Is there a D-Port 'log' exhaust manny with a larger outlet - 2.25 or bigger?

[Ragtop Man]

Or did I hallucinate that while singing "Ride Pontiac Ride" with Cindy Fee...? #IYKYK

I recall a back and forth here on the topic - I may have even started it. Thought there might be some that would pass a visual for anyone but a serious know it all.

Got a cracked left AND right on my '67 GTO that make a cold start sound like the blacksmith shop from hell. They need to come off, and if there is a similar looking but better performing alternative, I'm in.

It's not a drag car, I like the RARE HO mannys but a few of those $600 dates are tough on the wallet.

Thanks as always, Mighty Chiefs.

[b-man]

Not really, the outlet size on some matches up to 2-1/4” pipe at best.

The gory details:

http://forums.maxperformanceinc.com/forums/showthread.php?t=630943

[grandville455]

Hedman shorty headers are nice for those cars,ran them on my 74 years ago

[ponchjoe]

I don’t believe eanyone makes but just like HO manifolds you can machine them to 2.45 I think. I also remember someone in the forums taking about this years ago so you can do some searching

[b-man]

There’s no way to machine a 2.45” outlet. A 2.25” pipe barely fits inside the hold down flange.

There would be nothing left if you tried to machine the opening to 2.45”, 2.125” is already pushing it.

People have modified log manifolds for class racing to accommodate 2.5” pipe by welding on a new outlet.

The HO manifolds with 2.25” outlets can be machined to 2.45” of course but after that the tapered sealing surface becomes quite narrow.

[hurryinhoosier62]

There’s no way to machine a 2.45” outlet. A 2.25” pipe barely fits inside the hold down flange.

There would be nothing left if you tried to machine the opening to 2.45”, 2.125” is already pushing it.

People have modified log manifolds for class racing to accommodate 2.5” pipe by welding on a new outlet.

The HO manifolds with 2.25” outlets can be machined to 2.45” of course but after that the tapered sealing surface becomes quite narrow.

BART, how about having a set extrude honed?

[b-man]

BART, how about having a set extrude honed?


Juice ain’t worth the squeeze.

For the cost of that procedure you could purchase at least one new set of reproduction HO manifolds. And there’s really not much to gain if you did.

[hurryinhoosier62]

Juice ain’t worth the squeeze.

For the cost of that procedure you could purchase at least one new set of reproduction HO manifolds. And there’s really not much to gain if you did.

I’m leaning heavily toward seeing if porting the “long branch” manifolds for my ‘64 is a possibility. Don’t need the hassles of headers.

[b-man]

About 25 years ago I looked into the cost of that on a stock iron intake, they quoted me $400.

I can’t imagine what it would cost to do a set of long branches now.

There’s not gonna be any night and day difference in flow after paying probably more than the manifolds cost you in the first place for the work.

Just run the manifolds as is with the nicest exhaust pipes and mufflers you can dig up.

[Ben M.]

There’s not gonna be any night and day difference in flow after paying probably more than the manifolds cost you in the first place for the work.
Agreed. My opinion is that unless you're building a race motor that needs the flow of 4 tube headers just put factory-style HO manifolds on your car if you're looking to get rid of the factory logs and you've maxed your bang for the buck and effort while keeping it a relatively easy to maintain setup. That extra 0.125-0.25 ground out of a manifold is a lot of work for no discernible gain. Your butt dyno might be all smiles, but that just could be the lighter wallet at work.

I've put unmodified HO manifolds on every car that I've redone exhaust on and been perfectly satisfied and happy with them.

[SD455DJ]

Or did I hallucinate that while singing "Ride Pontiac Ride" with Cindy Fee...? #IYKYK

I recall a back and forth here on the topic - I may have even started it. Thought there might be some that would pass a visual for anyone but a serious know it all.

Got a cracked left AND right on my '67 GTO that make a cold start sound like the blacksmith shop from hell. They need to come off, and if there is a similar looking but better performing alternative, I'm in.

It's not a drag car, I like the RARE HO mannys but a few of those $600 dates are tough on the wallet.

Thanks as always, Mighty Chiefs.

Having been involved with Pure Stock racing for over 30 years now, my brother Dan and I have seen log manifolds perform amazing well in mildly cammed Pontiac engines. We have also dyno’d a RAIII 400 from a ’69 TA to compare the long branch manifolds to the standard logs and to RA manifolds. The ’69 400 4-bbl engine came with all three manifold types in the GTO and Firebird lines, so was a great engine to compare the manifolds and how they impacted power and not over-cammed either.

The long branch F-body manifolds made the most power on the 068 cammed 10.5 to 1 compression 400 making 370 hp @ 4900 rpm and 454 lbft. @3600 rpm. RA manifolds made 368 hp @ 4800 rpm and 448 lbft. @ 3600 rpm. The factory logs manifolds made 360 hp @ 4800 rpm and 442 lbft. @ 3500 rpm. They don’t give up too much to the high performance manifolds in a more tame stock engine.

The log manifolds lost only 8-10 hp/6-12 lbft. torque at the peaks, and 3-5 hp/3-6 lbft. average across the rpm pull range pf 3000 to 5000 rpm. That equates to 13.5 to 13.6 to 13.7 quarter mile times, so only a 0.2 second spread between the manifolds. Any larger cam than the 068 and the spread becomes greater as the logs can’t flow what the RA manifolds can and become a choke point above 5000 rpm.

The stock outlet size on most log manifolds is 1-7/8” to 1-15/16” (1.9" give or take). They can be opened up to 2-1/8” max. The factory RA manifolds are 2-1/16” to 2-1/8” stock while the long branch are 2-1/4” to 2-5/15” stock. The RA manifolds are brittle gray iron and very prone to cracking, so not recommended to open the outlets and further (they crack easily on their own without any modifications). Opening up the log manifolds to 2.1” will help make a tiny bit more power but probably isn’t worth the effort on a stock street engine.

FWIW, my ’70 Tempest Pure Stocker runs low 13’s through the stock log manifolds (1.9” outlets) into a 2.5” mandrel bent full exhaust system with 3.42 rear gears. I was going to open the outlets up to 2.1” when the engine was out, but it slipped my mind and didn't do it. The engine is very mild with 9.95 to 1 compression, a Summit 2801 cam (214/224/112 @ .444”/.466” lift), non-ported small valve heads, stock cast iron intake and Q-jet carb with a race weight of 3800 lbs. It dyno’d at 380+ hp at 5200 rpm and 450+ lbft. torque at 3600 rpm. I do believe the manifolds are limiting the trap speed to 103 mph and would do at least 105 mph with RA manifolds, but they aren’t allowed on the car/engine combo.

My recommendation is to find good condition log manifolds (shouldn’t be too hard to find) to replace cracked ones and install a good high flow exhaust system (Pypes or equivalent) …if your engine is stock/near stock.

Dennis