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.

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.

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

Pete

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?

I would guess the one that has the largest area?

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

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:

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..

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

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

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

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

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: