Average RPM slippage on a conv

ken robinson · 03-26-2017, 02:58 PM

Whats the average rule of conv. slippage = in RPM +/- ? I'm trying to see what the top end RPM is with different rear gear ratio's .... RPM x tire dia. / by MPH X 336 = ring & pinion ratio . That formula dosen't account for conv. slippage , and is giving me the wrong gear ratios ....The car goes thru at 6750 x 28 tire / average 115 mph x 336 = 4:85 gear . But thats not true because it runs a 4:30 not a 4:85 . What would it go though with 4
:56 like 7150 rpm in average air ? My math / formula is wrong or I'm missing some thing .

ss3011 · 03-26-2017, 03:53 PM

Also if you have bias ply slicks you get some tire growth . Radials not so much .

GTX JOHN · 03-26-2017, 07:03 PM

Hard to put a number on slippage from this little info.....Converters vary
greatly. MY best advise is just trial and error if you do
not have a Data Monitoring System to fall back on.

S/ST 3040 · 03-26-2017, 08:01 PM

Quote:

Originally Posted by ken robinson

Whats the average rule of conv. slippage = in RPM +/- ? I'm trying to see what the top end RPM is with different rear gear ratio's .... RPM x tire dia. / by MPH X 336 = ring & pinion ratio . That formula dosen't account for conv. slippage , and is giving me the wrong gear ratios ....The car goes thru at 6750 x 28 tire / average 115 mph x 336 = 4:85 gear . But thats not true because it runs a 4:30 not a 4:85 . What would it go though with 4
:56 like 7150 rpm in average air ? My math / formula is wrong or I'm missing some thing .

115 x 4.30 x 336 / 28 = 5934 RPM (drive shaft RPM)

5934 x 100 = 593400 / 6750 = 87.9% (or 12.09% slippage)

115 x 4.56 x 336 / 28 = 6293 (drive shaft RPM)

6290 / .879 = 7159 RPM

The 4.56 gear should let the converter show better efficiency but, no way of knowing
exactly how much. Like was already stated, tire growth will affect the final number.

Dyno · 04-11-2017, 10:27 PM

5% slippage is a good number to shoot for.

jaf2021 · 04-14-2017, 06:38 PM

What if your % is 112?

Dyno · 04-14-2017, 09:39 PM

you are slipping 12 %

jaf2021 · 04-15-2017, 09:10 AM

Converter too loose????
I would have to double check but I think there is about a 1200 RPM drop between gear change(PG)

Mark Yacavone · 04-15-2017, 12:24 PM

Ken, Ever try a 4.10 with that converter?

ken robinson · 04-16-2017, 11:55 AM

I have not tried the 410 gear yet . I need to try the lower 1st gear before I try the 410 . Its a low rpm torque combo mainly so I see your point Mark . Thanks

03-26-2017, 02:58 PM	#1
ken robinson Member Join Date: Dec 2001 Location: tomsriver nj Posts: 441 Likes: 37 Liked 164 Times in 69 Posts	Average RPM slippage on a conv Whats the average rule of conv. slippage = in RPM +/- ? I'm trying to see what the top end RPM is with different rear gear ratio's .... RPM x tire dia. / by MPH X 336 = ring & pinion ratio . That formula dosen't account for conv. slippage , and is giving me the wrong gear ratios ....The car goes thru at 6750 x 28 tire / average 115 mph x 336 = 4:85 gear . But thats not true because it runs a 4:30 not a 4:85 . What would it go though with 4 :56 like 7150 rpm in average air ? My math / formula is wrong or I'm missing some thing .

03-26-2017, 03:53 PM	#2
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 885 Likes: 63 Liked 221 Times in 102 Posts	Re: Average RPM slippage on a conv Also if you have bias ply slicks you get some tire growth . Radials not so much .

03-26-2017, 07:03 PM	#3
GTX JOHN VIP Member Join Date: Jun 2009 Location: Boulder City, Nevada 89005 Posts: 2,530 Likes: 2,222 Liked 1,808 Times in 572 Posts	Re: Average RPM slippage on a conv Hard to put a number on slippage from this little info.....Converters vary greatly. MY best advise is just trial and error if you do not have a Data Monitoring System to fall back on. __________________ John Irving 741 Stock 741 Super Stock

04-11-2017, 10:27 PM	#5
Dyno Senior Member Join Date: Dec 2002 Posts: 870 Likes: 918 Liked 605 Times in 177 Posts	Re: Average RPM slippage on a conv 5% slippage is a good number to shoot for.

04-14-2017, 06:38 PM	#6
jaf2021 Member Join Date: Oct 2004 Location: selmer,tn Posts: 110 Likes: 13 Liked 5 Times in 5 Posts	Re: Average RPM slippage on a conv What if your % is 112?

04-14-2017, 09:39 PM	#7
Dyno Senior Member Join Date: Dec 2002 Posts: 870 Likes: 918 Liked 605 Times in 177 Posts	Re: Average RPM slippage on a conv you are slipping 12 %

04-15-2017, 09:10 AM	#8
jaf2021 Member Join Date: Oct 2004 Location: selmer,tn Posts: 110 Likes: 13 Liked 5 Times in 5 Posts	Re: Average RPM slippage on a conv Converter too loose???? I would have to double check but I think there is about a 1200 RPM drop between gear change(PG) Last edited by jaf2021; 04-15-2017 at 09:14 AM.

04-15-2017, 12:24 PM	#9
Mark Yacavone Veteran Member Join Date: Mar 2002 Location: Miles From Nowhere Posts: 7,414 Likes: 2,581 Liked 4,447 Times in 1,693 Posts	Re: Average RPM slippage on a conv Ken, Ever try a 4.10 with that converter? __________________ We are lucky we don't get as much Government as we pay for..... Will Rogers

04-16-2017, 11:55 AM	#10
ken robinson Member Join Date: Dec 2001 Location: tomsriver nj Posts: 441 Likes: 37 Liked 164 Times in 69 Posts	Re: Average RPM slippage on a conv I have not tried the 410 gear yet . I need to try the lower 1st gear before I try the 410 . Its a low rpm torque combo mainly so I see your point Mark . Thanks