Et street radials on a 4 speed ?

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couper 340

couper 340

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HI GUYS , I was getting ready to buy a set of mickey Thompson et street radial for
my 340 duster 450hp at engine . Then i read that with a 4 speed they will not hook up well and they sad to use the et bisa ply . My reason for looking at the et radial was so i didn't have to run a tube or drill my rims but if they are not going to work well i dont want to waste my money and not be happy with them . ANY ONE RUNNING THEM ON A 4 SPEED CAR WITH LEAF SPRINGS A CAL TRAC'S? THANKS
 
I have some 325/50-15 BFG drag radials. Street suspension. No SS. No traction aids.About 425 Hp, 3.09/Direct box with a GearVendor O/D. Gears I have tried:3.55,3.91,4.30,4.89,5.15. All 60 ft @ 1.9 to 2.1 and mph at about 7.9/eighth.
So Im none too happy with those results. Like I said tho;street suspension. They spin most of the way through the eighth on our crappy airplane landing strip of a track.
As a sidenote; I rented them out to a guy with a Coronet with a hot 440 Automagic and a small NOs plate.On a different track, he loved them. No results available.
 
I run 275x50x15 M/T drag radials with a stick. There are two left SS springs back there. I dump the clutch at 4000 and go with no noticeable spin and that is without a line lock. It is a heavy car though at 3700 Lbs. 60 ft's run 1.7 to 1.8 for mid 12's. I drive to the track at 26 PSI and race em at 16 PSI. Two of my buddies run them also in 12 second 4 speed A bodies.
 
Are you street driving or hauling the car to Mason/75-80? With street use involved, I'd probably do the ET street your thinking of. If you're trailering to the track, a bias ply with tube is the way I'd go...

Not sure what size you're dealing with? Unless you're running a small tire that needs to be at a really low pressure, the slick/tube combo doesn't necessarily need to be pinned? imo. In my day, a well mounted bias tire of adequate size & pressure had no rim/spin issues on mid/high 11sec & slower cars, including some sticks.
 
couper 340 said:
CUDA 69 What ratio rear gears are you running ?
Click to expand...

I have 391's with an Eaton TruTrac from Dr. Diff. The Tremec trans has a low 3.27 first, and fourth runs 112 MPH at about 6000 RPM through the traps. I also took a suggestion from Rich Ehrinberg and mounted a set of kicker shocks horizontally to the axle. They dampen windup from launching and hard braking without constricting travel. It makes a versatile set up on a budget.
 
Do you have a picture of the shock set up?
 
I have a set of center lines for track use only 15'' x8 was going to mount et 255/60-15 or 275/60/15 street radial have two rears 3.55 and 3.73 will try both . i am going to the track on my BFG 245/60-14 to make some passes so i will know what height tire to buy 26'' or 27 '' height. when i know my top speed and rpm at the finish line i should have a better i dear on height
 
i have competition engineering shocks fronts set to 90/10 rear set to 60/40 rears are bolted to caltrac
 
couper
Have you got a calculator?
A change in tires from 26 to 27 is about 4%. At 5500 thats about 220rpm. Thats hardly worth a trip to the track.
The rear change from 3.55s to 3.73s is a change of about 5%. Thats about 275rpm at 5500.

Heres the formula;........MPH= (RPM x TC) / (1056xR1xR2)....

Flipping things around; RPM = (MPHx1056xR1xR2 ) / TC
where TC is Tire circumference; which is Pi x D, where Pi = 3.1416, D = diameter
And where R1 is rear gear, and R2 is tranny gear.
The following is for M/Ts. Autos may/will be slightly higher due to TC slippage.I have no idea of the caliber of your combo, so will just work it out for 106mph in the qt.

EQ1.....RPM = {106 x 1056 x 3.55 x 1.0} / (26x3.1416),Therefore RPM = 4865 in direct
EQ2.... RPM = {106 x 1056 x 3.73 x 1.0} / (27x3.1416),Therefore RPM = 4922 in direct; Thats a 57 rpm diff.
If using 3rd gear, RPMs will be 40% higher using the 3rdgear ratio of 1.40. Unfortunately neither of these gears play well in 3rd at 106 to 111 mph, pulling rpms near/over 7000. To run a 3 gear QT, a 3.23 would play well; pulling around 6000@106. A 4 gearQT would like 4.56s; also pulling about 6000@106.
So plug some numbers in and save a trip to the track.
If you expect 5% more MPH, your RPMs will be the same 5% higher.If you go to 15% more gear, your Rs will rise the same 15%. If you expect 5% more mph AND will use 15% more gear, you could expect to add the 5 and the 15 for rpm and get; 111Mph@5906 using 4.30s over 3.73s.

EQ3; The math goes like this; RPM ={ (106+5%) x 1056 x (3.73+15%) x 1 )} / (27 x 3.1416) = (111.3 x1056 x 4.29 x 1) / (27 x 3.1416) = 5944RPM
the proof is; 5944(from EQ3)/4922(from EQ2) = 1.207 which is about plus 21%! and the estimated;5944/5906 = 1.006 or less than 1% error.
At the track its usually best to use the larger diameter of 2 tire sizes available.The footprint increases faster with an inch of diameter than with an inch of width.The ratio is about 3 to 1. And tire pressures play a huge role in the footprint as well.
Just trying to help.
 
look like a good low price up grade with the kicker shocks.
 
A J Thanks for the info . Will still go to the track for test and tune just to see how close i am to paper, and just to see how it will go down the 1/4 as it was just finish before the winter .
 
couper 340 said:
look like a good low price up grade with the kicker shocks.
Click to expand...

It sure makes for a versatile car. I can drive it to work or autocross and road course with the 17 inch wheels, then bolt on the 15 inch Rallyes with the M/T's and go straight to the drag strip.
 
old man Rick they have closed down 75/80 drag way for good in 2013 to built houses .
only mason DIXON left .
 
Thanks couper. I haven't been "back home" to visit for 6/7 years. Sad to see it closed.....again. :)
 
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