Gear oil for a box with an LSD

D

Djaraceandrally

Daily Driver
Hi oil, (see what I did there?!)

Just wanting opinion on oil viscosity in a gearbox with an LSD.

I have a Bacci Romano 5 speed dog box with their LSD and I trying to buy the right oil.

People who run this box in the UK say run a 75w/140 synthetic in (they are recommending lucas oils version) as the 75w/90’s is like water, when warm - but I contacted Bacci directly and they are saying 75w/90 Synthetic (and Mobil lubricants)

Ive run the latter in RWD Mk 2 escort LSD’s - but obviously, thats just the diff, not the gear box - where the X is both.

Anyone got experience of oils in these boxes and does the higher second number relay to slicker or stickier change.

Or should I just go for the Bacci recomendation? (Its not under warranty) just want to be sure if I go thiner, its not at a detriment to the gearbox gears.

Oh, and we can get redline MT90 here - its not a matter of cost (though redline is 2x more!!), just want to ensure the best for the box

Cheers,

Dave
 
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Djaraceandrally said:
Hi oil, (see what I did there?!)

Just wanting opinion on oil viscosity in a gearbox with an LSD.

I have a Bacci Romano 5 speed dog box with their LSD and I trying to buy the right oil.

People who run this box in the UK say run a 75w/140 synthetic in (they are recommending lucas oils version) as the 75w/90’s is like water, when warm - but I contacted Bacci directly and they are saying 75w/90 Synthetic (and Mobil lubricants)

Ive run the latter in RWD Mk 2 escort LSD’s - but obviously, thats just the diff, not the gear box - where the X is both.

Anyone got experience of oils in these boxes and does the higher second number relay to slicker or stickier change.

Or should I just go for the Bacci recomendation? (Its not under warranty) just want to be sure if I go thiner, its not at a detriment to the gearbox gears.

Oh, and we can get redline MT90 here - its not a matter of cost (though redline is 2x more!!), just want to ensure the best for the box

Cheers,

Dave
Click to expand...
Hi Dave, I recall you had sourced an RSX LSD (Torsen). What made you decide not to use that one? I am considering ordering an LSD (from RSX). I do not race or track the car, it would be to a) strengthen the box (given the 170-180 hp at the crank; probably 140+ at wheels based on how the car is currently set up) and b) “coolness” factor in the pursuit of optimizing the X!

Would the LSD just increase strength on starts (/ launches, if that was something someone was going to do). What about driving once things are moving? Would it protect against a jerkier shift if that happened by accident?

Thanks and curious what you and people think?
 
CanuckX1 said:
Hi Dave, I recall you had sourced an RSX LSD (Torsen). What made you decide not to use that one? I am considering ordering an LSD (from RSX). I do not race or track the car, it would be to a) strengthen the box (given the 170-180 hp at the crank; probably 140+ at wheels based on how the car is currently set up) and b) “coolness” factor in the pursuit of optimizing the X!

Would the LSD just increase strength on starts (/ launches, if that was something someone was going to do). What about driving once things are moving? Would it protect against a jerkier shift if that happened by accident?

Thanks and curious what you and people think?
Click to expand...
Take the time to read this write up in differentials..

For the majority of road cars, adding a LSD is of very limited value and not a substitute for proper chassis up.

"With low powered cars running slicks (Formula Ford, F2000, and on fast tracks Formula Atlantic), the open differential is the best choice. These cars simply do not have enough power relative to their grip to cause wheel spin if the chassis properly set up. A number of years ago, famed race car designer David Bruns explained to this writer that “springs put the power down, anti roll bars tend to lift the inside wheel.” Therefore if wheel spin is a problem with low powered cars, increase rear spring rate, and reduce swaybar stiffness at the rear. This will keep the roll couple the same, yet the springs will plant the weaker tire. Additionally, caster tends to unweight the outside front and inside rear when the front wheels are turned. Therefore a reduction in caster will help inside rear grip."

