2.5 or 3 inch exhaust

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s13grady
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2.5 or 3 inch exhaust

Post by s13grady »

I am going to be buying a turbo kit for my car and i havent decided on an exhaust.

I dunno if i want 3 or 2.5 inch. which is better.
i will be running a cat with it too.
I dont want it too loud either

Just curios to know everyones setup including cats/resonators etc..

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hey

Post by klattr1 »

4"!!!
jk, just go with 3" and call it a day.
i run not cat nor the resonator on the apexi n1 (3")
check out some of my vids for the sound.
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Post by Rick »

I was going to switch to a 4" this winter if I were to keep the car by using a double u-joint that I built, where I could move my steering shaft over 1.5"

For now I use 3" and I dont think its restricting me, however I have run faster E.T.'s with just running an open downpipe.

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Post by Jordan Gladman »

Im running 3" with cat, resonator and muffler...

I like the car to be nice and quiet while im cruising, makes the external dump seem that much louder when it opens :D
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Post by Greaser »

Jordan Gladman wrote:Im running 3" with cat, resonator and muffler...

I like the car to be nice and quiet while im cruising, makes the external dump seem that much louder when it opens :D
on the 360hp setup i ran a 2.5" exhaust with no cat. 15psi oh and on my 357hp sr20 i ran a hks hyper 2.5" exhaust 15psi again. i've had some luck with quiet small exhausts.
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Post by Greaser »

Rick wrote:I was going to switch to a 4" this winter if I were to keep the car by using a double u-joint that I built, where I could move my steering shaft over 1.5"

For now I use 3" and I dont think its restricting me, however I have run faster E.T.'s with just running an open downpipe.

Rick
i wouldnt even worry about it. i ran 4" on my sr20 and it was a MAJOR pain in the ass even if the steering knuckle was away. I'd run the 3" until your feet then 4" all the way back. but thats me, and it would be easy.
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Post by s13grady »

thanks for the info,

my original plan was to get an apexi n1, and run a high flow cat with it, so i think that is wat i am going to do, i want the exhaust to be kinda loud, also ill running an hks bov so i dont think i will have any trouble hearing it over an exhaust.

Thanks
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Post by Greaser »

gradys13 wrote:thanks for the info,

my original plan was to get an apexi n1, and run a high flow cat with it, so i think that is wat i am going to do, i want the exhaust to be kinda loud, also ill running an hks bov so i dont think i will have any trouble hearing it over an exhaust.

Thanks
GRady

def get a cat. the girls that smell you will like the lack of the stench of no cat exhausts. oh god that **** makes me so sick now when i get near a car without a cat. theres a new cat in the jegs catalog that is standard 3" pipe. the unit itself measures 4" all the way around and is only like 12" long. the actuall catalyst material is only like 4" thick by 3" diameter. I would do that one. alot less catalyst material than the other "highflow" units out there.and its alot less of turbulant flow going from big back to small like in standard cats.
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Post by slow4dr »

I can get the larger diameter(3.5"-4") stainless piping for pretty cheap. Probably around $10-$20 a bend if you guys need any.
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Post by Greaser »

slow4dr wrote:I can get the larger diameter(3.5"-4") stainless piping for pretty cheap. Probably around $10-$20 a bend if you guys need any.
wtf!?! i think i paid like 40 a piece for 4" 90' bends from hooker header. i have 2 of them left thank god i never finished that hellish setup. it was a MAJOR PITA i will NEVER do that again. MASSIVE amounts of stress trying to put that **** together. hahah now you know why i'm retired.
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Post by slow4dr »

Greaser wrote:wtf!?! i think i paid like 40 a piece for 4" 90' bends from hooker header. i have 2 of them left thank god i never finished that hellish setup. it was a MAJOR PITA i will NEVER do that again. MASSIVE amounts of stress trying to put that **** together. hahah now you know why i'm retired.
8) I hate piecing together an exhaust system. The only way to do it IMO is to swedge each end so they fit into each other.
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Post by SOHC_KAT »

I have 3'' All the way No cat no nothing. I was thinking to put a cat.
Couse youre rite the smel is not very good ! So im goin to get the jegs catalog. To check the one youre talking about Thanks !
Oh And my freand did a kat dohc i h ave the sohc wel he did a 3'' on his and he took it to the dino. Then after like a week he took the 3'' of and did 4''. He ses that it wasent worth the troble he got no difreans out of it :(
May be thats just him :D
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Post by slow4dr »

