LSD or not?

[anthonym]

Both my sevens and my previous car have had LImited Slip Differentials. MY present LSD is 3.62:1 and I am being offered a 4:1 NON LSD diff.

 

I have 15" wheels on, but usually run 13" wheels.

 

I am wondering what to expect as regards increased acceleration and would like to hear experienced about this.

 

And more importantly, will I miss the LSD? I do not know what it is like to not have one.

 

I am being offered this for 600 pounds is that fair?

 

Apparently a 4:1 is unusual in some way for my car, which is a dedion BDR. Why might this be so?

 

I am looking at this as a way to shorten the gap between second and first. I have a long first BGH type 9 box.

 

Would like to hear informed opinions please?

 

THanks for your attention.

 

Anthony

[The Pikey]

600 quid is a lot of money for a diff even if it is a rare (but not super sought after) 4.1 ratio. Personally I would find a 3.92 diff and stick your LSD in it. Then sell the 3.62 as a open diff. I have a Duratec-BGH and a 3.92. It's geared at about 160mph at the rev limiter in 5th. Perfect for me

 

I bought a 3.92 for 60 quid and a 3.62 for 50 quid only an hour ago on EBay so they are not difficult to find.

 

Jason

[paul richards]

I am looking at this as a way to shorten the gap between second and first."

 

Changing diff ratio won't change that.

[The Pikey]

Quoting Paul Richards: 

I am looking at this as a way to shorten the gap between second and first."

 

Changing diff ratio won't change that.

 

 

I think it will.

 

here

 

J

[Shad]

 

 

Edited by - Shad on 23 Jun 2012 22:02:27

[rj]

No it won't change the gap. It will move the shift-point in MPH, but not the drop in revs from 1st to 2nd if you change at max RPM.

 

LSD any time if you have anything more than 150BHP.

 

 

[anthonym]

I did not realise that the limited slip mechanics can be separated and fitted to another diff.

 

60 quid is a mere fraction of the price.

[rj]

Anthony

 

Have a look at Angus' page here

[paul richards]

Quoting Jason Fletcher: 

Quoting Paul Richards: 

I am looking at this as a way to shorten the gap between second and first."

 

Changing diff ratio won't change that.

 

 

I think it will.

 

here

 

J

 

Jason

Not sure how you think it will change the gap.

Changing the diff will simply lower the overall gearing in every gear. The ratios for 1st and 2nd will not be changed. The maximum speed in each gear will reduce and therefore in MPH terms there will be less gap.

However, when reducing the gap between gears you are looking to drop into the power band when changing up and this will not change as engine revs will remain the same.

Hope this explains. 😬

[The Pikey]

Paul

 

I'm still struggling with the one 😬 Although I undertand that fitting a different diff is not going to change the cogs of the gearbox I am still thinking that if Anthony ups his diff ratio than he will have a shorter gap between the changes which is I think what he's looking for.

 

I have used that link to work the two out, what do you think?

 

Differential Ratio: 3.92

1st Gear Ratio: 2.74

2nd Gear Ratio: 1.81

 

1st Gear = 77.93 km/h

2nd Gear = 117.97 km/h

 

40.04 kmph difference

 

........................................

 

Differential Ratio: 3.62

1st Gear Ratio: 2.74

2nd Gear Ratio: 1.81

 

1st Gear = 84.39 km/h

2nd Gear = 127.75 km/h

 

43.36 kmph difference

 

Jason

 

 

[paul richards]

Jason

As I said and you have demonstrated there is a MPH difference. However the point of reducing the gap between gears is to do with engine revs to make the most of the power band.

For example.

Lets say your power band (where the car pulls well) is between 3000 and 5000 rpm.

You accelerate in first gear to 5000 and change into second gear and your revs drop to 2500. You are now out of the power band and car will not pull very well and your acceleration will be slowed. It does not matter what your maximum speed in each gear is.

 

In this example, what you are looking to do is bring the 2 gears closer together so that when you change gear at 5000 your revs do not drop below 3000.

 

Imagine driving you car in first and then changing into third instead of second. It's just the same if the gap between first and second gears is too much.

I'm finding this difficult to explain in writing. Hope this helps. 😬

 

[Silver Machine]

I think it is explained very clearly.

[maxdog]

"Jason

As I said and you have demonstrated there is a MPH difference. However the point of reducing the gap between gears is to do with engine revs to make the most of the power band.

For example.

Lets say your power band (where the car pulls well) is between 3000 and 5000 rpm.

You accelerate in first gear to 5000 and change into second gear and your revs drop to 2500. You are now out of the power band and car will not pull very well and your acceleration will be slowed. It does not matter what your maximum speed in each gear is.

 

In this example, what you are looking to do is bring the 2 gears closer together so that when you change gear at 5000 your revs do not drop below 3000.

 

Imagine driving you car in first and then changing into third instead of second. It's just the same if the gap between first and second gears is too much.

