Does anyone know the tallest slick tire I can put on my Z? Reason being, I got 4.10's with a Th350, so I was already just about topping out at the end of the 1/4, using borrowed slicks from a friend. Now I just put a 100 shot to it, so I'm thinking I'm def. gonna need to get some more gear out of her. I ran a 13.3 not tuned w/out the spray last summer. Yes, I know the gearing is prolly too tall, but I put the 4.10's in it back when the car was a manual with the original 5 speed and when that blew a muncie 4 speed. Any help on the tire size?

 

I guess I'll be putting the tires on my old set of stockers, 15x7 alums.

 

What RPM are you at when you are at when crossing the 1320 foot mark?

 

like 7K, and thats def. all the higher i wanna go. this thing is still my street driver.

 

if you're crossing the finish line at 7000RPM with 4.10's and a 26" tall tire you'd have to be going over 130mph (considering the proper gear). Biggest tire you could fit without any modifications whatsoever to your wheelwells would probably be a 27x11.5 QTP or ET Street. With some wheelwell massaging you could go 28" with a little more than massaging you could go 29-30"

Will these tires work right on a stock 15x7 rim though? probably not.

 

im running a 29x11.5 hoosier quicktime pro slick under my car and all i had to do was beat the inside of the well a little for it to fit. im running a 15x8 wheel with a 4.5 inch backspacing. also have a 2 inch drop and dont have any problems as of yet.

 

A car that runs a 13.3 should be trapping NOWHERE NEAR 7000 RPM with those gears. You should be at around 103-105 RPM, which would be somewhere around 5600-5800 with 26" (roughly stock) tires. A little less with slightly larger tires of course.

That works out, assuming good traction, to about 375 HP at the flywheel.

Add a 100 HP shot to that, you'll be at 475 HP, more or less.

That should take you to the low-mid 12s, like 12.3 or so; at maybe 110 MPH. Still NOWHERE NEAR 7000 RPM.

Factory tach, eh??

Some valid RPM numbers would be helpful; although they're pretty easy to calculate.

 

the slicks that i borrow are def bigger than what you are posting is stock. I guess that's my fault for posting their size. I dont remember how tall they were and when I asked, he seemed to think 27".

Also I have an autometer 5inch tach with shift light. As I remember I had the light set on 6800 and it was lighting up at the end. The tranny is a th350 with 4.10's. Hopefully I am wrong and I'm not recalling correctly. After all if was some time ago the last time I ran.

 

That's not right.... your RPMs shouldn't be even close to that....

Run your numbers through any RPM/gear/mph calculator. They don't work out.

And as far as the tire diameter, that's less than a 4% difference.... 4 mph, AT MOST, at 7000 RPM. Or, look at it the other way, if you trap at 7000 RPM now, and you trap at the same speed with the larger tire, that's 300 RPM at the traps, AT MOST, from the tire size.

What converter is in it? Sounds like it's "slipping" by 1000 RPM or more at the big end.

I think, if that's really the case (which it's hard for it not to be), that you should try getting a handle on that before adding more tire. Put more power to it, and the RPMs might go up ALOT more than what you can adjust just with tire size. Maybe a smaller converter with the same stall "spec". A smaller converter will typically "lock up" closer at high speeds, because the stator spacing and other things, don't have to be so de-coupled to make it stall higher. You can get a better approximation to an ideal "switch" (zero coupling below stall, 100% coupling with no "slippage" above stall) with a smaller one.

 

the converter is a brand new boss hog 2800 stall, and i dont think its slipping. I guess my tach might be off, but the car was screamin pretty good. I think I'll just put the bigger tire on it, and take to the track and see. I'm not really losing anything going with the bigger tire since I dont have a pair of slicks right now anyways. I'm hoping I am just remembering the RPM's wrong and over time my thoughts have exagerated them.

 

I have a 28x11.5 with no modifications to the well at all, mounted on pro stars

 

thanks bluebeast, thats all i wanted to know. what tire would fit under stock wheel wells. 28's it is, thanks

 

I had 28x10.5 ET Drags on 15x8 rims with 5.5" backspacing and they rubbed the front of the wheel wells pretty good. I dunno how BlueBeast managed around that... maybe the 8" wide rim bulged the tire a little bit. Either way I'd imagine it'd be so close to the wheelwells that you'd have to beat them in regardless... Remember that slicks grow going down the track.

 

yeah, I was figuring that I would have to do some massaging. But now I know at least they will fit

 

28" will work just fine on a 8 inch wide rim, its the backspacing of the rim you have to measure! Look up in this post, I recall someone mentioning 4.5 B.S., Thats pulling the tire in closer to the well.
So use a baseball bat and roll the quater panel lip or message the inside wheelwell a little.

Also I ran 4:10 with a TH350 low ratio gear set and went into the traps @ 5700-5800 rpm best time13.97-stock converter and chassis(when I first started the 1/4 mile).
Later
Rotten

 

high gear clutch slippage in a T350? - very common... I'm only turning around 6k at the traps w/ my 3.73's. I'm not going to change the gear until I run her again after all the work is done.(...lets' just say a SERIOUS diet) - My 315's measure out at around 26", and I'm trapping at over 125 even if I'm screwing around... I look into the tranny/converter for the high rpm issue - I know that's not what you were asking about, just my - as for the tires, I think you're on track...

 

I bought 28" tires and put them on my original set of alum. wheels. With my 4:10's and the th350, 3200 stall, i ran a 12.1@115mph. The motor was still pulling at 7000 rpms, and i had let off before the quater mile mark. I know my converter is not slipping like you say. So there are the facts