Exaust Port Shape...

[texasz]

Ok, I an trying to figure out what shape the exaust ports are on different heads.

E31 - square

E88 - square

N42 - square

N47 - round

P79 - round

P90 - square

P90a - square

This information came from http://www.geocities.com/MotorCity/2824/heads.html as well as people in this forum.

I am want to make sure I know what I'm getting into here (my plan is to put a P90 on an F54 non-turbo block which will have flat-top pistons and carbs).

EDIT: Forgot to ask which is considered to be better, round or square exaust ports?

EDIT: I'm updating the list above as the answers come in.

[kmack]

I have an E31 and an E88 head sitting on my garage floor right now. Well, actually the E31 went up on the engine last night. Anyway, they both have square exhaust ports. Only the intakes are round.

[z-ya]

Your list is correct, and the P90a has square ports just like the P90.

Pete

[texasz]

Ok, the list of exaust port shapes is now complete. Thank you to all who contributed!!

Now the question remains as to which is considered to be the best port the round or the square?

[Zedrally]

I would guess the one that has the largest area?

Can everyone go back to the're heads and please measure.

[JEFF]

I am using a N47 ( round port ) with the steel liners removed.

It flowed 23% more air through the exhaust ports than the E88

that I had on before this one.

Bench flow tested at Diemler/Chrysler Tech Center in Auburn Hills Michagan. Helps to know someone......:classic:

[2ManyZs]

Seems like I read somewhere that the N-47 even with the liners flowed better than most of the rest...

I still believe in the E-31.... With L-28 valves of course..

[JEFF]

I only had the two heads to compare. I was just happy to have 23% than I had before.

2Many - Why the E-31.... With L-28 valves. Are the port angles the key improvments on the E31?

- Jeff

[Zvoiture]

The N47 consistently gets a bad rap. I have read several places something to the extent of, "...it is impossible to remove the liners without ending up with an incredibly f'ed-up head...." Now here's someone who has done it--with success. There are a ton of N47 laying around out here that nobody wants because they are "smog heads (with liners)." I would love to hear or read detailed descriptions from someone who has done it.....How far in there are they actually attached? What tools/approach was used to cut them out?

steve77

[JEFF]

Zvoiture - The N47 'smog liners' are cast into the head. They go from the exit to 1/8" from the valve seat. I used a 3/8" Ball end carbide bur bit, (not a ballnose) with a 3/16" shank. I tilted the head on a hand crank sine table.With the spindle on the mill running at 18,000 rpm and light cuts tilting the head as needed to get all that I could. I ended up flipping the head over (comb. cham. up) to get the rest out. I used a dremel with a sanding roll to smooth out the cutter marks by hand.

I now have a small groove in the casting where the liners used to be. All in all the job looks great.

Why did I do this to a N47 ???? Because it is the only L28 head that I have, & wanted to put the F.I. on my L24 block.

Did it help the flow of the N47 ??? I am ashamed to say that I did not perform a 'before' test......

- Jeff

[z-ya]

I built a 9.8:1 L28 using an F54 bock and an N47 head last winter. It's going in a track car I'm building with some freinds. I'll let everyone know how it performs. I didn't do anything to the liners, just left them in there. I am using a round port header on it.

Basically, I didn't use the N47 by choice, but when you are given a rebuilt N47, and a nice round port 6-1 header, it's an easy decision to make.

Pete

[beandip]

from what I have been reading the thing to do is leave the liners in place as they flow fine with them and the little if any improvement in the removal isnt worth the effort. I have left mine in and I will post what happends , when I get on the road. This is a P-79 on a F-54 flat top running 9.5 to 1 and SUs . :classic:

[texasz]

beandip, how did you get a 9.5 compression ratio out of a P79 on an F54 with flat top pistons? I have read that the this should be much lower, in the 8's somewhere. This is a stock configuration, I have one sitting in my garage now. The only difference is that you've converted to carbs and the one I just got last week has FI (again, this engine came stock with FI which I will be removing to go carbs).

[z-ya]

Unless you have shaved the head, and shimmed the cam towers, your CR will be around 8.5:1. If you use an N42 or N47 head, you CR will be around 9.8:1.

Pete

[texasz]

Ok, I have another thread going on compression ratios for the P90 here: http://www.classiczcars.com/forums/showthread.php?s=&threadid=7109

I have read that more than about 10:1 is not drivable on the street and I want to keep mine streetable. So...what is my best bet? I've read all the information on this and other sites and taking everything into consideration it seems as though the P90 head is my best bet (I will be using an F54 block) but the compression ratio is around 8.5:1. Is this good enough or should I try for something in the 9's? If I should try for a higher ratio then how?

Car use: I plan on autox and occasionally driving to work just to enjoy it and keep things moving properly...NOT my daily driver, just a fun car that would be used for autox.

Cost: CHEAP! I have to keep my expenses down and have remedial mechanical skills so any shaving etc would require to part going to a machine shop (I could probably remove and reinstall it but maybe not much more).

[z-ya]

I would use the F54 blcok, and pick up an N42 head. If you have the P90, you can sell it easy to a turbo guy.

If you can't find an N42, then look for an N47. They are the same but the N47 has round exhasut port liners. N47s are cheap and easy to find.

You can run 10:1 on the street. I know someone running 10.5:1 without problems. Yes, you must only run 93 octane or better fuel. The timing needs to be set correctly, and a high performance ignition and coild should also be used.

Pete

[texasz]

Currently I have the F54 block (flat-top pistons) with a P79 head on it (was pulled from a running '82 280Z). So either way I would have to buy the new head, which ever turns out to be the best.

What's the difference between the N42 and the P90? They both are from the 280 so the sizes should be the same (right?) and they both have square exaust ports. I have read that the P90 is supposed to flow better yet the N42 does show to give higher compression with no mods. Now the N42 has bronze valve seats which I have read make this head expensive to rebuild and as I recall require you to run a lead additive in your fuel. I have also read that you should use the N42 and N47 only with dished pistons and the E31, early E88, P79, P90, and P90a with flat-top pistons. What about this information?

Then there is the E88 head which shows to have the same compression as the N42 on an F54 block. So why not this one?

I'm really quite new to all this and am trying to learn as much as I can but there is just SO much to know! So please forgive my lack of knowledge and numerous questions.

[beandip]

the head was milled .03 but the towers were not shimmed. that is he limit any more off the head and it must be shimmed . the geometry has been checked and the engine has 38k on it and all looks perfect, doing the measureing and checking the volume of the combustion chamber gives me 9.4 actually but higher would have been more to my likeing. This is strictly a street cruser.

[beandip]

here is a web page that will give you all the answers. I am giving you all of it as it appears on my screen when I bring up the page . I tried to pass on another address from the same master page and it wouldent work for that person so let me know if this dosen't work and I ll print it and mail it to you . I dont want to unless there is no other way the last one was over 35 pages. Here goes, http://www.geocities.com/row4navy/head2.html good luck Gary