil maks it to the galleries then hook the coil back up and start.
Oh yea and with the mods you have done you should be geting around 230 hp. not sure exactly, but close.

DoTheDrew888

Well, I was planning on doing this without pulling the engine. I wasn't going to pull out the crank shaft, just drop the pistons in from the top while the head is off. Is that a bad idea?

EatmyDust

Well I wouldn't say it's a bad idea, it just has to do with your work habits, and what kind of work you do. if it were my engine I would go ahead and put the main bearings in to warenty my crank life incase the old ones start to dump preasure. you know the bearings are so old already why not just replace them I call it preventative maintenance. you will be fine with the ones you have in ther. but like I sayed it depencs on how many miles you want out of your engine. Anything I say is going to be right by the books. I am a student at UTI, but I have also ben working on cars for a good wile befor I was even in high school. I don't know everything but I know how to figure stuff out and I can usually fix a problem. I am a pro Technition the best of the best. The steps I told you about the dial indacator and all that is only to get the max miles and life out of your engine, do not forget to plastigage your bearings on installation, if you don't you are looking for trubble.

DoTheDrew888

plastigage??? Please explain.

EatmyDust

Plastigauge is this stuff you buy at the auto parts store for oil clearance test. what you do is look up and figure out what oil clearance you are supose to have when you put your new rod bearings in, you put a little piec of that plastegauge on your rod jurnal and torque your rod cap to specs, then take the rod cap back off and measure the peic of squshed plastigage with the peice of paper that came with it, and that will tell you the clearance you have to little clearance is not a good thing and too much is not a good thing either. you run this test on each rod, and main jurnal if you want to be posetive about the shape your parts are in. I will say that I don't think you will run into any problems, cause these cars, or should I say engines were well built. it is all preventative, but if you are going high performance you have no exscuse for not do all of the things I have mentioned. if you spend all that money on those parts, and don't check those things you could have something rong, and just destroy those parts, and cost you even more money than it was befor, because you then have to corect the problem you had, and fix the damage it caused, if in fact the damage is reparable.

DoTheDrew888

Thanks for the advice Eatmydust. Very helpful.

DoTheDrew888

New question... Will using one rod from a differnet set then the other five throw off the balance of my engine? Is there ANYTHING else I have over looked in this project?

EatmyDust

well bood question I would think think that it would be ok, but I would tell you to weigh each one, and that should tell you a lot. Remember that your clearance should be the same, or really close to the other ones to be fine. just install it in the corect direction, (hint) or it wont be good.

DoTheDrew888

Ok, here is an update on the project. What I will be doing is rebuilding the engine. I am going to keep the N47 head and get it ported and polished. I bought a F54 engine with a P79 head and flattop pistons. I will be running the flattop pistons with the N47 head. I also bought a performance cam: .460 Lift and 270/280 duration. I have all the necessary parts to put it together so now im just waiting till I have time. Hopefully (if everything works out) I will have some 6-2-1 headers ready to go on before I am done building.

Now for a few questions....

LWW said that my compression with an N47 and flattops would be about 9.8:1 but I have read other places that it will be 10.4:1. First off, what is my compression ratio going to be? Second, will I be able to run on 91 octane gas with this setup?

Also, How much is an estimated cost for a machine shop to port and polish the N47 head? Has anyone had this done? If so, how much did they charge?

Lastly, I know that the F54 block is supposed to be better becaused of the siamesied cylinders but is it really THAT much better? I am probably going to use which ever block has the best cylinders (least amount of wear). Do you guys have any input on this?

Thanks for all your help,

-Andrew

theramz

The P79 and P90 heads have the same size combustion chambers so you will have 7.4 to 1 on the F54 block. Great for a turbo but not FI. The N47 will give you 8.3 to 1. You can increase this a little by milling the N47 head. You can get to 9.4 to 1 by using 240Z rods. Source of info-zhome.com. You will be able to run 87 octane with either.
I can remember when gas was 97 octane and 91 was the cheap ****. In the mid 60's "Flying A" sold 105 octane!

EatmyDust

Yes with the set up you want being the flat tops with the N47 head will get you like 10:1. you can run 91 fine, but no I wouldn't recamend milling your head with all thes parts, just think you have a over head cam, if you mill the head it brings the head closer to the block yes increasing compresion, but also increasing the amount of slack in your timeing chain. besides if you mill it then you can't run pump gas cause you will be around 12 or 13:1.

N47 block again is fine but you are right about going with wich ever one with less wear. the N47 head is harder to port out, because the sleves. can't give you an estimate on machine shop because well the econemy is different in different states. I know it will take a few hours to complete the jop. could cost around$250-$300 who knows?

DoTheDrew888

Thanks a lot man, you have been a big help. I wasn't planning on getting the head milled, just getting the intake and exhaust ports cleaned up a little bit. Other than that I was just going to put it all together and hopefully have some fun with it? I have read about similar setups getting between 190hp - 230hp at the wheels. Anybody have any estimates on my setup?

theramz

When you mill a head you shim the cam towers up by an equal amount. From what I've read you will never get over 9.5 to 1 with standard flat top pistons.

EatmyDust

You will be getting about 220 hp, or some place around that.thermaz you should talk to motor sports reps, some of them are geting like 13:1.

theramz

Yes, I would like them to tell me how to get 13 or even 10 to 1 with stock pistons!
Are we still not milling the head? I would love to contact them, do you have the source?

EatmyDust

the number is 1800-633-6331 talk to a sales rep, they can give you some names of some companys that will custom make sum pistons meaning convexed, and I will tell you it cost a little bit to have done but you never know till you try.

theramz

I guess we got off track from the original question. If you want real info from someone who has done all this for real go to http://www.kaynor.net/v8-240z/240z.htm. He will show you exactly what you get with the P79 P90 and N42 head. I called msa and they said JE pistons will make custom pistons per your supplied specs for around $150 and up each. It certainly pays to do your own homework since there seems to be a lot of wrong information out there.