Drag Racing Tech - Finally hit 11s after 9" rear and 90/90 intake but lost mph?
NW Iowa WS6
04-30-2012, 09:07 AM
Ran yesterday April 28, 2012 at Thunder Valley Dragways. Total mods are in my sig but more importantly the mods that changed from last year:
- stock rear with 3.73s to 35 spline Moser 9" Wavetrac with 4.11's
- stock driveshaft to PST 3.5" aluminum
- Ls6 intake with stock ported throttle body to TPIS 90/90 (haven't retuned)
- LS6 clutch with aluminum flywheel to Spec 3+ with steel flywheel
- 18x10.5 wheels with 26" Nitto 305's to 15x10s with 26x11.5 ET Street bias ply
Last year did firstname.lastname@example.org with a 1.76 60' and a DA of 1520. Yesterday did email@example.com with a 1.64 60' and a DA of 1310
I thought with 18 pounds each lighter wheels, 90mm intake, 3.73's to 4.11s I would pick up a mile or two despite the rear being heavier and the flywheel being 8 pounds more. Does the 90/90 intake not help at all without a tune and does the rear end and steel flywheel rob that much power from everyone?
04-30-2012, 09:16 AM
Weight be it static or rotating weight has changed.
Heavier Rear end (axles and diff included)
If your DS was Aluminum, you have a heavier than stock unit.
Clutch upgrade is probably a few pounds heavier.
The Wheels are an improvement but not sure, did you do the ET Street Bias Ply or DR?
The car is probably not seeing the intake difference as adjusting the tune for maximum return is in order. I personally on a cam only, my car, never saw a meaningful difference. Honestly for what the car is, a LS6 was fine and swapped back.
04-30-2012, 06:05 PM
The mph loss seems right to me.
The better your 60' the fatser your ET, the more the mph drops, power being equal of course.
Why u ask? :confused:
When you take longer to get to the 60', your are under power for a longer period of time, building speed. It's like getting a head start,mph-wise to the 60' point. Just because u r reaching a given point QUICKER doesn't mean you are going FASTER at the given point.
Looking over your recent mods I am not surprised one bit that your mph dropped and I definately agree w/ Black-you need to get back on the dyno with the new intake and you need to dyno the car with the tires you are racing with on the car. :nod:
Congrats on the 11's. :thumb:
04-30-2012, 06:36 PM
^ That, and you went from a radial to a bias ply, and you have more parasitic loss with the inefficient old 9". You could slip a 275/60 on there and get some of your mph back, but I wouldn't bother with it. Mph does not win races. Do what the gents above said ;)
04-30-2012, 06:48 PM
Id agree here, I would bet it take more power to turn the 9" than it did with the old rearend.
NW Iowa WS6
04-30-2012, 09:26 PM
Thanks guys, this is what I wanted to hear actually :P that something isn't messed up. I knew 9" were known to lose about 15-20 on the dyno but I thought my lightweight wheels and 4.11's would make up for it but oh well its only 1mph and I talked to my tuner and he said now with the 90mm intake I won't really gain anything until it's tuned and he would like to do a Speed density to get rid of the 75mm bottleneck MAF between my 85mm inlet lid and TB even though it isn't maxed out he said it'd be worth a couple ponies on top of just a basic MAF retune. I bet even a 31 spline 9" spool wouldn't have lost as much as this 35 spline limited slip either.
I guess I'm gonna have to just keep lowering that 60ft. This was opening track day for the season here since they stripped the track last fall and last year at this time I was only getting 1.8-1.9 60's in this track prep with no rubber or sticky stuff laid down. A buddy of mine there was doing 2.0's that same day and he never did worse than 1.7's at the end of last year. Now at 11's are hit, 1.4? 60's is my new goal!
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