actually it idles surpisingly smooth witha vacum readings at 19 i park and 14 in gear,no tach hooked up yet but id say about 750-850 in gear.Im still trying to get a prom programmed for it,where did you get yours at?The zz4 cam has a ton of torque.

 

i agree completely. last may i cracked my windshield at a track event from chassis flex. my problem has been that the frame has become a part of the suspension. the front suspension and rear suspension have become so tight they distribute alot of force into the frame, which has become the weakest part of the suspension. i have a 4-speed car and have fabricated a crossmember for it that attatches the framerails together roughly 1/2 way between the front and center crossmembers. it also makes the engine a stressed member which you definately feel but otherwise stiffens the car up.
i'm trying now to find engine or transmission mounts that could be used and may make a kit for this. in the meantime, if anyone is interested you can e-mail me for pics.

 

When I had the the body sand blasted the next thing I did was seem welding the whole frame. The factory used spot welding and I remeber reading a early 90s Corvette mag and it mentioned that the frame will be 100% stiffer when seem welded. I have no driving experiences until next summer, but I'm pretty sure that there some thruth in this. :cheers:

 

Clutchdust, I have a 4-speed car and have fabricated a crossmember for it that attatches the framerails together roughly 1/2 way between the front and center crossmembers. it also makes the engine a stressed member which you definately feel but otherwise stiffens the car up.


Are you referring to a '55 Chev. Sedan style of bellhousing?

The '55 - '57 Chev. had a bellhousing with mounting pads on each side. The frame had arm extensions that bolted to the bellhousing with a cushion mount much like the later side engine block mount. The '55 also had engine block mounts off the front of the block that sat on a stud with a cushion.

My old 440 duster had an 8 point cage with solid motor plates in between the water pump and block and then between the bellhousing and the rear of the block. It was really stiff.

Id like to see a lot more input on this subject. The more data there is to process the better chance we have of a major brainstorm producing solutions to all of our problems.

I wish I could put an 8 point in my car that wasn't intrusive. I wish I had an old parts car left to experiment on. JIM

 

prosouth, i'm sure it's very much like that although i have no experience with the '50s cars. i'm using a lakewood scattershield and fabricated crossmember. the whole thing assembled looks kind of like the aluminum dana 44 'batwing' used in the '80 and up vette rear ends, only bigger and upside down.
i thought about going with the front and mid-mounted plates but wasn't impressed with the thickness as advertised through jegs and summit. what i've fabricated is very stiff by itself and then when bolted to the scattershield is probably the strongest part of the frame. i used 1" angle iron and 3/4 iron pipe welded together to make everything up. i have pictures but no web hosting so if anyone is interested, let me know and i can e-mail some.

 

Clutchdust, e-mail me the pictures and I'll post them. This is an interesting subject. I'm interested in finding ways of stiffening the frame without intruding into the usefulness of the car, i.e. 6 or 8 point cage.

 

Here is the picture of clutchdust's stiffener that connects to the bellhousing.

That is very interesting. If there is a way to triangulate the front kick-up back to this area, some flexing of the front suspension would be reduced.

 

This is a very good thread. After making the cross-brace that used the engine as a stressed member, did you get a noticeable increase in vibration through the steering wheel or floor boards? My '63 convertible has quite a bit of flex and cowl shake. I'm considering installing a removable roll bar for safety, a place to mount a shoulder harness, and for stiffening of the frame/body. I sometimes autocross the car in exhibition class for fun.

 

Nice thread. I saw this on the web a while back. I was thinking the cross-bracing could go behind the X-member to stiffen things up. Perhaps the X-member could be right in the middle of the "X". Of course it would be easier if the car had no under-body exhaust... :p:

http://www.progressiveautomotive.com/53CV.htm

 

Who makes these "Shark Bars"?

 

Thanks for posting Clutchdust's picture. If you will notice the two holes on the side of the Blowproof Bellhousing that are located in the flat spot. This is where the mounting pad for a '55 Chev. bolts to it. Then there was a tube arm on each side from the frame to this area much like he has.

