Porsche G50 Info

Chris Kouba

Supporter
When I get around to building my own GT, having this forum around is going to be like having the answer key to a homework assignment.

Nice work Lynn.

Chris
 

Lynn Larsen

Lynn Larsen
Chris,

Just to make sure you're clear on what's available:
75W90
75W90NS
ShockProof Lightweight
ShockProof Heavyweight

are all separate products and then there is also Red Line's Friction Modifier (FM) for LSDs. (Nothing says you can't mix them though, indeed one older Red Line recommendation was for 3 parts 75W90 and 1 part Lightweight Gear Oil. Lightweight Gear Oil is yet another product, not to be confused with Lightweight ShockProof Gear Oil. It can be confusing. Trust me, I found myself confused on a number of occasions: Now wait a minute, was NS for synchros or for N-on S-ynchros??? It is actually recommended for synchromesh transmissions :)

The bottom line is that think that PHII's recommendation, as reported above by KalunD, is spot on in a GT40 with any kind of built SBF. If you were running a stock SBF and using the car for occasionally bopping around town in style, then you could use 75W90NS (it's doubtful this kind of car would have an LSD, but if it did, then I'd add just enough FM to quiet the LSD chatter.) FM really shouldn't be needed with 75W90, Lightweight ShockProof or Heavyweight ShockProof, but it is the ace in the hole if you should experience LSD chatter, but, again, the rule of thumb is "only enough FM to do the job." Luckily for us, getting gear lube into/out of the tranny is fairly easy; for our poor Porsche brethren, it is a bit of a PITA.

So, once you've decided which gear oil to use, how much do you put in?? It seems that best way to get it at the right level, is to pull (or loosen) one of the output flanges and fill until the oil leaks out of the opening. (retorque to 19-22 ft.lbs. for '72+) This will get enough oil in the gearbox to adequately oil the diff gears/clutches (the ring gear will dip into the oil and spray the pinion at much lower levels.)

I really think that if you are running much HP, you should seriously consider a cooler with the return directed at the diff (a cooler alone will help though.) If you follow the KISS principle, this can be done fairly easily and for a reasonable price and is a cheap insurance policy. You can also spend a lot of money and have a very elegant oiling system in your gearbox. If you need maximum performance and you do this, you can reduce the oil level to reduce the drag it causes. (For most of us, the gain would be negligible.) I don't think I've said anything new here, but I've tried to get a broad discussion in one spot so the newbee, if he doesn't read anything else, will have the basics.

Regards,
Lynn

PS: My daughter tells me that I turn a simple answer into a class lecture - who me??? Nahhhhhhh.
 

Tim Kay

Lifetime Supporter
[ QUOTE ]
........I turn a simple answer into a class lecture


[/ QUOTE ]
Any other class I would be sawing logs but this one has my full attention. Thanks professor Lynn /ubbthreads/images/graemlins/wink.gif
 
[ QUOTE ]
It seems that best way to get it at the right level, is to pull (or loosen) one of the output flanges and fill until the oil leaks out of the opening. (retorque to 19-22 ft.lbs. for '72+) This will get enough oil in the gearbox to adequately oil the diff gears/clutches (the ring gear will dip into the oil and spray the pinion at much lower levels.)


[/ QUOTE ]

Lynn, in the DRB circles up here we just tend to add 3.5l of oil and that's it. Simple as that. That's the information that is passed on from the factory. May not be the most exacting way...but boy it's easy. /ubbthreads/images/graemlins/smile.gif
 
Being new to this Forum, hopefully you can help or direct me .
I require info on gear change assemblies for G50 within the GTD chassis.
I have two Ultimas with Rod change which work well but in a 40 space is restricted for rods .
Do you know of anyone who has or uses cable change.
Any info would be great
Thanks
 
they use their own brand (Swepco),but in the pits the secret is "Red Line" not the German oil.The G50 seems to work just fine with 5 and 600 hp....but remember these are track cars not clutch drop in 1/4 milers........all the some do that too.....the big difference was the depth of the bell,a deeper one for a rubber clutch center and the more normal one (not so deep)
 
My GTD with Renault R-30 has been running with Red Line 80W140 for 13,000 miles - many of these on the track. Haven't had any problems and it shifts great using the original cables. Remember there is a lot of heat in close proximity to your transaxle in a GT40.
 

