Engine/Tranny Question

[panic]

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[Rex Schimmer]

Transmission ratios become more important when engine power bans get narrow. The narrower the power ban the closer the ratios need to be, especially the last shift. If the spread between the last two gears drops the engine to a point that the engine is not generating enough horse power to overcome the aero load at that speed you will not go faster, again this is assuming that you have some idea of what the aero load is at your target top speed and that your engine is sufficiently powerful enough to attain that speed. When using big engines like Dave has with very broad power bans transmissions like TH400s and Powerglides can be used because when the last shift is made the engine is not brought down below the power required to maintain the shift speed. Looking at the additional information that Dave is providing it looks like his problems are more engine related than transmission related and once he gets the engine happy it will probably pull right thru once in high gear (again assuming that his final ratio is not to optimistic).

I have seen a number of cars set records using high gear only, they were on the long course, had good torque producing enginies and had pretty good push trucks but it can be done without a trans. I have related this story several times but back in 02 or 03 the no. 302 roadster, runs XXO/FR has a strong GMC six and likes nitro set their record at around 204-5 and broke the trans, but they wanted their dad to make a run so they took the guts out of the tranny, locked it in high gear and pushed him off, it grunted and groaned but ended up reseting the record at 208, high gear only.

This isn't a dark science, it is knowing the engine power curve, the loads that the car will see at the desired speed, aero and rolling, and then establishing the ratios starting from the top gear going backwards.


Rex

[Dave Haller]

Rex,
Thanks very much for that input, I will put it to good use. Getting the engine freshened up, will dyno again then figure out the rest as you suggest.

[jimmy six]

Rex, That was me (JD) in 2003 in our #292 XXO/FR. My son set the record in 02 at 202. On my first run in 03 I took out the drive gear on the cluster. Back in the pits we took out the cluster over filled it with tranny oil and I qualified at 2005. I left the truck to early and blubbered it a lot until I figured out how much to give it. Did better the next morning, still left the truck to early but knew how to drive it better and went 215 in the last mile. In 02 we had 30" tires, in 03 I had 32" tires, both of use use a 2.56 rear gear. It was the 72% nitro that made it all happen. High gear only was used a lot in the 50's and 60's especially on a load.

In 04 we came back with the Tex OD trans and lost the cylinder head after we qualified at 211.

[Rex Schimmer]

Jimmy,
Thanks for filling in the details, didn't mean to give the credit to the wrong people. I just remember being there and seeing it and being really impressed! 72% in the tank!! man those GMCs like their "soda pop"!!! Nothing like "the can", high gear only and a good push truck!!

Jimmy, thanks again and also for the great show in 02.

Rex