Slicks vs Drag Radials

[khan0165]

Hey folks,
I've posted questions before for slicks, and I'm still trying to aquire the latest and best knowledge. I'm really getting into drag racing now, and love to tweek and test to get the best ET and trap speed from my setup.

I am running 27x10-15 Hoosier slicks behind a 8.5" rear with 3.42 gears. This rear backs a very mild sbc350, putting maybe 320rwhp (400+ at flywheel).
through research, taller is better than wider, specially under 600hp range. So the ideal size I've been told for G-bodies is 28x9-15... making my 27x10-15 too wide and too short.
However, will a shorter tire not help my trap speed with 3.42 gears? I suppose a 28" or 30" tall tire would be fine with 3.73gears. But is the height necessary with my 3.42s?
In any case, I am considering selling my 27x10-15s and getting something skinnier, mostly because the 10s are too wide and I've been forced to buy shitty heavy wheels to get the small backspacing.

can we discuss the Pros & Cons for Slicks vs Radials?

are slicks necessary with the amount of HP I'm putting to the road? If I get radials, what would I gain? What would I lose? Should I get something 28" tall, or is 27" fine with my 3.42 gears? Should I keep the slicks I have now?

any input is appreciated! Thanks

 

[monte olrac]

I can't say anything about the tire sizes, 3:42 gears are just a step down from 3:73's so you'll be in the same ball park, now as far as slick vs radials get slicks if you are just using the tires for racing and have a diffrent set of wheel for the street, get radials if you use the same rim for racing and street duty

 

[gto78]

Hey folks,
I've posted questions before for slicks, and I'm still trying to aquire the latest and best knowledge. I'm really getting into drag racing now, and love to tweek and test to get the best ET and trap speed from my setup.

I am running 27x10-15 Hoosier slicks behind a 8.5" rear with 3.42 gears. This rear backs a very mild sbc350, putting maybe 320rwhp (400+ at flywheel).
through research, taller is better than wider, specially under 600hp range. So the ideal size I've been told for G-bodies is 28x9-15... making my 27x10-15 too wide and too short.
However, will a shorter tire not help my trap speed with 3.42 gears? I suppose a 28" or 30" tall tire would be fine with 3.73gears. But is the height necessary with my 3.42s?
In any case, I am considering selling my 27x10-15s and getting something skinnier, mostly because the 10s are too wide and I've been forced to buy shitty heavy wheels to get the small backspacing.

can we discuss the Pros & Cons for Slicks vs Radials?

are slicks necessary with the amount of HP I'm putting to the road? If I get radials, what would I gain? What would I lose? Should I get something 28" tall, or is 27" fine with my 3.42 gears? Should I keep the slicks I have now?

any input is appreciated! Thanks

I'm pretty sure straight slicks are better than drag radials, but I never tried drag radials.

As far as tire height goes here's what I did in the past when I used to drag every week: We had a chart of all our times, and each time we made a change like different jets, different timing, or tire sizes we would note that on the chart and also ONLY make that one change for the whole night of racing, and get 5 or 6 solid runs without changing anything except tire pressure to hook up.

Our car is somewhere around 400 hp, 3.73 gears, and we drag raced with a turbo 400 transmission. Our goal was to cross the finish line just a split second before hitting the shift light, meaning we just peak at 5800 rpm in third gear as we crossed the finish line. If we crossed at 5300 or something like that, then we wasted 600 more rpm (our theory anyway). We tried several different tire sizes and heights/widths. Our best time by far was reached by using 26X10 mickey tompsons. Every time we tried listening to everyone else and go with taller tires our time would drop off dramatically. Taller tires are better for traction, but the larger diameter is harder to accelerate- that's just standard rule of physics. If we went with something like 4:10 gears than the taller 28" tires would have been good for matching the rpm we wanted at the finish line.

Anyways, that was my experience, if you don't have big gears than there's no point in big tires. Also, if you have decent traction then I don't see the need for taller tires.

One more thing, at the track I had a major difference between running 3.42 gears and 3.73 gears. With 3.42 gears we're still trying to make power long after the finish line, and running low 13's. With the same car and 3.73 it peaks at 5800 rpm right after the finish line and running low to mid 12's.

 

[khan0165]

gto78,

thanks for that man, very thurough explanation!
Yeah, I definately find the car has trouble reaching it's power band in 3rd down the trap. I find with the cam I have, she peaks between 5800 and 6000rpm. I shift at 6000rpm, anything beyond she starts to fall in power. Maybe to hit my 12s, I need to invest in a new gear.

I did find I had some traction issues. I was still spinning the slicks in 1st and 2nd... but I think the big issue was bad burnouts. A linelock is going in this summer, and that should resolve that.

I think in the mean time though, I just need to not go to such a shitty track... go somewhere where I don't need to worry about pot holes and bumps, ha ha.

 

[gto78]

You're saying you have traction problems in 1rst and 2nd gear?? Wow that's crazy, do you have an open rear end? What pressure are you running the slicks?

Just another FYI, I listened to all the big mouths at the race track tell me what you "have to do" for years. They all said you can't run 12's with an open rear, and that you "have to" run at least 28" tall slicks.... Well we had an extremely low budget and couldn't afford a posi unit for a long time. So we spent a lot of time tuning instead of throwing in tons of parts or lots of money. We made it into the 12.8's with an open rear and slicks.

