mark kibort

Since there has been a lot of hotly contested subjects with debates ranging from Gear ratio effects on acceleration to what oil to use, I thought i would take the heated discussions that stray away from the subjects that are being discussed in case anyone wanted to delve more into them for better understanding or comparisons.

The discussion here should be polite, respectful and filled with only facts/theories. Humor is always welcome as it takes the dryness out of some of the topics.

some of the possible discussion topics could be:

Gearing as it effects HP and relates to available HP.
HP vs engine torque
928 Oiling issues/crank-Piston design
suspension set up and design
928 Stroker engine design
928 Braking forces and Power
928 engine building components and tuning
Race-craft video/comparisons, techniques
tires
effect on HP for different weight wheels , tires and flywheels
performance comparisons to other cars (928s and others)

Any others are more than welcome.

mark kibort

There was some talk about changing the rear end only of a automatic 928 transmission to get better acceleration.

in a nutshell... as i have said many times before, gearing doesn't give HP. it only optimizes the HP you have. its a series of trade off per gear. gear spacing is really the only way to gurantee better HP utilization. so what does a lower rear end give you? it provides an entire shift of the gear ratios up or down. in this case of putting a 2.75 on a 2.2 gear box, the entire gear set is brought down by about 23% . this means, your shift points are lower by 23% and your torque in those gears go up by 23%. it also means that the speed after each shift is at an even larger disadvantage for a period of time to make the end result no change in overall acceleration. However, if you have a specific speed range you spend most of your time at , it can be quite useful to go back and forth between rear end options.

example: if you want to spend most of your time at between 90 and 115mph, the 2.2 5 speed is optimal because you would be using its 3rd gear in an ideal way. however, if you want to have more acceleration between 75 and 95mph, the 2.73 gear boxes and their 3rd gear work better there. same thing happens in the lower speed ranges. and there are trade offs along the way. if the rear end is changed alone, this 23% change from a 2.2 to a 2.75 can almost equal the natural spacing of the gears themselves, creating a super low 1st gear and a no change of final gear (5th is basically the same ratio as the previous 4th gear) . but the changes of the entire gear box from a 2.2 to a 2.75, will only shift the entire gear ratio set by about 13% down, with 5th dropping the entire 23%

something to think about when wanting to make a change of gear box or change to only the rear end ratio.

stuartbrs

Hmmm the improbability drive seems appropriate for this thread.. from that tome of Physics, the Hitchhikers Guide.

"The principle of generating small amounts of finite improbability by simply hooking the logic circuits of a Bambleweeny 57 Sub-Meson Brain to an atomic vector plotter suspended in a strong Brownian Motion producer (say a nice hot cup of tea) were of course well understood — and such generators were often used to break the ice at parties by making all the molecules in the hostess's undergarments leap simultaneously one foot to the left, in accordance with the theory of indeterminacy.

Many respectable physicists said that they weren't going to stand for this, partly because it was a debasement of science, but mostly because they didn't get invited to those sorts of parties.

Another thing they couldn't stand was the perpetual failure they encountered while trying to construct a machine which could generate the infinite improbability field needed to flip a spaceship across the mind-paralyzing distances between the farthest stars, and at the end of the day they grumpily announced that such a machine was virtually impossible.

Then, one day, a student who had been left to sweep up after a particularly unsuccessful party found himself reasoning in this way: If, he thought to himself, such a machine is a virtual impossibility, it must have finite improbability. So all I have to do in order to make one is to work out how exactly improbable it is, feed that figure into the finite improbability generator, give it a fresh cup of really hot tea... and turn it on!

He did this and was rather startled when he managed to create the long sought after golden Infinite Improbability generator. He was even more startled when just after he was awarded the Galactic Institute's Prize for Extreme Cleverness he was lynched by a rampaging mob of respectable physicists who had realized that one thing they couldn't stand was a smart-***."

Randy V

Speedtoys

linderpat

Mark - the only one hotly contesting any of these things is you

jcorenman

Brilliant, exactly on topic.

And may he rest in peace: Douglas Adams, 1952-2001.

CJ8 2 928

Mark in a nutshell can you tell me the advantage or disadvantage of an 89 rear end ? tks

GregBBRD

Thread correctly titled:

Kibort turns ridiculous theory into fact once everyone else gets tired of arguing the absurd and gives up."

James Bailey

This has to be one of the funniest comments in years......

SeanR

Besides that they are now 26 years old and most likely graduated college?

FLYVMO

Most likely they have been "driven" hard too during those college years...

mark kibort

really? you havent been paying attention. there are those that have others that back the incorrect to make it correct. just because a bunch of people believe something... doesnt make it true.

you have to tell me what you want out of the car and i can then tell you if the gear box is correct. there is a reason that for most pro teams they have different ratios for every type of track. sometimes lower, sometimes higher ratios
Your last statement in the discussion of forces on the driveline where you say forces are limited by the traction, and fact that there are more forces on the driveline due to gear rations and vehicle speeds . What you said, was perfect for you .. you said that its above your " paygrade". you are absolutely right. you know it all greg and are unable to learn a one fact more!

if you dont know something, you dont have to mock it.. why not discuss and try to understand it?

GregBBRD

The force on the drive train is limited by the amount of traction the rear tires have, on one end, and the force that the clutch can hold on the other end.

This amounts to 400-450 ft. lbs....on the very best of days.

There is no other magically "Kibort" force involved.

But you will argue that until the sun doesn't rise...just because you don't like to be wrong.

No one here has the energy to argue with you until the end of time....so we just give up. Once we give up, you immediately think that makes your ridiculous statements fact.

That's why this thread is a complete waste of time!

hwyengr

Dear 928 Forum technical experts,

Nobody will doubt your positions as the pre-eminent minds in the field if you let Kibort's theories go unchallenged. All he does is double down anyway. If you've got him on ignore, trust that impulse.