HP Manifold Performance

[John Milner]

How restrictive are the stock HP Manifolds?  I am going to be running a 440 in my '68.  However, I am not a fan of headers or spending $800 on a good set that will actually fit.  My engine setup is the following:

440 .040 six pack pistons, 9.5:1 compression
906 heads ported with 2.14 1.81 valves
Comp XE285HL 241 247 .545 .545 110
CH4B intake with 770 Holley

It is just a street car and won't see much track time.  Hoping to be in the 450-500 horse range. I was just wanting to see if I would be leaving a considerable amount of horsepower on the table by using the stock HP manifolds.

[c00nhunterjoe]

Yes, compared to headers they are quite restrictive. Your best option for running them is to gasket match their ports and notbing more. On that setup, probably worth 20-30hp loss depending on how much the heads actually flow.

[John_Kunkel]

Way too many variables to make an exact statement. For a street car, the results of installing headers versus HP manifolds might be disappointing on the old butt-meter.

https://www.youtube.com/watch?v=Y7_lSU3D0jw

[cdr]

When running the stock exh manifolds the camshaft needs to be in the 112-114 lsa, I would go 114 

[Challenger340]

Yeah, the 110* lsa is hurting you with H.P. manifolds, you should see close to 425 to 450hp though ? Again, lots of variables.

[BSB67]

How restrictive are the stock HP Manifolds? 

7

Hoping to be in the 450-500 horse range.

450 possible.  Not to sure with that cam.

[John Milner]

How restrictive are the stock HP Manifolds?

7

Hoping to be in the 450-500 horse range.

450 possible.  Not to sure with that cam.

Thank for the replies everyone. It sounds like some good performance can be had with the HP manifolds.  I guess if my Chevrolets or Pontiacs outrun my Mopar I can swap to headers.

[heyoldguy]

On a 440 with stock 906 heads, stock intake and stock carburetor, HP exhaust manifolds, summit 6400 cam and 7.5:1 compression, when we switched to headers we saw a 15 lb-ft increase @ 2,500 rpm, +14 lb-ft @ 3,500 rpm, +18 lb-ft @ 4,500 rpm, +22 HP @ 4,800 rpm and + 16 HP @ 5,500 rpm.

[Dino]

On a 440 with stock 906 heads, stock intake and stock carburetor, HP exhaust manifolds, summit 6400 cam and 7.5:1 compression, when we switched to headers we saw a 15 lb-ft increase @ 2,500 rpm, +14 lb-ft @ 3,500 rpm, +18 lb-ft @ 4,500 rpm, +22 HP @ 4,800 rpm and + 16 HP @ 5,500 rpm.

In other words, not worth the headache on a street car.   

Soooo glad I got rid of these damn headers and found some nice HP manifolds.   

[Mike DC]

  
Here is the perfect link.  A HOT ROD magazine test from 2001 (that was already 16 years ago!) comparing manifolds, shortys, and full-length headers on a mildly built-up 440.  Who says all-brand magazines never do any good Mopar tech?  

http://www.hotrod.com/articles/mopp-0106-manifolds-vs-headers/


short answers:  


--  The power outputs are exactly what you'd expect:  manifolds < shortys < headers.  The proportions suggest it's just the pure and simple size of the items.  Nobody is ever gonna make a compact header with a few different twists or a slightly bigger tube and recoup what is lost compared to full-length headers.  

 
--  The power gains are steadily ramping up over the RPM range.  But even with full length headers you won't really feel much difference under 3000-4000 RPM.  The manifolds work fine until they start getting overstuffed and it takes some revving to do that.  If you drive the engine like a pickup truck then replacing the manifolds with headers is fixing something that isn't broken.  But if you drive the engine like a drag racer then yes, please switch to full-length headers.
 

[JR]

I switched from HP manifolds to ceramic coated shorty headers, and definitely noticed a power difference on the butt Dyno. Not to mention, much cooler underhood temps, and a 20 lb weight reduction on the nose. (36lbs vs 17 lbs.)

I love the Shorty's, I'll never go back. I think the important thing is to buy a quality set if you're going to headers.

[BSB67]

You think that is a good article?  It is of little real value to me.  You cannot draw any conclusions that can be extrapolated to any other situation.  Most magazine articles and other dyno cessions posted really are not conducted and reported in a way that there is much real meaningful information.  They are done in a hurry up fashion to get something published before the deadline.

I actually think that O2 sensors, flow benches and dyno have made only a small amount of people smarter and the rest of the hobbiests dumber.

[BSB67]

I switched from HP manifolds to ceramic coated shorty headers, and definitely noticed a power difference on the butt Dyno. Not to mention, much cooler underhood temps, and a 20 lb weight reduction on the nose. (36lbs vs 17 lbs.)

I love the Shorty's, I'll never go back. I think the important thing is to buy a quality set if you're going to headers.

Were there any other changes to the exhaust system or did you splice the new headers directly into the old exhaust system and changed nothing else?
What cam was in the motor?
Heads?
Compression ratio?
What is the before and after hp, or track data and atmopheric conditions?

