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Your 4-link pictures appear to show your 4-link with no load on the suspension. What is your IC with full car weight on the wheels? I suspect your IC is too short and too low. (Please use inches forward of the rear tire contact point and inches above the ground. If you can provide me with the location of the 4 bolt holes that you are using while the car is on the ground, I can provide the IC location.)
With my '89 drag Vette, I have had good luck without wheelstands using a loaded IC of 41" and 8" (1.27-sec 60-foot time).
Your 4-link pictures appear to show your 4-link with no load on the suspension. What is your IC with full car weight on the wheels? I suspect your IC is too short and too low. (Please use inches forward of the rear tire contact point and inches above the ground. If you can provide me with the location of the 4 bolt holes that you are using while the car is on the ground, I can provide the IC location.)
With my '89 drag Vette, I have had good luck without wheelstands using a loaded IC of 41" and 8" (1.27-sec 60-foot time).
Your car looks awesome!
-Larry
..... What does your car weigh ? ... front and rear ? mine is 1660# in front and 1760# rear ... The 1st pic (Gainesville) has the I/C 64" forward of the rear axle C/L and 13"above ground with the car level and chassis loaded at the rear ... the front is on jackstands as eyeball centered to the front axle C/L as I could get them ... The last pic has the I/C 26" forward and 10"up ... The 4 link bar holes at my starting point (1st pic) was with the sill level @15.75" above garage floor , rear axle C/L @20.75" loaded ... the lower link bar is up 16" in front and 15" rear ... the upper link bar is 24.25" up in front and 25.3875 in the rear .....
Do you have any pics like this with the suspension compressed, because the bars in this have you with an incredibly high instant center if it is actually compressed here.
..... This pic was taken during the set-up phase of the initial install of the 9" rear axle ... the I/C was calculated at that time and was originally separating the tire and fender pretty much the same as the pic from 2-19... see above thread for the particulars about the I/C from the 1st pic and 2-19 pic .....
..... Unfortunately I live alone and do not have pics of the rear suspension with me in the drivers seat ... I will be getting back under there and will snap a pic of the suspension loaded sometime later this week .....
I agree. I think overall all your shortening of the swing arm length by pulling the IC back is actually making things worse, especially if the anti-squat percentage is being increased as a result. With greater-than-100% anti-squat, the IC rises when you accelerate and the rear ride height rises, and the shorter you make the virtual swing arm, the more it increases (even if anti-squat stays the same).
If you can lower rear ride height safely (with respect to tire clearance), I'd try that along with maybe raising the top link one hole or two (looks like the lower links are already as low as they go?). Another thing that could help would be to lengthen the wheelbase by both upper and lower links the same amount. Even 1/2" would help if you can do that safely.
..... I agree as well , Now ! ... I was following the advice of another youtube chassis guy and took the I/C to the rear of the car to minimize the wheelstands and it has demonstrated that I need to go in the other direction ... my next move will be farther forward and as close to anti-squat as I can and then go from there ... I have adjustability range in both bars that I can go pretty long ... the rear tire is about 1/4" more rearward in the wheel openings and with these tires I'm about maxed on safe clearance .....
..... What does your car weigh? ... front and rear? mine is 1660# in front and 1760# rear ... The 1st pic (Gainesville) has the I/C 64" forward of the rear axle C/L and 13" above ground with the car level and chassis loaded at the rear ... the front is on jack stands as eyeball centered to the front axle C/L as I could get them ... The last pic has the I/C 26" forward and 10" up ... The 4 link bar holes at my starting point (1st pic) was with the sill level @15.75" above garage floor, rear axle C/L @20.75" loaded ... the lower link bar is up 16" in front and 15" rear ... the upper link bar is 24.25" up in front and 25.3875 in the rear .....
To compute your IC, I also need to know the horizontal distances of all 4 of the 4-link attachment holes that you're using forward of the rear axle centerline. As you have indicated, the two forward attachment points are 16" and 24.25" above the floor; and the two aft attachment points are 15" and 25.3875" above the floor with the car level.
Lower forward: (horizontal?, 16)
Upper forward: (horizontal?, 24.25)
Lower aft: (horizontal?, 15)
Upper aft: (horizontal?, 25.3878)
When lowered to the floor and settled, how much will these vertical measurements decrease?
To answer your questions, my car is quite light - 1050 front and 1150 rear. It runs 9.0s at 148 mph (NA) with 454 BBC LS7 with a solid flat tappet cam.
..... When lowered to the floor the vertical dimensions will all change by 7.0" ... the rear bolt holes (upper & lower) are 1" forward of the center of the rear axle ... the upper is 4.625" above the axle center and the lower is 5.75" below the axle center ... the lower front bolt hole is 17.3875" forward horizontally from the rear bolt hole roughly 4 degrees up toward the front of the car ... the upper front bolt hole is 12.75" forward horizontally from the rear bolt hole and is about 6 degrees down toward the front of the car ..... This is the data from the Gainesville wheelstand and Avatar pics ... it is not the same setting for the last pic I posted from Saturday 2-19 .....
C409,
Comparing the different pictures of your car, including the one in your signature, we can see that the gap is huge between the back tire and the lip of the quarter panel in the latest one. Obviously, the car is doing different things now on the launch but not what you desire. Can you post a picture of the four link bars with the car on the ground and possibly with you sitting in the drivers seat?
Mike.
