transmission

[zefarelly]

what sort of losses are usual on a rear wheel drive car, from flywheel to wheels ?

what difference does a straight cut box make (apart from being a bit stronger and noisier) is it considerably more efficient at transmitting power ?

I'm nearing the stage where I need a SC box, although 2 manufacturers have quoted wildly different prices for gear kits and there doesnt seem to be any differernce between them. . . . steel baulk rings is another option on top, which as I understand will just make it more reliable as they are a weak point

[1200Datto27]

Straight cut boxes do (if designed properly) reduce power losses through drivetrains, as they have less end thrust causing drag on the bearings, and also have lower friction loads on the teeth, but higher overall loads due to a reduced contact patch.

The actual gains involved are hard to judge, unless you have run the engine on a dyno, and then installed it and run on a chassis dyno, but even so these figures can only give a broad idea, as when you install the engine in the car, there will be differences in the power output caused by the installation. Just minor things like airflow around the engine bay making temps different, or voltages changing due to a different grounding used can make a 2 ~ 3 % difference in power.

[Anuauto]

Depends how tight the diff is set? Typically on a rwd Ford with something less than 200bhp, most seem to claim 20-25 bhp losses but I have seen 40 with a tight diff for hillclimb hairpins. S/C kit from either Quaife or TranX should be much the same price for popular Ford boxes but not sure about rarer types.

[zefarelly]

well the two mentioned vary by hundreds, although Tran-x utilise the std main shaft, which should be quite adequate as without cheating I'm never going to get more than 150 BHP

I'm stuck at 120 at the moment!

the main reason for upgrading is reliability, I've generated a crunch changing down to 3rd after 7-8 races, possibly my poor driving, but equally possible is the extra power and revs Im throwing through it

[1200Datto27]

What oil are you running in the box?

[zefarelly]

just castrol regular stuff at the moment . . . .most fancy synthetics just **** past the oil seals ! I'm open to suggestions though !

[1200Datto27]

I run a modified "standard" synchro gearbox ie, using standard manufacture gears, just different ratios from other gearboxes from the same manufacturer, and about 150hp at the flywheel.

The oil that I use is Castrol SAF-XA and the thing just slices through changes without any issues, and very quickly considering that it is a synchro box. People have thought that I had a dog box due to the shift speed.

Give the oil a try, you may need to change it, run the car for 20 k's, drain it and refill with new oil to flush out the old stuff properly from the box, but after that you should notice a big difference. Also, when you drain the old oil, check for any metal in the oil, if it is magnetic, then you have either a bearing or gear/shaft issue, non magnetic and a bronze/copper colour then it is the synchros, and aluminium is usually shift forks.

With the oil seals, are they the ones around the input/output shafts? if so, they are usually very easy to replace, and worth doing, if it is around the joins in the case, you may need to crack the case open and create a secondary seal with silicone or the like.

[zefarelly]

sounds good to me . . . . where do you get it from ? DT ?

I'm going to whip the box out soon and have a sniff around . . .I doubt I'd get anywhere near 20k without striping/checking it anyway !

[zefarelly]

isnt SAF-XA LSD oil ? isnt that thicker than yer average cog bos oil (as well as smellier if my stuffs anything to go by !)

[Al Weyman]

What gearbox is it for example a Cosworth Serria box requires a special oil from Ford more like an auto trans fluid, my old chevy camaro with a Muncie 'Truck' box requires an 80 grade oil so be careful you dont get bum advise by being none specific.

[zefarelly]

3 rail ford 2000E, bog standard, all good as new though with fresh bearings, seals and layshaft

[graham bahr]

how much power you loose through the transmission also depends on how much your trying to put through it in the first place, but i would expect you to loose around 20 brake, straight cut gears only seem to give a marginal power saving. steel bulk rings require regular lapping in with grinding paste to keep them working properly, unless your really hard on bulk rings i.e you break them, stick to bronze they are cheaper and much more gentle on the other gearbox components.
SAF is diff oil, mainly used in bmw and some japanese diffs, its also bloody expensive compaired to EP80/90 i cant see any point in putting it in a gearbox, castrol syntrax 75/90 is a bit thinner than traditional 80/90, i've used it a lot in beemer boxes and it tends to give a slicker cold shift, but i can see any reason for you to use anything other than normal ep80, we once had an e type on the rollers, and compared the power at the wheels figure running both ep90 and engine oil in the gearbox, the difference was a mere 4bhp, which was bugger all considering we had something like 220 at the wheels .

