Haven’t been running 1/4 mile and made one pass a few weeks ago and numbers seem off so just curious what typical rpm gain would be.
The car is 95 Monte Carlo 900 up 548, glide , 4.30 rear gear and 100” rollout rear tires.
I want to hear some typical numbers first then I will post what it ran. Mph and rpm on this run seemed off. It does run 5.30s in summer heat.

500-700 depending on convertor slippage

That’s what I was thinking. I will have to go verify tach settings but on that pass the shift light came on a second time a good ways before the finish line and I am shifting at 7500 and usually cross through 1/8 at 6600. All the times on the slip seem to be correct just puzzled by the MPH and what I think the 1/4 finish line rpms were. Car went 8.45 @ 168 according to slip and I would expect it more around 160.

For E T you can take the 1/8 mile time and multiply by 1.58 and it's usually real close to the 1/4 mile time.
Also another formula is this. Multiply your ET by your mph, it should be close to 1320.. If it's less then your mph is low, if its higher than 1320 then you run good mph

quote:

Originally posted by 27Keith:
Also another formula is this. Multiply your ET by your mph, it should be close to 1320.. If it's less then your mph is low, if its higher than 1320 then you run good mph

Would this also work correctly for 1/8 mile ?

Well I was in the trailer this evening messing with the car and found second shift point was set at 7000 so that would be why it came on so early now I just don’t believe the mph.

quote:

Originally posted by markemark:

quote:

Originally posted by 27Keith:
Also another formula is this. Multiply your ET by your mph, it should be close to 1320.. If it's less then your mph is low, if its higher than 1320 then you run good mph

Would this also work correctly for 1/8 mile ?

Never hear that formula before but it seems very close. I used my 1/8 times as well, and it seems pretty accurate as well, (I just used the 1/8 mile figure in feet, of 660 instead of the 1/4 mile 1320 Ft). Cool.

The ET times MPH is called the “hook factor.” The 1320 number has no relationship to 1320’ in a quarter mile. Our dragsters are around 1335.

There’s more info at this link which says optimum hook factor is 1350. He starts talking about it on pg 4 #19: https://www.gregraven.org/hotw...nd-MPH-Equations.pdf

quote:

Originally posted by 183N:
The ET times MPH is called the “hook factor.” The 1320 number has no relationship to 1320’ in a quarter mile. Our dragsters are around 1335.

There’s more info at this link which says optimum hook factor is 1350. He starts talking about it on pg 4 #19: https://www.gregraven.org/hotw...nd-MPH-Equations.pdf

Interesting. My Cobalt is 6.94 and the roadster is 6.95.

On 1/8th mile I use 1.90 as a multiplier.

4.45 @ 156 = 694 * 1.9 = 1318