[vertigto]

Originally Posted by 1965gp

To be fair- I’m a flowmaster guy. I like that sound. this is also a stock 403 so i didn’t expect any cam sound.

My 69 GTO with log manifolds and flowmasters costs less and sounds better.

Me too. My Flowmaster 40s are loud and a little obnoxious, but it's the sound I prefer. Once over 35+mph, it ain't bad inside the car.

[kingbuzzo]

I'm going the other way...performance be damned...i need the ground clarence...

I'm told it's minimal for a street car.

[Formulajones]

Originally Posted by Fishin2Deep4U

Sorry to drag one back up.

But does anyone have any testing for the practical max HP limit for a transverse system vs a conventional dual muffler setup? Thinking all 2-1/2".

I need to do something with my 1st gen Bird and I really like the transverse design. Just don't want to give away a bunch of power everywhere. Not a big deal way up on top for me as I am rarely spinning it that hard.

Dave

There is no restriction with the transverse, provided you use a good transverse like the Pypes or dynomax 2 1/2" mandrel bent systems. With that said there are no gains to be found going dual mufflers all else being equal. I've been back and forth with that with no ET to be found on a mild 12 second car and in fact it's fine on an 11 second car.
There are Pypes Transverse systems used in the PS drags with those cars running deep into the 11's and high 10's, and the rules dictate a stock configuration exhaust and has to be 2 1/2" maximum. In fact that exhaust rule is still applied in the FAST class too, and plenty of those cars going even quicker.

If you really started pushing the HP pipe size would be more of a player.

I think where this stems from is the old stock type transverse systems from 50 years ago or the reproduction Gardner stuff. I tested that too and I can say without a doubt if you use a stock type transverse with crush bent 2 1/4" pipes and the stock type muffler from Gardner, it's a huge restriction. My bird was stuck at 14.0's at 98-99 mph with that system.

As soon as I replaced that with a Flowmaster Force II transverse system (2 1/2" mandrel bent) it immediately went 13.70 at 102 mph and a couple more passes was going 13.60's. Never touched a thing under the hood.
Granted the Flowmaster chamber muffers are pretty restrictive themselves, yet that system was worth a solid 30+ HP over the stock Gardner transverse setup.

I later installed a Pypes setup, still transverse, still 2 1/2", but the muffler design is worlds ahead of any chamber design. This system also has an "X" cross vs an "H"
I have the car now going bottom 13's in the heat consistently with a best of 12.79 at 106 mph. Still the same bone stock RAIII engine.

[Fishin2Deep4U]

Originally Posted by Formulajones

There is no restriction with the transverse, provided you use a good transverse like the Pypes or dynomax 2 1/2" mandrel bent systems. With that said there are no gains to be found going dual mufflers all else being equal. I've been back and forth with that with no ET to be found on a mild 12 second car and in fact it's fine on an 11 second car.
There are Pypes Transverse systems used in the PS drags with those cars running deep into the 11's and high 10's, and the rules dictate a stock configuration exhaust and has to be 2 1/2" maximum. In fact that exhaust rule is still applied in the FAST class too, and plenty of those cars going even quicker.

If you really started pushing the HP pipe size would be more of a player.

I think where this stems from is the old stock type transverse systems from 50 years ago or the reproduction Gardner stuff. I tested that too and I can say without a doubt if you use a stock type transverse with crush bent 2 1/4" pipes and the stock type muffler from Gardner, it's a huge restriction. My bird was stuck at 14.0's at 98-99 mph with that system.

As soon as I replaced that with a Flowmaster Force II transverse system (2 1/2" mandrel bent) it immediately went 13.70 at 102 mph and a couple more passes was going 13.60's. Never touched a thing under the hood.
Granted the Flowmaster chamber muffers are pretty restrictive themselves, yet that system was worth a solid 30+ HP over the stock Gardner transverse setup.

I later installed a Pypes setup, still transverse, still 2 1/2", but the muffler design is worlds ahead of any chamber design. This system also has an "X" cross vs an "H"
I have the car now going bottom 13's in the heat consistently with a best of 12.79 at 106 mph. Still the same bone stock RAIII engine.

Very much appreciate the info.

I wonder if a case can be made for max HP for a given pipe size. I am not making big power at all. I am going to throw a set of heads on and would like to get to 500-550 and still have great street manners. The transaxle setup would be much better clearance wise even though I would most likely have to fab up the axle area pipes to clear the suspension and 315's.

[Quad]

Rocky Rotella's 2011 book "how to rebuild Pontiac v-8s" has build details of two 68 Firebirds, a Pure Stock & a F.A.ST. Both had the Pypes 2 1/2" crossflow muffler. The F.A.ST. had measured output of 650hp @ 6400rpm and "quickest so far of 10.2 @ 132.2mph".

[Formulajones]

Originally Posted by Fishin2Deep4U

Very much appreciate the info.

I wonder if a case can be made for max HP for a given pipe size. I am not making big power at all. I am going to throw a set of heads on and would like to get to 500-550 and still have great street manners. The transaxle setup would be much better clearance wise even though I would most likely have to fab up the axle area pipes to clear the suspension and 315's.

Absolutely a case can be made for max HP for a given pipe size. I was just simply pointing out how the transverse 2 1/2" system is being used in some pretty fast cars, and that's because of rules. If they allowed larger systems you can bet these guys would have something bigger on there. But it shows how fast you can go with a transverse system, and 2 1/2" pipe size.

