Currently running on a 4.05FD and 205/50/15 BFGs, with my ITR trans, trapping around 127ish. The FD is great for extending my gearing just enough to avoid shifting to 5th at the finsh line which I had to do with the stock 4.4FD, and its great for highway driving (mainly a street car but I do hit up the track for local events). 80mph cruise is around 3900RPM with the 205/50s which is great. But my BFGs are getting worn out, and I think its time for something else. I blow thru 1st-3rd rather easily, street and track.

I was thinking maybe trying the 225/50/15 BFGs. But the fact I smoke thru the current ones I have, even when warmed up a bit, makes me want to avoid BFGs. Plus I have been reading the M&H DOTs are great. But they are BIG. Im just not sure of their fit or if going to a tire that big with my longer FD, is going to be a problem and cause the gearing to be too long. Top speed theoretically will be around 180mph with 8500RPM limit, give or take a few, which is long, even compared to my current gear ratios.

My goal at this point is to bring down my ETs (ie lower my current 2.2 60ft). I know the MPH is there for where I want to be (since this is mainly a street car anyway). Will upgrading to a bigger tire with the 4.05FD be a problem and extend my gearing too much and make the car feel like a pig? I definitely noticed a difference when switching to the longer FD initially, but I felt it was for the better and actually HELPED with traction. The 4.4FD and 205/50 is useless on the street. I do plan to upgrade the suspension to more of a drag setup, and to allow for bigger tire in the front (raise it up), but as of right now Im on the stock shocks with H&R sports. Maybe I should beef up the suspension first? A decent gear-based boost controller is not in the budget right now, so for now Im just on the spec b2.

Thanks for any suggestions or info.

 

http://autocrossing.com/cgi-bin/gearcalc.cgi

 

ive already worked out all the numbers. Im asking if this much gearing is going to make my car feel like crap (ie a slow pig).

 

i cant say what that would do for your car.....

but i do know that on our car with 28inch tires/stock ls trans(4.2 final) we would cross through the traps in 3rd gear....... when we switched to the b16trans/4.7 final it allowed us to be in the powerband more(upon gear changes), and cross the traps @ the end of 4th.

if you put all your numbers in that gear calculator, it should give you a pretty good idea of what is going to happen...

i belive it said we would be able to go somewhere around 220 mph in 4th with the 28's/ls trans, we would have to be racing a 1/2 mile to take advantage of that.

 

I understand what you are saying, but I guess Im more concerned with if that is too much gearing for my power level. I dont intend to increase power at this point and Im not concerned with 200mph top speeds. Im more interested in fine tuning the setup I have now. I can put the numbers in that calc all day long but its not going to tell me at what mph or RPM Ill be crossing the line at. Im wondering if doing this is going to hurt acceleration at this point or if I have enough power to pull through it. Do you understand what Im trying to say? Maybe Im missing something you are trying to tell me.

 

how much power are you planing on making or making already ? it should give you an idea of your targeted trap speed. you want the quickest acceleration possible. with the 4.0 final you are significantly lowering your acceleration.

 

I know it is lowering my acceralation a bit, but I think that probably helped more than harm at this point. It helped stretch my gears a little and helped gain some traction on the top end of the RPM band.

At this point Im thinking I may just put the bigger tire on and see how it is. If it sucks Ill put the stock FD back in and run the bigger tire. That will put me about where I am now with the 4.05FD and 205/50 smaller tire.

Here is some data with and without the 4.05 and the 235/60 M&H DOT 8500RPM for example:

with 4.05
4th max speed MPH 143.3

with 4.4
4th max speed 131.9

As you can see there is quite a difference with the longer FD and bigger tire. Im positive that I will not be anywhere close to the 140mph mark with the big tire and long FD, so thats essentially wasted gearing on the top of 4th. Or can you look at it the other way and say thats longer gearing, more traction, quicker 60ft, and more MPH in 1-3rd? The problem Im having is balancing the two.

Basically if I went back to the stock FD, and ran the bigger 235/60 tire, Ill have just slightly longer gearing than I have now, which sounds nice because I really like how the powerband is stretched right now. I dont know if I have enough power to pull me to 131mph, I guess it will depend how the tire hooks and how I get thru 1-3rd gears.

I may just try it out with the FD and see how it is. If it sucks I can just pull it out. Im just wondering how much ET Im going to gain with so much more traction in 1-3rd and if it would be worth it.

Or I guess I could just upgrade my suspension and keep my current setup and see what happens lol. I guess bench racing is only good for so much


Modified by RTW DC2R at 10:29 PM 2/27/2007

 

I am trapping at 131mph on 24.5X9x15 slicks shifting at 9000 in each gear and stay in 4th. hope that helps

 

when does your car stop making power ?

 

around 9K on the boost controller, but I usually shift around 8500.

I think Ive narrowed it down to either the BFG 225/50 and the 4.05FD, puts 4th gear max around 134mph, but possibly sacrificing some traction 1-3rd. A little suspension work might help this setup too.

Or the M&H DOT 235/60 with the stock 4.4FD, which puts 4th gear around 131mph but probably with better traction all the way down the track. Suspension might not be as big of a deal here with the stickier tire.

I think my car has enough power to pull close to that MPH with traction so I think its a toss up now between these two setups. Since the car does see some street and road course use, I do like to have the longer FD as it will help with traction when using Azenis out on track. Gotta figure out what I want to sacrifice.

 

a smaller tire is going to be alot easier to spin, and when you do finally get traction, it will take longer to accelerate with the 4.0 FD.

a tall tire would be harder to spin(should be easier to get it to hook up) + the 4.4 will make the acceleration quicker. (imo, this is the better combo) although you dont want too tall of a tire, if you arent making crazy power. there are sfwd cars making more power than we do with our car(we run 28's, they run 24.5's) and there e.t.s are nothing to shake a stick at. we have 60's in the 1.30's.... i belive the top sfwd cars are 60'ing in the mid-high 1.50 range. with the taller tire, you should be able to pour alot more boost into the car as well.