HP Manifold Performance

[heyoldguy]

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.

Until you've tested it, it's hard to believe just how restrictive the stock intake is. I was stunned when I flow tested a stock 1969 intake on an Edelbrock RPM cylinder head and then compared it to the RPM intake manifold. The intake port on the head would flow 276 cfm @ .500" lift, I added a 850 cfm carb and used a stock iron intake and it restricted the flow to 199 cfm. Just switching to the Edelbrock RPM mainfold increased the flow to 240 cfm.

[PRH]

Between the ex manifolds and the stock 4 bbl intake........ That 505 definitely has 2 strikes against it.

The guy putting it together said to me, "think it'll make 500hp"?

I just kinda chucked and said, "never say never........ But........ I highly doubt it".

When we were discussing the plan for this motor, I was thinking 550tq/425-450hp.

Swap the intake, add some headers....... Should easily make over 500hp.

[Mike DC]

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.

Having non-rams-horn manifolds would be a factor.  All manifolds are weak next to headers but some are still better than others.  Straight iron logs are pretty bad.  

Some of the newer Chevy LS motors have stock manifolds shaped like Mopar B/RB hi-po ones.  

[firefighter3931]

Here's another "manifold" build to chew on :

A buddy is restoring a 64 Polara with the basic 426 street wedge under the hood. He was wanting it to look completely stock as if it came out of the factory. I did talk him into a set of 440 Stealth heads to make it pump gas friendly but that is the only concession.

Basic breakdown of the build ;

-413 truck block bored out .070 to produce 426ci
-Forged crank, reworked stock rods, measured 9.8:1 compression
-Stealth heads with basic prep, valve job, guide clearance adjustment (no porting)
-Carter 750 AVS carb
-Dual point distributor (best power @ 34* total timing)
-Stock 64 intake with very restrictive intake runners (reminded me of the old SP2P)
-Stock 64 "log" exhaust manifolds (definitely inferior to the later HP manifolds)
-Cam is the Crane H278 grind which is a "manifold friendly" cam:

222/234@.050
.467/.494 lift
114 LSA installed @ 110 lobe centerline

Dyno results : 352HP/450Tq and it's all done @ 5200

The engine idles great and makes lots of vacuum. Idles as smooth as a 318 2bbl. Overall he is happy with the manners but is a bit disappointed with the power numbers. This car will never see the track and is 100% a cruiser that runs skinny bias ply white walls. He was hoping for 400hp/500tq but those manifolds really choked it up. I offered up my CH4B while it was on the dyno but he refused to even test it. I'm pretty sure he didn't want to know how bad that factory intake was holding it back so he's left with a stock looking, underwhelming motor. As they say ; it is what it is.


Ron

[PRH]

It would have been interesting to play with a few things on that 426 build.

Intakes, magnum hp manifolds, and some cleaned up mildly reworked stock valve size 915's and/or 516's.

I'm not sure the big valves and added runner volume really does anything for you on a really mild small bore build like that.

Sounds like it made what it "should" though.

Where were the tq/hp peaks?

Basically, I'm looking for the 505 build to make 100tq/100hp more than that 426.

I'm a big believer in building the motor "bigger" if you're wanting to keep the overall character of the build on the mild side, and you want to use ex manifolds.

[Challenger340]

The only part I hate about commenting is having to go dig around for the Dyno Sheets later ?

We did a 400 Block based "451" awhile back, but done a little differently for a "resto" street car using H.P. Manifolds.
The guy had to have VERY quiet running, so no potential Piston noise common with many of the lower C.D. 451 Pistons.
As close to "stock" under hood appearance as possible

3.75 Stroke Source Crank
Diamond Custom Piston on 1.72" C.D.
383 Length H-Beams
Our std 12 Hr prepped Stealth Heads (for stock appearances)
Eddy Performer rpm (ground off external markings, and hidden)
CompCams Hyd Roller on 112 lsa, can't remember but I think high 230's or very low 240 @ .050 ?

