2.5 vs 2.25 diameter exhaust

Discussion on fuel delivery & intake/exhaust tech & mods.
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kevink
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Re: 2.5 vs 2.25 diameter exhaust

Post by kevink »

s/c'd cav wrote: Thu Aug 27, 2020 10:05 am
Willigaf wrote: Wed Aug 26, 2020 7:49 am I was skeptical after reading this thread and my friend reminded me about a vid I'd seen on youtube. I was ready to leave the exhaust alone. Engine masters on the motor trend channel had done this a while ago and no, their 514 making like 650+ on the engine dyno doesn't really compare...

But all other things the same, they dynoed with 2.5 inch exhaust and then gained like 15 crank with 3 inch.

I AM trying to make about 615-620 at the crank, so if I can find a 3 inch cat back for a friendly price I'll probably grab it.
that 15hp at the crank , is with in the error factor at the wheels

but as i said before , a track only car will benefit from it , more than a street car will
But 15 crank is 15 crank. If the 15hp is at the crank, then you have 12hp at the wheels assuming 20% loss no matter what the roller says. People get way too hung up on dyno numbers. It doesn't matter what a roller says.

15 crank/12wheel is a huge amount of power when you're NA and have everything else basically maxed out which is exactly what a 615-620fwhp 364ci engine is. Yes, you can build a 9000 rpm engine and make way more than 620crank, but that is a totally different world. Cost per HP when you are already maxed out becomes extremely expensive, and the cost difference between 2.5" exhaust and 3" exhaust is minimal and very well worth it when you're already at 1.7hp/ci.
2011 9C3: 11.48 @118.
s/c'd cav
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Re: 2.5 vs 2.25 diameter exhaust

Post by s/c'd cav »

kevink wrote: Thu Aug 27, 2020 11:13 am
s/c'd cav wrote: Thu Aug 27, 2020 10:05 am
Willigaf wrote: Wed Aug 26, 2020 7:49 am I was skeptical after reading this thread and my friend reminded me about a vid I'd seen on youtube. I was ready to leave the exhaust alone. Engine masters on the motor trend channel had done this a while ago and no, their 514 making like 650+ on the engine dyno doesn't really compare...

But all other things the same, they dynoed with 2.5 inch exhaust and then gained like 15 crank with 3 inch.

I AM trying to make about 615-620 at the crank, so if I can find a 3 inch cat back for a friendly price I'll probably grab it.
that 15hp at the crank , is with in the error factor at the wheels

but as i said before , a track only car will benefit from it , more than a street car will
But 15 crank is 15 crank. If the 15hp is at the crank, then you have 12hp at the wheels assuming 20% loss no matter what the roller says. People get way too hung up on dyno numbers. It doesn't matter what a roller says.

15 crank/12wheel is a huge amount of power when you're NA and have everything else basically maxed out which is exactly what a 615-620fwhp 364ci engine is. Yes, you can build a 9000 rpm engine and make way more than 620crank, but that is a totally different world. Cost per HP when you are already maxed out becomes extremely expensive, and the cost difference between 2.5" exhaust and 3" exhaust is minimal and very well worth it when you're already at 1.7hp/ci.
youll never feel it or see it at the track , unless you are able to knock off pass after pass exactly the same

only place youll feel it is your pocket
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kevink
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Re: 2.5 vs 2.25 diameter exhaust

Post by kevink »

Of course you would. The difference from 600-615hp at about 4000 pounds is around a tenth of a second. That's huge!

I agree that you won't feel it on the street, though. You can't put that kind of power down on the street, even with a 275/60/15 tire on these cars. It just spins. But it's power none the less, and for those who are trying to maximize their combo, it's very cheap power.
2011 9C3: 11.48 @118.
s/c'd cav
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Re: 2.5 vs 2.25 diameter exhaust

Post by s/c'd cav »

kevink wrote: Thu Aug 27, 2020 2:19 pm Of course you would. The difference from 600-615hp at about 4000 pounds is around a tenth of a second. That's huge!

I agree that you won't feel it on the street, though. You can't put that kind of power down on the street, even with a 275/60/15 tire on these cars. It just spins. But it's power none the less, and for those who are trying to maximize their combo, it's very cheap power.
and that 1/10th youll never feel , and like i said unless you are dead nuts constant , you can be off a couple tenths from run to run

there are cars out there on 275/60 aka 28x10.5 putting down 2-3 times more power and hooking

the average person will only ever see a difference on the dyno and outta their pocket
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kevink
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Re: 2.5 vs 2.25 diameter exhaust

Post by kevink »

Just for the sake of argument...

