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Help with gear for consistency
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DRR Trophy
posted
I have a 68 Camaro I bought early this year turn key. It is a big tire car (14x31) with a 496bbc, glide and a 4.11 gear. The car was a grudge car with nitrous so it had the tall gear and tight converter. The guys at PTC set me up with a converter which helped a ton but I’m thinking of changing the gears to 4.88 or 4.56. The car pulls 1.45 60’ and runs 9.60s at 140 in the 1/4. My question is will lower gears be more consistent then staying with the tall gears? I’m not really concerned with speed, just consistency.
 
Posts: 32 | Location: Zachary | Registered: November 09, 2018Reply With QuoteReport This Post
DRR Trophy
Picture of 433red
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Your remark about not being concerned with speed is key. If you deal with hot tracks, a loose converter will be the answer regardless of gear choice. ***NOTE*** the selected gear/tire combination must be within the operating window the engine is designed to perform. My $.02
 
Posts: 102 | Location: Ga | Registered: July 28, 2007Reply With QuoteReport This Post
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Gasoline or Methanol?

Do you primarily run 1/8 or 1/4?

What is the RPM at the stripe 9.60 1/4 mile 140 mph?

Two or three speed transmission?
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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quote:
Originally posted by Mike Rietow:
Gasoline or Methanol?

Do you primarily run 1/8 or 1/4?

What is the RPM at the stripe 9.60 1/4 mile 140 mph?

Two or three speed transmission?


I run avgas and mostly 1/4. Rpm is about 6300. I normally shift at 7k. I run a glide with a 5500 8” converter
 
Posts: 32 | Location: Zachary | Registered: November 09, 2018Reply With QuoteReport This Post
DRR Pro
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^^^^^^^^^ jmho, but I believe your convertor stall is too tight by 500 - 600 rpm
 
Posts: 2421 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
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quote:
Originally posted by Fatboy81:
quote:
Originally posted by Mike Rietow:
Gasoline or Methanol?

Do you primarily run 1/8 or 1/4?

What is the RPM at the stripe 9.60 1/4 mile 140 mph?

Two or three speed transmission?


I run avgas and mostly 1/4. Rpm is about 6300. I normally shift at 7k. I run a glide with a 5500 8” converter


10 4, I raced on Avgas in 1996. It worked great, nothing wrong with it.

I figured the converter slip based on the info provided using an equation. It would give us an idea of one, the converter efficiency currently and two, what rpm the car would cross the finish line if you were to do a 4.88. I'm not going to be able to be of help because it is impossible for it to cross now at 6300 at 140 mph with a 4.11 gear. Are you sure it's a 4.11?

Here's what I have maybe I have the info provided wrong

4.11
31.5
6300
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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Picture of Curly1
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Couple of thoughts here. A 4.11 less likely to spin at the hit and therefore more consistent. (Use converter to get it in powerband and keep it there)With a 4.88 your tires and suspension must be working good or you will have issues worse than you do now. But you may be a little faster depending on cam etc.

A loose converter will be more forgiving at the hit and if you miss shift point any.

I did not see where you said what converter is stalling at now or what RPM you are shifting at?

From limited information we have hard to make a good recommendation but I think I would probably go with a lot more stall first.


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Posts: 3950 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post



DRR Sportsman
Picture of Bad News
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Everybody has a 5500 converter.....
Most do not know what the actual or flash stall is.
Add a camera to the interior and aim it at the tach, it will tell you a lot. Poor mans data recorder.
 
Posts: 868 | Location: ft laud | Registered: September 02, 2004Reply With QuoteReport This Post
DRR Pro
Picture of rusty
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5.56 gears,need to be around 7400 in 1/4.6400 stall


honesty is the best policy,insanity is a better deffense
1.036, 6.16@ 224

 
Posts: 1389 | Location: texas | Registered: February 17, 2006Reply With QuoteReport This Post
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posted Hide Post
quote:
Originally posted by Mike Rietow:
quote:
Originally posted by Fatboy81:
quote:
Originally posted by Mike Rietow:
Gasoline or Methanol?

