LSD ratios help
Discussion
I have turbocharged my 2000 1.8s and fitted a 6 speed box. Problem is that the 6 speed is close ratio but the top gear is no higher than the 5 speed so I'm still really revving on a 70MPH motorway run. Does anyone have any definitive information on which UK model had the highest possible diff ratio (but still limited slip). I have the car tuned up lovely and it will boost and pull hard from 1500 RPM so I get an average of 34MPG despite a huge amount of power on tap but I reckon with the right diff I could do a lot better and probably pay for the diff in fuel costs within a few months.
34mpg sounds very good - most standard cars are thought to be around 30mpg give or take a bit.
I might be completely wrong here, just learning this stuff myself from reading around, however this is from what I understand. Others will be able to comment if I'm completely off! You can go to 3.636 with a 6 speed. However you'd need to get the parts - you can get them new, or use some parts from an old Mazda 626. This might only be applicable to the Mazdaspeed version though - you'd need to check for details.
From what I've read in regards to changing to the 3.636 then it should be around 12% increase in efficiency in theory, but likely to be less in the real world. So unless you do the work yourself then there's not much point in doing it to save money on petrol by increasing fuel efficiency. Obviously you'd want the car to be a long-termer too. Some like to do it when you're having over 220hp approximately as you go through the gears too quickly and so can want the higher ratio, plus it decreases noise a bit on the motorway.
I might be completely wrong here, just learning this stuff myself from reading around, however this is from what I understand. Others will be able to comment if I'm completely off! You can go to 3.636 with a 6 speed. However you'd need to get the parts - you can get them new, or use some parts from an old Mazda 626. This might only be applicable to the Mazdaspeed version though - you'd need to check for details.
From what I've read in regards to changing to the 3.636 then it should be around 12% increase in efficiency in theory, but likely to be less in the real world. So unless you do the work yourself then there's not much point in doing it to save money on petrol by increasing fuel efficiency. Obviously you'd want the car to be a long-termer too. Some like to do it when you're having over 220hp approximately as you go through the gears too quickly and so can want the higher ratio, plus it decreases noise a bit on the motorway.
At the moment with the 6 peed and the current diff it's a stump puller which will do 1-2-3-4-5-6 by 30MPH and then happily pull up a steep hill without a down change. Pretty sure the diff change will help both MPG and my sanity. The 3.63 ration looks like a winner but it looks like they were only sold in Australia so finding one could be a problem.
I did come across this earlier today:
http://miataroadster.com/mazda/mazda_ring_pinion_s...
Trying to work out best diff for me to get at the moment, and have also been looking at ratios to go with it. Think I might have to go torsen since I might be buying a apartment soon (really nice one popped up), so with the other work I want done then will have to prioritise!
http://miataroadster.com/mazda/mazda_ring_pinion_s...
Trying to work out best diff for me to get at the moment, and have also been looking at ratios to go with it. Think I might have to go torsen since I might be buying a apartment soon (really nice one popped up), so with the other work I want done then will have to prioritise!
You will have a lot more torque than stock and it's a fairly light car so it should pull well, even in 6th. Mine has the 6-speed and standard 2001 Mk2.5 Torsen (I can't remember the ratio) so is geared for 80mph at around 3500. With the SC giving 240bhp and 200lb/ft it still pulls strongly in 6th from any speed.
Yes mine seems to be about those ratios, 22mph/1000rpm. Nice and nippy around town but with the rather loud 3" exhaust it's not too pleasant on the motorway. It boosts from around 1500rpm so at the moment I can drop into 6th at 30ish and still have good torque but I would happily lose that ability for a longer over all ratio. My run to work is 15 miles of straight national limit with not much traffic so a taller 6th might save me some wonga.
That link to the US site is handy. I'm over there next month so I might bring a crown wheel and pinion back with me.
That link to the US site is handy. I'm over there next month so I might bring a crown wheel and pinion back with me.
As a general principle you need to be trying to find around 27-29mph/1000 rpm in top gear with something like an MX5. Would be interesting to examine whether the diff mountings could be modified to take another range of casings, which would also open up an opportunity to get a proper plate differential into the car, as torsen type diffs don't give anything like the benefit of a plate diff in a rear drive car, especially in a track car. I would be up for the experiment.
How do you mean plate differential? A clutch one? If so there are already drop in possibilities. From my limited understanding you have viscous, torsen and clutch type differentials for the MX-5.
Viscous - not as good as the torsen.
Torsen - good apart from when one wheel has no grip, needs less work to look after it than a clutch diff. When too much power then will become more like an open diff.
Clutch - can be more noisy, need to change oil more often, can cause more wheel hop. However can handle higher power, doesn't have problem of losing power when one wheel has 0 grip. So better in snow/ hitting bumps or kerbs on track etc.
