Zipdrive

I have searched over the years and have read many varied posts about the desirement of moving the mounting location of the front a-arms for better handling. My un-answered question still is, "to what position and how is the handling/suspension better vs. different?"

Anyone know / experimented / results?

Zipdrive

Well, is this a conclusion? Lots of looking, but no concrete answers. Is it safe to conclude that modifications would make the car handle better, but none have been done before?

cosmick

If you raise the rear of the front lower arms, that will improve anti-dive, which our cars have far less of than the '80s 'vettes.
If you raise the inner ends of the front lower arms, you'll improve the camber curve for a lowered suspension, lowering the center of gravity.
Both of the above can be combined.
Mind your roll center in all of this.

Zipdrive

Cosmick,

To your point, how much do you raise the rear of the front arms? 1/4", 1/2", 1"? What are the draw backs (handling wise) of moving the mount?

I don't understand the "inner ends". Do you mean both mounts to the K-member? again, how much and what are the effects?

Thanks.

cosmick

I've never found any helpful details, I suspect it's trial and error to find what your car likes. There are ways of calculating the % of anti-dive, but just because the 'vette was like 47% IIRC, that doesn't mean our cars would like that much. We have virtually none. You can Google anti-dive for more info. I'd start at maybe 3/4" for ease of staying out of the existing holes. Or 1.5" if also raising the front ends 3/4"

Google can help you find the theoretical drawbacks, but the practical drawbacks won't turn up until someone tries it.

Yes.

IDK, I'd go about 3/4" to start, to stay out of the existing holes.

The theory is that you want the lower arms parallel to the road at the point of maximum body roll, to keep the most tread on the road when you need it most.
Tires roll under, so that means that when the lower arms are level, there should be negative camber. Tops of the tires leaning inward.
If you, or anyone reading this, is new to making these cars corner well and handle well, then this isn't stuff to be trying, especially for street use.
But if you're more advanced, then designing these extra mount holes into a custom tubular K member seems worthwhile.

Colt

Zipdrive, all of this is theoretical and most likely would work. But i doubt anyone has actually changed the angle of the control arms on these cars. Even though our suspensions geometry is not the best, it is that way for a reason. This reason is also why GM experimented with mcpherson struts only on the 3rd gen while the 4th gen went back to upper and lower control arms.

One of the reasons why our suspensions lack anti-dive is because strut type suspensions do not handle this well. They are known to become unbelievably harsh when this is done. While the Mcpherson strut made production simpler and cheaper, it gave up design flexibility.

Another down side to doing this is that you will introduce arc's in the movement of the suspension which will add bumpsteer.

But there is other ways to make your car handle well if that's what your intending. You dont have to do it totally through the geometry. What are your goals?

cosmick

What reason?

The flex of the strut shaft ( or rod, if you prefer ) can result in a stick-slip action that can cause snap understeer. Thus larger-shaft struts are preferred for race use.

This isn't matching what I've been finding about other such, like the Nissan 300ZX, the Ford Mustang, et cetera.

We already have bumpsteer, there are kits to correct this.

One thing I learned from the Mustang crowd, especially the Maximum Motorsports website, is they can swap later spindles to improve their Ackerman. But nobody ever compares theirs to ours, or notes if ours is good or bad. It would be helpful to know. I'd even try later Mustang spindles if there was evidence that it would help.

Colt

I thought i explained this; the reason is GM most likely engineered the suspension the best they could while maintaining their NVH targets. The suspension probably got too harsh when they dialed in a lot of anti-dive. This issues is well known with strut type suspensions, feel free to verify. Our cars were never meant to be road race cars.

I know this issue exists, but I have never experienced bind in the struts myself. Could be due to a number of reasons, maybe just good quality struts.

I dont know what you have read but mustangs suffer similar issues. A friend of mine had a very competitive SN95 mustang in his class and he always complained about the car nose diving. Those cars also suffer bumpsteer issues when low, as well as having roll centers go too low as well. This is widely known with those cars, but most likely only in the road racing community.

Other cars have gotten away with struts, most noteworthy are the old 911's. But those cars weigh nothing and had even less weight over the front ends. Because of this, they were able to hide the shortcomings of the design. And of course, as you know, all modern 911's use upper and lower control arms.

Now that I think about it, most cars have gotten rid of struts except for economy cars. Even the civic has upper and lower control arms.

yes. I hope your wheel doesnt hit it.

I really dont see ackerman being a problem with these cars as far as im concerned. I do notice it when im making parking lot maneuvers at low speed, but im not too concerned with that. You might not know but there can be some high speed benefit to have no or even reverse (or negative) ackerman.