Plenty for what we do with our average 500hp street cars. Of course larger pipe size would benefit even at that power level. I'm not aware of any transverse system being made that larger than 2 1/2" however.

[KSZR]

Originally Posted by Formulajones

There is no restriction with the transverse, provided you use a good transverse like the Pypes or dynomax 2 1/2" mandrel bent systems. With that said there are no gains to be found going dual mufflers all else being equal. I've been back and forth with that with no ET to be found on a mild 12 second car and in fact it's fine on an 11 second car.
There are Pypes Transverse systems used in the PS drags with those cars running deep into the 11's and high 10's, and the rules dictate a stock configuration exhaust and has to be 2 1/2" maximum. In fact that exhaust rule is still applied in the FAST class too, and plenty of those cars going even quicker.

If you really started pushing the HP pipe size would be more of a player.

I think where this stems from is the old stock type transverse systems from 50 years ago or the reproduction Gardner stuff. I tested that too and I can say without a doubt if you use a stock type transverse with crush bent 2 1/4" pipes and the stock type muffler from Gardner, it's a huge restriction. My bird was stuck at 14.0's at 98-99 mph with that system.

As soon as I replaced that with a Flowmaster Force II transverse system (2 1/2" mandrel bent) it immediately went 13.70 at 102 mph and a couple more passes was going 13.60's. Never touched a thing under the hood.
Granted the Flowmaster chamber muffers are pretty restrictive themselves, yet that system was worth a solid 30+ HP over the stock Gardner transverse setup.

I later installed a Pypes setup, still transverse, still 2 1/2", but the muffler design is worlds ahead of any chamber design. This system also has an "X" cross vs an "H"
I have the car now going bottom 13's in the heat consistently with a best of 12.79 at 106 mph. Still the same bone stock RAIII engine.

That is some great firsthand info! Thanks for sharing.

[Fishin2Deep4U]

Originally Posted by Formulajones

Absolutely a case can be made for max HP for a given pipe size. I was just simply pointing out how the transverse 2 1/2" system is being used in some pretty fast cars, and that's because of rules. If they allowed larger systems you can bet these guys would have something bigger on there. But it shows how fast you can go with a transverse system, and 2 1/2" pipe size.

Plenty for what we do with our average 500hp street cars. Of course larger pipe size would benefit even at that power level. I'm not aware of any transverse system being made that larger than 2 1/2" however.

I also have never seen anything larger than a 2-1/2” transverse system either.

Again, really appreciate all the data.

[Fishin2Deep4U]

Originally Posted by Quad

Rocky Rotella's 2011 book "how to rebuild Pontiac v-8s" has build details of two 68 Firebirds, a Pure Stock & a F.A.ST. Both had the Pypes 2 1/2" crossflow muffler. The F.A.ST. had measured output of 650hp @ 6400rpm and "quickest so far of 10.2 @ 132.2mph".

I have unfortunately never read that one. Might have to see if I can find a copy. Great info.

[Quad]

here's a 2016 thread titled; 1968 Ram Air 2 F.A.S.T. Firebird Breaks into the 9's !

http://forums.maxperformanceinc.com/...=797112&page=6

Page 5 has a link to an Hemmings article on the car. To me the whole thread is amazing reading.

[68 461 Bird]

Originally Posted by Formulajones

There is no restriction with the transverse, provided you use a good transverse like the Pypes or dynomax 2 1/2" mandrel bent systems. With that said there are no gains to be found going dual mufflers all else being equal. I've been back and forth with that with no ET to be found on a mild 12 second car and in fact it's fine on an 11 second car.
There are Pypes Transverse systems used in the PS drags with those cars running deep into the 11's and high 10's, and the rules dictate a stock configuration exhaust and has to be 2 1/2" maximum. In fact that exhaust rule is still applied in the FAST class too, and plenty of those cars going even quicker.

If you really started pushing the HP pipe size would be more of a player.

I think where this stems from is the old stock type transverse systems from 50 years ago or the reproduction Gardner stuff. I tested that too and I can say without a doubt if you use a stock type transverse with crush bent 2 1/4" pipes and the stock type muffler from Gardner, it's a huge restriction. My bird was stuck at 14.0's at 98-99 mph with that system.

As soon as I replaced that with a Flowmaster Force II transverse system (2 1/2" mandrel bent) it immediately went 13.70 at 102 mph and a couple more passes was going 13.60's. Never touched a thing under the hood.
Granted the Flowmaster chamber muffers are pretty restrictive themselves, yet that system was worth a solid 30+ HP over the stock Gardner transverse setup.

I later installed a Pypes setup, still transverse, still 2 1/2", but the muffler design is worlds ahead of any chamber design. This system also has an "X" cross vs an "H"
I have the car now going bottom 13's in the heat consistently with a best of 12.79 at 106 mph. Still the same bone stock RAIII engine.

I have been trying to decide on an exhaust system for our 68 Firebird and stumbled across this thread. Glad I did, thank you for posting this information!

[kingbuzzo]

I got the 2 1/2 transverse finally and no regrets.

Sounds good, looks good, and no more bottoming out!

Inexplicably has become a better car...

I ordered the too short tips by accident but the right ones are on the way...