Geez I am getting bad !    6 months goes by and I forget exactly WHAT we did or used inside an Engine ? arrgghh

Dyno 2" Headers for EGT was around 575 hp @ 56-5700 rpm ? and 560 Ft/lbs ?
then,
* switched to the H.P. Manifolds and 2 1/4" pipes
* installed factory Snorkel Air Cleaner.....
just over 500 hp ?... maybe 507 hp ?  if I remember right, after tuning, simulated highway drives on the Dyno, etc. etc., but still TONS of Torque down low.

[Mike DC]

The engine idles great and makes lots of vacuum. Idles as smooth as a 318 2bbl. Overall he is happy with the manners but is a bit disappointed with the power numbers. This car will never see the track and is 100% a cruiser that runs skinny bias ply white walls. He was hoping for 400hp/500tq but those manifolds really choked it up. I offered up my CH4B while it was on the dyno but he refused to even test it. I'm pretty sure he didn't want to know how bad that factory intake was holding it back so he's left with a stock looking, underwhelming motor. As they say ; it is what it is.

If he ever tried driving it with a stock-painted aftermarket intake + HP manifolds, I'll bet he wouldn't swap it back to stock.

[BSB67]

For five years there were five of us guys running 5 Mopars regularly at Test and Tune. They all got to be 400 hp ish cars.  Two were exhaust manifold cars, the others had headers.  There were probably over 1000 track pass between all of us.  We tested a mountain of stuff within the realm of fairly docile street cars.  We tried cams, carbs, intakes, exhaust systems, tires, gears, converters, heads, ignitions....It was a bit of a competition.  

The two manifold cars were usually the fastest, mine and another guy.  In the end, my car would run almost 109 mph @ 4200 lbs with a 2 1/2" compression bent head pipes, and 2 1/4" muffler.  Usually good air 1000-1500 DA or so. Moroso Calculator has it at 410 net actual hp.  Probably 440 corrected gross hp (dyno hp). So if you believe that article, my mild 440, with a .455" cam and stock valve sizes would make 70 more hp (i.e. 510 hp) with some headers. That means it would trap at 116 mph.  Okay.

We learned a lot of stuff during those years.  One fairly clear conclusion comparing the cars and the changes we made....if your BB mopar is well tuned and is around 400 hp-ish (i.e. a 12 second street car) with not a stupid cam (i.e relative small overlap) there is not that much difference between manifolds and headers.  Your probably looking at 20 hp, maybe 25, max.  Now if you have a 509 cam with manifolds, and make 400 hp, you might see a 50 - 60 hp jump going to headers.

One guy finally beat me pretty well.  He had basically my short block, but his was fresh, my heads but with bigger valves, his car was 200 lb less, had a small solid flat tappet, and he had a manual tranny, and went 112 mph with his brand new 1 7/8 TTI headers and full mandrel bent exhaust.

[PRH]

Last year we rebuilt a 440-6 that was the numbers matching motor for a Superbird that was being restored.

No block decking, .030 over, 2355 pistons, rebuilt the 906 heads, hardened ex seats installed, upgraded springs, flat mill minimum, zero porting.

It got a Howard's 720141-12 camshaft(279/289, 225/235, .490/.488-112), and was run on the dyno with 1-7/8" headers.
It made 495tq/410hp.

I don't know how much it would have lost with manifolds, but I have to think it would have been 20-30hp.

If I had it to do over I probably would have used the Crower 271HDP cam instead.

[Mike DC]

The two manifold cars were usually the fastest, mine and another guy.  In the end, my car would run almost 109 mph @ 4200 lbs with a 2 1/2" compression bent head pipes, and 2 1/4" muffler.  Usually good air 1000-1500 DA or so. Moroso Calculator has it at 410 net actual hp.  Probably 440 corrected gross hp (dyno hp). So if you believe that article, my mild 440, with a .455" cam and stock valve sizes would make 70 more hp (i.e. 510 hp) with some headers. That means it would trap at 116 mph.  Okay.

