Is 3" large enough for my SC-61?

[pboglio]

Hmm. IMHO, anybody who's asking a message board for advice on whether or not to run a 3.5" exhaust is not ready for it. By the time your making 500 w.h.p. or 680 crank h.p., you'll know the answer to your own question. Best of luck.

 

[suicidal2af]

I only know of one DSM that uses a 3.5 exhaust:.....Shep. And he's puting down a hell of a lot more power that most of us dream about.

Dre runs a 3.5", and he's dyno'd at...511whp? Something like that.

 

[Dirtboarder16]

I posted a link in the other SC61 thread of a honduh that made 607 WHP on an SC61 with a 3" DP, 3" full exhaust. I don't think it'll be a huge restriction for you, but you would probably see some good gains going to a 3.5" exhaust. I would be more concerned with running atleast a T3 exhaust housing over the smaller mitsu housing at that power level, rather than concerning myself with a 3.5" DP.

I saw the other SC61 thread but I'll have to check it out more closely. Thanks for the advice. It has a .68 T4 housing so that won't be a problem. One thing, though: is it just that a fwd honda civic has such little drivetrain loss or what, that it can make 607whp out of a turbo that's rated for a max of 680 crank horsepower? Usually, when a turbo manufacturer assigns a max horsepower rating, thats just what it is. The most horsepower the turbo can flow the air for under 100% ideal conditions. I didn't think many people met those power levels, much less surpassed them. Like I said, though, I'll check out the other thread.

Pboglio - I agree with you, but I don't want to put 3" on now and when I turn up the boost find out I should have gone 3.5" all along.

 

[4gsx63]

What is contradicting about questioning what Corky Bell said in his book? Corky's book said a 3" exhaust will support 800 horsepower. This thread was started to see if people agreed or disagreed with that. If 3" can support 800hp it can support 680. Where did I lose you? BTW, if you used proper spelling and grammar, I think people would take you more seriously.

If you know 3" can support 800hp (Corkey's book), why were you asking if 3" is good enough for SC61? It is call common sense! What is wrong with my spelling? You're not ready for either 3" or the turbo. Just buy some turbo kit off Ebay and call it done.

 

[pboglio]

Please read this thread: http://www.geocities.com/MotorCity/Track/6992/vizard.html
and specifically http://www.geocities.com/MotorCity/Track/6992/vizard9.jpg and http://www.geocities.com/MotorCity/Track/6992/vizard6.jpg

Note in the example that David Vizard states that a 500 h.p. V8 would need 1100 cfm of rated muffler to keep horsepower loss due to backpressure below 1% or 5 h.p.

Bsically, if you want to keep power loss due to exhaust backpressure down to 1% or less, select a muffler based on 2.2 cfm for every horsepower you make. So, your 500 w.h.p. is roughly 588 crank h.p., which means you ideally need a muffler rated at 1294 cfm (.2 psi drop) to keep your power loss down to 1% or less.

Or if you want to interpret it this way: .2 psi of pressure drop per muffler length of exhaust (16-22") based on a FULL length exhaust system (10-14 ft) would result in 1% or less power loss. Based on ~14 ft length exhaust system and .2 psi/ft requirement, I get ~1.5 psi of TOTAL system backpressure. This causes only 1% power loss, or 6 h.p. lost due to pumping work. Pretty straightforward.

The equation to figure out the flow rate of a straight thru muffler if its not stated by the manufacturer would be ROUGHLY: CFM @ .735 psi drop = (Pipe flow area)(115 cfm). This is the flow rate of a straight pipe of 16-22" in length, the best a muffler could flow. If you run a 3" muffler on a FULL length exhaust 588 h.p. setup, using a muffler flow rate of 812.5 cfm, according to David Vizards chart, you'll be sacrificing 17% power (this seems high) at 588 crank h.p., or roughly 2 psi backpressure in the muffler alone (see chart in above link). A 3.5" muffler would be rated at ~1105 cfm (.35 psi drop at 588 h.p.), much closer to the ideal for your horsepower goals. Thats right, the difference in pressure drop between a 3" and 3.5" muffler at 588 h.p. is 1.7 psi in the muffler alone. Its an asymptotic relationship, minor increases in flowrate create large increases in pressure drop for the same pipe diameter, look at the chart in the link, at some point you would become massflow limited by the exhaust restriction, just like a throttle.

