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Transmission and average HP!

If we can increase our average HP per gear we end up with a faster car.

There are several basic ways to increase average HP, make more peak hp, narrow the gear spacing to stay at a higher HP level, or build a motor with a wider power band.

Just changing the first to second gear spacing can add about 30% more HP at the 50mph shift point! Try to get that with any single motor mod.

Assuming a shift point of say 6500rpm and assuming 400chp-- I think we see 'about' the following relationships with a stock transmission:

At 15mph when we are accelerating from a stop we are at 2000rpm and making only about 60hp (no boost).

By 25mph we are pulling 3200rpm and on a good quick spool motor making about 180hp (full boost?)


With 1st to 2nd shift, we drop from 6500 to 3800rpm at 50 mph and from about 400hp down to about 260hp. Thus a total of 2700rpm drop and a 55% reduction in HP with the shift. Again, our HP runs from 260 to 400hp in second.

2nd to 3rd: drops to 4600rpm at 90 mph and 330hp with a 1900rpm drop. Thus our HP runs from 330-400hp. Not bad.

3rd to 4th: drops to 4700rpm at 130 mph and to 340hp with a total 1800rpm drop.


The biggest challenge seems to be the big rpm drop between first and second gear. Some 75hp or 30% could be gained if we had the same rpm drop going to 2nd as to 3rd and 4th. This should make a big difference in acceleration just past 50mph.(Freeway entrance speed.)

I have heard is said often that gears can "transform a car"! This seems to help me understand why this is.

Just something to think about.

Last edited by 911st; 02-24-2010 at 08:52 AM..
Old 02-19-2010, 10:00 AM
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Old 02-24-2010, 08:56 AM
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Nice Keith,, now you've given us another area to contemplate and conclude we won't be happy until we throw some more time and money at it!!! ;-)
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Old 02-24-2010, 12:37 PM
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Sorry Todd!
Old 02-26-2010, 09:17 AM
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Keith,

If I had to remove all but one of the mods I've done to the Old Sled the trans mod would be the one that would remain.

Cole
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Old 02-26-2010, 11:03 AM
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Just put a 915 in and be done with it, ha!

I actually never look at HP on the dyno, I really don't care what it is. I look at torque. Proper gear spacing will let you drop from redline into the meat of the torque curve on the upshift. By making the torque band as wide as possible you can accommodate larger gear spreads, so you grow into the stock 4spd.
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Old 02-26-2010, 11:46 AM
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Yes a 915 has lower ratios that maintain the motor at a higher average HP.

People mistakenly think Torque is what accelerates a car. Not really. Power dose.

It dose not matter if you make power at low rpm or high rpm. 300hp is 300hp.

However, one car that makes 300ft lbs might make 200hp and another that makes 300 ft lbs might make 400hp. With the best gear ratios it each car the second car is going to be a lot, lot faster.

Yes more TQ makes more power but more TQ at a higher rpm makes much more power.

Torque is just a mesurement of how much power our motors make from only three cylinders firing over 360deg of operation.

Torque is nothing until its effort is multiplied first how many events can be fit into a period of time (RPM) and then such power output is further multiplied by the leverage of the transmission (gear ratios).

It is however a good point of reference to as to how efficent our motors operate (VE) and where they operate the most efficently. Thus, it is as noted it is good to study carefully one's TQ dyno plots.

In some cases setting up a transmission where it drops RPM to TQ peak(old rule of thumb) will be a fast set up. However the true goal is to keep ones average HP as high as possable.









Now, if we decide to stick with a stock 4 spd transmission, we would want to build a motor with as wide of a HP curve as we can.
Old 02-26-2010, 04:10 PM
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I understand torque. Peaky HP sux on the street. The broad flat torque curve of a V8 will destroy a peaky 6 cylinder with the same WHP. That is where the turbocharged F6 shines, it behaves more like a V8. If you are building an engine for the 930 4spd you need as large and fat a torque band as possible. The gearing is not close enough for a peaky HP engine.
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Old 02-26-2010, 06:51 PM
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Brian,

The points I am trying to make are:
Quote:
If we can increase our average HP per gear we end up with a faster car.

