Question: Will opening up an exhaust cause power loss?

[Dads C5]

Also, the reason I want cutouts is becasue it is cheaper than a new exhaust system, but has the same effect! Plus, my Vette is an everyday driver so if I want quiet, then I just shut the cutouts! I just want to make sure I wont loose power, but from all of the replys and research, I will probably gain power!

Thanks Guys!

Great web site. Thanks for sharing.

 

[MBDiagMan]

dont mean to rain on your parade but if you go to big with the exhaust you will lose power, in the end its up to you but i promise you no matter how you tune it you will lose power if you take away all the back pressure . why not call some of the exhaust companys and hear what they have to say .good luck on what ever you do

On what do you base your statement?

 

[ZumZum]

dont mean to rain on your parade but if you go to big with the exhaust you will lose power, in the end its up to you but i promise you no matter how you tune it you will lose power if you take away all the back pressure . why not call some of the exhaust companys and hear what they have to say .good luck on what ever you do

That's an old tale and just plain not true. Especially with the L98.

 

[rickreeves1]

you will lose power if you take away all the back pressure.

:eyerole

 

[rlg]

I don't know if it applies to this application, But as far as back pressure is concerned, you will lose low end torque on a stock Harley with straight pipes unless you make other modifications. In fact, they sell torque cones to help with the issue.

I tried it. Went back to the Screaming Eagle II exhuast system.

Like I said , It may not apply here, But I figured some of you Vette owners out there might ride on two wheels once in a while like I do.

 

[jonszr1]

:eyerole

all i was doing was offering to share the experiences of 35 years of drag racing and building hot rods. believe what you want . if you do some homework on the subject you will find what i am telling you is true .good luck on whatever you decide

 

[84Turbo]

dont mean to rain on your parade but if you go to big with the exhaust you will lose power, in the end its up to you but i promise you no matter how you tune it you will lose power if you take away all the back pressure . why not call some of the exhaust companys and hear what they have to say .good luck on what ever you do

Feel free to rain all you wish. (I'm drip dry, and my plastic car doesn't rust.)
Two things: 1) How much backpressure do you think there is at the end of a set of open collectors? Real race cars are looking for maximum power. I see darn few racers putting a cork in the collector to "bump up" their horsepower. A street engine, similarly, is also an air pump. Restricting the flow of air does not increase VE, and therefore will not increase power.
2) There's a reason guys used to think that backpressure gave more horsepower. Without looking at the physics of it, they weren't totally offbase. They were wrong, but it was because they only looked at part of the equation. Can anybody give me the reason they often claimed that backpressure was necessary? (I know, I'm just offering up the opportunity for others to chime in.)

 

[jonszr1]

i will use my most recent example that happened to me . my 90 ported zr1 .i first went with a 3in band b the car ran 12.45@117.65 then after talking to some buddies who own spin tec mufflers ask me if they could build me a system .i said ok .they built me a 2/1/2 inch system with a dr gas x pipe the car ran a best of 12.10 @119.85 in 100 degree weather . they shared that too big a pipe causes the exhaust to lose velocity causing the exhaust to lose the ability to help pull it out of the combustion chamber . its not so much a back presure issue but sizing everything just right so the exhaust can pull the spent gases out as fast as possible . my car make 427 rwhp and is shifted at 7100 rpms. also think about why a merge collector makes more power . in the end it is up to the owner of the car to decide ,all i am trying to do is share what i have learned in over 35 years of drag racing , having held 3 different national records in various classes . good luck in what ever you choose

 

[84Turbo]

i will use my most recent example that happened to me . my 90 ported zr1 .i first went with a 3in band b the car ran 12.45@117.65 then after talking to some buddies who own spin tec mufflers ask me if they could build me a system .i said ok .they built me a 2/1/2 inch system with a dr gas x pipe the car ran a best of 12.10 @119.85 in 100 degree weather . they shared that too big a pipe causes the exhaust to lose velocity causing the exhaust to lose the ability to help pull it out of the combustion chamber . its not so much a back presure issue but sizing everything just right so the exhaust can pull the spent gases out as fast as possible . my car make 427 rwhp and is shifted at 7100 rpms. also think about why a merge collector makes more power . in the end it is up to the owner of the car to decide ,all i am trying to do is share what i have learned in over 35 years of drag racing , having held 3 different national records in various classes . good luck in what ever you choose

