3" Exhaust Question

[TURBOVAN]

i know if you have a fire hose and choke it down to a garden hose it can only flow as good as a garden hose. it can only flow as good as its smallest part. i'm confused about the exhaust systems, with a 3" down pipe and mandrel bent 3" system without a cat and with a high flow muffler would be as good as it gets ( with a muffler) but then i look at the output from the turbo itself, reguardless of the swingvalve size, i think its well under 3" so what am i missing? same as the exhaust manifold side i understand longer tubes is a good thing. but beyond that if you add the size of the ports on the head, and compare it to the size of the turbo inlet it don't seem that much improvement can be made other than longer tubes, am i right? i'm guessing i'm not but i don't understand why.

[Marcus86GLHS]

there's a lot of thermodynamic and fluid dynamics at play but let's bottom line it for you: dyno testing of replacing a stock 2.25" exhaust system w/ a quality 3" exhaust system show substantial gains in HP and torque at even at low boost levels.

[168glhs1986]

Quote:

Originally Posted by Marcus86GLHS there's a lot of thermodynamic and fluid dynamics at play but let's bottom line it for you: dyno testing of replacing a stock 2.25" exhaust system w/ a quality 3" exhaust system show substantial gains in HP and torque at even at low boost levels.

+1

[scott_s]

Part of the issue is pressure. The bigger exhaust helps create less pressure, there by helping spool the turbo, scavenge the cylinders. If you were to spray water or alky into your down pipe, it would help even more, as the hot gases would reduce in volume reducing pressure even more.

[2TL4TT]

I have a Lancer and I put a 3" swing valve and 3" exhaust on from Turbos Unleashed and it made a big defiance in HP and gas milage. if I keep my foot out of it I can get 34mpg, I was getting around 29mpg before. I had a turbo van with 3" and a stock swing valve and I only got about 22mpg. I would definitely go with 3" over 2.25 the HP difference is enough.

[Austrian Dodge]

I've read the most critical part of the exhaust system is right after it leaves the turbo. This is where the gases are hottest and they take up the most volume from heat expansion. Bigger is better and swingvalve size is critical for not only performance but for fuel mileage gains as well. Someone once posted on this forum that there is no benefit to a 3" swingvalve with stock turbos but 2TL4TT's results just disproved that theory. I need to pick up one of those TU 3" swingvalves before they run out again.

Scott, didn't you also see an increase in fuel mileage when you installed your 3" SV?

Andy

[impuresoul2k3]

It also depends on how long that restriction is, so even if the exhaust outflows the turbo, its better than matching the turbo and having a restriction all the way down

[Polygon]

Alright, to keep a long story short, once the exhaust leaves the manifold it should have all the velocity it needs. It is now your job to give it the least amount of restriction and let inertia go to work. This is done be increasing flow by using larger pipe, a bigger SV, and as few direction changes as possible. Thermal coating the manifold, exhaust housing on the turbo, and the SV will also improve scavenging and help speed up the flow.

Just remember that your turbo is a big restriction on the exhaust. Getting a bigger turbo will also help a lot if you're pushing a lot of air. At one point of modding the stock turbo will be too much of a restriction.

[ZachT]

all i can say, i got one of those 3in SV's from TU today, man, those things put a 2.5 to shame... in size. cant wait to see this thing move.

[Polygon]

You'll notice quite a difference. Here's a dyno run that TU did to compare the two.

[ZachT]

ok, i got a question.

i have a TU S70 turbo (.63 ehaust, quick spool) with a 3in SV, hell of an improvement over a stock T2 with a 2.25SV (.48 exh). at the moment i dont have money to run a full 3in ehaust to the bumper, but i have a 2.5 inch on it now with no cat and a muffler. it sounds pretty good. is it worth 25 bucks for that adapter? or should i wait 2-3 weeks and just get the damn exhaust?

also- what all is needed with the L body 3in (TU, $250). is that thing complete from the turbo to the bumper? i know i will need exhaust clamps. ill probably grab a 3in muffler too. but i will use my hangers. do i need a test pipe?