ok... ive read about starting speeds and cruise speeds but what about top speeds???
 

so.. this is my first post on this forum... im still in the stages of body work on my 69 camaro... but im trying to plan everything way ahead...

i read alot about people worried about the speeds and rpm of the 1st and 6th gear in t56 trannies.. but what i wanna know is what kinda speeds do you guys go in full out 5th and 6th gear??? and if you could include info on rpm, engine, and read end, tire size please...

I dont think that anyone goes full tilt in 5th or 6th. Most peoples setup would yeild 200 mph in 6th

Very few people if anybody has enough grunt to pull a T56 in top gear wide open. Most of the T56 cars wind out in 5th which is still an over driven gear and will easily bring the red needle to the end its travel on almost any speedometer. Ultimate top speed is determined by so many factors you could not even begin to determine what that would be in a general discussion. You need to know specific information with regards to exact tire sizes, trans gearing, axle gearing, engine HP at peak, what peak is, vehicle frontal area silhouette, etc…

ok first off i guess i was dreaming with a small block t56 combo that would do something like the "big red camaro"... which has a 540ci 800hp... to do 220mph

... ok so ... if you run which seems to be the avarage t56 set up being...
ls6/ls1 engine to t56 tranny... and gears something like 3.90 in the rear... i guess in the 1/4 you would only being shifting into 4th or maybe 5th gear?

... and for cruising 4th and 5th for getting up to speed and throw it into 6th once up to speed for cruising?

http://www.5speedtransmissions.com/calculators.html You can find what you want to know here.

thanx for the link... its also in my bookmarks...

im just kinda confused on a 400 or 500 hp car with a 6 speed... and since the most hp i have ever been behind the wheel of is 300 hp if i was lucky in my camaro before i took it apart... right now i drive a vw golf with 100hp 170ft lbs... and does about 130mph top speed in 5th gear and it feels like if i had a 6th it would still pull.

heres where the calculator wont help me i think... im not sure what ratios it takes to have the car still pull me to a high speed quickly... and all the local cars i see at the track use 4 speeds and automatics i think.. and are mostly just drag cars...

anyways i just about finished my body jig tonight.. so thinking gear ratios is not my thing tonight.. ill figure it out later... thanks

"Calculators" for top speed don’t work for one reason...none of them have the ability to compensate for the "wind wall" that all vehicles experience once they hit that magic mark around 150MPH. Getting a 300HP car to 150MPH is easy, the right gearing and almost any car can do that. Getting past that mark or anywhere even close to 200MPH requires huge amounts of aero work and massive HP to push past "the wall".

There are dozens of factory vehicles that are geared to do those insane top speeds; very few actually can hit the number though. I think there are only 3 vehicle produced domestically that even do 150MPH.

i guess thats why most of the funny cars are shaped like they are...

ok so i started reading about automotive aerodynamics, ground effects and downforce... and it sounds like thats getting way to complicated for my project... i think im just gonna go with the stock front and rear spoiler and lower it a little... and besides back to the point of the "big red camaro" i love this car... it does speeds around 220 mph with a stock looking body so it is possible to do in a camaro i guess. it just may not be easy

Let's use the benchmark 200MPH for an example. To run 200MPH will require somewhere north of 800HP for a 3500LB car. Look at Winston Cup cars. It is basically horsepower to weight ratio, although HP to weight to MPH is an inexact science, this is a very good ball park figure. You would need that kind of horsepower and torque to pull 200MPH speeds, assuming you can keep the car on the ground (not fly away) and cut through "the wall" Denny is talking about,

Here are some basic numbers for you.

Assuming a 6500RPM motor with sufficient HP / TQ - weight to pull the high gear, using a 26" tire, and manual transmission with no slippage..................................

