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lsd or not?
dilley - 7/10/06 at 11:38 AM

Ive just picked up my new diff its a 3.14 non lsd, I am currently running a 3.62 lsd,

Will I really notice a difference if I dont fit the lsd into the 3.14?

also....Im getting 122mph on the 3.62, what can I expect with the 3.14??

Thanks Andrew

[Edited on 7/10/06 by dilley]

graememk - 7/10/06 at 11:46 AM

because i'm an amimal i'd keep the 3.62 lsd

[Edited on 7/10/06 by graememk]

Peter M - 7/10/06 at 11:49 AM

gear/diff speed calculator

JoelP - 7/10/06 at 11:52 AM

3.14 will be good for 140 assuming you have bhp to match. Id run it open whilst saving for a quaiffe lsd, then decide when funds allow.

dilley - 7/10/06 at 11:53 AM

The 3.62 is no good for the engine, the gears are so short you cant take your hand off the stick.

dilley - 7/10/06 at 11:54 AM

whats the difference between the quafe and sierra lsd?

mookaloid - 7/10/06 at 12:04 PM

quote:
Originally posted by dilley
whats the difference between the quafe and sierra lsd?


The Quaife is a geared Diff - quite clever apparently.

The Sierra one is a viscous coupling which only works when the special viscous liquid heats up when a wheel spins - not really designed for performance cars - more for getting your 4x4 out of geting stuck in the mud.

Neither is a 'proper' plated LSD but the quaife is better than the standard sierra one.

There was a debate on here not so long ago about the benefits or otherwise of the LSD in these cars. The open diff was I think considered easier to drive with than the LSD which can catch the unwary driver out more easily.

Cheers

Mark

smart51 - 7/10/06 at 12:58 PM

I have a 3.62 LSD on my R1 engined car and find it to be just great. It has not caught me out at all and on the rare occasions when the read does step out, it is very slow and easily catchable.

A 3.14 diff will make all your gears 15% taller. You will get 15% less acceleration of the line but will have 15% more top speed in each gear. Your motorway revs will be 15% lower too.

As for the LSD, you are more likely to spin one rear wheel but less likley to spin both.

JoelP - 7/10/06 at 04:05 PM

i think with this many horses, the 15% less acceleration doesnt really apply as grip will be the limiting factor for the first few gears at least, i can only imagine how fast a turbo'd bec must get through the gears.

Wadders was saying that, from drag strip testing with different diffs, there is no apparent loss of acceleration caused by longer gears. Perhaps it is just offset by the fewer gearchanges and again the limiting grip.

wheezy - 7/10/06 at 04:30 PM

Iam looking for a 3.62 LSD at the moment so if you decide to change and are looking to sell just drop me a U2U.

Dave

smart51 - 7/10/06 at 04:42 PM

quote:
Originally posted by JoelP
i think with this many horses, the 15% less acceleration doesnt really apply as grip will be the limiting factor

from drag strip testing with different diffs, there is no apparent loss of acceleration caused by longer gears. Perhaps it is just offset by the fewer gearchanges and again the limiting grip.


My R1 engined BEC has no problems with traction on a dry road in any gear so a 3.14 diff would give 15% less acceleration in each gear.

The "in each gear" bit is important. 0-120 times would be the same in either case. Yes, you have less acceleration in each gear but can stay in that higher acceleration gear for longer. overall, you're the same.

In a standing start drag race, the 3.62 car would take the lead upto 50 MPH, then it would change into 2nd. The 3.14 car would still be in 1st and would catch up and slightly overtake, then it too would have to shift into 2nd. The 3.62 diff now has the advantage and will overtake, but then has to shift into 3rd. The 3.14, still in 2nd would pull back and overtake again, and so on.

JoelP - 7/10/06 at 05:27 PM

when people take about acceleration, in my books they are refering to how fast it gets to a certain speed, so to me, the acceleration that i am talking about remains unchanged if it takes the same time to get from 0-120.

What exactly do you mean by 'acceleration in gear'?

dilley - 7/10/06 at 06:18 PM

Ive changed the diff now, will my speedo be out? its runs off the engine.

JoelP - 7/10/06 at 06:46 PM

yes.

dilley - 7/10/06 at 06:55 PM

My speedo is reading the same as before I changed the diff is this correct?

MikeRJ - 7/10/06 at 09:26 PM

quote:
Originally posted by dilley
whats the difference between the quafe and sierra lsd?


The Sierra diff is a viscous unit which is sensitive to speed differences between the two wheels, i.e. the greater the speed difference, the more torque it applies to the slower wheel. Not the most effective type of diff as one wheel has to start spinning before it does anything.

The Quaife ATB (Automatic Torque Basing) is, as the name suggests, sensitive to the torque difference between the wheel. If the torque in one wheel is reduced, the diff biases the torque split to favor the other wheel. It's a very clever system, with one drawback: it uses the torque in the output shafts to operate the internal mechanism, so if one wheel is slipping enough to have negligible torque being transfered through it (e.g. wheel in air), the diff fails to do it's job. Generaly used more on FWD cars as it provides very smooth operation, so you don't get the car pulling violently as the standard plate type LSD's tend to do.

smart51 - 8/10/06 at 09:20 AM

quote:
Originally posted by JoelP
What exactly do you mean by 'acceleration in gear'?


Acceleration in one gear not through the gears. Usual figures are 30 - 50 in 3rd, 40 - 60 in 4th and 50-70 in 5th.

If two otherwise identical cars have a drag race, the car with a 3.62 diff will be faster off the line than one with a 3.14 diff. Acceleration in 1st gear will be 15% faster.