~Notable, open differential (non LSD) is the easiest to driven when the chassis is properly set up. Formula Atlantic open wheel cars are about 200-300 Bhp, about 1250 pounds.

In the Miata world, there is much TooT about adding a Torsen LSD, yet in the world of Spec Miata racing adding the Torsen LSD makes little to zilch difference in lap times. On public roads, even more zilch difference..


Bernice
 

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CanuckX1 said:
Hi Dave, I recall you had sourced an RSX LSD (Torsen). What made you decide not to use that one? I am considering ordering an LSD (from RSX). I do not race or track the car, it would be to a) strengthen the box (given the 170-180 hp at the crank; probably 140+ at wheels based on how the car is currently set up) and b) “coolness” factor in the pursuit of optimizing the X!

Would the LSD just increase strength on starts (/ launches, if that was something someone was going to do). What about driving once things are moving? Would it protect against a jerkier shift if that happened by accident?

Thanks and curious what you and people think?
Click to expand...
Hi, yes i did get that LSD, but then a bacci box with better ratios and a LSD became available and so I bought it - so the unused RSX will be up for sale.

Ive bought the box for my rally car, so uneven, varying grip surfaces and weather conditions are the norm, not super smooth tarmac circuits. I agree with bernice about letting the suspension do its thing to keep the tyres planted, but that doesnt work that well on Tarmac stages in the UK - very underlating, dirty, damp, rutted, cut up, icy, snow, mud… thats why most rally cars have LSD’s.

The initial reason I bought the RSX was to replace the diif cage arrangement on the standard box. Though Ive never broken one on an x1/9, I read it was a weak point if you have hard starts with a powerful engine and grippy tyres. I try and bomb proof as much as I can on my competion cars as the cost of the upgrades (within reason!) is soon forgotten about if you have failures in a event - you dont get your entry fee’s, transport, fuel, accommodation or anything else back if something goes bang on the start line or mid stage!! Overbuild, under worry!!

Anyway - gear oil viscosity - does the fact it gets v thin when hot provide less protection, even though its full synthetic ?
 
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Rupunzell said:
Take the time to read this write up in differentials..

For the majority of road cars, adding a LSD is of very limited value and not a substitute for proper chassis up.

"With low powered cars running slicks (Formula Ford, F2000, and on fast tracks Formula Atlantic), the open differential is the best choice. These cars simply do not have enough power relative to their grip to cause wheel spin if the chassis properly set up. A number of years ago, famed race car designer David Bruns explained to this writer that “springs put the power down, anti roll bars tend to lift the inside wheel.” Therefore if wheel spin is a problem with low powered cars, increase rear spring rate, and reduce swaybar stiffness at the rear. This will keep the roll couple the same, yet the springs will plant the weaker tire. Additionally, caster tends to unweight the outside front and inside rear when the front wheels are turned. Therefore a reduction in caster will help inside rear grip."

~Notable, open differential (non LSD) is the easiest to driven when the chassis is properly set up. Formula Atlantic open wheel cars are about 200-300 Bhp, about 1250 pounds.

In the Miata world, there is much TooT about adding a Torsen LSD, yet in the world of Spec Miata racing adding the Torsen LSD makes little to zilch difference in lap times. On public roads, even more zilch difference..


Bernice
Click to expand...
Thanks Bernice. I read the article. I agree with you (and with others, like Steve H in many posts) that an LSD is unlikely to be of any real benefit for a fast street setup used on smooth tarmac, etc.

However, if one has the objective of bolstering their gearbox in order to best handle higher engine hp, is it sensible to do? There is a lot of talk on this forum about weaknesses in the stock gearbox. To what extent is this talk/experience based on the gears themselves, or the differential cage/carrier? The RSX Torsen LSD replaces this with much stronger componentry apparently.

