4 replies to this topic

[Gilly112]

Hi guys, I'm wondering if you could help..

 

The whole business off fd ratios, diff ratios and gearbox ratios is confusing me.

 

Basically, I'd like my mini to cruise at 75/80 without deafening me too much, but be able to hit as close to 100 as possible, but not spoil the fun of acceleration.. 

 

Been reading up about final drive ratios and I've found the 3.1:1 ratio quite common and it sounds appealing. Given that I'm aiming for a powerful and 'torquey' engine anyway, what would be the best set of ratios for me, with 10 inch wheels?

In addition, I'd like to keep to an overbore to 1293, but would an overbore to 1380 help in terms of torque or top end as I've heard bad things about reliability and the fact that it restricts revs.

 

I've also found a link to the sort of setup I would ideally have..

 

 

Any response will be much appreciated 

[Ethel]

If that's your ideal it says he's running a 3.44, but you're better than me if you can get a decent impression via a wide angle internet did. Guess works site has a nice ratio calculator you can play around with to see where you power band will sit with various ratios. You can go for a drive to get an idea of the noise at your likely cruising rpm, find an incline, or accelerate steadily, to create the extra engine load of higher speed. A 1380 will do more for torque, breathing will be more the limiting factor as the revs go up. Getting 100mph performance would be easier with the 3.44, but in reality a 3.1 or 3.2 is likely to be easier to live with if you're going to be spending a lot of time on the motorway.

[Gilly112]

Thank you for the response!

 

So if I indeed went for the 3.2, but had a more powerful engine, would this eliminate the loss of acceleration that would be experienced through the change in final drive ratios? Then with the addition of a straight cut drop for example, I could enhance the final drive and keep more of the power?

[Ethel]

Don't think you want straight cut drops if you're looking to reduce noise!

 

Power is torque x rpm. Gears can be thought of as torque multipliers as they change the rpm relative to road speed. A higher ratio is always going to give more torque and better acceleration - unless it puts you a good way outside the engine's powerband.

 

Figure out where your engine is going to produce its power & have a play with Guesswork's gear planner. It's nice if you're sat in the middle of the powerband at your typical road speed in 4th, but you may find a taller final drive can make good use of 3rd gear.

[Gilly112]

This is very true! Thinking about it, I can put up with the noise on a very occasional long trip if it meant having fun on the small roads and in town where I live every day!

Thank you, that's some really good info actually, and the website is great! I've looked at the 3.2 and think it's the best way to go, 3.1 would be slightly too long. I'm aiming for 100/110 hp, do you know how much a standard gearbox can take? Are the straight cut drop gears relevant or would I need a full box? Sorry for the questions but there are so many different opinions on all of these topics! Really appreciate the help!