Need help with 1993 6.5

[1993chevyguy]

I have a 1993 chevy 6.5. I am looking for guys with knowledge about engine. I have to get a new down pipe, but I don't want to spend a lot on one that is only 2.5 inches.

[trbankii]

Just went through this on my truck the other year. Went with Kennedy’s 3” to 3.5” setup: https://www.kennedydiesel.com/detail.cfm?ID=34

As the first picture shows, just taking all the kinks out of the OEM downpipe makes a difference. Then you’re giving it another 44% increase in area from 2.5” to 3” diameter.

[DmaxMaverick]

Unless you have a NEED for greater volume, less is more, regarding the crossover pipe. A 2.5" is fine for most all applications, but I agree about all the kinks, which hinders smooth flow. The turbine is driven (more efficiently) at higher levels of heat and velocity. A larger pipe takes away from both. If it isn't a restriction issue, smaller is better. The crossover pipe is moving gas from only 4 cylinders, and shouldn't need to be larger than the manifold outlet diameter for efficient flow and heat retention. Loss of heat is loss of gas volume. Larger pipe is greater surface area which sheds heat at a greater rate. Transitioning from smaller to greater cross-sectional area pipe loses heat, and increases gas volume, which is what makes refrigeration work. All of this makes the turbine operate less efficiently, and increases lag. The GM-X turbines are relatively small as it is, and need all the help they can get. Ultimately, a 3" crossover pipe is not better than a (mandrel bent) 2.5" pipe, in almost every application.

[trbankii]

Completely agree on the crossover pipe, but the OP and I were talking about the downpipe.

[DmaxMaverick]

Completely agree on the crossover pipe, but the OP and I were talking about the downpipe.

Oops! Yeah, bigger is better. Smoother is better.

[trbankii]

No worries. Good to have the crossover mentioned in an exhaust discussion anyway.

[Coal Roller]

That was a good ooops Dmax. I never knew that about the function and physics of the crossover.

[arveetek]

I bought this Flowmaster kit from Summit Racing years ago, and it has worked just fine; still looks new, in fact! I'm very pleased with the quality:

https://www.summitracing.com/parts/flo-17220/overview/

It comes with both the downpipe and the crossover pipe.

The rest of my exhaust system is a slightly used Kennedy exhaust that I purchased from another TDP member. If you need to replace the whole exhaust, go with the Kennedy kit. You can also order the Kennedy downpipe by itself here:

https://www.kennedydiesel.com/detail.cfm?ID=253

Casey