C4 No Flex kit
11-11-2011, 11:27 AM
#1
Instructor
Thread Starter
C4 No Flex kit
Reading in the August issue of Auto Enthusiast about the C4 No Flex kit and was wondering if anyone has installed one of these on their car. For the kit at $500 plus for what you get is right pricey. If you do have one, does it get caught on lets say a driveway or railroad crossing. Anyone sell a like product for a little less loot?
11-11-2011, 12:54 PM
#4
Race Director
I wrote the article and that is my car in the pictures.
History: Gordon Killebrew was doing some work with Jason Francis who owns Vette2Vette in Streator, IL. Gordon noticed a convertible X brace that Jason had taken off of a wrecked C4 and mentioned that he had designed a better solution to eliminate the C4's flex problems. He told Jason that he presented the idea to the engineers while he was working at the Bowling Green factory but they axed the idea due to cost constraints. He told Jason that he could have the rights to the design as he considered him to be the son he never had.
Jason then went to one of the fabricators he works with and they made up a test set. After a few modifications the shop turned out a few sets and he started marketing them at trade shows and on his web site www.vette2vette.com
I became friends with Jason after purchasing used C4 parts from him and becoming impressed by his great service.
I have been to several of Gordon's classes and he even used one of my C4s as a demonstrator for a Bloomington Gold class. His knowledge of C4s is priceless!
I have had a few articles published by Corvette Enthusiast magazine (now Auto Enthusiast) and offered to write an article about the frame brace and attempt to have it published. After some negotiation on the price I took a set home and installed them on my 91 coupe A4 with performance axle and FX3.
The installation was easy, fit perfectly and now my 91 handles better with the targa top off than it did before with the roof on. There is a triple set of railroad tracks near my home. I would have to baby the car when I crossed these tracks before (even with the targa on) but now I can take them at the 25mph speed limit with the targa off with no noticeable cowl shake or flex. It feels like a new car on the twisties even with 105,000 miles on the clock. I love them!
The kit consists of 2 front brackets that bolt right into the front X brace holes that all 89 thru 96 C4s have and 2 rear brackets that bolt on to the lower rear dog bone. The braces are then connected by to rods with adjustable Heim joints at each end. Simply bolt the Heim joints to the front and rear brackets and tighten the snot out of them. This pulls the front and the back together but still allows you full access to exhaust and driveline components.
The difference in rigidity and handling is very noticeable and makes the old C4 feel like a sports car again.
The braces are no lower than the catalytic converter on my 91 and you can still access the stock jacking points.
The kit on a Forum member's ZR-1,
The kit:
Comes with all the bolts and washers (not pictured). The parts are all heavy duty. The manufactures is a "name brand" builder of tube frames for C1, C2 and C3 Corvettes that I don't think I am allowed to mention.
Disclaimer: I do not make any commission on these and do not work for Vette2Vette or its supplier.
Feel free to send me a PM if you have any questions.
History: Gordon Killebrew was doing some work with Jason Francis who owns Vette2Vette in Streator, IL. Gordon noticed a convertible X brace that Jason had taken off of a wrecked C4 and mentioned that he had designed a better solution to eliminate the C4's flex problems. He told Jason that he presented the idea to the engineers while he was working at the Bowling Green factory but they axed the idea due to cost constraints. He told Jason that he could have the rights to the design as he considered him to be the son he never had.
Jason then went to one of the fabricators he works with and they made up a test set. After a few modifications the shop turned out a few sets and he started marketing them at trade shows and on his web site www.vette2vette.com
I became friends with Jason after purchasing used C4 parts from him and becoming impressed by his great service.
I have been to several of Gordon's classes and he even used one of my C4s as a demonstrator for a Bloomington Gold class. His knowledge of C4s is priceless!
I have had a few articles published by Corvette Enthusiast magazine (now Auto Enthusiast) and offered to write an article about the frame brace and attempt to have it published. After some negotiation on the price I took a set home and installed them on my 91 coupe A4 with performance axle and FX3.
The installation was easy, fit perfectly and now my 91 handles better with the targa top off than it did before with the roof on. There is a triple set of railroad tracks near my home. I would have to baby the car when I crossed these tracks before (even with the targa on) but now I can take them at the 25mph speed limit with the targa off with no noticeable cowl shake or flex. It feels like a new car on the twisties even with 105,000 miles on the clock. I love them!
The kit consists of 2 front brackets that bolt right into the front X brace holes that all 89 thru 96 C4s have and 2 rear brackets that bolt on to the lower rear dog bone. The braces are then connected by to rods with adjustable Heim joints at each end. Simply bolt the Heim joints to the front and rear brackets and tighten the snot out of them. This pulls the front and the back together but still allows you full access to exhaust and driveline components.
