exhaust with forced induction

[Chevy1500z71]

is there any information out there on what an ideal exhaust setup would be with forced induction. from what i understand, generally you want your exhaust tubing to be 1.75 times your primary size, so around 2.75, id go 2.5 for more torque. but does all this hold true with forced induction? i mean, im putting alot of air and fuel through my motor, meaning alot more exhaust is being pushed out, wouldn't a 3" exhaust seem more appropriate? im just afraid of loosing all my torque. a smaller tube will pull more velocity, giving more torque, but what if it becomes a restriction at higher rpms and higher boost levels? i also read that you need about 2.2 cfm per hp, a 2.5" strait pipe only flows around 450cfm i would need about 600cfm per side to be safe. i dont know what to think about this whole deal, what your guys thoughts on this?

right now, if i run with my cutouts open, i loose alot of torque vs themk being closed, and they are set about 30" behind the collector on 2.25" pipe.


i have to redo the exhaust either way. heres my current plans 2.5-3" pipe strait back form the collectors even on both sides, not a single bend in the entire exhaust, have the h pipe by about past the driver seat, cutout, and then reducer cone directly to a 5" inlet flowmaster 40 race muffler (the smaller flowmasters dont flow enough cfm and i dont like the glasspack sound) and then directly to a big turn down tip. it would all be said and done before the gas tank, this way there are no bends in the system, very simple. the tips will be as far back as they can go without the driver side getting into the gas tan, so theyd be dumped just infront of the bed. i dont think it will be too load with such a huge 2 chamber muffler, and resonance wont kill me.

[darren250r]

Having it dump under the cab like that will likely make your interior noise pretty extreme. I don't think having a couple bends is going to make enough difference to make it worth hearing all that cab noise. Good luck.

[Chevy1500z71]

Having it dump under the cab like that will likely make your interior noise pretty extreme. I don't think having a couple bends is going to make enough difference to make it worth hearing all that cab noise. Good luck.

i can bend it up later if it bothers me. the idea is to get the cutouts as far back as possible. i need to get the wideband sensor far back, and i cant put the sensor after the cutouts(cutouts need to be but strait behind the collectors, not after the exhaust has bends), so i need to get the cutouts and mufflers far back, if its noisy, i can add a bend after the driver side muffler and route the pipes down the passenger side some. i dont know if i explained that well but it makes perfect sense to me lol. my driver side currently bends at about the front of the driveshaft, thats no good, the driver side needs to go all the way back to the gas tank to alow the cutouts to be as far back as possible.

some 45* turn downs angled 45* out(not directly against the ground) should reduce resonance. never point em at the ground.

that all deosnt really matter anyway, this thread is about exhaust size, not how loud its going to be.

EDIT: im building this system myself(i can weld, im not building a clamped up autozone special), i want to keep it simple and free flowing.

[the_target]

Go with a set of good long tubes, 2.5 all the way out.. Stay away from Flowmaster.... go woth magna flow.... TRUST me.. I have already blown out a new set of Flowmaster 44's at the seems :)

[Chevy1500z71]

Go with a set of good long tubes, 2.5 all the way out.. Stay away from Flowmaster.... go woth magna flow.... TRUST me.. I have already blown out a new set of Flowmaster 44's at the seems :)

i highly doubt ill have problems with a set of 5" inlet/outlet 6" case delta 40 race mufflers lol. theres a set on ebay for 75 bucks, new. they retail for around 200 a peice. im going to get them, ill roll my own cones and make them work. if i didnt do that id run some cheap cherry bombs, but i really am a fan of the chambered mufflers sound over strait throughs.

so you think 2.5 would be good? thats what i had been thinking but as i read up on it a bit more i start to wonder why theres no information on what forced induction deas as far as your calculations for proper exhaust size. wouldnt you think that a blower motor kicks out alot more exhaust?

[Chevy1500z71]

do you think ill get any egt reduction from a beter exhaust, right now im running a 2.25" setup, and iv got miles of pipe, small mufflers, it was good for my stock motor, but not enough for this one. i cant keep the wideband from overheating, iv got it about 20" behind the collector and its still exceeding 1100* egts(what it takes to trash a sensor) back there. iv been through 3 sensors in about 6 months! i cant afford it anymore.

cant move it any further back till this whole exhaust gets redone.

iv already got long tubes... of course, come on now. like id be running manifolds or shorties!

[the_target]

The issue is with the design, Flowmasters have a chambered design and are not pass though, thus with boosted motors they tend to burst at the seems so do speak, you need a pass through design. I am right now cutting off the Flowmasters and going magnaflow..... As for your high EGT's and WB you got somthing else causing the issue. I am running the same WB and I have it in the collector and have been for awhile no issues........ Yes I think 2.5 will suit you just fine, I am running a bigger motor and WAY more boost and its not the exhaust that is limiting me right now :).

