[64speed]

Me and Paul have been going back and forth about the engine build and want vs need for a while now. I think we've settled on a regular iron head 455 with some healthy upgrades but nothing to radical as I will drive this car almost daily year round. In your opinion on a healthy 455 are headers a worthwhile investment or would you just run manifolds. My local muffler shop is a magician when it comes to fitment etc. but it's still crush bent tubing at the end of the day. I don't do the clamp thing so any set I have installed will be welded from collector to tailpipes. I also want to run GTO exhaust splitters on the ends of the pipes. How much HP do you think I will leave on the table with a 2.5 inch crush bent exhaust and GTO tips and would you run headers or not?

[DOC]

If a true daily driver, I would consider HO manifolds and build motor for efficiency with a little extra go. that way you dont need to worry about the extra maintenance and noise that goes with having headers. If concerned about the bends just remember factory HO/ Ram air cars had exhaust manifolds and similar pipe and did quite well. If you want the nice exhaust sound, Put some good mufflers on it. and enjoy driving it every day.

[tom s]

X2 on RA exhaust.Tom

[74Grandville]

something similar to a summit 2802 is very streetable in a 455.

[goatless]

Or you can do some simple mods to your log manifolds and they'll flow all you're going to need… especially if you install a crush bent system behind them.

One of many threads on the subject- http://forums.maxperformanceinc.com/...d.php?t=630943

[Carmine]

Not to long ago, I read an article in one of my car magazines re. long tube headers vs. RA/HO factory headers. They were looking for performance and horsepower differences. From what I recall and I hope I read that right, up to a 450 hp engine, there was a 9-11 hp lost when using the factory headers vs. the long tube. More then 450 hp, the long tube were far superior. The technicians conducting the test, felt that the factory header was a very good piece of equipment.
My '71 came with a set of beat up, dented, played out, rusted long tube headers. Couldn't wait to get them off. Didn't now what to replace them with, so did a little research. Decided on the factory RA/HO manifold which I bought at Ames. I prepared it first with VHT manifold paint and bolted in on. Fit nicely and I'm glad I bought them. No regrets. They not only look nice, but the system sounds great, Carmine.

["QUICK-SILVER"]

You really need to be asking Mr. C about this. Cam choice and RPM range will determine how restictive (or not) exhaust can be.

2.5" crimp bend duals, out the back, with 2" round port long tube headers....shot my 455 HO in the foot. Headers uncapped it would burn the tires through all 4 gears. Pipes hooked up, tire chirp was all you got in third and fourth. 245ish @ .050 cam with a bunch of overlap.

Talk to Paul!!!

Clay

[tom s]

I just took a 450 HP 455 off the dyno,Joe Sherman has been building and dynoing engines for a very long time and he figured I gave up about 15 HP with the RA manifolds with 2 1/2 pipes over my 4 tubes.I would leave you cam selection in Paul's hands and your wallet.I ran a SP 2 hyd roller with a HSD intake.Tom

[Formulajones]

I like the RA manifolds but for them to work their best you really need a set of mandrel bend head pipes coming off the manifolds. Worth a few ponies.

Most comparisons you find with RA manifolds vs headers generally use a mandrel head pipe off the manifolds, which gives a better apples to apples comparison and shrinks the HP difference between the two.

Lots of dyno comparisons out there with RA manifolds with crush bent vs mandrel bent head pipes.

Personally I don't and won't use a crush bent system on any car at all anymore. Just too much to be gained and no drawbacks.

Like others mentioned, cam selection will play a roll. A custom grind with exhaust manifolds in mind can make a difference in power output.

[SD455DJ]

Originally Posted by Formulajones

I like the RA manifolds but for them to work their best you really need a set of mandrel bend head pipes coming off the manifolds. Worth a few ponies.

Most comparisons you find with RA manifolds vs headers generally use a mandrel head pipe off the manifolds, which gives a better apples to apples comparison and shrinks the HP difference between the two.

Lots of dyno comparisons out there with RA manifolds with crush bent vs mandrel bent head pipes.

Personally I don't and won't use a crush bent system on any car at all anymore. Just too much to be gained and no drawbacks.

Like others mentioned, cam selection will play a roll. A custom grind with exhaust manifolds in mind can make a difference in power output.

X2 on what Formulajones said. We have dyno's many Pure Stock Pontiac motors (RAIII's, RAII's, RAIV's, 455HO's, SD455's) with both short and long branch manifolds and by far the worse thing you can do to performance is to use crush bent head pipes. You could run crush bent pipes beyond the Pypes mandrel head pipes and maintain 75% of the power of a full mandrel system.

Dennis

[Formulajones]

Thanks Dennis, I think it's a small detail that is often overlooked.

I've posted this before, and falls right in line with what you have experienced, but I think it's still worth mentioning. My stock RAIII wouldn't break out of the 14's if it fell out of a tree with the stock transverse muffler Gardner crush bent exhaust system. No amount of tuning changed that.
I installed a 2 1/2" mandrel bent transverse system and the car immediately ran 13.60 right off the street with no other changes. That was using what is considered a not that great Flowmaster Force II transverse system with an "H" pipe. I found this out 18 years ago with a little stock 400. Now with the car responding to changes, I eventually tuned it to go a tad quicker at that time. Now running a Pypes SGF70 transverse system with an "X" pipe to see if it's worth a little bit, but that's another subject.

[SD455DJ]

Yes, I forgot to mention you would still need good flowing mufflers and at least 2.5" crush bent pipes the rest of the way, including the tail pipes. The 'X' pipe is always a good addition, at least the cars always seem to ET/mph better if they are making in the true 350-400 hp range.

Dennis

[Formulajones]

I'm glad to hear that Dennis, hopefully my car likes the X. I do like the sound of this system better overall.

[AdamIsAdam]

Wanted to throw this into the mix...

https://youtu.be/c7PfOXP2Vf0

[tom s]

I have not had good success with X pipes with street driving.The couple times I have used them they have had a terrible drone at about 2000-2100 in my cars.A H pipe cured it in my applications.FWIW,Tom

[AdamIsAdam]

Really?! I always thought done was caused and cured mostly by the muffler selection.

[tom s]

As I said in my applications,I have come to like the sound and performance of Hushpowers on my cars,my setup did not like the X.Tom

[napster]

Excellent thread. Very good information.

[Formulajones]

I've never had a drone issue with X-pipes. I have 4 different cars here with X's, using Pypes, Dynomax, Flowmaster, and one with race style mufflers.

The only one that drones is the one with Flowmaster mufflers. I've had 3 different brand mufflers on this particular car over a 25 year period and the Flowmasters are the only ones that drone. So it's not due to the X in the system, not on this car anyway. Going back to a Dynomax on this car in the future for better sound control.

That's pretty much been my experience with every car. Drone has been a product of which muffler is chosen, and a slight amount of sound is influenced with the size of the pipe, some is due to the size of the engine and compression ratio. But I could never get a sound change running H's or X's on any particular car here and I've run both H's and X's for years.

Doing another F-body as we speak with a SGF70 transverse setup and X pipe system. I'm expecting it to be very similar to the 4 other SGF70 setups I've used (and still run on another F-body) Nice mellow sound at idle and cruise, growls at WOT, but cruises with no drone and easy to carry a conversation and listen to the radio. It just doesn't grab attention unless you want it to.

Just appearance alone tells me the X should be more effective at what it's supposed to do, and testing has shown that. Even on my street cars I'm always looking for ways to improve power and efficiency. Gotta get all you can with these tight PS rules

[MD79TA]

Just reading here is some more infohttp://www.hotrod.com/articles/hppp-0312-headers-vs-manifolds/