My name is peter Burgess and I am a tuning junky
Discussion
Stan Weiss said:
If a Slippy diff is what we call a PosiTraction diff on this side of the pond? Then I would think that the extra rotational mass of the PosiTraction as compared to an open rear would show up.
Stan
You're thinking the drag could be from the extra hardware simply being dragged through the diff oil mix? I hadn't considered that - I was looking at it from the point of view of mechanical friction losses.Stan
As I understand it there are 3 types of LSD
Viscous as used in the Ford Sierra Cosworth ( and some other Sierras)
Plate diffs with adjustable ramps
ATB (Automatic Torque Biasing) gears
How they absorb power as seen at the wheels would be interesting but also how much faster you could go on the track if at all.
Viscous as used in the Ford Sierra Cosworth ( and some other Sierras)
Plate diffs with adjustable ramps
ATB (Automatic Torque Biasing) gears
How they absorb power as seen at the wheels would be interesting but also how much faster you could go on the track if at all.
I hadn't thought of the extra lump of oil on the diff causing power loss Peter, good call.
Paul, I will try and remember to ask what sort of lsd (non hallucinogenic variety) they have when I do cars with them.
On TR4s the FIA car was allowed an lsd but smaller engine, the big boys had big engines but no lsd, at power circuits the big boys won, at circuits with twisty bits like the hairpin at Mallory the FIA ones held there own by snapping at the heels of the big boys coming out of the hairpin.
On another note, about 14 years ago I had a V8 MGB roadster I loaned it out to a mate for sprint and hillclimbs, it ran a tuned 3.9 for several years with no problems winning its class nicely, we then bought a 4.6 and tuned that, twice it crashed coming out of hairpins which had us scratching our heads, it nearly spat me into a parked lorry trailer when I was testing throttle response with a new distributor. Frightened the cr*p out of me! Those in the know told me it needed a slippy diff to control the power output, once fitted the problem never occurred again, transmission losses not even considered
One of our championship winning MGB drivers used oil like treacle in his diff, it acted like a slippy diff when we were pushing the car around. On my old Clayton Rollers ( no coastdown facility) it always took around ten full power runs and cooling in between to get the most out of it, we think the treacl was sapping around 12 bhp until it warmed up. The reason was, first three or four laps gave lsd effect on bends so he could break away from the pack, rest of race running as usual diff as the grease/oil had thinned. It takes us back to aggregation of marginal improvements.
I suppose the pro race teams choose oils etc to give adequate protection for the length of the event. Thin oils sap less power but I presume do not protect as well on endurance events. It made us think you want as thin as possible in the transmission for drag racing as it is all over in a few seconds. Sa,me as we found around 10 bhp mors at thye wheels of Keith's(stepson) Camper van when we took the fanbelt off the ginormous cooling fan, It went from about 77 to 87 at the wheels, all important if you want to break that 19s 1/4 mile and be welcomed to 'The Club'. Running it without the fan for say 20 secs hard and the engine wouldn't even know it wasn't cooling properly. We were excited to find this and thought we were treading new ground....Keith's son Kev says.....they do that on the strip already Dad
Peter
Paul, I will try and remember to ask what sort of lsd (non hallucinogenic variety) they have when I do cars with them.
On TR4s the FIA car was allowed an lsd but smaller engine, the big boys had big engines but no lsd, at power circuits the big boys won, at circuits with twisty bits like the hairpin at Mallory the FIA ones held there own by snapping at the heels of the big boys coming out of the hairpin.
On another note, about 14 years ago I had a V8 MGB roadster I loaned it out to a mate for sprint and hillclimbs, it ran a tuned 3.9 for several years with no problems winning its class nicely, we then bought a 4.6 and tuned that, twice it crashed coming out of hairpins which had us scratching our heads, it nearly spat me into a parked lorry trailer when I was testing throttle response with a new distributor. Frightened the cr*p out of me! Those in the know told me it needed a slippy diff to control the power output, once fitted the problem never occurred again, transmission losses not even considered
One of our championship winning MGB drivers used oil like treacle in his diff, it acted like a slippy diff when we were pushing the car around. On my old Clayton Rollers ( no coastdown facility) it always took around ten full power runs and cooling in between to get the most out of it, we think the treacl was sapping around 12 bhp until it warmed up. The reason was, first three or four laps gave lsd effect on bends so he could break away from the pack, rest of race running as usual diff as the grease/oil had thinned. It takes us back to aggregation of marginal improvements.