Do you primarily run 1/8 or 1/4?

What is the RPM at the stripe 9.60 1/4 mile 140 mph?

Two or three speed transmission?


I run avgas and mostly 1/4. Rpm is about 6300. I normally shift at 7k. I run a glide with a 5500 8” converter


10 4, I raced on Avgas in 1996. It worked great, nothing wrong with it.

I figured the converter slip based on the info provided using an equation. It would give us an idea of one, the converter efficiency currently and two, what rpm the car would cross the finish line if you were to do a 4.88. I'm not going to be able to be of help because it is impossible for it to cross now at 6300 at 140 mph with a 4.11 gear. Are you sure it's a 4.11?

Here's what I have maybe I have the info provided wrong

4.11
31.5
6300


Mike I could be off with the rpm crossing. I’ve only made a few passes with it and it’s a lot faster then any car I have crossing around 140. It spoils me at that speed So I just glanced up at the tack.
 
Posts: 32 | Location: Zachary | Registered: November 09, 2018Reply With QuoteReport This Post
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posted Hide Post
quote:
Originally posted by Curly1:
Couple of thoughts here. A 4.11 less likely to spin at the hit and therefore more consistent. (Use converter to get it in powerband and keep it there)With a 4.88 your tires and suspension must be working good or you will have issues worse than you do now. But you may be a little faster depending on cam etc.

A loose converter will be more forgiving at the hit and if you miss shift point any.

I did not see where you said what converter is stalling at now or what RPM you are shifting at?

From limited information we have hard to make a good recommendation but I think I would probably go with a lot more stall first.


The converter is an 8” from PTC. I say it’s a 5500+- because I pulled the chip out of my 2step and held the transbrake. When I floored it it when to 5500

I shift the car at 7000
 
Posts: 32 | Location: Zachary | Registered: November 09, 2018Reply With QuoteReport This Post
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posted Hide Post
quote:
Originally posted by Fatboy81:
quote:
Originally posted by Mike Rietow:
quote:
Originally posted by Fatboy81:
quote:
Originally posted by Mike Rietow:
Gasoline or Methanol?

Do you primarily run 1/8 or 1/4?

What is the RPM at the stripe 9.60 1/4 mile 140 mph?

Two or three speed transmission?


I run avgas and mostly 1/4. Rpm is about 6300. I normally shift at 7k. I run a glide with a 5500 8” converter


10 4, I raced on Avgas in 1996. It worked great, nothing wrong with it.

I figured the converter slip based on the info provided using an equation. It would give us an idea of one, the converter efficiency currently and two, what rpm the car would cross the finish line if you were to do a 4.88. I'm not going to be able to be of help because it is impossible for it to cross now at 6300 at 140 mph with a 4.11 gear. Are you sure it's a 4.11?

Here's what I have maybe I have the info provided wrong

4.11
31.5
6300


Mike I could be off with the rpm crossing. I’ve only made a few passes with it and it’s a lot faster then any car I have crossing around 140. It spoils me at that speed So I just glanced up at the tack.


10 4 no problem. I'd do a 4.56 gear, it'll be a better choice bracket racing in that you'll be crossing 7100 7200 rpm in comparison to 7500 7600 with a 4.88.

If the converter is 5500 observed stall you might wanna shift it a couple hundred rpm lower for consistency or loosen it, a hair as has been mentioned. God luck
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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[/QUOTE]

If the converter is 5500 observed stall you might wanna shift it a couple hundred rpm lower for consistency or loosen it, a hair as has been mentioned. God luck[/QUOTE]

Thank you so much mr Mike. Can you explain this part a little more just so I understand the concept?
 
Posts: 32 | Location: Zachary | Registered: November 09, 2018Reply With QuoteReport This Post
<DOTracer>
posted
Be prepared to loosen the converter after putting more gear in as it will naturally want to tighten up due to less load.
 
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DRR Pro
Picture of Alaskaracer
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When bracket racing, a loose converter will yield best results with regards to consistency....and you can have a loose converter that has good top end lock up to help keep rpms reasonable these days. They can do pretty crazy stuff with the inner workings now, so don't let a loose converter scare you, there's way more to it than just stall....


