[Stan Weiss]

Over the weekend a few of us were doing a little bench racing.

Making only a change to a lower gear ratio will
reduce convertor slippage
drop converter flash stall RPM

What has anyone else found from only making a gear ratio change?

Stan

[Formulajones]

I've played around with that for years and even moved converters from one car to another with different rear gears. Shucks dad went through 6 converters in a period of about 2 years along with a gear change in between.

Had a discussion with Kris about this (Continental Converters) back when he built one of the last converters for dad's car before he closed his doors. I was getting ready for a rear gear change at that point and he was adamant that I don't drop the rear gear below 3.55's (was running 3.73's at that point) because he simply could not build the converter tight enough with the current parts available at that time.

I ended up doing 3.42's and even that small change made the converter way too mushy on the street, and at the track it was marginal with very little rpm change on gear shifts. So that converter came out.

Took 4 more tries with 2 different converter companies to finally get a converter that would hold the engine properly, drive nice, and perform perfectly at the track.

I'm sure you already know the answer Stan, Yes rear gear plays a big roll in how the converter will act.

[chuckies76ta]

Originally Posted by Stan Weiss

Over the weekend a few of us were doing a little bench racing.

Making only a change to a lower gear ratio will
reduce convertor slippage
drop converter flash stall RPM

What has anyone else found from only making a gear ratio change?

Stan

Stan: Thanks for posting. I went from 3.73's to 4.11 but I can't remember the changes. Was back a couple of years ago. I do believe we lost MPH.
I always gets confused when people talk gears. When you say lower gear ratio, are you referring to a lower number? Ex: going from say 4.10 to 3.90 gear set
Thanks

[Stan Weiss]

Originally Posted by chuckies76ta

Stan: Thanks for posting. I went from 3.73's to 4.11 but I can't remember the changes. Was back a couple of years ago. I do believe we lost MPH.
I always gets confused when people talk gears. When you say lower gear ratio, are you referring to a lower number? Ex: going from say 4.10 to 3.90 gear set
Thanks

Going from 3.73:1 to 4.11:1 is going to a lower gear ratio. Was the gear ratio the only change made at that time?

Stan

[chuckies76ta]

Yes it was . I was running 28” tires at that time. I have since moved up to a 29” tires. Thanks

[chuckies76ta]

Another scenario for you Stan. I have been thinking about going from the 4.11 gear set to 3.90 gear set. Are you saying that the converter flash will change? It's flashing to 6000 rpm right now. Less torque multiplication with the 3.90 gear causes converter to flash less. Does that sound right?

Thanks again.

[srmmmm]

Originally Posted by Stan Weiss

Over the weekend a few of us were doing a little bench racing.

Making only a change to a lower gear ratio will
reduce convertor slippage
drop converter flash stall RPM

What has anyone else found from only making a gear ratio change?

Stan

You are correct. A lower gear ratio reduces the amount of torque the engine must supply to accelerate the car - there is more "effective" torque applied by the driveshaft. This means a lighter load on the output side of the converter relative to a given rate of acceleration allowing the converter to be more efficient. A big benefit is reduced fluid temperatures from less slippage in the converter.

[Formulajones]

Originally Posted by chuckies76ta

Another scenario for you Stan. I have been thinking about going from the 4.11 gear set to 3.90 gear set. Are you saying that the converter flash will change? It's flashing to 6000 rpm right now. Less torque multiplication with the 3.90 gear causes converter to flash less. Does that sound right?

Thanks again.

Dropping the rear gear will cause the converter to flash higher. In essence It's working the converter harder to get the car moving.
Although in your case that's such a small gear change the effect on the converter won't be that big.

[rohrt]

I have the continental Jim hand special in my car. I went from 3:36 to 3:08. I can't say I notice much slippage in normal driving. I don't really climb the RPMs as quickly when getting into it, but the lower RPMs at 60mph is extremely nice. Flash stall is hard to judge as the tires go up in smoke to easily.

[Formulajones]

You have to be on a good prepped surface (track) and/or also run a sticky tire to get a better idea where the actual flash rpm is.

You may also be able to lug it in 3rd gear really slow and mash the pedal to see where it flashes, IF the transmission doesn't downshift. That'll give you a close idea but the gear multiplication isn't the same which may skew the results. I find the track with a sticky tire and first gear launch is the most accurate way.

