97WS6NY

i am going to use the gears to offset the larger diameter tire that i will be running at the track

94zrag

Cool, just checking.

97WS6NY

I am assuming that is good practice right, i want to run a larger diameter full slick at the track, do people usually go up in the gears when they do this?

Injuneer

You're sort of canceling the advantages of the gears by increasing the tire diameter.... larger tire diameter is the same as using a lower numerical rear axle ratio.

What kind of trap speeds are you running? How much HP are you putting down? How often is your car driven on the street with normal diameter "street" tires? All of this has to be considered to select the correct gear ratio and tire diameter.

97WS6NY

Basically I was thinking that I wanted somewhere around the same ratio as I would have with the 275/35/r17s with 4.11 gears, but I want to run a larger diameter tire so I firgured that stepping up to the 4.56s would get me back into that gear range, as i figure if I put a set of 315/60/r15 e.t. street etc, it reduces the drivetrain final drive ratio (including tire) compared to the stock size tire.

JakeRobb

I'm confused.

You're making two changes which completely counteract each other. You're gaining a small amount in the length of your contact patch, and keeping roughly the same overall gear ratio.

So what is the point?

97WS6NY

because i can't find a drag slick (non radial) that is low enough profile to give me me my taget final driveline ration with 4.11 gears

rskrause

You are choosing gears using an incorrect methodology if your goal is to maximize 1/4m. times. What you should do is estimate your trap speed based on hp and weight. Taking into account tire size, calculate the gear "backwards" so that you will go through the traps just past peak hp in fourth gear. My combo peaks at ~6,500 and goes through the traps in the low 140's, so 3.42's work out best, for example. In your case, I think 4.56's may be too much gear.

Rich

97WS6NY

OK, well, here is my setup:

97WS6, Fully forged 383 with LE ported Trickflows/Intake manifold (Compression is 11.4:1) , Bauer cam peeking at about 6800rpm. Comp Pro mag 1.6RRs, CSR waterpump, cloyes adjustable double roller timing, hooker super comp LTs, MSD 6AL, MSD coil and wires, 7 quart Moroso oil pan.
Will also be going to a modified super vic intake from Brett soon (as in 4-6 weeks) as well. Looking for ~ 480rwhp NA with peak occuring around 6800rpm. Also, a 200 wet shot. So track HP ~ 650.
Car is full weight 97 formula right now, will be shedding some weight, looking for about 3300lbs raceweight. 6 Speed. any help is greatly appreciated.

rskrause

4.11:1 rear end @ 6800 rpm:
1 - 47mph
2 - 70
3 - 97
4 - 126
5 - 170
6 - 252

Well, look at the speeds in 4th. Even with 4.11's you are going to hit only 126mph in 4th (assuming stock tire size). I think that you are going to trap faster than that, so you either need more tire or less gear. You DO NOT want to have to shift into 5th on the strip.

IF you are running a tire with a stock diameter I think 3.73's might be the answer.

Rich

97WS6NY

if you had to guess where would you put me at e.t. and trap speed? I have no idea, but i hope low 11s on motor and 10 on the juice

JakeRobb

That sounds right to me. Traps should in the high 120's on motor. I think rskrause is right about the 3.73's.

CMDTech

LMAO, people ask me all the time if my maroon 88 IROC with honeycomb rims is a Firebird/GTA. Apparently maroon IROC are pretty rare?!?