I just got done installing new upper a-arms, extended ball joints, and anti-bumpsteer blocks on my 76. The results look promising, but I'll have to wait a few weeks to find out how much it improves the car's feel on a road course. I'm getting the car ready for a track day at Putnam Park (no racing, just lapping with an instructor). I plotted my car's original toe change with the chart in Greenwood's VIP article, and they look almost identical. With the VBP bump steer blocks bolted to the steering knuckle, the bump steer was reduced quite a bit.

 

That's a pretty significant difference to your camber curve. That much just from the ext. ball joints, or do the upper A-arms have altered geometry too?

Also, interesting to see toe-in at both directions from static, if I'm reading it correctly.

Curious, have you lowered your Z and D heights to Power Book recommendations, or are you somewhere else?

Finally... I've got a set of Guldstrand's anti-bumpsteer blocks which I'll be installing once I get past an engine build up, and have been planning to calculate how the ackerman will be affected.

Btw, nice to see I'm not the only one interested in legitimate C3 suspension improvements around here.

 

TheSkunkWorks,

Actually the graph maybe is a little backwards ... it's a slight toe out at the extreme ends of movement but its still alot better than stock. I figure if I set my toe-in at 1/8" I shouldn't ever have a toe out condition like the factory settings were. If you look at the factory curve it explains why these cars understeer to some degree. As the car leans into the corners both tires understeer due to the car rolling.

I'm not sure how to measure the ackerman. Do you know how this is done and what is the preferred amount you want?

I'll post some pictures on here later of the new a-arms and my brake ducts I'm installing. I have the ducts welded up but I'm still working on routing the tubing ... there just isn't much room under there.

Other mods I've done is lower the car to approx. the recommended Z and D hieghts ... might be off slightly but not much. I'll have to check them again, because its been years since I lowered the car. In addition I've got the following setup:

1" front sway bar and 9/16" rear bar
Transverse springs front and back set fairly soft
Edelbrock IAS shocks
17" x 8" wheels with Nitto tires (thinking about going with Mich Pilots)
Raised rear differential per VIP program & stiffened mounts at frame
A-arm brace (tubalur type between a-arm mounts)
Stiffened sides of frame

Someday I may just get this car to handle ;-)

 

The achermann angle is the difference between the inside and outside steering angle of the wheels. It is all related to the wheel base and track.
The rear axle is considered a straight line and the lines from both front wheels should intersect the same point on the rear axle line when turning a corner. The car actually turns around this point.

If the lines do not meet at the same point on the rear axle line then one of the tyres will be scrubbing during a turn (usually the tyre on the inside of the turn as weight is transferred to the outside) The actual angle varies with different steering input angles but the lines should always intersect the rear axle line together.

In my experience, the achermann angle is set by the steering arms attached to the stub axle. On a rear steer car like the C3, if you move the Tie rod ends out from the centre of the car, the achermann becomes closer to "perfect". It only takes a few degrees change in the steering arms to correct the near parallel standard set up.
I did the evaluation to get my angles on a cad program after doing the initial calculations on a calc. I them mocked up the steering arms to check my results. This is on an End Take off R&P RHD steering conversion but is applicable to all C2/3 chassis.

So to summarise, you cannot specify a value for the perfect achemann angle unless you specify the wheelbase, track and angle of one of the front wheels, and then it is only applicable for that particular front wheel angle. And which angle do you quote? The angle of the other front wheel? the difference between the two front wheel angles?

I did my calculations with the inside wheel at 30 degrees (which happens to almost be full lock) and the outside wheel came in at 24.30 degrees.

On a side note, it has reduced my turning circle because the outside wheel does most of the work in a turn and it now turns less before the inside wheel hits lock.
I hope this made sense and helps,
Cheers!

 

Thanks RHD '68 L89 , I'll have to check that when I get finished with this project and see where to go from there. As with most cars, this thing is always a work in progress.

 

Nice graphs.
It's interesting to actually see a camber curve, don't think anyone has done that before!

So with the bumpsteer blocks your tie rods are too short. Norval found that same thing.

I wonder if you will be able to feel the oversteer on a hard corner.
It looks like about .075" at 1.5" compression?

Seems like a lot, but then again I believe cars should always understeer.

Can't wait to see what you say about how it feels.

 

Compared to the original curve though the bumbsteer is alot less than what factory put into the car. Plus I figure if I run 1/8" toe-in on the front, even with the remaining bumpsteer of .075" the front wheels won't actually be toeing out like before. I'll let you guys know how it feels after the track event.

 

Here's some pics of the setup so far. The brake duct is just mocked up to make sure it didn't rub on anything. On a true street car with all the panels, radiator, etc. it is tough finding a route for a brake cooling hose. I ended up using a 2" hose and welded a duct into the factory dust shield. At full rebound it does just touch the frame, so I'm going to add some hard plastic around the silicon hose at any potential rub spots to keep the hose in good shape.

 

Interesting stuff. I know with my car setup more for drag stuff....the front end goes through a pretty drastic toe-in change on the launch....one of those things I need to work on next. I was planning on using the bump steer kit too. I use the *fast ratio* holes now....does the bump steer block place tie rod in the center between the two? I've also heard the turning radius is worse with the kits....is that true?