This doesn't mean the muffler alone is creating this power drop, but that a muffler of this size would also be connected to an equivalent sized FULL exhaust system. This chart assumes the ENTIRE length of the exhaust system is going to be the same diameter as the muffler, and hence the power loss is due to the sum of all the pipes. David Vizard is making the assumption that most single exhaust systems are roughly the same length, which on passenger cars is correct, about 10-14 ft. Think of that chart as pressure drop per muffler length.

Using the above formula and chart, I can size in my head an exhaust system in 2 minutes. There is no EXACT number; pipe heat loss, pipe bends, pipe length, muffler construction all make exact calculations dubious at best. Use it as a GUIDE based on somebody who flow bench tests exhaust systems for a living and has engine dynoed the power differentials between different sized exhaust systems. You asked people for advice, but your not taking it, you just keep asking the same question over and over again. If you base your decision on a poll majority then your in deep shit. IMHO, base it on some established scientific evidence. Best of luck.

 

[Dirtboarder16]

Please read this thread: http://www.geocities.com/MotorCity/Track/6992/vizard.html
and specifically http://www.geocities.com/MotorCity/Track/6992/vizard9.jpg and http://www.geocities.com/MotorCity/Track/6992/vizard6.jpg

Note in the example that David Vizard states that a 500 h.p. V8 would need 1100 cfm of rated muffler to keep horsepower loss due to backpressure below 1% or 5 h.p.

Bsically, if you want to keep power loss due to exhaust backpressure down to 1% or less, select a muffler based on 2.2 cfm for every horsepower you make. So, your 500 w.h.p. is roughly 588 crank h.p., which means you ideally need a muffler rated at 1294 cfm (.2 psi drop) to keep your power loss down to 1% or less.

Or if you want to interpret it this way: .2 psi of pressure drop per muffler length of exhaust (16-22") based on a FULL length exhaust system (10-14 ft) would result in 1% or less power loss. Based on ~14 ft length exhaust system and .2 psi/ft requirement, I get ~1.5 psi of TOTAL system backpressure. This causes only 1% power loss, or 6 h.p. lost due to pumping work. Pretty straightforward.

The equation to figure out the flow rate of a straight thru muffler if its not stated by the manufacturer would be ROUGHLY: CFM @ .735 psi drop = (Pipe flow area)(115 cfm). This is the flow rate of a straight pipe of 16-22" in length, the best a muffler could flow. If you run a 3" muffler on a FULL length exhaust 588 h.p. setup, using a muffler flow rate of 812.5 cfm, according to David Vizards chart, you'll be sacrificing 17% power (this seems high) at 588 crank h.p., or roughly 2 psi backpressure in the muffler alone (see chart in above link). A 3.5" muffler would be rated at ~1105 cfm (.35 psi drop at 588 h.p.), much closer to the ideal for your horsepower goals. Thats right, the difference in pressure drop between a 3" and 3.5" muffler at 588 h.p. is 1.7 psi in the muffler alone. Its an asymptotic relationship, minor increases in flowrate create large increases in pressure drop for the same pipe diameter, look at the chart in the link, at some point you would become massflow limited by the exhaust restriction, just like a throttle.

This doesn't mean the muffler alone is creating this power drop, but that a muffler of this size would also be connected to an equivalent sized FULL exhaust system. This chart assumes the ENTIRE length of the exhaust system is going to be the same diameter as the muffler, and hence the power loss is due to the sum of all the pipes. David Vizard is making the assumption that most single exhaust systems are roughly the same length, which on passenger cars is correct, about 10-14 ft. Think of that chart as pressure drop per muffler length.

Using the above formula and chart, I can size in my head an exhaust system in 2 minutes. There is no EXACT number; pipe heat loss, pipe bends, pipe length, muffler construction all make exact calculations dubious at best. Use it as a GUIDE based on somebody who flow bench tests exhaust systems for a living and has engine dynoed the power differentials between different sized exhaust systems. You asked people for advice, but your not taking it, you just keep asking the same question over and over again. If you base your decision on a poll majority then your in deep shit. IMHO, base it on some established scientific evidence. Best of luck.

That is some great info. It puzzles me why the 500whp supra made roughly the same numbers on 3, 3.5 and 4 inch piping, though. Oh well. Enough fussing, I'm going with 3.5". Thanks for all your help.

And to the guy who can't let it go: I don't believe corky bell. That's the reason I posted this. I don't know how many times I need to say that but this is the last. According to Maximum Boost, a DSM (or any engine) making 500 crank horsepower will not benefit from an exhaust larger than 2.5" in diameter, but we all know that even stock cars can reap the gains of a 3" exhaust. I'm not even going to comment on the rest of what you've said.