If the same two otherwise identical cars take a certain corner in 2nd gear say, and they accelerate at full throttle, the one with the lower gearing will accelerate faster than the one with the taller gearing.

A car with a 3.62 diff will overtake faster on an A road if it drops from 6th into 4th than one with a 3.14 diff that also drops to 4th to overtake.

dilley - 8/10/06 at 10:29 AM

Just taken the car out, the 3.14 diff really suits it, I think it makes better use of the power, and pulls all the way to redline in top, the speedo is out, and I didnt realise to start with but 120mph did feel bloody fast as for not fitting the lsd into it....Im glad I didn't, it makes it less lively on the rear end and actually helps with grip, it will spin 1 wheel occasionaly but still maintains a straight line where as before it would spit you across the road, I think Ill leave it as it is.

As for the difference in acceleration when changing diffs, I dont think this applies to bec's as much as cec's as you have a much faster gear change as long as you dont drop the diff ratio to much, I think that it is worth playing with diff ratios to maximise power and the way it likes to be used.

NS Dev - 9/10/06 at 08:47 AM

quote:
Originally posted by smart51
quote:
Originally posted by JoelP
What exactly do you mean by 'acceleration in gear'?


Acceleration in one gear not through the gears. Usual figures are 30 - 50 in 3rd, 40 - 60 in 4th and 50-70 in 5th.

If two otherwise identical cars have a drag race, the car with a 3.62 diff will be faster off the line than one with a 3.14 diff. Acceleration in 1st gear will be 15% faster.

If the same two otherwise identical cars take a certain corner in 2nd gear say, and they accelerate at full throttle, the one with the lower gearing will accelerate faster than the one with the taller gearing.

A car with a 3.62 diff will overtake faster on an A road if it drops from 6th into 4th than one with a 3.14 diff that also drops to 4th to overtake.


Smart51 is quite right, its simple maths, the lower ratio (higher number) will accelerate quicker, due to providing more torque at the wheels. It may mean the engine is revving its bits off a lot of the time but then sevens are a pain in the a to cruise at over 100 anyway so top speed is pretty meaningless.

MikeRJ - 9/10/06 at 02:54 PM

quote:
Originally posted by NS Dev
Smart51 is quite right, its simple maths, the lower ratio (higher number) will accelerate quicker, due to providing more torque at the wheels.


However, unless you have a feather weight flywheel in a CEC, the acceleration will be not improved by the same amount as the ratio change (i.e. 15% increase in ratio will not provide 15% better acceleration) as the flywheel becomes a comparatively greater load as the diff ratio increases.

Alternatively this means that with a high ratio diff, lightening the flywheel provides greater improvements than it would with a low ratio diff.

[Edited on 9/10/06 by MikeRJ]

JoelP - 9/10/06 at 09:00 PM

Far enough, acceleration in gear is improved, but overall acceleration isnt. By saying that the 0-120 time is unchanged you really mean average acceleration is unchanged, since they may well reach 120 at different times depending on what point in the cycle the two cars are at.

If a 15% longer diff would result in 15% less acceleration in any gear, you should also point out that 15% of the time you will be able to use a lower gear anyway and actually accelerate better. Good point though

So in reality diff choice is mostly dictated by your desired top speed, and the different acceleration in different gears will entirely balance out.

dilley - 9/10/06 at 09:40 PM

unless your gearing is so short that you are for ever changing gear, this must slow down acceleration?? thats how it felt to me, an engine needs some resistance.

NS Dev - 10/10/06 at 08:54 AM

quote:
Originally posted by MikeRJ
quote:
Originally posted by NS Dev
Smart51 is quite right, its simple maths, the lower ratio (higher number) will accelerate quicker, due to providing more torque at the wheels.


However, unless you have a feather weight flywheel in a CEC, the acceleration will be not improved by the same amount as the ratio change (i.e. 15% increase in ratio will not provide 15% better acceleration) as the flywheel becomes a comparatively greater load as the diff ratio increases.

Alternatively this means that with a high ratio diff, lightening the flywheel provides greater improvements than it would with a low ratio diff.

[Edited on 9/10/06 by MikeRJ]


yep, agree!

NS Dev - 10/10/06 at 09:00 AM

quote:
Originally posted by dilley
unless your gearing is so short that you are for ever changing gear, this must slow down acceleration?? thats how it felt to me, an engine needs some resistance.


No no no!

sorry but that is utter rubbish!

Go out in a POWERFUL car!! The engine will not feel like it has any resistance in ANY gear, but its bloody fast!

The Ultima 720hp demo car pretty much lunges though any gear you throw at it, its just one big flurry of changes, but it still hits 230mph pretty damn fast!

Peteff - 10/10/06 at 09:47 AM

Why don't you go faster uphill then?

JoelP - 10/10/06 at 11:50 AM

i think what he means is that the engine only revs up so fast when in neutral, so if the gears were so short (and they would admittedly be ridiculously short!) that the engine couldnt actually rev up fast enough to optimise the shortness you have reached the limit. However, you would only get to this stage with a final drive approaching 40 or something!

smart51 - 10/10/06 at 12:49 PM

My car accelerates from 0 to 50 in 1st in about 3 seconds. Given that in neutral, my engine will rev from idle to 12000 in a fraction of a second, 1st would have to be increadably low for acceleration to be limited by the rev up rate of the engine.

dilley - 10/10/06 at 01:51 PM

I may hve worded that wrong, I am running >320-340bhp at the wheels, when coming onto boost with such short gearing it is out of its max power range so quick that every time you change gear the same thing happens, you cant change gear quick enough to optimise power.