[steve25]

Cut in stone facts are the lower your motors compression is from 9.5 the more the motor needs headers if your building it for performance and you want to even get to 90% VE in terms of even just a street build!

A set of exh manifolds that might just be cutting it for a 400 can turn into a nice size choke point once you try to exhale a 13% larger motor out of it like a 455 for instance.

[Sirrotica]

Originally Posted by Skip Fix

For all you guys that say factory manifolds are as good as headers look at the results in that factory test!

If you've ever looked at a Pontiac test, whether it was drag strip testing, or dyno testing, the shorty headers perform poorly compared to full length headers. The RA manifolds are very similar to the shorty headers, possibly even a bit better than the cast manifolds.

I've always used long tube headers on my cars (street, and race cars) unless the rules required cast manifolds. The extra tube length has always performed better, by a wide margin. It seems that no matter how you rework the manifolds, or what extension pipe you use, the headers always come out on top by a bunch, not just a small margin.

The most radical exhaust I used with RA style manifolds was, D port manifolds with a short stub off the manifold dumping into a 4 inch tube that terminated just in front of the rear axle. It was much superior to a stock 2 1/4" head pipe that I ran at the beginning of the racing season. This was a restricted class that had to use cast iron exhaust manifolds. The 4 inch pipes helped a bunch.

The 2nd picture with the checkered flag in my signature has the 2 1/4 inch pipes, if you look closely they come out behind the door. They eventually got flattened and resulted in a blown head gasket, necessitating a reconstruction of the head pipes. Since money was tight, and I had plenty of extra driveshafts, I cut the ends off the driveshafts, and used the thick wall tubing for exhaust pipe.

Engine was a 400, with 48 heads, and an 068 cam.

Since I ran oval track cars, and street cars there was no dyno involved, but I would never be happy with cast exhaust RA manifolds, if I had the option of full length headers, Just my experiences, YMMV.

[Formulajones]

Headers vs manifolds don't always show big differences like one might think. It really depends on a lot of factors.

Here is a 455 that Paul did, with a direct comparison between RA Manifolds and 4 tube full length headers.
Post #1 is dyno with the headers
Post #47 is some video of the pulls
Post #49 are the numbers with RA manifolds in place.

As you can see the manifolds actually did as well or better through most of the curve, and didn't loose the HP one might think. In fact, the biggest difference with the headers were all at 2500 rpm and below where you see the most gain. After 2500 rpm it's a wash.

The cam is a custom grind to Paul's specs for this build, that worked so well it's the same cam he spec'd for the 455 I built for John I posted earlier, which made 507hp with the exhaust manifolds in place.





https://forums.maxperformanceinc.com...d.php?t=808474

[taktikian]

Yes Steve, All that has been done to my 614 heads is a multi angle valve job as described in the old H-O books, port matching and cc'd at 70. Butler supplied the 27cc dished pistons to achieve 9.9 c.r. using the Cometic head gaskets. Factory intake and Q-jet just received from SMI supposedly now flowing 860cfm. Crower 60245 and factory RamAir exhaust manifolds. Forged lower end of course. I agree with you that I would be in the 480 hp range at best

[taktikian]

Thats kind of like how I felt. I selected a cam with a 112 lsa anticipating using the RA manifolds and 2 1/2 header pipe. If it does not produce the power anticipated headers are always an option . The builder might have a set to utilize if I request for a test.

[Skip Fix]

When I had my 614s on a 455 we had the pistons down .100 to reduce compression(not the best idea),HO intake 73 SD Q jet, Ultradyne 288/296 HFT made 430 HP on a very stingy dyno 2" headers through mufflers. One pull the mufflers popped of and picked up a bunch as it did uncorked at the track. 1/4 mph was 117 weighing close to 3900lbs.

I'd sure pay attention to cam choice using 614s mine had a 85% E/I ratio. Most of the Stock and SS RAIV guys run a single pattern.

[Formulajones]

That's an interesting point.

The 455 Paul did that loved the RA manifolds used 670 D-port heads done by Dave. I think the flow numbers were posted somewhere in that thread so the I/E ratio can be determined if interested.

The heads used on the 455 I did were factory 7F6 HO round port heads, while not 614 RA IV's, They are pretty good flowing heads that were ported to 280 cfm as checked on Paul's flow bench after he did some work to them. I think the exhaust was 222.

I have those flow numbers too and now you have me curious to go back and see what the I/E ratio is and compare that to the 670's that Paul tested earlier.

Both engines used the same camshaft, and both engines liked the RA manifolds.

Edit: Quick math on both I'm seeing an average of 76-79% for both sets of heads.

[SD455DJ]

This is a great topic and here are our SD455 experiences to add to the conversation. Since we are die-hard pure stock racers, so we always are interested in how good (or bad) the factory installed engines were.

Dan rebuilt my old ’73 SD455 for the new owner (in 2015) to go into the newly restored body (BG 4-speed TA) and was a stock rebuild. The bottom end was enhanced with new forged Eagle H-beam rods and .040-over mini-dome Diamond pistons with the std. ring pack, full floating pins, and zero decked with .040 quench. The oil pump was the original 80 lb.-er, so didn’t take advantage of less parasitic hp loss with a 60 lb. pump. The heads were cleaned up with a minimal cut and the chambers measured in at 108 cc’s, new Ferrara 1-pc SS valves and new springs with similar specs to the factory pressures. The mini-dome pistons got the compression up to 9.4 to 1. The original ‘Y’ cam and factory lifters were in great shape (46k miles) and reused along the factory 1.5 rocker arms and pushrods. The original cracked factory RA exhaust manifolds were replaced with RARE 2.5 outlet manifolds. The original factory intake manifold and 7043273 Q-jet were reinstalled too. So, other than the 1.0 higher compression and slightly lighter pistons, it was a pretty stock rebuild.

