for my new engine i want to kinda go undercover. build a 406 with iron heads , stock valve covers, 327 stickers etc... was wondering what it would cost me power wise going with a set of ported cleaned up rams horns. I run chambered sidepipes on my 65 vette and have been told the backpressure pretty much negates the headers better flow anyhow. anyone have any dyno experiance with this?

Too bad this question "popped" up this soon. We've begun testing stock cast exhaust manifolds brought about by the new classs of racing on the east coast here. We've only tested a handful so far, but the results were a little surprising. Two units left here to date with factory pipes.

The first was a true 350/300HP SB. Came off the dyno at 360 HP and 390 Torque. The unit was tested with the stock pipes AND a set of headers. Made no difference up or down in power.

The second was 496" BB stroker, cast intake (factory LS-5), Q-jet, Comp Hyd.Roller-retro, 9:1 C.R., and stock "oval" ports with small valves. I don't have the paperwork here, it may have had 2.190" intakes only, I don't recall. This came off the dyno at 410 HP and 485 Torque. Again, tested with both stock exhaust AND headers, same results, absolutely no difference.

Both are now in "100% stock" appearing vehicles. This was the reason for both tests.

As I type this we are waiting for some cast exhaust's to come back from "Extrude-Hone" in Pa. for some future tests. Some of these units are destined for "class" racing in Englishtown. Thanks, Gary in N.Y.

P.S. What we've seen from these particular tests is there's no loss/gain in certain applications. It ALL depends on the overall design of each individual unit as it come up for testing. There's less chance of gaining power unless the headers are "uncorked". I will add this however, it's somewhat on the expensive side getting a pair of stock cast pipes opened up, somewhere in the neighborhood of $700.00 per pair plus freight!

 

The large 2-1/2" outlet rams horn manifolds flow suprisingly well. If you have the small outlet manifolds you'll want to get a set of the large outlet manifolds, and do a little port matchup and internal cleaning (extrude hone). Annecdotally I have heard of big inch (434+) "stealth" small blocks running these with great results - I think they were running a few more degrees exhaust duration on the camshaft.

Thomas

 

So much for all the "advice" out there that adding headers is one of the first things you should do, and is one of the best "bangs for the buck".

I suspect a lot of that "street wisdom" is similar to the 4-banger guys infatuation with hogging out baffles from their airboxes- is it proven to go faster and make more power? No. Is it noisier and therefore SEEMS to be making more power? Yes.

 

for my new engine i want to kinda go undercover. build a 406 with iron heads , stock valve covers, 327 stickers etc... was wondering what it would cost me power wise going with a set of ported cleaned up rams horns. I run chambered sidepipes on my 65 vette and have been told the backpressure pretty much negates the headers better flow anyhow. anyone have any dyno experiance with this?

=
I do a "few" engines that have to use "stock" exhaust manifolds.
The 350's don't suffer too much in these classes but this is also partly because they are RPM limited too.
I have two 406" engines that do make pretty fair power, one reset the track record twice last year & won the championship. But,,, it made about 20 more HP with full length headers on the dyno.
These are 2bbl flat tappet solid lifter applications at pretty high compression & the manifolds were done by Brezezinski which is noted for his cast iron heads, intakes & ex manifolds among other stuff.
Also, this was with full exhaust that terminates in a "collector box" type single muffler which worked better than dual exhaust vs headers with mufflers.
In lower HP (especially limited RPM) applications the 2.5" rams horns work surprisingly well but in any fair test I have done headers picked up the power some.

 

I suspect a lot of that "street wisdom" is similar to the 4-banger guys infatuation with hogging out baffles from their airboxes- is it proven to go faster and make more power? No. Is it noisier and therefore SEEMS to be making more power? Yes.

To my knowledge 4th gen camaro v6's shave the ridges on the air box lid so there is less turbulance in the flowing air. This is way is the cheap way, but if you want to spend money you buy a whisper lid that will flow air better for more power. http://home.comcast.net/~grayman99/Air-intake.htm Please explain why this wouldnot work?

Altho I want to believe that manifolds are as good as headers because I am using 2" manifolds on my 300 hp 350. Can somone explain why people gain tenths of a second in the quarter mile when switching to headers. I understand manifols weigh more but for sure not more than 25lbs

 

$700 is alotta money to extrude-a-hone a set of ramshorns to me???????

I would get my trusty, B&D, 1/4" drill and some cheap chinese stones out and clean them up myself... May not be pro- done, but sure CHEAP enough!!

And I do know that installing a 2.5" x 6" or so long pipe nipple right at the 90 curve in the exhaust pipe straight down from the 2.5" ramshorns to create "dumps" really opens them up!! BUT boy, you talk about noise!!

And I've read the 20, (to 35), hp numbers several times before throughout the years like Mike mentioned... Going from hy-po cast-iron manifolds to cheap, 1.625" 4-tube, long headers...

