chas0218

So I have been running the numbers for tire height and rpm with cruising speeds for highway/city and strip performance. I have narrowed my choices down to 3 ratios 3.73, 3.90, and 4.10.

Now a little info on my car. I have a built 383 with XE 284 (2500-6500 rpm range) 3000 stall and current gears are 3.08 and 26" tire I am looking at stuffing a 27" or 29" tire under this in the near future.

The car is super doggy with the current gearing. This car is not a daily driver but a street/strip car. All I am looking for is to give those mustang guys something to cry about.

I am seriously thinking about the 3.90s but couldn't find a lot of info from guys running them, they seem like the best of both worlds.

86LG4Bird

iTrader: (1)

I think you need to decide first whether you're going to run a 27" or 29" tire.....big difference there!
If 29", you definitely want the 4.10's, since you say street/strip and not daily. 29" is HUGE on a 3rd Gen!
I don't know what dragstrip tires you're considering, but FYI, a 275/60/15 drag radial comes in at 28". With your setup and stated use, I'd want the 4.10's for a 28" tire.

I can see why it's a dog with that big cam and 3.08's. With more gearing, that 3000 converter will be good on the street, but will really limit your 60's and ET at the strip. That cam will want something closer to 4000 to really get the car off the line. And with that much converter, I'd want 4.10's. I guess the slant of my response is this: The cam in your setup pretty much dictates this is going to be more a strip car than a street cruiser, so might as well make the parts work well together. You're already pretty much committed to "radical" rather than "mild", so gear it up!

chas0218

I was looking at some 29" tires but have seen some conflicting reports that the tire will be sticking out past the side of the car on a 16" rim and some say it will fit and other say it will not. I would rather go with something around a 27" and not worry about fitment issues. A lot of the guys around my area I talk with were trying to get me to run that bigger 29" tire. I don't know their reason might be for the RPMs at the finish like or something I have no idea. The TC flashes to 3400 which I thought would happen. When I was looking into the RPMs based on gearing and tire at 70 mph the car would be turning around 2500 on the highway. I was liking the idea of 3.90s. best of both worlds and get those highway rpms down to 2300.

With the 700r4 will the lockup drop it further than the calculated rpm? Are the calculators assuming no lockup?

86LG4Bird

iTrader: (1)

calculators assume lockup (no slip)

chas0218

Will those 4.10s get me a better 60' than the 3.90s? I would like to be around a 1.60 60' on a sticky street tire. Do you think it is possible to do it with those 3.90s? I really don't want to have the car just knock the tires off from the start. Spinning ain't winning!

On a side note around my area it is highway driving to get anywhere, I could drive back roads but this is more a straight line car than a corner carver.

86LG4Bird

iTrader: (1)

Of course, the 4.10's will get you a better 60' than the 3.90's, all other factors being equal. Even with the steep 1st gear of the 700R4, you're still nowhere near the power level where there's such a thing as too much gearing for your 60'. I run 4.88's with 29 and 30" tires on my ImpalaSS. More weight and more power than you have, and best 60's are 1.43 naturally aspirated.
Also, with a steeper gear, like the 4.10 as opposed to your 3.08's, if you do slip the tire at the line, it will recover much better than the 3.08 gearing that sends wheel speed to the moon and never regains traction.
With 4.10's, you can still trap high 120's in Drive (1:1). That's good enough for low 10's
And yes, 1.60 is entirely do-able with 3.90 gears, IF YOU DO ALL THE OTHER PARTS RIGHT. 4.10's just make it more of a sure thing.

Just to be clear, we're talking optimizing strip performance here, not highway driving!

chas0218

Good you confirmed what I thought, you also answered my other question about trap speed. I think at 120 I will be close to my peak rpm around 6100 rpms which is almost the sweet spot. My biggest concern is I'm putting these gears into a 10 bolt which I feel should have no problem surviving behind my motor with a moderate stall and auto trans. The rear will be my weak link at this point,

86LG4Bird

iTrader: (1)

Yes, regardless of ratio, you're going to have to baby that 10-bolt.
Don't EVER start a burnout unless the slicks/DR's are wet. Don't waste its limited life doing dry hops.
It WILL break eventually.
Do you already have a functioning limited slip diff in it?
If you're replacing it, a clutch-type (Eaton, Auburn Pro, etc.) is preferred over a wormgear type (Torsen, Detroit TrueTrac, etc.) for durability. Even in the larger GM 8.5" diffs, those wormgear diffs don't hold up well to burnouts and launches.

chas0218

The rear I'm building has the torsen t2 with 28 spline axles. My biggest concern is if it hooks I don't want to be leaving a parts trail. I am hoping to keep the wheel hop to a min with adjustable shocks on all corners. I will have to play with them to get the right amount of anti-squat/squat. Most likely in the front I'll be running them on the softest setting to allow that front end to lift up and allow some weight transfer, I hope that will keep the rear from hopping too much.

I have been throwing around the idea of the mini ladder bar setup with fully adjustable swiveling rod ends. I know in corners it might bind the suspension so I was thinking with swiveling rod ends it would allow enough travel without binding. If I can't get it to work then I will just get an adjustable torque arm. In theory I have some ideas that I want to try. I know the mini ladder bar setup isn't ideal but I don't want to back half my car or modify the floors to fit a short ladder bar setup (at least right now).