Is 3" large enough for my SC-61?

[Dirtboarder16]

/off topic/ does anybody remember the thread that was on here a while ago where someone was talking about pressure ratio across the turbine and how the effect of lowering exhaust back pressure gets multiplied when you get back to the exhaust manifold? I can't seem to find it and I think this thread had some real world data on dsm's exhausts. //

I've read that post. I also used the turbine and compressor work formulas, equated them and solved for Turbine Inlet pressure, sourced from "Internal Combustion Engine Fundamentals". Got the whole shebang on a spreadsheet. Gotta input 5-6 variables, but shows the relationship between Turbine inlet pressure and EGT, boost pressure, outside air temps, compressor & turbine efficiency, and mostly exhaust system backpressure. I've seen guys post Turbine backpressures as low as 17 psi on a .48 A/R 50 trim to somebody stating Forced Performance ran 80 psi backpressure on a 20g TD05 wheel unclipped.

By far, and the reason I place such emphasis on this guy running a 3.5" exhaust at 680 h.p., is that reducing backpressure by 7 psi would drop turbine inlet pressure by over 15 psi, depending on turbine wheel efficiency. Thats a HUGE reduction in pumping work and gives a much bigger margin against reversion and knock.

Interesting point about the turbo-back pressure having a multiplied effect on the header back pressure. Hot exhaust gas reversion is not something I want a lot of at 10:1 CR. Also, it seems like everyone here, including yourself, believes that on the street (pump gas), 3" will be more than enough. If this is the case, there might be no reason for me to go 3.5", as even with water/methanol injection and a good intercooler, I don't think I'll be able to get much more than mid 400WHP before I see too much knock. At the track where race fuel is available will likely be the only time I will see the full 680 horsepower. With this in mind, running a cutout for the track, would there be any benefit in using 3.5" (14 feet of it, give or take), or will 3" be the best?

 

[1fast97gsx]

just go with 3 ... I have that same turbo on a built motor and I'm only running 3.

 

[Dirtboarder16]

just go with 3 ... I have that same turbo on a built motor and I'm only running 3.

Well not exactly the same turbo. My SC has a large T4 exhaust housing that should support more than 50 more horsepower than the SCM mitsu housing. Nice setup and great looking car, btw. Have you tracked it or been to a dyno? How's it feel? The thing is, just because 3 may work fine, doesn't mean gains can't be had from going a little larger.

 

[pboglio]

O.K., switching my thought process so I can think like a turbo V6 owner. Now, 680 h.p. on a roughly 3800lb car is about 10.3 @ 132 mph quarter mile time. Now, almost every ENTRY level exhaust upgrade for a V6 or V8 car is a set of DUAL 2.25's, which is already bigger than a single 3". The Buick GNX boys have a whole crap load of DUAL 2.5" exhausts, thats equal to a 3.5" single. Now, according to ATRperformance.com has a DUAL 3" exhaust for their car running 9's in the 140 mph trap speed. Thats right DUAL, not single 3". Maybe these guys know a thing or two about turbo V6 motors running high trap speeds. If I followed the lead from anybody, it would be from the GNX crowd, they seem to have done everything 10 years before us DSMers.

Is it just me, or is almost every after market exhaust system for a turbo V6 or N/A V8 like DUAL 2.5's, I just don't get why people are freaking about a single 3.5", if I stated DUAL 2.5" exhausts nobody would have said a word. Come on guys, the new Corvette Z06 comes with DUAL 2.75" exhausts, the aftermark ones are DUAL 3" pipes on a car with only 405 crank h.p. Not everybody wants to run a screaming open dump external or do some ridiculous looking side dump exhaust.

Dirtboarder16,

IMHO, your looking in the wrong forum to solve your problem, I'm sorry to say. Please, call any one of the Buick Grand National vendors who run a car faster than 130mph to 140 mph and ask them what exhaust configuration is best for a near 700 h.p. V6 turbo car which is street/strip dual duty. Thats what I would do if I was unsure.

