slow launch coming from transmission?

willtow

Daily Driver
Jul 9, 2012
29
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0
ive put together a little 79 malibu for 1/8th mile foot brake bracket racing below i will post all details on car....i have had it to the track 2 weekends in a row the car has done good overall but is lacking in the launch/60ft areas.

details-
car weighs approx. 33-3400? full body/interior racing buckets/deleted heater/ac box/removed inner bumper structure
350 .40 over
11.1 compression
aluminum 58cc 210int. runner heads
488/507 lift hyd. flat tappet cam adv.duration .288/.297
1.6 crane full roller rocker arms
performer rpm air gap intake
650cfm double pumper no power valve jetted 76 square
msd billet hei dizzy timing totalled at 37 degrees
powerglide trans w/manual valve body
3800 converter will hold on footbrake at 2500rpm and flashes around 3600rpm
4.56 gears spool with 28/10.0/15 slicks
90/10 shocks on front 50/50 on rear
so far after approx 12 passes the best et was 8.10/60ft 1.78/84.24mph with a most average pass of 8.16/60ft 1.79/83.30mph ihad a lil larger converter in the car first few passes and it ran 8.15/60ft 1.76/83.06mph this converter was a 4000 but wasnt working properly ....it seems to me the car is doing fairly good on topend but the launch is very weak and 60fts are slow compaired to other similar cars i run with ive got a couple that are running almost the same gear /converter running 1.58-1.64 60fts running high 7s in the 1/8th but these cars are running 350th and 400th trannys it seems there is a big debate over 350th/powerglide in bracket cars some are telling me my car is way to heavy for glide and others say i wont see no difference i do know there is a huge low gear difference from my 1.82 glide to the 350th but some say the glide will pick the lost time up from the higher gear mid track when your only making 1 shift instead of 2,,,,from what friends watching the car are saying the car does nothing when coming out of the hole it doesnt seem to me as it starts pulling good until it gets moving im stuck thinking myself its either transmission or fuel/carb issue? .it seems every body keeps going back to transmision ......i know this car has more in it just looking for insight on what others think open to all opinions......
 
A Powerglide is the wrong choice for your combination. With the Powerglide installed your combination is lacking sufficient torque multiplication at the starting to generate effective 60' times. You simply do not have enough starting line gear ratio to launch the car quickly. Your effective starting line ratio with the Powerglide is 8.2992:1. Your effective starting line ratio with a TH350 would be 11.4192:1. You have a good combination of parts, but the Powerglide is holding you back. A TH350 will bolt right in place of a Powerglide, and if your current torque converter is set up for a turbo spline (30 spline) then it will swap from your Powerglide to a TH350. Your combination could benefit from a purpose-built torque converter also, but the TH350 swap is going to really bring the combination together. I would expect 60' times in the low-to-mid 1.50 range with a TH350 installed in your car.
 

willtow

Daily Driver
Thread starter
Jul 9, 2012
29
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0
Pete@Hughes said:
A Powerglide is the wrong choice for your combination. With the Powerglide installed your combination is lacking sufficient torque multiplication at the starting to generate effective 60' times. You simply do not have enough starting line gear ratio to launch the car quickly. Your effective starting line ratio with the Powerglide is 8.2992:1. Your effective starting line ratio with a TH350 would be 11.4192:1. You have a good combination of parts, but the Powerglide is holding you back. A TH350 will bolt right in place of a Powerglide, and if your current torque converter is set up for a turbo spline (30 spline) then it will swap from your Powerglide to a TH350. Your combination could benefit from a purpose-built torque converter also, but the TH350 swap is going to really bring the combination together. I would expect 60' times in the low-to-mid 1.50 range with a TH350 installed in your car.


thank you for the info thats what i was looking for my glide is setup with turbo shaft already so converter will not be a problem as a matter of fact i just sent my good converter in to get rebuilt to the specs of my car and combo.hope to have it back next week and then i am planning on putting the 350th in the car ....my next question is i know the ratio of the 350 is going to greatly help get my car off the line will i see a negitive result on top end mph because of the extra shift? thanks again for your help
 