Mark Goulette
Owner/Driver of the Livin' The Dream Racing dragster
www.livinthedreamracing.com
"Speed kills but it's better than going slow!"
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Posts: 1464 | Location: Back home in Alaska! | Registered: February 13, 2011Reply With QuoteReport This Post
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quote:
Originally posted by Fatboy81:




Thank you so much mr Mike. Can you explain this part a little more just so I understand the concept?[/QUOTE]

You might consider experimenting with shift point for consistency. If you shift 7,000 rpm it'll drop back 1,500 rpm to your observed stall 5,500. If you shift 6,700 it'll drop back 1,200 rpm to 5,500 rpm observed stall.

Your observed stall won't change no matter what gear you run in it however the converter will get more efficient going from the 4.11 to the 4.56 and further efficient 4.56 to 4.88. Your converter efficiency looks real good though according to the math, with the 4.88 landing efficiency around 5-6% at the stripe and 7-8% 4.56. However, the car definitely needs more gear. Fairly light car I presume to be 2600-2700lbs. It just depends how hard you wanna spin the engine. The 4.56 or 4.88 will work fine for consistency.

This message has been edited. Last edited by: Mike Rietow,
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
DRR Sportsman
Picture of rs72z
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quote:
Originally posted by markemark:
^^^^^^^^^ jmho, but I believe your convertor stall is too tight by 500 - 600 rpm


This!!! Looser converter will be more consistent and faster by a .10 as well.
 
Posts: 206 | Location: texas | Registered: November 13, 2008Reply With QuoteReport This Post
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I tend to agree to an extent but from the info we have so far, the OP I presume according to the math, is working with a fairly light 2600-2700lb doorslammer with a mild BBC on gasoline. It definitely needs gear. If it were on methanol I'd definitely suggest a looser converter first, as the highest priority for consistency.
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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quote:
Originally posted by DOTracer:
Be prepared to loosen the converter after putting more gear in as it will naturally want to tighten up due to less load.


I agree with what DOTracer wrote.

Consider first installing the gear ratio you decided on. Then, after installing, figure out where the convertor is stalling during the run. Then decide if or where you want to change it to.

If you do not have a playback tach and are presently using analog MSD ignition (6al / 7al), consider purchasing a MSD Grid 7730 that will plug directly into these ignitions. Grid can do much in ignition control, but it also has Data Acquisition of what it controls built in. This can be very helpful in deciding what to do now and in the future.

Showing a graph of what the convertor is doing to a transmission shop can help them determine what changes need to be made internally.

Also, it has been my experience that a difference in weather conditions can change where the convertor is stalling by up to 150 rpm.

MSD Grid 7730 now on sale to the end of the year at Jegs for under $400 with promo code if a racing member of their site.
 
Posts: 2421 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
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posted Hide Post
quote:
Originally posted by markemark:
quote:
Originally posted by DOTracer:
Be prepared to loosen the converter after putting more gear in as it will naturally want to tighten up due to less load.


I agree with what DOTracer wrote.

Consider first installing the gear ratio you decided on. Then, after installing, figure out where the convertor is stalling during the run. Then decide if or where you want to change it to.

If you do not have a playback tach and are presently using analog MSD ignition (6al / 7al), consider purchasing a MSD Grid 7730 that will plug directly into these ignitions. Grid can do much in ignition control, but it also has Data Acquisition of what it controls built in. This can be very helpful in deciding what to do now and in the future.

Showing a graph of what the convertor is doing to a transmission shop can help them determine what changes need to be made internally.

Also, it has been my experience that a difference in weather conditions can change where the convertor is stalling by up to 150 rpm.

MSD Grid 7730 now on sale to the end of the year at Jegs for under $400 with promo code if a racing member of their site.


The only thing that can change stall is power, not in theory but in fact. Keep in mind the OP is 1/4 racing, the fact his converter will be more efficient with less slip going from a 4.11 to a 4.56 or 4.88 is what allows for the change, according to finish line RPM limits.
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
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