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SHM header dyno

S

SicSE

Veteran CEG'er
Joined
Sep 7, 2007
Messages
889
Location
Kennesaw, GA
This is a power output comparison. Open SHM headers vs. open SHM y-pipe, vs. 2.5" exhaust with no catalytic converter.

The PCM had trouble adjusting A/F to suit the open headers, even after over an hour of idling, driving the dyno rollers & general engine revving. But since the A/F stabilized before peak hp/tq, I consider the results dependable to use for comparison.

A few A/F graphs go stupid-lean at the end because the sniffer was blown out of the header and/or tail pipe.

I had to drop the smoothing down to 3 for the individual tests because there is a spike and break in the torque curve in an open header run that shows it's peak torque @ 212.

So without further ado...

Open headers
Openheadersdyno-1.jpg


Open y-pipe
OpenY-pipedyno-1.jpg


Test pipe exhaust
Testpipeexhaustdyno-1.jpg


More charts to come...
 
Open headers vs. test pipe exhaust
Openheadersvstestpipeexhaust-4-1.jpg


Open headers vs. open y-pipe
Openheadersvsopeny-pipe-4-1.jpg


Open y-pipe vs. test pipe exhaust
Openy-pipevstestpipeexhaust-2-1.jpg
 
Beans said:
So you made 10HP? Did you have precats before?
Click to expand...
No precats, just the main cat... I won't really have an accurate comparison of before & after the headers until I reinstall my cat. Plus I think some of my other runs were closer to 191. Regardless, I'm guessing I will have gained a solid 7hp once all said and done. :cool:
 
Its too bad you used SE heads.... You'd be killing it with 3 liter heads.... 210+
 
Pudmunkie said:
Its too bad you used SE heads.... You'd be killing it with 3 liter heads.... 210+
Click to expand...
Really? The highest untuned numbers I've seen were around 205.

I probably will eventually pick up a pair of 3L heads... I just want to see what I can get out of the hybrid for now.
 
I don't like the hybrids untuned... You should have much better results from an untuned full 3 liter.

Was Snob tuned? He wasn't dyno tuned, only had tings turned off and sme basic mail order stuff. (AFAIK). I pulled him in my old 3liter and I wasn't tuned for the full 3 liter, just for the splitport.
 
Good numbers man overall. I see adding the y-pipe helped you gain a couple tq.

No full exhaust numbers??

Quick question, how long is your y-pipe? Does it still have that cat? Also what is this test pipe? what OD, is it?
 
Harrry said:
I see adding the y-pipe helped you gain a couple tq.
Click to expand...
Yeah... and made it sound like absolute sh*t! Man it sounded like open headers and a huge, venting air compressor for the entire midrange. Worst rasp ever. :help:

Harrry said:
No full exhaust numbers??
Click to expand...
No, I didn't get to finish my cat so the test pipe had to stay in. The cat is only going to lower the numbers though... stay the same at best. Either way, I'll be doing a comparison once it's ready.

Harrry said:
how long is your y-pipe? Does it still have that cat? Also what is this test pipe? what OD, is it?
Click to expand...
I'd have to measure the y-pipe to be sure - it's the Y that came with the headers. Bank 1 is only maybe 5" inches long, and bank 2 is probably around 14" - no cat in there. Test pipe is 2.5", as is the Y merge, & the exhaust, back to halfway past the fuel tank where I stepped it to 3" for the last few feet of piping.
 
OH yeah, when i added my cats, i def noticed a drop of power at anything above 4k rpms. I probably lost 5-6whp. Which isn't much but when it astarts at 4k-7k the overall power loss def reduces the cars performance capabilities.

But without cats, my car was way tooo loud:blackeye:
 
SicSE said:
And just for the record Harry - told ya. :cool:
Click to expand...

What is the before and after comparison :shrug:




go to exhaust section for debate.

But i stand corrected. You stated pipe length causes restriction. I said it doesn't.
You said no restriction is best. Obviously from adding your y-pipe it tells me i'm right, it adds length and combines exhausts pulses. Did you gain 1 whp over the y-pipe??? Nope you gained power having the y-pipe.
So thanks for proving to me that pipe length means nothing. on our cars with our current application.

how was your car drivable when you had it at 1,500 rpms :laugh:
 
Harrry said:
Obviously from adding your y-pipe it tells me i'm right, it adds length and combines exhausts pulses. Did you gain 1 whp over the y-pipe??? Nope you gained power having the y-pipe.
:laugh:
Click to expand...

Having collector extenders always shows a gain in power and torque vs. open headers. This is proven 99% of the time on engine dyno tests, so that should have been no surprise. Now, the length is what requires testing to find what is optimal for the commbination.
-J
 
biminiLX said:
Having collector extenders always shows a gain in power and torque vs. open headers. This is proven 99% of the time on engine dyno tests, so that should have been no surprise. Now, the length is what requires testing to find what is optimal for the commbination.
-J
Click to expand...

I agree, but what most people should know, it is subjective to the engines capabilities.

You can't take a geo metro and put a 3 inch exhaust on it. :crazy:
 
This is the closest recent run I could find that had a similar A/F graph. Once the PCM leans things out some more, the numbers should go up a tad.

The red run is with gutted precats, a custom Y-pipe, custom cat and custom 2.5" straight-through exhaust. The blue run is with SHM headers, SHM Y-pipe, and the same exhaust, but with a test pipe in place of the cat, (I'm still working on re-fabbing the cat to put back into my exhaust).

Headerbeforeafter-3-1.jpg
 
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