You run your 600hp car with a 2.5" exhaust system and run an 11.00. What would it have run with a 3" system making 615? About 10.90. That is a result whether you felt it or not. Drag racing is not about feeling, but time slips.

A car putting down 1200-1800hp with a 275/60/15 is not dead hooking on the street, which is what I was talking about. The street. I think you misunderstood what I had said because nobody could possibly think that! That much power is not even dead hooking at the track on a 275, especially with this crappy IRS rear. Thh power needs to come on progressively, which is not what I would consider dead hooking with 1800hp.

Willigaf, definitely do 3" instead of 2.5" exhaust if your plans are really for600hp. At that point, the minimal cost of upgrading to 3" is well worth it, even if it's only worth 10hp. Where else are you going to get 10 or 15hp that cheap?
2011 9C3: 11.48 @118.
Numbah1
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Re: 2.5 vs 2.25 diameter exhaust

Post by Numbah1 »

CapriceX2 wrote: Wed Aug 12, 2020 2:40 pm I’ve read a lot of Vizard’s articles and he indicates that 2.25” pipes are good for up to about 415 HP without being a restriction. 2.5” should be good for up to 514 HP. I’d guess that 2.25” pipes are probably going to be a little small for you, but no idea if going bigger will get you 5+ HP.
Wtf article says "its better to be on the smaller side [of diameters]" and "to achieve zero loss you minimize back pressure" i literally got catted con pipes b.c a couple guys said that the stock cam likes back pressure lol

My cars cutting 9.0 in 3k DA to 8.6s at 0 DA leaving from idle without a tune. Thats stupid fast compared to others
Numbah1
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Re: 2.5 vs 2.25 diameter exhaust

Post by Numbah1 »

Numbah1 wrote: Sun Sep 06, 2020 5:43 am
CapriceX2 wrote: Wed Aug 12, 2020 2:40 pm I’ve read a lot of Vizard’s articles and he indicates that 2.25” pipes are good for up to about 415 HP without being a restriction. 2.5” should be good for up to 514 HP. I’d guess that 2.25” pipes are probably going to be a little small for you, but no idea if going bigger will get you 5+ HP.
Wtf article says "its better to be on the smaller side [of diameters]" and "to achieve zero loss you minimize back pressure" i literally got catted con pipes b.c a couple guys said that the stock cam likes back pressure lol

My cars cutting 9.0 in 3k DA to 8.6s at 0 DA leaving from idle without a tune. Thats stupid fast compared to others. I think 2.25 is acceptable for now
Numbah1
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Re: 2.5 vs 2.25 diameter exhaust

Post by Numbah1 »

Numbah1 wrote: Sun Sep 06, 2020 5:44 am
Numbah1 wrote: Sun Sep 06, 2020 5:43 am
CapriceX2 wrote: Wed Aug 12, 2020 2:40 pm I’ve read a lot of Vizard’s articles and he indicates that 2.25” pipes are good for up to about 415 HP without being a restriction. 2.5” should be good for up to 514 HP. I’d guess that 2.25” pipes are probably going to be a little small for you, but no idea if going bigger will get you 5+ HP.
Wtf article says "its better to be on the smaller side [of diameters]" and "to achieve zero loss you minimize back pressure" i literally got catted con pipes b.c a couple guys said that the stock cam likes back pressure lol

My cars cutting 9.0 in 3k DA to 8.6s at 0 DA leaving from idle without a tune. Thats stupid fast compared to others. I think 2.25 is acceptable for now
Numbah1
Posts: 75
Joined: Sun Jan 27, 2019 9:45 pm

Re: 2.5 vs 2.25 diameter exhaust

Post by Numbah1 »

So i ran 13.57 thru the mufflers and a 13.45 thru the cutouts. I thought the difference would be bigger. Maybe the exhaust is to small b4 the mufflers
s/c'd cav
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Re: 2.5 vs 2.25 diameter exhaust

Post by s/c'd cav »

cut outs or open exhaust isnt a high hp mod , its a sound mod
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