3" w/out a cat is plenty for 400WHP and probably wont hold you back untill 450.
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Post by nightwalker »

I've been browsing around exhaust shops and have noticed pretty nice 3inch cats (flangless) for a decent price. I'm building my own exhaust, 3inches, just mandrel bent pipes (straight as possible, one piece), catback, and a straight through muffler. Actually pretty easy. Saved me 300 bucks too. :)
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Post by Toahk »

Image

"It is easy to get overeager on fitting large-diameter pipes into an exhaust system. "the larger the better" is not the case. There is an exhaust gas velocity that ought not to be exceeded, I am going to suggest that for exhaust calculations, this velocity is approximately 250 feet/sec. The considerable expansion of exhaust gas due to the temperature increase also requires a significant increase in the desired volume of the tailpipe. The tubes for the hot gas on the exhaust side should therefore be largeer than the tuber for the cooler intake side. Base the calculation on the conditions as for the intake tubes, but use a maximum velocity of 250 feet/sec rather than 450 feet/sec. To size a tailpipe, you can adhere to this exhaust gas velocity or to the simple guidline of selecting a tube diameter approximately 10% larger than the turbine outlet diameter."

Was just reading my book and came across this.
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Post by SHIFT_KA24DET »

Good Information but from what I've Seen that info only apply's to N/A Cars.
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Post by Toahk »

Good Information but from what I've Seen that info only apply's to N/A Cars
Well it came from: Maximum Boost, Designing, Testing and Installing Turbocharger systems. Where have you seen this info stating it only apply's to N/A cars? I dont think they would include it in the book if it was for n/a cars.
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Post by SHIFT_KA24DET »

I'm talking from experiance, I worked at a 4WD Tuning Shop In Toronto
for Three years and on Turbo cars Bigger is Better (After the turbo that is)
But as far as N/A goes everything stated in that blurb from your book is true.
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Post by nightwalker »

...and then again, the FA guys have proven that a 3inch exhaust on a NA KA is not bad at all.
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Post by SHIFT_KA24DET »

I gained 15whp on my All Motor KA using a GP Sports Spec D 3" Exhaust.
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Post by s14_2Nv »

3 inch exaust on a n/a ka would give better top end power, but would reduce low end torque numbers wouldn't it.
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Post by SHIFT_KA24DET »

s14_2Nv wrote:3 inch exaust on a n/a ka would give better top end power, but would reduce low end torque numbers wouldn't it.
You are correct Phil
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Post by Greaser »

SHIFT_SR20DET wrote:
s14_2Nv wrote:3 inch exaust on a n/a ka would give better top end power, but would reduce low end torque numbers wouldn't it.
You are correct Phil

i disagree. only in header design does airflow need to be carefully looked at to make power. You cant make power with an exhaust system, you are only reducing its ability to rob power/torque over no exhaust at all. There isnt an exhaust on the market that you bolt on to an application where no exhaust was and gain power. there isnt an exhaust on the market that if you removed it you'd lose power.

corky bell and his book are for beginners imo. I've read it and after reading it have found his opinions to be far off, along with all the other info out there in the "market". turbo sizing is one place. soooo much stuff out there just doesnt add up. I gave up and just try stuff now.
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Post by Greaser »

Toahk wrote:Image

This chart is wayyyyy off. On a freinds 13:1 2.0 liter B18 with a 2.5" exhaust he put down 212fwhp with a 3" he put down 220fwhp and no ehaust put down 227fwhp. all motor. 9000rpm.

another example was one sr20 setup i had that went 11.50's 357rwhp@15psi using a 2.5" exhaust. Previous dyno made 400rwhp@15psi no exhaust. (this was the same setup i made a very detailed post on FA comparing my 350hp SR20 vs. Dennis from GA 350hp KAT)
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Post by Toahk »

good info. I shouldn't have taken what was in the book as a testimony, Ive also heard of bigger the better, and in this case it seems true. So people running anything over 3.5" + exhausts, any dyno numbers on those?
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Post by SHIFT_KA24DET »

