2.5" DP and Magnaflow--RESULTS UPDATE - Page 3 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 08-09-2007, 06:23 PM   #21
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Boss and boss'* boss are traveling, so I went home after lunch

LEAK FIXED!

But I didn't use the donut...it wasn't going to fit anywhere; I guess the different years used different DP'* and/or EM'* after all. Wonder if napa will take a return? (If not, anyone need a donut?)

Problem was something I mentioned earlier...the left side rear EM stud wasn't seated all the way in the manifold flange (I think you can make that out in one of the earlier photos); removed it, cleaned the threads with a dremel and wire brush, and it went back in smooth as butter. Reused the original flat gasket, flanges mated up nice, and BAM! No leaks

(Note to self: don't screw up the stud seating when doing the heads later )

Freeway testing confirms..."pfft, pfft" is gone.

Sound is "growlier" than before, which I like. Seems to accelerate better...and oddly, it seems like it doesn't decelerate as quickly when I take my foot off the gas

Scanning and tuning (perhaps this weekend) should say for certain if I gained anything.
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Old 08-09-2007, 06:42 PM   #22
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Excellent! Looking forward to seeing the results.
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Old 08-09-2007, 07:04 PM   #23
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Where have I been? Totally missed this thread. Glad you got it fixed, Andrew... I hope you have some good results with the 2.5" DP, as I'm itching to get one myself. Let us know how it fares in your VE tests.
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Old 08-09-2007, 09:58 PM   #24
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Quote:
Originally Posted by big_news_1
Where have I been? Totally missed this thread. Glad you got it fixed, Andrew... I hope you have some good results with the 2.5" DP, as I'm itching to get one myself. Let us know how it fares in your VE tests.
Got to open it up on my little stretch of deserted road in the foothills...initial quicky scans and VE calculations are pointing to good things
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Old 08-10-2007, 01:08 AM   #25
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UPDATE: After it cooled down to 70* F this evening, I took some more runs with scans, and did some more VE calcs...

WOW! Just WOW!!!

Preliminary estimates are +15-20 ft-lb torque at 4200 rpm, and at least +15-20 hp at 5200 rpm...and these scans (and estimates) were with PE turned off (i.e., with no added fuel under WOT, or 14.7:1 all the way to 6k rpm with no KR ) and without the extra 4 or 5 degrees of WOT spark advance I expect to be able to add before my tuning'* all done.

I had heard a bigger DP would reduce KR, but this is unreal. Also, I see nothing in the scans indicating any "low end loss"; makes me wonder if my old cat was plugged up or something...

I hope to have the full story by early next week.
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Old 08-10-2007, 01:10 AM   #26
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wow that nice keep us posted on the progress
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Old 08-10-2007, 01:42 AM   #27
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I gotta say, if it'* true that my old cat was plugged or whatever, this new cat may mostly be "giving back" lost power...I have GOT to get to a dyno sometime.
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Old 08-10-2007, 01:45 AM   #28
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did you look in youre old cat could you see daylight true it .i don't think mine was plugged but my new one is half the size
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Old 08-10-2007, 04:07 AM   #29
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Quote:
Originally Posted by agrazela
I have GOT to get to a dyno sometime.
Yes... yes you do! Quickly, before I come San Diego and start flour-bombing your house!
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Old 08-12-2007, 11:28 PM   #30
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Quote:
Originally Posted by agrazela
Preliminary estimates are +15-20 ft-lb torque at 4200 rpm, and at least +15-20 hp at 5200 rpm...
Uh, it seems I had a bit of a spreadsheet error in my earlier estimates, and imported the wrong "before" data...

After a number of additional tuning runs over the weekend, the final tally is about +4 to 5 ft-lbs @4200 rpm and +4 to 5 hp @5200 rpm.

Quote:
Originally Posted by agrazela
...the extra 4 or 5 degrees of WOT spark advance I expect to be able to add before my tuning'* all done.
I did manage to add 2 to 3 degrees of timing advance in many "high load" spots in the timing table (and as many as 6 degrees in low-to-medium areas), and this probably accounts for the increases.

I'll post the final VE curve tomorrow.
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