I'm not a big quarter mile fan, but 35 hundredths reduction in ET is rather significant. Being an engineer, I would need a bunch more data than you've supplied to convince me that choking down the pipe size accomplished this. (I also don't see any backpressure gauge readings posted while running with these two systems.)
I could be convinced that going from 3 inch duals to 2.5 inch duals with an X-pipe would increase power due to the 2.5 inch setup having more internal area (two 2.5 inch pipes are bigger than one 3 inch pipe) to allow the exhaust volume/mass to be dumped into from each of the headers. I tend to believe it's more of a volume (storage plenum) thing after the headers, producing lower instantaneous backpressure, rather than a conduit for pulsed flow. Given that there are mufflers at the end of these pipes, I don't see much possibility of persistent pulsed flow anyway.
Like I said, I'm an engineer. Give me the data, and I can be convinced. Without any data, I gotta go with the physics I know.

 

[jonszr1]

both systems are true duals. we didnt put any sensors in either systems . to us the proof is in the et and mph reductions. .the mph is the real key sometimes the sience gets in the way of what is the reality of the deal to go faster from point a to b . which is what we are after . the money to install sensors for4 the results you seek costs about 10-12 k and just not worth it unless we were trying to develope a system for sale which we are not . just some good friends who have been building exhausts for many years sharing their knowledge to help me out . bottem line it worked very well in my opinion .choose carefully or you will be spending money again to achieve the results you want

 

[TedC]

This is always an interesting debate. When researching dyno shops in my area, I was surprised how many cars are messed up by their owners who think bigger exhausts are always better. Specific to a stock L98, an ECM reprogram is required if you open up the exhaust too much. At WOT the L98 goes into a power mode and depends mostly on preset calibrations. Dropping the rear y-pipe and mufflers caused a lean condition on my 1989 when measured using an attached diagnostic tool. On my 1988, just installing muffler eliminators caused a lean condition. Here is quote that closely matches what my local dyno shop has been sharing with me.

"High velocities, that don't incur pumping losses are the rule!!! Just changing backpressure is a bogus way of trying to create the "ideal" pressure in the system. The exhaust system should work like a correctly conceived header. It should extract the exhaust from the header, to minimize pumping pressures. The only way to create a system that will serve as an extractor is to properly size the tubing to allow the flow velocity to create a sort of "vacuum" behind it. Just as with headers, creating a system that will provide the best of all worlds at all throttle positions and rpm ranges is impossible. It's all going to be a trade-off. You can tune for the throttle positions and rpm ranges where you desire the greatest performance, but you'll sacrifice performance at the other end of the rpm range."

 

[jonszr1]

the above is a very well put statement . do your homework before you change things and you will only spend money once

 

[rlg]

Here is what I did on the 90, a stock L98.

1. bought a chip ( to offset any problems with the ECM)
2. removed the entire exhaust system( It had Noise Masters and an after market Y pipe, the pre cats had been removed the repair leaked and looked like crap).

Bought a true duall sytem with an H pipe, then I replaced the mufflers with the stock type.

Runs great.


Some of you may not be able to do this because of State inspections.

