Determining shift point

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BracketNova
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Determining shift point

#1 Post by BracketNova » Wed Sep 09, 2009 12:24 am

In the simplest sense, am I correct to think that I need to shift at a given RPM that after gearchange RPMs fall to the engines peak torque curve?

There sure are alot of wiz-bang calculators out there. But I haven't seen a one address converter slip, which I would think would be a large factor if you were "computing" where to shift.

Thanks Folks!

Greg
"I always compare drag racing to lighting $100 bills on fire, only it's more expensive." - Craig W.

Check out my website...
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'71 Nova E85
6.69 @ 100.2 MPH 9/6/14
1.4257 60'
1700' DA

13:1 439 BBC
3330 lbs

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dadnova
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Re: Determining shift point

#2 Post by dadnova » Wed Sep 09, 2009 3:59 pm

Gotta plan, spend it before she can, and go as fast as you can.

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John_Heard
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Re: Determining shift point

#3 Post by John_Heard » Thu Sep 10, 2009 6:34 am

More details on your combo needed. Engine, Converter stall speed, rpm drop at the shift, what trans?

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BracketNova
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Re: Determining shift point

#4 Post by BracketNova » Thu Sep 10, 2009 10:44 pm

OK here we go...

weight w/ me: 3200

402 BBC 8.5:1 (i know, I think the guy I got the motor from sprayed it)
Oval port heads, port work with big valves
Herbert cb5k cam .596/.625 dur. @ .50 244/254 110c
850 carb e85

1.76 'glide with brake
6000 8" (I've never tried to flash it to this, but I leave at 4800 and it has no probs getting to the two step)
Friend bulit it, has two extra clutches in forward, one in reverse and a kevlar band (not sure if this helps)
RPM drop: sorry, never looked...gonna look this weekend

9" rear with 4.88's (I'm an eigth miler :-) )
29 x 12 slick


Desktop dyno says...564HP @ 6500 494TQ @ 5000 (I by no means live by Desktop dyno...it's just in my price range) If I claculate it my combo is putting out 400hp, that's why im looking for the half a dozen little things I may have missed to try and speed my car up a bit.


Best this year has been a 7.33 at 92.5

Best on gas and a dual plane manifold was 7.30 last year



I'll post rpm drops Sunday. Right now I shift at 6200 and it just seems like it's goin dead before I get there, was thinking I might be dropping rpms after I shift to where it would hit after my torque curve.


Greg
"I always compare drag racing to lighting $100 bills on fire, only it's more expensive." - Craig W.

Check out my website...
http://www.findmoneyraces.com


'71 Nova E85
6.69 @ 100.2 MPH 9/6/14
1.4257 60'
1700' DA

13:1 439 BBC
3330 lbs

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Re: Determining shift point

#5 Post by John_Heard » Fri Sep 11, 2009 6:30 am

I wonder if that's a bit too loose of a converter for that engine. Typically if you can feel it lay over before the shift, it started to do it much earlier than that, so start testing lower RPM shift points. Maybe it doesn't actually stall that 6000 RPM. If that was the case it's only gaining a few hundred RPM before the shift.

Do you have anything that records the engine rpm down track?

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BracketNova
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Re: Determining shift point

#6 Post by BracketNova » Mon Sep 14, 2009 12:44 am

Rpm drop was 800. I found that my 5800 chip worked the best out of my 5400,5800,6000 that I have. I moved my launch to 5000, I could get to it just as easily as 4800 but I didn't really see any benefit on my time slip. Even when I shifted at 6200 I never really felt the car nose over, it just seems a little doggy after it shifts. I gained .01 or 2 from dropping my shift 200 but going from 6000 to 5400 lost me .03.

No, I don't have anything to record. Sadly, I realized the hard way this weekend I really need a weather station. Dialed a 7.36 broke out by .007 with a .006 on the tree. I go to draglist and "back do" my weather. Probably not the most accurate but... anyways a run I made friday night was within 50 adjusted feet of my breakout run, my car's et was .0009 different. Had I had a weather station I would have put a 35 on it and put together a .010 package :(
"I always compare drag racing to lighting $100 bills on fire, only it's more expensive." - Craig W.