[Chevy1500z71]

The issue is with the design, Flowmasters have a chambered design and are not pass though, thus with boosted motors they tend to burst at the seems so do speak, you need a pass through design. I am right now cutting off the Flowmasters and going magnaflow..... As for your high EGT's and WB you got somthing else causing the issue. I am running the same WB and I have it in the collector and have been for awhile no issues........ Yes I think 2.5 will suit you just fine, I am running a bigger motor and WAY more boost and its not the exhaust that is limiting me right now :).

iv yet to see my little 2.25" delta 40s burst at the seams so i wont worry about it. not to mention, its a 6" case muffler, thats a big box, there not going to be alot of pressure in there like a smaller 40 serrier would have. i understand what your saying, and your right, but theres not going to be high pressure in a 6" case muffler, weather the design promotes pressure vs a flow through or not, it wont be enough to cause issues.

some people luck out with the lc-1s. i was lucky for a year or so untill i put the new motor in. they are extremely sensitive and not recommended to be run all the time like i choose to do, i have my lc-1 sending the simulated narrow band signal to my ecm, so its a big deal that it works well. they say the factory spend alot of time finding a sweet spot of 02 sensors. i used to think it was a bunch of bs because i, like you seem to be, was very lucky with mine working well. my luck ran out lol, i need to get the sensor in a good spot. im going to put it a couple inches down the h-pipe and then put a 1" extendo bung on top of that.

you should read through this exhaust article, very interesting. http://www.superchevy.com/technical/...xh/index1.html if you read through it you can see why i kind of just shop for cfm with mufflers, i know a 5" race muffler will flow at the very least 700cfm, more then enough. my 2.25" flowmasters probably flow in the high 200s, good for about 275hp lol.

at the very least, it was a very interesting article even if you dont care about having the perfect exhaust system.

[Chevy1500z71]

these are the mufflers ill be purchasing, they are overkill to say the least.
http://cgi.ebay.com/ebaymotors/ws/eB...K%3AMEWAX%3AIT

[Justin_Inc]

BIGGER IS BETTER when it comes to forced induction. On prettymuch any small block I build, the minimum exhaust size is dual 3" in a forced induction application. You are moving a substantially large amount of air you need to rid of it. Another thing that is a no-no are chambered mufflers like flowmaster.

BTW, those mufflers are pointless IMO, 5" honestly?

High EGT's could be caused by you're tune as well.

[Chevy1500z71]

BIGGER IS BETTER when it comes to forced induction. On prettymuch any small block I build, the minimum exhaust size is dual 3" in a forced induction application. You are moving a substantially large amount of air you need to rid of it. Another thing that is a no-no are chambered mufflers like flowmaster.

BTW, those mufflers are pointless IMO, 5" honestly?

High EGT's could be caused by you're tune as well.

iv got the thing running at 11:1 at wide open, i run it richer then id like (id prefer about 12:1) hoping it will run a little cooler. im spraying methanol, although that cools things down, after it has been burned, does it throw a hotter egt? iv been wondering about this.

mufflers are preference, lets not do the flowmaster/magniflow argument, i really would rather not make this thread an argument. we all know that those mufflers will flow and work fine.

as for the pipe size. this is the answer iv been looking for, someone who actually takes the forced induction in to acount when building the exhaust. ok, so 3" sound good, but am i going to loose my torque and throttle response at the sake of high rpm power?

[haulinit]

IDK about supercharged exhaust but if it were a turbo go as big as you want.

[Justin_Inc]

iv got the thing running at 11:1 at wide open, i run it richer then id like (id prefer about 12:1) hoping it will run a little cooler. im spraying methanol, although that cools things down, after it has been burned, does it throw a hotter egt? iv been wondering about this.

mufflers are preference, lets not do the flowmaster/magniflow argument, i really would rather not make this thread an argument. we all know that those mufflers will flow and work fine.

as for the pipe size. this is the answer iv been looking for, someone who actually takes the forced induction in to acount when building the exhaust. ok, so 3" sound good, but am i going to loose my torque and throttle response at the sake of high rpm power?

EGT's are based on air intake temp, air fuel ratio, and even engine timing.

I'm not going to get into a muffler argument, all of the proven data is out there for anyone that cares to look, i'm just going to say that the best muffler for a forced induction application is something that flows straight through.

As for exhaust size, you wont notice any loss in low end power, as a matter of fact, strap it to some rollers and I bet you'll pick up power over the peanut pipes you have now.

Supercharged exhaust goes on the same basic principle as a turbo, you are still moving a ton more air through the engine, however a turbochargers exhaust system is alittle more crucial for muffler selection and exhaust system design as the backpressure will hurt spool time.

[BaggedBurban305]

The smaller you make that exhaust the louder it will be.i run a 2.5" y pipe and 3" straight single exhaust to a single magnaflow muffler with 2 2.5" turndowns

[loafycleetus]

I have a Dual in/Dual out x-core magnaflow welded in to the stock pipes. My truck was very quiet with this setup until you really got into it which was nice. I had to chop the exit pipes off to fit a hitch. My "turndowns" are right in front of the rear axle and it is loud as crap in the cab now.