 

[swordfish]

I run a 3.5 inch exhaust. Cost the same to build as a 3 inch. Did I pick up power? You bet your ass I did. ... and I'm not talking about the butt dyno either. Turbo is a SC61 P trim. The rest of my setup is on my website.

jeff

 

[Dirtboarder16]

I run a 3.5 inch exhaust. Cost the same to build as a 3 inch. Did I pick up power? You bet your ass I did. ... and I'm not talking about the butt dyno either. Turbo is a SC61 P trim. The rest of my setup is on my website.

jeff

Nice website and one hell of a car. I like your philosophy too. When you say you picked up a lot of power from the 3.5" O2-back, were you talking with the cutout too? I see you had the E-cutout listed with your exhaust mods. Isn't that probably what made the most difference? Care to comment on how reliable and how loud the cutout is?

 

[CanadianTalon]

I saw the other SC61 thread but I'll have to check it out more closely. Thanks for the advice. It has a .68 T4 housing so that won't be a problem. One thing, though: is it just that a fwd honda civic has such little drivetrain loss or what, that it can make 607whp out of a turbo that's rated for a max of 680 crank horsepower? Usually, when a turbo manufacturer assigns a max horsepower rating, thats just what it is. The most horsepower the turbo can flow the air for under 100% ideal conditions. I didn't think many people met those power levels, much less surpassed them. Like I said, though, I'll check out the other thread.

Pboglio - I agree with you, but I don't want to put 3" on now and when I turn up the boost find out I should have gone 3.5" all along.

Part of it has to due with the inredibly high VE on some Honda motors, but part of it I think is the turbo is underrated. Keep in mind that was at only 27 psi as well, because he was only running a 2.5 or 3 bar map, so he's boost limited. I'm sure it would make even more power at 35 psi.

 

[swordfish]

Nice website and one hell of a car. I like your philosophy too. When you say you picked up a lot of power from the 3.5" O2-back, were you talking with the cutout too? I see you had the E-cutout listed with your exhaust mods. Isn't that probably what made the most difference? Care to comment on how reliable and how loud the cutout is?

Thanks for the compliments. The gains from the 3.5 exhaust were realized before integration of the cutout. The cutout didnt go on the car until the stock muffler went back on the car after I had the 3.5 inch setup for some time. I sold my old 3.5 inch setup so thats the reason for the partial stocker going back on. Now the stock muffler is coming back off the car because I am finishing up a new, lighter thin walled 3.5 inch setup. I should have it done in early Feb.

jeff

 

[Dirtboarder16]

Thanks for the compliments. The gains from the 3.5 exhaust were realized before integration of the cutout. The cutout didnt go on the car until the stock muffler went back on the car after I had the 3.5 inch setup for some time. I sold my old 3.5 inch setup so thats the reason for the partial stocker going back on. Now the stock muffler is coming back off the car because I am finishing up a new, lighter thin walled 3.5 inch setup. I should have it done in early Feb.

jeff

Thanks for the info Jeff. By now I have already ordered the 3.5" piping so we'll see how well it works. It's 14 gauge though, which is going to be a little bit on the heavy site, but should hold heat in better, improving the velocity of the exhaust gasses.


While we're on the topic of exhaust flow and restrictions, I have another question. I see a lot of guys running very tight radius 90 degree bent O2 housings, plenty of which are using large turbos and no doubt making a lot of power. I've read that the exhaust coming out of the turbine housing exits in a swirling tornado-like flow which travels through the exhaust much more efficiently than a turbulent flow. With this logic, many have told me that the longer the exhaust pipe coming off the turbo goes straight out without bending, the better. Can you see how this is contradicting? I realize there is very little room to work with and that's why the tight 90 degree bend is usually done, and I am in this same boat with the location of my turbo, but wouldn't that be horrible for efficient flow? Am I looking too much into this? I saw that the guy who posted his really short exhaust with the aeroturbine muffler was ridiculed for using that tight radius 180 degree bend like he did, but isn't a tight 90 just half as bad?

 

[pneumo]

That's the reason Buschur offers an alternator relocation kit; so you can run the exhaust straight out from the turbo. Or you could just relocate the oil filter so the first bend coming off the turbo isn't so tight.

 

[Dirtboarder16]

That's the reason Buschur offers an alternator relocation kit; so you can run the exhaust straight out from the turbo. Or you could just relocate the oil filter so the first bend coming off the turbo isn't so tight.

