S2K2GO!!

A helpful thread here over the last couple of days (Retrofit F22C into AP1? Possible? Easy...) led me to do some calculating to compare the two trannys. Old topic, I know, but with search back online(yes!) I see nobody had done it quite this way before, so some might find it interesting.

The main difference between the two trannys is that the secondary reduction(not found on most cars but located in the aft compartment of the s2k tranny) was increased from 1.16 to 1.208. In the main case 1st-4th were left unchanged but gearing was made slightly higher for 5th and much higher for 6th.

Net ratios(input shaft vs output shaft) and the spreads for each shift are listed below. Net ratios are simply the product of each primary gear ratio multiplied by the secondary reduction ratio. Spreads equal the difference between ratios for adjacent gears.

Notice that the net gearing is lower(higher net ratios) for the first FIVE speeds in the AP2(higher 5th in the main case is more than compensated by the lower secondary), but that shift-spreads are all magnified, especially between 4th and 5th when compared with AP1.

Conclusions supported(No new ideas here, several posters have said as much); 1- The AP1 tranny might be the better choice for F22 engine because its closer ratios make staying in VTEC between shifts easier, and it probably has enough torque to handle the taller 1st gear. 2- The AP2 makes a pretty good FIVE-SPEED transmission for the F20 and may be a better choice than the AP1 tranny because first gear in the AP1 is way too tall. The broader VTEC band of the F20 make it better suited to the larger spreads of the AP2. Unfortunately, sixth gear in the AP2 is pretty much wasted on the F20. 3- Lower gearing in the differential might be the best overall solution for early models.

Other opinions encouraged.

Net Ratios AP1/AP2
1st- 3.634/3.785
2nd- 2.372/2.470
3rd- 1.718/1.789
4th- 1.347/1.402
5th- 1.126/1.139
6th- .941/ .922

Spreads AP1/AP2
1st to 2nd- 1.262/1.315
2nd to 3rd- .654/ .681
3rd to 4th- .371/ .387
4th to 5th- .211/ .263
5th to 6th- .185/ .218

S2K2GO!!

Two wild guesses:

The F20/AP2 combo would have a greater top speed in 5th than in 6th, but not quite as high as the F20/AP1 in 6th.

The F22/AP1 would have a higher top speed than the F22/AP2, both in 6th.

I don't have the balls to answer either of these questions. Volunteers?

ap1_tot

okay too technical of a read haha. but i hope i got this correctly..
ap2 tranny + F20 ap1 motor = (1st five gears)

did i get it right?

S2K2GO!!

Sorry- I get a little carried away sometimes!

Yes, That's what I think. And I just ordered an AP2 tranny for my 2001. Knowing how little I've used 6th even on the AP1 Tranny, I doubt if I'll ever use an even taller 6th in the AP2.

Others might disagree, especially if they have power mods on the F20- I'd be curious to hear from those with actual experience with these tranny swaps.

street_ruler

part of me doesnt think your numbers are right.

in the ap2 trans i was under the impression that the 1-4 were left the same (other than the 2ndary reducer) and that 5 and 6 were made loger for better crusing rpm.


as for your conclusions, ive always felt that the gearing was fine but the v-tec cross over needs to come down a few hundred rpm in the ap2. too small of a window to make it really fun. another 500rpm and i think it would be a blast.

S2K2GO!!

The numbers are right, but I understand why there is confusion.

Most trannys simply have a published ratio for each gear. The s2000 is a compound transmission, so there is an additional reduction(the secondary) affecting all gears AFTER the primary reduction for each individual gear.

It is true that the gears 1-4 in the primary case remained the same, and that 5 and 6 were made taller. (5 went from .971 to .943, and 6 went from .811 to .763)

The AP2 also included a significant change to the secondary. The 1.16 ratio for the AP1 became 1.208 in the AP2, significantly lower gearing across the board. This affects all six gears.

To get the net ratio, equivalent to the simple ratio published for most trannys, you have to multiply each primary ratio by the secondary ratio. I'll give three examples from each tranny-

AP1, 3rd gear 1.481 x 1.16= 1.718net
AP2, 3rd gear 1.481 x 1.208=1.789net(lower gearing)

AP1, 5th gear .971 x 1.16=1.126net
AP2, 5th gear .943 x 1.208=1.139net(lower gearing)

AP1 6th gear .811 x 1.16=.941net (overdrive)
AP2 6th gear .763 x 1.208=.922(overdrive, higher gearing)

Even though the primary was raised in 5th, it is more than compensated by the amount that the secondary was made lower.

hope this helps- Otis

supahman04

Okay so what would the rpm's be with an F20/AP2 combo in 6th going 65 compared to 5th?

spets

A gearing calculator gives me about 4250 rpms @ 65 in 5th and about 3500 rpms in 6th.

supahman04

Well isnt that about the same as the AP1 tranny?

S2K2GO!!

The calculator gave pretty close numbers, but there is a difference between the two trannys.

My spanky new OEM bridgestones are 24.5" loaded a bit x pi= 77in./rev so 891.4 tire revs/minute at 65mph.

For the AP2
891.4 x 4.1(diff) x 1.139 (AP2 in 5th)= 4163 RPM 5th
891.4 x 4.1(diff) x .922 (AP2 in 6th)= 3369 RPM 6th(lugging li'l F20!)

For the AP1-
891.4 x 4.1(diff) x 1.126 (AP1 in 5th)= 4115 RPM 5th
891.4 x 4.1(diff) x .941 (AP1 in 6th)= 3439 RPM 6th(better, but still lugging li'l F20!)

OK, so maybe you can use 6th on a cool day above 80 MPH on flat ground, but I know that engine likes to sing and hates to grunt!

I AM biased, probably spent less than 30 min total in 6th in seven years of driving my stock 2001.