I would think that this style of mounting should strengthen the center of the frame. I have reservations about mounting it solid to "MY" bellhousing because of drivability and vibration.

(75BBC Stingray)I was thinking the cross-bracing could go behind the X-member to stiffen things up. Perhaps the X-member could be right in the middle of the "X". Of course it would be easier if the car had no under-body exhaust...



We are on the same page. I actually thought of going from the rear trailing arm mount area almost to the center of the trans'member on each side and then from the front frame corner Back to the same area on the trans'member. This would X the car. I haven't taken any measurements yet or checked to see if the front floorboard would allow it. If it would the '55 style bellhousing mounted with poly mounts to an arm much like Clutch's and an X would have to be strong. I would use steel rectangular tubing to tie it all together. I don't have the weight per foot of the 2x4 or 2x2 tube but I have access to it. It would not be that heavy.

I already had plans to tie the Trans'member and the rear corners of the frame at the T-Arms together. I know I can clear the exhaust to the rear of the trans'member. We'll have to see about the front section.

Just to the rear of the '80 Batwing will be a 2x2 tube from side to side to allow the 6-Link upper struts to be mounted, this should also help.The reason for this thought is that the Batwing is insulated with New Poly Bushings,but still not "Tied" to the frame. The struts will be insulated from the bar by their Poly Mounts so there will be no transfer of vibration from either point.

A four point Roll Bar with the rear kicks through the rear wall and as far to the rear of the frame as can be obtained would secure the rear section.

I just wonder if there is really a good way to support the center section. I hope the X will work out.

Anyone have a frame to try a layout on? JIM


[Modified by PROSOUTH, 9:17 PM 12/10/2002]

 

The VB&P shock tower bar made me think of how I could strengthen my frame and keep my motor from ripping loose the motor mounts. To handle the horsepower I'm going with a different approach. I plan on using motor & transmission plates with solid motor mounts in the stock locations. For the rear the 4 point Jegs roll bar will "be like Mikes" :thumbs: This would hold the motor in the frame and strengthen the frame at several points. I made the motor plates from .250" aluminum. The plates will also serve as a bracket for my remote reservoir power steering pump. Here is a pic of the motor plates so far. 2" steel tabs welded to the frame rails on each side and then bolted to the plates. The transmission plates are still on the drawing board but I plan to use .250" aluminum as well around the bell housing. Since I'm removing the T-Bar I'll need the frame to be as strong as possible… :crazy:

 

vettedan from http://www.vetteworksonline.com I'm own a small company in near Seattle, WA.
I enjoy autocrossing a lot and didn't like my body being thrown against the doors, so I designed a harness bar for the C3 Corvette. I was also tired of C3 crowd being left out of the harness bar market. Both Shark Bars do a great job holding the occupants in place while autocrossing; provides a very stable mount for a video camera and stiffens the body cage with no major modication to the Corvette.
Dan

 

I used Jim's Performance, in MD. I know it's out of the way for NJ, but I can't say enough about how much he's helped me out. (410-465-9569) Knowledgeable and reasonable. I had a spare PROM, so to work out some of the kinks, he's been rotating them with me.

 

I'd be very interested. E-mail is TPIShark@optonline.net
Thanks a lot. I've had similar ideas on this.

 

Thats who my brother uses and ive been trying to get ahold of him with no luck,so i can get mine.Hes really helped my brother out alot,very personable.Hes calling for me today to see if he can get ahold of him again.

