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Discussion Starter #1
Continuing from earlier post where I asked about using 3.15 gears with the Z06 drive train, I have since determined the car's "theoretical" top speed. It is a whooping "185", which would certainly be a big improvement just by swapping gears.


As amazing as that might be, a top speed of 185 is not too surprising with the benefit of taller gearing.

Since I was doing "what if" calculations with my CAR TEST program, just for fun I ran a prediction for the 2002 Z06 in bone stock configuration (ie, w/3.42 rear end). I am
totally shocked. Top speed (theoretically derived) is a lot higher than I thought.

My prediction software (which is generally very accurate) predicted 181.5 MPH!!! Again, this is for a "bone stock" Z06 with the 2002 specs on the LS6.

How can this be???

For a year or more now, everything I've read says the "2001" Z06 top speed is suppose to be 171. I am doing a fairly precise (albeit theoretical) calculation that says the car's top speed actually "should be" 10 mph higher than what GM claims and all the magazine writers seem to agree with GM.

Any comments from those that may know the real story? /phpBB/images/smiles/icon_wink.gif
 

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Z06 Maniac!!
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Z06s are redline limited in 5th gear to about 171 to 174, aerodynamics do not factor in. A rear gear ratio change would result in a higher top end just like you calculated.
 

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Doug Rippie states his C5 RSR has a top speed of 190 mph. He does'nt make any mention of a rear gear change. He states it has a functional rear spoiler which should clean up the flow in the rear if it works and 500 HP which together must be responsible for its top speed. My 02.
 

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Discussion Starter #4
FWIW, unless the Z06 max. velocity is "speed limited" as opposed to "rev limited", my S/W prediction program says a stock "2002" (and don't forget about the additional engine power at peak rpms), will reach 181.5 mph. This speed is predicted at about 6500 rpm which is BEFORE the point where the rev limiter shuts off the fuel.
 

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Don't forget that the Z06 gear ratio in 5th is lower (numerically higher) than that of the Coupe and Vert 6 speeds.
 

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Discussion Starter #6
Hey, give me a break. I'm not a Mathematician, but I already took the different gear ratios of the Z06 tranny into account.

Guys, what I'm looking for here is PROOF the GM rating is artificially low. As far as I know there has been no change in the Z06's top speed rating for 2002. How can this be? This in itself is seemingly illogical with an additional 20hp on top.

I also think the "2001", the cars out there now, was underrated by GM and its top speed is at least comparable to the Coupe at 175. I realize the aerodynamics are different and my prediction program takes that difference into account as well. Accordingly, CARTEST predicts the 2001 Z06 can pull to 179. I don't know about that, seems a bit high in relation to the Coupe. If true, maybe GM was trying not to steel the thunder of the ZR-1 just quite yet. Although I have no idea why that should stop them, but it wouldn't surprise me.

Given enough straight and level road under optimum conditions for making horsepower, and where talking about 5-6 miles, even the current car should do a lot better than 171.

I'm an open road racer and some of you may be also. In this type of "racing" venue there would be ample opportunity to find out the truth of the matter. My problem is I don't have a car yet. Soon to be rectified. /phpBB/images/smiles/icon_smile.gif

That's why I posted this to the forum to see if anybody else has taken there Z06 to its max speed potential. Albeit, that's no easy task, because like I said, you'll need at least 5 miles of clear, straight and level
highway out in the middle of nowhere, 100s of miles away from the city. /phpBB/images/smiles/icon_wink.gif
 

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I get similar results .. using values of

3.42 rear end ratio
27 inch tire diameter
.84 transmission ratio (5th on a Z)

I get 171 mph at 6115 rpm .. the speed predicted at 6500 rpm is 181.7.

The only 'iffy' value here is tire diameter. Anyone have a more accurate value?
 

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Discussion Starter #8
Jerry, I'm looking at a Goodyear tire chart right now and it says for 295/35ZR18 on a 10.5" wide rim, the section width is 11.85", overall diameter is 26.10, tread width is 10.8". So if this is correct and applies to GY's F1 SC tire, we can calculate the rear tire's circumference to be 81.99578". Let's just call it 82" even, or 6.833'. I entered this tire size enter into CARTEST as a "user defined" parameter and re-ran a prediction. All other parameter remain the same. It dropped ~1 mph, but still predicts over 180 mph top speed for a stock 2002 Z06. This speed is computed in 5th gear at just shy of 6200 engine rpm (slightly past the HP peak).

