Can someone do the math for me? What would the top speed be on a stock tranny with 315/18 R888's with a rev limit of 7800rpm.

1st gear 3.82
· 2nd gear 2.05
· 3rd gear 1.41
· 4th gear 1.12
· 5th gear 0.92
· 6th gear 0.75
· Final drive 3.44

 

Easy about 237 give or take a mph

 

Thanks Joe, I was considering doing the tranny before the Mile to beat Colby's 224mph. But in this case, as long as she holds, I'll keep her stock until she starts to break.

 

i went 231.7 at just under 7600 rpm FYI on stock trans with same wheel/tire setup.Just dont break it before TI, Tom will be upset.

 

You can have 224, I won't need it anymore after March. I might actually put some tape on the car, get rid of mirrors, and disable the spoiler this time. That should be good for 230ish, I just need to stop watching Joe's moonroof delete DIY or I'm going to psyche myself out!

Seriously Joe, I've watched the video and am seriously impressed with your steering input after the change in cabin pressure. I don't know that people appreciate how important SLOW HANDS are at that point.

 

lol dont watch it !Especially if you are going back.If i had the ***** at the time i probably could have saved it from running off on to the grass but didnt want to risk hitting the grass with the wheel turned as that would have most likely triggered a 200mph barrel roll so i just let it go straight to the grass.My advice is park it if it is windy like anything above 10mph side to side because thats what will upset these cars the most from my experience.Eric Carver reported the same thing in his GT2 at 206 mph on a similar windy day.What u cant see from that video that was even scarier than the sunroof delete and the spin was how bad the car felt at that mph.The front end was moving around so much it felt spooky right before the sunroof popped open.With no wind its a pretty uneventful ride but add in some wind along with the short wheelbase these cars have and it is effin scary at those speeds.

 

hey while you are doing the math what is the MPH at 7000 rpms in 5th?

 

Absolutely, better to make a fast , straight run through the field than an aggressive correction ending in an event.

My last run in October, after we had done 224.8 - was interesting. The wind had picked up and was blowing from the side. Somewhere after the 3/4 mile mark (and after the 180 "wiggle"), I got hit by a crosswind and the car moved about 8-10 feet to one side. All I could think was two things - don't lift, and don't make a steering correction! I did neither, but the movement scrubbed a little over 1 MPH off of previous run.

At these speeds, aero has more to do with it than HP. That's what we're working on for March - we'll see how it goes.

Sorry Todd, didn't mean to hijack the thread. After looking at the gear ratios this morning and a value of 28" on Dia of tires - theoretical is 255. To illustrate how much tires count for, a Dia of 25" tops you out at 225!

Oh, you also need to be very concerned about "sack" diameter at these speeds.

 

Here you go, now you can do the math your self any time you want. Imput all your parameters in all the boxes. The ones already there are just default items.

http://www.kenson.nu/ultima/930T.htm

http://www.gboxweb.com/gt2specs.html

 

do you have enough power to get to that rpm in that gear in 1 mile? you may go faster with a taller gear that keeps your engine in its peak power.


Joe,

I would think the light feeling you are talking about is "lift". And to further prove that point your sun roof was sucked out. There is plenty at play..

 

Okay, stupid question for the experts but I've always wondered about this...

If you are running a staggered setup (65 in the front and 71 in the rear), approx 25.6" and 28". Which size do you use to determine the speed? The car is a GT2 so no concern about the diff (abs may be another issue, but I'll deal with that). Thanks.

 

I should have enough power now. Tranny will stay stock until I need to upgrade.

 

This pic shows I'm at 173mph around 7000rpm in 5th gear. Stock tranny on 315/35/18 tires

 

240 in the mile with cd of31 is around 960ft lbs of torque at the rpm you need to rev at to get that speed.

 

960rwtq of torque at 7800 RPM to get 240 based on the .75 6th gear?