JKelly

Your car's weight and tire width will make up for the initial benefit of the 3.09.

Not to put you on the spot for being the one to go out and do this, but ever since people started posting their 1/4 mile slips on here, I have wanted to see what a race prepped 928 could do at a drag strip (non-supercharged). Probably many others too.

If I were going to drag, or even drive to the grocery store , I would put my $3000 into an SC, then I would put it into wheels and tires, then I would put it into a ring and pinion.......by that time I would be about -$8000 in the hole.

Dreaming about it is a lot cheaper.

Daniel Dudley

Mark, I've never done a 3300 RPM launch, Not to mention a 4000. Seems a bit brutal for a street car that I want to enjoy with minimal maintenance issues. But here's the Question anyway. What is the tecnique, and how does it affect clutch, driveline etc. I'm getting that you do this all the time. Given that most of us don't ... do you see where I am going here ? Any how, I am interested in launching and powershifting - even if I may never do it.

mark kibort

Scott and all,

I hear what you are saying, and much of the 3.09 will be subjective to usage. what i can tell you is that the only difference will be in the new sub-1st gear with a 12.5:1 ratio. after that, if i read your post correctly, its all the same.
you speak of a 2.75 or a 2.54 for the track, and again, ill tell you, it depends. The feeling i get from many of this discussion, is folks think there is some total gain that ALWAYS is there as soon as you get a numerically higher ring and pinion (ie 2.75, 2.54, 3.09 vs a 2.2) What folks seem to forget is first, its not just the rear end,its the end result in ratio. (rear end x transmission ratio) second, there are many trade offs as we have discussed in the past. the real answer for rear end changes is, "it depends".

You say , the higher the rear end ratio " the faster things happen" and this is not correct . again, with a 3.09, the only "faster " thing that will happen is potentially your launch to exactly 39mph. after that, nothing happens any different . as the subsequent gear ratios following the 3.09 vs a 2.2 after the sub-1st gear, are exactly (close) the same. All this is based on the assumption that a driver can take advantage of the 25% more average hp to the wheels over that gear range (not the 140% that one would first think due to the mechanical advantage of 3.09 vs 2.2) This is also do to the intimate relationship between torque to the wheels , through the gearing (ie HP) over a curved shaped rpm range. (ie torque changes from starting rpms to ending rpms, as does the HP) you can integrate the values with high resolution to get an accurate representation of what is actually available for accelerative forces to the rear wheel. You also say “ as I dump the car from 1500rpms “ 1st, I doubt that anyone just accelerates from 1500rpm as it is a controlled dump of the clutch from about 3k range and metering wheel spin. You say you get to redline and back again and there again to. Meaing you have 3 shifts to my 55mph. Hmm, I have to wonder how much is due to 6.5 liter and not the 3.09. remember the ONLY differernce of a 3.09 vs a 2.2 is the sub first for a net difference equivilant to 60hp ONLY to 39mph. (26% gain in HP/torque to the wheels, to 39mph)

The interesting thing about vehicles with powerplants coupled to gearboxes, is that they dont follow any real engineering convention. what i mean , is that in engineering school, you learn the concepts, and apply them to applications that are actually more straight forward. electric motors, other engines in other uses dont have variable fixed ratio gear boxes, and most are matched to their application using a 50% safety margin to avoid problems. in my teachings with teams of degreed professional engineers both mechanical and electrical, and many with even higher credentials, they absolutely understand the formulas, concepts better than most. (as i said before, many have forgotten more than ill ever learn) BUT, when it comes to applications such as our discussion, its amazing how they have to be reminded of what they already know.) Ive had this exact same discussion with these guys, even as recently as last week, that had some of the same assumptions as we have talked about here, only to have them end up on the same page after a few mins of white board talk. my specialty is power transmission systems. all we deal in my company with is servo, stepmotor, and ac motor variable speed motion systems, that can be closed, open loop, torque driven, speed driven, position driven, etc! this stuff barely scratches the surface, but is the foundation of many of our professional discussions.

The main point here is that gearing doesn’t provide HP. HP is what gets you to from point A to point B. Gearing only provides the efficiency for which the HP is applied.
With the 3.09, there is a more efficient use of the hp to 39mph because more of the hp is applied to the wheels over the speed range. PERIOD. All you need to do to check my work here is to grab any torque at any speed with ANY rear end, map it to the speed range and get the answer. Ive already done this for this example.

