Jim bailey - 928 International

Mark...funny cars have no gears minor detail ! It is OK to admit that you are wrong ...

mark kibort

you know what i meant! Yes, wrong about "funny cars". oh, i though it was ALL about gearing. there are gears on funny car, 1 and a bunch of clutches.
Mk

Jim bailey - 928 International

See Mark it was not hard to admit that you were wrong....now just expand on that a bit and accept that lower gears actually make a HUGE difference zero - 30 MPH and a lower final drive means that you have more gears which you can use in a 1/4 mile race ,more torque multiplication, more time with the engine near peak horsepower ... Like I said try doing a quick start using 2 nd gear then compare that to first gear let us all know the results most everything about a car is a compromise to do most things reasonably well but NOTHING exceptionaly well. Some people even strip down a 928 ,remove all the comfort ,A/C , powerwindows , power seats, beef up the suspension fit big tires a roll cage and go road racing ! Imagine that , modify the car to fit YOUR needs.

mark kibort

now you are combining several factors into 1. sure, IF you are able to control wheel spin, then yes, 0-30mph in .5 seconds you would have a better launch. BUT, if you use a given transmission and just shift the curve up or down, you dont know what you will get in the end. Part of racing is analyzing all of the variables for a given set of conditions. (ie hp, traction, weigiht, distance, etc)
that 0-30mph in 1st gear may work for 400hp, but may not work for 500hp, expecially since you are spending time focusing on the start, and most of the time spent at max hp is near the end (not to be confused with how important the start is, but all things being equal, like reaction and traction, the start is not the most important thing because of how short of a time that potential gearing advantage would be applied. and if you sacrificed the final gear of a 1/4mile, you could end up getting passed pretty easily.

if you can have it all, then yes, a low first gear and gears spaced close enough to apply the max hp to the wheels possible, and end up at the end of a 1/4mile run at near redline!

If you see my example above, you can see that a 50mph top speed in 1st is not that uncommon for drag cars. for our stock-ish 928S4s with near 400hp, the stock gear box is best due to the fact that redline in 3rd gear is near the estimated trap speed of 118mph, which would equate to a low 12 second run.
any faster, and some seriuos attention should be paid to the gear ratios. with a GTS gear box at 125mph, you would need 500hp to take advantage of it

mk

Jim bailey - 928 International

Mark...'but all things being equal, like reaction and traction, the start is not the most important thing " Please tell me you do not really believe that !

6.0-928S

50 MPH IN FIRST GEAR IS VERY UNCOMMON, IF NOT UNHEARD OF, FOR A DRAG RACECAR. PERIOD. You no sooner get past the tree & it's time to shift.
I wouldn't think of trying to tell a road racer about road racing. You should not try to talk for drag racers.
Jim, save yourself, run away, run far, far away!

Hammer

mark kibort

Yes, my first look at it would be to believe it.

remember, i know the start is MOST important. Im not double talking here, im talking about application of HP. if two cars get the exact same reaction off the light, and both have the same success with applying power out of the hole, a taller geared car will be at whatever disadvantage his gearing will produce.
However, he could actuallly make up for it by having a gear ADVANATAGE in the area of the track where the other car has to shift earlier before the end of the race.

Now, certainly, if you can change gears to optimize all the way, i totally agree, there could be an advantage to having the use of all 4 or even 5 gears over a run. BUT, if you only change the rear end and it gives you the 0-30 edge, but you sacrafice 100 to 120mph over a long period of time, the other car that redlines at the target speed of 120mph (based on the hp available for example) could catch up and pass the lower rear end geared car.

remember we went over this before. HP-seconds applied or you could use ft-seconds. its a energy equation that is pretty basic. the simulaltor is a pretty easy place to prove what im talking about. so far, it pencils out pretty close to what im talking about here.

in that screen shot i just posted, it shows a simulation of a 3200lbs car that is on its way to a 10second quarter. it is shifting out of 1st gear at 44mph.
if you cant control wheel spin (analogous to slip angle in road racing tire performance analysis) then the lower gears dont buy you anything. what would be the limitation . getting a gear box that shifts out at 10mph redline?? at some limit. lower is not always better. there is analysis that goes into gear box selection as it is done in road racing, for which i am very familar with.

certainly correct me if im wrong here, but im talking about the effects of changing rear ends to a higher numerical ratio and having sacrafices in other places if the entire run is not looked at for its effects. certainly there is a rear end that exists for a given car with a given HP and grip that will be right. what is it for a 928, you get my standard answer. it depends. For my car, it probaby would be a 2.2 with my 320rwhp and a target speed of 115mph at the end of a 1/4 mile. I would have 3 gears to work with. However, if i could assure traction, a 3.09 may work well if i get the extra gear for 1st as it looks like my 3rd (now becoming 4th) would be at the same 115mph. I think this is what you are talking about. Now, give me 700hp and suddenly, this package doesnt work too well as now i need 145mph and the time spent from 115 to 145mph is great enough to more than offset the problem the 3.09 5th would have compared to the 3.2 4th of the 2.2. (looking at launch grip as well as hp-seconds, or total ft-lb seconds spent from 115 to 145mph) its a 3.5% disadvantage for the time it takes to go the distance vs the 40% advantage for the time going from 0-39mph.(the 40% advantage is based on equal grip which obviosly there would be a lot less of an advantage . In fact, if the wheels are spinning from 0-39 anyway with a 2.2, it might just be worse with a 3.09.

this is all theory above and an interesting problem.

all i can say is, look at the guys using the 32" diameter tires. if they dont use anything greater than a 3:1 gearing for 1st x the rear end of 4.56, then it will see 50mph in 1st gear at 7500rpm. thats just basic math here.
If a 928 S4 reaches 50mph at its redline of 6600rpm, then both of the cars are geared relatively the same. (and will perform the same if they both have the same hp and hp curve shape) Jim, do you agree?