[Anuauto]

Cant speak for racing but for rallying, hillclimbs, sprints EP80 should be used in a 2000E box, std or SC/CR. Most of my experience is with Rocket 4 speed and T9 (Sierra 5 speed, non-Cosworth)and a lot of people have damaged T9s by using ATF as in standard car rather than EP80. Leaks in older boxes are often a groove worn in the shaft by the seal rather than the seal itself (space out new seal slightly is only solution to that short of a new shaft)

[1200Datto27]

Ooops, should have checked my paperwork properly, SAF-XA is Diff oil, not Gearbox! I use Castrol Syntrax 75/90 in the gearbox, and neither I, or the cars previous owner have had any issues with the boxes.

btw, the previous owner won 4 state and three national titles with the car, and other than changing the oil once a year, he had to do no other maintenance on it.

[StephenRae]

Just a thought, if a gearbox is sapping 20 bhp it can only be converting it, by friction into heat. Wouldn't it glow red hot if that much power was being lost.
I guess the diff is sapping at least as much power as the 'box.

[graham bahr]

your quite right in that the diff, wheel bearsing etc all add to the losses, but no the gearbox wouldn't glow, it might get warm, infact after a race the gearbox in my car (alloy casing) is hot enough for you not to want touch it for more than a moment

[StephenRae]

If my supposition is correct and there is nothing like 20bhp lost by the gearbox then the high cost of 'slicker' gearbox parts is less justifiable.
A friend of mine used to race motorcycles in the 1930s, he used to replace the oil with 'brasso' in a new gearbox for a gentle couple of hours, to loosen it off. I don't know how synchro rings would put up with this treatment.
He also tells me they used to dissolve boot polish into the fuel, the lead content would up the octane.

[graham bahr]

your right but then i only ever refer to transmission losses as a whole, as you cant seperate the differnt losses the various bits of transmission have, my race car looses around 10% through the transmission as a whole, so if you inclued a propshaft with 3 u/js and a bearing, diff and wheel bearings in the equation, then the losses in the box itself must be fairly low, and in almost all RWD gearboxes 4th gear is direct, so the actual gears themselves aren't doing any driving losses are further lowered.

i can see sense in the basso usage, but i would of hoped that manufacturing has improved since then rendering it unnecsasary, after all you wouldn't run your engine in with valve grinding paste in the oil? well i hope not.

[zefarelly]

interesting comments, I think I'll leave it where it is and try and concentrate on improving my race driving style !

now boot polish in the fuel and upping octane . . .thats almost a thread in its own right !

[dtype38]

Just got my race car off the dyno and can quote some real figures for transmisson losses on a rwd car just for interest.. Its a Jag engine on a 1991 Getrag 5sp synchro box on 75/90 oil, and Jag IRS diff and rear hubs. At max power of 229hp and 281Nm at the flywheel, I getting only 184hp at the rear wheels (ie losing 45hp or nearly 20%). Checking round, I'm told 20% is average for a Jag transmission, but I'm open to suggestions if anyone knows how to reduce it! Incidentally, 45hp equates to a 33kW heater which is why the transmission gets so hot... I was standing beside the car and I can vouch for that!

[zefarelly]

mine was the same, its pertly the transmission getting hot and the lack of airflow over the exhaust, an incredible amount of heat is emitted, and remember a lot of potential energy is lost through heat . . . .would it be possible that on a rolling road the car doesnt produce as much because of this? whereas on a dyno you can optimise the runing temperatures ?

this being the case, there doesnt seem much point for the likes of me using a dyno before putting an engine in a car as its just more expense I can't afford!