[71 T/A]

My 69 GTO's 462 build will be around 525 hp (maybe more) with KRE heads and OF 236/245 HRoller cam. Currently I have RARE 2.5" ram air manifolds that have about 10K miles on them and are as good as new. I'd like to retain these but hate to give up too much hp.

Would I lose at least 20hp with the RARE 2.5" manifolds and the 2.5 exhaust I have now with X crossover?

[steve25]

With a 462 cid motor you will drop off hp once the motor gets to about the 475 hp range with the high perfromance manifolds, but that's not to say that you can make over 500 hp, but yes it will be about a 15 to 20 hp loss at that point!

[tom s]

Are you ever going to race it on a reg basis?As this is the street section I would not not do headers onless a good HiPo castiron set of exhaust is not avail or I was going to race the car alot.JMO,Tom

[77 TRASHCAN]

there is a good read on SD Performance's website, under the tech column. They built a 400 block/4.5" stroke engine w/ ram air manifolds. It's not exactly like your build but gives an idea of how much can can be had w/such manifolds...

[tpssonic]

If the cam has yet to be ground, take the LSA out to 114+ if your compression ratio is not too high; you'll still have the cam lope and hp, and you'll reduce the the hp hit you'll take with the manifolds. Just a thought.

[71 T/A]

Cam will be on 114 LSA with compression at 10.37:1 along with 3.07 12 bolt, 3200 stall converter, Torker 2 and 1" Wilson 4-hole spacer.
Will race the car occasionally but not a lot.

[66bonne]

With that 3.07 rear gear I don't know that full tube headers would make much difference on the street or track. Is it an open rear? If it's a posi then I would invest in some gears first. Just my 2 cents based on personal experience.
If you want tube headers then you'll need a bigger [3"] exhaust all the way back. $$$$
Good luck with your decision. Hope to see you around sometime.

Jim

[66bonne]

Not to sound like a shill but if you decide to up the ante on the exhaust or new rear gears or whatever: Try my guys a ProFab Performance Plus at 727-849-9300. Outstanding work.

Jim

[ta man]

A fellow board member swapped to headers this year with a similar build but Edlebrock heads and picked up 4mph at the track..so 40hp?

[leeklm]

This is always an interesting topic for me, as I typically hate headers... My first 455 iron head build in the 66 made 400hp with the RA manifolds, and about 407hp with full length headers.

I then upgraded that motor to KRE 295 with stump puller, keeping the RA's. I never ran it on the engine dyno, but with the very noticeable seat-of-the-pants increase, I just left the RA's alone. Talking to Dave at SD, he did not feel I was leaving much on the table with that combo on RAs.

I am building my 73 to spend a little more time at the track, so am moving forward with headers just to be sure I am squeezing out every bit of HP the engine has to offer. We will see if I regret that decision Although installing headers with an automatic and no front clip should not be too much of a pain...

[Tom Vaught]

Originally Posted by steve25

With a 462 cid motor you will drop off hp once the motor gets to about the 475 hp range with the high perfromance manifolds, but that's not to say that you can make over 500 hp, but yes it will be about a 15 to 20 hp loss at that point!

I have seen 69 Grand Prix (390 HP Rated) STREET CARS many years ago run 12 teens with the old factory Long Branch Cast Iron manifolds. Not the RARE oversized stuff.

Wallace says that takes about 425 HP to do that.

The car was mild but quick. Would run around 110 MPH even with the low numerical ratio gear set and the Turbo 400 Trans.

How fast do you really need to be with a True Street car? Long Branch stuff works well.

Tom V.

[77 TRASHCAN]

Originally Posted by leeklm

This is always an interesting topic for me, as I typically hate headers... My first 455 iron head build in the 66 made 400hp with the RA manifolds, and about 407hp with full length headers.

I then upgraded that motor to KRE 295 with stump puller, keeping the RA's. I never ran it on the engine dyno, but with the very noticeable seat-of-the-pants increase, I just left the RA's alone. Talking to Dave at SD, he did not feel I was leaving much on the table with that combo on RAs.

