I dyno'ed yesterday to see what gains if any a mild DIY porting job would produce. I was hoping for 10-15 rwhp gain, but I gained only 3 rwhp and LOST 9 lbs of torque. The dyno owner indicated that I would have gained a bit more if the humidity (73%) wasn't so high. He also recommended that I should have upped the compression to 10.5-7 by milling the heads a bit.

I am a bit baffled by the loss of torque. All I changed from the previous dyno were the heads and the SVO 30#'s. I fattened up the WOT setting one notch to 2% rich to get the A/F to around the 12.5 level.

Forgot to add that I also installed 12 bolt with 4.11's and a steel drive shaft since I last dyno'ed.

[ January 06, 2002: Message edited by: Brother J ]</p>

 

[quote]Originally posted by Brother J:
<strong>Forgot to add that I also installed 12 bolt with 4.11's and a steel drive shaft since I last dyno'ed.
[ January 06, 2002: Message edited by: Brother J ]</strong><hr></blockquote>

This is probably where all your power went. The extra weight of the steel driveshaft and 12 bolt increased your driveline losses. I think I remember seeing something about short gears lowering dyno numbers while at the same time helping ET and trap speeds. Not too sure about that one, though.

 

Loss of torque, sounds like they're overported somewhere and lost velocity.

 

basically, you probably didn't do anything.. the 12bolt costed you a little.

it takes some pretty solid porting to make a diff.

 

[quote]I also installed 12 bolt with 4.11's and a steel drive shaft since I last dyno'ed.<hr></blockquote>

I lost 12 rwhp between stock rear with 3.73s and the 12-bolt with 4.10 gears, and I even added a carbon fiber driveshaft at the same time! Not sure how much that was worth over an aluminum one.

Loss of torque probably came from the rearend, much like how Corvettes always show less torque than F-bodies mod for mod due to the increased drivetrain losses they have with the independent rear setup.

Tony

 

I would redyno with stock injectors again. What were your final numbers?
I lost about 16 RWHP going from the stock rear to 12 bolt with 4.11s.
Cheers,
Chris

 

I guess I shouldn't feel too bad. I did not realize that 12 bolt and 4.11's would cost me that much in dyno performance. Good thing dyno results are not real world. Can't wait to see what the improvement will be on the track with the new gears. At least I saw a .2 reduction in ET from the heads/injectors before I broke the 10 bolt.

My current dyno results are:

362.2 rwhp
348.7 torque

 

13:1 AF is ideal for an NA application. You might made more power a little more lean.

 

so you going to go to the track this Saturday? <img src="gr_stretch.gif" border="0">
Jeff

[ January 08, 2002: Message edited by: FormulaWS6 ]</p>

 

My take on this would be to not worrie so much about the dyno, at least your question was answered about where your new power went, go to the track, dial in the fuel and have fun with it! <img src="gr_stretch.gif" border="0">

 

[quote]Originally posted by FormulaWS6:
<strong>so you going to go to the track this Saturday? <img src="gr_stretch.gif" border="0">
Jeff

[ January 08, 2002: Message edited by: FormulaWS6 ]</strong><hr></blockquote>


I am praying for good weather this weekend.
<img src="graemlins/gr_hail.gif" border="0" alt="[hail]" /> <img src="graemlins/fluffy.gif" border="0" alt="[Fluffy]" /> <img src="graemlins/gr_angel.gif" border="0" alt="[angel]" />

 

Brother J, if you did your own headwork and only did minor porting, the short side radius is where you could have given up power if you did. ON a different note, everybody knocks GM for using the 7.5 rear but the truth is its the quickest way down the 1/4! Guys get away with murder with some common sense and this rear, 3600 lbs is gonna be hard on any rear, just dumping clutch at 4500 is not being smart. Aftermarket axles, TA cover and a adjustable clutch(slips off the line, locks up at hi rpm) would be worth trying.Most failures with Zexel torsen rear seem to be axles, that says alot about this diff. Opinions?