Exhaust Header "Theory" and "Practicum" Discussion

[Hog]

I decided to start my own thread instead of cluttering others.

Speaking of restriction which causes backpressure. "The 1993MY upgrades included going to an exhaust that reduced backpressure by 2" of hg(mercury) was responsible for 6 bhp of the total power increase" of 20 sae net hp.

When the Engineer responsible for the MY1993 power upgrades (Mr. Graham Behan made the above statements, he uses bhp(brake horsepower). I have no idea if a brake horsepower is the same as a SAE net hp or not. If a BHP=SAE net hp, then the reduction in backpressure by 2" of hg, was responsible for 30% of the 20 sae net hp upgrades for MY1993.

I think that many people swap out exhausts (myself included), because it one of the few ways to completley change the personality of a car. While power increases are often stated as a main reason, in reality the search for the desired audible characteristics are the heart of the matter.

Some the nicest LT5 LT headers I have seen are the Baker Racing longtubes that member TPEPMEIE used on his custom-cammed 703hp dyno proven 427 monster.




The addition of longtube headers over OEM manifolds should increase scavenging of the exhaust gasses from the combustion chamber.

Will increased exhaust scavenging increase power output even if the total backpressure of the exhaust system remains the same?

There is no right or wrong in this thread, post up you "theory" and/or "Practical experience", all input and "ne off weirdo"or "cookie cutter system" discussion/dyno sheets/pics/magazine articles all welcome.

[Schrade]

Missed this one here Hog...

I had a few discussions yesterday with techs at FlowMaster, and DynoMax, about my drone, and other exhaust topics.

Ronnie @ FM said you'll DEFINTELY run cooler with headers over OEM hardware. I told him my cooling fans had not come on once, with Marc's 205'-coded chip, since my own swap. I haven't done any daytime stop n go driving yet however. A/C does trip fans - I had to check that to make sure.

He said he COULD see that an X-section would mimic a sound like an exhaust leak. He said that an H-pipe section would NOT likely do this. Hmmm...

He said he has hardware that I can put in which will reduce drone, although he was tentative about that, since the rear hatch geometry likely has more to do with that.

He doesn't like header wrap, except for near the END of the exhaust lines. Said only place for header wrap is dirt track mills, and that it could lead to cracked header tubes, not from moisture / rust formation, but from heat cycling and heat retention in the pipes. He prefers JetHot's Coatings. He said JH would keep the heat as well as wrap would. THAT I could not see...

He said I COULD probably put back in the OEM resonator, probably without re-introducing flow restriction. He said I could put in his Flowmaster® Part #: 15147S, definitley without putting flow restriction back into the pipes, and probably the SAME model hardware with 2.5" inlets / outlets, without putting flow restriction back in.

Today, we're up on ramps. More wrap is going onto the cross-over / X-section, and behind, to see what effect that might have in drone reduction. I'll measure sound level, and post results, before buying more hardware to put in in front of the pipes' split-off near the diff...

I'm considering also sound barrier of some sort, in addition to the cork sheeting that I put in yesterday, under the rear cargo carpet. That did marginally reduce again interior drone, in addition to the extra foam board on the backside of the roof headliner pad. I used a media player with a 5 band EQ to confirm that.

[KILLSHOTS]

Originally Posted by Schrade

Missed this one here Hog...

I had a few discussions yesterday with techs at FlowMaster, and DynoMax, about my drone, and other exhaust topics.

Ronnie @ FM said you'll DEFINTELY run cooler with headers over OEM hardware. I told him my cooling fans had not come on once, with Marc's 205'-coded chip, since my own swap. I haven't done any daytime stop n go driving yet however. A/C does trip fans - I had to check that to make sure.

He said he COULD see that an X-section would mimic a sound like an exhaust leak. He said that an H-pipe section would NOT likely do this. Hmmm...

He said he has hardware that I can put in which will reduce drone, although he was tentative about that, since the rear hatch geometry likely has more to do with that.

He doesn't like header wrap, except for near the END of the exhaust lines. Said only place for header wrap is dirt track mills, and that it could lead to cracked header tubes, not from moisture / rust formation, but from heat cycling and heat retention in the pipes. He prefers JetHot's Coatings. He said JH would keep the heat as well as wrap would. THAT I could not see...

He said I COULD probably put back in the OEM resonator, probably without re-introducing flow restriction. He said I could put in his Flowmaster® Part #: 15147S, definitley without putting flow restriction back into the pipes, and probably the SAME model hardware with 2.5" inlets / outlets, without putting flow restriction back in.

Today, we're up on ramps. More wrap is going onto the cross-over / X-section, and behind, to see what effect that might have in drone reduction. I'll measure sound level, and post results, before buying more hardware to put in in front of the pipes' split-off near the diff...

I'm considering also sound barrier of some sort, in addition to the cork sheeting that I put in yesterday, under the rear cargo carpet. That did marginally reduce again interior drone, in addition to the extra foam board on the backside of the roof headliner pad. I used a media player with a 5 band EQ to confirm that.