Well I guess you probably didn't read the whole thread, and I don't blame you, but this is going on a 3000GT not a DSM. Interesting info, though. Do many people go this extra mile to avoid the sharp bend? How many guys are making big power with a tight radius bend?

 

[pboglio]

Thanks for the info Jeff. By now I have already ordered the 3.5" piping so we'll see how well it works. It's 14 gauge though, which is going to be a little bit on the heavy site, but should hold heat in better, improving the velocity of the exhaust gasses.

While we're on the topic of exhaust flow and restrictions, I have another question. I see a lot of guys running very tight radius 90 degree bent O2 housings, plenty of which are using large turbos and no doubt making a lot of power. I've read that the exhaust coming out of the turbine housing exits in a swirling tornado-like flow which travels through the exhaust much more efficiently than a turbulent flow. With this logic, many have told me that the longer the exhaust pipe coming off the turbo goes straight out without bending, the better. Can you see how this is contradicting? I realize there is very little room to work with and that's why the tight 90 degree bend is usually done, and I am in this same boat with the location of my turbo, but wouldn't that be horrible for efficient flow? Am I looking too much into this? I saw that the guy who posted his really short exhaust with the aeroturbine muffler was ridiculed for using that tight radius 180 degree bend like he did, but isn't a tight 90 just half as bad?

Once you get your pressure drop around 2-3 psi or less using that big 3.5" tube diameter, what kind of power increases are you expecting from further reducing that already low number? I'd suggest a college level Fluid dynamics textbook just so you can figure out how all these tight radius bends, diffusers, etc affect your pressure drops. A tight radius (r/d=1) 90* bend is worth about 6 ft of straight 3.5" pipe, a moderate radius (r/d=2) 90* bend is worth about 3.5 ft. If you sized your pipes correctly, you should be dropping 1% power or roughly .1 psi/ft of straight tubing. So a tight 90* bend is costing you about .6 psi of backpressure. A moderate 90* bend would be .35 psi of backpressure. Is that really worth the trouble of routing a straight pipe off the turbo and having to cut thru body work to do it? If your going single turbo on a V6 you've already got more than one 90* bend after the headers anyway, what is 1 or 2 more bends after the turbo?

FYI, Turbotrix runs an EVO VIII that has over 500 w.h.p. and runs a 9 sec 1/4 mile. They use a 3.5" downpipe and 4" catback exhaust system. They also have a 90* bend off the turbo, just like every stock DSM.

 

[Dirtboarder16]

Once you get your pressure drop around 2-3 psi or less using that big 3.5" tube diameter, what kind of power increases are you expecting from further reducing that already low number? I'd suggest a college level Fluid dynamics textbook just so you can figure out how all these tight radius bends, diffusers, etc affect your pressure drops. A tight radius (r/d=1) 90* bend is worth about 6 ft of straight 3.5" pipe, a moderate radius (r/d=2) 90* bend is worth about 3.5 ft. If you sized your pipes correctly, you should be dropping 1% power or roughly .1 psi/ft of straight tubing. So a tight 90* bend is costing you about .6 psi of backpressure. A moderate 90* bend would be .35 psi of backpressure. Is that really worth the trouble of routing a straight pipe off the turbo and having to cut thru body work to do it? If your going single turbo on a V6 you've already got more than one 90* bend after the headers anyway, what is 1 or 2 more bends after the turbo?

FYI, Turbotrix runs an EVO VIII that has over 500 w.h.p. and runs a 9 sec 1/4 mile. They use a 3.5" downpipe and 4" catback exhaust system. They also have a 90* bend off the turbo, just like every stock DSM.

Everything I needed to hear and more. Can't tell you how helpful that is. Thanks!

 

[greycar]

3inch tubing is good for roughly 600whp. I made roughly 700 to the crank with 3 inch. and as far as I know the SC 61 is only good to about 550-600hp. 3.5 inch is good up to 900-1000hp range. I am going overkill next year with 4inch cause I going to make like 1400hp, you know what I'm saying BBBBBBBBOOOOOOOOOYYYYYYYYY, just kinding about the 1400hp but it would be nice.

 

[Nos~4G63]

When looking for exhaust to use on my car I read somewhere on this site that Shep made 700whp on 3'' diameter piping, How many of us are ever going to make more than that?

Plus I got my 3'' turbo back for $499 from RnR, The Buschur 3.5'' was about $900.