Is my Final drive ratio too low in my car?

dfree383 wrote:biggest thing to get right is going to be the convertor.

I said in the first post the converter is correct, just talking gear here.

Very interesting I have wondered this many times!

So how much will tire size change these final drive ratios?

Stock c-6 first gear ratio is 2.46 1st 1.46 second 1.1 third 2.46 x 4.30 is a 10.57 final drive.
stock power glide is 1.76 1st and 1.1 drive 1.76 x 4.30 is 7.568 final drive.
2.46 x 3.08 is 7.578 final drive.

whitefield wrote: So how much will tire size change these final drive ratios?

Stock c-6 first gear ratio is 2.46 1st 1.46 second 1.1 third 2.46 x 4.30 is a 10.57 final drive.
stock power glide is 1.76 1st and 1.1 drive 1.76 x 4.30 is 7.568 final drive.
2.46 x 3.08 is 7.578 final drive.

Tire dia 28 inches divided by 336 x rpm divided by final drive ratio = mph

(tire dia.) / (multiplier) x (rpm) / (final drive ratio) = (mph)
32 / 336 = .096 x 7000 = 672 / 7.578 = 88 mph

What about cam design and the width of the power band?

The narrow power band would need more gears and a wide band could use fewer gear changes. The big CID engines would "typicaly" have a wider power band wouldn't it?

My buddy's altered ran a 400 with a C6 and he forgot to pull it into 1st, left in second. The 1/4 et was almost identical.

Bill

billandlori wrote:What about cam design and the width of the power band?

The narrow power band would need more gears and a wide band could use fewer gear changes. The big CID engines would "typicaly" have a wider power band wouldn't it?

My buddy's altered ran a 400 with a C6 and he forgot to pull it into 1st, left in second. The 1/4 et was almost identical.

Bill

Been there done that................ Exactly

How much is lost on a gear change? I know there isn't much time involved but the engine (air flow) has to catch back up with the RPM drop.

Bill

i went from a c4/4.86 gear to a 1.76 glide/4.86 gear and didnt get any et or mph.with the glide i can leave on the brake without getten on the bumper so now i have some chance of goen faster.it'll depend on how it's used more than anything.i footbraked the c4 deal and 1.26 60',t/b with the glide at 3800-4200 and 1.26 60',so with a 3000-3500lb car i'm all for the 3 speed IMO.

IDT-572 wrote:

dfree383 wrote:OK so put a 3:00-3.50 in the car and use 1st and 2nd in the 1/8 and 3rd for the 1/4 mile?????

That's what I would do............

A good example is Coon's car ( I don't think he would mind me talking about it). He wants to drive it on the street some. But not lose anything at the track. It's going to have a c/4 (it's light and a 466 cid) with a stock first gear set and a 3.25 or 3.55 rear gear with 28x10.5 tires. Run it like a glide on the track and have third for the highway.

First speeb in a glide with a 5.43 rear gear is about the same as a C6 first speed with a 4.00 rear gear using the standard first speed gear set. It's all just math as Blake pointed out earlier so, 2nd speed with a 4.00 rear gear is about 5.84 using a C6.
A 3.90 rear gear would probably work "half way decent" with a C6 in the eighth and quarter mile tracks.

IDT-572 wrote:

rmcomprandy wrote:At 115 miles per hour, given a 32 inch diameter tire would put a 5.67 gear at about 7,100 RPM - a 5.43 gear about 6,850 RPM.

That would give you a 15.42 first gear FD. Like a 1.76 glide car with a 8.76 rear gear. I think that would be a tad to low.

Blake, I know of a certain iron headed NHRA Super Stock Mustang weighing 3,300 pounds, (and you do too), which has just under 800 horsepower and that car runs a standard ratio C4 along with a 5.43, (sometimes a 5.67), rear gear and he has NO problems hooking it with 101" radial slicks so, I would venture to say - "you need to work on the car" and get it right.

That trans with a high ratio first gear has no buisiness in a car with a big block Ford engine.

rmcomprandy wrote:

IDT-572 wrote:

rmcomprandy wrote:At 115 miles per hour, given a 32 inch diameter tire would put a 5.67 gear at about 7,100 RPM - a 5.43 gear about 6,850 RPM.

That would give you a 15.42 first gear FD. Like a 1.76 glide car with a 8.76 rear gear. I think that would be a tad to low.

Blake, I know of a certain iron headed NHRA Super Stock Mustang weighing 3,300 pounds, (and you do too), which has just under 800 horsepower and that car runs a standard ratio C4 along with a 5.43, (sometimes a 5.67), rear gear and he has NO problems hooking it with 101" radial slicks so, I would venture to say - "you need to work on the car" and get it right.

That trans with a high ratio first gear has no business in a car with a big block Ford engine.

I agree Randy.............. But also point out that he shifts on the north side of 8000 rpm and dose not have 750 ft lb torque at 5000 rpm and also runs mainly 1/4 mile deals , and a 3.59 stroke.

I haven't heard from Colin in a while, I wonder how he is doing this year?

Also it just seems odd now that when we talk about a little engine it's usually a 514 or a 521............

IDT-572 wrote:

rmcomprandy wrote:

IDT-572 wrote:

rmcomprandy wrote:At 115 miles per hour, given a 32 inch diameter tire would put a 5.67 gear at about 7,100 RPM - a 5.43 gear about 6,850 RPM.

That would give you a 15.42 first gear FD. Like a 1.76 glide car with a 8.76 rear gear. I think that would be a tad to low.