Switching to a Bacci Romano dog gearset would probably be a benefit, but that is very expensive and involves running a dog box.

And so holding aside speed and traction, would folks look to the LSD for strengthening purposes? Or is the weakness likely to show up in an unrelated aspect of the transmission in a higher hp application (and any chance of the stock diff being a reliability issue so low that it's not worth doing, even at 170-180hp)?

Thanks
 
The correct oil for the dog box will be the 75w90. There is no need for the 75w140. Heavier is not better.

An LSD will likely be stronger than the OE cast differential carrier. I have exploded many of these launching the car with the big 225/45-13 race tires. But as long as you are not doing high rpm clutch drops its not likely necessary.

And the LSD will do nothing for the weaknesses of the transmission; 3rd & 4th synchros, 1st & 2nd gear synchro hubs, reverse, etc...

Bernice's link above is spot on. There is very little need for an LSD in these cars when setup correctly. I tried one in my autocross car and it was faster with the OE open differential.
 
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CanuckX1 said:
However, if one has the objective of bolstering their gearbox in order to best handle higher engine hp, is it sensible to do? There is a lot of talk on this forum about weaknesses in the stock gearbox. To what extent is this talk/experience based on the gears themselves, or the differential cage/carrier? The RSX Torsen LSD replaces this with much stronger componentry apparently.

Switching to a Bacci Romano dog gearset would probably be a benefit, but that is very expensive and involves running a dog box.
Click to expand...
Properly made/designed straight cut gears will always be stronger and tougher than an identical size/loaded helical gear. This is due to the fact helical gears produce axial loading, straight cut gears produce not a lot of axial loading. Trade off is gear noise, which is why straight cut gear boxes are not tolerated in passenger production cars.

If Bacci Romano, inquire with them as to what the running torque ratings are of their alternative gear sets might be followed by the torque/hp curve of the engine to be used with this gear set.
https://www.bacciromano.com/en/vintage-car/fiat/

Gear boxes are rated by torque capacity not just hp.. if ya go race gear box shopping one of the first specs that comes up is the max torque spec, followed by maybe hp.. The Hewland LD200 in the LeMons exxe has a max torque spec of 165 lb/ft. This is the same transaxle gear set (Hewland MK) used in Formula Mazda and many others.
Hewland LD-200.jpg



How much more power is expected to be transmitted in-out of the exxe drive line?

Dog ring gear sets are often straight cut, intended to be used in real race cars, thus stronger than helical gear sets. Properly made straight cut gear sets are the choice for race or high performance duty..

All that aside, likely the most important consideration for alternative to stock gear sets is gear ratios matched to the engine's dyno power curve -vs- road/corner speeds. It is crucial to get the gearing proper to extract the most out of corner acceleration and proper track speeds. Ideal would be a gear set with individual interchangeable gears that allows selecting the closest ratio per gear selected to match engine power curve -vs- corner exit and track speeds.

This aspect of any alternative gear set is and should be absolute top priority and consideration for any choices for alternate gear sets.

Diversion note, this is the gear box in the Mori Seiki MS-850, there is 5 gallons of oil in the gear box, pressure lubricated, the lowest speed of 30 RPM can produce just over 2000 ft of torque and the lathe spindle is expected to hold over 2000 ft of running torque with a run-out of less than 0.0001" with a cutting tool loading (several thousand pounds easy) the spindle.. then be able to run up to 1800 RPM.
Very different than moto gear boxes in design, loading and more.



Bernice
 
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CanuckX1 said:
Switching to a Bacci Romano dog gearset would probably be a benefit, but that is very expensive and involves running a dog box.
Click to expand...
Dog drive gear sets do not have the problems designed in to syncros and they can be shifted a whole lot faster than any synchro box with more durability and all that.. There is a learning curve involved with dog drive boxes.

Aside from cost, gear noise and all that there are no negatives with straight cut gears, dog drive gear sets in race / high performance motos..
This has been the standard fare for real race cars for decades.. for all the proper reasons.