 

[84Turbo]

both systems are true duals. we didnt put any sensors in either systems . to us the proof is in the et and mph reductions. Proof, not really. ET and MPH doesn't tell you anything about what actually was happening in the exhaust system. One system was certainly more efficient than the other, but the reason why still needs to be explained. the mph is the real key sometimes the sience gets in the way of what is the reality of the deal to go faster from point a to b . I disagree. I think science keeps you from wasting time following after old wives' tales that get passed down over the years. which is what we are after . the money to install sensors for4 the results you seek costs about 10-12 k ???? and just not worth it unless we were trying to develope a system for sale which we are not . just some good friends who have been building exhausts for many years sharing their knowledge to help me out . bottem line it worked very well in my opinion .choose carefully or you will be spending money again to achieve the results you want

Your 2.5 inch system is not a true dual as most people define them. Your X pipe causes the exhaust from one bank to traverse both pipes. It does not stay on the same side as the engine bank it originated from. True duals, as most guys describe them, would restrict the odd number cylinders to the left exhaust pipe, and the even number cylinders to the right exhaust, with no "cross talk". An X pipe increases the downstream pipe volume seen by the exhaust flow. An increase in pipe volume will reduce the backpressure/restriction that the outgoing gas (from the cylinder) sees.
The sensors to do this test cost about 25 dollars. I mentioned earlier that you haven't posted any data regarding the backpressure that you insist is necessary. It's strictly anecdotal data you've supplied. A low pressure gauge (0-5 psig) plumbed into each bank will tell you which exhaust system is causing less restriction to the exhaust flow.

 

[TedC]

When I owned my 1988 vette with 50K on it, I tried several different cat back systems. The stock GM exhaust on an auto 1988 with 2.59 had only one working muffler tip per side. Using an adapter that plugs first into the O2 port, we were able to take back pressure readings. At shift points, the stock setup reading was ~6 PSI. No catback, it dropped to ~3 PSI. Muffler eliminators ~4 PSI, Dynomax ~4 PSI, and GM stock muffler with 3.08 (all tips open) ~4 PSI. The L98 is rated 5 more HP by GM when using the 3.08 axle because of the 4 open tips. The ECM was showing lean conditions when using no catback and with muffler eliminators. I loved the sound of the Dynomax, but the interior noise was really bad, even using a balanced y-pipe. Balance y-pipe did not change PSIs. The conclusion I made (maybe wrong) was that the converters had to go if I required a PSI better than the 3-4 PSI. A reprogramed chip would also be required.

 

[rickreeves1]

all i was doing was offering to share the experiences of 35 years of drag racing and building hot rods. believe what you want . if you do some homework on the subject you will find what i am telling you is true .

:eyerole

you will lose power if you take away all the back pressure .

This statement is spreading false information.

they shared that too big a pipe causes the exhaust to lose velocity.

This one makes more sense.

 

[JimBobC4]

i've been reading this thread since it started and wanted make one point

I think it depends on how you define the word "power"

are we talking horse power ?

or torque in this thread?

 

[84Turbo]

i've been reading this thread since it started and wanted make one point

I think it depends on how you define the word "power"

are we talking horse power ?

or torque in this thread?

Doesn't matter. Cylinder pressure makes torque. And you can't make horsepower without torque.

 

[92BlackVette]

Cut outs are junk, and a waste of MY time. I have manual cut outs on my 76 Vette, I disconnect them to impress my friends in my driveway and I would never drive with them like that! On my 92 vette, I have no mufflers, and I can't hear while on a cell phone, not to mention it's loud all the time.

I recommend to pick a situation:

1.) Loud Sound
2.) Mild Sound
3.) Quiet Sound

If I heard a C4 come up next to my 92 at a red light, and I heard them hit a cut out switch my GF and I would point at you and hope you also had a spoiler/wing installed.....:ugh

 

[ZumZum]

Cut outs are junk, and a waste of MY time. I have manual cut outs on my 76 Vette, I disconnect them to impress my friends in my driveway and I would never drive with them like that! On my 92 vette, I have no mufflers, and I can't hear while on a cell phone, not to mention it's loud all the time.

I recommend to pick a situation:

1.) Loud Sound
2.) Mild Sound
3.) Quiet Sound

If I heard a C4 come up next to my 92 at a red light, and I heard them hit a cut out switch my GF and I would point at you and hope you also had a spoiler/wing installed.....:ugh

Cutouts are really mainly for the weekend racer. If you drive your car to the track it's a helluva lot easier to open up the cutouts then to unbolt and drop the exhaust.