G-mod dimensions-definitive answer?

[bretcopsey]

I've been searching and seen a variety of measurements and finally came to the conclusion that I will need to ask specifically what will best work for my application. I have seen lowering the front hole by .75", .875" & 1.06". It seems the rear hole was always .75". Secondly, how far back to move the holes, .25" & .5" have come up.

I am building a jig and doing the cut/re-weld method. I am running stock control arms and spindles. How much so I need to move the towers for my application?

[David Pozzi]

I moved mine back .5" and got 3.5 deg positive caster with no shims. I'd think you could move it .75" to .875", I think the Global West upper arms have the UBJ moved about .875".

The upper ballljoints are more in-line with the rear hole, so the front holes will mainly affect anti-dive and have less influence on the camber curve, (my best guess).

My Guldstrand template seems to measure a bit different than Chicane67's, so we have a "problem".
I'd personally favor of the lower hole location, (chicane67 probably would not) but perhaps a better way is to get the template direct from Guldstrand and measure it yourself, and maybe call them and ask about it.

It's certainly possible that Guldstrand would change his mod as time goes by.

[chicane67]

Contrare' monfrare'.....

I dont have any feelings for either one over the other. There have been more than three revisions to the original drawing since 1966/67. Davids template is from an earlier year, much ealier than when I picked up the template I have, during the time of my employment.

The template that you will get from Guldstrand now, will be the same one I recieved in the early 90's.

I dont have both geometries loaded into our design software to make any plausible comments on the what and how's, the changes provide from one another. But I believe it comes down to the whole shabang..... all parts included, to make the best determination for your specific application.

I do however, second the choice to call ole Dickeypoo and get the answer from the horses mouth. I dont even remember the entire conversation I had with him on this very subject (it was pretty hard to digest everything that man pointed out.... more like information overload all at once, all the time) but I remember some vague comments on tire, dampner and other suspension kinematic development that made his point clear.

BTW, the cut and move method is the shiznit way to do it.... right.... the first time.

[bretcopsey]

I do thank you both for the input. I have the template from Guldstrand, but thought perhaps the other dimensions floating around may be better.

[cattoi]

Hi guys
I've completed the g-mod and it's time to get an alignment, does anyone have the correct alignment specs. for this mod?

cattoi

[chicane67]

Depends on how you are going to be driving it. The static numbers will vary from -.75 to -1.75* camber and +3 to +3.5 and toe will determine the resluting balance.

For a driver with smaller spring rates, -.75 camber / +3.25 to +3.5 caster and 3/16" total toe will be a good start for the street.

If your gonna be driving it hard on the street and/or the track, I would set it around -1.75 camber with the amximum caster you can get out of it with 1/16 total toe in to 3/16 toe out..... depending on what else you have on the chassis (tire and wheel size, spring rate, type of shock, stay bar, ride height...etc). Type of control arms will also be good information to share as well, as that will change everything pretty much if they are aftermarket.

[JohnUlaszek]

I ran into the same problem.
Given the variation in the manufacturing process, variablity of the different measurements, multiple different versions of the Guldstrand numbers, I took a best guess on mine and focused on making sure everything was perfectly symmetric about the center line within the ability to measure, short of using a CMM or a Faro Arm.
http://www.x1nova.com/Guldstrand.html

[cattoi]

Thanks for the help
I'm running stock control arms with Eibach big block 1" lowering springs, I don't remember what the spring rates are, with a 1" front sway bar. I will be driving primarily on the street but will also do some autocrossing also, I would just like this thing to turn decently, Is there any hope for me gaining better handling with this big block for autocrossing?

Cattoi

[RobM]

hey how does your car sit with those eibach springs? my car sits very high up with them and ive taken half a coil off already. whats yours like?

[David Pozzi]

Do all you can to reduce front end weight, run with a full tank of gas, don't do anything to lighten the rear of the car like remove rear seat or spare tire.

Get as much rubbber and rim width on the front as you can clear safely.

Driving,
Be smooth and use all the width of the course that is available, enter corners a bit slow, then use a light amount of throttle before the apex to shift a little weight from the front to the rear, set up the car to handle well (neutral) in this mode.

After you gain some experience, experiment with trail-braking into some of the medium speed turns, and adding a little oversteer to help you get around the tight stuff. Just don't add so much oversteer you can't exit corners under heavy acceleration. Your best attribute will be using your power, that means acceleration. Courses with 90 deg turns and medium to long straights will be the best for you.

A light flywheel like the L88 will give you some trailing throttle oversteer entering corners and can help you get the car turned more easily.

[cattoi]

excellent feed back, Thanks

My 68 sits a little lower than it did with the stock (new) front springs, but I have completely gone through the front end including sub frame bushings, I have not gotten everything back on the car yet (missing radiator, fluids, and hood) I'm hoping for a little lower (I would like atleast 1/2" -1" more out of the front) stance, when it's complete I'm hoping for at least another 1/2" (with the driver), how much did cutting 1/2 coil get you?
T Cattoi

[David Pozzi]

I don't recall how much drop I got, but it all depends on where the spring sits in the pocket, when you get just short of removing one coil and then finally get to a whole coil, the spring tip will drop down into the pocket and you will lose a bunch of height fast.

Be very careful not to go too low, I like low cars for autocross, but if the front ever bottoms out under max braking, the front end will push and you have a lot of weight up there to deal with, so you need to be a bit higher than a lighter car. Bumpstops can be trimmed, but watch the header to ground clearance or you will flatten the tubes.

[cattoi]

Thanks Pozzi

Tomorrow I go to the alignment shop, what should I request for a setup to start with?
I'm running stock ralleys (15 X 8) with 60 series tires but that will change to 95 ss camaro rims and tires 17 X 9.5 as soon as I can come up with the funding.

thanks for the help