Peter Delaney

GT40s Supporter
Hi Guys,

I am looking at a re-build of my G50-00 : when it warms up, it has a nasty rattling noise when idling in neutral, & sometimes in 1st at low revs/load. Synchros on 1st & 2nd are also fairly notchy & slow.

I have spoken to the experts at Albins here in Oz & they reckon it could be needle roller bearings in the back of the box, or maybe even the pinion bearing. So, I am going for a re-build. Albins' estimate is around AU$1000 for this, incl new bearings & synchros.

The big question is whether to spend the extra AU$2,750 to replace the stock 3.44:1 R&P with a new 3.10:1 setup.

I used Lynn's "gear speed calculator" (with some mods) to look at these 2 options (see attached spreadsheet) & the basic story is as follows :

a) MPH

Ratio / 1st / 2nd / 3rd / 4th / 5th (mph at 6,000rpm)
3.44:1 / 38 / 65 / 94 / 118 / 149
3.10:1 / 42 / 72 / 105 / 131 / 166

b) KPH

Ratio / 1st / 2nd / 3rd / 4th / 5th (kph at 6,000rpm)

3.44:1 / 61 / 104 / 152 / 190 / 240
3.10:1 / 68 / 115 / 168 / 211 / 267

Do you reckon it is worth the AU$2,750 for the new 3.10:1 R&P for a road car where the key speeds in 5th are :

a) MPH

Town 37mph 3.44:1 ==> 1,486rpm / 3.10:1 ==> 1,339rpm
H'way 56mph 3.44:1 ==> 2,248rpm / 3.10:1 ==> 2,026rpm
F'way 68mph 3.44:1 ==> 2,730rpm / 3.10:1 ==> 2,460rpm

b) KPH

Town 60kph 3.44:1 ==> 1,486rpm / 3.10:1 ==> 1,339rpm
H'way 90kph 3.44:1 ==> 2,248rpm / 3.10:1 ==> 2,026rpm
F'way 110kph 3.44:1 ==> 2,730rpm / 3.10:1 ==> 2,460rpm

Around town, you get a 147rpm drop, on the highway a 222rpm drop, & on the freeway a 270rpm drop. These seem like somewhat trivial rpm reductions for AU$2,750 !

Any comments would be greatly appreciated.

Kind Regards,

Peter D.
 

Attachments

Ross Nicol

GT40s Supporter
Hi Peter I think the Idea of changing to a 3.1 ratio is to get the lower gears a bit taller.With the 3.44 your able to cruise at 100kph doing 2200 rpm, pretty good for a v8 on the road.
Ross
 

Peter Delaney

GT40s Supporter
Thanks Ross - I should have made my motivation a little clearer. As you say, I'd like the lower gears a bit taller (specially 1st), and also not have the engine thrashing along on the freeway. All in all, I think that the spread of the gear ratios on the stock 3.44:1 is ok, as is the spread with the 3.10:1.

If anything, 1st & 5th are too low - but I was thinking that a simple R&P change might just solve everything & drag them all up.

I might be suffering a bit of memory loss, but I seem to recall that my old 89 Vette used to lump along under 2000rpm at 110kph - perhaps I was spoiled by that for "just cruising" ? I guess that I need to adjust my thinking about "cruising" in a 40 & get used to a bit of revving - my gut feel is that $2750 is a bit too much to pay for a 270rpm drop on the freeway !

After all, the exhaust note drowns out the sqeals from the wallet anyway !

Kind Regards,

Peter D.
 
Hello - (newbie)

You guys are very impressive, and quite well researched.

I drive an 87' 930 twin turbo with a G50/50 LSD, using Redline HD shockproof gear oil, mostly on the track. I will have a spare G50/50 available soon, was searching for pricing history, and came across your site.

Yes, the G50/50 was designed to handle a lot more HP/TQ than the standard G50. It also has taller gearing for over 200 mph. Mine holds over 600HP/500+TQ no problem, and the Redline handles the heat more effectively. I wasn't aware they also fit the GT40's. I rode in an old GT40 with a ZF box, if I remember correctly, and it was truly memorable.

Just wanted to say hello.

Glenn
 

Randy V

Admin
Lifetime Supporter
As long as this thread's been bubbled back to the top of the list - How are the G50/01 and other variants holding up after this time?

