Pro Stock John

iTrader: (34)

First off, I am not doing more gear. <img src="gr_stretch.gif" border="0">

But, I'm thinking out loud, I could probably run a 4.56 or a 4.88 with the tires that are out there, 28W to a 29 Hoosier. Heck, open up the rear fenderwell and stuff a 9x30 S/E tire in there.

I mean, the point of more gear is LOST at certain point right? I mean I could do a 4.88 and a 9x30 is that better than a 4.56 and a 28" tire? See what I mean?

Smoke_ur_5.0

iTrader: (2)

John...are you drunk already? Judging by the topic...lol! <img src="graemlins/gr_cheers.gif" border="0" alt="[cheers]" />

Terry Burger

iTrader: (4)

The more gear you run the less efficient the rear end becomes. You want to run enough gear/tire that you're able to hit your max 60', and stop there. If you have 4.56s/28s and are spinning, then 4.88/29s might be what you need, but you will lose some power with the 4.88s vs the 4.56s.

BIGBOS

Hmmmmm

<img src="graemlins/gr_chug.gif" border="0" alt="[chug]" />

steve

ive had the 4.56 gearin the car.
i am running a 29x11x15 hoossier also.


steve frank

Bob Cosby

[quote]You want to run enough gear/tire that you're able to hit your max 60', and stop there.<hr></blockquote>

I Disagree. That's only part of the equation. The obvious intention is to gear the car for optimum ET. I big part of that is the first 60 ft. However, the car still has to pull smartly through the first half of the track - and not completely and totally fall on its face at 1000 ft (perhaps 1100, but not 1000).

For gearing, I suggest your guide should be your 1:1 gear ratio near the end of your run. Most cars should be geared to go through the traps several hundred rpm above their HP peak. For example, I go through around 6500-6600 rpm. My HP peak is ~6100. I'm still UNDERGEARED, and could really use to go through around 6800-6900 or so.

As such, a 4.88/26" combo would work really well for me....but I'm a wimp, and don't want anymore highway rpm than I already have with the 4.56's. <img src="gr_stretch.gif" border="0">

I'm certainly part of the 'more gear is better crowd', but there's a lot more to it than the 60 ft. <img src="gr_stretch.gif" border="0">

Tim98TA

iTrader: (7)

[quote]Originally posted by Bob Cosby:
<strong>Most cars should be geared to go through the traps several hundred rpm above their HP peak. </strong><hr></blockquote>
I disagree there Bob. I feel that you should only be no more than 100-200 above your peak hp. If you are farther than that, your just using up your engine.

Tim

Terry Burger

iTrader: (4)

The discussion isn't staying in your power band the longest, rather how much tire do you want to run for any given effective rear end ratio.

Choosing your effective gear ratio is the first choice, then choosing your tire size and physical ratio is the second choice. Were talking about the latter here. What to do when you know what your effective gear ratio should be.

[ December 31, 2001: Message edited by: Terry Burger ]</p>

Bob Cosby

Tim. Ok...we can disagree. Could you please state your reasoning?

Also, may I make a suggestion? Don't take my word for it - go see what the *real* racers do. By real racers, I mean Stock and Super Stock guys, or people that class-race "purpose-built" race cars. Get THEIR opinion on how they gear their cars.

The entire philosophy is that the last 100-200 ft of the 1/4 mile just doesn't matter. If your only 100-200 rpm above your HP peak at the finish, then your hitting it very close to the finish. Too late....you need to gear the car to run best in the first half of the track. If you're in the limiter at the finish line - great, you're geared about right (assuming your motor doesn't fall flat on its face at its peak - not likely, and certainly not what an LS1 does).

BTW..in the context of this discussion, I'm not considering street driving at all.

Terry...I agree, but it is impossible to divorce one end of the track from the other. As such, you can't pick one without considering the other.

McRat

Kinda unrelated experience, but when I ran bikes, it's Bob's philosophy that gets best ET's. Too much gear works better than too little.

The first half of the track is the most important, because you are already going very fast at the 1/8mi marker. If you must lose acceleration somewhere (no set-up is perfect), you are best off losing it at the top end.

I'd gear my bikes so I'd be over-rev'g going thru the lights for the best ET's.

Tim98TA

iTrader: (7)

[quote]Originally posted by Bob Cosby:
<strong>Tim. Ok...we can disagree. Could you please state your reasoning?</strong><hr></blockquote>
Bob, your reasoning may very well have merit. After I posted, I was driving down the road thinking about it and I remembered someone telling me about the 1%/10% rule concerning gears/tires/hp. I'll let them explain it to you, because I am still a bit vague on how it works. I understand it, but re-explaining it, I may screw it up.

Tim

Colonel

How far above the HP peak you should be when crossing the line depends on how quickly your power drops off after the HP peak. If it drops off slowly (good flowing combo with a wide LSA) the best RPM to cross the line will be WELL past the HP peak.

