Exhaust Pressure Testing

[Mach9310]

@TEXAS HEAT at one point I just increased the 2.25” factory connect to 2.5” and saw a measurable reduction in backpressure.

@TEXAS HEAT and @Mach9310 i found that 2.5” jist isn’t big enough to support a forced induction coyote. If the goal is to be under 5 psi backpressure, as recommended by Vizard years ago and substantiated by my own testing, I found it’s going to take a true dual 3” or bigger front to back.

Thanks for the response. I’m going to give it a shot. Catless headers into the borla resonator into 3” turndowns. Hopefully it’s not too loud and it helps me get into the low 4s 60-130 while still running a 6 rib setup.

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[GregO]

as recommended by Vizard years ago and substantiated by my own testing

 

[TEXAS HEAT]

Where can I get a copy of that?

 

[TEXAS HEAT]

@TEXAS HEAT at one point I just increased the 2.25” factory connect to 2.5” and saw a measurable reduction in backpressure.

@TEXAS HEAT and @Mach9310 i found that 2.5” jist isn’t big enough to support a forced induction coyote. If the goal is to be under 5 psi backpressure, as recommended by Vizard years ago and substantiated by my own testing, I found it’s going to take a true dual 3” or bigger front to back.

Thank you @engineermike for your feedback. When you say measurable with the 2.5" versus the 2.25" how much of a reduction are we talking about? Obviously not under 5psi total reduction, but if maybe half of that would be worth it?

 

[engineermike]

Looks like the 2.25” section was adding about 2 psi backpressure on mine. See post #24.

 

[K4fxd]

if you can tolerate the sound of true dual 90° crankshaft V8’s….. yuck !

I grew up with that sound, I like it.

 

[Proshop]

Mine goes under the knife today… nothing less than 3” all the way through. Definitely interested to see the outcome. Thank you @engineermike for starting this post and all your testing and knowledge!

 

[K4fxd]

I'd like a bit more info on the 4x3 eccentric, if you made it or bought it and how you hooked it to the cat.

Thanks

 

[GregO]

Where can I get a copy of that?

I’m not much of a FB user but this is as close as it gets. Not to many forum uses bring up names like Vizard. Names like his are a trip down memory lane.
https://m.facebook.com/DavidVizardAuto/

 

[GregO]

I'd like a bit more info on the 4x3 eccentric, if you made it or bought it and how you hooked it to the cat.

Thanks

https://www.buyfittingsonline.com/s...-od-32w-eccentric-reducers-4-in-x-3-in-304ss/

 

[K4fxd]

so cut the end cap of the cat off an d weld it on?

I've noticed the gen 2's are 2 1/4 from the cat to the hook up.

 

[Exploded_Muffin]

Very informative thread, thanks @engineermike!

Currently making about 800 whp and my setup is:
1 7/8 catless headers (bottle resonators in place of cats) 2.25 factory connect magnaflow tru-x resonator custom 2.75 connecting pipes borla s-type mufflers

I had one of my welded rear O2 bungs blow out a couple months back during a pull and based off this thread I believe this was due to excessive pressure build up right before the factory connect neck-down (@engineermike, any thoughts on this?)

I purchased the stainless bros 3" straight through resonator to replace the magnaflow tru-x.
Had it welded to the headers but was way too loud and raspy. Quiet mode became worthless and I couldn't go over 3,000 rpm as it was loud even with light throttle in quiet mode.
Switched back to the the magnaflow tru-x's a few days later.
Will keep the 3" resonator anyway incase I can get it to work with a different exhaust system in future

Just a general FYI

 

[engineermike]

https://duvasanitary.com/product/butt-weld-eccentric-reducer/

 

[TEXAS HEAT]

Currently making about 800 whp and my setup is:
1 7/8 catless headers (bottle resonators in place of cats) 2.25 factory connect magnaflow tru-x resonator custom 2.75 connecting pipes borla s-type mufflers

I had one of my welded rear O2 bungs blow out a couple months back during a pull and based off this thread I believe this was due to excessive pressure build up right before the factory connect neck-down (@engineermike, any thoughts on this?)

I purchased the stainless bros 3" straight through resonator to replace the magnaflow tru-x.
Had it welded to the headers but was way too loud and raspy. Quiet mode became worthless and I couldn't go over 3,000 rpm as it was loud even with light throttle in quiet mode.
Switched back to the the magnaflow tru-x's a few days later.
Will keep the 3" resonator anyway incase I can get it to work with a different exhaust system in future

Just a general FYI

Hey Muffin, check out the Borla S-type with the 2.5" 60661 resonator. It's actually a very civilized system even without the big restriction (cats) and because it is dual 3" (besides the resonator) it flows so much better than the previous Magnaflow resonated X. When I removed it to install the new exhaust the body of the resonated x was heat checked, so much so that you could see where the exhaust gases were merging from the outside of the shell. That tells me that it was a huge restriction and that it was generating a lot of heat once I added the SC. I had it on my car from when it was NA and it never looked like that before I added boost.

On a side note, how are you liking the return style fuel system and e85? I've been mixing 1 gallon of xylene to 10 gallons of 93 pump gas to act as an octane booster since it has been so hot here in H-town lately. It raises the octane to 95 and keeps me from experiencing positive knock with the 115mm pulley and 100° charge temps.

[/QUOTE]

 

[TEXAS HEAT]

@TEXAS HEAT at one point I just increased the 2.25” factory connect to 2.5” and saw a measurable reduction in backpressure.

@TEXAS HEAT and @Mach9310 i found that 2.5” jist isn’t big enough to support a forced induction coyote. If the goal is to be under 5 psi backpressure, as recommended by Vizard years ago and substantiated by my own testing, I found it’s going to take a true dual 3” or bigger front to back.

How much of that restriction are the cats though? I'm FFE, so I'm hoping that I'm a little closer to being under the 5psi back pressure once I get rid of the 2.25" restriction.

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