Lost almost 1psi going from 3" to 4"

 

Well this should be fun

 

1.75 headers
2.5 off each header into merge

For the 4" it was same Y pipe but instantly went to 4" at merge ...so it was basically dual 2.5 forming into a 4"


No more timing was added ...wouldnt take more then 18* ...at 19* it lost power


Rpm graph was same

 

So i have kinda a generic question along these lines. So you make your exhaust better and that drops the boost you may/may not make more power, since you dropped boost is that necessarily "easier" on the motor?

 

The less boost your compressor of choice makes the less power that is extracted from the engine either through the crank (supercharger) or exhaust (turbo). In both cases, less boost is "easier" on the engine regardless of power.

 

In my case my blower is still spinning same Rpm just motor isnt backed up

I lost 1 psi .....went from 13 to 12 at peak

 

I ordered a 4" MBRP system, went to fit it and saw I had like 1/8" of clearance on my crossmembers. No way I was gonna deal with a rattling and clanking setup on a DD. I returned it the next day, my plan is to have the local mandrel shop make me a custom 3" system with a 30" magnaflow muffler, a 12" resonator before the muffler, and 3" tailpipe. I really think that Trick or kb or someone should offer a bolt-on exhaust for their kits, whether it's 3" or 4".

I would love to see pics of everyone's systems.

 

That area of tightness.
You just have to oval it in a vise and you have plenty of clearance.
I added 1 extra hanger in that area
No rattling here.

 

Ok that sounds like it would be effective. I decided to run a 3" system as I have heard more than one report on here of guys making no additional power going from a 3" to a 4" system on a stock motor / 10psi type deal. Now on a fully forged 370 with a Holley intake and all the fixings I'm sure a 4" system would pick up significant gains. But I think for my truck, all it would do is make it louder.

 

This info is not exactly pertinent but could offer some insight. On an LY6 with a single S475 T4, the 4" downpipe reduces to a 3" y pipe into dual 2.5" pipes with Magnaflow mufflers. With a 4" cutout before the Y my boost on the gate spring goes from 8 PSI to 12 PSI. The best I can gather is you will see a gain on anything 8 PSI or higher going from 3" to 4".