Bernice
 
Thanks Bernice and Steve. Bacci Romano actually makes a helical dog box gear set as well. I suspect it’s stronger than stock, but still a different approach to shifting.

My car is not being tracked. This is all “belts and suspenders” / ongoing quest for an “ultimate X”!
 
Rupunzell said:
Properly made/designed straight cut gears will always be stronger and tougher than an identical size/loaded helical gear. This is due to the fact helical gears produce axial loading, straight cut gears produce not a lot of axial loading. Trade off is gear noise, which is why straight cut gear boxes are not tolerated in passenger production cars.
Click to expand...

Aren't helical gears specifically created to be stronger than straight cut gears? More area, that's the point. The thrust load is taken up by the bearings, so the bearings need to be able to take it. But as far as strength, they can take more tooth load than a comparable width spur gear.
 
Design by design comparrison, yes I can see where you are going there and something I have thought about (sadly). In a helical gearset set, meshing gears effectively slide across each other during the period its engaged, Spur gears (straight cut) literally smash/mesh into each other (albeit small) at point of engagement. The end result is less side loading on the gears, as they aligned (or should be) reducing wear and more importantly for a race/rally car - power loss through friction, and as a side product, heat (though Ive never been able to measure that).

There is also a call, that because they are not mass produced, the quality “should” be better.

That said, I have some really badly produced gear-sets come out of places that are, how can I say, not known for quality. They had all the structual strength of a lump of Brie…and were machined by a distracted (by disney TV) 3 year old..

I can only quote power loss figures from my experience of BMC Mini Gearboxes, but its around 7-9 hp difference at the wheels on a engine producing 100hp (so average 8%) - the noise of course, is considerably more noticeable, especially if you have straight cut drops in there too. Also, I was told the oil (believe it or not), being squeezed out creates an audible whistle!

The advantage of the X Bacci dogbox is the ratios (you have choices), its Semi helical (so less side load/wear - but not completely straight cut) and its a dog box (so no synchro’s/hubs as per a stock box).

Downsides - you have to learn again how to shift and rev match
Expense
Parts not quite off the shelf
 
SuperTopo said:
Aren't helical gears specifically created to be stronger than straight cut gears? More area, that's the point. The thrust load is taken up by the bearings, so the bearings need to be able to take it. But as far as strength, they can take more tooth load than a comparable width spur gear.
Click to expand...
In Theory and how applied, helical gears are stronger than spur (straight cut).. depending on helical angle, torque transmitted and gear train velocities involved (higher velocities = lower torque), pressure angles and geometry. Regardless, there is no escape from the axial loading inherent in helical gears. This results in energy loss, energy loss = heat via friction. That heat has to go some where.. typically into the oil, bearings, housing and all that..

The common number for moto helical gear box loss runs about 20%, not a small number. Specially when the power being transmitted goes up-up. As exampled in the rotary powered LeMons exxe, the Porsche 901 cannot be touched after being run for hours, figure about 200 degrees on the housing.. This is one of the reasons gear boxes can be short lived in endurance racing. There were ideas of adding a gear box cooler to deal with this.

This is where straight cut (spur) gear boxes do have an advantage if they are properly designed/built. They can have lower power loss translating to lower heat and all related.

How good gears are made is fascinating and highly involved process, From Swiss MAAG gear hobbers to grinders to induction heat treating of the gear contact surfaces to proper set up of the gears..


Helical:

Spur:

Modern methods:

Grinding:

Grinding wheels:
https://www.youtube.com/watch?v=_D-iV9cGjF4&list=RDQMiHxaTaieU-E&start_radio=1

Induction hardening:
https://www.youtube.com/watch?v=wOv3i0eoo0Q

Laser hardening:
https://www.youtube.com/watch?v=fSEv-UI-n_4

Plenty more on YouTube..


Bernice
 
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