[Riderfan]

Hello all,

I have a 1970 GTO with a basically stock 350hp 400. A couple years ago I put on a Waldron repop exhaust system, with the factory style restrictive head pipes.

Keeping in mind I want to keep the 2" inlet mufflers (with reducers) would there be any noticeable performance gain by either having a local shop bend up 2-1/4" pipes, or maybe adapting Pypes 2-1/2" pipes (if this is even feasible)?

Some of you may be wondering why I didn't go with a Pypes system in the first place? At the time there was too many issues with the tail pipes bent wrong for the valence cutouts, and I already had repop splitter tips for 2-1/4" pipe.

I look forward to your input.

Keith

[64speed]

Crushed pipe should be avoided whenever possible but sometimes it’s just not practical. If you are trying to ring every last bit of power out of it I’d say no way but if it’s just a driver I think crush bent 2 1/4 has to be better than the same 2 inch. If crush bent is your only option why not get 2.5 pipes and the reducer you need before the splitter

[Formulajones]

I ran the factory Walker 2 1/4" crush bent system, with 2" tails.

When I pulled that off and switched to the Pypes 2 1/2" mandrel bent system my car picked up nearly a half second and 4 mph with no other changes.

I simply don't run crush bent or stock size piping on anything anymore.

What I do to keep the stock appearance, is run the better system as described, and then at the rear of the car I will adapt the factory tailpipe setup to the 2 1/2" system so when looking at the car from the rear, it appears stock. Tailpipes are all you see on a car anyway once it's on the ground.

I've also done this with some of the restorations I do here with excellent results and never an unhappy customer.

[SD455DJ]

Riderfan - I agree with Formulajones completely, but we have also seen some improvement when just the head-pipe is changed to the 2.5" mandrel style. The most severe hp loss comes with the first bend out of the exhaust manifold, so the bigger and smoother it is, the better off you are. Run the Pypes head-pipe full length (about 42") and don't cut it shorter, then transition into your Gardner system with reducers. That would net you about 2 tenths and 2 mph in the quarter.

Dennis

[Riderfan]

Originally Posted by SD455DJ

Riderfan - I agree with Formulajones completely, but we have also seen some improvement when just the head-pipe is changed to the 2.5" mandrel style. The most severe hp loss comes with the first bend out of the exhaust manifold, so the bigger and smoother it is, the better off you are. Run the Pypes head-pipe full length (about 42") and don't cut it shorter, then transition into your Gardner system with reducers. That would net you about 2 tenths and 2 mph in the quarter.

Dennis

That sounds like more bang for the buck than RA manifolds. Thanks!

And to 64speed & Formulajones, yup should've went with Pypes in the first place, but at the time it wasn't feasible. So now just trying to make the most of what I got (which is virtually brand new)

Thanks all for the replies/insight/advice.

Keith

[SD455DJ]

Riderfan - If you already had the manifolds, I would go the complete route that Formulajones suggests, but be aware that the Pypes mandrel system will need customization to fit properly. In another thread on this site, CCass from PY is having a new better bent 2 1/2" mandrel system bent and stocked that will require a lot less messing with and fit much better that the current system. It will cost more he said since they will require more work before they go out the door. I have a fairly stock '70 YH 455 (small valve Bonneville motor) with the stock A-body logs with 2 1/2" mandrel bent headpipes from PY back older 2 1/4" turbo mufflers and tailpipes that does a good job (in a '70 Lemans). We did opened up the exhaust outlet in the manifolds by grinding them to 2 1/8" to 2 1/4" since they were off the engine. That was as big as we could make them without before getting too thin for a good seal. The existing outlets were 2 1/16" (+), so we didn't accomplish much. The motor on the dyno with those log manifolds and the headpipes we used on the car made 390 hp/ 510 tq. easily with a mild cam (Summit 2802) and 9.9:1 compression.

Dennis

[Formulajones]

Just to help put this in perspective, the car and system I experimented with that I mentioned here was an F-body transverse system.

[Riderfan]

After reading the helpful advice here and some consideration (which I will bore you with-too much typing) I'm leaning towards replacing the the headpipes with 2-1/4" compression bent (that just sounds better than crush bent) pipes, reduced down the the mufflers 2" inlets and perhaps a crossover ('H') pipe.

Some details on my p-dude engine is its a 'basic 400' with many bottom end upgrades (forged pistons, I beam rods, moly rings, balanced, etc) and 'performance wise' it has milled 6X-4 heads (S/S valves, 1.77" ex) 9:1 CR, & an 068 cam, with a '68 intake & '70 log manifolds. Points distributor & Ames reman Q-Jet

Will never be on a track because there ain't one nearby anymore. So ET & MPH don't really matter, just 'spirited' driving while cruising around.

I doubt upgrading the head pipes will cost much so I'm not worried about the $$$ to HP. I'm curious if it worth the effort, in the sense will I even notice much of a difference?

I'm thinking I will, but I look forward to any opinions.

Keith

[Formulajones]

As Dennis mentioned, the headpipes are the most important part of the system when running iron manifolds. That first 90 degree bend coming off the manifolds is critical. Dennis has done some dyno testing in this area so he could give you exact numbers, but an educated guess would be 7-10 hp. Having a mandrel bend here is beneficial.
The further back you get in the system, the less critical it becomes. The 2" inlet mufflers are likely a bottle neck, and at some point off the manifolds you'll be reducing the size of the pipes, it will choke some HP even on a mild 400 build such as yours. Running smaller tail pipes after the mufflers aren't as much concern.

It's up to you and what satisfies you. Personally I've learned that even on a near stockish build such as my example above, exhaust is a big player and I don't like giving up anything, even on a street car that never sees the track. You're 400 probably isn't too far off from my own PS 400 build I mentioned above.

[455GRIN]

If you are going to the trouble of changing the head pipes then mind as well use a mandrel bend pipe. Back before we had all the mandrel exhaust systems, I brought a 90 degree mandrel bend elbows and had the exhaust pipe flanged and welded in when I was installing ram air manifolds. I just don't think the thought of crimped pipe at that location.

[64speed]

I wish I had a shop close by that would mandrel bend pipe but I think the closest place is in Atlanta and that’s a lot of interstate driving with open headers LOL

[Formulajones]

That's why exhaust kits are so popular. Mandrel bending, your choice of muffler and choice of material from any number of manufactures, so you can price shop too.

Finding a shop with a mandrel bender is next to impossible. Most shops won't spend $30,000+ $$$$ on a mandrel bender for the small amount of exhaust work they might get with it. Unless you're in a very classic car rich environment I doubt it would pay for itself. And if you found one I'm sure the cost goes up as well. Really makes these exhaust kits that much more appealing.