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  #41  
Old 22nd December 2010
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Originally Posted by TooMany2cvs View Post
For clarification, my answer above is based on the believed original box in my '90 car.
That seems high for a '89+ tranny, but perhaps there could be some speedo error involved. Between the two, the later trannys are the ones that spin faster, which produces the slower road speeds at a given RPM. On the other hand, it's also possible that in other parts of the world they used a 9:33 ratio in the '89+. Since I don't have access to those transmission, I cannot say for certainty that it is not the case. The ratio is stamped on the ring, so if you ever take the diff cover off (perhaps when you change the oil) you could find out for sure.

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Originally Posted by TooMany2cvs View Post
It shouldn't be - since the number of teeth in each set is known - it should just be straight mathematics.
It is simple math, but since there are 2 different pinion:ring ratios the results will vary depending on what a person has. I said hypothetical in that I haven't conducted an empirical test showing that my '86 SPG produces EXACTLY that RPM/speed combo and therefor should not be taken as gospel for an answer, just an example of how to calculate. It's pretty close, but I'd hesitate to call it a perfect example.

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Originally Posted by TooMany2cvs View Post
The tyres are irrelevant. If we're considering the _actual_ road speed versus speedo recorded, then they become relevant. But since we're merely considering tacho vs speedo, it's not. However, the accuracy and calibration of the speedo may also play a part in it, and is likely to vary between cars.
I agree, though I do think in terms of actual mph. Oddly, in the case of my SPG, using 205/60 R15 tires has brought the speedo to be nearly dead on. It always read faster than the actual radar speed prior to that change and the mileage showed a similar over clocking. I think the change from 195/60 to 205/60 is only a 3% change, but that was enough to match it up (not by design, I just prefer that tire size ).
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  #42  
Old 22nd December 2010
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Originally Posted by mmoe View Post
It is simple math, but since there are 2 different pinion:ring ratios the results will vary depending on what a person has.
I was thinking more in terms of the %age change from 6 or 7 to 8.
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  #43  
Old 22nd December 2010
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Originally Posted by TooMany2cvs View Post
I was thinking more in terms of the %age change from 6 or 7 to 8.
Yes, I just didn't want to have people think that they will get 27mph at 1000rpms when they didn't check on their own only to find they get 25mph. Since the results can vary, it is important that people do their own investigating based on their own vehicle. If you went so far back as to look at 4 speeds, I believe there are some that revert back to the 9:35 pinion:ring ratio, so even to say '88 and earlier are 9:33 could be misleading to some. Throw on top of that there are many '89+ trannys in '88 and earlier cars and vice versa. I can't predict every possible scenario, so the bottom line for anyone interested in knowing is that they must verify for themselves.
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  #44  
Old 22nd December 2010
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OK, here's the definitive answer to the question of how many mph one would get with type 8 primaries at 1000rpms (engine speed).

Since there would be 1000 rpms entering the transmission via the top primary gear, it would be multiplied by 1.375 times (33 teeth driving 24 teeth). This yields 1375 rpms at the input shaft of the transmission, which in 5th gear is a direct drive though to the pinion/ring gear. At that point the pinion gear is turning 1375 rpms but is reduced because it is 9 teeth turning either 33 teeth or 35 teeth. For the former, this reduces the wheel rpms to 375 rpms while the latter is 354 rpms at the wheels. At the stock 195/60 R15 tire size, there should be 833 revolutions per mile, which means it will take 2.221333 minutes per mile with a 9:33 ring/pinion and 2.353107 minutes per mile with a 9:35 ring/pinion. Divide 60 minutes by each result and you get:

9:33 with type 8 = 27.01 mph at 1000 engine rpms
9:35 with type 8 = 25.50 mph at 1000 engine rpms

While the ring/pinion get somewhat neglected in the equation in terms of people seeking out a lower rpm solution, the most economical way for a person with a late model transmission to produce the same result as switching primaries may in fact be to rebuild the tranny with an earlier ring/pinion, with the additional benefit that you now have a rebuilt tranny. The difference between a 9:33 and 9:35 ring/pinion is almost the same as the difference between type 7 and type 8 primaries. For example, type 7 primaries on a 9:33 ring/pinion tranny will produce 349 rpms at the wheels compared to 354 rpms at the wheels produced by a 9:35 with type 8s.

9:33 with type 7s = 25.1 mph per 1000 engine rpms (75.3 mph at 3000 rpms)
9:35 with type 8s = 25.5 mph per 1000 engine rpms (76.5 mph at 3000 rpms)
9:33 with type 8s = 27 mph per 1000 engine rpms (81 mph at 3000 rpms)

Those out there with type 7s in their '88 and earlier transmissions are already experiencing nearly the same road rpms as an '89 or newer with type 8s (which may explain why so many '88 and earlier cars including SPGs had type 6s, which are comparable to type 7s on '89 and newer).
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  #45  
Old 23rd December 2010
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Quote:
Originally Posted by mmoe View Post
At the stock 195/60 R15 tire size
Again, though, we're confusing indicated mph on the speedo with actual road speed. I don't know about over there, but over here speedo calibration HAS, by law, to be slightly optimistic. There's a %age range (10% is frequently quoted, but it's more complicated) by which it can over-read and zero tolerance for under-reading, so speedos are always calibrated to over-read.

Last night, I made a point of noting - I couldn't get above it, for greater accuracy, but at 2k rpm, the needle was a whisker under the half-way mark between 50 & 60 - safe to call that 54mph.
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  #46  
Old 23rd December 2010
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Originally Posted by mmoe View Post
OK, here's the definitive answer to the question of how many mph one would get with type 8 primaries at 1000rpms (engine speed).

