kooky trans fluid question

[speeder]

Been reading all of the trans lube threads and it reminded me of something; a while back a Porsche tech with quite a bit of performance/dyno experience told me that you can gain 2-3 rear wheel HP by underfilling 915 10mm.(below fill hole). Said that there was still PLENTY of safety lube-factor.

I'm sure someone is laughing at this, it's OK, but I figure this is the crowd to ask. Anyone with a trans leak notice your car getting quicker?

[cim]

porsche put the drain hole at exactly that position for a reason

[speeder]

Yes, and the reason could be required amount of lube plus 20mm. of "safety factor". We know these cars are over-engineered and that's why we love 'em.

[Early_S_Man]

You would never be able to 'feel' a 3 hp, or even measure it with a stop watch ... unless you were measuring 0-140 mph!

Obviously, a dry-sump system and oil cooler for a 915 would reduce drive-train losses in the transaxle, but it takes hp to run a pump, whether mechanical or electric!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[pjv911]

sounds very logical that the hp gain would happen. I also feel that a 3-4 hp gain at the rear wheels is something you will feel if you drive your car more than once a week.
A little hp here and a little there can ad up to alot of hp. Only thing thats questionable is will the unit be properly lubricated and cooled with less fluid.

[speeder]

One would not feel three rear-wheel HP? And we're spending a couple of grand,(SSI conversion), for maybe 10 flywheel ponies?

Maybe you are right, Warren, I'm just asking. I never understood why they took the power windows out of the Carrera CS. How much weight can that save? Like if I throw my backpack out the window I'll be faster?

[pjv911]

speeder why dont you ask warren if running your engine 10 quarts low on oil would give you seat of the pants power you can feel?

[speeder]

pjv- I don't understand your(second) post?
I would need to study a cut-away of 915 and understand oil distribution system in order to see if guy was full of *****. Or get a reply from someone who actually works on 915's. Since my trans does not have an oil pump, I'm assuming that it all works by splash from differential/lower shaft, and we are talking some heavy weight oil here. How much extra safety factor is there?

I was only half-joking about backpack- how much weight would translate into losing/gaining 3 REAR WHEEL HP? (More significant than engine measure, is this correct?)

Without naming source of claim, I will say that he has over 20 years of Porsche-tech experience, first at dealer then independant shop and racing experience. He has rebuilt 915's for this amount of time and claimed actual dyno results, not speculation. Also, we are talking about 10mm below plug, not a half-filled transmission. Only reason I'm questioning it,(besides my natural scepticism), is that guy has other unconventional opinions. He is either brilliant or a nut, I don't have enough tech knowledge to know for sure.

[pjv911]

I was just being sarcastic about the 10 qrts low part.
I do however own a import performance shop on long island in which i have a chassis dyno. I can tell you that 3-4 hp at the wheels is something you should notice if you have a good feel for your cars performance.
And yes you transaxle uses the rotational monentum to circulate its lubricant. When there is less to chern it will definetely free up some more ponies.
If i wasnt overloaded with working on all the jap crap turbo cars I would try the comparison myself to see if the gain is 3-4 hp as figured. Maybe in early january if the roads are clean i will drive my 911 in and try it on the dyno, But by then this will be a old topic and would only be shot down by all these know it all antique mechanics who live to answer all the posts. If i do it i will post it i guess.

[Clark Griswald]

Seems like an opportune time give a word of thanks to the the "know it all antique mechanics" who have helped so many board members fix countless problems. And the only thing they get for the effort is the knowledge that they helped a fellow 911 owner out and the perhaps the respect of most members of this board.

Good job.

[pjv911]

Well said clark.

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69`lightweight
RS carrerra clone

[Superman]

I say thanks to Warren also, and I hope no one consider me an antique. FWIW, it is my understanding that it would take an unusually sensitive @$$ to detect 3-4 hp even at the rear wheels. You probably cannot measure it with a stopwatch from 0-60, As Warren says.

I think removing the spare tire would result in a more pronounced performance increase.

