Tampa Racing - TECH: some gear ratio questions answered

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Jerome Soh
" Can you explain the advantages of your combination of Non-vtec engine with
GSR tranny. I believe thats what you have and remember you discussing it,
but cannot find any of my old mail about it. Is there a better combination
that results in lower gearing ratios?

The advantage doesn't exclusively lie in the combination of non-vtec
engine with GSR tranny. The advantage solely lies in the nice gear
ratios of the GSR tranny. In other words, you don't necesarily have to
have the non-vtec motor to take advantage of the GSR ratios. They,
along with the RS/LS (94+) and Type R tranny ratios are as follows:

RS/LS GS-R Type R
3.230 3.230 3.230
1.900 1.900 2.105
1.269 1.360 1.468
0.966 1.034 1.117
0.714 0.787 0.850
FD 4.266 4.400 4.400

Let's compare the GSR and RS tranny. The first two gears are the same.
However, 3rd and 4th gear are about 7% shorter, and 5th gear is 10%
shorter ((0.787-0.714)/.714). Let us assume that the final drive is the
same for now. In 3rd, 4th, and 5th gears, you will get noticeably
improved acceleration. It's _almost_ like having 7% more torque in 3rd
and 4th at any given time (it's not _quite_ like this, and I'll get to
that in a moment) and 10% more torque in 5th. This comes at the
sacrifice of top speed in any given gear. Now, with a 7000 rpm redline,
my top speed is about 220 km/h rev limited (it's still got lots to go...
it literally 'slams' into the limiter) with the GSR tranny. Personally,
I don't need to be up that high on the race track. On my home track, I
hit about 170 km/h down the main straight. On this particular track,
I'd ideally like to increase FD to get even better acceleration at the
expense of top speed, which brings us to the next topic: FD. FD is
exactly what it says... the final reduction through the tranny before
the driveshafts. It affects all gears. The total reductions for the
gears would be the gear ratio multiplied times FD. Thus, if your engine
is at 5000 rpm, and you are in 4th gear using a GSR tranny (total
reduction of 4.4*1.034=4.55), the driveshafts would be turning at 1100
rpm (the calculated speed using 577 mm as the nominal tire diameter
would be 120 km/h, which pretty much corresponds to my speedo). FD
increases the overall ratio for all gears without affecting gear
_spacing_. Gear spacing determines how much engine speed drops between
shifts. For 2-3,3-4, and 4-5, gear spacing is very good on the GSR
tranny. However, from 1-2 the gap is a factor of 0.59. Thus, if you
shift at 7000 rpm, you'll end up at about 4100 rpm (I always seem to end
up much higher than this when I powershift :) ). I suspect the reason
Honda did this is to give good starting power in 1st gear in a car that
doesn't have much low end torque. Anyways, looking at the Type R
ratios, one can see that the gap between 1-2 is 1.54, which is much
better. The gaps between the other gears remain the same as on the
GSR. Honda has basically just moved gears 2-5 'closer' to 1st gear. If
we ignore 1st gear, a Type R tranny is essentially a GSR tranny with a
4.7-4.8 FD.

Now back to the issue of why improving a gear by 7% isn't quite the same
as getting 7% more torque. When you do this, the top speed in that
particular gear will be reduced and thus you'll have to shift sooner.
Thus, you'll be spending the 'extra' time that you would have been in
the lower gear with the poorer ratios in a higher gear with the better
ratios. Even though the better higher gear has better ratios, it still
won't be as good as the poorer lower gear. But overall, the effect is
improved acceleration and lap times. There is a limit though. Shifting
takes time and thus you don't want to have a zillion gears spaced 0.99
apart with an engine with a big SPIKE for it's powerband :). That is
why Formula 1 and Indy cars are generally limited to 6-7 gears. Ramanan
has gone the other way by using a non-vtec tranny and GSR motor in hopes
of being able to stay in 3rd for his 1/4 mile run. With his particular
setup, that may just be the way to go for a 1/4 mile run. However, with
my 7000 rpm redline, the shorter gearing I can get the better. I have
to make 4 shifts during my 1/4 mile runs (I get into 5th), but all are
pretty quick and I'm definitely getting better times due to the gearing."

