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[fiftysixbowtie]

Replaced my P255's with P295's and they actually fit. I started a big conversation on Chevy Talk and now that I have them, I can add to it. Need to take pictures though. Now I have 4 more inches of rubber on the road. Hopefully I won't sit there and spin so much.
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John Rush

[David Graves]

that added quite a bit of rubber.. what rear end do you have under your car?

[fiftysixbowtie]

9" Ford posi. I think it's ratio is 3.55. Not sure if that's a good ratio but it was on the car when I bought it.
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John Rush

[57boxman]

I'm happy for you. Can't wait to see the new rubber. I'm supprised after reading the posts on CT that they fit but extreamly happy for you that they do. Some of the mods they were talking about were a little much!

I'm going to have to do some performance updates on my car to keep up with you.

At crusing speed what is your RPM? With your 5 speed a 3.55 maybe good?

I have lost the TV remote and need something to do. So I hope you don't mind me messing around here with the calculations.

I played with this http://www.race-cars.net/calculators/mph_calculator.html web site to see the crusing RPM vs out of the hole gear.

To make the numbers exactly correct we will have to find out your 5th gear Transmission Gear ratio tire, tire height, etc. But just for bench racing I made up some numbers.

My old Borg Warner transmission in 4th gear the ratio is 1 to 1. So, at 3000 RMS with my 3.23 rear axel gear ratio with my 24.5" tires I am going 68 MPH. When I had a 3.55 rear gear I was going 62.

I guessing your 5th gear is .80 to 1 and guessing your tires are the same height as mine. Doing the math, is 2500 around 65 MPH? If yes, with a 3.70 you would drop to 52 and a 4.11 to 55 MPH.

Will the ET change with a higher rear gear? I have always been told yes but have not been able to find math formulas that would tell the difference or data to support that claim. I may have been told wrong. I remember Tom saying when he changed gears his ET was the same? I believe he said that since the horse power was the same the ET would stay the same.

I wish someone would explain how that works to me. I put the question on CT but had no takers.
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Texas Classic Chevy Experience
http://www.texasclassicchevyexperience.com/

[wheezer]

Okay, I'll give this shot. Any power plant (motor) has a maximum power point, that being the point where torque and rpm are maximised. Torque times rpm equals horsepower. Horsepower is power. This band of power is normally a humping curve if the rpm is plotted against torque. The power increases from lower rpm till it peaks then it starts declining as the rpm continues to increase, consequently torque starts to drop off after the peak power point.
For a drag car to maximise is ability to accelerate it must theoretically always be at the motor's peak of torque and rpm (horsepower) for the entire run.
For most drag cars this is a narrow band of rpm. For street cars is much wider as their power band is wider albeit much reduced, i.e. 250hp vs 500hp.
Therefore, one wants the car to be at maximum power for the entire run which means lots of transmission shifts and rear gear to be maximise for the rpm in high gear through the traps.
Soooo.. street cars with multi gear manual transmissions and any rear differential and tire diameter will have the opportunity to reach their maximum power if they hold each gear from the start line to the maximum power point when shifting as described earlier. They are in essence working in the maximum power band for the motor. So rear gear differential, tire diameter, and overdrive transmissions really don't enter into the equation regarding drag strip et for street cars. As the street car's mph at the drag strip it is more truely the measure of motor power. It does not matter whether a street car passes through the traps in 3d, 4th, or 5th gear as the power available will provide its mph regardless. ET is another story.
Okay so theoretically the transmission that shifts the most times will likely stay in it's power band longer for the whole run and therfore run a quicker E.T. Questions?
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"A Classic Car is Not Aerodynamic"

[fiftysixbowtie]

Holy cow. You are obsessed. I couldn't possibly know those numbers but I'll start gathering data. I can tell you my low gear is 3.27 and my high gear is 0.68. I believe my rpm's at 70mph is 2100. I could be wrong so I'll pay closer attention. I also believe my tire height is roughly 24". I can't answer some of your other questions. Perhaps you should ask the performance forum in CT.
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John Rush

[fiftysixbowtie]

My post was submitted at the same time as Tom's meaning my comments were for Alan. As for Tom's post.... Yeah, what he said.
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John Rush