You should not experience a loss of MPH through the traps once the TH350 is installed. Worst case scenario the MPH will remain similar, but you should actually net an improvement. You're accelerating the car faster earlier on the track. You will also experience less RPM drop on each gear change which will allow the engine to spend more time in it's effective powerband and continue to accelerate the car rather than struggle to recover RPM on the gear change as the engine is doing now with the Powerglide. All of this is going to help contribute to improved torque converter efficiency and improved acceleration throughout the entire run.

A few suggestions on the rest of your combination:

1.) Your engine should respond favorably to a 1" open carb spacer and a 1/2" 4-hole spacer stacked on top of the open spacer. This combination of spacers will provide a bigger pressure drop below the throttle blades of the carburetor. The larger pressure drop will initiate more aggressive fuel flow from the main circuit in the carburetor. This should allow you to pull some jet out and pick up some power as well as clean up the fuel curve in general, especially since you're not running a power valve. You could step up to a 750 main body at that point and find additional power without sacrificing low-speed torque production.

2.) I would lock out the mechanical advance if you haven't already. Running total timing all the time should improve low-speed response, and will also help contribute to improved consistency on each pass.

3.) A 58CC combustion chamber shouldn't need 37 degrees of timing if it's a decent chamber design. 32 - 34 degrees should be ideal. You may want to try a hotter plug and less timing... the car may pick up a bit. I suggest an Autolite 3924 or Champion RC12YC if your heads accept a .750" reach 14MM spark plug with a gasket.

4.) Put a 6AL-2, Digital 6, or Programmable 6 MSD igntion box in the car. That way you can have a low-speed rev limiter for staging the car. This will help improve consistency from pass to pass. As you know, consistency is king in bracket racing. Also, the extra spark energy certainly won't hurt.

5.) Put a rear sway bar on the car or an air bag in the passenger rear spring if you haven't already. With the extra starting line torque multiplication provided by the TH350 your car is probably going to start twisting on the launch.

6.) You may want to experiment with a 275/60-15 drag radial tire such as the new Gen II M/T or Hoosier. The radial tire has a stiffer sidewall which will contribute to faster reaction and possibly help improve your 60-foot time. Drag radial tires also have significantly better stability down track, less rolling resistance, and make the car much easier to drive at high speed.
 

willtow

Daily Driver
Thread starter
Jul 9, 2012
29
0
0
Pete@Hughes said:
You should not experience a loss of MPH through the traps once the TH350 is installed. Worst case scenario the MPH will remain similar, but you should actually net an improvement. You're accelerating the car faster earlier on the track. You will also experience less RPM drop on each gear change which will allow the engine to spend more time in it's effective powerband and continue to accelerate the car rather than struggle to recover RPM on the gear change as the engine is doing now with the Powerglide. All of this is going to help contribute to improved torque converter efficiency and improved acceleration throughout the entire run.

A few suggestions on the rest of your combination:

1.) Your engine should respond favorably to a 1" open carb spacer and a 1/2" 4-hole spacer stacked on top of the open spacer. This combination of spacers will provide a bigger pressure drop below the throttle blades of the carburetor. The larger pressure drop will initiate more aggressive fuel flow from the main circuit in the carburetor. This should allow you to pull some jet out and pick up some power as well as clean up the fuel curve in general, especially since you're not running a power valve. You could step up to a 750 main body at that point and find additional power without sacrificing low-speed torque production.

2.) I would lock out the mechanical advance if you haven't already. Running total timing all the time should improve low-speed response, and will also help contribute to improved consistency on each pass.

3.) A 58CC combustion chamber shouldn't need 37 degrees of timing if it's a decent chamber design. 32 - 34 degrees should be ideal. You may want to try a hotter plug and less timing... the car may pick up a bit. I suggest an Autolite 3924 or Champion RC12YC if your heads accept a .750" reach 14MM spark plug with a gasket.

