Need Advice...
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Instructor
Joined: Jul 2003
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From: Little Elm Tx
Need Advice...
I have a 71 coupe 3 speed auto. Bored .30 with mild cam edelbrock performer and holley 650 dominator. She is a little sluggish off of the line. Do you guys think it is because of the tranny? I wouldn't mind putting in either a four speed auto or even a four speed manual. Also this tranny in there only has 13,000 miles on it just like the motor. Do oyu think there is a way to trade for a four speed conversion? Just wondering if anyone has experienced slow off of the line with 3 speed auto. I cannot slam the pedal down and peel out from a stop. Once I am going I can put it back into 1 or 2 (if have enough speed) and it will beat Newer Z28's and mustangs, but from a stop I have no chance at all. Please let me know your thoughts on this.
Thanks :chevy
Thanks :chevy
Burning Brakes
Joined: Nov 2001
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Re: Need Advice... (Clown Puncher)
I can't help with tuning, but a 71 coupe should be light enough to light-em up on command - even with the base motor.
What is your RPM when launching? Have you considered some power braking to get the RPM's up to around 2500 or so before launching?
What is your RPM when launching? Have you considered some power braking to get the RPM's up to around 2500 or so before launching?
Race Director
Joined: Mar 2001
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From: Living in the Hartland
Re: Need Advice... (Clown Puncher)
By mild cam what do you mean as compared to stock? What is your rear gear? Stall rate and rear gear a big factors for launch with an auto car. Also check your timing, if you haven't already recurved your dist it might help.
Safety Car
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From: Paducah KY
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St. Jude Donor '03
Re: Need Advice... (Clown Puncher)
If you've got the motor, the TH400 has plenty of guts. My guess is if you're developing plenty of horsepower at the crank then what you really need is a torque converter with a higher stall speed. You also did not mention what your rear gear ratio is.
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From: Little Elm Tx
Re: Need Advice... (Rolling Thunder)
Now you will see how ignorant I really am... I do not know the gear ratio. I do know that the rear end is only about 10 thousand miles old though. The tranny was rebuilt, and not sure what the torque converter stall is either. This car has alot of power and at about 40 mph I can drop it down into two and tear it up< sometimes even lay a scratch, but off of the line it is very pokey. at idle in gear it is at around 650 rpm. The cam is a Comp cam, not sure wich model. Wish I could give you more info. Is there any way to find out what the gear ratio is? :cool:
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Joined: Mar 2001
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From: Living in the Hartland
Re: Need Advice... (Clown Puncher)
Jack up the rear tires off the ground and spin the tire 1 time while counting the number of times the drive shaft rotates. 3 times equals about a 3.08 gear, 3 1/4 times equal about 3.36, 3 1/2 times equals 3.55 etc. Sounds like you got a black box of parts combo. Form your desc of the power curve I suspect you have either have a bigger cam than you think or your timing adv is coming on late.
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From: Little Elm Tx
Re: Need Advice... (Clown Puncher)
So is the concensus either Torque Converter or Timing issue? I will check the gear ratio when I get home. I am still not sure what the symptoms should be for one of these specific problems.
Thanks :auto:
Thanks :auto:
Safety Car
Joined: Aug 2001
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From: Waterford Mi
Re: Need Advice... (Clown Puncher)
Have your distributor recurved by Lars. It is one cheap power increase. What rpm's are you seeing at 70mph? That will give a good indication of what gears you have.
Cam, torque convertor, rear gear, and tire size have to work together for the best performance.
Cam, torque convertor, rear gear, and tire size have to work together for the best performance.
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Intermediate
Joined: Oct 2003
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From: Seattle WA
Re: Need Advice... (Clown Puncher)
This is very tough to give you he right answer without the rear gears, tire size, stall converter and the big question cam profile, compression. You see, all these way in to the factor. I race a 12 sec 1968 Firebird and run ARCO gas as I have for 13 years with the same engine. If you have highway gears you need to keep the duration down and lobe seperation up at around 114 degs(it will give you a broader torque band) and duration at 200-210 degs but it also has alot to do with compression also.Throw the compression to 10-1 and put a 3500 stall in it and 3:73s and it would haul butt but then you rev everywhere. Next choice is " Big Block" if you want brute force without the revs. Hope this doesnt confuse you.
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Instructor
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From: Little Elm Tx
Re: Need Advice... (Clown Puncher)
Ok found out Gear ratio is 3.08. I am curious how to adjust the timing adv, or vac adv. This car has an Electrical MSD Distributor and Ignition system. No points? right? It has a little computer mounted under the side of the engine compartment that runs the system.
Race Director
Joined: Mar 2001
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From: Living in the Hartland
Re: Need Advice... (Clown Puncher)
http://msdignition.com/downld.htm
Does not have a download for the corvette tach drive one (8572) but you can follow thw the directions for the other chevy ones.
[Modified by Fevre, 4:28 PM 10/28/2003]
Does not have a download for the corvette tach drive one (8572) but you can follow thw the directions for the other chevy ones.
[Modified by Fevre, 4:28 PM 10/28/2003]
