I can see the forest for the trees. I understand your point, and it was tell taken.

I dont know enough about top speed, and what kind of power it takes for a C4 with reach 200 mph, but I would love to try. I am pretty sure I have the powerplant to give it a shot.

 

I think there are two types of top speed......1) On concrete at a sea level track of some sort.... I'm not even sure where, but I know the old silver state classic, there were paved areas where you could stretch your legs, not sure what elevation that is at though. 2) Salt Flat top speed

I know on the Salt Flats, you need more power to achieve the speed due to the 1) Elevation of the salt flats 2) The heat of the salt flats 3) the salt itself, which kind of sucks your car in like mud and adds to the rolling resistance severely........ all 3 of those are substantial by themselves..... add them together and its my understanding whatever you think you need to reach a speed, add another 50 HP.... and even more.

Thus, when talking about top speed runs, it should be seperated which one they are.

On how much power to go 200 mph, I do not know, but I can share what I do know...... about 10 years ago, a California racer was part of the silver state classic, in his 86 C4 - 383, Superram motor, trick flow heads with a hyd roller comp cam and 355 rwhp, hit 186 mph..... that motor was probably around 425 flywheel...... was a full weight car, but for the racing, taped up all gaps on the front end of the car, I guess that helps a bit. Car was a manual transmission, but I do not remember what tranny it was.....

btw, at the recent Florida 1 mile run the OP has mentioned, a friend of mine in his C6 Z06 hit 174 mph....... he is pretty much stock, I think he has an air box of some sort..... I was impressed... it sounds fast anyway.

I also knew Rick Doria from way back in Southern California years ago, he's a well known road racer in those silver state road-race type events, and a very successful one. In his C4, he was reaching close to 220 mph speeds (210 at least) with only a 525 HP motor..... however, that was a race only car specifically set-up for road racing and I would estimate his race weight in the neighborhood of 2700 lbs... if that.... but I am not sure.

Btw, if you any of you socal people want advise on that type of racing, stop in at "Haus of Pizza" in Costa Mesa and talk to Rick about it.... Rick owns the Pizza restaurant and is there a lot.... or at least used to be. Its a tasty pizza too. He knows as much about top speed C4 racing as anybody considering he was the class record holder and the guy to beat for years.

hope this helps.

 

Another real-world example is this 377ci ZR-1 that ran last year at Bonneville. He hit 220mph on the salt, and said it was still accelerating after 4 miles, but that's all you get:

http://forums.corvetteforum.com/c4-z...p-date-13.html

 

The biggest obstacle I see is actually the transmission. The C6 ZR1 has a HUGE advantage...it's sixth gear is NOT an overdrive. Once you hit sixth in a C4, you're done. You'd need to regear the trans so it would pull consistently through all six gears. Like you said, it's all about proper gearing...

 

Good Point


Here is a Z06 with a cam and headers going 200+ (road is a closed course). I do not agree with the way he was driving in the beginning, but this is just for a speed example (I think he may curse due to excitement at the end so...)

 

What are the C6 ZR1 gear ratios?

I just did a quick search and found this:
1st-6th = 2.29, 1.61, 1.21, 1.00, 0.81, 0.67

 

vs C6 ZO6
1st-6th = 2.66, 1.78, 1.30, 1.00, 0.74, 0.50

I looked up a 1996 six-speed but got side tracked and lost the page and the copied text.

 

My box-stock C6 (LS2) factory rated at 400chp put down 360 to the wheels on a dynojet. It is also "rated" by Chevy to go 186 mph, though I never tried. I did hit 160 once, and accomplishing that was quick and easy. I have no doubt that the car would have topped 180. BTW, that was in UT, at the Bonneville salt flats (High elevation).


Not sure where you're sourcing your info from, but that is wrong. The transmission in the current (and last) Z06 features TWO overdrives; 5th AND 6th....just like the ZF6 in a C4.

 

I see you figured it out on your own.

For comparison, the ZF6 ratios are as follows:
1st-2.68, 1.80, 1.29, 1.0, 0.75, 0.50

Pretty darn similar to the Z06's Tremec.

 

SuperL98: interesting charts. I hadn't seen those before. Headlights up adds quite a bit!

Beach Bum: reading some of the Salt Flat racer trials-excess weight (even added ballast) is welcome for stability (traction?) in many cases. I was amazed as some of the race poundages those things scale in-of course.

Auroro40: thanks for posting a link-I hadn't noticed that in the ZR-1 section-that project is incredible! 220 mph.

I think it is safe to say you won't use 6th on a topspeed run unless you regear the rear axle (4.11, etc) and then you may have issues with driveshaft speed. I calculate that you can hit 212 or so with 5th at ~7200 rpm...I'm sure this is what Car and Driver did with their Lingenfelter SB2 Corvette.

Simple calcs show 200 equals 6800 rpm with my current setup-probably pretty close. Admittedly, I haven't included a variable for tire growth at that speed-surely there is some.

Of course no one has mentioned aligning your power peak with the rpm required to hit the number...in other words if you peak at 6000 and it you need 6800 on the clock...you ain't going to make it unless you still have enough power on the backside of the peak-unlikely.

 

We haven't talked about that, and I agree that going past the power peak...well, at that speed, I don't think the engine would. Tq is dropping fast, as load (drag) is increasing exponentially. You'd have to gear it to hit hp peak at or darn close to terminal velocity.

 

Not sure how you're doing your quoting, but I didn't make that bottom quote in your post..... not sure who did, I haven't really read this thread closely.

Can you change your post to reflect who made the quote ?

thanks

 

My bad. Fixed. Sorry Beach Bum.

 

Thanks !

On a seperate note, your stock C6 put down 360 rwhp ? Thats pretty impressive.... technology marches on ! It wasn't too long ago that 360 rwhp was a seriously hopped up stroked motor with a lopey cam..... now they're doing it off the factory floor in the base engines...... times have definitely changed !

 

200 mph in a mile....sounds like fun.

 

It did...I don't know if the dyno operator "adjusted things" to make it look better than it was or not, but that's what the print out I have, says. I tend to believe it, b/c it was also the fastest stock or stockish C6 in our area, (at the drag track) -by a lot. Boringest 360RWHP car you'll ever drive.

 

 

I'm running CNC Cylinder Heads ported LT1 stockers, and even though cylinder head technology has vastly improved since are heads were done. My car with the stock shortblock will trap 119 mph. Who knows, maybe eventually I'll build an engine based on your lower end and pick up a "better" set of heads.

 

Almost 200 mph/mile in a C4!!

http://forums.corvetteforum.com/c4-g...-5mph-run.html

 

If you check with ZFdoc, you will find that Rick Doria and other racers have had custom ZF gearsets made with more useful (less overdriven) 5th and 6th gear ratios for top speed.

At the Salt Flats properly balanced heavy cars have more stability. When I was there in 2006 helping "The Avanti Kid" (mostly I was just there for the fun), he was running ~ 700 lbs of balast. The salt is a unique racing surface: it can be about as hard as concrete, seemingly with the breakaway traction of ice. Another salt Flat oddity: a lot of racers favor an open non-posi differential to help with stability when the driven (power) wheel spins at high speed.

Thomas