Thread: Butterfingers

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I was polishing my '86 5.0 "swirl" heads, and once I'd ground off the emissions nubs from the exhaust ports, I decided to open up the exhaust ports slightly because, well, they're tiny. I had about another 3/16" of room to the gasket in every direction. Well, one thing led to another, and before I knew it I'd opened them clear out to the gasket scribes. Stepping back to look at it, all I can think is, "Wow. That's really big."

I can't really undo it and I'm not sure I want to; I just can't find any references to gasket-matching the exhaust ports except on sport-compact-buildup boards, and one mention on these boards where a guy said he killed his low end by opening the exhaust and intake ports too much.

The intake ports have been polished but haven't been ported. They're already within 1/16" of the gasket on all sides.

I'll be running around 9:1 compression on a dual-quad 289 tunnel ram intake with full-length 1 5/8" headers and a custom-ground cam of about .475-.480" lift at 220/220 duration and .110 separation (E303 grind with slightly smaller lift), pushing a built C4 with a shift kit and a 2400-2600 stall and 3.0 gears. (EDIT: The idea here is a daily driver setup that will scare the living hell out of the sport-compact crowd at the nearby college.)

The cam hasn't been ground yet; if there's a detriment to having hogged out the exhausts this wide, is it something I can salvage by tweaking the cam grind?

Originally posted by Was_II I just can't find any references to gasket-matching the exhaust ports except on sport-compact-buildup boards, and one mention on these boards where a guy said he killed his low end by opening the exhaust and intake ports too much.

Ever heard of an import with a Ford small block? No? Then I think you can open up the exhaust ports as far as possible to eleminate the #1 restriction in stock sbf heads.

I did some porting a while ago on a set of D8OE heads for a supercharged engine:





Exhaust ports shoudn't be completely matched to the gasket, you usually leave one edge protruding into the port as a "reversion dam". This keeps burned gases from re-entering the combustion chambers as pulses travel back and forth through the exhaust system.

Also I heard from several people that intake runners shouldn't be polished, a slightly rough finish will keep atomized fuel from sticking to the runner walls and leaning out the mixture.
Polished exhaust runners will however help to prevent carbon buildup, the same applies to combustion chambers, but removing material here will drop compression ratio, so remove as little as possible unless the engine will be supercharged (meaning a low static compression ratio is required)

Here's a pic of my combustion chamber polishing work:



The most work is necessary on the peanut sized exhaust ports, as I wrote above they are what really restricts airflow.

However if you want to put a ricer engine in your stang porting may reduce airflow velocity to a degree where it actually hurts performance

Hope this helps...

-Simon

You should open the exhausts and the intakes right out to the gasket line, but you should not polish the intake ports, only the exhaust.

Originally posted by CobraV8
:

http://img308.imageshack.us/img308/8...stports0lu.jpg

The most work is necessary on the peanut sized exhaust ports, as I wrote above they are what really restricts airflow.

That's about what I did to mine. I'm just double-checking; it seemed to make sense to hog them out, especially running headers, but last night looking at them with a fresh eye, my first thought was, "Da-a-a-a-mn." I wasn't sure if I'd overdone it.

I found a couple of websites on porting, but neither of them mention porting the exhausts. Polishing, but not porting.

Originally posted by CobraV8
:
However if you want to put a ricer engine in your stang porting may reduce airflow velocity to a degree where it actually hurts performance

Thanks, I'd rather not. I was just Googling and came up with a couple of sport-compact sites. Makes sense that reducing airflow velocity in a small engine would kill it.

if you want to port to a point that the gasket will have too much overlap.... then a solution for gasketing on the exhaust side is high quality assembly grease, the extra heavy stuff... put a thin cout on the mounting surface and evenly torque your bolts down.... i've run a set of headers for 3 years now like that without 1 leak problem

Hey, Sals.

I haven't had my coffee, yet; run that by me again? Are you saying to use the grease instead of a gasket? Or in addition to a gasket? I've got the exhaust manifolds ported right to the gasket; the headers are already gasket-matched.

you use the grease in place of a gasket.... some of the older print repair manuals even actually reccomend using the grease over the gasket