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  Question about shift points with C4 tranny.

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Author Topic:   Question about shift points with C4 tranny.
70coupe
Gearhead

Posts: 459
From: Toronto,Ontario,Canada
Registered: Aug 2000

posted 05-11-2003 10:28 PM     Click Here to See the Profile for 70coupe     Edit/Delete Message   Reply w/Quote
Most C4's I believe are 2.46,1.46 then 1:1 ratio's. So that means if I shift at 6200 my rpm with go down to about 3700 then back to 6200 then during my second shift down to 4300. When drag racing to get optimum 1/4 mile times I should be shifting at different rpms from 1st to 2nd and 2nd to 3rd due to the different ratios in the tranny? I currently have my shift light set at 6200 which is where I shift for both gear changes. Is there a special tach you can buy for the light to come on at different rpms for each shift or how do you serious racers dot it? Is there some time to be saved here? If you want to hit your highest torque 600 rpm can make a difference.

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scottford351
Journeyman

Posts: 90
From: reedsville ohio usa
Registered: May 2003

posted 05-12-2003 12:38 AM     Click Here to See the Profile for scottford351   Click Here to Email scottford351     Edit/Delete Message   Reply w/Quote
you could use a rpm switch to activate a second shift light. I shift mine at 2 different rpms too, the 1-2 I use the light the 2-3 I have to watch the tach.

------------------
91 LX 398w street/bracket 6.88 1/8 60FT 1.44

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70coupe
Gearhead

Posts: 459
From: Toronto,Ontario,Canada
Registered: Aug 2000

posted 05-12-2003 12:42 AM     Click Here to See the Profile for 70coupe     Edit/Delete Message   Reply w/Quote
Are you running a C4?
If so, what are your shift points?
I just want to see the difference in your shift rpm's.

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scottford351
Journeyman

Posts: 90
From: reedsville ohio usa
Registered: May 2003

posted 05-12-2003 01:04 AM     Click Here to See the Profile for scottford351   Click Here to Email scottford351     Edit/Delete Message   Reply w/Quote
yea I use a c4 I shift at 5400 into 2 and 6000 into high and cross the line at 6000

------------------
91 LX 398w street/bracket 6.88 1/8 60FT 1.44

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scottford351
Journeyman

Posts: 90
From: reedsville ohio usa
Registered: May 2003

posted 05-13-2003 01:32 AM     Click Here to See the Profile for scottford351   Click Here to Email scottford351     Edit/Delete Message   Reply w/Quote
Summit has a tach with a 4 stage shift light,and its cheap (SIT DOWN) $569.00. makes ya wanna by a extra one for a spare.

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steve'66
Gearhead

Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000

posted 05-13-2003 09:20 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
You have a high stall converter don't you? If your converter stalls at 4000 your engine will never see less than that through the pass. If your shift drops to 3500 then the converter will be multiplying torque at 4000 until the car's speed catches up. Known as letting the converter "eat". It's ok and it should help et. Shift just over your peak h.p. and go thru the traps even higher. We shift at 6000 (although the actual rpm 1-2 is more like 6400, and 6200 for the 2-3 shift) and go thru the traps at 6600+. The converter stalls at 4500, so who cares whether it drops under 4500 on a shift, since the converter will keep the rpms at 4500 minimum.

SteveW

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70coupe
Gearhead

Posts: 459
From: Toronto,Ontario,Canada
Registered: Aug 2000

posted 05-13-2003 11:32 PM     Click Here to See the Profile for 70coupe     Edit/Delete Message   Reply w/Quote
My convertor stalls at 4700. I currently shift at 6200 in both gears. I talked to Crane cams and they said I should be shifting at 6500 with my set up. I guess I will have to try both shift points. Someone said shift early from 1st and later out of 2nd. I go through the traps at 6600 as well.

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steve'66
Gearhead

Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000

posted 05-14-2003 12:14 AM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Yes,

Shift at 6500 and let the converter do its job.

SteveW

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