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Old 12-26-2008, 03:31 PM   #1
Tony Curcio
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Default Dragster Chassis Length

Is there a formula or rule of thumb for determining the approximate wheelbase that will be best for a certain power level?

I've been seeing some interesting deals on E-Bay and such, and have wanted to put together a 4 cylinder dragster as a sort of rolling test lab, comparable to an F/D or F/ED. These cars seem to have a shorter wheelbase than any of the small block V-8 dragsters, like a C/D, and they are definitely shorter than most Super Comp applications. And then the Top Fuelers are over 300" long.

Looks like there's a correlation between available power and wheelbase. Can anyone explain it?

In particular, is a 220" wheelbase too long for a naturally aspirated 4 cyl with automatic?
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Old 12-31-2008, 04:56 PM   #2
Charlie Yannetti
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Default Re: Dragster Chassis Length

Hi Tony....... I'm not sure on what kind of power you are planning to make, but both F/D and F/ED are great classes to get into......... I'm kinda remembering the numbers 215 to 225 in wheelbase, but I could be mistaken........ you might want to give Kurt a call at ProStart....... he has done the last two chassis for Al Ackerman and if you watch Comp performance records, you will have no doubts that Kurt knows what he is doing........ hope this helps
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Old 12-31-2008, 05:49 PM   #3
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Default Re: Dragster Chassis Length

Thanks, that is helpful.
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Old 01-06-2009, 07:10 PM   #4
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Default Re: Dragster Chassis Length

http://www.landsharkdragsters.com/
185" running low 7's.
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Old 03-10-2009, 08:16 AM   #5
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Default Re: Dragster Chassis Length

Yes, I can explain the long wheelbase business.

First, it must be recognized that the sanctioning outfits have specified minimums for the dragster classes. So, we couldn't go really short, even if we wanted.

The first hard tail dragsters had very short wheelbases and, in my opinion, were the best looking dragsters ever built. Mooneyes is my favorite. Still love to drive over to Garlits' museum and stare at it. But, that's just my opinion.

But, those early dragsters could be a little squirrely. So, someone got the idea that, if they were a bit longer, they might be more stable. And, whatta ya know, they were. But, there's an explanation...an engineering explanation...for what happened. Well, there's actually 2 engineering explanations, but one is of lesser importance. That one says that, yes, the dynamic equations indicate increased stability with a longer wheelbase. But, we know it can't be that simple, for there are short wheelbase open wheel race cars that handle very well...make that VERY well...at similar speeds.

Which brings us to the really important engineering explanation: Consider a conventional production car with rear wheel drive and a beam rear axle. As you're well aware, the driveshaft torque tends to unload the right rear tire on forward acceleration. The reaction to that torque is taken at the transmission/engine mounting points and is distributed...front-to-rear...in proportion to the front and rear roll stiffness. That portion which goes to the rear tends to cancel the unloading of the right rear. But, since some...usually most in a production car...goes to the front, the right rear is still light.

A solidly mounted rear axle has a very high...almost infinite...roll stiffness, so that was helpful to those early short wheelbase dragsters. But, there remained a great deal of torsional stiffness in the frame which extended to the front wheels. As a result, the rear tires were still far from equally loaded.

So, the major benefit of the long wheelbase is to essentially "decouple" the front end, causing essentially all of the reaction torque to feed to the rear, where it cancels the initial driveshaft torque and provides essentially equal rear tire loading (and increased safety).

Was there another option? Of course! Those early builders could have kept the front suspension and worked with it. But, that required development time and effort and...meanwhile...the long wheelbase dragsters were winning races.

(For the suspended full body cars, the anti-roll bar is the equivalent of the long wheelbase.)
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Old 03-29-2009, 11:02 AM   #6
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Default Re: Dragster Chassis Length

Quote:
Originally Posted by Tony Curcio View Post
Thanks, that is helpful.
Tony-you have a PM
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Old 12-23-2009, 04:00 PM   #7
Bill Baer
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Default Re: Dragster Chassis Length

Quote:
Originally Posted by Tony Curcio View Post
Is there a formula or rule of thumb for determining the approximate wheelbase that will be best for a certain power level?

I've been seeing some interesting deals on E-Bay and such, and have wanted to put together a 4 cylinder dragster as a sort of rolling test lab, comparable to an F/D or F/ED. These cars seem to have a shorter wheelbase than any of the small block V-8 dragsters, like a C/D, and they are definitely shorter than most Super Comp applications. And then the Top Fuelers are over 300" long.

Looks like there's a correlation between available power and wheelbase. Can anyone explain it?

In particular, is a 220" wheelbase too long for a naturally aspirated 4 cyl with automatic?
Well Tony here's my 2 cents worth, The longer the wheel base the more flex you can build in to the chassis itself and most comp dragsters also try to run the narrowest rear tire possible (the less rotating mass the better) And overall the longer chassis will hook up better but you want to be as close to the min. weight for the class as possible because to some extent the cylinder head (flow) will dictatate the power you can produce so in general if your car is heavy (above the min) it will require more ci. but a bigger is not always a more powerful motor. I have seen some of these 4 cylinder comp dragsters with very little and or smaller tubing beyond the drivers area.
So My thinking is to focus on keeping it light and flexable with light having priority. The basic correlation is that the more power you try to put to the chassis the more it needs to flex. The reason all of the top fuel cars are 300" is because that's the max allowed by the rules . And if you study what's going on with comp dragsters you note that the A/D and A/ED cars are longer than the B/D or B/ED's and that they in turn are longer than the D/F cars. What the super comp guys are doing has nothing to do with max performance were about consistency (the larger the tire the better)
So a 220 wheelbase would probably fine if you could get it down to the min weight, but a 200" or shorter car is probabley lighter.
There may be some of then out there but I have never seen a land shark car in comp so I don't know if they would work with narrow rear tires.
I also have seen very few suspended cars in comp which I assume is due to the added weight.

For what it's worth.
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