Time to buy new slicks

My slicks are seven years old. I think it's time to buy new ones. I'm currently running M&H 8.5/24.5-15's on my SRT4/automatic LSD van. Should I stick with that size or maybe get a different size that could possible get a better 1/4 mile time? My van weighs about 3600 lbs and the last time I ran a 12.6 I was making 360 HP/460 ft/lbs torque. Last time at the dyno I made 386 hp/480 ft/lbs of torque. Since then I upgraded the intake and I am estimating very close to 400 hp. I plan on dyno-ing it again after I get my input shaft installed and before Roadkill's Zie-tie Drags in January.

What's your trap RPM?

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Originally Posted by shadow88

What's your trap RPM?

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Are you referring to when I cross the finish line? If so, going by my data log it's 5500 RPM.

I love my m&t 24.5 x 9 x 13. I get better 60' then I did with M&H 24.5 x 8.5 x 15 and m&t 26 x 8 x 15 , but they would obviously require you to get new wheels and possibly brake modifications depending on what brakes you have.

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Originally Posted by lengel

I love my m&t 24.5 x 9 x 13. I get better 60' then I did with M&H 24.5 x 8.5 x 15 and m&t 26 x 8 x 15 , but they would obviously require you to get new wheels and possibly brake modifications depending on what brakes you have.

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Thanks for the input. I have big Grand Caravan brakes in the front and Iroc R/T vented discs in the back.

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Originally Posted by A.J.

Thanks for the input. I have big Grand Caravan brakes in the front and Iroc R/T vented discs in the back.

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What size rotors are they? I had 11" spirit rt brakes when I was running the 15" wheel. I needed to swap to a 10.25 brake to use the 13" wheel.

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Originally Posted by lengel

What size rotors are they? I had 11" spirit rt brakes when I was running the 15" wheel. I needed to swap to a 10.25 brake to use the 13" wheel.

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11" or 11.5" I can't remember. I really want to keep my 15" rims to keep costs low (in the process of buying a $2350 metal lathe to machine transmission parts for torrington bearings).

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Originally Posted by A.J.

Are you referring to when I cross the finish line? If so, going by my data log it's 5500 RPM.

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You have room for more rpm... go with a shorter tire... better yet, borrow a set to try.

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Originally Posted by 85glht

You have room for more rpm... go with a shorter tire... better yet, borrow a set to try.

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That's what I was getting at. I have 24.5-8-15 and 23-7-15 and the trap rpm is almost 400 rpms different. Overall,the 23 inch tires weigh less too. I'd borrow before I buy, but it's an option to gain a little

I did a trans swap for a gear change... went from a 3:90 FD to 3:50 FD. my car did not like running the 24.5” slicks with the 3:50 FD... now with the 22” tires, my car was much happier... although on the nitrous it was almost not enough tire... might try 23” next