Rakkasan

In another thread I said I was contemplating putting side pipes on my '66 vert. One of the comments that had me puzzled was the intimation that adding side pipes would reduce the amount of horsepower. I asked a corvette owner and specialist who said the opposite was true, that you would actually add horsepower since there is less to restrict the flow of the exhaust. Not that it would make a difference to me if it didn't but if adding horsepower is what's going to happen then just one more reason for me to add the pipes.

65tripleblack

there's a lot about this.
check the archives.
it all depends on the mufflers you decide to put under your covers.
yes. GM stock or stock reproduction mufflers will kill horsepower.

62Jeff

Stock for stock, factory sidepipes kill horsepower compared to the factory undercar exhaust system.

Your mechanic may have been thinking about adding sidepipes with the associated Hooker headers ("the old days") which would definitely improve things.

Somewhere in the past 6 or 7 years I remember reading an actual pseudo scientific test on the forum with before/after comparisons in a stock-for-stock scenario.

63Corvette

I think it depends on what KIND of side mounts that you are talking about. My Hooker sidemounts seem to work pretty good for me.

AmericanPie

The Hookers look great but for those wanting to keep their car appearing as stock as possible while adding some HP, aren't some of the larger diameter aftermarket sidepipes such as Sweet Thunder a good alternative? Or are they more restrictive than the undercar system, as well?

Does the main restriction in ANY sidepipe system (compared to an undercar system) lie in the two tight 90 degree bends that are required?

I would imagine this whole issue affects big blocks more so than small blocks which don't pump as much air. Has anybody ever done some A/B dyno testing sidemounts vs. undercar?

DansYellow66

That's the urban legend - not too hard to believe if your speaking of the original, small diameter GM sidepipes. However, a lot of owners are using Allens and Stainless Works sidepipes in 2-1/2 and even 3 inch diameter now.

I'm still waiting for someone to take their car and do a back-to-back chassis dyno comparison with 1. factory undercar exhaust 2. factory GM sidepipes and 3. 2-1/2 inch Allens sidepipes and put up some real facts.

But to my knowledge no one has attempted a true comparison like this.

ZEEEE06

Downdraft

I am having Stahl build headers with 1 3/4 primaries and also 3 inch side pipes with STS interal baffles. The sidepipes will be covered with Allen's original looking covers for the 2 1/2 side pipes that are spaced out another 1/2 inch. The headers will bolt on my new 383 setup with AFR heads. Looking forward to the December arrival!!!!

69ttop502

A search in C3 tech section would provide ample information, although the stock chambered type exhaust wasn't a C3 option. It is true that a well engineered undercar will almost always out flow a sidepipe systen when mufflers are used. I have dynoed many different combinations on my 69 big block. What is a restriction on a high horse big block, may not be a restriction on a base small block. Chambered pipes kill a healthy big block for sure.

Bill

65tripleblack

I have a dyno test of open headers v. Classic Chambered VettePacks.

larrywalk

If nothing else, measure the OD of the stock under car system. For a SHP small block it is 2 1/2 inch. Then compare the OD of the pipe which connects the stock exhaust manifolds to the side exhaust - the small diameter may surprise you!

As an example, on a '69 BBC vette, I measured one at 1 7/8"! That really IS a restriction compared to under car exhaust!

Willie'sVette

As a new owner of a '66 427, 390HP w/ OEM sides, I could use some learning here...

Since mine is a recent Top Flight, I'm assuming it's OEM stock...what r the sizes of my setup? What is meant by & is mine, "Chambered"?

I'm having trouble understanding why I'm losing more HP than if the exhaust was going through a muffler, could someone explain.

Thanks for the info, I'll really like to better understand my car.

wow

The big bend of the exhaust to the side pipe is the reason some people think you lose horsepower. But so what. Horsepower simply is top end. You lose a few horsepower, you lose a few mph off the top end. You will probably never see the top end of your car anyway. No one talks about torque, which is what we feel when we accelerate. You might lose a few foot pounds of torque with sidepipes, but the look and sound overcome the loss of either HP or TQ. Go with the sidepipes, you won't be sorry.

Mike Ward

I wouldn't assume that at all.

KC John

I'm no expert, but the bend is much less of a bend than you will find on some header pipes, so it doesn't make sense to me that would be the cause. I think it is just not enough room for the volume of air at high rpms that causes the loss of HP.

However, I agree that most will never realize the loss of power because most don't drive their cars hard enough to notice.

Dennis Beck

I always watch these sidepipes rob horsepower threads.I have a zz383 Stroker with Patriot headers into Allens Stainless sidepipes. Well GYA (Grab Your A$$) because this combo screams. I can't even imagine I could detect IMA (In My A$$) any loss in HP versus under car exhaust.

Dennis

65tripleblack

It was an azzhole who once said that all **** fixated people were stupid. He may have been right!

Hitch

I thought Stahl stopped making headers in June of 2011? Is he still making them?

Dennis Beck

I would have expected this from you.

69ttop502

Ok. I have spent quite a bit of time with different exhausts on both an engine and chassis dyno. Engine dyno #'s are on my 614 horse 502. The chassis dyno #'s are from my 502 in its stock crate form, where with open Hooker sidetubes it made right at 350 hp to the tires on a Dyno Jet. To summarize, any type of exhaust where there is a protrusion into the exhaust flow, it will create a restriction if you have enough motor. Most glasspacks, chambered and these type of exhausts fit into this category. The Dynomax ultra Flow type of muffler does not have this protrusion. Now what is a restriction on my 614 horse motor, may not be a restriction on a low horse stock motor. A 2.5 inch Sweet Thunder type muffler was a huge restriction on my motor, to the tune of 50 horsepower. I tried dynomax race bullets in 3 inch size as well as the STS baffles cut in half and uncapped, and these two combo's were within 10 hp of open pipe.

Now to those of you who don't believe the bends in a side exhaust system do not pose a restriction. The Hooker primary tubes are much longer than ideal. I lost mid thirties in horsepower with my OPEN Hooker sidetubes, compared to the dyno shop's 36 inch primary conventional header. You just cannot generalize here. Everything depends on the motor. My engine builder who owns the dyno said a rough idea is that 3 inch pipes with a staight through(non protruded) muffler and a well designed exhaust system will support 600 horsepower. Now I have seen guys on this forum with 2.5 inch Hooker Max Flows say they didn't restrict a 650 horsepower motor. In my observation that is not the case. Look at 427Hotrod's exhaust system on his 67. I am sure if he could make more power with sidepipes he would be running them.

Bill