We learned a lot of stuff during those years.  One fairly clear conclusion comparing the cars and the changes we made....if your BB mopar is well tuned and is around 400 hp-ish (i.e. a 12 second street car) with not a stupid cam (i.e relative small overlap) there is not that much difference between manifolds and headers.  Your probably looking at 20 hp, maybe 25, max.  Now if you have a 509 cam with manifolds, and make 400 hp, you might see a 50 - 60 hp jump going to headers.

One guy finally beat me pretty well.  He had basically my short block, but his was fresh, my heads but with bigger valves, his car was 200 lb less, had a small solid flat tappet, and he had a manual tranny, and went 112 mph with his brand new 1 7/8 TTI headers and full mandrel bent exhaust.

All true.  Swapping to headers and getting a 60-70 hp gain is a lot for any motor.  That article's motor must have been a whole notch hotter than stock.  Probably lots of cam overlap.  Maybe opened up heads too.    They should have made it clear that the deck was so stacked in favor of headers with the motor they used.  
 

[BSB67]

All true.  Swapping to headers and getting a 60-70 hp gain is a lot for any motor.  That article's motor must have been a whole notch hotter than stock.  Probably lots of cam overlap.  Maybe opened up heads too.    They should have made it clear that the deck was so stacked in favor of headers with the motor they used.  
 

And that is my point.  The magazines are full of aftermarket advertisers.  Chrysler is not advertising exhaust manifolds.  The deck is stacked.  It has to be.

Listen, if you don't mind headers, and you have the money,  and you are looking for all the power you can get, it would be silly to not put on headers.  If you get the right size, headers are one of the very few performance add-ons that adds power everywhere in the power curve.  Let's just be realistic about what we are talking about when it comes to a slightly warmed up street car.

Finally, ( I probably should not say that), if you have a mildly warmed up street car with exhaust manifolds (or not), and you want another 20 to 30 hp and you are contemplating spending another $750 to get it, try instead going to the track with a hand full of tools.  I promise you can find the 20 to 30 hp.

[PRH]

I guess I look at it differently.

While there will be exceptions to this, I feel like if you're really after making some power, you're definitely stacking the deck against yourself by not running headers.
It's not just the power the headers themselves make, it's all the doors they open up for doing other things that often don't work well with manifolds.
Sure, if you're only looking at making 350-450hp from a big block with the better of the factory ex manifolds, that's not going to be that much of a challenge........ But beyond that power level, you'll really start to see diminishing returns.

I'll say it again........... some of the higher output FAST motors I've tested would have gained 75-100hp by installing headers and then taking advantage of them by installing a cam to exploit the reduction of exhaust back pressure and the addition of proper scavenging. Two changes......headers, cam.......75-100hp.

The best FAST motor I've tested that used magnum ex manifolds didn't make as much hp as a fairly bread and butter stock stroke 440 based bracket build with std port heads and a flat tappet cam........ And the FAST build was probably 2.5 times the cost.

I've been involved with several ex manifold combos that run pretty quick, but it's certainly possible I'm missing something in how I approach those builds, and that there's a better/easier way to go about it.

I rebuilt some 351C 4bbl heads for a guy a few years ago who thought he wanted to play in the FAST series a couple times a year. He built a fairly mild 410 stroker, and I got him a manifold friendly solid lifter cam.
Dynoed the motor, made around 445 iirc, ran like a peach with the manifolds on it.
He's a long time Ford guy and has tons of parts kicking around.
Installed some old used 1-7/8 headers on it..... Picked up about 40hp.
I used to work with a guy that oval track raced Cleveland Ford based motors, and I can tell you the cam I used for the ex manifolds wasn't at all what we found to make big power in the racier header applications, so I'm pretty confident changing the cam in that 410 to something more "normal" would have picked up an easy 30-40hp.
Cams like that simply don't run well with plugged up exhaust.

My point is, anyone that thinks they can easily overcome not using headers, and that they'll have the same power with the same $$$ spent, with the same amount of effort is just kidding themselves.