Check out my website...
http://www.findmoneyraces.com


'71 Nova E85
6.69 @ 100.2 MPH 9/6/14
1.4257 60'
1700' DA

13:1 439 BBC
3330 lbs

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supernova
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Re: Determining shift point

#7 Post by supernova » Mon Sep 14, 2009 6:30 am

I agree with John on the converter being to big. Here's one reason why. A dual plain intake will only flow good to about 6500 rpm's and if your converter is 6000 that's only a 500 rpm difference if your converter stalls that high. Thats way over the tq curve of where you motor should be making good power. In this case I don't think bigger is better.

I have a Chevelle with a big block in it with a dual plain intake and a cam almost like your's (.610 lift) and man it pulls like a freight train at 3500 rpm's, dead at 6200 rpm's. It is a 4 speed and the shift point is 6000. I will dump the clucth at 3000 and floor it.

If it were me I would put a much lower stall converter in it and see what happens. Say a 3500 rpm stall.

My thoughts on the mater. :smt003
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Re: Determining shift point

#8 Post by John_Heard » Mon Sep 14, 2009 8:03 am

Sounds to me if it's laying over after the shift you're dropping below stall speed and it's being doggy trying to lock back up. I'd bet an RPM curve would show it flat lines on the lower rpm shift point. Maybe you can find someone that has a tighter converter you can try and see if it likes it. Dropping it 1000 rpm might be a big help.

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Re: Determining shift point

#9 Post by BracketNova » Wed Sep 16, 2009 10:15 pm

Yeah I could see that. When we sent the info into trans specialties we used the cam info it came with the motor. I bought the motor used from a guy who bought it in a ride...but then he sold the ride less motor. So I got a deal on a engine. Anywhoo, i bought a converter bases off what we thought it would run. The cam was way off to be running on motor alone. I decided to call doug herbert and see what they recommended after giving them the run down the guy said, "what's the catch?" Then went on to say that he was amazed that the car made it down the track. Unfortunately I'm passed my time period to get my stall moved, but I'm sure I can pay to have it changed. All my friends run dragsters or 8 second door cars, so I probably have the smallest converter.

I'm probably going to wait a bit on making converter changes. my 'lil 396 is showing 20 - 30 % leakage and I have 118cc combustion chamber heads. I'm on the fence...i'm going to at least re-reing it and have the heads milled down a bit (it there's room). But, I am somewhat tempted to throw some 12:1 pistons in it while I'm in there. But If I'm going to do that...why not build a 468?

Anyways, 'preciate the input fellas

Greg
"I always compare drag racing to lighting $100 bills on fire, only it's more expensive." - Craig W.

Check out my website...
http://www.findmoneyraces.com


'71 Nova E85
6.69 @ 100.2 MPH 9/6/14
1.4257 60'
1700' DA

13:1 439 BBC
3330 lbs

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BracketNova
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Re: Determining shift point

#10 Post by BracketNova » Wed Sep 16, 2009 10:21 pm

oh and I have a single plane manifold on it now. I also portmatched the runners to the heads.
"I always compare drag racing to lighting $100 bills on fire, only it's more expensive." - Craig W.

Check out my website...
http://www.findmoneyraces.com


'71 Nova E85
6.69 @ 100.2 MPH 9/6/14
1.4257 60'
1700' DA

13:1 439 BBC
3330 lbs

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Chevyfireball
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Re: Determining shift point

#11 Post by Chevyfireball » Sun Sep 20, 2009 7:08 am

With 8.5:1 compression I'd be chucking a blower on that thang.
'It Ain't Over Til It's NOVA'

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BracketNova
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Re: Determining shift point

#12 Post by BracketNova » Wed Sep 23, 2009 6:27 pm

If it is supplied, I would be more than happy to sit behind it 8-)
"I always compare drag racing to lighting $100 bills on fire, only it's more expensive." - Craig W.

Check out my website...
http://www.findmoneyraces.com


'71 Nova E85
6.69 @ 100.2 MPH 9/6/14
1.4257 60'
1700' DA

13:1 439 BBC
3330 lbs

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