Engine placement in a dragster

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by rb0804, Oct 25, 2017.

  1. rb0804

    rb0804 Member

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    Anyone have any data on mid plate distance from the center of the rear on a dragster? I did a search last night and found some good information on funny cars and front engine dragsters, but nothing about rear engine dragsters. What about crankshaft center line and rear end ride height of the car? Does changing one of the above mentioned paramaters work better than the other? I remember Bob Meyer saying that moving the engine ahead 8” in the funny car only moved 80lbs on the front tires. Will changing one or more parameters shake the tires more than the other? Does one setting work better for an automatic car than a clutch car? How does overall wheel base factor in? If one were to add length to an existing chassis, where would be the best place to add, between the engine and the midplate, the front motor plate and the driver or from the driver forward? Thanks for the space.
     
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  2. Soldierboy0098

    Soldierboy0098 Active Member

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    I can tell you on dragsters you want the motor 41-45" out as per Brad Hadman. -Trev
     
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  3. Bob Meyer

    Bob Meyer Comp Eliminator

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    Back of block to axle C/L = 46.25" w/CS-1 Lenco, 42.5" w/CS-2 Lenco.
    You'll hear lots of theories, non chassis building tuners and engine builders believe it should be farther back. Fact: farther back means much larger clutch changes to accomplish anything, the thought of the word "tickling" is history ! Also, moving the rear axle back does nothing to loosen the chassis stiffness. There is much more..........
    BTW: reading stuff on the internet WILL cost you in the long run ! ;)
     
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  4. TADHemiracer

    TADHemiracer Member

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    Isn't the engine distance further out for Bruno or converter driven dragsters, also 2 spd or 3 spd?
     
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  5. rb0804

    rb0804 Member

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    So what I’m gathering from the post above is that further back is better,(ie less distance from the rear of the block to the centerline of the rear). The CS1&2 are comparable in weight with the primary difference being that the 2 is shorter than the 1 which allows one to move the engine rearward. So moving the engine back or the rear closer would increase the initial hit of the tire and also makes for a tighter tuning window (ie a small change makes a bigger difference)? Am I getting this right?
     
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  6. Bob Meyer

    Bob Meyer Comp Eliminator

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    Think chassis stiffness........ what is the strongest thing known, a triangle ! Count how many you have between back of block and axle mount upright. Usually 8, four per side. Build car with engine 3.75" farther back, calculate 8 triangles 1.875" shorter. You will understand why the chassis is much stiffer ! Now lets move the housing back thinking "we'll fix it", did the chassis get softer ? Nope! Is the clutch easier to get a small change response ? Nope !
    Getting weight to transfer is the plan........if it's already there....?
     
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  7. rb0804

    rb0804 Member

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    So stiff equals poor weight transfer? More of a flexi flyer car would be better? Still kind of confused why a CS2 trans would require a different engine setback? Why not put them all at 46” and run a drive shaft if thats better, which is what I think you are saying?
     
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  8. Bob Meyer

    Bob Meyer Comp Eliminator

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    Bingo !

    Some believe : as the CS2 is shorter, we can move the drivetrain back 3.75" and pick up 200 lbs. on the rear wheels ! False.........
    FACT: 38 lbs. ! (at 285" w.b.) Guess what.....now balance factor is screwed up, and chassis is stiffer, and more than likely, you add 40 lbs. to front end and suffer with heaver car!

    Bet you can't guess how I know this !!!
     
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  9. rb0804

    rb0804 Member

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    I would have to guess that you either built a car or helped someone who did just want you stated and it didn’t work so well. Have any trade secrets you’d like to share about front/rear weight percentages? If your weight percentage works out to be a known good combo, does it really matter where the mid plate is? I assume it works out to 42-46 range mentioned above? The A-Fuel stuff seems to have the engine AND driver pretty far back. What’s your thoughts on moving the driver forward 18-24 inches? I like the idea of being able to get the camshaft out of the engine and not hit the roll cage with it still in the car. What about front to rear ride height? The higher we place the rear in the car, the lower the chassis will be to the ground as well as the engine (depending upon oil pan to ground clearance). Is it better to have the rake from the rear to the front or from the front to the rear? I have seen cars both ways, but don’t recall how they behaved.
     
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  10. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    43-46 is what most TAD's out there are. Some of the older ones are a little further back.

