looking for a thread

[scooter]

hey guys wheres the thread on the frankenstein trannys to get different gear ratios... it seems that the search tool is dead :p

 

cheers

[datzenmike]

http://community.ratsun.net/topic/72438-trying-to-confirm-some-info-on-280zx-transmission-ratios/

 

http://community.ratsun.net/topic/59611-mongrel-box-revisited/

 

http://community.ratsun.net/topic/49938-the-mongrel-gearbox-for-the-4x4-guyand-the-land-speed-record-guy/page-3

 

???

[scooter]

yes these are what i was looking for mike,

 

but these are mainly b series trans...  I'm running a D21 71C and what i'd like to have is a taller first gear and maybe have a closer 3rd like ericjb's thread was about. 

also When driving normally, the trans is just fine, But when I run it at max effort at the drag strip I get grinding between gears, So I'm going to take it apart and check the synchros as I didn't do this when I put the L bell on it and it was just a trans from pick a part anyway. my 5th is pretty close to 4th, I don't think I can get closer, but a 10-15% taller first would be sweet.

 

The car ran a 8.54 at 80mph 1/8th mile with shitty heavy grinding first second third. I think I could get damn close to 8.00 if I could get it to bangshift properly. it 60 foots like a boss.. I bet theres nearly a second lost from shitty shifts.

 

im also pulling the ford 8.8 diff out and putting in a ford 7.5. The reason for doing this is the ford 7.5 is 50 pounds lighter and they are common with 4.10's around here. I'm using a 28 spline ford 8.8 so any added strength is in the carrier itself. right now I have 3.73's and I see benefit in going to 4.10's as I'm barely in 3rd gear at the end of the 1/8th mile. But, this will make first gear really short.

 

but with the car being soo light and only a 4 cylinder although I do have nitrous and slicks on it.  

 

 

Another option is to go even lower and launch the car in 2nd gear... hmmm

[datzenmike]

You want first to be as high a gear as the tires can handle. Ideally you want to use all gears and be near redline at the finish line. Using only two gears is the fault of the 3.73 differential. Try the 4.11s first. This will affect all gears and make them seem much closer together. That 2 to 3 gap will still be there but you will be through it much faster with a 4.11. If strictly racing or auto-X, a 4.375 or 4.625 could be used. For the street start off in second.

[scooter]

using a gear ratio calculator, with 4.56's would put me at 85 mph with the slicks on at 7000rpm in 3rd gear (24.5 inch tall slicks)  , which would be pretty close to revved out in 3rd gear.. which would be good for 1/8th mile drag racing.

 

If I could get rid of one shift the car would go much faster, less time spent shifting.  But if I started in second it may be too tall, as it would be about 25% taller than first gear with the 3.73's.

 

I'm not sure if the car would pull it, right now its not spinning, launching around 5000rpm with nitrous activating on WOT. But on the other hand first gear is really short, I'm shifting within a hundred feet.. ish.

 

Going down to 22.5" slicks, this starts looking better for launching in 2nd gear, but starts getting strung out with the speed coming out at 84mph at 7500 in 3rd. 

this probably wont work as I'm already at 80mph going through the speed trap. dropping gear is going to make it pick up.. and this was also on the 75 shot, not the 100 as the motor started popping in higher gears with the 100 shot.. which may get better with dropping gear... and some help from nitrous experts.  ​which means theres more left in it... bwahahaha

 

maybe i'll just have to try it, launch it at 7000 and slip the clutch a little and prey I don't strip gear teeth.

 

The goal to all this is to run an 8.00 1/8th mile or better. I don't think theres an all steel bodied full interior 4 cyl L series Datsun that's coming close to this. if there is, I wanna see it.

 

this ratio is looking better on paper, but i'd probably have to change to the car OD if I want to do some cruising. going to 4.56 and using a s13 KA 5th gear raises my 100kph rpm by 300 (3300rpm) vs 3700 in 5th with its current gear and 4.56's (22.6 inch tall toyo's).  right now I'm right around 3000 at 100k.

[datzenmike]

Start with improving your shifts. They shouldn't grind. What gear oil you using? Try the Delco (friction modified) Synchromesh Transmission Oil from GM. I have a well used 71B and now I can downshift where before it would fight me and often grind... to the point I shopped bothering with it. Up shifts are faster and with less effort. WAY better when the oil is cold too.

 

If the torque curve is very peaky then you need to use gears that are closer together. The shift RPMs should drop you right into near maximum toque in the next gear