I'm finding this difficult to explain in writing. Hope this helps. 😬"

 

This

 

have an .xls if you want it, shows the shift points in RPM nicely PM and I'll send it over :)

 

If you want to change the enormous gap between 1st and 2nd you have three basic options;

 

1 buy a Quaife box or similar with custom ratios

2 buy a 6 speed

3 fit the SPC first gear mod - I have this and must say it transformed my 98 road sport (there are now three ratios available)

 

Edited because I missed the bit where you state long 1st already fitted - what ratio is it?

 

Edited by - maxdog on 25 Jun 2012 10:45:11

[LesG]

Anthony, the easiest and cheapest thing to do is buy a secondhand 3.92 open diff, then swap your crownwheel and pinion sets over. I did just that on my car and it works very well.

 

If you then find it hasn't worked for you, you can always swap back, and sell your unwanted diff.

[Dignity]

Quoting RJ: 

 

LSD any time if you have anything more than 150BHP.

 

 

My car drives fine without an LSD.

It was fastest 0-60 at this years Dunsfold handling day (morning session).

 

It's a great option but by no means essential IMO

 

[anthonym]

3.92 at 50 quid seems better than 4:1 at 600 quid, to put it mildly, and if I can transfer my limited skip bits that's perfect.

 

Anyone want to swop a 3.62 for a 3.92 ?

 

I want to do this regardless of the gear gap issue to get more poke (acceleration).

 

I believe based on an expectation from Brian of BGH who built the box it will be 2.83 for first in

 

 

It has become apparent there may be nothing wrong with the ratios and instead the clutch has been "dragging".

Reverse selects ok so I am hoping the syncro is not goosed.

I have adjusted the clutch but unable yet to test due to rodent eviction requiring refurb, in progress.

 

 

 

 

Edited by - anthonym on 25 Jun 2012 23:48:13

[jonboylaw]

LSD was the best upgrade I made to mine, great fun now getting the back end out ;)

[Garth]

Trying to find BGH and SPC contact details - is it BGH Geartech in Kent? Ditto for SPC - is it SP Components Ltd in Redditch?

 

Opps posted in wrong thread!!

 

Edited by - Garth on 10 Aug 2012 20:38:16

[anthonym]

the answers are both yes.

[A_redstone]

Hello

 

I am thinking of adding an LSD to my car , never had one before, read lots of comments about how beneficial it is etc

 

It will be a 140 Supersport....Caterham want £998 +VAT for it

 

Question is : Will this benefit me and how , baring in mind its for road use mainly.

 

I enjoy the drive and handling in my car, so dont want to "spoil" it !!

 

Advice very much appreciated

 

Thanks

 

Andy

[jingars]

Andy,

 

I am in a similar position to you. Had my 1.8K for five years and this week have ordered a Titan LSD from Phil Stewart at Road and Race Transmissions.

 

It is not the most cost effective way of doing things, but in I have ordered the Titan LSD in a complete replacement casing and am dropping my final drive from 3.92 to 3.62. The car is 17 years old and started off life as a 1.4 with a six speed box. It is now a 1.8 K with a six speed box, so is a bit buzzy on the motorway. Phil does think that a change of final drive ratio will better suit the car in 1.8 guise.

 

So whilst you are considering changing oily bits at the back of the car, have a think about your final drive ratio as well - as per the earlier postings on this thread.

 

I would suggest speaking to Phil at Road and Race. He spent 25 minutes on the phone with a technical numpty like me; it is clear that he wants to ensure the potential customer understands the ramifications of what they are buying.

 

I can't answer how the addition of a LSD will change the handling of your car as I don't know myself - but I am aching to find out; I do not yet have a delivery date and it is just killing me. I am like a kiddy on the run up to Christmas

[Bob_r]

In simple terms, if when cornering you lift the inner rear wheel off the ground, a common occurence when racing, with a standard diff you will lose drive to both rear wheels, you will sense this mostly by a brief rise in engine revs. In a highly tuned engine this might cause it to be buzzed (valves hitting pistons). Under the same conditions the LSD will maintain drive to the outer rear wheel and improve stability and corner exit speed.

An LSD is essential if you want to go drifting.

 

 

 

 

[paul jacobs]

May I also add an addendum Bob? As well as transmitting drive to the more heavily laden wheel, to much throttle could also cause it to lose grip, which could easily catch out a novice. It could also increase understeer if set up to tightly.

 

Another scenario where an LSD will shine, is on hills with hairpin bends, whether road or hillclimb 😬

 

Paul.

[A_redstone]

Well this sounds exciting

 

It would be the caterham version that goes into all their production models right now....

 

Possible the combination of LSD and supersport could transform the car for £3500 ?

 

Thanks

 

A

[Bob_r]

Thanks for your comments Paul, it seemed to me that some of the comments above were over complicating the subject at the level of information requested.

To comment on the diff ratio question, a 4.1 ratio will raise the engine revs for any given road speed, possibly reducing the potential top speed of the Car. There will be no detectable change in any other characteristics of the vehicle. The only time that I have used a 4.1 ratio was when racing on Oval Circuit's where it was desirable to pull as many revs as possible, because oncemoving, gear changes were not required. After all, the Ford 4.1 diff was typically used in Anglia Vans. The most desirable diff for Race Cars at the same time was a 3.7 if my memory is correct.