I know there is a TorsenII(R) (think that was the name) that is similar to a normal Torsen, but can sometimes be pre-loaded so that you avoid the problem of 0 grip x Z = 0. But I don't think you can get this for the MX-5.
A really stupid question, but trying to learn! In regards to the gear ratio (for examples parts in link above), are they in the differential or connected to it?
Viscous - not as good as the torsen.
Torsen - good apart from when one wheel has no grip, needs less work to look after it than a clutch diff. When too much power then will become more like an open diff.
Clutch - can be more noisy, need to change oil more often, can cause more wheel hop. However can handle higher power, doesn't have problem of losing power when one wheel has 0 grip. So better in snow/ hitting bumps or kerbs on track etc.
I know there is a TorsenII(R) (think that was the name) that is similar to a normal Torsen, but can sometimes be pre-loaded so that you avoid the problem of 0 grip x Z = 0. But I don't think you can get this for the MX-5.
A really stupid question, but trying to learn! In regards to the gear ratio (for examples parts in link above), are they in the differential or connected to it?
in answer to your question, the final drive gears consist of a crownwheel - bolted to the diff unit, whatever type it might be, and the pinion, which lives in the nose of the casing and is driven by the prop.
Torque biasing diffs generally act quite successfully as a traction aid, avoiding hopelessly spinning one wheel, as long as the other wheel is firmly on the ground. They are also relatively placid, safe things that do not bite an unwary owner.
What a plate (clutch) type diff gets you, depending on how it is set up, is actual power transmission to both wheels under power, and if you hit a kerb hard on track, the inside wheel will not spin the power away,that the outside wheel could be accelerating away from the apex with! Properly set up a plate diff will also be a steering aid, as it can lock up on lift-off, allowing tail-out antics on the way IN to a corner having braked later, when a torque biasing diff would just stay open and be useless.
Then there is the whole business of dialling in crownwheel and pinion ratio to gear ratios to engine power spread....
Torque biasing diffs generally act quite successfully as a traction aid, avoiding hopelessly spinning one wheel, as long as the other wheel is firmly on the ground. They are also relatively placid, safe things that do not bite an unwary owner.
What a plate (clutch) type diff gets you, depending on how it is set up, is actual power transmission to both wheels under power, and if you hit a kerb hard on track, the inside wheel will not spin the power away,that the outside wheel could be accelerating away from the apex with! Properly set up a plate diff will also be a steering aid, as it can lock up on lift-off, allowing tail-out antics on the way IN to a corner having braked later, when a torque biasing diff would just stay open and be useless.
Then there is the whole business of dialling in crownwheel and pinion ratio to gear ratios to engine power spread....
Thanks, that's what I thought in regards to the crown wheel and pinion, but wasn't sure.
In regards to plate diffs then there are a number available for the MX-5 normal 1.8 diff already. I was asking about a particular one the other day. From the ones I know of:
Kaaz
Cusco
OS Giken
I believe the Tochigi-Fuji is too (came after Torsen II on cars from Mazda).
The Tochigi-Fuji has had some issues though in regards to reliability. The OS Giken is supposed to be amazing but is pricy (I'm looking at getting one). Currently trying to weigh up costs versus benefit. Will be road use but potentially snow 6 months of the year. So not losing all power when one wheel has no grip would be nice. But less friendly potentially, more expensive to buy and run, and won't need the extra benefits of not losing power over bumps... Hopefully car will be up to around 220hp so also could be good to have a stronger LSD.
What is meant by being 1 or 2 way (or potentially 1.5) in regards to the clutch LSDs, and what are the benefits/ downsides of either?
In regards to plate diffs then there are a number available for the MX-5 normal 1.8 diff already. I was asking about a particular one the other day. From the ones I know of:
Kaaz
Cusco
OS Giken
I believe the Tochigi-Fuji is too (came after Torsen II on cars from Mazda).
The Tochigi-Fuji has had some issues though in regards to reliability. The OS Giken is supposed to be amazing but is pricy (I'm looking at getting one). Currently trying to weigh up costs versus benefit. Will be road use but potentially snow 6 months of the year. So not losing all power when one wheel has no grip would be nice. But less friendly potentially, more expensive to buy and run, and won't need the extra benefits of not losing power over bumps... Hopefully car will be up to around 220hp so also could be good to have a stronger LSD.
What is meant by being 1 or 2 way (or potentially 1.5) in regards to the clutch LSDs, and what are the benefits/ downsides of either?
Edited by NRS on Tuesday 23 July 15:33
If i was given the task of fitting a plate diff in an MX5 I have a particular UK manufactured unit in mind, i've been using them for ten years now in both front and rear drive cars driven to events and subjected to everything from track days and hillclimbs to endurance races round Spa. i have found them to be totally reliable, and can be set up to a client's specific requirements.
Gassing Station | Mazda MX5/Roadster/Miata | Top of Page | What's New | My Stuff