Hi guys!

I was looking on the internet about the possability of switching between your exhaust system and open headers, when I read this :

"ive done dyno testing at school and we switched between open header, 6,12, and 18 inch extensions, bullet mufflers, and turbo (http://camaroforums.com/forum/showthread.php?t=37625#) mufflers. the most hp was produced with the 6 inch extension. the most torque produced was with the 2 mufflers. although the top numbers were only different by a few digits on our mules, the power band was completely different. at specific rpms, open headers had as much as 60 lb ft less than with mufflers."

According to this guy, you'll get less power with open headers???
Is he right?

And does anyone know something about this method of switching betweem open headers and exhaust system?

Thanks!

Elias

I seriously doubt a properly tuned engine will make more power with mufflers. If that were true then pro stockers and comp eliminator cars would have them.
I suspect if in the author's testing they made more power with mufflers then they have headers with too large diameter pipes.

Yes, I was thinking the same : why is every racer using OH then?

I've found this site here, http://www.quicktimeperformance.com/ , and the sound of that Charger is so amazing! I wonder what happens if you put it on a serious GM Big Block!

Problem is, on the site, you have so many things to choose...

Elias

The author states that at 'some rpm' the engine made more power with mufflers.
Perhaps at low rpm the engine would like the backpressure provided by the mufflers.

Ok, he's just talking crap :D
But I see you have strip cars, do you run OH?

Elias

For what it's worth, Comp Cams Camquest 6 shows peak torque and HP as well as average torque and HP down on some combinations with open headers as compared to using mufflers.

Elias,
Indeed I do have some strip cars. Hope to be running my 68 Caprice 'stocker' this weekend and it has open headers with extentions after the collector that are 17 inches long. Mufflers would kill that little 327 low compression small valve engine. Only makes 370 hp at the crank.
My other cars are of the street/strip variety so indeed they have mufflers.

The problems start,when you go to open exhaust with an engine that is designed and tuned to run with mufflers in place.
Make any changes here.. will have you re evaluating the induction package and valve timing events to fully compliment the reduction in backpressure and the most likely increased scavenging effect during the overlap period.
If I read you correct..the electric cut outs are fine for parade grounds and cruise ins as an attention getter.They typically install after the collector reducer in street exhaust systems..not quite the same as an open collector.You would need to qauntify the results on the track or a chassis dyno.

[QUOTE=Eleanor's Nemesis;1459381]Elias,
Mufflers would kill that little 327 low compression small valve engine. Only makes 370 hp at the crank.

At 1.13 hp/cube..very respectable with your combo of parts.:cool:

I would think that the extensions would equalize the cylinders making more power ?
I was taught to put extensions on the headers, then paint a line on the pipe length, make a pass, and at the end of the quarter cut off the motor, mark/measure the pipe where the paint is burnt off and cut pipe... now the exhaust is "tuned".

Thanks George. The thing I like about stockers and super stockers is the challenge og getting the most out of stock and stock like parts.

Mike above
The author states that at 'some rpm' the engine made more power with mufflers.
Perhaps at low rpm the engine would like the backpressure provided by the mufflers.
Yep..I was running 1/4s in my street car years ago with headers both with dropping out the collectors and thru the mufflers....but was not excessing 4800 to 5000 rpms
2 1/2 " pipes
Mufflers on ran consistant .3 sec faster and couple mile faster
Then I replaced the headers with truck rams horns thru the exhaust again dropped times around .2 sec but mpg stayed near the same

Headers are tuned with the primary lengths for a partular rpm range, usually up around the 5500 + range.

Im still running the truck rams horns.

Quite a few years ago now I had a 67 Pontiac Parisienne with a 406sbc in it. The car ran mid 13's. I had 4 into 1 x 1.75" headers with 3" collector, twin 2.5", X pipe, 2.5" aerochambers dumped in front of diff. Took off the exhaust system & fitted up some 3" extensions & drove from home to the track. The car sounded awesome but was not that happy to find out it ran a couple of tenths worse & slower mph.

I am sure the more high performance engines do go better with open headers though otherwise everybody would run pipes & mufflers !

