[elefantrider]

Good thread going here.

It looks like Pypes sells two types of downpipes.

One with the flanges (DS10S) and one without(DGA20S).

The set without flanges are not necked-down and would have less restriction but it looks like they will only work with RA manifolds:

http://www.pypesexhaust.com/downpipes.html

I suppose we cannot get these for Logs because the sharper radius requires the flanges to be pre-installed.

[elefantrider]

Originally Posted by SteveOw

Nope, no theory. In my case the center was flaking off, like it was really catching heat, so when I started to polish things up it would just flake off like rotten metel. So I took it out. Now looks great, all polished up and I think things will flow better with it gone. One bad note, I am sending my pypes down pipes back tomorrow, the coller will slip right over the bell at the end of the pipe. When I tighten the coller to the manifold the pipe will just pull loose. It just pulls it over the bell when tightened. Anyone ever have this problem ? Very Disappointing.

Maybe they were defects.
Did they replace with new ones with a larger bell?

[1967Tempest]

I just installed DS10S and DGU11 . They were not that tight of a fit. But I had to remove and reinstall them together for the correct geometry. They sound great. Manifolds wil quiet mufflers and tailpipes and it is still pretty loud outside of the car. Inside it is nice and quiet. A small amount if any of get-up from the start and no lose of top end with manifolds.

Granted I am less then 400 HP. I would recommend the Pypes numbers above and manifolds.

Dave

[zeebo]

Originally Posted by goatless

Well, you learn something new everyday. So the heat riser flapper thing went away in '69 and came back again as part of the emission control system in the mid '70s?

Jack, that center port divider is another thing the Pontiac engineers changed their mind on- I've got a bunch of sets of logs and only a couple have the divider. I don't recall the dates on the ones with them or without.

The set on my Lemans right now are '70 castings that don't have the divider.
BTW, my lemans ran a 12.76 at Lebanon Valley yesterday with logs... and G70-14 Polyglas tires. Those log manifolds aren't the hinderance that most people believe!

correct..i do not know the exact date they stopped with the heat riser valve, but i know that 72 thru 74 pontiacs do not have them..they returned in 75 with the cat. converter. i personally dislike these, not only for the restriction, but for the fact that they can seize up and stick closed, severely damaging your engine.

unless you are doing a 100 point resto, id leave it out, and even if you do a 100 point resto, id tack weld it open..

i think opening up the log outlet and extrude hone polishing sure cant hurt..plus with good mandrel pipes that dont neck down you should be good up to 1hp/cu in....

[1967Tempest]

Yeah I tack welded mine open.

[elefantrider]

Removed mine and put a pipe plug in the holes.

[68 Firebird]

This is an excellent thread full of good info. My question is this, do the original
FB manilfols have a heat flapper in them. the reason I ask is because i don't recall
mine having them when I removed them during resto 10 years ago. I just sandblasted
them and coated them with exhaust calyx.

I do plan to remove mine again and clean them ports up and resize exhaust exit
hole.

Gerry C

[Engine-Ear]

Glad to see this thread.

Good tech, B-Man!

[Donovan]

Originally Posted by 68 Firebird

This is an excellent thread full of good info. My question is this, do the original
FB manilfols have a heat flapper in them. the reason I ask is because i don't recall
mine having them when I removed them during resto 10 years ago. I just sandblasted
them and coated them with exhaust calyx.

I do plan to remove mine again and clean them ports up and resize exhaust exit
hole.

Gerry C

My Firebird was a california car and did not have a flapper assembly.

[sixtysix]

Is the heat riser necessary with an automatic choke?

[goatless]

Some years didn't have the flapper at all. So, no not necessary.

[b-man]

Here's a pair of 1959 389 log manifolds.

Pontiac exhaust manifolds have a nice free-flowing design, much less restricted than the standard exhaust manifolds of most other makes.





I'm particularly fond of the driver's side manifold with the center outlet, purely from an aesthetic standpoint. A pair of these would look great on a fenderless late '20s or early '30s roadster with an open engine compartment.

[Greg Reid]

It's funny that I still can't see any photos that are posted through photobucket. I see nothing in your post but the script Bart. The email alert shows links to the photos but when I click on them, "This site can't be reached".
Strange.

[Greg Reid]

Nevermind...I just realized that it's only my job's network that filters PB out. I just looked at the 'Post a photo that you took' thread and noticed that a couple of pics I viewed at home are not viewable here.

[1967Tempest]

Im curious why they cut out the center on one side and not the other.

[242177P]

Originally Posted by 1967Tempest

Im curious why they cut out the center on one side and not the other.

If you study the firing order, the driver's side has two consecutive fires, 5 and 7. Five (center) absolutely has to get out of there before seven (rear). Could be the reason it has a center outlet? On the passenger side the exhaust exits in a more orderly fashion. The only thing that comes remotely close is four and six (both center) but there's a pause while three does it's thing.

But wait! There's more! (there always is) Let's not forget about the exhaust crossover. When that flapper is closed, the passenger side's center is now the exit. Forget what I said about orderly. Everybody on that side is now trying to exit through the intake manifold. And you've seen the size of that exit. Can you say gridlock? Hey, let's knock out that wall!

I'm sure that only scratched the surface, and I could even be wrong.

[KSZR]

I've got a 72 Lemans I've had for 30 years. It was my high school project. It's got a 400 bored 30 over, #16 heads, 068 cam, cast iron manifold with Q jet with dual snorkel, log manifolds and 2.25 crush bent exhaust with quiet mufflers. HO racing carb and distributor kits.

Running a fresh 200-4R transmission and 12 bolt 3.55 rear end.

With my dragy my best 1/4 mile run is 14.59 at 96 mph. Thought it would be better.

Always wanted to do the ram air manifolds but then I saw this post!

How much performance gain would I get with the log manifolds opened up to 2" and a pypes 2.5" mandrel system?

VS what I have now?

VS ram air maniolds and pypes 2.5" mandrel system?

Thanks! Kent Kelsey

[Ccass]

Originally Posted by KSZR

I've got a 72 Lemans I've had for 30 years. It was my high school project. It's got a 400 bored 30 over, #16 heads, 068 cam, cast iron manifold with Q jet with dual snorkel, log manifolds and 2.25 crush bent exhaust with quiet mufflers. HO racing carb and distributor kits.

Running a fresh 200-4R transmission and 12 bolt 3.55 rear end.

With my dragy my best 1/4 mile run is 14.59 at 96 mph. Thought it would be better.

Always wanted to do the ram air manifolds but then I saw this post!

How much performance gain would I get with the log manifolds opened up to 2" and a pypes 2.5" mandrel system?

VS what I have now?

VS ram air maniolds and pypes 2.5" mandrel system?

Thanks! Kent Kelsey

vs a crimp bent 2.25" you should drop a 1/2 second in the quarter mile. I don't think hogging out the end of the manifold flange will affect performance that much.

[KSZR]

Originally Posted by Ccass

vs a crimp bent 2.25" you should drop a 1/2 second in the quarter mile. I don't think hogging out the end of the manifold flange will affect performance that much.

Awesome thanks! Any opinion on what the ram air manifolds would add to that?

[Ccass]

Originally Posted by KSZR

Awesome thanks! Any opinion on what the ram air manifolds would add to that?

maybe another 1/10-2/10 if they were port matched and polished? The big question is finding a pair. They are out of production now. The whole Pontiac industry has been out for a while. So they are really hard to find.