But back to the topic at hand, there's no one im aware of that has changed the angle of the front control arms. These cars are not very popular road racing cars and thats the only crowd that would do it. Its a bit more involved than simply cutting off the mounts from the k-member and rewelding them in a new position.

cosmick

No. Their first priority was re-using the '79-'81 front lower control arms and coil springs. In the 'pre-'82 F-cars, they had the lower arms mounted level. That's why they continued to be level, which with struts puts any anti-dive into the angle of the struts. Also, racers were running 1,000 lb/in front springs, so there wasn't much brake dive.
Those arms were shared with the fullsize cars, mostly sedans and wagons rather than sporty coupes. So there the NVH mattered, causing the larger bushings for '79, compromising the F-twins even further. Production compromises kept the F-twins more affordable. Even then, Herb Adams, Dick Guldstrand, and others were offering solutions to the bushings, et cetera. The guys developing the '82 Z28 knew that.

Actually, back then GM still cared how the Camaros did in motorsports. Camaros were the IROC cars from the mid-'70s, long before the IROC-Z street version. The third gen was designed to fit the big block, was designed as the Z28, then the lesser versions came after the '82 Z28 was finalized. Also, these were designed for the '81 WS6 wheels, as old photos prove.

Stock Mustangs have little anti-dive, true enough, but those guys are managing to get some without much harshness.

At least those pony boys have the choice. And most of us would choose whichever gives the most lateral Gs below 100 MPH, as few of us do much racing at sustained speeds much above 100 MPH. For the 1/4 mile, even if the car can exceed say 120, that's no practical call for reverse Ackerman.

It is the topic; making changes to the geometry. Changing any one aspect affects all the others. It's a suspension system.

I agree with that.

Anymore, they were, but today's awareness of handling, suspension, modification, wasn't shadetree stuff then like it is now. There were no online forums, the magazines were mostly about the dragstrip, and on F60-15s it hardly mattered anyway. When the Gatorbacks came along, that's what got the ball rolling. Just as EFI was still primitive in the mid-'80s, so was the concept of handling on sticky street tires. We've come a long way.

We're to the point now that a higher end, pro-built "Pro Touring" or "G-Machine" build that will see track days would incorporate this sort of stuff. Even now I'm custom building someone a grand tourer '83 RX-7 with a V6, and while it's not a racer, it still got an FC3S IFS swapped in, adjustable for anti-dive, and I had to engineer that in. Once finalized at Bondurant's, the chosen adjustments will be welded permanently. Just making an example here that even home-garage builders, aspiring to turn pro by proving what's possible on a budget, can and will get into whatever's necessary for proper results. The information's out there. Going beyond bolt-ons is scary to most enthusiasts, even most custom shops who claim to be pros, but now I've done it, I can't see why it scares them. They dare attempt LSx swaps to every car on earth. And few attempt big brakes without buying a bolt-on kit. Again, why not? I did it to the FC3S IFS, got 11.75" ( to clear the car owner's chosen wheels ) x 1.26" rotors with 4-piston Brembos for under $400. So why buy a $ 1900 kit? Anyway, it's about experimenting safely, to get big improvements for little funds. Poor guys have just as much right to go fast as rich guys. That's why the SBC caught on, that's why turbo LSx swaps are in every driveway.

True, buy why cut them off? This is something you could try in the GM K, but would be better to design and build a new tubular K for, based off the best of the existing aftermarket Ks. Besides, what would you cut? We're going up, not down. Maybe necessary to cut the GM welds to open it up for access, but you'd be adding, not subtracting.

Getting these things to handle predictably and pull 1.3Gs on treaded tires is already possible, without trying anything in this thread. But if someone really wanted to try for 2g without swapping to a later 'vette IFS, then the above mods would become necessary.

Colt

Because people race them doesn't mean they were designed to be a race car. Save for a few classes that were designed to have F-bodies compete in them like CMC or American Iron, what other series were there where the 3rd gen fbody was a popular car? All the roundy-round guys don't touch them either. I stand by my original assessment saying that they were never designed to be road course cars. GM could have reused the older control arms and changed the angle of them from more anti-dive. But they didn't.

Also, anyone trying to make an f-body pull 2g's must be a masochist. I also don't see that happening for many reasons no matter how good the suspension is. It would be easier and cheaper to start with a better platform.

Where did you get this 100mph figure for reverse ackerman? or any speed for that matter?

The OP asked if anyone has tried changing the angle of the arms, and the answer to that question is "no". All of this other talk is a digression and exactly what he said he found already - people talking about it but it never being done. Futhermore, if you are not pushing the car to the limit on a road course, you many never find the limitations to the suspension.

cosmick

What are you, 16? Stop arguing and go do your own research.

DBLTKE

iTrader: (1)

What makes anyone think that nobody has changed the angle of their A-arms? That's something that drop spindles and extended ball joints accomplishes.