Starting line ratio too steep?

casrak7 · 06-14-2020, 11:26 PM

Have a 2990 lb raced weight car on a 28x10.5. I want to run the car 1/8 mile. It's a 360 cube small Chevy. It makes 621 hp at 7300. It makes 483 ft lbs at 6000. It has an A1 6300 converter and a well built th350 currently. Right now it has a 4.30 gear and is not optimal for either the quarter or eighth. But I want to cross the eighth around 8000 rpm in high. I can buy a 5.71 gear which should put me right about there, assuming 5 percent converter slippage or so. The starting line ratio will be steep with the 3 speed auto. (2.52 first). Is this doable in your experience? Starting line ratio will be 14.39.......

Adger Smith · 06-14-2020, 11:42 PM

When you go over geared the converter will act tighter. That may be the downfall instead of too much ratio.
Why do you want to cross the 1/8 at 8,000 RPM with an engine that make peak power 700 RPM below that?
I would think something in the 7500 range might work, but I don't see your dyno sheets like you..
5.40 ish Maybe?.= 1360

casrak7 · 06-15-2020, 12:07 AM

Well..... At least in the quarter mile, according to Larry Meaux, every single three speed auto record that he has ever seen that was data logged......... The shifts occurred 300-500 after peak power, and they crossed the stripe 800-1000 past peak power........ That's quarter mile. And those are his words exactly. I assumed he had seen alot of data logs to make that statement.

Stan Weiss · 06-15-2020, 12:24 AM

Like Adger said watch how the convertor behavior changes

I know this is the reverse of what you are doing.

I know some people who are setup and race 1/8. Once a year there is a big 1/4 mile race and they change to a higher rear gear ratio and the increase in convertor slip on the top end is very noticeable.

Stan

Adger Smith · 06-15-2020, 01:08 AM

Quote: Well..... At least in the quarter mile, according to Larry Meaux, every single three speed auto record that he has ever seen that was data logged......... The shifts occurred 300-500 after peak power, and they crossed the stripe 800-1000 past peak power........ That's quarter mile. And those are his words exactly. I assumed he had seen alot of data logs to make that statement.
I know I've seen a lot of data in my cars and customer cars and Larry and I have been around a while. If your engine falls off on power like a rock dropping of a cliff after the 7300 it will slow you down going to 8,000.
I'm no rookie or keyboard guy, just trying to pass on some info and help.
If Larry is your Hero PM me and I will give you his cell #. You can get all the information instead of part of it.

casrak7 · 06-15-2020, 01:27 AM

I'm certain your right..... And im certain the power hangs on quite well with this engine. The heads and induction are outstanding on this engine. Far more than what it needs to be honest. I have a couple numbers for him actually. And he explained the gearing as such......It should cross the line with it's tongue hanging out because there is far more et found in the front two thirds of the track than the last third. I just wondered if hooking a 14-1 starting line ratio was going to be too difficult

Stan Weiss · 06-15-2020, 01:46 AM

Quote:

Originally Posted by casrak7

I'm certain your right..... And im certain the power hangs on quite well with this engine. The heads and induction are outstanding on this engine. Far more than what it needs to be honest. I have a couple numbers for him actually. And he explained the gearing as such......It should cross the line with it's tongue hanging out because there is far more et found in the front two thirds of the track than the last third. I just wondered if hooking a 14-1 starting line ratio was going to be too difficult

If that is the case then it is time to get a higher ratio gear set for the trans.

Stan

Jeff Stout · 06-15-2020, 09:31 AM

I run a 28x10.5 tire 400 sbc at 600hp. I went from 4.30 to 4.88 and run 400t trans. No problem on prepped track. The rpm curve when releasing trans brake looks very nice. The dip is very little to none. Now when I race no prep this set up won't work. I run a 4 link car and double adjustable all the way around and can not get it to leave decent. To much SLR. I have tried second gear leave but with a 6100 converter it just drives through it. If my math is right 2.48 first and 4.30 gear is the same as 2.20 first and 4.88 gear. So maybe first gear change would help the SLR.

Jeff Stout · 06-15-2020, 09:41 AM

My 2.48 and 4.30 was 10.66 SLR. If you did 2.10 and 5.71 that 11.99SLR. It would be better then your 2.52 1st but still might not enough for no prep. If your running prepped track disregard.

gfbdiesel · 06-16-2020, 03:11 PM

what kind of 60 ft are you looking for??

06-14-2020, 11:26 PM	#1
casrak7 Junior Member Join Date: Jul 2011 Posts: 63 Likes: 0 Liked 3 Times in 2 Posts	Starting line ratio too steep? Have a 2990 lb raced weight car on a 28x10.5. I want to run the car 1/8 mile. It's a 360 cube small Chevy. It makes 621 hp at 7300. It makes 483 ft lbs at 6000. It has an A1 6300 converter and a well built th350 currently. Right now it has a 4.30 gear and is not optimal for either the quarter or eighth. But I want to cross the eighth around 8000 rpm in high. I can buy a 5.71 gear which should put me right about there, assuming 5 percent converter slippage or so. The starting line ratio will be steep with the 3 speed auto. (2.52 first). Is this doable in your experience? Starting line ratio will be 14.39.......

