700R4 engine RPM limits

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peejay
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700R4 engine RPM limits

Post by peejay » Sun Jun 19, 2016 10:09 am

I have kind of an unusual problem. I'm slowly but surely losing the ability to push hard with my left knee. (Not the unusual part) This makes driving a manual transmission difficult to excruciating. So I figure my options are hand control for the cluch or convert my cars to automatic.

I actually prefer automatics for various reasons so this is the route I want to go first. The unusual problem is the car that I'd prefer to have an automatic sees revs a little north of 10k at the dragstrip and is kept in the 5k-9k region during 1-2 minute timed course runs. And I expect to be able to drive the car for several hours at a driveshaft speed of 5000-6000rpm.

If I were to convert this car to a 700R4, what horrible failures could I expect from a transmission and what could I do to keep it reliable?

Dogwater
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Re: 700R4 engine RPM limits

Post by Dogwater » Fri Jun 24, 2016 1:30 pm

I wouldn't consider a 700r4 for those kind of rpms or duration. I have one in my 78 Camaro that I rebuilt but it's babied pretty much. A 4k85e might be a better choice.

Rizzle
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Re: 700R4 engine RPM limits

Post by Rizzle » Fri Jun 24, 2016 6:34 pm

What type of engine/power/ torque are you making? Vehicle weight? What is your current trans and rear gear?
The wide gear spacing of the 700R4 might be detrimental for track use - a 200-4R could possibly be a better fit.


It seems there are a few import cars that have used vacuum boosters for the clutch, 3000gt and nissan z32 came up quickly in a google search.

peejay
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Re: 700R4 engine RPM limits

Post by peejay » Fri Jun 24, 2016 8:25 pm

I'm looking into the vacuum booster clutch setup. Looks promising. I also found that pedal "placement" seems to help out, if I can get the pedal pad moved higher up relative to the floor then clutching isn't as difficult.

Engine has never been dynoed, but it's somewhere around 250-300hp and 180-ish ft-lb (two 1000cc injectors run out to 90-95% duty cycle, extrapolate from that how you wish). Currently i'm running 4.78s but I've been putting together a new rearend with 5.43s. Most courses have straights short enough that I struggle to hit 7500-8000 with the 4.78s (second gear, maybe 2.2-2.0 ratio depending on what trans is in it) so I'm hoping the shorter gears will let me use a bit more RPM.

The easy answer is switch to a lower revving engine but I've found that less revs also makes for less drivability, larger engines aren't as easy to pedal and to be frank with this engine I spend maybe 1/3rd of the time actually on the throttle.

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Re: 700R4 engine RPM limits

Post by pdq67 » Fri Jul 01, 2016 12:29 am

Rizzle wrote:What type of engine/power/ torque are you making? Vehicle weight? What is your current trans and rear gear?
The wide gear spacing of the 700R4 might be detrimental for track use - a 200-4R could possibly be a better fit.


It seems there are a few import cars that have used vacuum boosters for the clutch, 3000gt and nissan z32 came up quickly in a google search.
Again!!

Hard to help if we don't even know what engine you have....

Please.....

pdq67

Rizzle
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Re: 700R4 engine RPM limits

Post by Rizzle » Fri Jul 01, 2016 11:59 am

With your engine on the low torque range (Possibly a 13B wankel?), you might have the most luck using a lighter duty transmission to keep the rotating weight down, making it live longer at high rpm. I'd think something around the TH180C (3spd) or 4L30e (4 speed OD TH180). They are mildly popular, but I don't think 9000rpm input speeds are commonly done for these types of transmissions, so having an expert go through it would be ideal.

ozmuscleowner
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Re: 700R4 engine RPM limits

Post by ozmuscleowner » Thu Jul 07, 2016 12:58 am

make sure you have a trans blanket at the RPM speeds your wanting to spin it to,...or some type of scatter shield for that auto because if it lets go at that speed its not going to be pretty ...even inside the car

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