[c00nhunterjoe]

Im loving following this.  Great conversation going. I will ask- why are so many people anti-header? Ive used several brands of different tube sizes over the years and the only drawback ever would have been a starter swap. But lets face it, how often do you replace the starter? Mine went 16 yrs with 2 header tubes nearly touching the stock unit and it outlasted the engine. Spark plugs had plenty of clearance including the 2 1/8 tubes on my car now. My 383 had $110 heddman 1 3/4 tubes on it and never had an issue with leaks. So what gives?

[JR]

Im loving following this.  Great conversation going. I will ask- why are so many people anti-header?

My best guess is the vintage mopar crowd is very resistant to change. I cant think of any other genre of car community where 1950s-70s era engineering is commonly touted as superior to everything we've learned in the subsequent 50 years.

Not picking on anyone here, just an observation from being around Mopar guys.

[PRH]

I think part of the attraction for the pro-manifold guys is the fact that its a little more insulting when your freshly defeated opponent looks under the hood and sees them.

It's like a master/card moment:

- TTi ceramic coated headers, $900

- mandrel bent 3" exhaust system attached to your TTi headers, $600

- the expression on the persons face you just beat when they look under your hood and see you don't have those things?  Priceless.

[flyinlow]

One thing I have always wondered about on the HP manifolds is the firing order. 1-8-4-3-6-5-7-2   the 7 cylinder fires right after the 5 cylinder (duh) . The 5 cylinder exhaust has to go past the 7 cylinder with it just starting to dump into the manifold. It would appear pretty restrictive? The 8-4  would have the same issue to a lesser extent. Other wise the HP manifolds look relatively streamlined.

I have Hedman Elite long tubes. Happy with them.

[Brass]

I will ask- why are so many people anti-header?

I've never had headers myself but I've heard a lot of complaints about them.  Some detractors seem to cite cost, convenience, fitment, and ground clearance.  Some say heat is an issue and others say sound and appearance too because those are subjective.  By all reports, TTI and Doug's headers seal pretty good but that hasn't always been the case before they were available, and most really hate leaks.  Speaking for myself, I didn't feel like adding headers as another project while coordinating a fresh build.  With other things to spend on and think about, I mostly wanted plug & play.  So I asked Dwayne to hook me up with a manifold-friendly cam.  I can still switch to headers in the future but the gains will not be as much as if I had chosen a cam with headers in mind.  It was a tradeoff for sure but the car will spend most of its time in miserable traffic anyway.  Also, I felt it would take a very long time for the small bump in mileage to offset the cost and hassle.  Negated even further by a heavy foot no doubt.

[alfaitalia]

I want headers for mine...even with the slight loss of low torque that could well result. Whether my bank account will allow it is quite another thing!

[c00nhunterjoe]

I want headers for mine...even with the slight loss of low torque that could well result. Whether my bank account will allow it is quite another thing!

How will you lose torque with headers? The increase is in all rpm ranges.

[alfaitalia]

Well it may ne different on BB motors as its relatively new to me.....but any other motors I've seen a dyno charts for after headers being fitted it either showed a small loss of torque at low revs or the same.....of course the power increases well over stock as the revs increase. These were on motors with no other changes being done at the same time as the header change for an accurate before/after dyno run...some stock engines some not. I would not expect a gain at low revs due to the relative lack of back pressure not helping to hold the mixture in the cylinders on the valve overlap part of the cam. The lumpier the cam the worse it is. Happy to be proven wrong on these motors though!!

[firefighter3931]

It would have been interesting to play with a few things on that 426 build.

Sounds like it made what it "should" though.

Where were the tq/hp peaks?

Basically, I'm looking for the 505 build to make 100tq/100hp more than that 426.

Sorry for the late response Dwayne. I spoke with Mike last night and got more info. 