06-14-2020, 11:42 PM	#2
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,348 Likes: 433 Liked 676 Times in 260 Posts	Re: Starting line ratio too steep? When you go over geared the converter will act tighter. That may be the downfall instead of too much ratio. Why do you want to cross the 1/8 at 8,000 RPM with an engine that make peak power 700 RPM below that? I would think something in the 7500 range might work, but I don't see your dyno sheets like you.. 5.40 ish Maybe?.= 1360 __________________ Adger Smith (Former SS)

06-15-2020, 12:07 AM	#3
casrak7 Junior Member Join Date: Jul 2011 Posts: 63 Likes: 0 Liked 3 Times in 2 Posts	Re: Starting line ratio too steep? Well..... At least in the quarter mile, according to Larry Meaux, every single three speed auto record that he has ever seen that was data logged......... The shifts occurred 300-500 after peak power, and they crossed the stripe 800-1000 past peak power........ That's quarter mile. And those are his words exactly. I assumed he had seen alot of data logs to make that statement.

06-15-2020, 12:24 AM	#4
Stan Weiss Senior Member Join Date: Apr 2020 Location: Phila, PA Posts: 606 Likes: 0 Liked 545 Times in 291 Posts	Re: Starting line ratio too steep? Like Adger said watch how the convertor behavior changes I know this is the reverse of what you are doing. I know some people who are setup and race 1/8. Once a year there is a big 1/4 mile race and they change to a higher rear gear ratio and the increase in convertor slip on the top end is very noticeable. Stan

06-15-2020, 01:08 AM	#5
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,348 Likes: 433 Liked 676 Times in 260 Posts	Re: Starting line ratio too steep? Quote: Well..... At least in the quarter mile, according to Larry Meaux, every single three speed auto record that he has ever seen that was data logged......... The shifts occurred 300-500 after peak power, and they crossed the stripe 800-1000 past peak power........ That's quarter mile. And those are his words exactly. I assumed he had seen alot of data logs to make that statement. I know I've seen a lot of data in my cars and customer cars and Larry and I have been around a while. If your engine falls off on power like a rock dropping of a cliff after the 7300 it will slow you down going to 8,000. I'm no rookie or keyboard guy, just trying to pass on some info and help. If Larry is your Hero PM me and I will give you his cell #. You can get all the information instead of part of it. __________________ Adger Smith (Former SS)

06-15-2020, 01:27 AM	#6
casrak7 Junior Member Join Date: Jul 2011 Posts: 63 Likes: 0 Liked 3 Times in 2 Posts	Re: Starting line ratio too steep? I'm certain your right..... And im certain the power hangs on quite well with this engine. The heads and induction are outstanding on this engine. Far more than what it needs to be honest. I have a couple numbers for him actually. And he explained the gearing as such......It should cross the line with it's tongue hanging out because there is far more et found in the front two thirds of the track than the last third. I just wondered if hooking a 14-1 starting line ratio was going to be too difficult

06-15-2020, 09:31 AM	#8
Jeff Stout VIP Member Join Date: Dec 2001 Location: phoenix Posts: 1,407 Likes: 53 Liked 654 Times in 254 Posts	Re: Starting line ratio too steep? I run a 28x10.5 tire 400 sbc at 600hp. I went from 4.30 to 4.88 and run 400t trans. No problem on prepped track. The rpm curve when releasing trans brake looks very nice. The dip is very little to none. Now when I race no prep this set up won't work. I run a 4 link car and double adjustable all the way around and can not get it to leave decent. To much SLR. I have tried second gear leave but with a 6100 converter it just drives through it. If my math is right 2.48 first and 4.30 gear is the same as 2.20 first and 4.88 gear. So maybe first gear change would help the SLR.

06-15-2020, 09:41 AM	#9
Jeff Stout VIP Member Join Date: Dec 2001 Location: phoenix Posts: 1,407 Likes: 53 Liked 654 Times in 254 Posts	Re: Starting line ratio too steep? My 2.48 and 4.30 was 10.66 SLR. If you did 2.10 and 5.71 that 11.99SLR. It would be better then your 2.52 1st but still might not enough for no prep. If your running prepped track disregard.

06-16-2020, 03:11 PM	#10
gfbdiesel Junior Member Join Date: Oct 2019 Posts: 10 Likes: 0 Liked 2 Times in 2 Posts	Re: Starting line ratio too steep? what kind of 60 ft are you looking for??