    Moving the motor out is definitely the trend
     
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  11. Bob Meyer

    Bob Meyer Comp Eliminator

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    rb; if I knew who I'm talking to, I may share a little more, but since you asked, I'll share this: on the only blown car I ever moved the motor back, I never told anyone, but the driver went ahead 2 inches, but I missed the target balance and it needed 40 lbs. in front to maintain the 500 lb. number I like. I'm not into the "Wild Bill Shrewsberry" deal. (Still a top 5 car 4 straight years)
    I've had Champs on 3 continents, but even in semi-retirement, I still haven't gone stupid, just "invalidated" ! (inside heat treat joke!)
     
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  12. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    While Uncle Bob's court is in session -

    What's your thought on percentages vs a target number (ie 500).

    I had this argument recently, would be interested in your take and experience.
     
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  13. KZ5 Blown SBC

    KZ5 Blown SBC Member

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    Since were on the subject what about pinion angle is there much too be had there.
     
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  14. Bob Meyer

    Bob Meyer Comp Eliminator

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    Will; I'm a little out of the loop, don't know what today's minimum weight is, but more than likely, 25-28% with driver would be a safe number. This is all based on 285-290" blown car, A/F cars, your results WILL vary. The car must steer with at least the right front on the ground. You can learn an awful lot by watching the left front, but if your car has sufficient front crossmembers and diagonals, and no boingy stuff, the car will steer fine.
    KZ; wrong term to use, pinion angle has to match crank angle.
    Think "crank bolt to the ground" , no door car suspension terms or for that matter wheelie bar playing terms. Simply weight transfer, and where the weight starts from. If it has to start from below level, time is wasted. In other words "First motion MUST be forward........not down!
    Barnyard logic Bob
     
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  15. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    After working with some door cars the past few years, really started to think of weight more as a percentage number than 'x' lbs on the nose or a target front half scale number. So many TAD's now days are a good bit over the 2050 minimum (471 cid cars are 2075).

    My point was by taking 20-30 lbs off the back of the car, you could take enough weight off the nose to get the percentage back where it was before.

    Let's say the car weighed 2130 and you took 30 lbs off the back half of the car. Let's also say that the front half scale weight was 25%, making the back half 75%.

    The front half would weigh 532.5, back half 1597.5.

    If you took 30 lbs off the back, the back would now weigh 1567.5. If you divide that by .75, you get 2090. Multiply that times .25, you get 522.5.

    So by taking 30 lbs off the back, you could take 10 lbs off the front of the car to get the percentage back. to 25/75.

    The old guy I was arguing with told me the car didn't know percentages, it just knew how much was on the nose.
     
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  16. Bob Meyer

    Bob Meyer Comp Eliminator

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    I think you're on the right track with those thoughts. If the car needs weight on the front all year, there may be a need on a special day, but I see no value in running an overweight car. I also understand that too much rear weight means you lose fine adjustments with the clutch, meaning you have to make 15-20 gram changes to see any difference, one way or the other. If you can tickle it with 2-4 gram changes, and see that change do what you want, you have a car you can go anywhere with and do well (if you have a good record book). Of course there are many factors other than the car, i.e. driver weight, engine angle, cockpit length comfort vs. driving with knees in front of your eyes, dangerous slip tubes, insane tires/pressure, and thoughts of "this is my combination and I'm sticking with it" ! I'll just let the world ponder..........WTH is he thinking ! :D I've turned down a few cars through the years, simply because I won't follow the "customer is always right" line of thinking. Safety has always been my #1 concern, #2 is being extremely competitive.
     
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    Last edited: Nov 8, 2017
  17. KZ5 Blown SBC

    KZ5 Blown SBC Member

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    Bob if you dont mind can you send me your number so I can pick your brain thanks
     
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  18. rb0804

    rb0804 Member

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    Are all slip tubes dangerous or only certain ones? I remember hearing a story of someone’s car being double slip tube and the engine would try and fall out when they jacked it up. Will a slip tube car work better than a non-slip tube car? What about a cable car? Any advantage there or not worth the extra complexity? I am looking at this from a tuning prospective, not a chassis building prospective, but it’s nice to have an idea of the results of different changes in case we want to make changes or try something different, possibly even a new car someday. PS I sent you a private message as well.



    To Mr. Will Hanna, in your example of the 471, I come with with 2085 minimum, not 2075. Am I missing something or did you make an error? If it’s no longer 5 lbs per cube over 464, I need to make some adjustments to the car.

    471-464= 7 multiplied by 5 = 35 plus 2050 = 2085

    As always, thanks for the space and the the replies!
     
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  19. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    The maximum CID at 2050 is 466 not 464, so it's 5 lb per cube after 466.
     
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  20. Bob Meyer

    Bob Meyer Comp Eliminator

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    619-440-7701 6-8 P.M PST Mon.-Thur. is best.
     
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