[PunchT37]

Timely thread. I was thinking of going from 3.55`s to 3.31`s or already avail 3.08`s with a Jim Hand converter.

[ta man]

I've ran the same convertor for almost 20 years behind 3 different 455 builds from 375 hp to 600 hp. and with 308's 342's and 373's. 10 inch Continental. The convertor was built originally for 3.42 gears and the old school 041 cam 455 engine in a 3800 lb car. It was a great setup felt tight and marginal slippage at the track. The engine progressed to a SD KRE 290 head engine with an OF cam..approx hp around 550.. This engine eventually wound up in another car with 308 gears and the same convertor. On the street it took a little more throttle to move but not extreme, at the track there was a higher slippage in drive but over all performance was good. Engine was upgraded to more head flow and an updated cam with a little more lift. Convertor felt the same. I swapped 373's in a few years back and the convertor felt much tighter on the street..less slippage up hills..at the track it resulted in pulling the front wheels a few inches..dropping the 60 foot times and also had less slippage out the back. Just my results with a well built convertor.

[slowbird]

Originally Posted by ta man

I've ran the same convertor for almost 20 years behind 3 different 455 builds from 375 hp to 600 hp. and with 308's 342's and 373's. 10 inch Continental. The convertor was built originally for 3.42 gears and the old school 041 cam 455 engine in a 3800 lb car. It was a great setup felt tight and marginal slippage at the track. The engine progressed to a SD KRE 290 head engine with an OF cam..approx hp around 550.. This engine eventually wound up in another car with 308 gears and the same convertor. On the street it took a little more throttle to move but not extreme, at the track there was a higher slippage in drive but over all performance was good. Engine was upgraded to more head flow and an updated cam with a little more lift. Convertor felt the same. I swapped 373's in a few years back and the convertor felt much tighter on the street..less slippage up hills..at the track it resulted in pulling the front wheels a few inches..dropping the 60 foot times and also had less slippage out the back. Just my results with a well built convertor.

Have you been out yet this year? Haven't seen any updates.

[slowbird]

All I'll say about this is have yet to see a gear change really make a big difference at the track. Most time people think it'll really effect things and usually it doesn't. It most definitely does effect how the converter feels/acts though

[chuckies76ta]

Originally Posted by Formulajones

Dropping the rear gear will cause the converter to flash higher. In essence It's working the converter harder to get the car moving.
Although in your case that's such a small gear change the effect on the converter won't be that big.

Thanks Larry.

[johnta1]

Might be interesting to add what transmission is being used along with the gear change?

[chuckies76ta]

I’m using a TH400

[ta man]

Originally Posted by slowbird

All I'll say about this is have yet to see a gear change really make a big difference at the track. Most time people think it'll really effect things and usually it doesn't. It most definitely does effect how the converter feels/acts though

For our big torque engines..that make good power over a wide range..no huge difference in et.

[ta man]

Originally Posted by slowbird

Have you been out yet this year? Haven't seen any updates.

Soon...been a busy year and the car has taken a back seat to life. My daughter was married this year so the focus was on her. I'm hoping to get out at least 3 or 4 times before the snow comes.

[Cliff R]

I've ran 3.23's, 3.42's and 3.73's. Even greater changes in effective gearing using tires from 26" to 30" tall, and did some back to back testing in that area a few years back. I saw very little difference anyplace with the same Continental "tight" 10" converter.

However, I also did some converter testing for Kris at Continental and saw HUGE differences with some of the prototypes he sent. I tested several higher stall versions of the Continental 10" unit and they responded quite differently than the original "tight" 10" unit. Matter of fact the really "loose" versions with much higher flash stall HATED the 3.42 gears and/or tall tires. WAY to long to "roll-out" with those converters compared to the "tight" 10" unit.

With the original 10" unit changing gears or shorter tires just "buzzed" the engine harder on top end and I saw little if any difference in either ET or MPH, which surprised me at the time. These big torque 455's just LOVE tight converters and well coupled above the stall speed.

Something else I noticed were shift points. All of my 455's using that same converter really didn't care where you shifted them. 5000rpm's, 5500, 5800rpms showed very little change in ET or MPH. So the engine is a big player here as well.

"Lock" a 400 based engine build down that hard with gearing, converters or tall tires and it's not going to be overly happy about it, especially one with higher compression, good head flow and cammed to make peak power at high RPM's.......