What size exhaust to run?

[CLASSIC87']

Im looking to take the truck in this week to get exhaust installed. The Y-Pipe is getting cut out & just going to run straight exhaust off of the stock manifolds. How big of pipe should I be asking for? I have 3'' on there now...which appears to be stock. The motor is a crate 350TPI- also stock.
Thanks!
Anthony

[grinch4om]

Run As Big As Possible. It Wont Hurt And If You Ever Do Anything Else To The Moter, System Is Ready

[ocbaud]

Originally Posted by grinch4om

Run As Big As Possible. It Wont Hurt And If You Ever Do Anything Else To The Moter, System Is Ready

um..... no


i'm making around 400hp and you dont see me running 3" dual exhaust, reason being is that i dont need it.

if you go to big you loose back pressure, you loose back pressure you loose a lot of low end power, something these trucks need being so heavy. the best for a stock 350 is 2.25" dual exhaust IMO. 2.5" would be good if he plans on adding more power down the road. i myself run 2.5" duals with an H-pipe.

[piecesparts]

Originally Posted by grinch4om

Run As Big As Possible. It Wont Hurt And If You Ever Do Anything Else To The Moter, System Is Ready

Actuallly the "Run as Big as possible" is a thought that is not absolutely true. There are studies that outfits like Flowmaster and Gibson have done and the size of the exhaust depends on what you are running as a motor and what speeds you drive. A big block motor that is worked over really will stand up to a 3" exhaust system, but a small block that is pushing a happy 450 Hp or less will need smaller piping to be efficient. The theory on exhaust pipes works in a situation that the cooling gases are collapsing as they go towards the rear of the exhaust. This will assist in removing the hotter exhaust gases from the headers or manifold if they work on the principal of a vortex eductor. If you run to big of exhaust pipes the gases will become "Lazy" and cause a reversionary effect and actually keep the exhaust gases from exiting properly. Thus Bigger is not always better.

I run a 383 stroker motor with full length exhaust. I have dual pipes crossed over at the tranny's rear end and the mufflers and piping are 2 1/2" inlet and outlet. I contacted Flowmaster and they ran a program that puts the 3" piping breakover just above my HP rating and I am real happy with the sound (loud) and the performance and gas mileage (15 MPG). I would consider the 2 1/2" before the full length 3".

[Jim85IROC]

Originally Posted by piecesparts

Actuallly the "Run as Big as possible" is a thought that is not absolutely true. There are studies that outfits like Flowmaster and Gibson have done and the size of the exhaust depends on what you are running as a motor and what speeds you drive. A big block motor that is worked over really will stand up to a 3" exhaust system, but a small block that is pushing a happy 450 Hp or less will need smaller piping to be efficient. The theory on exhaust pipes works in a situation that the cooling gases are collapsing as they go towards the rear of the exhaust. This will assist in removing the hotter exhaust gases from the headers or manifold if they work on the principal of a vortex eductor. If you run to big of exhaust pipes the gases will become "Lazy" and cause a reversionary effect and actually keep the exhaust gases from exiting properly. Thus Bigger is not always better.

I run a 383 stroker motor with full length exhaust. I have dual pipes crossed over at the tranny's rear end and the mufflers and piping are 2 1/2" inlet and outlet. I contacted Flowmaster and they ran a program that puts the 3" piping breakover just above my HP rating and I am real happy with the sound (loud) and the performance and gas mileage (15 MPG). I would consider the 2 1/2" before the full length 3".

I'm not agreeing or disagreeing with the backpressure arguement, but I found it funny that the two exhaust companies that you mentioned who say backpressure is good are the two exhaust companies who are known to have the most restrictive mufflers.

[Srubydo1986]

im running a 2 1/2 with at frist stock 350 now mild set up and it does just fine.


Engine is a 1989 gm engine with an eldelbrock intake (carberated made it that way was trottle body) then platium acdelco plug 8 mm sparkplug wires and an accel high temp coil. Also has an edlebrock carbrator, other then that shes all stock.

[Ivan D.]

On a 350 don't go bigger than 2.5" if running duals, if running single 3" is what you want. Dual 3" is what 500ci and up big-block engines need, small blocks just ain't got enough flow to utilize the huge pipes - what will happen however is that exhaust gases cool down faster and slow down, thus losing scavenging effect. Also someone brought up the loss of backpressure, which may be good for high-revv engines but in a street-driven truck no backpressure ain't all that great.

Really if you want a sweet flowing exhaust you should start with 2.5" piping and after the mufflers downsize to 2.25", that keeps escape velocity high as gases cool down. If you are building a torque monster start with dual 2.5" and merge them to 3" single, after the muffler you may downsize to 2.5" or keep it at 3". If I had different headers my personal choice for my 350 would be exactly the single, only without a muffler and running up behind the cab with a flapper valve like a tractor

[72short]

i have full 2.5" flowmaster super 40's with hedmans and everyone in town loves the way it sounds. I cut the pipes shortly after the cab with a small turnout loud, but it sounds so good

[Ivan D.]

Originally Posted by 72short

i have full 2.5" flowmaster super 40's with hedmans and everyone in town loves the way it sounds. I cut the pipes shortly after the cab with a small turnout loud, but it sounds so good

My exhaust ends about a foot behind the end of the cab, I have two Super Turbo mufflers on it and instead of turndowns I did two straight pipes with a 45* slant cut, sounds real nice and oddly it ain't too quiet either.

[MylilBowTie]

I have hooker headers with 2.5 collectors, 2.5 in pipe, 2.5 muffler, 3.0 tail pipes from the mufflers exit to the sides behind the tires.

Sounds pretty good to me but its a little on the quite side. I believe its the catalytic converters that are stealing some of the sound. I've not noticed any difference in the low end that I can tell. I have a 355, th400, 3.08 gear ratio, 31x10.50 tires.

[Ivan D.]

Originally Posted by MylilBowTie

Sounds pretty good to me but its a little on the quite side. I believe its the catalytic converters that are stealing some of the sound.

Yep, cats are the evil when it comes to exhaust sound, I drove my Lincoln with just the downpipes for quite a while (so manifolds, 2 cats per pipe, and turndowns under the front seats) and it didn't make it too loud at all. Lost the cats and it woke it up to the point at lights people ask me if I have a 460 in it, wish I had, lol

[EAST SIDE LOW LIFE]

I'm running dual 2.5' pipes with (Flowmaster mufflers) from the headers back. To give it that "Hot Rod" look I finished off the exhaust with 4' s/s tips. Sounds good seems to work well. I've always ran 2.5' pipes with a small block but then again both of my trucks are not stock. I agree with the others that 2.25' to 2.5' is the right size pipe to go with nothing larger.

esll.

[CLASSIC87']

Thanks for all the input guys...
I'm looking at doing the 2.5" pipe... regular 40 series Flowmasters mufflers with turndowns on the backside. I'm not looking for anything excessively loud... just some rumble. Good/Bad?

Anthony

[MylilBowTie]

Its all personal choice but If I were to get new mufflers. I would say I would be looking at some dynomax ultraflo mufflers, hooker aero chamber mufflers, pypes street pro mufflers.

Aside from the mufflers and the configuration of the exhaust. Engine size, compression ratio and cam will make the exhaust sound different.

[grinch4om]

my experience has been biggest that will fit from 5.0's to fe fairlanes to 440 mopars. low end loss has never been an issue and time slips to prove it. when I worked at a shop that made exhaust for show and drag cars ,I was able to try different sizes for the cost of pipe. these real world test I did is where these statements come from. I don't drive a dyno. Dynos information is good but there are morre things to consider than those numbers.