 

[98TalonTSi]

Just to clear things up for my own mind, when you refer to these size exhausts, your talking literally from the turbos turbine housing to wherever it ends. i.e. a true 3" turbine, a true 3.5" turbine...

 

[pboglio]

All of my arguements exclude wave tuning, which is seriously affected by pipe diameter and length. I think however that somebody looking for 680 top end and launching at 5000 rpm is going to have to compromise on one or the other.

Run as big of a pipe as you can as close to the turbo to get the max benefit. Obviously a diffuser of the proper divergence angle is required right off the turbo to avoid a sizeable pressure drop. Having 1 or 2 ft of smaller pipe is harmless and might be good for tight quarters near the engine. But yeah, run a 3" or 3.5" or whatever pipe as close to the turbo as a properly sized diffuser cone (Hooker or Flowmaster sells these) allows.

One of the biggest stupidest misconceptions I've seen stated on DSMtuners is if its not full 3" or full whatever then somehow its some major restriction. Completely untrue, you just get the added pressure drop of the smaller diameter pipe. Another misconception is that you ALWAYS have to go from small to big or whatever, absolute bullshit. You can go up and down in size if the sucker is shaped like a Venturi and get minimal flow losses. Why somebody would do that I don't know but its possible to do if needed.

Now the exception is a neckdown that causes the exhaust velocity to get up around MACH 1 or even less, then everything goes out the window and it wouldn't matter if you had full 4" pipes on both sides, you would be choke flow restricted by the neck, even though it has almost no length to it. That is an extreme example.

You can add up the pressure drop of any number of countless exhaust setups: 2.5 downpipe/3" catback or 3" 02 housing/3" downpipe/3" catback. Whatever works best. I personally felt a moderate drop in low end torque off boost just from going stock to 2.5" downpipe, on both DSMs I owned, so for me a perfect compromise is 2.5" downpipe/3" catback exhaust. Whatever works best.

 

[Dirtboarder16]

O.K., switching my thought process so I can think like a turbo V6 owner. Now, 680 h.p. on a roughly 3800lb car is about 10.3 @ 132 mph quarter mile time. Now, almost every ENTRY level exhaust upgrade for a V6 or V8 car is a set of DUAL 2.25's, which is already bigger than a single 3". The Buick GNX boys have a whole crap load of DUAL 2.5" exhausts, thats equal to a 3.5" single. Now, according to ATRperformance.com has a DUAL 3" exhaust for their car running 9's in the 140 mph trap speed. Thats right DUAL, not single 3". Maybe these guys know a thing or two about turbo V6 motors running high trap speeds. If I followed the lead from anybody, it would be from the GNX crowd, they seem to have done everything 10 years before us DSMers.

Is it just me, or is almost every after market exhaust system for a turbo V6 or N/A V8 like DUAL 2.5's, I just don't get why people are freaking about a single 3.5", if I stated DUAL 2.5" exhausts nobody would have said a word. Come on guys, the new Corvette Z06 comes with DUAL 2.75" exhausts, the aftermark ones are DUAL 3" pipes on a car with only 405 crank h.p. Not everybody wants to run a screaming open dump external or do some ridiculous looking side dump exhaust.

Dirtboarder16,

IMHO, your looking in the wrong forum to solve your problem, I'm sorry to say. Please, call any one of the Buick Grand National vendors who run a car faster than 130mph to 140 mph and ask them what exhaust configuration is best for a near 700 h.p. V6 turbo car which is street/strip dual duty. Thats what I would do if I was unsure.

Thanks for all the great advice. Also, the car is FWD, so it is actually 3000lbs and would be more like mid 12s at close to 140 . We did have a member go 11.3 @ 133 on drag radials with a similar setup, though. You're probably right that I should have checked out the GNX boards first but I'm much more familiar with things here and at 3Si. I'll check them and the supra boards out now, though. I'm puzzled along with you why everyone runs dual 2.5s and no one thinks twice, but 3.5 is like "". Come to think of it, a lot of our N/A guys making 220-250 crank hp run dual 2.5s and some larger.