Hey Schrade,

If this guy said you could put the stock resonator back on without reintroducing restriction, then I would be very leery of anything else that he told you. He must have no idea that the stock early (90-92) resonator is BY FAR the most restrictive piece of the exhaust.

Were you ever able to talk to GC about that Corsa resonator?

[mike100]

I added headers to a stock catback and the mid range torque was definitely improved. There was some top end gain too, but not as much up high as when I went with the SW 3" x-pipe system I now have.

header theory states that the primary diameter is the limiting factor in peak hp potential and the length of the primaries has a lot to do with how the torque curve will be shaped. longer tube runs tend to equal more area under the curve before the tq peak.

This video makes the concept pretty clear:
https://www.youtube.com/watch?v=c7PfOXP2Vf0

[Schrade]

Originally Posted by KILLSHOTS

Hey Schrade,

If this guy said you could put the stock resonator back on without reintroducing restriction, then I would be very leery of anything else that he told you. He must have no idea that the stock early (90-92) resonator is BY FAR the most restrictive piece of the exhaust.

Were you ever able to talk to GC about that Corsa resonator?

Haven't gotten up with Daryll yet there Chris; I posted in your thread @ him after you mentioned it - haven't seen him on the boards lately.

After the FM tech said what he did about the OEM resonator, I reminded him that early Z had tighter resonator inlet than later Z; he just said, "Oh', and qualified his 'possibly', on putting it back, with no flow restriction put back.

He did say, as I knew, that the cooled gases had much less volume. He knows more exhaust tech than I do, so I couldn't debate it. And I'll LISTEN to anything, THEN judge...

But when he said C4's hatch geometry had more to do with drone / drone reduction, without pimpin' his hardware as absolute cure for the problem, I give him a little more credence.

So I'm still thinkin' on what to do here on it. More wrap in the meantime; harmonics HAS TO change with wrap, as opposed to strictly metal.

AND I'm wondering here, WRT to wrap on the last 2 20" sections, whether to wrap each individually, or wrap all the way around BOTH, together, or wrap in a figure 8, from the X-section to the diff joint split-off...

Did you get your OBX's on? And what do you have behind it? How's it sounding? And interior drone?

[XfireZ51]

Anybody make a Tri-Y header for the LT-5? Sometimes I wonder if my motor would benefit from 2" runners.
The Watsons I have on there now are 1 7/8".

[KILLSHOTS]

Originally Posted by Schrade

Haven't gotten up with Daryll yet there Chris; I posted in your thread @ him after you mentioned it - haven't seen him on the boards lately.

After the FM tech said what he did about the OEM resonator, I reminded him that early Z had tighter resonator inlet than later Z; he just said, "Oh', and qualified his 'possibly', on putting it back, with no flow restriction put back.

He did say, as I knew, that the cooled gases had much less volume. He knows more exhaust tech than I do, so I couldn't debate it. And I'll LISTEN to anything, THEN judge...

But when he said C4's hatch geometry had more to do with drone / drone reduction, without pimpin' his hardware as absolute cure for the problem, I give him a little more credence.

So I'm still thinkin' on what to do here on it. More wrap in the meantime; harmonics HAS TO change with wrap, as opposed to strictly metal.

AND I'm wondering here, WRT to wrap on the last 2 20" sections, whether to wrap each individually, or wrap all the way around BOTH, together, or wrap in a figure 8, from the X-section to the diff joint split-off...

Did you get your OBX's on? And what do you have behind it? How's it sounding? And interior drone?

Yep, they're on. Coated OBX with no cats into Corsa, so it's basically straight pipes. From a sound perspective - as far as I'm concerned - it's the perfect combo. Quiet enough so that I can leave the house at 6:30am on a Saturday to go to Cars & Coffee without waking the neighbors but when I nail it, there is virtually NO sound restriction. Haven't driven it on the highway yet but being Corsa, I'm assuming there is no drone. I'm very happy with it. I do now see the value in cats, though. They would cut down on the smell and the fouling of the tailpipes a bit, and would possibly burn off some of the unburned fuel that causes the cloud behind the car on deceleration. Then again, they would cut down about 5-8 HP, too!

[Schrade]

Originally Posted by KILLSHOTS

Yep, they're on. Coated OBX with no cats into Corsa, so it's basically straight pipes. From a sound perspective - as far as I'm concerned - it's the perfect combo. Quiet enough so that I can leave the house at 6:30am on a Saturday to go to Cars & Coffee without waking the neighbors but when I nail it, there is virtually NO sound restriction. Haven't driven it on the highway yet but being Corsa, I'm assuming there is no drone. I'm very happy with it. I do now see the value in cats, though. They would cut down on the smell and the fouling of the tailpipes a bit, and would possibly burn off some of the unburned fuel that causes the cloud behind the car on deceleration. Then again, they would cut down about 5-8 HP, too!

Yeah - me and you like it, but neighbors? THey don't hear it? Hmm...

[Schrade]

Re: Exhaust Header "Theory" and "Practicum" Discussion

Theory is that what goes up, must come down.



Practicum? That theory in practice. And practice sure don't make perfect, gettin' this hardware down, to do some more wrappin' and take the edge off of the drone.

[Kevin]

that is the exact system I want.