Agreed, it would have been great to play with some "stuff" while it was strapped down on the pump but that wasn't really in the cards. Mike reiterated that he was only interested in tuning it with the parts he had picked for the build. He spent lots of time and money sourcing the "correct" date coded 64 intake/exhaust manifolds so they were there to stay. He was having detonation issues with the old iron heads and hated the pinging issue so the Stealth heads were a concession he was willing to make. The Cam was another concession but it's fairly mild and basicly a better version of the stock cam with similar manners and better performance. The builder did port match the intake and opened up the exhaust manifold to 2.5in at the headpipe.

The engine was tested from 3000-5000 and at the beginning of the pull it was making 465tq and starting to drop.....I thought he had told me 450Tq but it was actually higher. At 4600-5000 it was making between 350 and 352hp but my recollection was that it was starting to fall off at 5200. I was there on dyno day and on a few of the pulls it was spun up to 5500 or so. The sheet he got from the builder shows 3k-5k so that's all he has for data at this point.

It'll be interesting to see how that 505 performs on the pump. Hopefully it makes a good number and the customer is happy.



Ron

[c00nhunterjoe]

Well it may ne different on BB motors as its relatively new to me.....but any other motors I've seen a dyno charts for after headers being fitted it either showed a small loss of torque at low revs or the same.....of course the power increases well over stock as the revs increase. These were on motors with no other changes being done at the same time as the header change for an accurate before/after dyno run...some stock engines some not. I would not expect a gain at low revs due to the relative lack of back pressure not helping to hold the mixture in the cylinders on the valve overlap part of the cam. The lumpier the cam the worse it is. Happy to be proven wrong on these motors though!!

If you lost power going to headers, the tune is off, whether carb'd or injected. The long tubes increase scavenging which is a win win in all ranges on all engines.

[c00nhunterjoe]

I think part of the attraction for the pro-manifold guys is the fact that its a little more insulting when your freshly defeated opponent looks under the hood and sees them.

It's like a master/card moment:

- TTi ceramic coated headers, $900

- mandrel bent 3" exhaust system attached to your TTi headers, $600

- the expression on the persons face you just beat when they look under your hood and see you don't have those things?  Priceless.

Its definatly the bragging rights, but the avg joe doesnt have the engine to do that with on manifolds. As you stated, you need big cubes to do it and you still leave power on the table. Also to be fair- your prices above are for new, top of the line parts. If you purchase a set of hipo manifolds remannd, they are in the 6 to 700 range as well. I paid 150 bucks for my tti headers used, and have the summit racing brand 3" exhaust kit that i bought new on sale for $180. I think it is 250 today but dont hold me to that number. Regardless, i just cant see the justification for manifolds unless you run F.A.S.T, have a 100 point show car, or want to have the bragging rights and wallet to build the motor to choke through manifolds and make enough power to go fast.

[Mike DC]

And that is my point.  The magazines are full of aftermarket advertisers.  Chrysler is not advertising exhaust manifolds.  The deck is stacked.  It has to be.

Listen, if you don't mind headers, and you have the money,  and you are looking for all the power you can get, it would be silly to not put on headers.  If you get the right size, headers are one of the very few performance add-ons that adds power everywhere in the power curve.  Let's just be realistic about what we are talking about when it comes to a slightly warmed up street car.

I agree that magazines are stacking things for advertisers in general.

But I gotta echo what CoonhunterJoe said - HP exhaust manifolds are not a junkyard/free option in the 21st century.   They are a swapmeet & reproduction item.  You can get a set of cheapo full-length headers for less, and that was already true 15 years ago.   If you find a set of B/RB manfoilds in a junkyard these days they will be the log-type ones that really choke things down.  

I think article writers tend to look for attention-grabbing performance gains in general.  Sometimes that means glorifying the aftermarket stuff they get handed.  Other times it doesn't.  

[firefighter3931]

With regards to manifold testing on the dyno ; the testing I've seen or read about usually has a set of straight down pipes attached at the exhaust outlet. It would be interesting to see a test with a nice mandrel bent x-pipe system installed instead of the straight pipes to see how much of a difference it would make. The "X" has a distinct advantage in breathing vs a straight pipe which would help with reduced backpressure and increased scavenging.

How much it would help is an interesting question ? 


Ron