QuickVet

I’m looking to try some Drag Radials from BFG. I need to purchase them soon if I am going to try to race in a couple weeks.

As of now my car crosses the finish line at about 6000-6200 rpm. Due to the 4.11 gears and 3000-stall converter, I have been getting 1.75 sixty-foot times with my current Hoosier QuickTime Pro tires. They are 26" in diameter. Although I'm not totally sure about the section width but I think its 10.5”s or so (??). Perhaps I already have to much tire.

What I’m looking to do is switch to the BFG that might last a little longer, and hopefully make me go quicker due to the stiffer sidewall, that should help on the top end. My 300hp isn’t much for pushing slicks down the track. Here is the problem. I don’t know if I should get the greater diameter tire or the tire with the same diameter. Do you think the taller tire would help or hurt my times? Both of the tire sizes below will fit my car. My thinking is that the car may already have too much gear (dad does not) and that maybe top end will be better with the taller tire and I think it would still be able to hook up just as well. My dad thinks I should purchase another pair of what I already have. What do you think? Please help. Here are my choices:

Size: P275 / 50 R15
Rim: 7-11''
Tread: 10.0''
Section: 11.3''
Diameter: 26.1''

OR

Size: P275 / 60 R15
Rim: 7-11''
Tread: 8.8''
Section: 11.1''
Diameter: 28.0''

(Please correct me if I am wrong about what will fit)

GrandSportC3

Due to your gearing I would recommend 275/60R15's...

L-82kid

Quickvet,

I see that you are running in the mid 12s, what kind of cam and heads do you run?

Thanks,
Kevin


[Modified by L-82kid, 10:51 PM 9/7/2003]

QuickVet

I am running a lunati Bracket master II cam. It is very large for my lil 350 cubes. I would recommend smaller. It has 300 advertised duration and 515 lift.

The heads are zz4 heads that i bought new for about 500 bucks for the pair. With my stock short block they should be good for about 9.5 - 10.0 to 1 compression ( i think)- because they are only 58cc. I am also using the thinest head gasket available.

I see that you have the chambered exhaust. Any comments on them? Do you like em. Are they too load? Im thinking about upgrading to a 2.5" exhaust. Do you think the chambered is more restictive then the regular pipes with regular muffs? Are the pipes really straight?

Thanks,
Aaron


[Modified by QuickVet, 10:58 PM 9/7/2003]

L-82kid

I have the chambered exhaust system but never heard it on my car. I still haven't got my car running yet, everything is done I just have to put the motor and tranny back in. My dad's 69 vette had 2.5" chambered pipes on it and it sounded good. The only thing I didn't like about the exhaust was that is was only really loud at WOT (i want loud at cruising speeds also). Also I heard that the chambered pipes are very restrictive and choke power. So I decided not to use the chambered pipes and got flowsmasters 40s instead. I'm hoping that the flowmasters will sound louder and flow better then the chambered.

Thanks,
Kevin


[Modified by L-82kid, 11:10 PM 9/7/2003]


[Modified by L-82kid, 11:11 PM 9/7/2003]

QuickVet

thanks for the input. That is what i heard as well. but nothing could be worse then my current 2.25". It was definatly built by Bubba. It has way to many bends and crimps. Perhaps Allens Exhaust could build me what im looking for. I will email em.

Anyone else think the taller tire would be good? or should i stick with the same diameter i have now?

PRNDL

Father knows best! :lol:

Allen's is a bit pricey and not necessarily better than what you can get elsewhere. After my vast experience with do-it-yourself exhaust work I think it is most cost effective to find a good shop to bend a custom system for you. MJ

QuickVet

hmmmm.....

QuickVet

Gordon, what size you running?

The Money Pit

The problem in a drag car is hooking off the line,not top end rpms.From the look of your launch,you don't spin with the current tires,so my guess is you'll hurt the ET by switching to taller tires. Big cams lose low end so I would not do anything to reduce your effective gear unless you have problems hooking off the line.

jpatrick636

How well are you hooking up off the line?
What is your target RPM across the line? It should match your shift RPM.
Where does your HP peak?
What is your actual stall RPM? What percentace of your total torque do you have at that RPM?

QuickVet

that sounds very logical to me. :yesnod:

QuickVet

im getting 1.7 sixtys
i cross at about 6000-6200. i shift at 5800, car dont make much past that. doesnt lose much when i shift there. I have tried many shift points and 5800 works the best. max power is about 300 at 5800 or so.
Actual stall RPM i dont know, the converter is for 3000 so i would guess slightly lower then that.
Im sure im putting 300TQ at 2800 RPM.

anyone know for sure those 26" diameter tires WILL fit ????

jpatrick636

Based upon what I know so far and assuming you have a 1:1 final drive in your transmission:
If you go to a 28" tire your RPM across the line will be 5272 which is too low for your combination.
If you are not spinning your tires off the line, the larger diameter tires will hurt you. If you have a traction problem, some combination change might help you.
The goal is to maximize the launch and be at the peak across the line.
Too much gear and you will run out on the top end and not enough gear you will not get your full potential.
Based on your times, it looks like your motor can take the RPM's you are turning at the finish (assumption). This indicates to me that you have a good combination with the 26" tire.
Do you feel any loss of exceleration? Have you had it on a dyno? Have you tried higher shift points? Without knowing what the motor's peramiters are, It becomes trial and error.
That leaves your suspention tuning to maximize your launch.
Drag shocks on the front.
Small front tires.
No front sway bar.
Progressive shocks on the rear.
Stiff rear spring.
Preload the rear to compensate for torque at the launch.
You might want to go to the drag racing forum for more tips.
This is all I have without taking all the variables into account.
Good luck
Have fun

PS The Nitrus will change everything.

If you want to Email me a complete and detailed breakdown of your whole drivetrain including engine specs, I'll run some numbers for you.


[Modified by jpatrick636, 5:54 PM 9/10/2003]