I know this is a very difficult question to answer since there are so many variables involved. However, I'm more interested in getting an understanding of gear ratios than a 100% definate answer (although a 100% definate answer is always good too )

What I am trying to understand is how to determine proper gear ratios for a project car I will be building. Right now, I am bouncing between a modified 700R4 and a 2004R, which both cost the same and will handle the same amount of power. Correct me if I am wrong, but the gear ratios of the 2004R are: 2.74 first, 1.57 second, 1.00 third, .67 fourth.

After playing with an online speed calculator, I found that I could get to 60 mph in first gear with a 2004R and a 3.08 rear gear. This got me wondering about acceleration vs. gear ratios. With this particular setup, the engine has less mechanical advantage and would accelerate slower than a car with say 3.55 gear; HOWEVER, when including time to shift from 1st to 2nd... which ends up being faster?

So, for arguement sake, here is the car: 2800 curb weight, 450HP/465 ftlb engine, tire diameter of 26.7", and a 2004R transmission installed. Excluding atmospheric conditions (wind drag, temperature, etc), which would be faster, 3.08 gear ratio or 3.55 (or higher numerical gear). Throw in the 700R4 as well to make your point if you want. I'm interested in 0-60mph, 1/8 and 1/4 mile times.

If your asking "Why", lets just say the C6Z was the inspiration for this question. BTW, the main reason behind this line of questioning is to prevent me from peeling out on light-moderate throttle every time I stop at a light (primary use for this car will be the street with the occasional track session) since the car is very light, the engine will have some good power, and the tires will not be as wide as I want them to be (275 width is probably the most that will fit without modification).

 

I take it that this is the wrong place to ask this question. Anyone know where I can find an answer?

 

355 would be better for 1/4 mile performance but the 200 4r is a very expensive tran to keep running under high hp.

 

I might look at things from another prospective, specifically your motor...how high do you plan to rev it through the traps?...I feel you can go as tall as 3:73's for street use if you are comfy with the rpm you will be trapping...I assume you have already addressed the differential issue...

 

I have gotten a few PM's with some good info. I guess there is a bit of a misunderstanding. I'm not really getting specific information as far as "run x transmission with y gears for your setup" yet. I'm also not building an all out drag racer. I figured I would post here because drag racers usually really knowledgable about optimal gear ratios. If anyone could help me understand, this would be the area to start.

What I'm looking for is knowledge. Since the car is so light and wont be able to fit the amount of rubber I'm accustomed to, I'm trying to figure out what range of gears I should use. This car will be on the street more often than on the track, so running a really high numerical gear is pretty much out of the question. I'd like to have an overdrive for when I cruise.

I used the above mentioned info for sake of argument so we all are on the same page, its just a hypothetical. I was intrigued by the C6Z's ability to go 0-60 mph in first gear and wondered if it can be replicated with an automatic. So far, only a 2004R and a 3.08 gear are capable of doing that. Is it practical? I dont know, figured I'd ask around.

One person did make a good point about peak power. For an all out drag racer, that is a really important factor but since the engine doesnt exist yet, I have absolutely no idea where peak power will be. So far, my choice of parts will put the peak at the upper RPM range (AFR 195cc heads and Edelbrock RPM intake. Cam hasnt been chosen yet). The engine will be built where there is enough low end torque to be streetable and have enough high end power to have some fun when I want to. That is about as specific as I can get at this time.

Thanks for your help.

 

OK..... we've got a car that is limited as-to tire-size, so we can't use over-sized tires to help with traction, but the car is very light-weight, so it'll get-moving fairly-easy, and it might-not need so-much gear/TQ-multiplication:
a little-weight over the drive-tires might be something to consider, to aid in traction for quick acceleration.


I'm guessin' you'll need to turn almost 7000 RPM with a 200-4R (2.75:1 First Gear Ratio), 3.08s, and a 'typical' 27"-tall tire, which isn't impossible (with AFR 195cc heads and Edelbrock RPM intake, can we assume it's a carbed-motor? ), so while it's 'numerically-possible', 'practical' might-be another story:
here is something to consider, comparing this project to a C6Z:

* the C6Z has a computer that is constantly fine-tuning the motor while it accelerates to 60 MPH in 1st Gear, getting every-last ounce of power from it by making infinitely-small adjustments, while you'll be relying on a 'dumb' carburetor

It may be difficult to 'have the best of both worlds' while using a carburetor, 'specially when going-against a highly-sophisticated EFI.




The more TQ you can build, I believe the less TQ-multiplication (gear-ratio) you'll need, even more-so in a light-weight car with limited tire-size:
lotsa good-thinkers in this section, so I'm sure you'll get varying opinions (meaning that 'I' get to learn-sumpin', too)


Just my idle-ramblings.....

 

I put tons of mid to low 10 second passes on my TH200R4 and had no issues.. Other than the purchase price and a different governor ($100), I didn't spend a cent on the tranny except for routine maintenance (fluid changes)

 

Not a major drag racer here, but just figured I would give you a heads up on what I am doing on my two cars:
1. 86 Monte Carlo SS - 350hp/389tq plus 100hp shot of NOS
This car will be driven on the street and track. I am having the factory rear (7.5") replaced with a Strange Engineering S-60 rear. Factory was a 3.73 posi, the S-60 will have the same. Tire size is 26.7" tall. Transmission is a 2004R. One thing that I did not see you mention was a torque convertor. In this one, I am using a 2400 Holeshot by B&M. Due to the weight of the car (3800lbs or so), it acts as though it is a 2800. The convertor is also a lockup style. The lockup is controlled by a B&M Torque Convertor Lockup Switch. At 80mph, in lockup mode, I am running around 2600 rpm. With the lockup off, I am running around 2900-3000 rpms. I have yet to run it at the track, as I just added the NOS and the rear end to the car, so I can't give you any numbers there.
2. 86 Corvette - 434 w/ 700R4, 4 Link GM 12 Bolt rear with 4.56 spooled gears - In the process of being built
As for my Corvette, this car is being built for my track time than street time. It will be driven to and from the track, though. I will be running 30" tall tires on the Corvette. With the .70 4th gear ratio, I should be turning roughly 2700 rpms at 80 mph with the 30" tall tires and the 4.56 gear ratio in the rear. When I hit the traps on the Vette, I should be in 3rd gear, at around 6700 rpms.
Again, I am no gear expert...nor drag racing expert. The shop that is doing the work and I came up with these ratios based on what I was going to do with the car. The Monte Carlo, we decided to keep factory gearing, as I knew what it ran on the street and the car will see some track time. The Corvette is the one that we really looked at with the gears to figure out how to get as much as possible out of it, yet still make it decent to drive on the street. Neither car is one that is going to get great gas mileage. That is what my DD is for (even though it doesn't get great fuel economy with a 5.7L Hemi under the hood )

 

Considered that. The only extra weight I might put in the back is an IRS instead of the live axle that they spec.



This is the lines of my thinking. Question is "how much less"?

Very good information for the future.

I wont know that until my engine is built. Dont really see a point in choosing one until my engine is built and dyno'ed.

 

Agreed. But have you thought about whether you are going to go with a lockup or non-lockup convertor? If you go with a lock up, you might be able to go with a little more gearing, than with a non-lockup. That is why I inquired.