[JUDGE3]

always used headers. have the rare round port o/s ported manifolds now. lucky to have grabbed a set it seems. was surprised at how close the data is below from a great article previously posted. hmmm seems tweaks in other areas, suspension/fuel delivery would easily make up the difference for quarter mile times. like the f.a.s.t. guys do.

455 Dyno Test Results With Compression Bent Exhaust Extensions

Part Peak HP/RPM Peak Torque/RPM Avg. HP Avg. Torque

Hedman 443 at 5,400 479 at 4,300 424 456

RARE Ram Air 423 at 5,300 471 at 4,300 409 439

[steve25]

Looking at your posted numbers and what is the most important in regards to over all performance is the average hp and Tq numbers .

The choice for me would be clear.

Let’s look at just the rear wheel torque difference of let’s say a 3.00 ratio with no first gear factored in or torque converter multiplication.
The header set up nets you 1368 ft lbs, and the manifolds net you 1317.
50 ft lbs is a big plus I would want at my right foots command !

Another way to look at it is that a extra 50 ft lbs makes up for your power losses of driving your water pump, Alt and power steering.

[Tim Corcoran]

For a street car the RA/HO exhaust manifolds are a great option. Doesn't look like your giving up much. What is the combo?

[JUDGE3]

good article posted by zegermanham member.

headers always outperforms manifolds yes, I was just surprised at how close the manifolds are in comparison. figured a much bigger spread.

https://www.motortrend.com/how-to/hp...-vs-manifolds/

(see if link works this time)

[Skip Fix]

I think Lee Atkinson here on his personal bone stock 455 TA on his own chassis dyno posted a bigger change when he swapped on

[Quad]

SD performance have a good tech article on this topic. RARE OS manifolds can make almost as much power as headers. OR a lot less. Link below explains.

https://www.sdperformance.com/moreTech.php?newsID=39

[Formulajones]

Seems to rely a lot on the combo. Paul did back to back dyno testing on a 500hp 455 with sd ported heads and Paul's custom hydraulic roller and the manifolds were within just 3-4 HP and actually made more average torque on that engine.

That engine was for a member here and there was a nice thread on it a few years ago with all the build details and the dyno sessions.

[Skip Fix]

I think you are going to find it very combination specific on how much. Heck my 385-400 hp RAIV 400 liked smaller headers. My buddy's 455 E head ported by Dave and solid roller lost 40 hp on the dyno going from 2" to my 1 3/4-1 7/8 Hedmans. And an Edelbrock exhaust port is smaller than 1 3/4.

But looking at some of the cross sections of the RARE Paul used to bring to events they are pretty narrow.

[Verdoro 68]

My recent chassis dyno results really has me rethinking my decision to stick with R/A manifolds. What are the cam specs and head flow combos that tend to benefit more headers vs. losing very little with manifolds?

[Skip Fix]

http://forums.maxperformanceinc.com/...ht=header+dyno
Lee's numbers

[Skip Fix]

Look up the "collector" on the top.

[Formulajones]

Originally Posted by Verdoro 68

My recent chassis dyno results really has me rethinking my decision to stick with R/A manifolds. What are the cam specs and head flow combos that tend to benefit more headers vs. losing very little with manifolds?

There are quite a few variables. The entire build thread on the engine I spoke of is still here somewhere. I've put links to it in the past when this subject comes up. I think that engine made 520's for HP and near 600 ft lbs. It had iron d ports ported by Dave. I think around 260 CFM, and the hydraulic roller is the same one I've used, Paul's custom grind
239/243 on a 112 lsa.
The neat part is Paul posted the entire dyno graph back to back with headers and RA manifolds and they follow each other withing 3-4 HP and actually better torque with manifolds.
Owner of the car used to post here, can't remember his name.

['ol Pinion head]

SD CNC ported open chamber mod 670's on a 413 for James (vidguy).
Ended up being installed with 2.45" outlet RARE manifolds. Still impressed with this build!

http://forums.maxperformanceinc.com/...d.php?t=795059

[JUDGE3]

currently have the performer rpm intake, what impact would moving to a torker2 single plane intake have in using the rare exhaust manifolds?

comp cams h/r cam:

GRIND # P8 3317S /3318S HR110.0 Lunati 1.65 rockers

DURATION @ .050 INTAKE 242

DURATION @ .050 EXHAUST 248

VALVE LIFT INTAKE .540

VALVE LIFT EXHAUST .562 LOBE SEPARATION 110.0

INTAKE C/L 106.0

[jhein]

My motor made 429hp/522 tq with RA manifolds and 439hp/519tq with headers. Personally, for a strictly street car, I don't think that's enough of a difference to deal with header hassles.

[scott70]

My mild 455 made 491 hp with hooker 1.75 headers and made 475hp with 2.25" ra manifolds with a 2.5" mandrel bent headpipe.

[tom s]

I dont believe anyone could feel 10 HP on a 500HP pontiac in the ass dyno!Tom

[Stan Weiss]

On a flow bench. Would the exhaust port flow differently with a header tube and a manifold attached to the port? Would you then want to have a different exhaust lobe for headers verses a manifold?

Stan

[PAUL K]

Correct me if I'm wrong, I didn't have a bunch of time to read these comments or the article. But it looks like most folks feel the headers aren't worth the bother over the RA manifolds. But there is a bigger gain with the headers compared to RA manifolds than there is with the RA manifolds compared to the logs.

Why are the RA manifolds worth the cost, two year wait time when you could lose less (than the difference between headers and RA manifolds) using log manifolds which usually can be had for free.

[Verdoro 68]

Originally Posted by jhein

My motor made 429hp/522 tq with RA manifolds and 439hp/519tq with headers. Personally, for a strictly street car, I don't think that's enough of a difference to deal with header hassles.

Your engine is probably the closest to mine in terms of configuration, although your aluminum heads flow more than my cast iron ones. I'm totally comfortable giving up 10hp. For headers to be compelling I'd probably want to see a 20+hp gain.