what is the biggest down pipe i can run on my 97 ext. cab? gonna be stackin it pretty quick so i wanna know if i can squeeze a 4" on it without a body lift

 

4 will fit fine 5 gets real tight with the auto trans

 

i have a 4inch down pipe on my truck and it fits just fine

 

will a 5 in. fit on a 5 speed and if so where could i get one??

 

there is a good amount of space around a 4" with a 5-speed but i think it might rub in some spots with a 5". i dont know where to find one you would probably have to have it made. i dont think it would be nesesary to have it that big unless you plan on building a monster sled puller and in that case just put a stack out the hood.

 

It is a waste of time and money to fool with the 5" downpipe. The turbo outlet is slightly smaller than 4", and is the choke point for outflow. Once you have the 4" downpipe you will be good for as much fuel and exhaust gas flow as you can generate up to around 1,100 horse power. Once you do the larger downpipe you really need to pay attention to the back pressure 18" after the turbo outlet, as that is where the exhaust harmonic that assists with gas evacuation begins to falter. So, do not install your splitter for the 4" or larger duals until after that 18" or you will create a pressure ridge that actually slows evacuation.

The 4" downpipe fits just great.

 

mine runs 4" to 5" flexpipe to the 6" stack. theres is enough room for the 5" just about up to the engine itself

 

dont forget to get rid of that stupid elbow attached to the back of the turbo if not ull end up with a 2-1/2 into 4inch downpipe

 

You might have to get a new turbine housing exhaust plate built. I think that the S300 is only 4in. Kinda a waste to back to 5in from 4in outlet, IMO. 5in down pipe would be tight. I have 5in off my BTH-3B and it rubs on the firewall and transmission support. Makes the truck shake like an old muscle car with a big cam.

 

if you want to monkey with a 5 inch exhaust

http://www.modsfortrucks.com/display...7&f=10&n=10&o=

 

thanks for all the help guys. gonna be stackin my truck here within a couple weeks and im tryin to save some money rather than just buying a complete 4" turbo back system. the stack kit hooks up to a 4" pipe into 5" into 6" chrome turnouts. thanks again

 

I agree 100% on pipe size. The factory exhaust with a high flow or deleted muffler will most likely do what you want. After that, the 4" will flow all you would need for a truck you could actually drive on the street.

 

A larger downpipe will increase the delta P across the turbine, which helps spoolup. It also helps to slow the flow and reduce the "swirl" turbulence out of the turbine, which also helps flow.

The trick is that you can't transition to the big pipe too rapidly. That's why some people have noted negative results with the 5" dp or even 5" exhaust. These 5" systems are often designed to mate up to the stock elbow, which is tiny, and the transition from that small area to the large pipe is too drastic.

The *only* performance difference worth considering from one exhaust manufacturer to another is how this transition is handled. The more space devoted to the transition, the better.

The angle of the tube walls should not exceed 15 degrees. That means no less than 3" of transition length for every inch of diametrical change. The shallower you can make that angle, the better. IMO, even 15º is pushing it.

Since 5" DPs often have the the same transition length as the 4" DP, the 5" can be too drastic of a change, causing turbulence of loss of performance.

Aside for transitions that are often mishandled, a 5" would have no negatives at all from a performance standpoint. Fitment is another matter.

jh