One thing I don't quite understand, though, is how 3" can be perfect on a 2.0L making 500 crank hp, but it is too small for a 3.0L making the same. At the same horsepower level, shouldn't airflow be the same?

 

[1fast97gsx]

Well not exactly the same turbo. My SC has a large T4 exhaust housing that should support more than 50 more horsepower than the SCM mitsu housing. Nice setup and great looking car, btw. Have you tracked it or been to a dyno? How's it feel? The thing is, just because 3 may work fine, doesn't mean gains can't be had from going a little larger.

I will dyno it this summer ... I just kinda quick read this post, but how big is the actual exhaust outlet side on the exhaust housing on the turbo? I used to have the t3 exhaust housing and the outlet was only 2.5" out of that ... same as my scm.

 

[Dirtboarder16]

I will dyno it this summer ... I just kinda quick read this post, but how big is the actual exhaust outlet side on the exhaust housing on the turbo? I used to have the t3 exhaust housing and the outlet was only 2.5" out of that ... same as my scm.

It's a .68 A/R T4 housing with a 3" V-band outlet. Still trying to figure out the best exhaust diameter.

 

[1fast97gsx]

I would just go 3 with a cutout right before the cat to open the flow up a tad more.

 

[dsmrunaway1]

1FAST97GSX...WHAT DO U THINK OF THE SCM 6152E TURBO..I JUS ORDERED ONE THIS MORNING..AND WONDERING WHAT U THINK...IS IT A CRAZY TURBO....AND TO GET ON TOPIC....JUS BUY A 3.5 INCH ....U KNOW UR ALWAYS GONNA WANNA GO BIGGER SO ULL HAVE IT IF U EVER UPGRADE....PLUS ITD BE COOL TO SAY U HAVE 3.5 INCH EXHAUST......

 

[1fast97gsx]

well shep was running 3.5" last I checked and making 1000 hp? I think for a 500 hp car 3" is plenty. Turbo is nice though and top end is a lot of fun. Kinda needs high boost and race gas to really unleash it's potential though imo.

 

[Dirtboarder16]

well shep was running 3.5" last I checked and making 1000 hp? I think for a 500 hp car 3" is plenty. Turbo is nice though and top end is a lot of fun. Kinda needs high boost and race gas to really unleash it's potential though imo.

I think its possible that shep would have ideally gone bigger. I think I read that 3.5" is class mandated so even if it was choking his top-end flow, that's the largest he could go. I'm gunna snoop around the supra forums for some answers once my membership is activated.

 

[4gsx63]

There are many dsms making over 600whp with 3" exhausts. How many people making close to 600whp with the SC61 that you know or heard of? People with the slowest dsm tends to want the biggest shit available.

Why would you want to run full exhaust if you plan to make 600whp anyway? :thumbdown

 

[Dirtboarder16]

There are many dsms making over 600whp with 3" exhausts. How many people making close to 600whp with the SC61 that you know or heard of? People with the slowest dsm tends to want the biggest shit available.

Why would you want to run full exhaust if you plan to make 600whp anyway? :thumbdown

It's not a dsm, and I don't plan to make 600whp because the turbo is not capable of that much. Who do you know who is making that much with a 3" turbo-back? I didn't know there were so many.

Edit: realized you contradicted yourself. You said there are many making 600whp with 3" exhausts, and then you say why would I or they want to run a full exhaust. Also, what makes you think you can't have a full exhaust with that kind of power? I've been browsing the supra forums for an hour and people making over 1000whp are running full exhausts. 600whp may be a lot for your 2.0L but its not the end-all.

