Full exhaust on a 800hp street car

[338Raptor]

Is anyone running a full exhaust system on a street car with more than 800 flywheel horsepower?

I’ve used a couple online exhaust size calculators. They say I need 3.25” dual exhaust to support 800 horsepower. Since exhaust pipe doesn’t come in 3.25” diameter I’ll need to step up to 3.5” or settle for 3” and lose some power. Routing dual 3.5” to the back of the car is going to be a challenge. Routing 3” will be a little less of a challenge. But not restricting power is my main objective.

Does anyone have direct experience with this?  Do I really need 3.5”?

[mike7570]

Electronic cut outs.

[Heo]

Use four pipes that give you the same area as two 3,25" pipes
it is easier to route them and they give you more ground  clearance

[Barry_R]

I have 3.5" from the collectors to the back bumper.  It's not particularly easy but it can be done.  This is with ladder bars and coil overs, stock gas tank.

[wowens]

I used 3.5" reducer at header to oval tubing with a X pipe fabricated from two 90*  oval tubing bends. Spin tech mufflers and oval tubing out the back. Sounded like a high compression small block @ 9k rpm.
385 engine, 565ci, 818 @ flywheel. No data to confirm any HP loss, but ran well.

[shady]

For what it's worth, Barry's car sounds like no other and I like it. A lot.

[My427stang]

I'd go 3.5 oval, with X pipe, all cruves mandrel bent and fit to minimuze flow disruption and use an absorption (not Flowmaster style) mufflers as far back as you can.

Be very careful on muffler choice, some cores are pretty small from Borla, although in general I love their mufflers

[338Raptor]

I like the suggestion of 3.5” oval with mandrel bends.
Which 3.5” in/out mufflers flow well and are relatively quiet?

[My427stang]

I run Jones Full-Boar perforated tube stainless on my truck and it's pretty quiet, although even with a 3 inch mandrel bent it barks with your foot in it.  That's a real good option and the price is better than others for a stainless body

Magnaflow and Dynomax Ultraflo both should be OK when your foot is out of it too.  Perforated tube with packing is pretty gentle until you get in it.  The X or H will calm it down when you want it to as well.

[cjshaker]

Where can you get 3.5" oval tubing with mandrel bends? I didn't even know it was possible to mandrel bend oval tubing,

[338Raptor]

I found these sources online.

http://mandrelbendingsolutions.com/oval-tubing/

https://www.racemufflers.com/Oval-Exhaust-Tubing-s/1832.htm

[plovett]

I run 2x3.5" pipes on a 550 hp street car.  Could I get by with 2x3"? Yeah, I suppose so.  I have run 2x3" over the axle and out the back.  I now use 3.5" pipes because my collectors are 3.5" and I don't like to neck down the exhaust right after the collector. At least not until after my crossover pipe.   And since I am dumping the exhaust in front of the rear axle, it is only another couple of feet.  So 3.5" all the way for me. 

But 800hp needs some serious exhaust, in my opinion.   I say do what you have to do.  Dump it before the axle or out the side or use 4 pipes, but don't choke an 800 hp engine.   

I think you need at least 3.5".  More is better, until you are just adding weight with pipes that are bigger than you need them to be.

JMO,

paulie

[bill_396]

I have a full length 3 1/2" with X-pipe system on my 68' Mustang fb. I used all stainless mandrel bends except the turn-ups after the mufflers, could only find inconel mandrel bends with a tight enough bend radius. My pipes are hooked to REF header with merge collectors.

[mbrunson427]

Here's a setup we built for the '65 Galaxie Tunnelport. 3" Piping, not 3-1/2". Figured that if we wanted all the power, it could be loud. For normal street driving, it'll only be kind of loud. The cut out pipes dump right after the mufflers (did this so it hopefully won't beat your ear drums inside the car), the muffler pipes will continue on to the back of the car. Once the rear axle goes back in the car the exhaust system can be finished, weld it all out, and send off to get coated.

I would think that a 3" system like this would suffice for 800hp? But maybe it won't.

[cjshaker]

I found these sources online.

http://mandrelbendingsolutions.com/oval-tubing/

https://www.racemufflers.com/Oval-Exhaust-Tubing-s/1832.htm

Interesting, thanks for the links.

But I'd have to say, I don't see any way to get curves while going over the rear axle, using those bends.  Not to mention the 'flat' part of the oval is on the 'side' of the tubing (as it would be used to go over an axle), which means it's taking up valuable space. Space that just isn't there on many cars. I just don't see how oval tubing could be used in a full system, unless it was dumped out the side, and I'm really not a fan of that. One problem going down a track, or even a highway, and you'll be spraying your tires with oil. My instinct tells me that that would not be a good thing.