Blake, I know of a certain iron headed NHRA Super Stock Mustang weighing 3,300 pounds, (and you do too), which has just under 800 horsepower and that car runs a standard ratio C4 along with a 5.43, (sometimes a 5.67), rear gear and he has NO problems hooking it with 101" radial slicks so, I would venture to say - "you need to work on the car" and get it right.

That trans with a high ratio first gear has no business in a car with a big block Ford engine.

I agree Randy.............. But also point out that he shifts on the north side of 8000 rpm and dose not have 750 ft lb torque at 5000 rpm and also runs mainly 1/4 mile deals , and a 3.59 stroke.

I haven't heard from Colin in a while, I wonder how he is doing this year?

Also it just seems odd now that when we talk about a little engine it's usually a 514 or a 521............

That's just the bracket race guys talkin' ... the "Class Racer" guys are still talkin' about the 429's and 460's however, there are a lot less of them.

I think Colin's racing the STOCK 2010 CJ Mustang this year but, I'm not sure.

Just to clarify, that 429 engine in his '05 Mustang does make around 700 lb/ft of torque at about 5,500 RPM though.
And, (for those non believers we have talked about), he runs closer to 9,000 RPM "out the back door" with iron heads and Steel valves.
It's all about MAINTAINANCE and keeping it right.

A 3.25 gear with a 2.46 first gear fd is 7.995 1.46 second gear fd is 4.745 and 1.1 third 3.575 fd 3spd trans.
A 4.30 gear with a 1.76 first gear fd is 7.568 and drive 1.1 fd is 4.73 2spd trans.

Doing the math on this it looks like it would accelerate or launch the same and run the same e.t. and mph with the three speed. It also looks like to me that you wouldn't have to turn the engine as many rpm as the 2spd, and that the three spd would take more advantage of the torque.

whitefield wrote:A 3.25 gear with a 2.46 first gear fd is 7.995 1.46 second gear fd is 4.745 and 1.1 third 3.575 fd 3spd trans.
A 4.30 gear with a 1.76 first gear fd is 7.568 and drive 1.1 fd is 4.73 2spd trans.

Doing the math on this it looks like it would accelerate or launch the same and run the same e.t. and mph with the three speed. It also looks like to me that you wouldn't have to turn the engine as many rpm as the 2spd, and that the three spd would take more advantage of the torque.

You just turned your 3 speed into a 2 speed, it will never get into third through the 1/8th. And third in a 3speed would have a 3.25 FD.

Other than that you are correct. Perfect example of Coon's deal.

rmcomprandy wrote:

IDT-572 wrote:

rmcomprandy wrote:

IDT-572 wrote:

rmcomprandy wrote:At 115 miles per hour, given a 32 inch diameter tire would put a 5.67 gear at about 7,100 RPM - a 5.43 gear about 6,850 RPM.

That would give you a 15.42 first gear FD. Like a 1.76 glide car with a 8.76 rear gear. I think that would be a tad to low.

Blake, I know of a certain iron headed NHRA Super Stock Mustang weighing 3,300 pounds, (and you do too), which has just under 800 horsepower and that car runs a standard ratio C4 along with a 5.43, (sometimes a 5.67), rear gear and he has NO problems hooking it with 101" radial slicks so, I would venture to say - "you need to work on the car" and get it right.

That trans with a high ratio first gear has no business in a car with a big block Ford engine.

I agree Randy.............. But also point out that he shifts on the north side of 8000 rpm and dose not have 750 ft lb torque at 5000 rpm and also runs mainly 1/4 mile deals , and a 3.59 stroke.

I haven't heard from Colin in a while, I wonder how he is doing this year?

Also it just seems odd now that when we talk about a little engine it's usually a 514 or a 521............

That's just the bracket race guys talkin' ... the "Class Racer" guys are still talkin' about the 429's and 460's however, there are a lot less of them.

I think Colin's racing the STOCK 2010 CJ Mustang this year but, I'm not sure.

Just to clarify, that 429 engine in his '05 Mustang does make around 700 lb/ft of torque at about 5,500 RPM though.
And, (for those non believers we have talked about), he runs closer to 9,000 RPM "out the back door" with iron heads and Steel valves.
It's all about MAINTAINANCE and keeping it right.

Randy,

Colins car is a good example where a 3 speed transmission is better suited : 1/4 mile and high rpm shift points. He needs the low rear gear to get his engine in it's( Happy Place)................

Blake check me on this 1.1 x 3.25 =3.575 That is what I came up with!1.0 x 3.25 = 3.25. Blake you are right in the 1/8th mile you wouldn't be in third gear, but 1/4 mile would be good. I think it would also go back to how many rpm you want to turn wheather or not you get in to third. The converter ,tire size ,and cam would play a big part in how many rpm that you would turn and where you would shift at. I would think ! Just my thoughts

Whitefield I thought 3rd or drive was 1 to 1 not 1.1 to 1 are we wrong??

Blake is right I don't know what I was Thinking ! . Sorry can't type my thoughts the way they are in my head. I wasn't trying to miss inform anyone, I'm trying to learn about this myself.

Go back to the first page of this thread and to what "feetfirst" said - pick the RPM at what MPH you wish to run at the finish line and work the math backwards. Take whatever you get at the starting line and MAKE it work. The finish line RPM will be a bit higher than the best shift RPM point. Anything else would be even more of a compromise.

If you have to, use the first speed of the transmission, (you may need to change it and maybe not), to get closer to what you WANT. This will take advantage of everything the ENGINE has - with a Glide or a 3 speed.