With your referenced 3.90 gear and over drive with a .064 5th gear, she will run just tick north of 200MPH, on the dyno

You could also do it with a 2.56 gear and no overdrive and come up just a few MPH shy of 200MPH, on the dyno

Now weather she will do 200MPH driving, that is where all the aerodynamic crap comes in. And that math is probably far beyond anyone's capabilities here.

the Calculators that I posted were just for reference, I cant remember the exact numbers but once you reach 175 to go faster you have to increase your HP exponentially. unless you can decrease your drag. We have cars that run at Bonneville and we have learned first hand how important every little thing is. We even calculate how much drag the tires have since this is a open wheel car.

There are tons of things that matter, one more is that it will require more HP to drive anything once you get passed a 1:1 ratio.

James, since I do not come from a top speed enviroment, I always wondered if a overdrive and rear gear set up that equals a the final drive of a 1:1 drive ratio would pull the same. For example the final drive with a .064 overdrive on a 3.90 ratio would be equal to a 2.50 ratio 1:1 trans high gear. Would the overdrive 3.90 run the same as the 2.50 ratio 1:1? Would it take more horsepower to pull the overdrive 3.90?

"A car having a final drive of 2.98 and a direct 4th gear has the same overall ratio as a car with a .80 overdive 5th and 3.73 final drive. The car with the overdrive will use more horspower and generate more heat thru the transmission, then the direct drive box. However maybe the 3.73 rear may offer more low speed punch on turns."

took this from near the bottom of the page ----> http://www.5speeds.com/ratios.html

this is kinda a different answer than your looking for i think... but it sheds light in that area...

I guess I can understand the heat part pretty well, but it seems insignificant for a top speed blast. Actually, while it might be long term hard on parts, heat to some degree is good. For example you want heat in your gear boxes before you run you car be it at the dragstrip, roundy round, road coarse, etc. There is always a warm up period.

I really wonder about the extra horsepower to pull the overdrive. I am usually pretty good at figuring this stuff out, but this one has me stumped.

It would seem that if the final drive ratio is the same, then it is the same. I struggle to figure out where the horsepower absorption comes from in the overdrive situation, if the final ratio is the same. My assumption that is even if a rocket scientist does the equation, the net result is .07635 HP loss or something, LOL!

just a guess
 

I am thinking the overdrive would take more HP. Based on roatational energy and friction. Just for discussion. The drive shaft turns 2 times to get the wheels to turn one. 2 to 1 ratio. Lets say that it takes 4 rotation to turn the tires once, 4 to 1. Put an over drive on the 4 to 1 to make it a 2 to 1 and the drive shaft will need to spin 2 times faster or 8 times to equal the ratio along with the gears. More heat, friction, mechanical loss from the multiplication of the overdrive.

Just my guess.

NASCAR guys are running a 1:1 final drive.

You got it right and just for reference wind resistance cubes with each 1 mph increase. to put this in perspective it takes roughly 500 whp to get a 3rd or 4th gen camaro to hit 200 with out tkeing into account rolling resistance which squares with speed.

Close - wind resistance is a square function of velocity as in v^2. Rolling resistance is only a function of the normal force (with no exponents), which is just the force exerted vertically on the tires due to the mass of the vehicle. The only thing that might increase rolling resistance would be any sort of downforce a car might produce at speed. Otherwise, once a car is rolling and neglecting things like a tire's size change, the rolling resistance is the same at any speed.

As for a 'wall' at 150 mph - I wouldn't think of it as a wall necessarily, but I'd imagine that the forces get to be big enough that a car can take off and act like an airplane without the right aero work. There's really no need for any production vehicle to worry about these kinds of speeds unless you're talking Corvette, Camaro, Mustang, and few others. Joe Schmoe probably doesn't care, but lift forces big enough to counteract gravity = big lawsuit.

Ryan

At the same engine rpm,the OD trans would be spinning the ring & pinion(also driveshaft) alot faster = more friction & drag.

It takes approximately 450rwhp and the right gearing to push a C4 Corvette to 200mph. The aero characteristics become a little scary above 175,though.
My 90 ZR-1 with 420rwhp and a 3.45 rear cog would run 192mph in 5th gear (ZF6 trans). Doug Rippie was driving and I was in the passenger seat (with Simpson harnesses as tight as possible :lol: ).