..... Yes , there is a lot of separation in the 2-19 pic ... I/C was approx 3" above anti-squat and only about 7" forward of the front lower bolt hole of the link bar ... well behind CG ... I will get some pics of the chassis loaded but the wheels/tires gotta come off in order to see the 4-link bars .....
..... When lowered to the floor the vertical dimensions will all change by 7.0" ... the rear bolt holes (upper & lower) are 1" forward of the center of the rear axle ... the upper is 4.625" above the axle center and the lower is 5.75" below the axle center ... the lower front bolt hole is 17.3875" forward horizontally from the rear bolt hole roughly 4 degrees up toward the front of the car ... the upper front bolt hole is 12.75" forward horizontally from the rear bolt hole and is about 6 degrees down toward the front of the car ..... This is the data from the Gainesville wheelstand and Avatar pics ... it is not the same setting for the last pic I posted from Saturday 2-19 .....
Here's the data I used after subtracting out the raised height:
Lower forward: (17.39, 9)
Upper forward: (12.75, 17.25)
Lower aft: (1, 8)
Upper aft: (1, 18.39)
This makes an instant center at 66.7" forward and 12.0" above the ground.
Send me the new hole locations and I'll calculate the current IC.
Here's the data I used after subtracting out the raised height:
Lower forward: (17.39, 9)
Upper forward: (12.75, 17.25)
Lower aft: (1, 8)
Upper aft: (1, 18.39)
This makes an instant center at 66.7" forward and 12.0" above the ground.
Send me the new hole locations and I'll calculate the current IC.
..... Where does that put the I/C relative to the anti-squat line ? .....my calcs had the I/C at 64" forward and 13" above the floor and about 5" below A/S ..... 96" wheelbase with 27.5" tires at both ends .....
..... Where does that put the I/C relative to the anti-squat line? .....my calcs had the I/C at 64" forward and 13" above the floor and about 5" below A/S ..... 96" wheelbase with 27.5" tires at both ends .....
Sorry, I don't know the height of your center of gravity which is needed to draw an anti-squat line, but I think you are close to 100%. However, comparing our cars, your IC is about 20" forward of your CG; while mine is 14" aft of its CG. For this coming season, I'm going to move mine forward about 10" to control the hit off the brake better. In your case, you may be better off by moving your IC aft and lowering it a bit to keep the percentage rise the same. YMMV Good luck!
..... I have calculated my C/G at 46" forward of the rear axle C/L and 18" above the ground based on the 48.5% front 51.5% rear weight distribution and rear camshaft height . I wasn't aware that the anti-squat line was relative to C/G in any way ... my understanding is that Anti-Squat is drawn from the bottom center of the rear tire contact patch to the top center of the front tire ... I may be wrong but thats how I interpreted it ... My original settings resulted in the highest wheelstand yet ... every movement of the I/C towards the rear of the car had little to no affect on the tendency to lift the front ... I'm going to try some new double adjustable front shocks (on the way) ... limiting the front suspension movement to less than 3.5" (where it is currently) ... extending the I/C forward 10-16" and on or slightly above the A/S line ... and 65# of weight between the rails in front of the radiator , I bought a 2"x 6" x 19" piece of tool steel at the local metal supply store ... while "wheelies" are impressive , they can be counter productive to the forward motion of the car and damaging if they get excessive .....
Cool picture!
Back to the original question... To control wheelies with a far forward IC, more front shock extension damping and more weight will help, but moving the IC back to under the CG (-46") should be even better in my opinion - but only testing will tell. Are you heading to Bradenton this weekend? Keep us in the know!
Snow fun in MO
-Larry
Cool picture!
Back to the original question... To control wheelies with a far forward IC, more front shock extension damping and more weight will help, but moving the IC back to under the CG (-46") should be even better in my opinion - but only testing will tell. Are you heading to Bradenton this weekend? Keep us in the know!
Snow fun in MO
-Larry
..... No racing for me this weekend ... too much to do to the car ... aside from the rear suspension work , I need to make new limiters for the front spring and last weekend I broke the bottom mount completely off of the alternator and I noticed a broken mounting ear on the Power Steering Pump/ Alternator to block bracket ... there is a points race at Immokkallee (3hr drive each way) but there's nothing scheduled at Bradenton that I would fit in ... i will post progress reports ... Thanks for your input ! .....
..... This Video is VERY informative and is especially important for C4 4-Link set-ups with unequal length bars ... at around the 10:00 mark he starts discussing the shorter upper bars effects .....
..... No racing for me this weekend ... too much to do to the car ... aside from the rear suspension work , I need to make new limiters for the front spring and last weekend I broke the bottom mount completely off of the alternator and I noticed a broken mounting ear on the Power Steering Pump/ Alternator to block bracket ... there is a points race at Immokkallee (3hr drive each way) but there's nothing scheduled at Bradenton that I would fit in ... i will post progress reports ... Thanks for your input ! .....
Do you think this started from the hard landing you had the other evening?
Do you think this started from the hard landing you had the other evening?
..... Quite possible ... I took the alternator to the local guy and when they tested it , it was dead ... there was some internal damage that he described as centrifugal that might have been the smoking gun ... based on pulley sizes (crank vs Alt) there is about a 3:1 ratio of overdrive (I didn't do the math) ... Sooo , shifting at 7200 engine rpm converts to over 21,000 alternator rpm ... a friend said his Power Master alternator came with a warning label that said the warranty would be void if spun over 6,000 engine rpm .....
