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Author Topic:   Gear Change Question? Please Help
tee1up6134
Dirt Full Roller

Total posts: 32
posted June 01, 2004 07:42 AM  
I am currently running a 5.83 at 7000 rpm on a 1/4 mile always really dry slick track with a very strong motor. What would happen if I went down to a 5.43? It just seems like I cant touch the throttle in the corner or she wants to break loose. Any suggestions? thanks

NJantz
Dirt Forum Champ
Total posts: 755
posted June 01, 2004 10:10 AM  
If you have got your car as hooked up as possible then you should try a 5.43 or a 5.67. Or even a more mild cam that has the powerband at a higher rpm range.

Are you racing at Ft. Morgan?

mod70
unregistered Total posts: 755
posted June 01, 2004 11:00 AM           send a private message to NJantz   Edit/Delete Message   Reply w/QuoteBBBBBB
It's harder on an engine to bog it down than to let it spin. 7000 is a good number to turn. You might try to take some power from it by taking some timing out of it, or changing the cam, however I think your problems may have more to do with the setup than the RPMs you're turning. Please post your setup and we may be able to find something there that could help you.

BB46
Dirt Full Roller

Total posts: 32
posted June 01, 2004 02:15 PM  
From what I have always heard RPM's kill motors the fastest. I think somebody told me a long time ago that after 7000 every 100 (Or something like that. could have been 500) RPM more you double the stress on the rotating parts. Never heard that "Bog down" theory before. Seems bog is just load. Isn't it?

mod70
unregistered Total posts: 32
posted June 01, 2004 03:04 PM           send a private message to BB46   Edit/Delete Message   Reply w/QuoteBBBBBB
Too many RPMs will definantily hurt a motor, but placing too much of a constant load on a motor can produce alot of stress too. Most motors have a range where they work best in. I guess the question should also include how low it turns at it's slowest point.

dogwalker
Dirt Full Roller

Total posts: 65
posted June 07, 2004 12:46 PM  
You may want to try a few things out there before you get another set of gears. For now I would try more left bar angle (or try a shorty left bar) to gain more angle/bite coming off 2&4. Use a very gentle right toe, and consider moving the pull bar up one hole on the chassis end so the chassis doesn't try to hook immediately. Sometimes it's just that darn slick out there.... that's when you can slow down and go fast!

zeroracing
Dirt Forum Champ
Total posts: 1875
posted June 07, 2004 03:13 PM  
i know alot of guys will disagree on this one but you may try a 6.00. this will slow the tire speed down and make it easier to hook up the tires.
that is why on a slick track people can run 6.00 on 3/8 mile tracks.
by break loose is that both tires or does the rr outdrive the lr so that the car wants to spin out on the gas.
try a little stiffer lr spring or little less bar angle in the rr. also more in the lr.
i would consider going up in gear so you can slow the wheelspeed down.
also as far as bogging a motor down.
that will kill the crank fast and the bearings and over revs will kill the rods and vavle train fast.
both are hard on a motor. i would rather turn 100 more rpm then bog a motor down, unless i had really good crank and bearings and mains.
good luck, but my advice as odd as it may seem is to slow the wheelspeed with a 6.00 gear and then you will get more bite and turn the same or less rpm.

govitt1
Dirt Roller

Total posts: 25
posted June 07, 2004 04:08 PM  
We run very similar conditions on a 1/4 mile track. I run a 5.67 and turn in the ballpark of 5800. A lot of guys out here run the 5.83 and say they are in the 7000 range. I wish I could get in the 6500 range but the 5.67 seems to work pretty well if your engine has good torque at that rpm.

dogwalker
Dirt Full Roller

Total posts: 65
posted June 07, 2004 04:43 PM  
6.00's are not a bad idea with a good motor! ....matching wheel speed and RPM works well to give the car more punch coming off the corner on tacky and would be less likely to loose traction (as much) on dry. Tee1up will be running around 7500 at the end of the straight with 6.00's though. Need more info if wheels breaking loose causes "loose" condition or if both tires are roasting evenly. I would look for more bite before gears....5.83's @ 7000 sounds pretty decent. NJantz may be on to something.

hiredgun
Dirt Forum Racer

Total posts: 78
posted June 07, 2004 08:27 PM  
I lean towards zeroracings thinking.
As it is now you show to be running around 95mph top speed. depending on how smoooth you are a certain % is wheel spin .
when it goes slick the track slows down , the 6.00 will help you keep the tires under you and not blast you right through the power band, dont be surprised the rpm may stay the same.
i will pm more fyi