One of the things that Msniper said was interesting. He said there was some kind of “stored energy gain” in the 3.09 gear that carries on to the other gear rates of acceleration. If the rate of acceleration is higher from 0-39mph, as soon as the gas pedal lifts, acceleration is 0. at that point, the 2.2 with the 8.9:1 1st gear has the same rate of acceleration when it gets to the same speed (rpms) as the 3.09 with the 12.5:1 sub 1st gear. Theoretically, the 3.09 will have a small lead all the way to the end, and have an overall faster rate of acceleration based on the advantage in the Sub 1st gear, because it had the lead at 39mph. All rates of acceleration at an speed after that would be the same. So, when folks say that the 3.09 helps in all gears, or that you can feel the faster rate of acceleration ,they are just fooling themselves. Take one look at the ratios of the overall gear box, and compare them. Actually after 39mph, the S4 with 2.2 has 2 of the remaing 3 rations with BETTER acceleration rates due to slightly lower gear ratios past the sub 1st gear of the 3.09. (ie 8.9 vs 8.3 in the next gear, 3.09 vs the 3.2 :1 ratio of the last gear of the 3.09 gear set up, and the middle gear of 5.9:1 is identical)

This discussion has been more constructive than the last.
However, there has been some incorrect concepts presented and ive just tried to correct them and produce the net potential gain of such a modification . Its not a gain overall. It’s a gain in the Sub 1st gear range of 26% to 39mph (or 60hp on a 300hp car) after that, no difference. I have always said, that it has the potential for better launch and acceleration than a 2.2 from 0-39mph. That has never been in question (however, I have interest in seeing it applied.)

Mk

Tom. M

Mark K wrote:
hammer, do you really think a .1 of a second is going to put someone in your rear view mirror.

I was watching some drag racing on ESPN recently and 0.01 secs...was close (as in a wheel or so diff)......0.1 secs was an eternity (In the drag racers world...)...yes..almost a car length...

Later,
Tom
89GT

mark kibort

i spent some time doing this yesterday. yes, its brutal. can only imagine how long those CV or half shafts would last doing it repeatatly.

however, the 3300 or 4500rpm launch differences for the 3.09 vs the 2.2 is keeping the wheel speeds idential. meaning, if you dump a clutch at 3300rpms in a drag, for all things to be equal, it would be 4000rpms plus to keep wheel spin starting speed equal.

I certainly have a respect for a guy that can do this well. its so easy to spin the wheels uncontrollably drag racing with our cars . (or any car) this is the real art of drag racing and im sure, with practice, the 3.09 would help here too (if the geartrain can take it! However, the 25% gain from 0-39 and less than 10hp gain overall for a 1/4 mile drag, all for $3000 seems a bit pricey

MK

mark kibort

we are not talking 4.99 second 1/4s here, we are talking 12 second 1/4 miles where .1 second is a half of a car length. that doesnt put someone in your rear view mirror does it?

MK

Tom. M

All wrt. perspective.....Depends on how you have your rear view mirror adjusted...hahahaha.......

Either way...first across the line wins...no matter what gearing....

Later.
Tom
89GT

GlenL

Waiting for the wife to come home. Got a few minutes.

Snips not noted.

A manual gearbox is very straightforward. What the education provides depends on what elective you take in the last year. Only takes first-year physics to master this stuff. We're not talking fluid mechanics or astrophysics here.

Wandering off a bit here, Mr. Kibort. Velocity gets you from A to B and that's the integral of acceleration which is the result of force. Based on previous discussions I know you're a "power integral" thinker. That's fine. I'm a "force" person myself. It's more elemental. As they say, "F=ma and everything else is derived."

The practical effect of gearing is, as Mr. Ott stated, to select the output angular velocity, and torque, of the tranny. This sets the RPM of the engine and the force at the contact patch. It's not about "efficiency" per se.

m21sniper

I already have a hi-stall converter though.

Heh, i'd love to swap in a 4.09 ring and pinion to go with my 2500rpm stall converter.

LOL...what a total 1/4 mile beast i'd have on my hands.

m21sniper

.1 sec is 14.8 feet for a 14.0 flat car.

14.8 feet might as well be a mile, so yes, it's a LOT. But then, 1.48 feet is all it takes too.

Any gain, even 2hp or a loss of 20lbs, is worth the effort if it puts you in the winners circle.

Shaving 100lbs only nets ya about .1 in the quarter too(though it is a floating value). Anything you can do to improve the power to weight ratio of the vehicle is definitely worth the effort.

PS: Hammer, i cleared out some space in my PM box. Sorry bout dat.

Ketchmi

"however, the 3300 or 4500rpm launch differences for the 3.09 vs the 2.2 is keeping the wheel speeds identical. meaning, if you dump a clutch at 3300rpms in a drag, for all things to be equal, it would be 4000rpms plus to keep wheel spin starting speed equal."