Traction was not an issue once we figured out the best tire pressure for our tires. We ran somewhere around 13 psi if I remember correctly.

Another thing that is pretty important is to dry off the tires before getting to the starting line. I watched people with traction problems repeatedly pull up to the burnout box and literally destroy a new set of slicks in less than 3 months just because they do rediculous huge burnouts. Right after that they roll forward and I watch the front soaking wet tires leave a big sopping wet path all the way up to the starting line. No matter how big a burnout you do it's worthless if you leave a wet path to drive on.

Also what sometimes happens is you launch and everything's fine, then after about a full car length the rear tires hit the wet spot that the front tires are putting down, and THEN you start spinning the tires again.


The best thing you can really do is drive around the burnout box and then back into it.

 

[gto78]

One more post sorry. What is your times, and what is your 60 foot time?

I don't want to piss anyone off, but if you have the opportunity I would really try to borrow a 650 double pump and set it up and run it for a month or two. If you jet it right, you would be absolutely amazed how much better it will run. I don't think a 350 CID engine will use 750 cfm of air at 5800 rpm, and you probably don't get enough cfm across the venturis to properly atomize the fuel from the bowls, etc. etc.

I really didn't believe the Holley formula when it said a 630 cfm was what we needed for our 400. We bought a new style 650 holley and installed it in place of the 750 double pump. Right out of the box it was a little rich so we jetted down a little bit, then figured out the best power valves. Our times improved about .4 of a second and 3 mph.

 

[jimmyp618]

In drag racing first rule of thumb is the wider the rear tire the better . The taller skinner tire would be a waste of money. All tires skinny out at wot. I run mt et street drag radials w 14-17 psi and at wot there is probably only 5" of tire on the ground if that. i wouldnt run anything on a drag strip under 9-10 at the ground before launch.

 

[shotgun]

What radial you talking about, race or DOT?

A taller tire has a larger footprint so traction will be better. But if it's puts you out of your power band , that's no good either.

Radials do not grow like slicks do. Depending on your combo that may or may not be an advantage.

Radials should be run at 16+lbs of pressure. I run around 18#.

I love my radials, they hook until you see cord (been there,done that) and they are very stable at the top end.

I use the tire that the Super Stock guys run, 30x9, seem ok when lifting the front 6" off the line on my way to a 10-oh pass. :lol:

 

[khan0165]

here is a video from end of last summer...
http://www.youtube.com/watch?v=2sJCSP0fUkM

The car has run a best of 12.9sec at 108mph on slicks, by the previous owner.
With me, it has runs around 13.5sec without slicks, and low 13s on slicks, on a very poor track (pot holes and bumps everywhere).

This video shows how badly the car was struggling last summer, for these reasons:
- I had not lashed the valves properly, and it was really down on power. Notice how it boggs... I shoulda caught onto that.
- I accidently left my brake proportioning valve (which is connected to rear brakes) cranked up too high. Because of this, I could not do a proper burnout, and even burned my posi a little.
- My traction problems were caused by the bad burnouts... you can see in the video how it slips in 1st, and slips a little into 2nd. I only got one good run off the line, and ran a pathetic 13.5sec @ 97mph... the valves really hurt my top end.

I was really careless at this day at the track, and the car did terrible. I also later paid for the bad valve lash when I lost a couple rods.

gto78, I am running a 750 double pumper, but it has been jetted down to 78/82 if I remember correctly... It also needs a retune, maybe even a cleaning.

I was running the slicks at 17psi, and got it down to 15psi when it hooked in that last race. Here's another angel of it:
http://www.youtube.com/watch?v=pFJ2aVti ... re=related

I didn't want to go too low because I'm not running tubes...

So, long story short, I guess I have a few other issues to resolve before tires...

 

[gto78]

...gto78, I am running a 750 double pumper, but it has been jetted down to 78/82 if I remember correctly... It also needs a retune, maybe even a cleaning...

So, long story short, I guess I have a few other issues to resolve before tires...

When I had the 750 we didn't go bigger than 72 in the primaries, any bigger and the times would fall off. I'm not saying you have the wrong jets since I know nothing about how your car is running, but some people put too big of a jet to compensate for an incorrect float setting or for a wrong accelerator pump set up. There is a "trick kit" made by Holley and it has all the different cams for accelerator pumps. Some have a quick initial spray, some have a consistent spray throughout the entire gas pedal stroke etc. It also comes with different/bigger accelerator pump nozzles. If you have a bigger accelerator pump it will get rid of the initial "bog" when you floor it.

Sometimes when the carb is too big and the vacuum signal is weaker, you have to run big jets just to get the fuel to siphon out of the bowls. Also, putting smaller jets doesn't make up for a big carb, the only way to change cfm is to limit the opening distance of the butterflies or just install smaller carb. Another option that's good for a street car running 3.42 gears is to use a vacuum secondary carb instead of a double pumper.

Try lowering the tire pressure one more pound. You could add a slippage mark and if the tire spins on the wheel than screw the tires to the rims. You could also do a few dry hops before pulling to the starting line, to clean off the tires and make sure it's getting traction.

Looks like your staging in a pile of rubber since no one at the track is sweeping it off the starting line, that sucks. Maybe if you stage a little bit toward the left or right of that debris it may help traction.