FASTLAP
Dirt Maniac

Total posts: 171
posted June 08, 2004 05:05 AM  
I agree with both NJ and Zero. My opinion is to make sure you feel your setup is right on the money. If so, then I would consider slowing the wheel speed down. Less wheel spin, more traction.

racer18d
Dirt Roller

Total posts: 14
posted June 08, 2004 06:15 AM  
Explain to me how adding gear slows wheel speed down on the dry slick track because where we run it might as well be on an ice rink. I have just never heard of this before. Thanks

Kromulous
Dirt Forum Champ
Total posts: 796
posted June 08, 2004 06:27 AM  
Its basicly all theory. A bigger rear gear ratio will produce over all less wheel speed, thats a fact.

I suspect the theory is with the bigger gear you would end up using less torque (from the engine) to accelerate to the same speed, aka the taller gear. The overall speed of the car would be less, given the same distance, but accelerating to that point should be quicker with the taller gear.

Its basicly a duality. Easier to accelerate but at the same time because of the taller gear the potential for spinning rear tires is higher.

jws
Dirt Maniac

Total posts: 115
posted June 08, 2004 07:28 AM  
I'd be careful with using a higher gear to reduce wheel spin. I think what might be happening is that you are taking your engine out of it's optimum torque range coming off the corner. I know that some of the late model guys do that very thing on dry slick tracks. It may work but it's hard on parts. By the way, I quit building stroker motors for this very reason. Way too much off the corners, even on heavy tracks.

juliaferrell
Dirt Freak

Total posts: 370
posted June 08, 2004 11:17 AM  
If set up properly you should come off the corner straight enough that there's no way the throttle can spin you out. If you mash down on it the thing should just spin straight down the straightaway. If the throttle spins you out then your setup is not tight enough or too tight and flipping you over in the middle.

HERNDON
Dirt Full Roller

Total posts: 73
posted June 08, 2004 02:40 PM  
Try to retard you're timing, first. We always go down a few degrees between the heat and feature because the tack dries out so much. This always compensates for my eager foot!!!

IowaFuzzy1
Dirt Maniac

Total posts: 136
posted June 10, 2004 12:22 AM  
Without knowing the specs on your engine,it's really only a guessing game ,also what are your percentages frt.to rear&side to side. sounds to me like you should try a little chassis tuning first.5.43 definately not the way to go unless it's high banked and you can ride the rim.The 6.0 theory can work,but you have to be HOOKED UP,so you're back to the chassis.
We run a 5.43 on a 3/8 banked fairly slick track with a 18 degree 367, car weighs 2450 and turn 74to7800.
Lots of good advice here,GOOD LUCK

------------------

dirtywrench13
Dirt Freak

Total posts: 324
posted June 12, 2004 05:48 AM  
I THINK I'D JUST TRY ADDING 40 LBS TO THE TAIL OF THE CAR. IF IT SLOWS U DOWN OFF THE CORNER,CHANGE GEAR TO A 6.00 AND ADD HALF THE WEIGHT.

tee1up6134
Dirt Full Roller

Total posts: 32
posted June 14, 2004 07:16 AM  
Car is 53% rear full of fuel. 52% cross. Where would you suggest putting the weight on the chassis.

tee1up6134
Dirt Full Roller

Total posts: 32
posted June 14, 2004 07:17 AM  
Car is 53% rear full of fuel. 52% cross. Where would you suggest putting the weight on the chassis.

jws
Dirt Maniac

Total posts: 115
posted June 14, 2004 07:38 AM  
Put the weight on the rear! That is a very low rear % for a modified. I don't know anyone running less than 55% and most guys are up aroung 57 to 60 full of fuel. If you are hurting for forward bite that's the first thing I'd change. By the way see the topic titled "How much is to much" for more about rear %.

NJantz
Dirt Forum Champ
Total posts: 755
posted June 14, 2004 08:57 AM  
Definitely get your rear percentage up. In fact, that's what I'd try first. You need 58-60% for an IMCA mod. If you are getting pulled off the corners with a good motor and a 5.83 gear then you need to work on getting forward bite and probably sidebite as well if its loose when you touch the throttle.

[This message has been edited by NJantz (edited June 14, 2004).]

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