Uh Mark, what would the torque value difference be between 3300 and 4500? Also, multiplied by the final drive ratio, what is the applied torque to the ground? Wheel speed doesn't matter in this, it's applied torque if traction is not a consideration. Once again, just for Mark, IF TRACTION IS NOT A CONSIDERATION. For the math challenged, multiply the torque output at 3300 times 2.2 for the applied torque. Then again, multiply the torque value at 4500 times 3.09 and see the result.

Then to make things equal, multiply the torque output at 4500 rpm times 3.09 vs. the torque output at 4500 rpm times 2.2 and see what applied torque you have.

Apples to apples, engine torque at 4500rpm X 2.2=how much applied torque and engine torque at 4500rpm X 3.09= how much applied torque. Given traction is not a consideration, which car is going to acellerate better?

And I told myself I wasn't going to be drug into this one...

Imo000

This is where your lack of experience in 1/4 mile racing becomes evident. Wheel spin at launch is always necesarry. The hard part is to be able to get just enough to get the best lauch possible. The last thing you want is slipping the clutch and frying/over heating the disks. Spinning the tires should act as a clutch. Even the top fuel dragster spin the tires at launch (I not talking about staging). If you think this is easy, go give it a shot. Track conditions change by the minute and sometimes the use of traction compound (traction spray) will make tire spin extremly difficult to predict. Wheel spin is good, both for the drivetrain and for the ET.

mark kibort

Hey, i hear ya!!

i would think with that little bubble on the side, you could find me there, but hanging in there (all things being equal besides the 3.09!)

MK

mark kibort

how do you do that snip thing??? (computer challenged!)

Not going to get way into this, as I know you have always been a force guy.
sure, F=ma. I know this stuff is not complicated, however, with a gear box involved, there is a certain amount of not conventional thinking needed to understand the integrate HP used by car over a period of time (or average torque used or needed over a period of time and at a the different speeds. (kind of a definition of HP by substitution) . what i have found with most engineers, is that they seem to forget that the gearing is variable to a certain extent (number of gears, closeness, etc) and after they are reminded that its the integrated Hp over the speed range that acclerates the mass, they get it. Its all about trade offs with gearing, and speed ranges.

time and time again, someone thinks that just putting a lower rear end gives you better acceleration over infinite speed ranges and this is just not true. as we discussed with the 2.75 box and the 2.2 box, depending on the range of speeds used, and the gear box spacing is near identical to 4th gear, there can be no difference, depending on the speed ranges used. I made the mistake of saying " There is no difference with a certain gear box change over an infinite speed range" what i should have said was that at certain speed ranges, there can be a significant difference either way. agian, it depends.

yes, we all know now, acceleration is the first derivative of velocity. do you think a run on chassis dynomometer gives torque for which HP is "derived"? it measures change of speed of known intertia, and then actually calculates torque. based on the spark signal, it can then give you a torque calculation, other wise it will only give a HP number and a MPH number for the run. without knowing the engine speed, you only get HP. after getting a spark signal, it then automatically gives a geared , back to the engine, value. (kind of diverging here, but its part of the concepts)

I can reword the "efficiency" functionn of the gear box by saying it is used to help the system realize more of the potential of the engine's HP . (efficiency was just an easier to conceptualize term)

what louis said, basically defines one of my loose definitions of HP. it's resultant torque found through the gears. Good example, find any equal hp point at any speed of two vehicles , and you will find the same torque at the wheels, regarless of engine torque and gearing. think about that one for a second. So, the more you can put max hp to the wheels over the operational speed range, you will have the most torque to the wheels for more of the time.

mk

mark kibort

Uh Dave, you are seriously getting poor grades for reading comprehension. (unless you missed that post, If so ill post it again) Ive already given you the exact torques for a 3.09 at 4500rpm (x 3.09) and the torques of 3300rpm with a 2.2 (x 2.2). the difference over the speed range (3.09 going from 4500rpm to 6500rpm) vs the 2.2 going from 3300rpm to 4500rpm) was 26% . so, based on equal wheel spin control, the difference is 26% or 60hp from 0-39mph. I think ive said this 100 times now. ive aways assumed we would have equal wheels spin or talent behind the wheel

what part of this am i not making clear? and, how did you miss this the first time.

what you left off below was what i already provided. the average torque or hp in the two speed ranges . integrate over 100 or 500rpm periods and you get a pretty accurate representation. I did one comparison for HP and one for torque ( speed range 3300 to 4500 on the 2.2 and 4500 to 6500rpm on the 3.09) their has never been a doubt about the increase of available hp or torque. what was in debate was.
1. the amount of effective benefit , that being a calculated 26% to 39mph
2. that there is no differnce past 39mph, as the subsequent ratios are the same
3. there is no cumulative /stored energy benefit after 39mph (as MS sniper mentioned)


MK