Out of curiosity I re-ran the prediction again for a 3.15 rear gear and it still
calculates top speed to be 185.

Incidently, there is a noticeable gain in 1/4 mile trap speed with a 3.15 as well; almost 4 mph better than stock. This is probably due to the fact that an extra shift from 3rd to 4th gear can be avoided with a 3.15 rear.

Also, zero to 60 time only takes a very minor hit (less than a tenth of a second). With better gas mileage on the highway as well makes a 3.15 gear change seems very beneficial.

It's time for renewal of the decade old Corvette motto, "Life Begins at 180". But this time it can be synomous with the new Z06 KOTH Corvette. /phpBB/images/smiles/icon_wink.gif
 

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Using 26.1 as tire diameter, I get 175.7 mph at 6500 rpm .. a little closer to the official GM prediction.
 

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Don't tires change size when going fast like that? I remember that when some people were calculating top speeds of Cobras a while back...not sure how much they change.
 

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dsinned, here is your break, tire height, tire height, tire height. The Z06 is redline limited to about 175 according to all the automotive press and GM. I guess you'll need to change a ratio somewhere! /phpBB/images/smiles/icon_smile.gif
 

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dsinned,
I will be in the Silver State Classic in September. I will let you know what my particular Z06 will do, unless I'm teched to a max of 165. If this happens I will only go 165 but I'll let you know the RPM's.
 

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FWIW, the November, 2000 issue of Road & Track tested the top speed of a new unmodified Z and 5 other much more expensive sport cars at the state of the art Volkswagen Ehra-Lessien test facility in Germany. Top speed of the Z was 174.8 mph achieved at 6,500 rpm in 5th gear. Cars were driven by Wayne Taylor, Cadillac Team LMP driver and former Le Mans winner. Taylor couldn't get more than 4,000 rpm in 6th Gear. Seems like a Gertag 3.73 rear end in a slightly modified Z would do a whole lot better in top speed, especially with improved rear air management a la C5R, or?
 

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Discussion Starter #15
Yep, tire growth as speed increases is taken into account by my CAR TEST program as well.

Personally, I tend not to believe magazine tests of a car's "theoretical" top speed.

They usually test when conditions could be unfavorable, or on crummy roads, or simply don't have enough long straightaway (5-6 miles) to allow enough running room to get up to full speed.

ORRing is one of my favorite motorsports and I recommend all of us in the Western region of the U.S. meet at the Pony Express in about
two months (7-9th of September) to find out what these babies can really do.

Please goto: http://www.openroadracing.com to find out about this upcoming event and/or sign up. If this will be your first time, please mention on your entry form Dennis D. referred you to the event.

BTW, the weekend before last the traditional PEx race in Northern Nevada was held on June 24th. There was a rather poor turnout, only 81 cars, but there were still lots of Vettes (many C4/C5s).

I sat out the race as I have done it many times before in my currently owned C4 cars. Instead, I volunteered to be a course worker and was in-charge of the only "official" radar station on the course. It was along one of the longest straights (close to 10 miles long). It was great fun watching all the car pass by a peak speed. The fastest that day was a friend's race prepared C4 which blew by me at 219.6 mph. Then, about
20 miles down course, he had a tire blowout and lost control of his car. Needless to say, it was a total wipe out. The car was
demolished. Miraculously, both driver and navigator were not serious injured.

This I think is a testiment to how well run
these type of events are that after 12 years
of ORRing there have been so few casualties
and at this particular event (8 years old, generally two events per year) there has never been anyone seriously hurt.

Unfortunately, there was only a single Z06 entered in the event (owned by a friend who came all the way from Florida). That car failed to make the run for some reason. I
think the owner was fearful of overheating his transmission as the OAT that day was in
the 90s.

Needless to say, I was very disappointed he did not run. Opportunities to run your car
up to full speed for a distance of 85 miles on a closed rural highway do not come along very often.