I have probably done butt meter 100 times and its been wrong 50% of the time when the changes are actually measured at the track?

[alfaitalia]

I rarely find (on cars or motorcycles) that any changes made to make a vehicle quicker or faster on the track, make the same vehicle nicer to drive on the road. Sacrificing torque for high revving power..even if it's quite a bit more power..do not usually make for a flexible torquey road motor. And that's what you need in a nice driving street car. I would have low rev torque over high rev power on the street every time. Is what makes the car feel alive.

[Mike DC]

You think that is a good article?  It is of little real value to me.  You cannot draw any conclusions that can be extrapolated to any other situation.  Most magazine articles and other dyno cessions posted really are not conducted and reported in a way that there is much real meaningful information.  They are done in a hurry up fashion to get something published before the deadline.

I actually think that O2 sensors, flow benches and dyno have made only a small amount of people smarter and the rest of the hobbiests dumber.

I think it tells the average hobbyist with a street car what he wants to know.  What are the relative gains from three of the most popular choices for this part?  It's a simple 3-product comparo on a popular engine.

Much more could be said about choosing headers for a racecar.  Primary diameters versus displacements & RPM, collector lengths, etc.  But a reader who is interested in that stuff was never considering shorties or manifolds to begin with.  That guy just needs a different kind of article.

Granted, one big article could combine both sets of issues.  That's the most informative way of all.  But on the other hand that would be a long one with a bunch of tables to wade through.  And most readers, being either the street car builder or the racer, would only be interested in half the stuff in the big epic article.    

[BSB67]

You think that is a good article?  It is of little real value to me.  You cannot draw any conclusions that can be extrapolated to any other situation.  Most magazine articles and other dyno cessions posted really are not conducted and reported in a way that there is much real meaningful information.  They are done in a hurry up fashion to get something published before the deadline.

I actually think that O2 sensors, flow benches and dyno have made only a small amount of people smarter and the rest of the hobbiests dumber.

I think it tells the average hobbyist with a street car what he wants to know.  What are the relative gains from three of the most popular choices for this part?  It's a simple 3-product comparo on a popular engine.

Much more could be said about choosing headers for a racecar.  Primary diameters versus displacements & RPM, collector lengths, etc.  But a reader who is interested in that stuff was never considering shorties or manifolds to begin with.  That guy just needs a different kind of article.

Granted, one big article could combine both sets of issues.  That's the most informative way of all.  But on the other hand that would be a long one with a bunch of tables to wade through.  And most readers, being either the street car builder or the racer, would only be interested in half the stuff in the big epic article.    

What was the cam specs?  what is the CR?  how was it set up on the dyno? were there exhaust pipes?, what size? Were there mufflers? what kind? Did the headers have collectors? Was the carb tuned for each?  Without knowing any of that stuff, you really cannot conclude anything.  Dynos/dynoshops are not normally set up for manifolds.  I wonder how they cobbled that together?

At a minimum, you need to run the same complete exhaust system for the comparison of one exhaust to the other for the data to have any meaning, especially for a street guy.

[JR]

I switched from HP manifolds to ceramic coated shorty headers, and definitely noticed a power difference on the butt Dyno. Not to mention, much cooler underhood temps, and a 20 lb weight reduction on the nose. (36lbs vs 17 lbs.)

I love the Shorty's, I'll never go back. I think the important thing is to buy a quality set if you're going to headers.

Were there any other changes to the exhaust system or did you splice the new headers directly into the old exhaust system and changed nothing else?
What cam was in the motor?
Heads?
Compression ratio?
What is the before and after hp, or track data and atmopheric conditions?

I have probably done butt meter 100 times and its been wrong 50% of the time when the changes are actually measured at the track?

I only changed to headers when I compared them. Drove it back to back over a weekend before and after in 85 degree, Southeastern​ humidity. Both times ran through the complete exhaust with stock style mufflers.

My 440 is a complete turd though, built from what I had lying around at the time.
Fuel injection, 9 to 1 compression pistons, 452 heads, Comp XE268 cam, and mild converter.
(Maybe the low power of my engine is why the difference was so noticable.)

But my car sees 80% highway driving/20 percent Autocross use, and absolute power wasn't my main pursuit. I wanted lower underhood temps and less weight on the nose. Any extra power was a bonus.

I'm not saying headers are gold and everyone should swap. I'm just saying in my case they're great, they definitely made power, lowered weight/underhood temps, and I'm glad I have them.

[BSB67]

So the headers were tied into the old exhaust?

[JR]

Yes, both HP manifolds and shorty headers were tied into the same, full exhaust, and the EFI tune was reset to allow for the difference in the exhaust. No other changes were made.

[PRH]

440 .040 six pack pistons, 9.5:1 compression
906 heads ported with 2.14 1.81 valves
Comp XE285HL 241 247 .545 .545 110
CH4B intake with 770 Holley

It is just a street car and won't see much track time.  Hoping to be in the 450-500 horse range. I was just wanting to see if I would be leaving a considerable amount of horsepower on the table by using the stock HP manifolds.

That wouldn't get very close to 500hp on our dyno.

