automatic transmission push start

[DKrause615]

I'm looking for some help on deciding if I want to run mt three speed automatic again this year or switch to a manual transmission.

Last year,  my first trip to Bonneville we ran a c4 automatic.  Top speed 205mph should have been tacking 6800 rpm.  We had a 28" tire 1:1 through the tranny with a 2.75:1 gear.  I was tacking 7800 rpm.   1000 RPM slip is too much, so for this year I decided to eliminate the torque converter and run a direct shaft from the crank into the C4.  I am planning to start it in neutral, and then get pushed until maybe 50 or 60 mph and then drop it in first.  Now I am worried that this may not work.  I would like to run Jerico 4 speed but I hate to shell out the big $$$$$$$$.

Question is-------  Has anyone pushed started convertless automatics up with success?  

[SPARKY]

yep  the Ratical has run a PG with no converter  bbc chevy

[Tman]

Nathan Stewart told me they run a c4 w/o converter and do just as you are describing.

[bill78]

The procedure you described works perfectly. You don't have to get up to 50 or 60 mph. What we did was to just get the car moving, pull into 1st gear and put your foot in it. It's a 5 mile drag race.

[Elmo Rodge]

That's the setup I'll be running. C-4 no converter. Wayno

[John Burk]

Look at the c4 ratios and convert that to rpm drop and see how that looks .

[grumm441]

Wouldn't you just run a lock-up torque converter
G

[desotoman]

The car in my avatar, runs a TH350 Chevy without a converter. Never had a problem.  

Tom G.

[DKrause615]

Thanks to all the replys to my question.  Looks like this should work without a problem.   I'm gona run 'er.    Another concern for discussion, is there is a big rpm drop between shifts on a 3 speed.  the ratios are 2.46:1, 1.46:1, and 1:1.  Shifting at 8000 you drop way down to about 4500 and just lug the motor up to top speed.  In high it seems to take awhile.  I guess thats just land speed racing?

[hotrod]

Have you checked to see if you can get a locking torque converter, that locks up solid but gives torque multiplication at lower rpm.
Some of the newer cars do that to improve fuel mileage and the torque converter torque multiplication would help deal with those big ratio jumps on shifting.

Larry

[SPARKY]

The huge drop is the reason I run a Shorty Glide with a Gear Vendor, the last step is only 22% puts it right back in the power curve. 

One of the things I like best you can have the GV set up for LSR and  (FREEWHEELS if you blow UP which we have twice)  then with the C 4 you would have a 4 speed----you never have to lift either.

[panic]

Good point - the GV RPM drop is closer than (almost?) any automatic, which is what you need going into high gear.
Bad: $$$, short D-shaft.

[desotoman]

I don't know if they are available for the C4, but I have different than stock gear ratios in my transmission, so my RPM drop is not as bad. My transmission is also set up to freewheel, so when pushing off all the driver has to do is bring the RPM up until the trans engages and drives off the push truck.

Tom G.

[Rex Schimmer]

What motor are you running? If you have a pretty stout engine,i.e. lots of cu. inches, then the 3 speed should  be OK as you should be pretty close to your torque curve at 4500 which means it should pull top gear pretty well. Lots of gears and close ratios are really for engines with narrow power bans so that they will accelerate through the gears without lugging. If you have a dyno sheet for your engine and if you have a good estimate of what your cars top speed should be then you can back into what the horse power requirement would be when you shift from second to third and then looking at the rpm drop vs. the dyno curve and see if you have the hps to accelerate.

Example: Using your set up, C4 tranny, 28 inch tire, 2.75 rear gear. At 7000 in top gear your speed should be around 212 mph. At 8000 in second gear, assuming second ratio is 1.46 per your post, the speed would be 166 mph and if your max speed of 212 mph required 700 hps then the hp to run at 166 would be about 48% of the 700 (this is using the aero horse power requirement being a function of the cube of the speed) which is 336 hp. So if you motor is making over 336 hp at 5480 rpm (which is the rpm that the engine would be turning in top gear at 166 mph) you should be able to accelerate and with 5 miles to do it in you should be bumping your max speed way before the 4 mile.

Rex

[DKrause615]

Wow, lots of good "technical" information here  Thanks.  I'm on a budget so the overdrive is not going to happen.  Judging from the responses on push starting,  I'm going to run without a converter, get pushed off, drop it in gear, and drive away from the push truck. 

For those who wanted to know what I was running, it is a 2000 Mustang with a 342" small block.  We ran the C/FALT class last year, and ran 205.   I was happy with that.  The motor dynoed at just over 600 HP an 600 ft above sea level.  I had to lean it considerably to get it to run decent at Bonneville, so the actual HP would be much less.

I had a big conversation with Rick Gold at the fuel truck.  His advice was to try some nitromethane so this years moter will be a bit different.  I will run 358" small block ford.  An old NASCAR block and crank, new Crower rods and Mahle pistons.  My big expirment this year will be to run mechanical fuel injection and a Methonal Nitromethane blend.  It should make lots of power.  I understand that nitro likes to be lugged, so maybe the big split in gear ratios wont be so bad after all.

I JUST HOPE I CAN KEEP IT TOGETHER!!!!!!!!!!!!!!!!!!!!!