As I said the next ORRing event at the same
location (Battle Mountain, NV) is 7-9th of September. I hope there will be a whole lot more Z06s entered. I'll be there and quite
possible in my new Z06 if I get it delivered in time. Hope some of you will decided to be there too. TRUST ME, it is a whole lot of FUN!!! /phpBB/images/smiles/icon_wink.gif
 

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if you do cams arent guys taking these to 7000rpms+ etc? what are the speeds up there, and what has anyone gotten theres up to. I'd really like to have a 200mph vette. I know i need more hp and torque, but i guess it would be in 6th gear instead of 5th...or do you just have to change the ratio of 5th...or just rev higher? in the evo's that im used to 7400rpm's is the usual limit...and when you build the motor you can take it to 9000rpms..which is instead of 113-115 in 4th...is 138 or so. so the ability to rev out the motor will increase the top speed to what from 5th and its usual 171mph top speed
 

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dsinned said:
Jerry, I'm looking at a Goodyear tire chart right now and it says for 295/35ZR18 on a 10.5" wide rim, the section width is 11.85", overall diameter is 26.10, tread width is 10.8". So if this is correct and applies to GY's F1 SC tire, we can calculate the rear tire's circumference to be 81.99578". Let's just call it 82" even, or 6.833'. I entered this tire size enter into CARTEST as a "user defined" parameter and re-ran a prediction. All other parameter remain the same. It dropped ~1 mph, but still predicts over 180 mph top speed for a stock 2002 Z06. This speed is computed in 5th gear at just shy of 6200 engine rpm (slightly past the HP peak).

Out of curiosity I re-ran the prediction again for a 3.15 rear gear and it still
calculates top speed to be 185.

Incidently, there is a noticeable gain in 1/4 mile trap speed with a 3.15 as well; almost 4 mph better than stock. This is probably due to the fact that an extra shift from 3rd to 4th gear can be avoided with a 3.15 rear.

Also, zero to 60 time only takes a very minor hit (less than a tenth of a second). With better gas mileage on the highway as well makes a 3.15 gear change seems very beneficial.

It's time for renewal of the decade old Corvette motto, "Life Begins at 180". But this time it can be synonymous with the new Z06 KOTH Corvette. /phpBB/images/smiles/icon_wink.gif
Not sure where or how your are doing your math. Here's mine numbers

3.15 gears 26.1 Overall Diameter 6500 = 191 5th gear .084
3.15 gears 26.1 Overall Diameter 6600 = 194 5th gear .084
:cheers:

.
 

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dsinned said:
Yep, tire growth as speed increases is taken into account by my CAR TEST program as well.
So what is the factor for tire growth as a function of speed? I would think it depends on each individual tire due to construction/material issues. I wouldn't think the circumferece would grow more than 1% ~2%.

As far as using tire sizes for the calculations, IMO it's not nearly as accurate as actually measuring the rolling circumference of the actual tires on the car at operating temperature/pressure.

I measured the actual rolling circumference of the rear tires on my Zee when it was new ... got 80.50 inches. If you calculate the circumference from the tire size of 295/35-19 the calculated circumference comes out to 82.09 inches ... that's about 2% higher than actual.

If I use 80.50 inches in the top speed cruncher, I come up with a top speed (at 6500 redline, since this car has enough HP to pull redline in 5th gear) of 172.5 mph. If I use the calculated circumference of the rear tires I get a top speed of 175.9 mph.

BTW -- most stock Z06s with 405 HP put down about 350 SAE RWHP on the dyno. Calculations (which account for aerodynamics and rolling resistance) says that 350 RWHP is good for 184 mph ... if the gearing is perfect to take full advantage of that HP. :jammin: 85 RWHP of that 350 is just to overcome rolling resistance, the other 265 RWHP is to overcome aerodynamic drag. As it's geared stock, the Z06 will redline in 5th gear before reaching it's true top "theoretical" speed potential of 184 mph.

Of course, if you go out and do a (safe) top end run with a GPS on board then that's what your car can really do. :D
 

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An additional major factor limiting top speed is aerodynamics. The post referring to the C5R mentioned the rear wing to smooth air flow as well as horsepower.

WIthout changing the shape or CD of the car you would have to have a major, major increase in horsepower to get up over 190 mph no less approach 200 mph.

That is why it is so difficult for cars to go over 200. Look at past mag test of cars with 700-800 hp. Few get over the 200 mph barrier. It is very hard and expensive to accomplish.

Even the Ferrari Enzo just breaks 200 mph.

:z:
 

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I have driven a few Z06s to their top speed. A Z06 regardless of horsepower(600RWHP and less) will be limited to 174-176 if it still has the factory 6600 rev limit. The range i am giving you takes into account differnt weather conditions.
 
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