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'83 SC

[pjv911]

If thats what warren says then by all means it must be unmeasurable. Maybe we should all just leave well enough alone and leave all the research and development stuff to people like yourself.Besides its way to big of a job to drop the fluid level 10mm in gearbox isnt it. Removing the spare tire is much easier. Just imagine if you did both then maybe your sensitive @$$ could feel it.


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69`lightweight
RS carrerra clone

[speeder]

I don't know if this is correct formula, but my SC has about 17 lbs./HP. (It is stock). So if spare tire weighs approx. 50lbs. you would be right, Superman. (If weight gain/loss :HP are that interchangable. Are they?)

If this formula is correct, then SSI conversion @ 2G's for exhaust, muffler, oil lines and labor= 10HP=170lbs. If this is true then after you do the SSI's, you take your 170lb. buddy for a ride to show off your new improved 911 and there is NO IMPROVEMENT to show off! (Other than sound, of course). Point is; weight/HP are NOT that interchangable- I took a 6'6" 230lb. pal on a fast run of Mulholland and very slightly felt the difference in my car. We are talking about a powerful car that hardly knows when it is going up a hill with me in it. Rear wheel HP is significant, and I think that someone with a chassis dyno,(pjv911), understands this.

FWIW, I appreciate almost all of the input on this board and definitely Warren and Chuck. Like I said, I knew someone would ridicule this, I don't care. I am always fascinated by HP that costs 0.

[This message has been edited by speeder (edited 09-29-2001).]

[Superman]

Well, I appreciate the differing views and would respectfully submit the following. If you've got 17 lbs/hp, then you must be carrying your entire family. My car weighs about 2600 lbs, and with 180 hp, it has under 15 lbs/hp. The spare tire is kinda heavy. I can DEFINITELY notice the difference when someone is riding with me. SSI upgrade adds more like 15 hp, and maybe 20, to an SC. Less to a Carrera.

Further, weight loss beats the poop out of horsepower gains. First, it is usually much less expensive. Second, it improves your car's handling and braking as well as acceleration. It's a brute fact that a 2300 lb car can go around a corner quicker than a 2600 lb car.

Here'a another factoid. Gear oil weighs almost nothing (yes, Superman exaggerates). Lift a bottle pint of 90wt next time you're at the auto store. Feels like whipped cream. Petroleum oil is interesting in that the thicker it is, the lighter it is. it's all much lighter than water.

And finally, performance minded people will go to great lengths to get tiny performance improvements so, more power to ya. For me, I'll not run my transmission deliberately low on oil.

Again, I respect everyone here. Even Krazy Kurt. Just expressing my views.

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'83 SC

[Jack Olsen]

Said that there was still PLENTY of safety lube-factor.

He's correct, Speeder. When I got my 911, I took it to my brother's, and one of the first things he suggested I do was to change the transmission fluid. Why? Well, he knows the things. He's an engineer who designs transmissions for Daimler-Chrysler.

Two cups of blackish, maybe 27-year-old goo came out of the thing. I was alarmed that the box was running on about 1/6 the correct amount of fluid. He wasn't. He was concerned about the age of the lubricant, and what showed up on the magnet. He pointed out that the gears would get sufficient lubrication from half the fluid I had. Not ideal, certainly, but enough to function.

10mm low should be fine, in my opinion. Transmissions are designed with the knowledge that most end-users will neglect them. How many Porsche owners change their transmission fluid annually? I'm sure it's a tiny subset. Cynically, my brother pointed out that most transmissions currently being manufactured are engineered to perform reliably for the full length of their warranty period. Not more.

Now, on the other hand, 3 hp is a pretty modest gain, considering the increased diligence about the fluid level that you'll have to maintain until the next change. Taking the spare out is easier.

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Jack Olsen
My Rennlist page • My Pelican Gallery page • My Porsche Owners Gallery page

[This message has been edited by JackOlsen (edited 09-29-2001).]

