well this isn't ATX but rather MTX..however I believe the #'s should still help you.
My friend has a Saturn that he rebuilt a DOHC engine in. It's been ported and polished with the idea of having a 100 shot. Before he put his racing cams in he wanted to get some base numbers. So he decided to go to the track on 2 seperate nights to figure this out. 1st night was all N/A runs on street tires. He ran all night long 16.1-16.3's
I ran 16.1-16.3's as well with my 18's, kit and intake only.
Next week he ran a 35 shot and ran 14.8 all night long. Never doing worse then 15 flat.
Now here we are 2 weeks later and his Spec stage 2 clutch is destroyed due to faulty manufacturing. After speaking with Spec's tech's they determined his clutch never once worked correctly and that he should see at least .15 off his track time when they send him a replacement.
What we can see is that with a 35 shot he droped at least 1.1 seconds off his 1/4 time, possibly more. So I'd say it's safe to bet that a 50-75 shot on an ATX cougar will result in at least a 1 second drop in 1/4 time.
On a side note for those motorheads who want to know. Spec was going to send him a replacement clutch, but he elected to take a 3/4 refund and buy the stock clutch kit. Reason being is the Saturn clutch has proven to hold up to at least 100 runs at 100 shot wet kit. And it's only $130 and we get our Autozone discount.
He's also recieved his 8lb fidanza flywheel (think it's a fidanza)
Installed the racing cams (proven to improve stock saturn times by .5, will be way more with his built motor and nitrous)
and lastly is installing a LSD with welded in Dif pin. We're estimating a 12.5-12.9 run next summer with a 75 or 100 shot. This is based off of
www.streetdesignauto.com 's car running mid 13's and they helped him build his car with more/better parts.