I am building my 73 to spend a little more time at the track, so am moving forward with headers just to be sure I am squeezing out every bit of HP the engine has to offer. We will see if I regret that decision Although installing headers with an automatic and no front clip should not be too much of a pain...

I've seen headers be a maintenance issue w my stuff, and others. It's just something that has to be checked from time to time (my opinion) to make sure everything is holding up.

I've seen a lot of folks just slap their headers on, and not even look at the gaskets to see if everything was kosher, or check the header to head area on the headers to see if it's straight, or IF the header tubes against the head were flat.

Plus, there's many products on the market to help the header "headache", locking bolts, bolts w/ special washers. Several vendors sell gaskets nowadays that seal much better. Those old white asbestos gaskets, that always blew, are things of the past. I sold auto parts from 1985-1998, saw great strides in gasket technology, many have come along since 1998. I keep hearing about a company called Remflex, I don't know if their gaskets can be used for headers, OR if they even sell header gaskets, I'd like to know, I hear nothing but good about their products...
Jeff

[A.W.Dille]

Since I went with the Fel-Pro gaskets on the headers in my GTO I haven't had any issues. I've been running headers on it since 1987, only street use only now but would like to try some RA manifolds sometime just to see if there would be a difference but I keep thinking about the weight of the manifolds over the headers. But similiar performance can be had with the long branch manifolds and properly thought out exhaust system.

[Formulajones]

I've never had issues with any street car of mine with headers. Daily drive them for dozens of years and never have to touch them. I don't feel that just because this is a street section that it excludes headers in any way.

If you are looking for the most performance, headers will do that every time over stock exhaust manifolds, ram air or not. It's not just the peak HP numbers to be concerned with, it's the torque curve the long tube headers will produce below 4,000 rpms, and that's what you feel in a real street car.

Nothing against RA manifolds, I like them just as much as the next guy, but unless you are PS class racing where they are required, or just don't care about total power production, then you can't go wrong with a nice set of long tube headers.

If you go the RA manifold route, take tpssonic's advice and pay close attention to cam specs, and keep the overlap to a minimum so you don't take as much of a hit on power production using the manifolds. They just can't scavenge as well as a long tube header.

[71 T/A]

It's a 3.07 posi rear. I think it wouldn't make much difference with headers if I kept my 2.5" exhaust. If I went with 3" at least to the mufflers, then there would be more to gain.

Originally Posted by 66bonne

With that 3.07 rear gear I don't know that full tube headers would make much difference on the street or track. Is it an open rear? If it's a posi then I would invest in some gears first. Just my 2 cents based on personal experience.
If you want tube headers then you'll need a bigger [3"] exhaust all the way back. $$$$
Good luck with your decision. Hope to see you around sometime.

Jim

[Formulajones]

Get it on the dyno before you make that claim, you'll likely be surprised at the difference.

[71 T/A]

Originally Posted by Formulajones

Get it on the dyno before you make that claim, you'll likely be surprised at the difference.

On a 498 motor, SD Performance found only an 8 hp gain from 2.5 RA manifolds to Hooker headers. That engine used the same OF HR cam I'm using but my motor is 462.

[HWYSTR455]

Remember, consideration is needed when camming an engine that will run manifolds, LSA and RPM range are major factors. Manifolds favor wider LSAs, and generally prefer to stay under or around 5500 RPM.

If you take an engine with a single profile cam and headers and slap manifolds on it, you will see a greater impact/drop in performance than if it had a split profile favoring the exhaust side. (and wider LSA)

All pretty much what some others have been saying...


.

[71 T/A]

That's true. The cam SD Performance used in their test was on a 114 LSA and is what I'll use.

[Overkillphil]

There are always exceptions in this hobby but the general rule was that good quality headers (properly selected for the application) improved things across the board including power, efficiency and even mpg. But maybe that's "old school physics".