 

prosouth, i was wondering what those two points on the bellhousing was for. i had considered using those as mounting points initially anyway but decided against it just because i didn't know what it was for.

as for vibration, yes. it is much more noticable. that's why i'm considering a redesign that utilizes transmission mounts so they can be swapped for rubber or poly for regular driving or solid for track.

in addition to this brace, i also solid welded all the seams on the bottom of the frame and patched over all the holes i could get to. the car is definately stiffer from a torsional perspective, however this does very little for frame 'bucking'.

my thought on a four or six or eight point cage is simply that it boxes in a portion of the frame that is already fairly well supported. now the only cage i can see being noticably stiffer over the length of the frame would be an eight where the forward bars tie into the frame up by the door hinges. that being the best short of a full 10 or 12 point cage. like i said earlier, i cracked my windshield at a track event. had i cracked the back glass then that might be an indication the rear needed reinforcement. as it was the windshield, i felt it more benificial to strengthen this portion of the frame.

an additional modification i'm still considering is welding a length of angle iron down the straight outside portion of the frame under the rocker sill to help box that portion in even more. just measuring the 's**t-to-worth' ratio.

 

I think this is a very interesting discussion. An important piece of information that we need is, How is the frame flexing? Is it longitudinal or diagonal? I'm sure it's a combination of the two but one is likely to be more prevalent than he other. A cross brace will help with diagonal flexing (to some degree) but won't really help longitudinal flexing. We also need to know where it is flexing. Otherwise random bracing may or may not solve the problem.

 

:iagree: i still think the main portion of frame flex is this area between the front and center crossmember, it is the longest portion of unsupported, ungusseted framerail on the car. it also supports a great deal of weight and is subject to the most amount of torsional force. in a case where the c-3 suspension has been significantly stiffened, you transmit even more of the forces into the frame. it also doesn't help that this 'weekest link' is located relatively equally spaced from both suspension points to act almost like a lever against this point. even with the factory crossmember the frame is extremely subject to torsional forces. the way i picture the c-3 frame is take an aluminum ladder and put a piece of pipe about 4-5' long in the two end rungs, then have people at other ends twist in opposite directions. now what do we have to do to eliminate that twist?
ultimately what we as c-3 owners would like is to have a frame with comparable stiffness to the c-5. the reason the c-5 is such a fantastic car isn't it's revolutionary suspension because (news flash) it's not that revolutionary. the front is an evolution of the c-4 which is an evolution of the c-2/c-3 front suspension and the rear is similar to multiple other ultrahigh performance cars-nothing really new. where the c-5 is so far ahead is the chassis stiffness that keeps so much of the outside forces in the suspension where it was designed to be. that is why the c-5 can have such a beautiful ride and still have world class handling. ideally, the frame is supposed to stay perfectly ridged and keep everything mounted to it exacty where it's supposed to be. and the suspension is supposed to absorb, counter and rebound all the irregularities and outside forces encountered by the car during driving.
where it becomes so tricky with our cars is the limited amount of space with which we have to work. hell, you can't even fit a cup holder inside the car so how do you strength a chassis on a car this narrow? look at the solution dave mcclellan had for the c-4. the frame is very similar in basic layout as ours with the two biggest differences being 1) they didn't cut out a portion of the frame box to mount the t-arms and 2) the frame walls are about twice as tall as ours. i'm sure everyone here has at least ridden in a c-4 and noticed the c-4 ingress/egress issues created by the stiffer frame. still same basic type of frame design (ladder frame) but stiffer primarily due to the cross section of steel absorbing forces. the c-4s are still subject to some of the same issues ours are and that is torsional force. ever heard c-4 owners complain of cowl shake? ever heard any of them say the car is noticably stiffer with the top on? i have. the c-4 frame is more resistant to the 'bucking' because of the cross section but they still have a nearly identical span of unsupported and ungusseted frame rail. that's why they came up with the x-brace for the 'verts, and that is just a band-aid. the c-5 frame is the solution. now, how do we do the same thing to our cars?
whew! sorry guys.

 

I think that defines the problem fairly well. As you said, the only way to add stiffness is too increase the effective section width of the frame. The most ideal way (structurally speaking) is a cross braced cage. This will give you the maximum section width within the confines of the vehicle. Obviously this isn't an option for some. So there are other ways that aren't as good but are at least an improvement. Using some concepts from the C5 could work. Such as adding a center spine in the drive shaft/transmission tunnel, then cross bracing that to the outer frame rails. Tying into an arrangement like your bell housing brace would work well.