There are several basic ways to increase average HP,

make more peak hp,

narrow the gear spacing to stay at a higher HP level,

or build a motor with a wider power band.
In support of that, and to begin what I thought might be a fun topic, I did a fair amount of number crunching, referencing of gear charts, looking for & referencing a representative dyno chart, and study to come up with some very specific info that helped me better understand a little bit what is happening with a 930.


In reply I believe your points so far are basically:

1) Put in a 915.

2) Achieving highest average HP per gear is not important and one "should look at Torque".


I am thinking most built 930's are going to make enough torque to brake a 915 at some point.

And as to the Torque v HP, all motors make torque and horsepower so one can not build one motor to make Torque and build a different one to make Horsepower.

As such and to be even more literal, torque is not a good measure of what accelerates a car. Horsepower to weight is.


If you mean to infer:

A 915 has better (tighter) gears that keep the motor operating higher in the power band more of the time.

And -- that building a 930 that makes as much power as possible in the low to mid RPM range over building for peak HP, makes for a faster car.

If so, we are saying the same thing but just differently.
Old 02-27-2010, 02:13 AM
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We are saying the same thing but just differently.
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Old 02-27-2010, 05:43 AM
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Quote:
Originally Posted by 911st View Post
And as to the Torque v HP, all motors make torque and horsepower so one can not build one motor to make Torque and build a different one to make Horsepower.
The fastest cars are the ones with the most area under the torque curve, the late John Lingenfelter lived by this rule.

If you look at 3 turbo cars like a Mitsubishi Evo, Subaru WRX STI, and a BMW 335xi, they all sit around 300HP, but the BMW has a torque curve that is literally flat from 1500-5000 RPM (artificially so). In turn, it's faster 0-60 and 1/4 mile than both the other cars. What's more interesting, is recently they have dropped the twin turbos, and gone with a single twin-scroll turbo and still accomplished the same thing. Some early tests even have the single spooling up sooner than the twins, and pulling to the same redline.

That would be perfect combo for a 4-speed tranmission, and a model to strive for, but way too much technology to retrofit to a flat 6.

Keith, you owe it to yourself to test drive a BMW 335i or 335xi, impressive torque!
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Old 02-27-2010, 06:21 AM
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911st wrote;
"Now, if we decide to stick with a stock 4 spd transmission, we would want to build a motor with as wide of a HP curve as we can."

I respectfully disagree with the whole premise of tailoring an engine to fit transmission characteristics. To be kind, you are being penny-wise and pound-foolish. Who would build an engine to meet the characteristics of a transmission, when it is more cost effective to change gear ratios, ratio spacing, R&P to achieve a desired goal?

Gear ratios are a means to an end, implemented to achieve a stated goal, achieving optimum performance (MPG, E.T., Lap Time) for its stated environment. Be it street, highway or track, a transmission is selected AFTER the engine design is complete, not the other way around.

On the whole HP vs. TQ thing.....simply put, Torque GETS you there(i.e. acceleration), Horsepower KEEPS you there (MPH). They are interrelated. Transmissions are TORQUE multiplication devices NOT HP multiplication devices.

Rant over.....sorry.
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Old 02-27-2010, 07:02 AM
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Keith, buddy, not sure I agree with you at all about Torque v Power. Here are a few equations for you:

(SI Units)
Torque = Force x Perpendicular Distance
Power = Force x Velocity
Force = Mass x Acceleration

(Imperial Units)
And Power = Torque x RPM/5252

To my understanding, it works that Torque gives you Acceleration, whilst Power gives you Top Speed...