Kaz Mori
"Jerome mentioned the ideal of having infinite gears. On a related note,
Nissan has mated a 200hp engine to a CVT, and Honda claims it can build a
CVT that can take up to 300hp... As you know, until now, the only "real"
CVT was the one that's in the HX, but only takes 117hp or so.

Hmmm... The CVT is actually quite efficient, and it infinitely geared --
if it's strong enough, we may see it in place of the sequential shifters..."

[Ed : okay this is initially Ramanan's thoughts, but read his followup
a bit later, and he's had a change of thoughts.]

Ramanan Thiagarajah
"Reading Jerome's article on the differences between running the LS tranny
and the GS-R tranny, irrespective on which motor combination, I have some
input on the application-side of it. Leaving the number-crunching and
theoretical side out of it... (once an understanding of the numbers have been
established, testing follows) here goes on what happened from a GS-R to LS
tranny switch on the B18C motor.

The first outcome is lower figures on the dyno... this is in the 9 - 12%
range. The thing is that most dyno-testing is done in 3rd gear and just a
7% reduction (as Jerome's figures indicate) is accurate, but it ends up
being more because it just takes longer for the motor to wind out... every
increment in RPM's is affected... the gearing itself produces lower torque
values and at the same time the motor's capacity to rev-up decreases also.

On the track... 60-foot etc. DOES NOT CHANGE... this follows from the fact
that 1st and 2nd gears are the same. On the switch to 3rd, however, there
is a noticeable RPM drop and it just takes that much longer for 3rd to wind
out.From around 6500 to 9000 RPM's it seems that the car MOVES more... even
though it revs out noticeably slower. E.T's are affected slightly (around
15/100 to 20/100 seconds slower) and MPH seems unaffected (this is difficult
to determine as I was bracket-racing and couldn't really guage this
accurateley)

On another point. A friend had the B18C with the GS-R tranny and made an
almost IDENTICAL power-band on the dyno as I did with the B18C and the LS
tranny. Peak horsepower was identical as well as the curve from 6000 to 9000
rpms (this being appropriate for drag-racing). On the track.. after at least
10 - 12 runs... (driver-error can be discounted)... E.T's were consistently
0.4 - 0.6 seconds apart with the B18C/LS outdoing the B18C/GS-R.

The part I am not clear in is if the power-band and tranny combo is more
important than just the tranny itself. I mean if a motor made peak horsepower
but a very poor band and we had a tranny (very short gears) that made use
of this very narrow band of horsepower, then it would be good..."

--- discovery! ---

"Never mind the hype on the numbers and the ratios of these trannys, but
god---m.... this thing is crazy. It is a TREMENDOUS difference (seat-of-the-
pants type) after the switch from LS to Y2 <=== my correction.

First gear pulls much harder, but the crazy part is the switch to 2nd... oh my!
The rpm's drop literally about 50% of what they used to.. at a 8500 shift it
drops to ~7100 and spins literally (no exaggeration) the WHOLE of 2nd gear...
and these arn't stock VX tires... DUNLOP SP2000 205/50/15's. Shift to 3rd and
it lights up... the drop is the same.. to 7100. You don't notice how quicker
it revvs up until you hit 3rd... it is a HUGE difference. 3rd obviously takes
a little longer to wind-out and hit 4th... tires spin a bit and in my estimate
the 1/4 ends just before the end of 4th. With 20" slicks I estimate the 1320
ending at around 8700 in 4th gear.

To whoever reads this... guys/girls... if you can somehow get this or the
Type-R tranny.... or at least the gears and switch them to your LS or GS-R's...
PLEASE DO SO.... the difference is incredible. I have NEVER felt such a big
difference out of anything that I have done to the motor... I don't know how
this will translate to E.T's but it WORKS.... I am just so ecstatic."