Project "Payback" - Page 186 - Lateral-g Forums

Vegas69 · #**1851** 12-08-2010, 01:25 PM

Look at that weight transfer.....

It would be great if this was drag racing and I had the travel available. Since the Optima Challenge, I know the driver and car need help to get where I want to be. My first obstacle is that I've found that my rear shocks are bottoming out big time. I don't know if removing the rear sway bar made it that much worse or I've just been to dense to notice.

I did know the RR was but the LR always had a little left until recently.

I decided to start from scratch and design a new bracket to increase my shock travel by 5/8". Any more and I will run into rear differential cover to crooss member contact or tunnel to pinion housing contact. The brackets are being cut now. Number two is the spring rate is clearly to soft. So I started from scratch and did a base spring rate calculation. To do that, you loosen the spring adjuster collar until the spring is at full length with just a hint of tension. You take that measurment and then drop the car on the ground to see how far the spring is compressed.

Free length is 11.75"
Compressed is 8.25"
11.75-8.25=3.5"
Current Spring Rate is 175=152 Adjusted due to 20 degree angle
3.5 x 152=532
Desired bump travel 2.58
532/2.58=206 Spring rate needed

So basically I need about 50 lb/in more than I currently have to control the weight. I'm going to start with a 220 lb/in spring and go from there. The ideal compressed spring length is around 9.34. That is over an inch more than I have now!!! I'm positive that my shocks were bottoming out under acceleration and some cornering. I'm hoping the extra spring rate and 5/8 extra shock travel keep the rear from bottoming out.

Up next may be the front springs. I have a feeling they are a little soft as well. I really want to keep the ride nice so I need to walk a fine line. I really want to get the car where it stays flatter in all the events. To much body roll and weight transfer is not good for what I do with the car. Stay tuned..

BBC69Camaro · #**1852** 12-08-2010, 01:37 PM

Sorry to hear your spring rates are off. What do you have in the front?

Frank set me up with 225lbs/in rate in the rear which sounds like from your calculations should be good, which makes me glad. I have 550lbs/in up front but that is with a BBC.

Car looks and sound great on the track thou, wish I was at the same point you are

I'm still scraping stuff off my roof

Vegas69 · #**1853** 12-08-2010, 03:05 PM

I have 450's up front. With an all aluminum big block it puts me at about 500 lbs for the engine vs around 750 for a iron big block. I'll let you know how the 220's work out.

**GregWeld** · #**1854** 12-08-2010, 03:55 PM

Quote:

Originally Posted by Vegas69

I have 450's up front. With an all aluminum big block it puts me at about 500 lbs for the engine vs around 750 for a iron big block. I'll let you know how the 220's work out.

I was running 450's up front on the Nomad.. it's a SBC so is probably about what the ZL1 BBC is.... and I went to 550's up front and the ride GOT BETTER not worse.

These things all aren't what they seem on paper. I'd have bet my last buck the 450's would give nice ride and the 550's would be harsher... but go figure. I also changed the shocks from QA1's (they suck) to Strange.... so that may also have helped with the overall ride quality. My sister got in the car - I didn't tell her I'd done anything -- and she says -- Have you done something to the ride? It used to ride like crap!

She's right of course.... Gee.... come to think of it -- I sure hope she got home okay.

Vegas69 · #**1855** 12-09-2010, 12:14 AM

What's that Nomad weigh, 6000 lbs?

I agree, I just don't want to swap both ends at once. I may go to 500's just to split the difference.

**GregWeld** · #**1856** 12-09-2010, 05:24 AM

Quote:

Originally Posted by Vegas69

What's that Nomad weigh, 6000 lbs?

4023 #'s to be exact and weight balanced by a professional race shop here.

It's "svelte" like me!

mfain · #**1857** 12-09-2010, 09:52 AM

Hey Todd, car is looking great! I have a question about your rear spring rate change. Obviously you are doing that to carry the weight and to prevent the shocks from bottoming. Are you concerned about making the car "looser" by increasing the rear roll stiffness without also increasing the front? Stiffer springs on the rear will definitely induce more oversteer, although not nearly as bad as bottoming a shock in the middle of a turn. I remember that you were fighting a loose condition early on. IMHO, You might have to sacrafice a little ride comfort (stiffer front springs) to get the car back in balance.

Pappy

**tones2SS** · #**1858** 12-09-2010, 10:08 AM

That's one mean looking car.
Good luck with the spring rate.

Payton King · #**1859** 12-09-2010, 10:09 AM

I would guess Stielow's car's motor weighs about what yours does and he is running 550 front and 275 rear. I think Rupp runs 550 or 500 front with a 275 rear. Mary Pozzi's 2nd gen runs a custom 275 lbs rear leaf.

Not getting into sway bars or sizing, but I would probably start at 550 in front and 275 in the rear. Seems to me with 3 different style suspension set ups, the 275 seems to work with these cars.

Vegas69 · #**1860** 12-09-2010, 10:33 AM

Pappy, you are absolutely right. Since I unhooked the sway bar, the car is actually a little to tight. I dropped the air pressure in the tires and it tightened it up even more. My thought was that the correct spring rate and more travel may balance out the car with the current front spring. Who knows....

Payton, listening to Mark's interview after the challenge is what got my wheels spinning. He mentioned 550/250 in the interview. His car looked really sporty. You are probably right, who better to copy! I think you have me talked into swapping the front springs.