 

[lambertvr4]

I've tuned a Civic (2.0L, 10:1, SC61) to 620wHP. 3" downpipe to just under the driver. We never dyno'ed it with the full exhaust since it wasn't required in the class. On the road you could tell a slight difference with the rest of the exhaust on. Nothing major though.

If you think you'll need 3.5" exhaust, get it. You're not going to get an agreement on here.

 

[Dirtboarder16]

I've tuned a Civic (2.0L, 10:1, SC61) to 620wHP. 3" downpipe to just under the driver. We never dyno'ed it with the full exhaust since it wasn't required in the class. On the road you could tell a slight difference with the rest of the exhaust on. Nothing major though.

If you think you'll need 3.5" exhaust, get it. You're not going to get an agreement on here.

Thanks to you and the few helpful members in this thread. Maxing out an SC61 on a civic is one heck of an accomplishment. Nice.

I am moving my search to the turbo buick forums. There are a lot more guys there who know how to make big power.

 

[4gsx63]

It's not a dsm, and I don't plan to make 600whp because the turbo is not capable of that much. Who do you know who is making that much with a 3" turbo-back? I didn't know there were so many.

Edit: realized you contradicted yourself. You said there are many making 600whp with 3" exhausts, and then you say why would I or they want to run a full exhaust. Also, what makes you think you can't have a full exhaust with that kind of power? I've been browsing the supra forums for an hour and people making over 1000whp are running full exhausts. 600whp may be a lot for your 2.0L but its not the end-all.

no no no! You contradicted youself! You stated "According to Corky Bell (i think most probably know who he is), a 3" exhaust will support like 800 horsepower." Then you all up in here asking whether 3" is good for SC61 while you already know that turbo is not capable of not making?

 

[Dirtboarder16]

no no no! You contradicted youself! You stated "According to Corky Bell (i think most probably know who he is), a 3" exhaust will support like 800 horsepower." Then you all up in here asking whether 3" is good for SC61 while you already know that turbo is not capable of not making?

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.

 

[pboglio]

You guys wanna see what kinda backpressure is possible on a 600 w.h.p. restrictive exhaust setup? Take a look at this link, remember, this is a 2003 Ford Cobra Supercharged running a stock dual exhaust system:

http://www.mustang50magazine.com/techarticles/138_0303_COBRA/index1.html


Thats right, 30 psi backpressure on a non-turbocharged car. Overall a really cool dyno tuning session that shows all the wacky stuff they tried to squeeze out more power.

 

[Dirtboarder16]

You guys wanna see what kinda backpressure is possible on a 600 w.h.p. restrictive exhaust setup? Take a look at this link, remember, this is a 2003 Ford Cobra Supercharged running a stock dual exhaust system:

http://www.mustang50magazine.com/techarticles/138_0303_COBRA/index1.html


Thats right, 30 psi backpressure on a non-turbocharged car. Overall a really cool dyno tuning session that shows all the wacky stuff they tried to squeeze out more power.

Interesting read. This, however, seems to show proof that at or just above the 500whp level, a 3", 3.5" and 4" exhaust all make within a few whp of each other. Very interesting.
http://www.supraforums.com/forum/showthread.php?s=&threadid=246842&highlight=goliath+exhaust

 

[93AWDTalon1]

One thing I don't quite understand, though, is how 3" can be perfect on a 2.0L making 500 crank hp, but it is too small for a 3.0L making the same. At the same horsepower level, shouldn't airflow be the same?

I always thought the same thing

 

[pboglio]

O.K. here's a direct dyno comparison between a 2.5" exhaust and 3.0" exhaust on a DSM running a 20g. Notice the big increase in the midrange, even with the same A/F values. Draw your own conclusions.

 

[Dirtboarder16]

I appreciate you posting that, but I'm not sure of its relevance to what we've been discussing. My conclusion is that the dsm is beginning to outflow the 2.5" piping at the 300whp mark. That doesn't really help me decide at what level it would begin to outflow the 3" piping.

 

[CanadianTalon]

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.