But anyway, more interestingly (and with complete sincerity) is the word "dose" (in American English) the same as "does" (in British English)?.. Or is this just a little typo? You catch me out sometimes when I'm reading your posts! To me, "dose" fits in the sentence "a dose of salts", "a dose of insulin", "a dose of morphine", etc. etc.

I'm honestly not 'taking the piss', I just struggle to translate sometimes! (I know, for example, 'color' = 'colour' and 'center' = 'centre', etc. but this is a new one to me.)
Old 02-27-2010, 09:10 AM
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Dave,

I mostly agree, that sentence got left behind when I was a hurry to get out the door and did not mean to leave it in undeveloped.

However, most 930 builds here are within some type of constraints like keeping CIS over going with EFI.

If we start with a clean slate and open budget we probably want a 6 speed dialed in to how we are going to use the car. If not, a 5 speed with tailored ratios, if not better gear spacing on our 4 spd.

If not-- maybe we should at least be sensitive to the limitations of the stock transmission gearing when making other mods and trying to shoot for a fat power curve as possible so that 2700 rpm drop going from first to second dose not leave so much potential on the table.


WinRice,

I grew up dreaming about Lingenfelter. He was the master of not only increasing the VE level of a motor over anything his competitors could but also doing so over a wide power range. He could have built motors to have made even more impressive gross HP numbers if he wanted.

However, if anything his builds are a lesson in building a motor with a wide power band that would work well with existing gears than building a motor to make the highest peak HP that might need to be beat hard or use special gears to work its best.

Thus, higher average HP over higher peak HP.


The new BMW turbo 6's are a study in making as broad of a power curve as possible. They forgo big HP choosing higher compression in I think the 10/1 range and run low boost over what Porsche's approach. On top of this BMW gets to use other more modern tricks like variable cam timing, run closer to the edge with knock sensing, and other goodies like specially tuned intakes to further broaden the power band. They also probably run more boost early in the rpm range and tapper it as the rpm increases for an even fatter power band. Still, they put a lot of gears with closer ratios behind it.

What can we take from this?

We might choose to build a motor that runs say 8.5/1 compression and .7 bar boost with cams that make power early for a nice low to mid range power curve that is as fat as possible in say the 4500-6500 rpm range.

The other direction would be to build something like a 6.5/1 motor that runs 1.2 bar boost with cams timed to make its power a bit later in say the 5000-7000rpm range.

Both builds have almost the same effective compression ratio. However the high compression build is going to be noticeably more responsive making about 10% more power pre boost and coming on boost and power early in the power curve for a relatively more responsive motor.

However, the low compression / high boost alternative will end up making about 30% more gross power power over its 2000rpm power curve but will probably be a dog comparatively off boost.

Most likely the higher compression low boost motor would be a lot more fun to drive in town and with a good driver might be faster than the big HP motor in most street and Drivers Edd track situations.


Anyway, we have a major drop in average HP with our huge 2700 rpm drop going into second gear (v about 1800 drop in the other gears or ). Ignore it and we are leaving a major opportunity on the table whether we fix the gears or build a motor that is least effected by it.

I guess the same can be said for our steep first gear.

BTW, a 930 that can make about 400cwhp is making about 260chp at 50mph with the shift into 2nd. If your are racing Brian on to the freeway with his 915, he will be making about 100hp more between about 50 to 70mph than you and he is going to get a big jump on you right where it counts.
Old 02-27-2010, 09:39 AM
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TJ,

Appreciate the input. I am learning all the time and am somewhat limited by my lack of formal mechanical education.

Here is the example I might give. One motor makes 400 ft lbs of TQ and 200hp. The other makes 300 ft lbs of TQ and 300hp.

Both have transmissions that keep them in there ideal power-bands and all other factors like weight, friction, air resistance, traction.. the same. Which car will be faster? I believe the higher HP motor will be.

I wonder, maybe the 'rate acceleration increases' or delta is faster with more TQ but the acceleration its self is greater with more HP.