Greaser wrote:
SHIFT_SR20DET wrote:
s14_2Nv wrote:3 inch exaust on a n/a ka would give better top end power, but would reduce low end torque numbers wouldn't it.
You are correct Phil

i disagree. only in header design does airflow need to be carefully looked at to make power. You cant make power with an exhaust system, you are only reducing its ability to rob power/torque over no exhaust at all. There isnt an exhaust on the market that you bolt on to an application where no exhaust was and gain power. there isnt an exhaust on the market that if you removed it you'd lose power.

corky bell and his book are for beginners imo. I've read it and after reading it have found his opinions to be far off, along with all the other info out there in the "market". turbo sizing is one place. soooo much stuff out there just doesnt add up. I gave up and just try stuff now.
Header Design has alot to do with your power range but explain
to me why on my all motor KA I gained 15 hosepower to the
wheels when I bolted up a GP Sports 3" Exhaust? I thought
you said no Bolt on exhaust gives you power gains?
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Post by Greaser »

SHIFT_SR20DET wrote:
Greaser wrote:
SHIFT_SR20DET wrote:
s14_2Nv wrote:3 inch exaust on a n/a ka would give better top end power, but would reduce low end torque numbers wouldn't it.
You are correct Phil

i disagree. only in header design does airflow need to be carefully looked at to make power. You cant make power with an exhaust system, you are only reducing its ability to rob power/torque over no exhaust at all. There isnt an exhaust on the market that you bolt on to an application where no exhaust was and gain power. there isnt an exhaust on the market that if you removed it you'd lose power.

corky bell and his book are for beginners imo. I've read it and after reading it have found his opinions to be far off, along with all the other info out there in the "market". turbo sizing is one place. soooo much stuff out there just doesnt add up. I gave up and just try stuff now.
Header Design has alot to do with your power range but explain
to me why on my all motor KA I gained 15 hosepower to the
wheels when I bolted up a GP Sports 3" Exhaust? I thought
you said no Bolt on exhaust gives you power gains?

No bolt on exhaust gives power gains over an application where no exhaust previously was. That exhaust you have was replacing an exhaust that was more effective at reducing noise and limiting airflow for silent operation. It was more effective and reducing HP/torque. I bet if you dynoed with the exhaust off completely you'd gain another 2-5hp. Dont read so quick grasshoppa :D
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Post by SHIFT_KA24DET »

Greaser wrote:
SHIFT_SR20DET wrote:
Greaser wrote:
SHIFT_SR20DET wrote: You are correct Phil

i disagree. only in header design does airflow need to be carefully looked at to make power. You cant make power with an exhaust system, you are only reducing its ability to rob power/torque over no exhaust at all. There isnt an exhaust on the market that you bolt on to an application where no exhaust was and gain power. there isnt an exhaust on the market that if you removed it you'd lose power.

corky bell and his book are for beginners imo. I've read it and after reading it have found his opinions to be far off, along with all the other info out there in the "market". turbo sizing is one place. soooo much stuff out there just doesnt add up. I gave up and just try stuff now.
Header Design has alot to do with your power range but explain
to me why on my all motor KA I gained 15 hosepower to the
wheels when I bolted up a GP Sports 3" Exhaust? I thought
you said no Bolt on exhaust gives you power gains?

No bolt on exhaust gives power gains over an application where no exhaust previously was. That exhaust you have was replacing an exhaust that was more effective at reducing noise and limiting airflow for silent operation. It was more effective and reducing HP/torque. I bet if you dynoed with the exhaust off completely you'd gain another 2-5hp. Dont read so quick grasshoppa :D
I indeed read it too quickly. My understanding of your
statement was that you were stating that no aftermarket
exhaust that replaces your stock one will give you power.

My Bad... :oops:
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Post by Slip_AngleSX »

The only problem i see with a 4" exhaust or open header is that you lose bottom end too much for the top end you gain, but i guess it all depends on if youre drifting, auto-x, or drag racing too. But yeah bigger will make more OVERALL horse power. I guess that makes thias a good recap on everything that was already said...oh well.
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Post by Greaser »

Slip_AngleSX wrote:The only problem i see with a 4" exhaust or open header is that you lose bottom end too much for the top end you gain, but i guess it all depends on if youre drifting, auto-x, or drag racing too. But yeah bigger will make more OVERALL horse power. I guess that makes thias a good recap on everything that was already said...oh well.
theres no loss of low end going open header or big exhaust. you gain everywhere.
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