flynhi

How difficult is this conversion? Is the result worth the effort?

Twin_Turbo

rear, relativly easy...fixes the toe control problem (well it improves it, it can be done better than the C4 does but that's going into details)

the front is much harder, the suspension cradle also mounts the engine. You have to use it in order to use the front steer end take off rack, that means you have to cut off the original frame and weld in a custom section.

doug_dayson

Kind of a waste to use the wimpy C3 frame if going to all the trouble, much better to use an aftermarket tube frame for C3 body and C4/5 suspension, like this for example (there are many available now)...

http://sriiimotorsports.com/pages/691639/index.htm

Doug

Twin_Turbo

wimpy C3 frame can be fixed easily

Travis Johnson

So if bolting up a C4 rear suspension and strengthening the frame are so easy, then how do you do it?

72LS1Vette

Rowley Corvette in Mass. also sells a C3 frame that will take C4 suspension components. Expensive, but you don't have to do anything but bolt stuff on.



Rick B.

69427

I'm currently in the middle of this conversion. The rear went fairly well, while the front is making me work for everything. Part of the additional difficulty on my application is that I am retaining the stock C3track width (versus the C4 track width) so I can retain (the stock offset) 15in wheels. This required narrowing a bunch of stuff. I built a custom front crossmember to mount the lower A-arms and eventually the steering rack. As TT mentioned, it gets a bit crowded up front, so the going has been slow. Right now I'm trying to figure out how and where to mount the front rack to minimize bump steer issues (and hopefully still be able to connect it to the steering column). It's been an interesting experience, particularly dealing with multiple items that want to occupy the same space.

jr9170

How much do they sell for?

GoldenRod

Unless you are going to replace the frame in its entirity, I think the rear is a worthwhile swap, but the front not so much. You can go with tubular or aluminum parts up front (just saw a new place making aluminum a-arms for our cars, can't remember where) and add rack & pinion without all the headaches of extensive frame mods. That being said, I'm probably just going to build a separate frame up starting with one of the tube frames available for my '82.

flood

C5's are pretty cheap now-a-days.

just a thought, ignore me.

Little Mouse

stopped at the vette museum at bowling green on my way to
the street rod nationals they had a complete C5 chassis sitting
out in the midldle where you could walk up touch it look it
over, that frame is strong the rear suspension built the way an
IRS should be, shame chevy waited until 97 to do things right.

Travis Johnson

So what are the steps for the c3 to c4 rear suspension conversion? Basically welding on a few new brackets? Where would someone get started?

doug_dayson

Full cage, though that's a pain for a street car etc...

Doug

doug_dayson

Body off, new suspension pick up points, full cage etc...

Not easy, especially for a street car.

Doug

doug_dayson

If a street car without a full cage, then best to get aftermarket tube frame...

http://sriiimotorsports.com/pages/691639/index.htm

...next best is to have Car Creations mod your stock frame (unless you of course have the skills and equipment to roll your own)...

http://www.carcreationsinc.com/html_2/63home.html

Doug

Travis Johnson

Those prices are ridiculous, maybe I can afford that in another 20 years. Car creatons looks like a total ripoff, you could almost get two new frames for that. If I was gonna do a new frame I'd do something like this http://rowleycorvette.com/frames-new.html or a art morrison, those are still expensive but at least below 4k.

Obviously from the comments on here people have done it, I'd like to hear what theyve done. Or what can be done to the to the c3 suspension to get similar performance. I'm trying for figure out what kind of rear suspension to use to handle a 500hp engine and improve the handling along the way. Looking at prices for c3 upgrade components the c4 looks like a cheaper better alternative.

doug_dayson

C2/C3 can handle 500HP no problem, though you'll never get C4 handling and braking performance out of one without a tube frame, or full cage on a stocker (assuming C4 suspension components etc).

The C4 frame is WAY stiffer (I have a modified 71 Coupe, and a 91 Z07 Coupe).

That said, if building a cool street car then the various aftermarket C3 setups work well for minimum bucks...

Doug

Travis Johnson

Ok, thats what I wanted to hear. I'm trying to plan out a C3 build with an LS1/T56 ands there wont be much money left in the budget for driveline upgrades.

Eventually I'd like a C3 that performs as good or better than a new vette, but it will most likely come in stages.

doug_dayson

Very cool, though to get it to handle and brake like a C4/5/6 you'll need to address the suspension etc. To my way of thinking you'd want to make the frame work as well since you're going to be doing a lot of fabrication/money spending.

The C3 frame can work with a real cage, but then that's a hassle in day to day use and luggage room etc (if these things matter to you?).

If you keep the C3 suspension stiff it can do ok on smooth surfaces, but it won't compete on rough surfaces. If you don't keep it stiff the brake dive and bump steer are pretty bad. If you have lot's of HP then you'll need to keep the rear stiff to avoid breaking stuff too, so then the front needs to be stiff as well etc. It will not ride as good as a C4/5/6 either (if a street car this might matter).

IMO, if you're doing the LS1/T56 then you should do the C4 suspension at the same time, as otherwise you'll need to take it all apart and fab everything up again (possibly move the motor mounts etc?).

If a street car, it'll still be great with say something like a VB&P setup and some proper steering (Steeroids or the Jeep Box), and the LS1/T56, though it won't handle and brake like the newer ones.

Doug