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Author Topic:   Perfect Engine Combo
Dirt Administrator

Total posts: 5060
posted August 12, 2002 06:39 PM UIN: 16262997
I know that there has to be a formula to figure how much torque you can put on a certain square area of tire patch before it will spin. I have been trying to find something that will tell me exactly that. For a modified with limited tires, this could be extremely helpful to get you in the neighborhood. 2500 lb car at 60% rear.... Which means there are 1500 lbs on the rear tires.....will be more under some dynamic circumstances. In a perfect world, if you had chassis dyno numbers and engine numbers, there has to be a way to figure how much torque you can put on the rear wheels before they spin. If you were to build a motor to that spec, then again in the perfect world scenario, you could flat foot the motor and not spin the tires. Yes, track conditions will make a difference, but there has to be a ratio or adjustment in the forumula for different situations of track conditions. I am very interested in this. I feel like this is something that could make a huge difference in everyone's program if we could figure this formula out. What is unique about this, is that it would be consistent and every car wouldnt have to be chassis dynoed to get you in the ballpark. Can any engineers or anyone out there help me with this? I would like to build a calculator to do this with someone's help. I am no engineer, but I feel like there has to be a way to do this.

PS....I know that this formula has to exist, but I may be behind the times in getting it....Someone please help!


[This message has been edited by jammin (edited August 12, 2002).]

Dirt Freak

Total posts: 240
posted August 12, 2002 07:11 PM
You need a mathmagician... LOL
seriously though, I will ask a friend that is an engineer and builds airports, I also know a Russian math genius, I guarantee he will come up with something.

Dirt Administrator

Total posts: 5060
posted August 12, 2002 08:15 PM UIN: 16262997
Thanks 51!


Dirt Roller

Total posts: 24
posted August 13, 2002 06:43 PM
Hey jammin a couple of years ago circle track did a series of articles on full utilization of the tire contact patch. I don't have the magazine anymore but I think it had a formula for force on the tires contact patch. It was very intricut.

Good Luck

Dirt Maniac

Total posts: 121
posted August 13, 2002 07:41 PM
Hmmm I think-- straghtaways-pedal to the metal x feather it in the curves - driver error = the perfect set up!!!!

Just kidding jammin-- But i think you might be onto something here. We have at our track an a-mod driver( very experienced) and a b-mod driver(son--16 yrs old-not so experienced) winning almost every race.

His secret I believe is being able to do what your looking for--The perfect traction with the perfect set up.. Both the drivers can take there cars around the track anywhere they want and never slide or spin out. There cars goes high low or in the middle --whereever they put it. This I think is the secret to winning-- find those magic numbers and remember if your spinning wheels your not going anywhere till they grip agian..

Just my 2 cents worth--Hope you find that formula----- Wheels

Dirt Full Roller

Total posts: 41
posted August 14, 2002 12:00 AM
not trying to be funny my father found something like what you are lookin for but it was useing a 99 s_10 4.3 vortec motor with a car weighing 2250 and about 60% rear the chassis are stines the track 1/4 and the pedal to the metal dont let off because you will get passed because it would take a second to get the momention back but it is like what you said look into it

Dirt Administrator

Total posts: 5060
posted August 14, 2002 09:33 AM UIN: 16262997
Thanks guys, I know that everyone has different ideas and thoughts on this, but my thought is that if you can get as close as possible with an engine combo for what your car is capable of without change, that you may be as fast or faster than those guys adding lead to make their car hook up with larger motors. I have been running a really basic engine combination some at the local track with these outlaw mods....5-10k motors and have been running with them. Been running midpack,which is acceptable with an IMCA setup, but I put a carb from KP on the car, it ran much better, gave me about 700 more RPM's out of the little motor, but now I am out of my range for the car and I have to add lead to make it stick. Tire temps on back are even, but just hot. I am spinning now. If you take a look, adding lead is going to take some of that speed away from you in momentum, and you may gain it back because of the motor on the end, but overall, it may not be as fast as the car can go with a larger motor combo. Thats why I am looking at this. What do you think?


Dirt Roller

Total posts: 14
posted August 14, 2002 03:26 PM
I read somewhere that a tire works because of friction. And that friction is caused by tire spin. So, the perfect scenerio would be a slight tire spin all of the time at full throttle. So I think choking the motor down to a point that it will just hook and go is not such a great idea. RookieRacer has a good point too about losing momentum. Sounds Like You Need a $5000 dollar traction control box. LOL

Dirt Forum Racer

Total posts: 77
posted August 14, 2002 08:33 PM
Jammin,you are thinking too much,just keep tweaking on the car,making small changes,you will get there.90% of racers, out think themselves 95% of the time,keep it simple.

Dirt Newbie

posted August 14, 2002 10:38 PM
I think the key is to have a motor that's easy to drive and predictable. I ran a motor last season that dynoed at 450hp at 4800 rpm, and 523hp at 7000 rpm. Don't sound like much until you see the line on the graph going perfectly straight between those 2 points. I've seen dyno sheets for similar engines that made up to 580 hp, but the graph looked like a sketch of the view out of a Denver hotel room. BIG peak right in the middle of it. Nice to brag about, but I drove by a LOT of motors like that. I sold that motor at the beginning of this season to build my son a b-mod, and the guy who bought it's won nearly half the races he's started with it. Incidentally, by now this motor's got over 50 nights on's built right too, but that's another whole discussion. Anyway, driveability's the issue, it's SO not about horsepower.

my $.02,

Dirt Administrator

Total posts: 5060
posted August 15, 2002 08:27 AM UIN: 16262997
racer, I think about this stuff so I can be more educated to make decisions on and off the track, workin' the brain so to speak. But I do know for a fact that I just drove our old mod out of the ballpark somewhat by giving myself more power. This shows me that this might have been avoided with some numbers at hand.


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