On a fairly conservative dyno with Pypes 2.5” headpipes (4’ long) dumping into the dyno cell 6” sewer extensions into the sound chamber, the best numbers were 417.9 hp @ 5000 rpm/500.0 ft.lbs @ 3600 rpm. FYI…the SD455 Whistled at 8.2 compression prior to the rebuild and was already .030 over with old TRW SD pistons from an old 1978 rebuild. It looks like the original engines power numbers would have been pretty close to the McCully dyno test of 384 hp/458 lbft with Firebird exhaust, however, with the smaller ‘Y’ cam maybe closer to 365 hp/475 lbft. We now wished we had headers to compare to.

I believe the McCully tests were with the ‘K’ cam (308/320) and the Firebird exhaust was the more restrictive std. duals for a ’70 T/A or RA Formula, so not the SD system with bigger pipe and better muffler the production SD’s eventually got. It seems like the long stroke (read 455 with higher piston speeds) engines respond to headers better than the shorter stroke engines, so I believe headers would/could make a 50 hp difference on a 455.

Dennis

[steve25]

I agree also that since these test where done in 71 that they would be using the K Cam.

Thanks for posting your dyno test!

[Cliff R]

I've done a handful of 455 SD engines here, at or very close to "stock" with only a "mild" HR cam upgrade.

Attached is the cam card and dyno sheet from one I did a few years ago. The block was zero-decked, Icon pistons, 1016 head gaskets, stock intake, carb and distributor. I used the 60lb oil pump instead of the 80.......Cliff

[SD455DJ]

Cliff, What was the compression on that SD455 you dyno'd?

Dennis

[Cliff R]

I did not calculate it out, but close to stock.

I didn't cc the heads and they had been cut once before. I only had enough removed from them to clean them up. Best guess around 8.5 to 8.8 to 1 with the flat top Icon pistons and 2 valve reliefs.

I'd add here that the engine made around 16" vacuum at idle speed and dead smooth clear down to 600rpms with that "little" roller cam in it. Considering it quit around 5200rpms also tells me it would have loved another 10 degrees seat timing.

One has to consider that the 455 is a HUGE engine and when you outfit it with good flowing heads they gobble up 230 @ .050" camshafts and beg for more. I saw the same thing way back when I built a 455 topped with early Edelbrock round port heads. I used the Crower 60919 cam and although it made great power, 505hp/551tq it was DONE at 5100rpms.......

[Skip Fix]

I know there was a guy in the old NMCA Pure Stock with and SD 455 that always did well in class racing. Heck they P&G'd us when you won class and checked idle vacuum to factor for cam HP.

[taktikian]

If the manifolds really would cost 50 h.p. I would have to reconsider. That is alot of power to leave on the table.

[steve25]

I ran this solid roller cam in a .030” over 455 with mildly ported 1971 # 96 heads with 1.65 rockers in NA form before I plopped a blower on it.

The motor had 8.8 comp and once warmed up would idle rock solid at 800 rpm .

[Formulajones]

Originally Posted by taktikian

If the manifolds really would cost 50 h.p. I would have to reconsider. That is alot of power to leave on the table.

It's really a case by case basis. As you can see from what I linked in a previous post, not all these Pontiacs respond to headers. Even a pretty healthy engine like that 455 was making over 500HP and breathed just fine through the manifolds, the headers didn't do anything above 2500 rpm. But that's why we test these things. You would really need to put your engine on a dyno and test to know if it's worthwhile or not.

[steve25]

Please keep in mind that rust pimples inside used exh manifolds or headers especially in bend areas can cut deeply into hp numbers and make quite a difference!

Years upon years ago I was in a dyno test of a car club members SBC 350.
The test started with the guy using his ram type exh manifolds that he had been running in the car forever!
Now these are the best flowing exh manifolds you can run on a early SBC,

After 4 pulls and maxing everything out I said your still down like 35 hp from where I think you should be at 6000 rpm,
On a hunch the shop owner pulled out a set of far more restrictive BUT new truck type emissions log manifolds and we did a swap.

On the next pull the motor was up 25 hp at 6000 rpm and the BSFC numbers where a tad better to boot!

Don’t overlook possible issues like this folks!!

[Skip Fix]

Talking even about header tests I have a set of 1 3/4-1 7/8-3.5" step Hedmans The Edelbrock exhaust port is barely 1 3/4 in size. We swapped them on a friend's roller cam E head 462 640 HP over the 2" and LOST 35 hp! Kind of shocked even the dyno operator we lost that much.

[PAUL K]

Originally Posted by Skip Fix

Talking even about header tests I have a set of 1 3/4-1 7/8-3.5" step Hedmans The Edelbrock exhaust port is barely 1 3/4 in size. We swapped them on a friend's roller cam E head 462 640 HP over the 2" and LOST 35 hp! Kind of shocked even the dyno operator we lost that much.

That is surprising. On a 750 horsepower 455 there wasn't a lot of difference between some 2" Hooker SC and a pair of Doug's 1 7/8.