What is it, an LS-6 will pick up 75 hp going from factory stock to open headers if not mistaken...

pdq67

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this site sells them for $475.
http://www.castheads.com/corvette_systems.php

I didn't read into it but for a set of extruded 2.5 manifolds that seems like a good deal because 2.5" manifolds are not getting cheap.

Brian

 

this site sells them for $475.
http://www.castheads.com/corvette_systems.php

I didn't read into it but for a set of extruded 2.5 manifolds that seems like a good deal because 2.5" manifolds are not getting cheap.

Brian

These are not extrude honed, the openings are just machined so they are as big or bigger than your heads

 

Something to remember about headers is the kind of power you gain. 20hp is great, but if it's only at the very top end of the power band it may not make a huge difference. My experience is that a better flowing exhaust will give you gains everywhere including fuel mileage.

Steve

 

Quoting manifolds through an exhaust system and open headers on an LS6 is hardly fair. You would need to compare open headers to open manifolds, and I doubt a huge difference would be found.

 

"Quoting manifolds through an exhaust system and open headers on an LS6 is hardly fair. You would need to compare open headers to open manifolds, and I doubt a huge difference would be found."

Just a point of reference is all b/c it's been measured!!!

The point is! The better we can make our engines breathe, the more power they make is all..

pdq67

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Agreed!

 

Can you use rams horns in Chevelles? I thought there were some serious clearence issues?

 

Can you use rams horns in Chevelles? I thought there were some serious clearence issues?

no they won't fit a chevelle, the frame is in the way.

You might be able to mount them upside down. ha ha

 

that's what I've always wondered, how much difference between rams horn and the chevelle type manifold with rear dump. the rams horn type just will not fit a Chevelle without extensive rework of the crossmember.

 

I dont know about this. My 70 convertible is stock with the exception of a very mild cam, an aluminum dual plane, and a 600 cfm vaccuum sec holley carb. Its a weekend cruiser and wanted to keep it quiet so I stuck with the factory cast iron manifolds, into a 2 1/2 bolt on system I bought from hooker. Last year I took out the cast iron manifolds and put on a set of hooker cheapy headers with small tube diameter primaries. I dont see a huge difference under 2000 rpm of so, but when I hit the 2500-3000 range it sure does feel to me that its pulling quite a bit stronger. I know dynos are much more accurate than an individuals nerve ending in his ass,,,,but my old man who has raced for years said the same thing before I gave him my opinion. To each his own...I'll take the headers every time....I cant imagine racers and street car owners using them as the #1 low buck performance for who knows how many years for no good reason. Even the big 3 factories offer upgrades and racing options in the 60's using headers...what for no performance gain. I would think exhaust companies would be making a killing selling high dollar high flow cast iron manifolds if they actually worked better.

If it was the case that cast iron flows as well in most engines as headers I like most of you probably lost a lot of money as a kid buying fat high temp wire sets and wire loom organizers.... only to have to replace them cause you burned em on headers; espcially when the factory wires work so well on stock manifolds!

 

This story is not scientific by any means.

Way back in the stone age when I was 20 years old, LOL, I bolted on my first speed parts. Back in those days I had a 283 in my Chevelle. With a tax refund check for financing, I installed an 1850 Holley carb and a Holley intake. I was so bummed out becuase I spent so much money and got zero performance. My Chevelle ran the same and got really crappy mileage with the new set up.

Then I bolted on a set of Hedman headers. The car came to life!!! I could do burn outs with that little engine. It was very fun to drive. The engine was fresh with the addition of the carb, intake and headers.

Then I stuck a cam in that little engine and lost all the low end torque but I could spin that baby to 7000 RPM.

All I can say about this topic is that for sure in that instance the headers made a huge differance.

I sometimes wonder about engine dyno testing and chassis dyno testing. I know they are the best tools we currently have available for measuring the specific output of an engine. But do they really simulate what an engine and car can do on the street or track? Hmmm...

Interesting! I'm all ears on this one...

 

As I posted earlier, in any test I have done headers made more power.
The tests I posted earlier with rams horns vs headers on the 406 are not a normal stock cast vs header test.
The cast iron rams horns along with the head pipes & attending 2 into one collector system & mufflers were in the $1000 range.
Lot of money to lose 20 HP if you don't have to run em,,,

The difference would have probably been a lot more with stock exhaust manifolds vs headers in my opinion.

Anyone who tells you dumping all four cylinders into one log & terminating them into a 2.5" pipe is going to make the same power as a set of full length headers & a collector is in my opinion wrong in almost all cases.
And the more power you are making per cylinder, the bigger the difference is going to be

Tom,
Not a huge difference between Brezezinski's rams horns & the rear dumps he does,, I think it was on the order of 10 HP from memory but it's been a while & again, this was not with stock parts.

 

First 2 things I always put on SB Chevys were headers and a scatter shield. I always felt headers prevented the exhaust from #7 blowing into #5.