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Old 02-24-2008, 07:24 PM   #1 (permalink)
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how many millimeters is "lowered all the way" on stock bolts

I'm interested in measurments of lowering the C-5 all the way on stock bolts. It has been said that the max lowering for best performance is 12mm.

my car was lowered all the way when I bought it. How much do I raise it up to achieve the 12mm?

The other option (since I like the look of it lowered) is to buy better shocks so I don't hit the bump stops on the stock shocks. anyone with experience here?

thanks in advance,
D.
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Old 02-25-2008, 09:37 AM   #2 (permalink)
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Re: how many millimeters is "lowered all the way" on stock bolts

It varies with each car. Usually maximum lowering with stock bolts will result in @ 15mm drop from factory OEM ride height. There must be at least 2 thread rows visable on the rear bolts. The Z Axis ride height should be measured at specific points on the chassis....consult the Service Manual.

Note that maximum performance with stock bolts can ONLY be gained with a complete T1 suspension package. This includes T1 Shocks, T1 Springs, T1 Sway Bars, T1 End links, T1 Bushings in T1 A-Arms, T1 Camber Keys. The installation of a T1 suspension actually raises the ride height slightly.
You should ONLY opt for a complete T1 suspension IF you are participating in SCCA T1 competition.

So raising your car IF it was lowered to 15mm and then raising to 12mm will not produce any decernable improvement. If maximally lowered on stock bolts, a slight improvement can be gained if you install '04 shocks, which have better rebound settings.

If you ONLY want to lower using stock bolts, there are some additional things to do to improve performance.
- Set Rake to 1/2' - 3/4".
- Corner Weigh, Corner Weight
- check Cross Corner Weight % Difference (this is the most important suspension spec.)
- set up the car with a more aggressive street alignment
- Use an even more aggressive Track or AutoX alignment if competing

IF You are competing and the rules allow, lowering more than the stock bolts will increase the performance dramatically. This lowers the CG and Roll Center which is advantageous to suspension performance. Even better than a full T1 set up.
You then will need :
- longer Hardbar Titanium rear spring perch lowering bolts
- Hardbar SS front spring bolts with shorter Delrin bushings
- Shorter shaft/body shocks. I recommend Mallett/Penske DA's

There are then mirad other options to consider.

Last edited by DJWorm; 02-25-2008 at 09:40 AM.
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Old 02-25-2008, 11:39 AM   #3 (permalink)
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Re: how many millimeters is "lowered all the way" on stock bolts

So I take it that just upgrading to Bilstein Sport shocks won't make a dramatic improvement.

I've changed the aligment to a "more aggressive" measure (-1.2deg camber up front)

Any good books on the rake angle. weighing the corners, etc.?
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Old 02-25-2008, 11:41 AM   #4 (permalink)
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Re: how many millimeters is "lowered all the way" on stock bolts

Thanks DJ Worm! as always, a wealth of info for us weekend racers.

I really should buy a book on this stuff!
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Old 02-25-2008, 04:33 PM   #5 (permalink)
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Re: how many millimeters is "lowered all the way" on stock bolts

Required Reading & References:

1. Corvette Service Manual - Helms (applicable year)

2. How to Make Your Car Handle - Fred Puhn

3. Brake Handbook - Fred Puhn

4. Engineer to Win - Carrol Smith

5. Tune to Win - Carrol Smith

6. Nuts, Bolts & fasteners - Carrol Smith
"Screw to Win" - Carrol Smith

7. How to Build Chevy LS1/LS6 V8's - Will Handzel

8. Chevy LS1/LS6 Performance - Chistipher Endres

9A. SCCA GCR's (current year - downloadable in PDF from SCCA site)
9B. SCCA Solo Rules " "
9C. SCCA Time Trial Rules " "

10. GM Performance Parts Catalog (current year)

11. Publication:
SCCA "Sports Car" magazine (monthly member benefit)
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Old 02-25-2008, 05:59 PM   #6 (permalink)
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Re: how many millimeters is "lowered all the way" on stock bolts

One turn of the lowering bolt is equal to ~2mm. Therefore, the difference between 12mm lower than stock and 15mm lower than stock is only ~1.5 turns. The maximum you should lower an otherwise stock car is 12mm according to GM. That's ~6 turns.

Max lowering, although it does depend on the individual car, is closer to 20mm+ lower than stock (not 15) or ~10 turns.

Thus, to raise an individual corner back to stock ride height you need to raise a maximally lowered corner ~10 turns.

Last edited by No Doubt; 02-25-2008 at 06:03 PM.
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Old 02-25-2008, 07:31 PM   #7 (permalink)
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Re: how many millimeters is "lowered all the way" on stock bolts

Quote:
Originally Posted by No Doubt View Post
Max lowering, although it does depend on the individual car, is closer to 20mm+ lower than stock (not 15) or ~10 turns.
I agree. I got just shy of an inch lowering my fronts to the max without cutting any bushings. I didn't lower the rear to the max and I found that the rear had more adjustment than the front and I'd lose the rake discussed by DJ above. On my stock suspension with the front fully lowered, I lowered my rears to about 2-4 threads showing which gave me about 1/2" of rake.
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