WHAT WOUOLD BE TE DIFFERENCE IF I USE A 4.1 AND A 3.7 RATIO.... WHAT WILL BE BETTER FOR QUARTER MILE PURPOSES... ALSO WHAY AXLES SHOULD I USE

having a 4.1 ratio diff will give u a better acceleration but you will have a small decrease in the top speed on the 3.7

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why are you yelling we are not deff

the best way to find out what ratio you need is by starting with what you got and if your going to race it at the track when your at the finish line you see what rpm your at and you go from there becuase every car is different if your rpm is down you need to go up in ratios if you are reving to high go down in gears thats the best way ... you want to be at your max rpm at the finish line

right now i have the stock differential and the stock axles of the b110 datsun1200 coupe... i bought a 210 dif and axels... should i test the car with the stock or should i swap the parts? since it is in the workshop still, i have time to change those parts.. whay would you say billyberch

if you want change them as standard are not strong but if you have raced it already you should roughly know what rpm you were at if you havnt just change it you have nothing to lose ...THE BEST WAY TO FIND OUT EXACTLY WHAS YOUR CAR S DOING IS DO WHAT I DO AND ALOT OF OTHER PEOPLE DO IS HAVE A CAM CORDER IN CAR SO IT LOOKS AT YOUR DASH

i havent race it yet thats why i think i must change the stock dif now that is at the workshop... or should i use the stock b110 datsun 1200 coupe dif???

you might aswell change it than it will better than standard

hello datto love!! I must say I do like your set up thats done well. im doing one so much like that set up with a a12 but no turbo. it looks good clean. I will try sending photos when Im done.

with turbo cars - it's not so much the risk of wheelspin that makes higher gears (like 3.7s) work better than lower gears (like 4.11s) - it's because of spoolup time. If you launch hard with a low geared diff (like 4.11s or 4.88 or something) you'll actually hit the redline in first gear, before the turbo has spooled up fully and got full boost. Then you have to jump off the throttle and back on when you shift into 2nd, and it only really gets full boost by the time it is half way through 2nd gear. So if you run higher gearing (3.7 or 3.5:1 if you can find it) you actually get to build up some boost in first gear and make use of it before you have to shift to second.

Normally for drag racing the 'best' diff ratio is the simple to work out. Find out what rpms the motor makes the highest hp at. then add 5% to those rpms. So lets say the motor makes 120bhp at 6000rpm. 5% of 6000 is 300 - so 6000 plus those 5% is 6300rpm. Basically you then choose a diff ratio that has the car going through the finish line/traps area at peak hp plus 5% rpms - or in this case 6300rpm. Obviously you might have to go with 6100 or 6400 depending on what ratios you can find, but that is the well proven ratio to aim for.


This works for everthing except turbo setups, for the reason above. They tend to go faster with higher gearing, because they can then use 1st gear.

There is of course other ways to handle that situation. You could select a gearbox that had a different first gear ratio, so that it wouldn't run out of rpm in 1st so quickly (so if there was a close ratio gearset, that would be the choice over the standard gearset in the gearbox). The other option is to go to an auto, where you can build boost off the line with a loose enough convertor, and you don't have to lift off the accelerator to change gears.

This sort of thing (the spoolup issue and having to upshift before getting full boost) occurs on some drag cars, and but it can be even worse on a circuit racer - as they have to spool the turbo back up after each corner. That is where each gear ratio becomes very important so they can exit the corner with the engine rpms just high enough to produce boost without too much delay, but not too low so they can hang on to that gear and really accelerate out of the corner and down the straight without losing too much time/spool with too many upshifts.

Once you get to the stage of mega power outputs and an auto, you end up having too much torque/power to get good grip at the start. In those situations, some guys have run quicker by starting the auto in 2nd (though these are usually big hp v8s). Which is why some drag cars run just as fast, and more consistently, with a 2 speed powerglide and a slightly looser torque convertor than they do with a 3 speed auto and a tighter (or the same) torque convertor.

I absolutely love manual gearboxes, especially for a street car - more balance and control of the car is possible through hard corners, but for drag racing only - there's some really good benefits available by going to an automatic transmission. Yes they do rob a little bit of power compared to a manual, but with enough boost, that isn't usually a problem, and being able to launch with decent boost, and not have to lift off for the gear shifts - it really adds up.