Elias,
Indeed I do have some strip cars. Hope to be running my 68 Caprice 'stocker' this weekend and it has open headers with extentions after the collector that are 17 inches long. Mufflers would kill that little 327 low compression small valve engine. Only makes 370 hp at the crank.
My other cars are of the street/strip variety so indeed they have mufflers.

That's cool man, never heard of it before ; stockers.
370 hp with only a 327 engine is certainly not bad!

The problems start,when you go to open exhaust with an engine that is designed and tuned to run with mufflers in place.
Make any changes here.. will have you re evaluating the induction package and valve timing events to fully compliment the reduction in backpressure and the most likely increased scavenging effect during the overlap period.
If I read you correct..the electric cut outs are fine for parade grounds and cruise ins as an attention getter.They typically install after the collector reducer in street exhaust systems..not quite the same as an open collector.You would need to qauntify the results on the track or a chassis dyno.

But check this out http://quicktimeperformance.com/OVAL/
After installing those electric (oval) cut outs, they get a gain in both hp and torque? But I don't know if they made any changings to the backpressure or so...
I would guess not, because they still use the stock exhaust system too.

Mike above

Yep..I was running 1/4s in my street car years ago with headers both with dropping out the collectors and thru the mufflers....but was not excessing 4800 to 5000 rpms
2 1/2 " pipes
Mufflers on ran consistant .3 sec faster and couple mile faster
Then I replaced the headers with truck rams horns thru the exhaust again dropped times around .2 sec but mpg stayed near the same

Headers are tuned with the primary lengths for a partular rpm range, usually up around the 5500 + range.

Im still running the truck rams horns.

But running for example 69 DZ302, they revv'd to 8500 rmps, so I guess when you fit OH to a Z/28, you would get more hp/torque, no?

But check this out http://quicktimeperformance.com/OVAL/ After installing those electric (oval) cut outs, they get a gain in both hp and torque? But I don't know if they made any changings to the backpressure or so...
I would guess not, because they still use the stock exhaust system too.But, look at the test vehicles they used, PCM controlled, automatic tuning is taking place.

Back pressure is reduced as a hole is less resistance than tubing, bends and mufflers.

Elias -

What you're asking (open headers vs. headers plus exhaust) is a pretty well documented topic, and it depends on the type and design of the header and exhaust system. Definitely not total BS.

Many "off the shelf" headers are designed primarily to fit the given engine and car as best as possible, and secondarily to "improve" performance. There are a lot of compromises in an mass-market header.

But to maximize performance on a given engine, and, even on the same engine, maximize performance for whatever atmosphere might be at the track that day, a lot of racers have headers that can have the collectors (where all the tubes meet at the end) changed. Changing the length and size of the collectors can have big effects on how the car peforms.

This link provides a pretty decent explanation of how it works; from the link:

'Experimenting with collector length is a decades-old trick, but there are some simple facts to remember before tweaking away. "A longer collector will typically make more torque, while a shorter collector will typically make less torque but more top-end power," Lemons says. "If a car has a full exhaust system, it will be less sensitive to the length of the collector. With open headers, sometimes it's pretty common to use a larger collector in addition to collector extensions to fine-tune the torque requirements to launch the vehicle out of the hole."


http://www.chevyhiperformance.com/tech/engines_drivetrain/exhaust/0808chp_chevy_header_and_exhaust_tech/header_collector.html

So as the article implies, sometimes having an exhaust system (as long as it is not too restrictive) sort of has a similar effect of lengthening the collectors, so for some conditions and some exhaust setups, it is not inconceivable that a combo with a full, well designed exhaust could outperform the same combo with open headers.

Another article about collector length.

http://headersbyed.com/hc_cheapperfgains.htm



Another way having an exhaust system attached can actually help performance is when a crossover is used. You can probably start googling and reading about crossover shape (x vs. H), positioning, etc. I believe it has been demonstrated that position doesn't matter, because the old trick of positioning the crossover where the hottest exhaust pulse ends (shown by putting a crayon mark on the exhaust pipe and watching where it stops melting) doesn't really apply; as discussed above for changing atmospheric conditions, the location of the end of the hottest exhaust pulse varies so much with engine RPM, tuning, and other conditions, so it is really okay to put the crossover where it fits best under the car.

