Variation on Stop

66chevron · 08-04-2014, 07:37 PM

Our car is experiencing significant variation in the early part of the track while on the stop. Off the stop performance is fine and repeatable. 3000#, 468 BBC, 1.76 glide, 5400 spragless converter, inline stop one way only air, hard linkage, 9.40's wide open. Not shifting on the stop as the car weight/HP didn't like that. Have varied on/off times, shocks, tire pressure, RPM, rebuilt the entire throttle linkage. Also ran a converter with a sprag earlier in the season, similar variation. Left yesterday at 4000, on at .001, off at 3.00. 60' times were 1.77 and 1.82. Similar results leaving at 4800 and on at 0.15 (to flash the converter), .02-.05 60' variation. This is not a new combination or new car, been stop racing for most of the last dozen years. Almost like the car will not coast the same twice in a row.

I have purposely not mentioned any manufacturers as everyone I have talked to has been helpful and I will not indict any of their equipment.

Appreciate any advice cuz we are stumped.

Don Higgins · 08-04-2014, 10:06 PM

Can you borrow someone else's carb to test? I keep one in the trailer as a backup and let people borrow it if they have similar problems.

Only have a few choices. Carb, converter, suspension are most common problem when you go through this issue.

Tom Goldman · 08-04-2014, 11:16 PM

One thing often overlooked when a car is inconsistent on the stop is front end toe and rear axle being square in the chassis.
If toe is excessive or the rear axle is even slightly crooked, the car will roll differently as the track conditions change during the day, i.e. , slower 60' after the track has been sprayed or dragged and faster 60's when the track has been run in.
Does your car have motor plates or stock mounts ? either way don't overlook chassis flex or engine limiter problems.

C and W Racing · 08-05-2014, 08:09 AM

When is the last time you cleaned your air bleeds in the carb? I make a habit of cleaning them every race because of chasing a simular problem
Chuck

66chevron · 08-07-2014, 08:11 AM

Thanks to everyone for the ideas. Checked front end alignment and chassis squareness last night, have some work to do there. Will also go through the carburetor as I do not have a spare to use, and pay special attention to the air bleeds. Also have a spare torque converter and an under the carb stop to try in case those things do not work.

Our next outing will be the US131 divisional, will let you know what happens.

66chevron · 08-25-2014, 06:38 AM

Raced the US131 divisional, by chance pitted next to Don Higgins so I got the benefit of some live advice. Somewhere between a front end alignment, squaring the chassis, going through the carburetor and installing an under the carb stop the car was much better. 60' times repeated and with a little tuning on the shiftpoint the car was competitive. Thanks again for all of the advice.

08-04-2014, 07:37 PM	#1
66chevron Junior Member Join Date: Mar 2005 Posts: 13 Likes: 1 Liked 0 Times in 0 Posts	Variation on Stop Our car is experiencing significant variation in the early part of the track while on the stop. Off the stop performance is fine and repeatable. 3000#, 468 BBC, 1.76 glide, 5400 spragless converter, inline stop one way only air, hard linkage, 9.40's wide open. Not shifting on the stop as the car weight/HP didn't like that. Have varied on/off times, shocks, tire pressure, RPM, rebuilt the entire throttle linkage. Also ran a converter with a sprag earlier in the season, similar variation. Left yesterday at 4000, on at .001, off at 3.00. 60' times were 1.77 and 1.82. Similar results leaving at 4800 and on at 0.15 (to flash the converter), .02-.05 60' variation. This is not a new combination or new car, been stop racing for most of the last dozen years. Almost like the car will not coast the same twice in a row. I have purposely not mentioned any manufacturers as everyone I have talked to has been helpful and I will not indict any of their equipment. Appreciate any advice cuz we are stumped.

08-04-2014, 10:06 PM	#2
Don Higgins Junior Member Join Date: Jul 2007 Location: mapleton, IL Posts: 47 Likes: 0 Liked 0 Times in 0 Posts	Re: Variation on Stop Can you borrow someone else's carb to test? I keep one in the trailer as a backup and let people borrow it if they have similar problems. Only have a few choices. Carb, converter, suspension are most common problem when you go through this issue. __________________ Don Higgins - Super Comp #360H

08-04-2014, 11:16 PM	#3
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,468 Likes: 873 Liked 838 Times in 232 Posts	Re: Variation on Stop One thing often overlooked when a car is inconsistent on the stop is front end toe and rear axle being square in the chassis. If toe is excessive or the rear axle is even slightly crooked, the car will roll differently as the track conditions change during the day, i.e. , slower 60' after the track has been sprayed or dragged and faster 60's when the track has been run in. Does your car have motor plates or stock mounts ? either way don't overlook chassis flex or engine limiter problems. __________________ Tom Goldman 1500 SG , 1506 STK

08-05-2014, 08:09 AM	#4
C and W Racing Senior Member Join Date: Jul 2007 Posts: 557 Likes: 6 Liked 13 Times in 3 Posts	Re: Variation on Stop When is the last time you cleaned your air bleeds in the carb? I make a habit of cleaning them every race because of chasing a simular problem Chuck

08-07-2014, 08:11 AM	#5
66chevron Junior Member Join Date: Mar 2005 Posts: 13 Likes: 1 Liked 0 Times in 0 Posts	Re: Variation on Stop Thanks to everyone for the ideas. Checked front end alignment and chassis squareness last night, have some work to do there. Will also go through the carburetor as I do not have a spare to use, and pay special attention to the air bleeds. Also have a spare torque converter and an under the carb stop to try in case those things do not work. Our next outing will be the US131 divisional, will let you know what happens.

08-25-2014, 06:38 AM	#6
66chevron Junior Member Join Date: Mar 2005 Posts: 13 Likes: 1 Liked 0 Times in 0 Posts	Re: Variation on Stop Raced the US131 divisional, by chance pitted next to Don Higgins so I got the benefit of some live advice. Somewhere between a front end alignment, squaring the chassis, going through the carburetor and installing an under the carb stop the car was much better. 60' times repeated and with a little tuning on the shiftpoint the car was competitive. Thanks again for all of the advice.