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Author Topic: late model drivetrain swap  (Read 4387 times)

Jon Doersch

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late model drivetrain swap
« Reply #75 on: February 17, 2010, 03:47:14 PM »

OK. Sounds good. As I said, I am much more familiar with some other makes...
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Jon Doersch

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late model drivetrain swap
« Reply #76 on: February 17, 2010, 03:48:55 PM »

O and since the 700R4 has such a steep first gear, I was thinking a rear end in the 3.08 to 3.23 range will be more than enough, although I may even go with 2.73...
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Leaburn Patey

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late model drivetrain swap
« Reply #77 on: February 17, 2010, 04:08:42 PM »

The 2.73 er 2.76 gears will be a dog with OD.
Ask Steve.for example.
He experimented with 3.23 / 3.55  and different tire sizes so the OD wont bog out the motor.
He had 2.76 gears in the Polaraco and it was giving the Maggie's computer fits.
At highway speeds,his motor was lugging at a lower than normal RPM the pooter was used to running.
The 3.23 put her up at a more normal RPM range and much nicer to drive on the I-80.
 
Think about it..How long/far you drive in first gear?? So it may be steep,but the trans will shift quickly up to the next gear.
A Docker installed a gear vendors overdrive unit and ended up swapping in 3.55's
 
 
CBarge2010-02-17 21:12:09
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Jon Doersch

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late model drivetrain swap
« Reply #78 on: February 17, 2010, 04:18:46 PM »

You are right, but part of it has to do with how much power the engine ends up making as well...Correct me if I am wrong but I thought that the motor in Steve's project was a 318 Magnum motor...With the small displacement and less torque, I can imagine the headaches on the highway...If I end up with the power and torque that I want I could probably get away with less gear...Thats how new Corvettes end up without gas guzzler tax. Still with the weight of the car I was thinking a little more gear would be good to get things moving....
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late model drivetrain swap
« Reply #79 on: February 17, 2010, 06:08:25 PM »

Steve's engine was built with a cam to give it stump-pulling torque where it is needed. This is the reason for keeping with what would be considered an RV cam for the 361, the 440 cam (stock), which is more lift and only about ten degrees more duration, and for a hydraulic flat tappet, it still falls in the 258degrees of duration, which is pretty small on the duration and the .442ish lift is still small, it is a basic bottom end cam and will handle 3.23s and .74 overdrive, which would give you a 2.39 final gear ratio, the little extra added power would make up for the weight.
Here is a link to PAW, a parts warehouse I use, they have stock ground cams along with a bunch of other ones, no specs because they are 50 state factory cams, but a call or email would give you that info.
http://www.pawengineparts.com/PDF_Files/PAW_Catalog/Cams-Valve%20Train.pdf
 
Like Steve's 5.2, he has the advantage of a roller cam, which allows good lift and short durations, flat tappets have limitations, so short durations where you need the torque (250-260max duration) can only have a lift around .450-.460 because the lobe becomes such a point and the lifters wear them out quickly, rollers just go over the point no problem. So when we built his design, he was able to get the .457 lift on that 250degree duration safely, which builds torque because it builds compression instead of bleeding it off to allow higher rpm from overpressuring and limiting top end power.
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