My 04.5 CTD would do a consistent 15.0@92mph with only the BD on 90hp.
My 08 PSD will do a consistent 14.4@88mph with the SCT.

Does that mean the cummins gets going quicker then falls off? Does the Cummins have more top end? i just dont get why the mph are so different for 6 tenths of a second.

 

It is because of your acceleration, faster acceleration that levels off at a lower speed at the top of the 1/4 can easily beat a higher top speed. For example if truck #1 launches and reaches 90 mph by a third of the way down the track he is already ahead of truck #2 that reaches 90 mph after half the track. it makes sense in my head, hope that helps.

 

Cummins with the bullydog has no low end and pulls hard on the big end which is why your mph is high, will also usually see a high mph if you spin bad off the line.
The PS is leaving harder more then likely cutting a better 60' and mayber 1/8 time then the cummins but falls off on the big end a runs less mph.

 

Thanks for the quick replies. The CTD with bullydog did seem to have better top end than the PSD which is wierd because the PSD makes all its torque at 2000rpm

 

ET reductions are generally made in the front half of the track. MPH is often interpreted as an indicator of horsepower, but is only calculated over the last 66 feet of the track. I wouldn’t hang my hat on the mph = hp interpretation though. If you look at the incremental times on the time slips, I’d bet the PSD will have MUCH better front-half times, especially in the 60 foot and 330 foot times. If you calculate the “split” times, my guess is the Cummins actually covers the last half of the track as quick if not quicker (take the quarter-mile ET minus the eighth-mile ET – you can do this with any incremental times).

There are many things that could go into variations like you are seeing. One of the biggest contributors might be the gearing (which is an oft-used trick for reducing ET). It is not uncommon for the NHRA classification of Stock to use gear ratios around 6:1 in order to reduce ETs. You’ll see many run high 10’s or low 11’s at only 110-120 mph. Their proverbial tongues are hanging out for the last half of the track, as they will be running 100 mph or so at half track, and gain very little mph over the last part of the track. Traction weighs in, as do weather conditions, weight of the vehicle, where in the beams the vehicle was staged (can make as much as .05 difference alone without significantly affecting mph either way), torque converter specs, and COUNTLESS other factors. It definitely sounds like the PSD is much more optimized for reducing ET than the Cummins.