when is 3" exhaust not enough?

[92tsiawdguy]

Im at a cross road, im currently finishing my build and im stuck on the exhaust. Im looking to put down 600hp and im not sure if a 3" turbo back will be enough. I dont want to do a 4" turbo back so im thinking 3" to 4" adapter then 4" straight out of the front bumper. Im not too worried about noise. I just like the way my apexi n1 looks. So will a 3" turbo back support 600hp or am i better off just building a 4" bumper through exhaust will an inline muffler?

 

[VETTE_50_TH]

3 in def supports 600. Ive seen plenty of people do it. But i always had a thing for side exit mufflers.

 

[92tsiawdguy]

Ive seen people do 600hp on 3" but i was wondering if it will be choking more hp then it should.

 

[VETTE_50_TH]

If it aint broke, dont fix it you know? Plus for the, lets say, minimal gains, how much would it cost to actually get 4 inch aluminized steel for a decent price. It cant be cheap right now. Esp when you need 12 feet of it.

 

[92tsiawdguy]

id need 3ft to get it out of the front bumper. Or i will need to make a 3" turbo to catback downpipe. pipe would be about the same plus i can sell my apexi for extra money since its only got 300 miles on it.

 

[pboglio]

Here's a link that might provide some insight:

APS DR Series 3.5" Turbo to Tip Race Exhaust

Down at the bottom there is backpressure data. Most of the systems are 3" with and without cats, the last system in the chart is the 3.5". Looking at that, I'd say 600 h.p. could benefit from the bigger exhaust.

 

[1gDSM4g63]

I'd say the cost of a 4" side exhaust would be pretty much even if you went with a 3" fabricated v-band o2 housing plus regular 3" Mitsubishi downpipe. I mean it cost me $525 to have someone fabricated my side exhaust.

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However if you went with a downpipe you could have an option of leaving it open.

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[92tsiawdguy]

ill be building it myself so it will be cheap.

 

[habitatguy187]

Not sure how accurate it is, but I found this to be interesting.

no i believe your info is incorrect andy

okay, I found the article by David Vizard, and it was actually in Super Chevy magazine. It's a long article, so I'll supply you with his exhaust math below:

according to Mr. Vizard (who's theories I happen to value) you need to flow 2.2 CFM (cubic feet per minute) of exhaust per 1 HP. Therefore you first need to know what your flywheel HP is, and multiply it by 2.2

So for an example if your engine produces 500 HP at the crankshaft, then that's 500x2.2=1,100CFM. Now remember that because you're using dual exhaust and therefore will have two exhaust pipes (left and right) then you need to divide this total CFM figure by2. So that's 1,100 CFM cut in half.... or 1,100 divided by 2=550 CFM. So you'll need an exhaust pipe diameter that will flow 550 CFM. with that in mind here are the pipe diameters and their flow rates (according to Mr. Vizard)...

2.5" diameter=560CFM

3" diameter=672CFM

3.5" diameter=784CFM

4" diameter=896CFM

so just do the math above using your engine's HP and you'll be able to determine how big of an exhaust pipe diameter you'll need. I hope this helps you.

or

In general 1 inch Hg backpressure = 1 HP lost

For reference, we have the following conversions factors:

1 ATM = 14.7 PSI = 76 cm of Hg = 29.921 inches of Hg = 1.013 bar


So do a little more math and and it wouldn't be too far off to say that a 500 hp engine could see as much as 20% power loss from a single 3" exhaust.

As found in this thread.

 

[DSMDriver69]

Go for a 4 inch side exit. Also i see you live in KC, i wanna see this beast when you finish it .

 

[92tsiawdguy]

I actually work in lenexa at the wonder bread bakery so im not far from you.

 

[Gamble97]

There was some dynoing done on this recently and I don't remember what forum. But it showed hp loss and tq gained with 4" exhaust compared to the 3"

 

[92tsiawdguy]

depending on how much hp you are pushing that will change, say im pushing 700hp on a 3" exhaust. Im going to gain more hp and tq switching to a 4" but at 300 hp going from 3" to 4" would kill the hp. Thats why im asking it 600 hp enough to justify a 4" exhaust.

 

[habitatguy187]

There was some dynoing done on this recently and I don't remember what forum. But it showed hp loss and tq gained with 4" exhaust compared to the 3"

That seems strange to me. If anything I would think that torque would be lost and hp gained, that or no change at all on a "lower" hp car.

 

[99gst_racer]

I'd say the cost of a 4" side exhaust would be pretty much even if you went with a 3" fabricated v-band o2 housing plus regular 3" Mitsubishi downpipe. I mean it cost me $525 to have someone fabricated my side exhaust.

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^^^ That right there costed you $525???


I wouldn't be able to sit down for a week....
Looks really nice though.

 

[e85_4g63]

wow! I'm firing up the tig, who wants a 4" side exit.. on sale only $500, and I'll even pay the shipping for that price!

 

[jking29]

^^^ That right there costed you $525???


I wouldn't be able to sit down for a week....
Looks really nice though.

If that cost $525, you have about $4000 worth of work under your hood don't you Paul?

 

[99gst_racer]

^^^ More.


My SS side exit exhaust was around $65. That included the header wrap and the 4 PBR's that I drank while making it.

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[dsm-onster]

Electronic cutout ! Have both.

 

[92tsiawdguy]

I'm going with a 3.5" side exit exhaust with a 12" round muffler. Total cost is around 200 for more then enough parts. I'll tig it up and get some pics.

 

[1gDSM4g63]

^^^ That right there costed you $525???


I wouldn't be able to sit down for a week....
Looks really nice though.

Well it took 5 hrs of labor x $105 per/hr and I didn't stand there watching them but I won't question them as the bends are well done and it's not like your setup where it's just a straight pipe coming from after the downpipe. Plus $525 it worth it to me. An o2 housing, downpipe and exhaust would add up to more than that.

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[habitatguy187]

^^^^ You should cut your motor mount bracket.

 

[pj91gsx]

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wow! that looks awesome!!

 

[99gst_racer]

Well if took 5 hrs of labor x $105 per/hr and I didn't stand there to watch them but I won't question them as the bends are well done and it's not like your setup where it's just a straight pipe coming from after the downpipe. Plus $525 it worth it to me. An o2 housing, downpipe and exhaust would add up to more than that.

Well, that was my point. Most DSMers wouldn't be willing to spend over $100 per hour for someone else to cut and weld on 2 feet of pipe. Most (myself included) would consider that to be an overpriced labor rate. But like I said, it's a nice piece and I'm glad you're happy with it.

 

[dsm-onster]

AMEN! being a dsmer means learning how to use an arc welder