1/4 mile Shift Point

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684door

684door

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I have a stockish 383. It is a stock rebuilt 1968 2 barrel engine that has had the following added: Mopar purple Roadrunner Resto Cam, Edelbrock Torker Intake, 850 Holley Double Pumper, Edelbrock 75 cc RPM heads. The car is a 4 speed with 4.10 gears.

I have only had it to the track a few times and have shifted at 5000 RPM. Is this a bit too low?
 
You need to experiment with several rpm points and compare time slips. You are looking for shift points where the motor rpm doesn't drop to a point of being out of the power band. Basically if the motor is laboring and not pulling hard when you upshift you shifted to early.
A video camera recording of the tach lets you replay each pass and you can look at the rpm drop on each shift.
My 340 low gear set 904/3.91 runs best with a 6k 1-2 shift and 6200 2-3 shift.
 
The advice above is dead on. Maximum acceleration will occur when your shift points are at the maximum torque applied to the axle. If you put your car on a chassis dyno, you will find the optimum rpm to shift at. The flatter the torque curve is, the less difference a few hundred rpm will make.
 
Everything mentioned is spot on. I guess what I am asking more so is what would be a safe or highest shift point for a stock 383. Thanks
 
Download a g-meter app that works off the accelerometer chip, not GPS. Most phones that the screens turn have them.
Then, as mentioned, use a camera and the g-meter and tach to find where your acceleration drops, and start experiment shifting a few hundred below, up to g-drop.
This will tell you when the engine, in it's condition, wants to shift, not where anyone thinks it should.
 
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One 383 might blow up at 5,000 rpm and another might go to 6 or so. Like mderoy340 said, it's all about when it runs out of power.
 
A 383 stroke is 3-3/8". A 340 stroke is 3-5/16". A difference of only 1/16" or 1/32" on the radius. I kinda look at a 383 as a bigger 340. If it's in good shape I wouldn't be worried to 6000 rpm.
But as already stated, running some documented test runs is your best bet. You might consider a blow proof bell housing as you go forward.
 
Your on the best dyno you can get on. The track. Change the shift points and look at your times. Good record keeping is the key here.
 
KosmicKuda said:
A 383 stroke is 3-3/8". A 340 stroke is 3-5/16". A difference of only 1/16" or 1/32" on the radius. I kinda look at a 383 as a bigger 340. If it's in good shape I wouldn't be worried to 6000 rpm.
But as already stated, running some documented test runs is your best bet. You might consider a blow proof bell housing as you go forward.
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Shorter stroke than a 350 Chevy. (3.48")
 
Track testing is the only way to really figure it out.

But here's a question I've pondered...how do you figure out where to even begin, rpm wise?
 
I go through at about 5000 to 5100 rpm. I just want to know if 5400 rpm is too much for a stock bottom end.
 
684door said:
I go through at about 5000 to 5100 rpm. I just want to know if 5400 rpm is too much for a stock bottom end.
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toolmanmike had the most proper answer to your question. Nobody can say what the safe maximum RPM is for your engine. If somone says you should be able to shift at 6000 or 6200 RPM and it breaks a connecting rod at 5800 RPM you are going to be pissed off.
All anyone can say is what their experience with THEIR 383 proved. In my case, my first build was a mismatched 383, stock crank and rods, heavy TRW flat top pistons, Mopar .509 camshaft, single plane M1 intake, and 750 vacuum secondary carb. In my heavy car with automatic trans, I shifted at about 6000, and engine was up to about 6200 RPM before the shift was completed. Test yours as others have stated IF you are comfortable with the idea that anything can possibly happen.
 
All good points guys. These big blocks are new to me. I ran a 273 for years, shifted 7000k went through the traps at 7000k. I think I will just try to sneak up on it.
 
Chances are the top end will let it run higher than the bottom end will live at - depending on what was done and how well it was done during the rebuild. I wouldn't hesitate to take a stock lower end to 6K. But the cam you have will probably peak lower, and be dropping off around there - hence the advice to do trial and error and a log book is your friend.
 
I used to bracket race my parents new factory stock 383 automatic Road Runner back in the day. Leaving the slap stick in drive, it would shift at 4500 RPM. When shifting manually, I always used the factory installed tach and shifted at the 5500 RPM redline. Never had a problem (ran very low 15's with a 3.23 open rear end).
 
Thanks for the info. Now I know what a stocker redline was at, I can play around 5500k and under to find the sweet spot.
 
Stone stock 1965 383 with intake and cam I shifted at 6200-6300 for a couple years, rebuilt motor same crank/rods but with arp rod bolts, forged pistons I shift 6800 now and it loves it
 
When you feel the engine stop pulling, shift.
 
684door said:
I have a stockish 383. It is a stock rebuilt 1968 2 barrel engine that has had the following added: Mopar purple Roadrunner Resto Cam, Edelbrock Torker Intake, 850 Holley Double Pumper, Edelbrock 75 cc RPM heads. The car is a 4 speed with 4.10 gears.

I have only had it to the track a few times and have shifted at 5000 RPM. Is this a bit too low?
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Perhaps, Try upping the shift point 200 rpm and make a run. See what the timeslip shows. I have all my stuff dyno'd but you can figure it out at the track too.

Mine shifts at peak HP (5800) and goes through the traps 400 over
 
I have a 400-2 bbl with 151k on it when it came out of original car. Re-ring and bearing I run to 6000. Your results may vary.
 
We shift ours at 11500. And it's a little motor 305 cubic inches.i know its not Mopar.
images-48.jpg
 
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