Might get close with some headers(450-475) depending how good the heads are.

It's a lot harder to make any real power with ex manifolds than most people think.

[Mike DC]

What was the cam specs?  what is the CR?  how was it set up on the dyno? were there exhaust pipes?, what size? Were there mufflers? what kind? Did the headers have collectors? Was the carb tuned for each?  Without knowing any of that stuff, you really cannot conclude anything.  Dynos/dynoshops are not normally set up for manifolds.  I wonder how they cobbled that together?

At a minimum, you need to run the same complete exhaust system for the comparison of one exhaust to the other for the data to have any meaning, especially for a street guy.

You're right.  The article should have done a better job about giving the rest of the exhaust system consistency & specs.  And the fact that certain cam specs work better with one exhaust setup than another, needed to be addressed. 


But lots of guys will buy a car/engine and drive it for years without even knowing the cam specs or compression ratio.  That guy will ask about the manifolds/headers question and he just wants a ballpark answer.  The same racers who give very detailed answers to a camshaft question will just roll their eyes and say "Oh lord, stock manifolds are gonna cost a ton of power."  No shit.  That's not a very helpful answer.  The HOT ROD article gives a more helpful answer to the question without risking going over the reader's head with details.  And IMO just seeing the proportional differences between the results is more valuable than any of the specific data. 
 

[BSB67]

Yes, both HP manifolds and shorty headers were tied into the same, full exhaust, and the EFI tune was reset to allow for the difference in the exhaust. No other changes were made.

That was all good info that completes the picture....thanks

[PRH]

As an example of how bad it can be if you're not paying attention.....
(I had nothing to do with this build)

Fresh rebuild of an original 71 440-4hp.
Recon original 346 heads, hardened ex seats, comp 911 springs.
Icon makes a couple of std replacement type pistons, low cr and hi cr...... Of course this was done using the low cr version with the resulting cr being 8.2:1.
Comp xe268h cam, stock intake, magnum ex manifolds, edelbrock 750 carb.
2.5 exhaust pipes, no mufflers, stock air filter installed.......

427tq/304hp........ At the crank!!!

Motor runs fine, no issues, no noises.......no power.
It probably made a peak tq number a little higher than that, but they started the pulls at 3000rpm, which is where the highest tq number was seen, and it dropped like a rock after that, so the actual peak was probably occurring at a lower rpm. Peak hp was at 4700rpm.

Customer obviously isn't happy with it since its weaker than when it was stock.

The decision was made to take a big swing at it.
505, 10:1, prepped/blended stealth heads, custom mild hyd cam, 800 Ede AVS carb.
Will still run the OE intake and exhaust manifolds....... Should be back on the dyno fairly soon.

This will be the mildest of these types of motors I've been involved with, but I'm not expecting big numbers at all.
I figure........ A gain of 125-150ft/lbs, upwards of 150hp........ So...... Still pretty far away from 500hp.
This motor will not only have the ex manifolds on it, but also the highly restrictive stock 4bbl intake manifold.
It may not be able to carry the tq curve high enough to get to 450hp.

We'll see.

[heyoldguy]

On a 440 with stock 906 heads, stock intake and stock carburetor, HP exhaust manifolds, summit 6400 cam and 7.5:1 compression, when we switched to headers we saw a 15 lb-ft increase @ 2,500 rpm, +14 lb-ft @ 3,500 rpm, +18 lb-ft @ 4,500 rpm, +22 HP @ 4,800 rpm and + 16 HP @ 5,500 rpm.

In other words, not worth the headache on a street car.   

Soooo glad I got rid of these damn headers and found some nice HP manifolds.   

The engine was making a whopping 413 lb-ft @ 2,500 rpm and 276 HP @ 4,100 rpm with the cast iron HP manifolds. But I'm wondering if anyone has checked the fuel economy after changing to headers. I remember when we were putting headers on 40-50 years ago (Lordy, am I that old?) that there was always a significant increase if mpg with the headers. I haven't checked anything like that for a long time, but about ten years ago my son put a set of headers on his 1989 318 pickup and gained some 3 mpg.

[PRH]

For the most part, it's a pretty safe assumption that the more power the motor makes, the more difference there will be.
However, I have seen some pretty low hp combos respond very well to the addition of headers.

10-15 years ago, I was working with a builder here who did a lot of these low cr 2bbl sb Chevy motors.
The rules were: 8.5cr, stock 2bbl intake, OE 1.72 valve heads, hyd cam, stock rockers, no stud girdle, holley 4412 carb, stock non-ram horn ex manifolds, 2" max diameter ex pipe.

Most of them made in the mid-270's for hp, if you had the good heads.
The less desirable heads would struggle to get to 270hp.
The good heads and an acid ported intake with what we had found to be the "best" cam for that application could get you into the 280-285 range. That was as good as we ever saw from one(and those had won several track and series championships).
Take one of those 280+hp motors, pull off the manifolds and install some decent 1-5/8 x 3 headers with 12" collector extensions........ They'd pick up 40hp(320hp+).

A few years later the rules changed to allow headers and solid lifter cams, and then they were in the 350hp range.