What's everyone using for gear lube?

Thanks...
 
nice set of posts on gearing I intend to adapt a tiptronic transmission to a poly phase electric 400V AC water cooled traction motor producing 240 NM of torque from 2000 RPM to 8000 RPM with a top end of 11000 RPM should be interesting in a 13500 lb car. SO
should be abel to reprogram the control unit to optimize regenerative breaking for ultra caps and battery charging. I will keep you posted as things progress. russell
 

Cliff Beer

Supporter
nice set of posts on gearing I intend to adapt a tiptronic transmission to a poly phase electric 400V AC water cooled traction motor producing 240 NM of torque from 2000 RPM to 8000 RPM with a top end of 11000 RPM should be interesting in a 13500 lb car. SO
should be abel to reprogram the control unit to optimize regenerative breaking for ultra caps and battery charging. I will keep you posted as things progress. russell
Hi Russel, sounds like an interesting project! Nice to see an electric motor application get some upcoming spot light!

13,500lb car? I guess you're planning on including a whole lot of batteries.......??
 
I've been searching the internet for info on my G50 just to compare with what you guys have noted here, and by far this is the best source for plain language,condensed infromation concerning ratios,lubricants and performance mods with references to suppliers, that I can find. One more reason I'm glad I joined this forum a while back. A.J.
 
Hi

Would anyone have a picture of the exploded veiw of the G50 box pref : the 01
Cheers Keron
Keohep did you manage to get the exploded view of the G50 Transaxle you were looking for if so where did you find it?

I need the same thing.

Cheers RobRoy
 

Howard Jones

Supporter
I Have a R21 with the Chris Cole one piece shaft and Quaife installed. The ratios are as follows. 1st-2.66 2nd-1.75 3rd-1.38 4th-1.03 5th-.82 with a R&R ratio at 3.44. With a Torque V8 Engine and max revs at about 6K. These are about as perfect as you can get IMHO.

I cruise (5th) at 80MPH at about 2850 RPMs and that seams to be the sweet spot for my SBF 302. 1st is just low enough to pull on and off trailers and leave stop lights. You can use it to move along in very slow traffic 5-15 mph without changing to 2nd all the time as you would with a 3.4 1st.

On track I never use 1st and seldom 2nd (maybe one corner per track) when it is useful. If you run slicks instead of street tires you will never use 2nd as the corner speeds will go up quite a bit. The taller 2nd is just about right for the slowest corner most of the time. 4th will get you to about 140MPH which I think you will find is about the max speed at most tracks unless you are running Road America or Road Atlanta or have huge HP. If you NEED to go faster then the .8ish 5th will get you to about 170. That's enough, believe me.

Power. A 400HP 375 ft/lb motor will pull these gears easy. I have about 360HP and it's just fine unless I get below 2300 revs off of a slow corner.

Use you gear calculator and see how close you are to these.

1st 2.66 51.9mph @ 6K
2nd 1.75 78.9mph
3rd 1.38 100.1mph
4th 1.03 133.4 mph
5th .82 168.4 mph

3.44 final and a 26.6" tire

Lastly If you don't have a limited slip in the box now, save up some more money and put one in if you run more than 375HP on track of even very briskly on the road. Best performance upgrade you can do after very good tires.

If you spare money on the gearbox then the entire experience is effected. The wrong gear will always be the wrong gear. Spinning the inside tire will always spin the single tire without a proper LSD. Get the gearbox right and you have gone a long ways towards getting the whole car right.

Save the money on Trans-axle coolers, lines and pumps until you know you need them. Install a oil temp port and the fittings for the cooler system in the gearbox when you have it apart and cap them, then you can go from there later. You will not overheat the box on the street no matter how hard you drive. It takes at least 30-40 Min's of track time on a 100F day to begin to heat mine up beyond 180F gear oil temp. I have very seldom run my cooler. Never on the road and only once in a while on track. The sessions are just not long enough to build up a lot of heat.

On the other hand I do have a Quaife TBD and I believe that they do not generate as much heat as a clutch pack type LSD.

By the way I put nearly the exact gear ratios and Quaife TBD in my G50 that is in my SLC, I like them so much. (plumbed for cooler and caped for now).

Spend the money you do have on the gear box and spare it on other more upgradable things you can do later. You won't regret it.
 
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