Mk



.

mark kibort

hey, im just a theory guy in this subject matter, granted!

but, if you look at the screen shot, here is a 10 second ET car, with a trap speed of 132mph , weighing 3200lbs and running in 1.2seconds to 44mph, pulling 1.1 acceleration G's and shifting to second at 44mph. this looks like it would be a street type car,meaning smaller tires, but if it was a 800hp drag car, it may reach 50mph in 1st gear i would imagine.

As a note, he is in 3rd gear to redline and is in that gear for 6 seconds while he is in 1st for 1.2 seconds for a 5x factor. this means if you took this car and geared down his 1st gear by 10% (assuming traction was not an issue), he would have a 10% advantage out of the hole, but in a later shift 4th gear, he would be at a disadvantage, from 118mph to 132mph.(10% lower redline mph in 3rd so now he has to shift to a 4th gear with 30% less of an advantage for longer period than in 1st.) it would net out a higher ET.

mk

Jim bailey - 928 International

NOPE...Mark you are wrong...the simulation is NOT real world. Drag racers measure their 60 foot times ! street cars maybe have a 2 second 2.2 second 60 foot time ! for a 14 second 1/4 mile. That first 60 feet is key to the entire run. I will not respond to this again so go ahead have the last word just do not think that it means you WON, sometimes it is simple not worth the effort .

mark kibort

Jim, i never said simulation is real world, nor did i discount the value of the 60ft time! the start is key, obviosly, you are not reading my post. what I said, was that there are trade offs with a rear end gear change only. you are not listening. Not listening is a form or arogance. it either means you think you know it all, or you dont care.

I only use the simulation to show the trade offs, which are more than a good indication to the effects of gearing. These days top race teams use simulations because they are so accurate. (both drag and street) In fact, they also then coorelate actual telemetry data with simulation to make sure their similations are the best indication of what will happen with change.

If you re-read my post, you can see that i was saying that if only a rear end change is made, you may not be able to gain acceleration due to traction, and even if you did, you COULD have a situation where at the end of a drag, the car that is optimized to redline and putting more HP to the ground at the end of the race, COULD have an advantage. This is the only and main point. This is independant of the many variables of traction on the start dictating the very important 60ft times. Look at the simulation above. this run actually had a shift into 2nd at 48ft!!! obviosly it was geared pretty low too!

The only think i have WON here, is if you can finally agree that changing rear end has varied effects, Not all of them positive. as i aways say when someone asks what the effects will be of such a change, " it depends". If it ALWAYS worked, then what would the limit be???

mk

mark kibort

http://www.dragtimes.com/2006-Ford-M...ecs-11787.html

Again, you post something about 14 second 1/4mile times, yet i was refering to a car with much more hp and times in the 11 to 12 second range.
Here is a Mustang street car with a 60ft time of 1.6 seconds.

eitherway, 14 or 11 second ET, both types of drags have to consider the trade offs before just doing a rear end change. If this is not a slam dunk, just as it isnt in a Road race car. You saw, even anderson with his change to a 2.7 vs his old 2.2 gear box, saw no improvement to his times at willow sprinigs, except he said he was shifting more!


Mk

Jim bailey - 928 International

Mark I think you have been studing this ..."Commonly employed debating technique
Lately I have found myself in e-mail discussions with Induhviduals who employ debating tactics that are very similar. I suspect they are learning these methods in some sort of top-secret Induhvidual training facility.

The Induhvidual debating technique involves four steps:

Exaggerate your opponent's statement into an absurd absolute.
Make an inappropriate analogy.
Change the topic to something easier to defend.
Claim victory. ...." you are still wrong about lower gears ! The old very brown I have tires which range from 225x50x15 up to 295x35x18 and the way the car feels changes drastically with the smaller diameter tires...As I said before try a drag racing start using second gear it will help you understand ...
the concept in the real world

928FIXER

Just put the lower final drive ratio in...You'll love it.It puts the power to the ground at speeds that won't send you to jail!
I swapped in a 4 speed auto with a 2.75 ratio that came out of the 3 speed matic into my 230HP US spec 79 928 and made a screamer out of it.Hazes both tires(yes locker)and goes sideways if the road is crowned,just screams to redline and barks both tires on 1-2 and 2-3 upshifts.I can't wait until I get time finish the repaint and drop in the 300 hp euro motor.

mtcarrera

I guess I don't know what is meant by a "lower power band", since power is supplied by the engine, not the transmission. If you mean lower gearing, then there is a fairly straightforward answer that will lower 1-4 by about 18 percent and leave fifth the same and not involve the ring and pinion. This is a MAJOR improvement for the earlier cars which provides acceleration improvements that equate to a 40-50 horsepower increase. If this is what your're after, post back and I'll post an explanation.

mtcarrera

And, upon re-reading the original post, an 85-86 car woud indeed have to to a ring and pinion change to lower the overall transmission ratios. The very early cars, however, can change to a later "fifth gear" and get the advantages outlined above. Did it, LOVE it.