For best ETs use just enough tire for traction and run as much gear as your engine's power range will allow. Of course, for more consistancy use more tire than usually necessary.

I shift at 6800 but cross the line at about 6900. I don't know where my HP peak is but I feel that my power drops off pretty quickly after the HP peak due mainly to the restrictive LS6 intake manifold. It feels like it pulls like an ox up to a point and then really drops off quickly. Not that this is a problem. I just chose my gearing accordingly.

Best ETs will come with enough gear that your trap speed suffers a little (assuming adequate traction.)

Bob Cosby

[quote]I shift at 6800 but cross the line at about 6900.<hr></blockquote>

That's likely very close to optimum. Many hard-core guys will go even a couple hundred rpm beyond that (in relation to their shift points). I already mentioned that my car is under-geared, mainly because I'm not willing to make the street sacrifice required to get those optimum ET's.

[quote]Best ETs will come with enough gear that your trap speed suffers a little (assuming adequate traction.)<hr></blockquote>

Agree with this too. I think you will find that best MPH will be when your car is very close to the HP peak in the lights...perhaps a tad beyond.

Trevor @ Texas Speed & Perf.

iTrader: (3)

[quote]Originally posted by Colonel:
<strong>For best ETs use just enough tire for traction and run as much gear as your engine's power range will allow. Of course, for more consistancy use more tire than usually necessary.</strong><hr></blockquote>
right on You don't want to run more tire than you have to. I've seen a few low 13-second cars at the track running too big of a tire, and one guy in a Galaxie was running a 28x11.5x15" ET Drag to run 13.20's! <img src="gr_eek2.gif" border="0"> You want to run the least amount of tire that will still allow you to hook. Anything beyond that is slowing you down. A little "overkill" isn't uncommon for bracket racers, especially if you run at tracks that aren't exactly known for their track prep.
Also keep in mind that the more sidewall you go with the more you'll have to worry w/ tire growth on the big end.

Visceral

iTrader: (1)

Welll...hrm. In the old days is was some much simpler...and along the lines of Bob's *and* Col.'s reasoning.

Gearing/Tire diameter- hit the RPM you are comfortable as the "redline" 10 feet after the finish light in the 1:1 gear (or 2nd with a glide, whatever ratio 2nd is).

Tire Width- Run the norrowest tire you can still plant with your chassis, your stall, and your power level.

That simple, and it will give you your fastest ETs in a *racecar*. If you have to turn around and drive the thing on the highway, you've got some compromises to make.

Seems with LS1s, which *generally* make great power to the redline, this would especially apply.

chris

Pro Stock John

iTrader: (34)

I can't take any more gear than I have now.

I have an automatic with 4.10 gears.

I pretty much have horrible gas mileage.

I don't know that I would run more gear with my motor, but if I had a 7000 rpm solid roller stock cube car I would consider running a 4.57 gear with 28" slicks.

Skelton

You gear for et and use clutch setting/converter choice and chassis setting for 60ft. In my internal stock ls1 car, best rpm through the traps is around 6100-6200 which is 700-800 past peak. On a modified production 331 cube 57 chevy we ran in the early 80's, we launched at 9k, shifted at 8k and trapped around 9100 rpm. Its much better to accelerate the first 1000-1100 feet and let the speed obtained carry you the rest of the way as long as the motor can handle the r's. That works for most cars with less than 1000hp but each car is different. Testing is the only way to obtain best et.

Joe Kizzire

To start with you want to build your engine with a rpm range that's going to work with the known gear ratio (through trial and error) to be used so that you cross the finish line a little past peak hp.

10%/1% engine...
Keeping in mind what I said in the beginning an engine needs to develope peak hp and stay close to peak for a few hundred rpms after. The rule of thumb as it was explained to me is a engine needs to make 1% of peak hp over 10% of the rpm range.

Example: At 6000 rpm my engine made 439.4 hp and at 6700rpm it made 439.6 with the peak of 445.0 at 6400. It held 1% of peak power (4.5 hp) for 10% of rpm range (6000 to 6700rpm).

When your power band is 10/1 range then you can gear the gear as stated before by Bob Cosby and it will perform at it's best. This theory work for roadrace car also.

If you have a engine that has a peakie hp curve
(pulls up to peak hp and then falls off like a rock) then you have to compensate with gear which in turn hurts your ability to get the car off the starting line.

Ragtop 99

iTrader: (7)

[quote]Originally posted by Pro Stock John:
<strong>I can't take any more gear than I have now.

I have an automatic with 4.10 gears.

I pretty much have horrible gas mileage.

</strong><hr></blockquote>

What if you run larger street tires? I haven't looked at availabilty (which could kill this idea in its tracks), but if you move up from 40 series to 50 series or 50 series to 60, you could move up to 4.33's and not effect your highway rpms.

Pro Stock John

iTrader: (34)

I could move up to 275-60-15 radials now, they would be 28 inches tall. HackerJoe has that setup now. I couldn't stuff a taller radial in the car.