I suppose the pro race teams choose oils etc to give adequate protection for the length of the event. Thin oils sap less power but I presume do not protect as well on endurance events. It made us think you want as thin as possible in the transmission for drag racing as it is all over in a few seconds. Sa,me as we found around 10 bhp mors at thye wheels of Keith's(stepson) Camper van when we took the fanbelt off the ginormous cooling fan, It went from about 77 to 87 at the wheels, all important if you want to break that 19s 1/4 mile and be welcomed to 'The Club'. Running it without the fan for say 20 secs hard and the engine wouldn't even know it wasn't cooling properly. We were excited to find this and thought we were treading new ground....Keith's son Kev says.....they do that on the strip already Dad
Peter
PaulKemp said:
As I understand it there are 3 types of LSD
Viscous as used in the Ford Sierra Cosworth ( and some other Sierras)
Plate diffs with adjustable ramps
ATB (Automatic Torque Biasing) gears
How they absorb power as seen at the wheels would be interesting but also how much faster you could go on the track if at all.
I had a Sierra style viscous diff on the V8S. It was better than an open diff, but out of slow corners it was ineffective and spun the inside wheel - very frustrating. The problem is that it only transfers torque based on speed difference, not on torque, and by the time there's enough speed difference for it to work, the inside tyre has already got so much slip on that it has very little grip. When I changed it to a fairly loose ramp style plate diff the improvement in traction was quite dramatic and it spins both wheels or neither under the vast majority of conditions.Viscous as used in the Ford Sierra Cosworth ( and some other Sierras)
Plate diffs with adjustable ramps
ATB (Automatic Torque Biasing) gears
How they absorb power as seen at the wheels would be interesting but also how much faster you could go on the track if at all.
I have a Torsen (helical) diff in my mr2.
While it improves traction, there is a downside : pre-LSD, too much power meant the inside (unloaded) wheel would spin. With the LSD, the limit is much higher, but when you overpower the grip, both wheels spin and the rear goes sideways (rapidly).
I've never spun it, but turning right at a wet T junction requires restraint. Dry is just grip and go.
While it improves traction, there is a downside : pre-LSD, too much power meant the inside (unloaded) wheel would spin. With the LSD, the limit is much higher, but when you overpower the grip, both wheels spin and the rear goes sideways (rapidly).
I've never spun it, but turning right at a wet T junction requires restraint. Dry is just grip and go.
Figures relating to bhp at flywheel vs bhp at the wheels on t'internet seem very scarce with no one really committing. I found a link to an article about Roush Cup engines...
Plus, Roush says parasitic losses are surprisingly minimal, with about 850 of those 900 ponies reaching the rear wheels. Maximum torque is delivered at 7000 rpm, while peak power typically comes around 9000 rpm, though the engine is capable of revving considerably higher depending on the track.
http://www.roadandtrack.com/motorsports/news/a8027...
Peter
Plus, Roush says parasitic losses are surprisingly minimal, with about 850 of those 900 ponies reaching the rear wheels. Maximum torque is delivered at 7000 rpm, while peak power typically comes around 9000 rpm, though the engine is capable of revving considerably higher depending on the track.
http://www.roadandtrack.com/motorsports/news/a8027...
Peter
it is a can of worms, it depends alot on the specifics obviously.
Alot of the engine dyno stuff ive seen uses a completely different exhaust to when installed in the chassis and probably there are a whole host of other differences in accessories used or lack of air filters etc that make it a less than ideal comparison
as for the nascar losing merely 50hp is that to the tire or to the road
Alot of the engine dyno stuff ive seen uses a completely different exhaust to when installed in the chassis and probably there are a whole host of other differences in accessories used or lack of air filters etc that make it a less than ideal comparison
as for the nascar losing merely 50hp is that to the tire or to the road
It is tantalising isn't it? To the wheels, at the wheels, at the bit of tyre that grips? Exactly what I thought It seems no one wishes to test these things. I suppose, it doesn't really matter as long as engine and transmission are performing at their best.
Can of worms. It is why I decided we would run full systems on our engine dyno, otherwise it seems like a waste of time.
With regard to filters...twice now I have seen V8s on the rollers with 'as dynoed' engines running way too rich, pop off the supplied filters and mixes and bhp seem correct so I get the feeling dynoing had been done without airfilters as the mix was spot on without! The engine builder, had supplied everything, including the dyno tuning!
Years ago (30?) the Don part of Aldon (cut his teeth at Rover) said I would be surprised to find out how little transmissions (inc wheels/tyres) really lose. I suppose that has stuck with me ever since.
