i need some enlightment... i found the gear ratios of the kits ive heard of and was wondering in laymans terms or at least speed vs rpm wise the difference between them and if yall feeling generous what it would be good for with a stock 4.10 rear, ie auto x, drag, etc.

thanks



gear 1st 2nd 3rd 4th 5th 6th

stock 3.483 2.015 1.391 1 0.806

os giken

3spd 2.714 1.742 1.267

5spd 2.578 1.772 1.289 1 0.821

quaife

SET 1 2.564 1.67 1.277 1 0.794

SET 2 2.35 1.55 1.24 1 0.881

dog/6spd 2.823 1.941 1.513 1.2 0.958 0.78



it lines up perfectly while editing...

 

I made an excel spreadsheet, but the forum wont let me upload it. PM me with your email address if you want it. You can change the transmission ratios, final drive, tire size, and shift rpm(across the top), and it will calculate speed in gear at any rpm, how much rpm drop there will be between shifts, etc. I have another one thats basically 2 of those on one page thats nice for comparing 2 different setups.

 

thank you very much

 

For drag racing you need the very high ratio first gear to launch the rig. The heavier the car the lower first gear. Revs come up to the red line quickly in first so the shift to 2nd will come right off the line. Then whatever spreads the HP curve can handle up through the gears. As the speed goes up, the ratios need to be closer together right up the the 4-5 shift, or 5-6 if you have that. Why? Because there is little aero drag at lower speeds. The 4-5 or 5-6 will be made with the highest aero drag, hundreds of pounds, trying to slow the car. There is no drive during the shift, and the car slows dramatically during the shift. Even with a dog ring box it is the case. If you are really good it may not be a huge amount but its there. So if you have the same RPM drop in the 5-6 shift as in the 1-2 shift the engine will reengage the drivline at an RPM below that in 2nd gear, and loose a ton of time getting back up on the cam (tune) or peak HP RPM.



The shift RPM is determined by the HP curve of the engine. You wind the engine in the lower gear until you can make the shift and the engine RPM after the shift is still in the Best power part of the curve. Or else the car falls flat on its face until the engine can pull it back into the best power part of the curve.



In road racing we start out with a first gear (1.94:1 or a 1.96:1 ) that is taller than your street 2nd gear. This is because we have a rolling start, plus we want more gears to use at different locations on the track. More gear choices is way better if you have a peaky engine. So, we use all 5 or 6 gears. The very tall first gear would be used in the slowest corners. The cars seldom slow below 40 MPH during the race.



Look at you data recording to see what the RPM drops are after your best shifts, and select the gear you are shifting into so as to maintain the engine in the power band (graph the dyno sheet and look at it as you select trans gears).



In any case, the two top gears must be very close together. The engine should peak a bit early on the straight. It is the first man to his top speed that wins the race. Seldom the man with the highest top speed.



Lynn E. Hanover

 

I should have mentioned that:



Top gear for racing transmissions should be straight through the trans (main shaft and tail shaft locked together) and not an overdrive as in the stock trans. In top gear there is the top speed of the unit. So all available HP should be spent doing top speed, and not heating gear box oil in a loaded gear interface.(as in the overdrive 5th of the stock box.



Any time the box is in other than straight through gear, (or reverse) it is using two gear interfaces to reduce tail shaft RPM below input shaft (engine) RPM, or as in a box with an overdrive top gear, to increase tail shaft RPM above input shaft (engine) RPM. In a constant mesh transmission, all of the gears (except straight through and reverse) are in mesh all of the time.



That's where the "Constant" in constant mesh, comes from.



For example, in a street box, 1st, 2nd, 3rd, and 5th use 2 gear inter faces (4 gears counting the input shaft to counter shaft gear set)) to perform their reductions or increases. Then 4th is not a gear at all but is just locking the input shaft (engine RPM) to the tail shaft (engine RPM) and the only reduction is the final drive. And 5th gear is a 4 gear 2 interface increasing set. So the tail shaft turns slightly faster than the input shaft.(engine RPM).



When an interface is loaded it makes heat from friction and that causes the gearbox case to get bigger and that lets some of the press fits get loose, and that makes things wear out more quickly than they should and in some cases break when they should not have, or would not have if you had a trans cooler to cool the trans oil. Road racing a stock trans is like throwing a yard dart into the air. It may not hurt anyone the first 10 times you do it, and then oops. Somebody is dead or badly injured.



So race cars have transmission coolers. Now there are folks who run endurance races with supposedly stock cars and seem to do fine. but those are IT cars or Showroom stock cars or similar, making very little HP. And those guys bring extra transmissions and drive shafts with them.



When I was young, I determined that 3rd, 4th and 5th were closer together than 2nd, 3rd, and 4th. So we ran a race with a really short final drive ratio (IN the 5s) (to account for 5th being an over drive). When we got home I discovered that the tail shaft housing was full of cracks, and the yoke bearing sleeve was outside of the tail housing on the yoke. Oil was all but gone from the box. We had turned the drive shaft over 10,000 RPM on each pass down the straight. We had no trans cooler.



Hint don't turn the drive shaft over 10,000 RPM at any time. Racing lubricants designed for synchromesh transmissions run much cooler than the street stuff. Use Redline lubricants where possible.



More about transmissions any time you like,



Lynn E. Hanover



Please sent me a copy of your spreadsheet.



lehanover@aol.com

 

theres a decent spreadsheet on paul yaw's website too



in NASA we've been doing standing starts here and there, exciting!

 

So let's say we're on a buget(aren't we all!!)and want to put together a roadracing trans for a light(1900to1950lbs)car(Fpprod-type Miata) producing moderate HP(200to225hp 12a) and have a bunch of stock transmissions to pull parts from.What might be a good combination?I have an early RX7 4sp and a few each of Miata and 1st gen RX7 5sp.Also in the pile is a B2000 pick-up trans I got for a possible shorter 5th gear ratio.I wasn't planning on running the 5.13 rear(people warned about winding out too much and using up the motor quickly)but rather something like the 4.89(not sure of the exact #--I forgot). Right now I just cannot justify the cost of a "real" race box unless I find a super deal on one.I also will give up some with penalty numbers (added to my hp to lbs ratio) in my NASA class if I do go dog box or sequential.



Dave D.