Maybe that is the same as saying acceleration v speed in a technical sort of way.

Still spit balling. I makes sense that the greater the TQ the more or faster something can be moved. That is, one could have a 300lb weight on the end of a 1 foot lever and is would do more work than a 200 lb weight. However, if you use the 200 lb weight twice and the 300 lb weight only once, you do more gross work with the 200 lb weight. TQ as it applies to our motor's on a dyno is a measure of only one event shall we say (or three cylinders firing with one rpm) where as HP is how much work can be done with each event times how many events that can be fit into a period of time.

Again, we are probably saying the same thing but doing so differently.


I am still learning here and hope to continue to do so with good positive discussions of this type.

The best.
Old 02-27-2010, 10:06 AM
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Quote:
Originally Posted by cole930 View Post
Keith,

If I had to remove all but one of the mods I've done to the Old Sled the trans mod would be the one that would remain.

Cole
This is somewhat off topic but clarifies the problem, in my mind anyway. Look what Cole says, remember what RUF did very early on for performance and finally what significant change did the factory finally make over the many years the 930 was in production? Fix(Cole) or add a gear (RUF, factory).

I question, how much money is spent on trick components building torque and HP into these engines to make the vehicle deliver impressive performance while retaining an unacceptable transmission?

Assuming a cost benefit evaluation, aren't you money ahead to fix the trans. problem over the power problem?

Last edited by copbait73; 02-27-2010 at 06:22 PM..
Old 02-27-2010, 06:18 PM
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Quote:
Originally Posted by copbait73 View Post
This is somewhat off topic but clarifies the problem, in my mind anyway. Look what Cole says, remember what RUF did very early on for performance and finally what significant change did the factory finally make over the many years the 930 was in production? Fix(Cole) or add a gear (RUF, factory).

I question, how much money is spent on trick components building torque and HP into these engines to make the vehicle deliver impressive performance while retaining an unacceptable transmission?

Assuming a cost benefit evaluation, aren't you money ahead to fix the trans. problem over the power problem?
The only problem with the 930 transmission is the the gear spacing and the relatively high R&P. With the torque of these cars under boost, they really don't need another gear.

You guys with all your talk of broad flat torque curves, more gears.........you starting to sound a lot like turbo-water-pumper lovers. LOL!
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Old 02-28-2010, 04:40 AM
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Originally Posted by 911st View Post
If we start with a clean slate and open budget we probably want a 6 speed dialed in to how we are going to use the car. If not, a 5 speed with tailored ratios, if not better gear spacing on our 4 spd.
I can't say I agree with you on this point. If I came across a free 5 speed I'm not sure if I would install it or just sell it to someone else, I wouldn't even consider a 6 speed with my current power delivery.

You have to keep in mind that when you add gears you also add shifts to get the same work done. Each shift then multiplies other issues like lag. Once you start bumping power the 930 gears don't feel so long anymore.
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Old 02-28-2010, 05:26 AM
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As Will states, you grow into the 4spd as power mods are added to the 930 engine.

I joke about adding a 915 but if you have a stock engine that is leaps and bounds THE cheapest way to reduce lag and make better use of the available power.

Torque vs HP talk has been done to death 50 years ago. You need look no further than drag racing to get your answer. Turbos and superchargers rule. That is torque. If HP ruled you'd see Indy cars lined up at the lights.
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Old 02-28-2010, 06:47 AM
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+1 copbait
---

Brian,

As to TQ/weight, I understand what is being said. I might not think it is technically proper to describe a built motor as 'making torque'.

However it is a 'generally accepted term' to describe a motor where the cams are timed and the other factors of the motor are tuned to make power lower in the RPM range. This type of motor is much more drivable and responsive in daily driving.

Ergo, I surrender said argument to differences in vocabulary.

Last edited by 911st; 02-28-2010 at 10:43 AM..
Old 02-28-2010, 10:30 AM
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