Cut-out size-does it matter?

[turbovanman²]

I am going to run a cut-out this year, I run a full 3 inch system so would running a 3.5" cut-out make any difference or just stick to a 3 inch cut-out, they are both the same price?

[RoadWarrior222]

Use the 3.5" then you have something to blame when it assplodes.

[OmniLuvr]

i believe shadow is running a 4" dump... but if it is a choice between 3 or 3.5, id go 3.5, but i would also run a 3.5 dp to the dump.

[puppet]

Sure it matters ... bigger is better.

[shadow88]

I don't see how there would be any more power from a flare up to a 3.5" cut out from a 3"

Here's the kicker. Some of the electric cut outs are measured on the I.D. so you may need a spacer so the blade doesn't hit the flange.

[RoadWarrior222]

Put it this way, if the exhaust outlet of your turbo is 3" or has the same area, and a 3.5" cutout gets more power, then the gas is still expanding and your turbo ain't doing such a good job.

[22shelby]

Put it this way, if the exhaust outlet of your turbo is 3" or has the same area, and a 3.5" cutout gets more power, then the gas is still expanding and your turbo ain't doing such a good job.

wow... wait ...what????

esplain please..

[roachjuice]

you can only flow as much as your smallest restriction. i dont think it will make a difference.

[turbovanman²]

My dp is like 3.25", so I'll just go with the 3.5" unit.

[Rattlesnake]

I'd say go with the 3.5 and this is the reason: The exhaust closest to the walls will flow slower because of friction and that will prevent your turbo from spooling faster and you don't want that if you have a big turbo like the GT35R. If you widen the exhaust pipe you are spreading the friction point further apart causing a greater amount of volume of exhaust to exit through a wider passage with minimal frictional loss. Now remember that the wider you make the pipe the slower the exhaust gas is going to flow and due to that loss of speed it will cool down and that is also bad. Make sure that you adjust you AFR to maintain the EGT you motor is used to. When I installed the boom pipe in my car I had to lean it down to bring my EGT up. Or do what I did, make an afterburner and see that GT spool a lot sooner.

Good luck Simon!

Reinaldo Moloon

[turbovanman²]

Thanks man, I'll update when she gets all done.

[Ondonti]

You will still have the 3" on there so 3.5" will be completely worthless

3.25" into dual 3" is not going to have a restriction even if you have 18 mufflers on one of the 3" systems.
Now, if you do what I am going to do, which is put a 2" full exhaust on the car with a 3.5" or bigger downpipe, then a 3.5"/4" cutout might be a good idea. 2" pipe is enough to make good power below 3000 rpms, which means I can pass on the freeway without being loud.

Rattlesnake, maybe you have some typos in your post because it does not make sense.

[puppet]

I don't see the mismatch as relevant in this application. The idea of a cutout is to evacuate exhaust backpressure as quickly as possible ... not important to keep diameters matched if fitment isn't an issue. The larger exit diameter will also propotionally reduce the effects of the rest of the exhaust systems piping .. ie. pulse interference by existing elbows, CATs, mufflers .. etc.

The exiting decible level may also be effected in a positive way by using a larger exit diameter. An ovaled slice into his 3" DP as a transition to the larger diameter cutout would be the right thing to do IMO.

[Ondonti]

I don't see the mismatch as relevant in this application. The idea of a cutout is to evacuate exhaust backpressure as quickly as possible ... not important to keep diameters matched if fitment isn't an issue. The larger exit diameter will also propotionally reduce the effects of the rest of the exhaust systems piping .. ie. pulse interference by existing elbows, CATs, mufflers .. etc.

The exiting decible level may also be effected in a positive way by using a larger exit diameter. An ovaled slice into his 3" DP as a transition to the larger diameter cutout would be the right thing to do IMO.

I don't see anything about matching on here. The fact is that exhaust can decrease in size slowly through out your exhaust system because when the exhaust cools down, it loses volume.

3.5" cutout with a 3.0" exhaust is like having a 4.5" exhaust on your car, something you can do 1250hp and more. No, it can't be argue'd as being superior in this situation. If cost is a factor, there is a great reason to not do it.

[puppet]

The fact is that exhaust can decrease in size slowly through out your exhaust system because when the exhaust cools down, it loses volume.

Used to think this way too. On a stock app I'd be with you 100% but on my car, I've blown 3" elbows off from internal pressure @WOT. Right in front of the fuel tank which is 5-6' back I'd say. Joint was clamped with one of those SS band type clamps. Pretty tight fit so it took a lot of internal pressure to push off. When it let go, the car pretty much took off for that instant before I got out of it. The power difference was very noticeable. Just my take on it.

[turbovanman²]

Used to think this way too. On a stock app I'd be with you 100% but on my car, I've blown 3" elbows off from internal pressure @WOT. Right in front of the fuel tank which is 5-6' back I'd say. Joint was clamped with one of those SS band type clamps. Pretty tight fit so it took a lot of internal pressure to push off. When it let go, the car pretty much took off for that instant before I got out of it. The power difference was very noticeable. Just my take on it.

Removing my cat and Ultra Flo muffler and simply running a Superturbo muffler made a very noticeable difference in power and less lag.

[RoadWarrior222]

Joint was clamped with one of those SS band type clamps. Pretty tight fit so it took a lot of internal pressure to push off.

Eh? I'd expect that to fall off an N/A car. Band clamps are for flexible pipe/hose to rigid pipe only. Rigid pipe joints need a U clamp capable of crushing/crimping the pipe.