JIM

 

Thanks for that, RHD '68 L89. So if I'm reading between the lines correctly, after I install the bumpsteer blocks, which move the connection in towards CL, my ackerman steer angles could actually decrease (relative to the orig. setup), as 427Hotrod mentions? Clarification??

The two reasons I'd prefer increased ackerman steering are 1) it appears more ackerman would improve turn-in on slow tight corners (auto-X, hairpins...), reducing the need for a toe-out setup as a crutch, and 2) with manual steering it's bound to help in the parking lot.

Jason Staley, I see you're upper A-arms now. Are those the ones from SpeedDirect or elsewhere? Nice pics.

Jim, when I was drag racing seriously back in the late '70's to early '80's, we found significant time (talking several tenths here) in front alignment during a chassis shake down. We knew the steering angles changed adversely with travel, but didn't know it was called bumpsteer. However, the ET slips proved that our theory, though a bit Bubba, actually worked. We jacked the front up to about 90% droop, then set toe to 1/8 in (compensating for compliance in the suspension) and camber to zero (I forget where we put castor). Voilà! The reduced scrub resulted in over 1/2 sec in the quarter!

From that experience, I'd suggest getting some good pics of your car at WOT somewhere near mid-track and calculating its ride height "in anger". Then, find that point in the charts and adjust accordingly to get everything pointed perfectly at that height. I can almost guarantee you'll find some time.

Oh, and the blocks put the tie rod end 1/2 way between the std. and quick steer holes, down and in.

 

Yep....saw pics one time of my old Camaro on a launch. Those cars go negative on camber like crazy on launch as well as toe in. I used some offset upper shafts and aligned everything as youy mentioned...picked up a solid 2 tenths.

Our cars are opposite..they go positive on camber on launch (extension)...and gain even more toe in at the extremes! If you look at my car at rest, it appears to have negative camber..which it does....but going down the track with nose up some..it's about right. I've also adjusted toe for track runs....which causes some inside wear on tires on the street....because it's right on the edge of toe out..to get it right for the track. That's why I'm thinking of using the bump steer kit to play with it all..to hit a happier medium overall.

But as it sits....you can drive it with your knee at 141 mph through the traps!



We *could* make a new center link..and change length of arms..that is the ideal solution. Or you can use extended tie rods ends and spacers to help a little...just trying to decide best method.

I know Norval worked all of this out on his car....I figured I'd hit him up when I got close to messing with it.


JIM

 

I'm surprised Norval hasn't chimed in on this one, already.

Here's a pic of my block, so you can get a clear view of it.

 

Thanks..great pic!

That does the job of spacing the tie rod down, shortening the rod and picking a midpoint for steering ratio all in one I suppose huh?


JIM

 

I've got a feeling I'm going to be having more conversations with Guldstrand...

 

I have to use the bumpsteer block to lower it other wise it will hit my tire

I'll probably end up with the bumpsteer block and a stud

 

It's a PITA fitting 3 Inch ducts I think I'll get it fine though after I order 90* eblows

Are those the Howe ball joints

I've been wanting to get those for awhile

 

Stop it!
You are making me remember things!
OK, I did the conversion about 5-6 years ago so the memories are a bit fuzzy. I did not take measurements of the standard set up but i knew it did not have the correct achermann angle in the steering from the factory. I was engineering from scratch to fit the ETO Rack. I also had a bare chassis which made it easier to move things around to get them in the right position.

From my analysis, I found if the outer tie rod ends are in a direct line (F to R) with the line drawn between the upper and lower ball joints then the two wheels turn the same amount, i.e. parallel steering. The inside wheel scrubs on corners as described earlier.
By moving the outer tie rod ends out a few degrees the inside wheel now turns tighter than the "straight" set up.
Unfortunately I did not compare the original tie rod end position so maybe moving it in actually does work.
I know I did end up moving the tie rod position down to help remove bumpsteer, similar to the guildstrand blocks.

 

427Hotrod, yes the tie rod is centered between the two stock locations. You have to remove the steering arm and drill out both holes for the 5/8" bolts. As to the turning radius, I didn't see a change ... the steering arms still hit their stops just like before.

TheSkunkWorks, the arms are from Savitske Classic & Custom. The ball joints are 3/4" longer and lower friction than the Moog ones I've used. The red portion of the a-arm is anodized aluminum. The change in a-arm angle is close to the modification that Guildstand use to make by cutting out the a-arm towers, removing 3/4" of material from the bottom, and rewelding in the a-arm bracket lower in the frame. The ball joint is obviously a lot easier.
http://www.scandc.com/suspensions.htm#streetcomp2plus

Yellow73SB, yeah they are the Howe Ball joints ... Savitske customized some SPC a-arms and installed the correct ball stud for C3's. You might be able to fit 3" ducts but your going to have to do some cutting of the inner fender well or it will have to hang low and come up from underneath the chassie. I would have loved to gone this route, but in an effort to not cut up the body it forced me to go with 2" hose and it still slightly touches the frame at full travel. If you get the 3" to fit, please post some pics.

 

It hang a bit low but I made 1/8" aluminum covers to go on the low part

It's still an inch or so higher than the spoiler

 

I'm with you ... I could see how that would work.

Where did you put your inlet ducts? I'm thinking about installing mine up under the front end in the factory spoiler. I have the small standard plastic version.