Peter
It seems no one wishes to test these things. I suppose, it doesn't really matter as long as engine and transmission are performing at their best.Can of worms. It is why I decided we would run full systems on our engine dyno, otherwise it seems like a waste of time.
With regard to filters...twice now I have seen V8s on the rollers with 'as dynoed' engines running way too rich, pop off the supplied filters and mixes and bhp seem correct so I get the feeling dynoing had been done without airfilters as the mix was spot on without! The engine builder, had supplied everything, including the dyno tuning!
Years ago (30?) the Don part of Aldon (cut his teeth at Rover) said I would be surprised to find out how little transmissions (inc wheels/tyres) really lose. I suppose that has stuck with me ever since.
Peter
When measured on rollers the greatest variable is the tyre contact area ad the speed of the tyre.
Twin roller setups absorb more power than single roller as they have two tyre contact patches. And, using a lower gear always gives higher wheel power as the tyre is rotating slower. More is gained in the measurement in a lower gear than is lost in not using a direct drive gear for the measuring.
It is even more muddled when a diff ratio is changed. Lower diff ratio, higher measured wheel power due to lower tyre speed.
This where the benefit of coastdown losses come in. Although they are not a true measure of power loss under load, they give an indication of tyre drag and can help indicate an issue.
If one wanted to avoid this vagary, a hub dyno would be the dyno of choice. Rototest have some interesting figures on their web site which suggest 9% loss compared to manufacturer claims is the median number for all the production cars they have tested
WRT LSDs and losses. I can't think of any reason why the choice of LSD should make any difference as on the rollers the diff is inactive due to both wheels turning at the same speed. Slightly different oil drag due to the oil type required and/or increased oil drag due to the design of the unit, but this would be pretty small.
Twin roller setups absorb more power than single roller as they have two tyre contact patches. And, using a lower gear always gives higher wheel power as the tyre is rotating slower. More is gained in the measurement in a lower gear than is lost in not using a direct drive gear for the measuring.
It is even more muddled when a diff ratio is changed. Lower diff ratio, higher measured wheel power due to lower tyre speed.
This where the benefit of coastdown losses come in. Although they are not a true measure of power loss under load, they give an indication of tyre drag and can help indicate an issue.
If one wanted to avoid this vagary, a hub dyno would be the dyno of choice. Rototest have some interesting figures on their web site which suggest 9% loss compared to manufacturer claims is the median number for all the production cars they have tested
WRT LSDs and losses. I can't think of any reason why the choice of LSD should make any difference as on the rollers the diff is inactive due to both wheels turning at the same speed. Slightly different oil drag due to the oil type required and/or increased oil drag due to the design of the unit, but this would be pretty small.
years ago 4th made more than 3rd on the twin roller dyno dynamics i was using so its not so simple as faster more losses. i always do it 4th now and it is what it is however you just have a standard way to do things, strapdown, tyre pressure, gear ratio, same wheel tire combo including tire specifics. and if any these change forget about comparing to previous results, start again. if you are just tuning/calibrating the ECU then it doesnt matter so much as long as back to back runs are repeatable.
ive done multiple mods that seemed to have lost a bunch of power enough that you would feel them but sometimes i wonder if much of it is a figment of the beast rather than a real change. especially when you change things back and the power never comes back...
ive done multiple mods that seemed to have lost a bunch of power enough that you would feel them but sometimes i wonder if much of it is a figment of the beast rather than a real change. especially when you change things back and the power never comes back...
GreenV8S said:
You're thinking the drag could be from the extra hardware simply being dragged through the diff oil mix? I hadn't considered that - I was looking at it from the point of view of mechanical friction losses.
I was talking about the extra weight that the clutches and plates or whatever is used to limit slip adds in the way of rotational mass.Stan
Stan Weiss said:
GreenV8S said:
You're thinking the drag could be from the extra hardware simply being dragged through the diff oil mix? I hadn't considered that - I was looking at it from the point of view of mechanical friction losses.
I was talking about the extra weight that the clutches and plates or whatever is used to limit slip adds in the way of rotational mass.Stan
All the LSD bits are no more than 200 mm dia. tops, so if it weighs an extra 5 kg, with the mass concentrated 100mm from the centre, the total inertia will be 5kg x 0.1m x 0.1m, or 0.05 kg.m.
The diff is also only spinning at between 1/2 and 1/3 of the roller speed (depending on roller & tyre size), which lessens the effective inertia.
In comparison, a single small roller is around 0.4 kg.m2
Well, that's two hours gone from my life.
