Porting iron exhaust manifolds

[travis]

Have any of you guys ever tried porting exhaust manifolds and seen a noticeable power increase?

How thin can you go before structural integrity becomes an issue? Particularly in the vicinity of the exhaust port flange?

[6 cylinder puller]

Do it a lot in the classes that say stock appearing. Can’t say I ve dyno tested it but It probably would help some but it’s not going to get close to what a good header would be or even a average header

[Carnut1]

Yes, the thinner it is the more likely it is to crack. If you need to push the casting spray weld outside. I never took exhaust manifolds thinner than .125". Thanks, Charlie

[PackardV8]

One F.A.S.T. hemi spent $5,000 on extrude honing and hand porting the exhaust manifolds and then they cracked.

[travis]

One F.A.S.T. hemi spent $5,000 on extrude honing and hand porting the exhaust manifolds and then they cracked.

Ouch!

[cv67]

Say a rams horn for instance?
Went to town on a set spent a LOT of time, you cant get to every spot on those to make a difference.

Owner felt nothing unfortunately. It wont hurt but probably wont help you either.

[travis]

Say a rams horn for instance?
Went to town on a set spent a LOT of time, you cant get to every spot on those to make a difference.

Owner felt nothing unfortunately. It wont hurt but probably wont help you either.

Actually another low budget small block ford this time. The pinch right at the port flange is pretty bad. You definitely can’t reach much in there.

[dwilliams]

Some manifold openings are 1/8" or more smaller than the port openings. I've port-matched various SBF and SBC manifolds to get rid of the step.

If it was stepping up into a bigger manifold I wouldn't have bothered.

[groberts101]

I've done lots including some of the rarer 289 hi-po/428/429 CJ stuff. Bunches of truck stuff too. Generally good for a few ft/lbs across the curve and maybe upwards of 5-6 horse until you get over about 5,500 when they quickly revert to their previous cork-like status.

[MichaelThompson]

I spent two solid days porting the inside and grinding the outside of the ugliest small block Ford manifolds you’ve ever seen.

I did those for a ‘39 Ford hot rod that was getting freshened up. Owner didn’t want to change the exhaust system.

I made them work as good as I could and they were pretty when I got done.

Don’t know how much they helped but that thing ran good!

[jeff swisher]

Pontiac 400 with 16x heads and 236@ .050 cam .490" lift.
1977 TA and buddy pulled the stock ex manifolds off and stuck some triY headers on it.. he said the headers made no difference.
I can see that as you many times need to rejet.

So I ported his ex manifolds for free to prove a point and he stuck them back on and said it was much quicker.

1969 396 11:1 compression oval open chamber heads Ported with 2.19-1.88 valves and 230@ .050 cam 280H. stock truck ex manifolds were removed and full length headers installed.
It felt no different and kept blowing header gaskets.. buddies toy.
I ported his manifolds and gave them back and said try them now.
It picked up power.
His ex ports on heads were 1.75" square and the headers I seen laying in the garage had smaller round entrances on them.

Really people round small hole is what I was thinking for a square ex port..I just shook my head.

Last one or 2.

I told my buddies I would run 13's with my stock weight 78 nova and 350 with cast flat tops.
With a single point distributor and Iron ex manifolds and Q jet iron intake.
I did to the tune of 13.028 @ 110.

Now headers made it much snappier out of the hole and up to 4000 rpm but say 4000-7000 it felt the same.

Onto a 388" small block.. ported ex manifolds and 214-224 cam RPM intake ported 624 heads.
Ran great and was done at 5800rpm. Felt like it was trying to nose over or just go flat.
Installed full length headers and it was a different animal.
Pulled super hard to 6700rpm.

I recently installed full length headers in place of manifolds I ported 350" 268H 10.3 compression.
2.25" pipe with turbo muffs to 3" with 2.5" perforated core glass packs
No gain..
Got louder. I rejetted and it improved the power a bit.

Conclusion : mismatched port is a negative hit.
smaller engines can get by with less manifold. or say engines making less power or moving less air can get by with less manifold.

[Newold1]

In my old experienced mind there are only two scenarios to rework and run cast factory stock exhaust manifolds:

1. You are mandated by class rules to run them which I think is an absolutely stupid rule requirement when racing of any kind!

2. You absolutely have more time than sense and you are a a masochist!

Throw them in the scrap pile and put on a decent set of headers! Done!

[PackardV8]

Or:

3. One is running something other than a SBC.

Priced a set of custom headers for an obsolete engine/chassis lately?

[Frankshaft]

Well, all I know, on F.A.S.T. race applications that require manifolds, the engines lose 100 hp with the manifolds from the headers on the dyno. keep in mind, these are very high end engines that make some serious horsepower for what they are, much like a super stock drag race engine. Manifolds absolutely kill power. Can you make seemingly good power with them? Sure, but trust me, you aint making anywhere CLOSE to the same as a good set of headers on a real race engine. Period. I have personally seen engines pick up 50+hp from a shitty set of catalogue headers, to a nice set of custom made headers. And, I promise, the shitty catalogue headers make more than ex manifolds.

[Newold1]

PackardV8

If you are affording the expense and effort of running an obsolete antique engine/ chassis combination in any class racing events and you can't afford a decent set of customized headers, you are most likely constrained by two things:

One, you are probably not winning many races or placing well.
Two, YOU ARE A MASOCHIST!