[speeder]

Superman- I was guessing my car's weight. I dunno what it is without looking it up. Don't SC's weigh like 3 thou and early 911's 2600? At any rate, my spare is an inflatable mini that does not weigh much. Removing it would not equal ONE HP and if it did weigh anything it would be removing weight from the wrong end of car. There is no question that lighter is better, but I think that MAYBE 100 lb. increments might be noticable. I could definitely feel that 230 lbs. extra in my car on the twisties, but it did not downgrade performance as much as I expected. This is why I posed the power window question- that is symbolic only. Like taking a crap before driving and expecting better performance. Just complete BS. Less friction in final drive, however, that you will notice.

Jack- thanks for the input. I had a feeling that was the case w/ fluid levels. Does everyone here know what 10mm. looks like? The reason I am sceptical is because it is such a small amount. I would say, "I wonder if any racers have tried it", but one has for sure- the guy who told me. He did not think it a big deal, sort of an off-hand remark while discussing trans oil.

[emcon5]

The spec book says an 82-82 911SC weighs 1250 Kilos, or 2755.5 lbs. I don't know if I would notice 3hp, (I kind of doubt it) but I do notice a difference if I have someone else in the car. There is a big difference with a full vs empty gas tank.

10mm is under half an inch (.393")

Tom

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82 911SC Coupe

[Superman]

I drive across the scales from time to time (weigh station scales are ON when the weigh station is closed). I usually have to get out of my car to read the meter. It has never weighed 2700 lbs. With 3/4 tank of gas, it weighed 2580 the first time I put it on the scale.

Randy Wells' car, featured in the current Excellence is in a class that requires ordinary stock parts to be in place. Randy elected to go with a lightweight stock carpet pieces.

All auto racing champions agonize insanely about weight. And the tip about tranny oil is another one of those tiny improvements found to try to get an edge. The accumulation of all those small decisions about hp and weight, IS the difference between 1st and 2nd place in serious competition.

It is interesting and believable that trannies can survive low oil levels.

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'83 SC

[Clark Griswald]

10 mm is about 1 cm

One trick used by some drag racers when they need to squeeze out the last few hundredths in a quarter is to draing the differential.

Obviously this shortens life, so they don't do it all the time. And they are only running 1/4 mile. I've even seen a dry sump differential system designed to try and get the benefit all the time.

Drag racers also use windage trays and crank shaft wipers to minimize oil induced friction loss on the crank.

I also believe that Porsche designed the trans fluid level with a healthy margin of safety. I would go as far as to say few owners change their trans fluid regularly, if ever. And they had to plan for some loss of fluid through leakage and evaporation over the trans life.

So it seems reasonable to me that you could safely run the trans oil a bit low, provided you change the fluid regularly. I have no idea how much HP would result from 10 mm. It would be easy to determine the level, just by tilting the car to the side when filing.

Bruce Anderson shows a picture of a 915 in his performance handbook that has been modified with a pump and external plumbing to squirt oil on critical points. Unfortunately he provided very little information, only a picture. The mod was performed to extend the 915 life when mated to a high torque motor.

Seems like an enterprising 911 hot rodder could use a similar concept to create a dry sump (damp sump) 915 with an external tank, pump, cooler, and squirters. That way you run the 915 nearly empty and minimize power loss due to oil friction.

If 10 MM low can get you 3 HP, maybe a real dry sump will get you 6-10 HP.

I would gladly take such an easily had 3 HP. My arse may not feel that one change alone, but combine it with a few pounds of weight loss here, and couple more HP there, and next thing you know you have a fast car.

I have made plenty of little incremental weight reductions, each taken individually are insignificant, but added all up and it makes a big difference.

- remove spare
- remove jack
- remove tool kit
- lite weight battery
- SSI exhaust
- Air conditioning partial delete
- removed front splash tray
- Gas tank never more that 1/2 full
- Take poop before driving

Add it all up race fans and that is approaching 200 lbs savings (and save for the SSI, cost very little). It would take about 15 HP to deliver a similar lbs/hp improvement. My arse can feel that.