But, the point of a crossover is that it helps equalize flow and other conditions between the cylinder banks, and the flow of gases from one bank can actually help "pull" the gases from the other bank (it is called "scavenging").

Here's one article I found quickly, but there will be tons more available online:

http://www.boyleworks.com/ta400/psp/exhaust.html

So, no, a statement that a certain combo can perform better with exhaust than with just open headers cannot be dismissed as BS. There is a whole lot more to it.

If you don't richen the mixture with open headers, you'll have a lean mixture and less power.

Elias -

What you're asking (open headers vs. headers plus exhaust) is a pretty well documented topic, and it depends on the type and design of the header and exhaust system. Definitely not total BS.

Many "off the shelf" headers are designed primarily to fit the given engine and car as best as possible, and secondarily to "improve" performance. There are a lot of compromises in an mass-market header.

But to maximize performance on a given engine, and, even on the same engine, maximize performance for whatever atmosphere might be at the track that day, a lot of racers have headers that can have the collectors (where all the tubes meet at the end) changed. Changing the length and size of the collectors can have big effects on how the car peforms.

This link provides a pretty decent explanation of how it works; from the link:

'Experimenting with collector length is a decades-old trick, but there are some simple facts to remember before tweaking away. "A longer collector will typically make more torque, while a shorter collector will typically make less torque but more top-end power," Lemons says. "If a car has a full exhaust system, it will be less sensitive to the length of the collector. With open headers, sometimes it's pretty common to use a larger collector in addition to collector extensions to fine-tune the torque requirements to launch the vehicle out of the hole."


http://www.chevyhiperformance.com/tech/engines_drivetrain/exhaust/0808chp_chevy_header_and_exhaust_tech/header_collector.html

So as the article implies, sometimes having an exhaust system (as long as it is not too restrictive) sort of has a similar effect of lengthening the collectors, so for some conditions and some exhaust setups, it is not inconceivable that a combo with a full, well designed exhaust could outperform the same combo with open headers.

Another article about collector length.

http://headersbyed.com/hc_cheapperfgains.htm



Another way having an exhaust system attached can actually help performance is when a crossover is used. You can probably start googling and reading about crossover shape (x vs. H), positioning, etc. I believe it has been demonstrated that position doesn't matter, because the old trick of positioning the crossover where the hottest exhaust pulse ends (shown by putting a crayon mark on the exhaust pipe and watching where it stops melting) doesn't really apply; as discussed above for changing atmospheric conditions, the location of the end of the hottest exhaust pulse varies so much with engine RPM, tuning, and other conditions, so it is really okay to put the crossover where it fits best under the car.

But, the point of a crossover is that it helps equalize flow and other conditions between the cylinder banks, and the flow of gases from one bank can actually help "pull" the gases from the other bank (it is called "scavenging").

Here's one article I found quickly, but there will be tons more available online:

http://www.boyleworks.com/ta400/psp/exhaust.html

So, no, a statement that a certain combo can perform better with exhaust than with just open headers cannot be dismissed as BS. There is a whole lot more to it.

Eric, always when I see you posted on my topic, I get a smile, because I know an awesome reply has been made. ;)

But now, the brains about exhaust gases are so complicated!
Anyway, I get most of the things said on those links you provided.

quote :" A longer collector will typically make more torque, while a shorter collector will typically make less torque but more top-end power "

What's better for drag racing, torque or top-end power?

If you see this picture, this is a system to change from "open headers" to your stock exhaust system.

http://img651.imageshack.us/img651/594/qtpexhaustsetup2010cama.jpg
You can see that those valves are no where near the collector, so other than having an awesome sound, will it hurt/improve performance? (this is a 2010 Camaro SS)

Because this is something completely else than open headers. It's just actually shortening the exhaust system?

But there is also something like this, which looks more like open headers:

http://img715.imageshack.us/img715/8518/qtpsetup2.jpg

What do you think when it comes to performance? Because here, the valve is placed directly behind the collector, so it's more open header, I guess...

Thanks a lot!! :beers:

Elias