The difference in rigidity and handling is very noticeable and makes the old C4 feel like a sports car again.
The braces are no lower than the catalytic converter on my 91 and you can still access the stock jacking points.
The kit on a Forum member's ZR-1,
The kit:
Comes with all the bolts and washers (not pictured). The parts are all heavy duty. The manufactures is a "name brand" builder of tube frames for C1, C2 and C3 Corvettes that I don't think I am allowed to mention.
Disclaimer: I do not make any commission on these and do not work for Vette2Vette or its supplier.
Feel free to send me a PM if you have any questions.
11-11-2011, 05:08 PM
#8
Burning Brakes
with the targa on it's not *terrible* but definitely could be improved. With the targa off, you can definitely feel the flex.
Looks like a nice product, but the price is a little nuts.
Looks like a nice product, but the price is a little nuts.
11-21-2011, 07:22 PM
#12
Le Mans Master
On some of the California freeways, even with the top on, the cowl shake gets really bad! You can visibly see and feel the steering wheel shake and it is disconcerting. If there was a way to fix this (and now there is!) I'd sure get it on my C4!
11-21-2011, 10:59 PM
#16
Max G’s
Sorry, can't see the value in this. I occasionally autox my complete stock 91 and never have flex issues. If anything was going to tie the frame it would be a cross brace, attached diagonally, not longitudinally. If you want an example of how stiff your frame is on your C4, take a jack and place it in the center of the car and jack it up. I bet the whole side will raise up. I will say not sure about verts, but I do know coupes. Spend your $500 on a better mod. Not trying to offend anyone, but it is what it is.
11-22-2011, 08:14 AM
#17
Le Mans Master
Sorry, can't see the value in this. I occasionally autox my complete stock 91 and never have flex issues. If anything was going to tie the frame it would be a cross brace, attached diagonally, not longitudinally. If you want an example of how stiff your frame is on your C4, take a jack and place it in the center of the car and jack it up. I bet the whole side will raise up. I will say not sure about verts, but I do know coupes. Spend your $500 on a better mod. Not trying to offend anyone, but it is what it is.
11-22-2011, 08:22 AM
#18
Pro
Member Since: Jun 2011
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Vet is not a sub frame car.
Sorry, can't see the value in this. I occasionally autox my complete stock 91 and never have flex issues. If anything was going to tie the frame it would be a cross brace, attached diagonally, not longitudinally. If you want an example of how stiff your frame is on your C4, take a jack and place it in the center of the car and jack it up. I bet the whole side will raise up. I will say not sure about verts, but I do know coupes. Spend your $500 on a better mod. Not trying to offend anyone, but it is what it is.
11-22-2011, 12:01 PM
#19
Instructor
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I could see this helping fore-aft rigidity which is something you would notice over things like railroad tracks and probably if you could measure on hard launches as well. The sills are so high on C4 to counter the rigidity lost when they made a targa top, I see this as just beefing them up even more. As for price, seems fair.
11-22-2011, 07:33 PM
#20
Safety Car
What you guys don't know about C4 frame flex wont hurt you. Dave McLellan in his book Corvette from the Inside, clearly states and I am paraphrasing here. They had to raise the door sills and add reinforcement to high stress areas. They barely got the torsional frequency above wheel hop frequency with the top ON. With it off, it is just below that. Wheel hop in a C4 14.5Hz, the top ON is like 17hz. A C5 FYI, is about 21 with the TOP OUT!!! With latches, no bolts, so Dave fixed the issues in the C5. Dave McLellan NOT Dave Hill. The C5 was 90-95% done when Dave Hill took over in mid 93.
The C4 structure was originally designed to be a t-top car with low sills. Mr. Lloyd Ruess a GM exc. nixed this because he wanted a targa. It was too late in the game to change the chassis except to make it work, and that is what we got.
FYI, some time ago I read that a national champion auto-x'er made runs with top on and off on a C4. No difference in times.
Supposedly, Mr. Gordon Killebrew designed the above pictured devices, they found that the flex was result of the welds flexing. This solved that and was proposed for production, but cost and near end of C4 run nixed the idea. That is the word on the street anyhow.
The C4 structure was originally designed to be a t-top car with low sills. Mr. Lloyd Ruess a GM exc. nixed this because he wanted a targa. It was too late in the game to change the chassis except to make it work, and that is what we got.
FYI, some time ago I read that a national champion auto-x'er made runs with top on and off on a C4. No difference in times.
Supposedly, Mr. Gordon Killebrew designed the above pictured devices, they found that the flex was result of the welds flexing. This solved that and was proposed for production, but cost and near end of C4 run nixed the idea. That is the word on the street anyhow.