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#1
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Convertor Slippage and Rear Gear Ratio Change
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
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Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#2
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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. |
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#3
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Quote:
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
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68 Firebird. IA2 block, 505 cu in, SD Performance E-head, Solid roller 3600 weight. Reid TH400 4:11 gear. 29" slick. Best so far 9.95@134 mph. 1.43 60 ft. 76 Trans am, TKX .81 o/d, 3.73 Moser rearend, 468 with KRE D-ports, Doug headers, 3" Exh. |
#4
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Quote:
Stan
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Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#5
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Yes it was . I was running 28” tires at that time. I have since moved up to a 29” tires. Thanks
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68 Firebird. IA2 block, 505 cu in, SD Performance E-head, Solid roller 3600 weight. Reid TH400 4:11 gear. 29" slick. Best so far 9.95@134 mph. 1.43 60 ft. 76 Trans am, TKX .81 o/d, 3.73 Moser rearend, 468 with KRE D-ports, Doug headers, 3" Exh. |
#6
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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.
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68 Firebird. IA2 block, 505 cu in, SD Performance E-head, Solid roller 3600 weight. Reid TH400 4:11 gear. 29" slick. Best so far 9.95@134 mph. 1.43 60 ft. 76 Trans am, TKX .81 o/d, 3.73 Moser rearend, 468 with KRE D-ports, Doug headers, 3" Exh. |
#7
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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.
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#8
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Quote:
Although in your case that's such a small gear change the effect on the converter won't be that big. |
#9
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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.
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#10
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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. |
#11
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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.
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#12
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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.
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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
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#13
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Quote:
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#14
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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
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#15
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Quote:
Thanks Larry.
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68 Firebird. IA2 block, 505 cu in, SD Performance E-head, Solid roller 3600 weight. Reid TH400 4:11 gear. 29" slick. Best so far 9.95@134 mph. 1.43 60 ft. 76 Trans am, TKX .81 o/d, 3.73 Moser rearend, 468 with KRE D-ports, Doug headers, 3" Exh. |
#16
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Might be interesting to add what transmission is being used along with the gear change?
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John Wallace - johnta1 Pontiac Power RULES !!! www.wallaceracing.com Winner of Top Class at Pontiac Nationals, 2004 Cordova Winner of Quick 16 At Ames 2004 Pontiac Tripower Nats KRE's MR-1 - 1st 5 second Pontiac block ever! "Every man has a right to his own opinion, but no man has a right to be wrong in his facts." "People demand freedom of speech to make up for the freedom of thought which they avoid." – Socrates |
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#17
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I’m using a TH400
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68 Firebird. IA2 block, 505 cu in, SD Performance E-head, Solid roller 3600 weight. Reid TH400 4:11 gear. 29" slick. Best so far 9.95@134 mph. 1.43 60 ft. 76 Trans am, TKX .81 o/d, 3.73 Moser rearend, 468 with KRE D-ports, Doug headers, 3" Exh. |
#18
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For our big torque engines..that make good power over a wide range..no huge difference in et.
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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
#19
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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.
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466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
#20
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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.......
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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