gear ratio

The only resentment I have for clutch guys is that's all there was going fast when we started running a blown converter car 10 yrs ago.LOL. We applied clutch tuning techniques and our program was a joke.
If it rattled and had low wheelspeed they would say throw more power at it. Guess what? It rattled harder. When I see shake regardless of wheelspeed I pull a little timing and it has worked well so far.I know there are national level guys that throw really aggressive wheelspeeds and maybe can go to the other side of the curve but I wonder how big that tuning window is.
For the guy starting out it's a lot simpler just to back into the tuneup soft and go from there.

 

You're absolutely right.. Can't ever listen to clutch guys when running a converter. lol. You get torque multiplication from the converter and have to run a calmer gear generally where a clutch guy can go kamikaze with gear in comparison to achieve the same torque multiplication. That's part of the problem. Clutch guy throws more at it, usually because the wheel speed is slow early, even taking off @ 7k. Converter guys knock the tire off leaving over 5500. But unless the motor is weak(or roots blown), you won't see a clutch car with a ton of gear leaving at 7k either.

 

When you say gear do you mean first gear ratio or rear gear??? ADRL performance has made gear ratios very important in the last few years. The screw blowers need big rpm through the traps so they run a 5 something in the rear. The first gear is selected by what the engine can pull and have some tuning window(on a converter car anyway).I think the latest theory is to run a tall first gear 2spd so it will stay in low a LOOONG time and multiply torque. It also has minimal rpm drop at the shift.
The big variable is conv slip. They were locked up tight but I think they are moving toward looser even through the traps so you can't tell what the ratio really is...see Lowmad passes.

 

I was referring to rear gear. I think I hear this deal the most from bracket or people that are relatively new to racing. Usually it's some guy with a 4.10 gear and wants to go to a 4.88 for the 1/8th. For those deals I guess I just don't grasp what they think they will accomplish, particularly if the track is the normal local condition, etc.

 

More about ratios

There sure is a lot of good info in this thread, so maybe I can add my $.02 worth and not sound like I am completely in left field.
We run an altered very similar to the one in question except the heads are "off the shelf" Brodix 2x's, and we have a conventional 14-71 at 20% over.
It has run a best of 6.55 @ 209MPH with a 1.02 60" time, but it generally lives from 1.03 to 1.05 in the 60" and the mid 6.60's.
It is very consistent and we have never seen over 20 pounds of boost.
The car weighs 2180# on the starting line.
We also are running a slightly smaller tire (16 X 32.5 X 15)
I agree with the guys that are saying keep the converter multiplying torque and try to stay above the 7.0 mark in total gear multiplication. You have to consider the torque converter able to multiply torque at somewhere between 2:1 and 3:1 depending on how aggressive the fin angles and stator are. If you do that, the math starts to look a lot like the clutch cars who are actually reducing applied torque by slipping their clutch.
By the way since this is a thread on gear ratio ...(wait for it)
we are running a 1.80 glide with a 3.40:1 ring and pinion.
We did not start there, but we learned that the only number that suffered was the 60" time and the 60 to 330 progression always improved with each change, and the total ET did not slow down.
The car became WAY more consistent and drivable, and when the track goes away we are still OK (most of the time).
For what it's worth.

 

what sort of g meter reading would you say was high enough to not get weak shake

is this what your calling the top of first gear shake when the clutch get together with the motor?

thanks

Graham

 

More questions on gear ratio

Kendrick,

What size of converter (actual stall speed and size) do you use? I have thought about this combination and actually purchased a set of 3:50 (currently run 4:10) gears but have never tried the combination. My car is similar (altered with 1:80 low) except my weight is 1950lbs ready to race. The only way I could see this combination not suffering ET is to have a fairly high stall speed.

Dave

 

We have a few converters that we use, but the current one is an FTC 101 which is a 10 inch torque converter that stalls about 6500 to 6800 depending on timing and weather. It slips about 10% in the traps (1/4 mi) but we have run converters that slipped anywhere from 22% to 4% and there was NO gain in ET or MPH from that, but it did make the tach read different.
Where this came from is watching the fast guys with clutches as they made more power they used less gear and slipped the clutch more. It also seemed strange that my 11 second 3500 lb. street car from 20 years ago could possibly require the same gear as a six second altered or dragster.

 

Thanks for the info,

Dave

 

Do you converter guys look for the same number .5 in to the run as us clutch guys?

 

We watch .10,.25 and .50 shaft speeds. Everybody throws numbers around to try to figure out how the car is getting up on the tire. Our old heavy car always ran slower shaft speeds and the sidewalls looked like they were close to shake but it would go downtrack all the time. I've seen cars with a lot of shaftspeed have nice round tires and a really nice blacktrack but they couldn't repeat so I assume the window was small.

We have a lighter car now and everything in the combo is different. We're testing saturday on a slick track and my theorys may prove wrong.
One of the biggest things I see with converter cars is nobody wants to take power away from a racing engine.Almost nobody will back into a tuneup and have the car look like a turd. It takes patience but we spent 7 months building the car and i'm willing to kill a weekend and know what I have with a methodical approach vs. swinging for the fences and risking hurt stuff and useless data.

 

Something different?

Since we are on the gear ratio topic here is my dillema. Front engine dragster, 505 ci BBC on 70% nitro, injected not blown, PG, 4200 stall, 3.50 gears, 33 x 12 Hoosiers and leaving off the foot brake. at 6lbs it shakes then goes up in smoke so I tried another pound or two to try to increase wheel speed and it just instantly smokes the tires. Next step I am going to try is a retard to 28 degrees at the hit and ramp back to 42 just before the shift. Any other ideas?

 

Hey Nitro Mas
Not sure about injected nitro....but your P/G probably has a 1.80 low gear and the rear gear is 3.50 = 6.30 overall 1st gear ratio....most of the fuel funny cars and altereds (blown) use a 3.70 rear and real soft 1st gear (18%) for an overall 1st gear of 4.36....so the 1.80 is probably too much gear for the injected nitro with a torque converter driven car...
I always wondered if you could run a converter driven blown or injected nitro car in high gear only.....would a P/G, lencodrive or Bruno hold the torque leaving in high gear only? This is actually a question for a transmission expert on this forum....

 

I have thought about leaving in high gear but worry about all the heat from slippage damaging the clutches. Also thought about going direct drive but didnt want to hassle with a clutch. I agree with you that I may need to change gears.

 

We were having awful launch problems a few years ago with too much 1st gear....(1.80 low with 4.30 rear). Frank Parks (Neil & Parks Racing) was at KC and pitted next to us....his advice was to leave in 2nd gear....first 2 runs were violent tire shake and the 2nd 2 runs leaving in 2nd gear were both 6.40 @ 217 straight as a string...we have a Lencodrive 3 speed and now run it as a 2 speed...1.44 first with 4.10 rear

 

Nitro Mas: My buddy has a injected nitro FED also, his is SBC powered and running high % of nitro. He also has a powerglide with 1.80 first gear, and had problems with tire spin, shake, etc. He started out with 3.90 gears, and has been steadily lowering the gear ratio, down to the 2.91's he's running now. With each decrease in ratio, the car has gone quicker and faster, and the shake and spin has gone away. He also had the converter tightened up. He's running a lots of fuel and lots of timing too. I guess the conclusion is that "Nitro likes a load"!