I have owned both C4's and C5's. One big improvement of the C5 is its extrodinary stiff frame with the center tunnel. The other is its great suspension. One of the reasons, I moved back to a C4 is that, to me, a C4 is a funner (made up my own word) car to drive. The C5 was smooth, powerful, quiet, but, in a word, boring.
At least to me, I can play a lot more with my LT4, missing and grinding gears, wondering how to get that rattle out of the dash, cursing whoever thought a Bose system with separate amplifiers was such a smart thing.
Also, lots of people have commented that the C5 front suspension has a lot of "Chatter" and "Rattle" when hitting road bumps. To me, this is more obvious in a C5 than a C4, but that may be my imagination since the C5 is a quieter car and you may notice some things that are hidden in the C4 squeeks and rattles.
Now to clarify my statement: With Dave's under carriage brace, the rigidity of the frame gives the feeling that it is equal to what I experienced in a C5: a firm, secure frame with no flex and yet very comfortable while giving a great amount of feedback to the driver as to the car's ability to execute the commands of the driver. The Cross Brace does nothing to the suspension but the limiting of the flexing may improve overall handling. Not too sure and I do not race so cannot give it a fair comparison.
As to the Targa Truss vs. the Cross Brace, I do not believe they can be considered similar. The Targa Truss replaces the top. Now it may be stronger and firmer than the top, but, it is still a top replacement. Off with the top, on with the truss.
The Cross Brace is always on the car so, when the top is on, you have the car braced by both systems. I have not tried to drive the car with the top off to see how much the Cross Brace adds by itself but, at the least, it will be better than before.
In addition, the Cross Brace extends from the corners of the frame to the oppisite corner. This, I believe, maximizes the amount of firmness that is added to the car.
Also, I believe I started this topic in my quest to find a way to drive the C4 with the top off and not feel like the car is self-destructing. The Targa Truss was an option that I passed on since I did not want to have something that needed to be mounted and unmounted every time the top went off or on.
Was very plesantly surprised to notice how the Cross Brace improved the ride of the car.
Still stick with my recommendation: If you want to greatly improve the ride of your C4 and have a more enjoyable driver, try Dave's Cross Frame. Will commit to this: The value for money I spent on the Cross Frame exceeded any other bolt on I have tried, including exhaust systems, intake systems, chips, chip programers, short throw shifters, and all of the other fun things we buy for our Corvette's.