4th gear
30 psi(went up to 32 after runs) 73.4 and 19.6 losses = 93
26 psi(staid same after runs) 72.5 and 20.9 losses = 93.4
15 psi(went up to 17 after runs)71 and 22.4 losses = 93.4
To be expected I suppose, as tyre resistance goes up power at wheels will go down.
What I do find interesting, why did 26 psi stay static ( that is the correct running pressure for the tyres)?
Peter
4th gear
30 psi(went up to 32 after runs) 73.4 and 19.6 losses = 93
26 psi(staid same after runs) 72.5 and 20.9 losses = 93.4
15 psi(went up to 17 after runs)71 and 22.4 losses = 93.4
To be expected I suppose, as tyre resistance goes up power at wheels will go down.
What I do find interesting, why did 26 psi stay static ( that is the correct running pressure for the tyres)?
Peter
one thing to add about your dyno installation Peter is that we've always found running the tube in tube type of propshafts between the brake and engine is very beneficial to absorbing vibration and they aren't much more than a regular prop
http://www.baileymorris.co.uk/en/bespoke-propshaft...
http://www.baileymorris.co.uk/en/bespoke-propshaft...
Thanks for that link Matthew.
That would be ideal on the smaller Clayton engine dyno we have lying around as it has a flange style coupling and the dyno is 'stand alone' as would be the engine. The SF901 uses the engine to become rigid, it has a bell housing and spigot shaft just like a gearbox. The engine is bolted in place and the end of the spigot shaft is supported in the end of the engine crank. The instructions say this fitting method, along with a flexiplate clutch is necessary. I notice folk make adaptors to either bolt onto the end of the crank or onto the flywheel rather than use the clutch assembly from the test engine and changing the spigot shaft for each different engine.
Peter
That would be ideal on the smaller Clayton engine dyno we have lying around as it has a flange style coupling and the dyno is 'stand alone' as would be the engine. The SF901 uses the engine to become rigid, it has a bell housing and spigot shaft just like a gearbox. The engine is bolted in place and the end of the spigot shaft is supported in the end of the engine crank. The instructions say this fitting method, along with a flexiplate clutch is necessary. I notice folk make adaptors to either bolt onto the end of the crank or onto the flywheel rather than use the clutch assembly from the test engine and changing the spigot shaft for each different engine.
Peter
Just doing test runs on a new hub dyno today - the test hack was giving 118 kW at the hubs - it usually runs about 110 kW at the wheels on a chassis dyno. So that's 8 kW / 7.5% loss in the tyres.
There's obviously more losses in the driveline - the diff is likely to be 90-95% efficient, so there goes another 5-10%.
This is not a scientific back to back test, just an observation. If we get time tomorrow we'll do a set of runs on the hub, then put the car on the rollers and run it again.
There's obviously more losses in the driveline - the diff is likely to be 90-95% efficient, so there goes another 5-10%.
This is not a scientific back to back test, just an observation. If we get time tomorrow we'll do a set of runs on the hub, then put the car on the rollers and run it again.
I'd have to check.
It's got thousands of hard dyno miles on it, so there will be less than it had when it left the factory, for sure.
An engine dyno isn't the problem - it's getting the engine out, and fitting it to the dyno complete with full factory exhaust and inlet system, to make any comparisons valid. Not a trivial task.
It's got thousands of hard dyno miles on it, so there will be less than it had when it left the factory, for sure.
An engine dyno isn't the problem - it's getting the engine out, and fitting it to the dyno complete with full factory exhaust and inlet system, to make any comparisons valid. Not a trivial task.
Which is exactly the problem we see about engine dyno, so only going down that route after 30 years
I was wondering about the engine power as it seems to fall in line with what we find.
If you divide your 118 by .95 for the diff then .97 for box one would get 128 KW /171 bhp, the quantity losses look like we get on the coastdown losses, 18 KW/25 bhp losses, coincidence I know but it does give us comparable figures for testing like for like models. Biggish tyres and high speed we would expect you run at another 5+ losses so that is why I guessed at 175 But, like we all keep saying, guesswork.
Peter
I was wondering about the engine power as it seems to fall in line with what we find.
If you divide your 118 by .95 for the diff then .97 for box one would get 128 KW /171 bhp, the quantity losses look like we get on the coastdown losses, 18 KW/25 bhp losses, coincidence I know but it does give us comparable figures for testing like for like models. Biggish tyres and high speed we would expect you run at another 5+ losses so that is why I guessed at 175
But, like we all keep saying, guesswork.Peter
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