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Thread: Suggestions for chassis performance

  1. #1

    Suggestions for chassis performance


    Newbie asks advice for chassis adjustments. Two videos from same pass:

    9.15 @ 146mph
    1.306 60ft

    The car:

    It's a -84 tube chassis Toyota Corolla
    509 BB chevy, about 750hp
    PG, 1.76 first gear
    4.11 Rear gears
    2380 lbs, 59% front, 41% rear (I know, iron headed BB weights)
    Shifting at 6000rpm, 6400rpm max rev limiter because I can't attach a chute. The rear of the chassis is made of under 1" tubing.
    New Super Gas/Pro Stock GY tires, 32x14x15
    Racing Super Pro ET, All NHRA rules.

    Should I do something with the chassis? Loosen the inbound setting at rear shocks? Higher and shorter IC with the 4-link? Looser front end? 4.33 gears and more revs? Or what? Obviously, I want to get the car in to the eights. Please mama, I want to go fast! :lol: Also, lifting the front tires wouldn't hurt.

    Any suggestions are welcome.


    Mikko "dr" Niemi
    Finnish Super Pro ET 1984

  2. #2
    Senior Member EXPERT BUILDER
    Join Date
    Dec 2006
    The nose of that car is on the heavy side. Any weight you can move back would help a lot.
    Print out and read the "sticky" at the top of the chassis and suspension page. Lots of info there to get started.
    Personally I would like to see a little more gear in that thing, depending on what rpm you want to cross the finish line at.
    What do you mean that the rear is under 1" tubing and you cannot attach a chute?

  3. #3
    I mean that the chassis from the rollcage back should be upgraded to install the chute mount, it's too weak now as the chute will pull 1-1.5G.

    I want to cross the finish line below 7000rpm and I think that moving from 4.11 -> 4.33 and 6400rpm -> 6800 rpm would help maybe 0.1 - 0.2 seconds and it still would stay under 150mph.

  4. #4
    With the weight I have few options:

    a) add weight to the trunk. Not so interested.
    b) buy aluminum heads, that would lose 80lbs and get the car maybe in the 57/43 range. Too bad I haven't 3000$ right now.

    I could also try to remove the alternator from the front end but I think that would do more harm than good.

    Is it possible to make a car this noseheavy to work better without moving weight? The wheelbase is only 100" so I think that helps a little with the weight transfer in the start.

    How would looser front end and/or looser rear shocks inbound affect?

  5. #5
    well i'm not a chassis builder, but it won't work being that nose heavy. you have about zero weight transfer.

    think of it like a teeter-totter. the more weight you have on the back the better it hooks. that is why a dragster works so well, they have 70 some % on the rear.

    just my .02

  6. #6
    I estimated that if I add 100lbs ballast to the trunk, I would get 55/45 weight distribution. Is this worth trying? Will my ET's be faster or slower?

  7. #7
    Senior Member MASTER BUILDER
    Join Date
    May 2003
    Owingsville, Ky
    If the car is spinning, then the ballast in the trunk would help the ET. But in your case, when the car left the line, I saw at least 3 wrinkles in the slick and the car accelerated straight forward and didn't "fish tail" any. So, IMO the ballast might help pull the front wheels, but would not help on the et.
    The spring rate on the front end could be too stiff. When I built my car it was recommended for me to install the 400lb/in front springs on my struts, because of the weight. It wouldn't pull the wheels, but the car would work OK. I then changed the springs to 350lb/in and 1" longer to help hold the front up, and then the car was able to pull the wheels a few inches and run a little quicker.
    It is like mcracecars stated that your car needs more gear. If you are trying to get a car to run ET and not MPH in the quarter, you need to get it to accelerate as quickly as possible down low. I run a 4.56 gear in my car with the 16x33 slicks and my car has always been a little softer on the bottom end with the powerglide 1.76 and turns a little more MPH on the top. Moving the shift point up would probably help, also. I would think that you are losing some usable HP by shifting so low. Where does your engine make peak power? If not known, what size is your cam as that would give an idea?
    Your 60ft ET is not that far off from what is predicted for your 9.15 quarter mile ET as it shows that it might be a 1.27. This is the link to some good calculators

    At the speeds and times that you are wanting to achieve, I would add the bars to the rear that would allow installing the chute. I have had rear brake lines break before. You might be able to come off from the main hoop and add some larger bars that are tied to the inside of your existing framework to make a tether point.

    Good luck on the 8's,
    Bill M

  8. #8
    Administrator RACING JUNKIE
    Join Date
    Mar 2004
    Quote Originally Posted by triniemi

    I want to cross the finish line below 7000rpm and I think that moving from 4.11 -> 4.33 and 6400rpm -> 6800 rpm would help maybe 0.1 - 0.2 seconds and it still would stay under 150mph.
    That might work but go to a 4.29 gear,shift point will be 6800 and cross the finish line 6800,
    8.90 @ 150 mph should be real close,thats what I ran for a set up years ago
    There Is 1 Thing Better Than Cubic Inches,,,More Of Them

  9. #9
    Thanks for great advices, I really appreciate them.

    The cam is 272/278 @ 0.050, 0.708 lift and Crane states that it is a "oval track" profile whatever that means. Heads are ported Merlin iron rectports, big Dart single plane manifold and a 1050 Dominator. Headers are quite big, 2.375", so that might cost some torque. 12.4:1 compression (measured). I think 650 ft-lbs @ 5000 and 750hp @ 6500 is quite close. I use 50% Sunoco GT 104+ and 50% Shell V-power as fuel.

    So get the car to the eights, I will try to:

    1) Install the chute. I have to remove the body from the car to do this and relocate the fuel cell so it'll take time and people. And beer.
    2) More gear and rpms. 4.29 or 4.33. 4.56 is too much if I want to stay below 7000. I believe I'll do this during the long and dark Finnish winter.
    3) Try the ballast. It's cheap and easy to do and I can try it this summer. Should help also in the slippery airfield-tracks we have.
    4) Aluminum heads to reduce nose weight if I can find the money. AFR 335 CNC's would be the dream.

  10. #10
    Administrator RACING JUNKIE
    Join Date
    Mar 2004
    4.29 and 4.30 (30-7) are the same gear use the pro gear if at possible

    4.33 (39-9) I don't think that gear will work very good for you,you may not even see a difference in RPM from the 4.11 (37-9) gear that you have in the car now,just my .02 cents here of coarse
    There Is 1 Thing Better Than Cubic Inches,,,More Of Them

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