4.) Put a 6AL-2, Digital 6, or Programmable 6 MSD igntion box in the car. That way you can have a low-speed rev limiter for staging the car. This will help improve consistency from pass to pass. As you know, consistency is king in bracket racing. Also, the extra spark energy certainly won't hurt.

5.) Put a rear sway bar on the car or an air bag in the passenger rear spring if you haven't already. With the extra starting line torque multiplication provided by the TH350 your car is probably going to start twisting on the launch.

6.) You may want to experiment with a 275/60-15 drag radial tire such as the new Gen II M/T or Hoosier. The radial tire has a stiffer sidewall which will contribute to faster reaction and possibly help improve your 60-foot time. Drag radial tires also have significantly better stability down track, less rolling resistance, and make the car much easier to drive at high speed.

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in response to your recommendations -

1. i just installed a 1 inch open phenolic carb spacer a couple of days ago let me see if i get any improvement with it and i might go ahead with your recommendation of stacking a 1/2 4 hole on top of it (if hood clearence inst a a issue i havent go my big hood yet)

2.mechanical advance hasnt been locked totally out i removed and locked out the vacuum advance and am running lightest springs in advance i might consider locking it out i almost did when putting it all together...

3.ive run timing at 34-40 degrees with good fuel so far 36-37 seems to be what it likes still tuning it in though.and im running a auto light 3924 plug ...

4.ive already got digital box here just havent put it on yet....

5.already have a 7/8 sway bar on the rear with a set of 50/50 shocks and iceman adjustable upper arms

6.ive got a set of 26 tall tires i my try after transmission is swapped

i talked with my converter builder this morning the converter is gonna be set-up to go 3000 on foot brake without pushing to bad and flash stall around 4200 that what he is recommending for the car/drivetrain combo

pete thanks again for your insight on this
 

willtow

Daily Driver
Thread starter
Jul 9, 2012
29
0
0
Pete@Hughes said:
The new converter sounds like it should be right on the money for your combination.
i got the 350th trans and converter put in last weekend but didnt make it to the track i did make it last night though the first pass was not what i was expecting ran a 8.44 with 1.78-60ft at 78.9 mph made two passes identical to this my refreshened converter isnt doing what its supposed to its foot braking at a max of 2300rpm before it starts to push the brakes and is flashing at 3400-3600 from what i could tell....
(the converter in my first post was a jegs/bm convertor i used while i sent my good converter in to get freshened up and tuned to my car it was going 2800-3000 on footbrake at launch and flashing just under 4000 but wsnt working right ) the converter was supposed to be close to same as it was with just a little more stall .......after those 2 passes i got to thinking and looking for answers as to what slowed the car down so much when i expected to see i big pickup over what it had been doing i found 1 problem i guess putting dist. cap back on the distributor got moved i checked the timing which is locked out it was at 26 degrees i pulled it back up to 36 degrees and made another pass the 60fts dropped to 1.72 ran 8.10 at 80mph that was the last pass i got to make still tryin to figure out what is going on the car should have 7.80s times in it no problem but i cant get it there the only thing im concerned about of what ive done is the converter i hate to do it but im thinking of sticking the jegs converter back in it........
 

barnym17

Dragway Regular
Jan 6, 2008
858
0
0
ohio
I was in your boat last year running low 8's with a similar combo swapped the glide for a th 350 60 was quicker et was the same.Mph dropped by about 2. Plus the car was harder to hook up. Did the same swap in a buddy's camaro at 3600lbs was running 7.20 to 7.30 with glide picked up to 7.0's.
 

lilbowtie

Pro Stocker
Oct 5, 2004
1,736
0
0
Canton Mi.
Willtow
I have to agree wirh others that the glide isn't helping the 60 ft's. Your 210 runner heads aren't helping your bottom end either and if you have your power valve blocked you need to jet up to account for it.
On the other hand its a bracket car the soft bottom will keep you consistant and less prone to traction issues.
 

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