Since there would be 1000 rpms entering the transmission via the top primary gear, it would be multiplied by 1.375 times (33 teeth driving 24 teeth). This yields 1375 rpms at the input shaft of the transmission, which in 5th gear is a direct drive though to the pinion/ring gear. At that point the pinion gear is turning 1375 rpms but is reduced because it is 9 teeth turning either 33 teeth or 35 teeth. For the former, this reduces the wheel rpms to 375 rpms while the latter is 354 rpms at the wheels. At the stock 195/60 R15 tire size, there should be 833 revolutions per mile, which means it will take 2.221333 minutes per mile with a 9:33 ring/pinion and 2.353107 minutes per mile with a 9:35 ring/pinion. Divide 60 minutes by each result and you get:

9:33 with type 8 = 27.01 mph at 1000 engine rpms
9:35 with type 8 = 25.50 mph at 1000 engine rpms

While the ring/pinion get somewhat neglected in the equation in terms of people seeking out a lower rpm solution, the most economical way for a person with a late model transmission to produce the same result as switching primaries may in fact be to rebuild the tranny with an earlier ring/pinion, with the additional benefit that you now have a rebuilt tranny. The difference between a 9:33 and 9:35 ring/pinion is almost the same as the difference between type 7 and type 8 primaries. For example, type 7 primaries on a 9:33 ring/pinion tranny will produce 349 rpms at the wheels compared to 354 rpms at the wheels produced by a 9:35 with type 8s.

9:33 with type 7s = 25.1 mph per 1000 engine rpms (75.3 mph at 3000 rpms)
9:35 with type 8s = 25.5 mph per 1000 engine rpms (76.5 mph at 3000 rpms)
9:33 with type 8s = 27 mph per 1000 engine rpms (81 mph at 3000 rpms)

Those out there with type 7s in their '88 and earlier transmissions are already experiencing nearly the same road rpms as an '89 or newer with type 8s (which may explain why so many '88 and earlier cars including SPGs had type 6s, which are comparable to type 7s on '89 and newer).
Man I really enjoyed this reply. I enjoyed it that I wish i lived close by so I can learn so much more from you. Cheers and thanks. Now i am interested in knowing more about the custom ring/pinion to get my rpm's even lower. I have had much better luck with 89+ gear boxes so i would rather get a custom Gear/pinion made than take my chance on a pre 88 box.

Quote:
Originally Posted by TooMany2cvs View Post
Again, though, we're confusing indicated mph on the speedo with actual road speed. I don't know about over there, but over here speedo calibration HAS, by law, to be slightly optimistic. There's a %age range (10% is frequently quoted, but it's more complicated) by which it can over-read and zero tolerance for under-reading, so speedos are always calibrated to over-read.

Last night, I made a point of noting - I couldn't get above it, for greater accuracy, but at 2k rpm, the needle was a whisker under the half-way mark between 50 & 60 - safe to call that 54mph.
what gear box # do you have and what primary gears does it have?
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  #47  
Old 25th December 2010
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Quote:
It is possible to install a 9:33 ring/pinion into an '89 case.. ...As far as getting the absolute highest speed per RPM in 5th, this would be the combo to do so.
Are the gear ratios of 1-5 actually different pre and post '89? I understood the synchro design changed in there somewhere, and the pinion size, but I thought the gear ratios themselves stayed the same?
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  #48  
Old 6th January 2011
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well im interested
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  #49  
Old 9th January 2011
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Originally Posted by glorydaze View Post
Are the gear ratios of 1-5 actually different pre and post '89? I understood the synchro design changed in there somewhere, and the pinion size, but I thought the gear ratios themselves stayed the same?
All gears would be different in the end (all else being equal), just from the pinion/ring being different. Even if you take the pinion/ring out of the equation, the gears 1-4 differ in ratio in these categories:

(1) '88 and earlier 5-speeds have the same gear sets (4 speeds shared some parts, not others).

(2) '89/'90 (5 speed only at this point) has a different gearset including gears 1-4, cluster gear and constant mesh gear. Reverse gear/reverse idler gear also changed (and oddly matched the reverse/reverse idler gear from late 70's 4 speeds, like chillcasts, a great source for unchipped reverse gears).

(3) '91 and newer have yet another 1-4 gearset, cluster gear and constant mesh gear. Reverse gear and reverse idler gear remain the same as '89/'90 (and some late model 4 speeds, such as chillcast).

The changes in ratio are not always wholistic. For example, and without having the numbers in front of me, 1st gear in and 88 may have 34 teeth (just a guess, not factual) while 1st gear in an 89 may have 33 teeth. At the same time, 2nd gear may have 25 teeth for both 88 and 89. There was some definite variation from year to year, but not necessarily in all gears. The only way to know for sure is to count the teeth. You can't mix these up, since the corresponding teeth on the cluster gear will only work with the proper mate. For all practical purposes, an '88 gearset must be maintained 1-4 with the cluster gear. The same is true for the other sets. You can, as we've discussed before, change the constant mesh gear from one year to work with another. This allows some fine tuning of the gears.

I can say the the shortest gearset possible would be the '88 and earlier 1-4 with the appropriate cluster gear combined with a '91-'93 constant mesh gear. 5th gear is only affected by the pinion/ring combination, either 9:33 or 9:35, but 1-4 can be adjusted with the constant mesh gear. If you had a 9:33 pinion/ring and you added type 8 primaries, you may very well wish to have a '88 or earlier gearset paired with a '91-'93 constant mesh gear just to keep your 1st gear from getting to tall (due to the type 8 primaries). Remember, a 9:33 pinion/ring combo with type 8's would in theory be similar to a 9:35 pinion/ring with type 9's (if they existed). The gears would be very uncomfortably tall from a stop, so some thought should be given as to how to make the system all work together to produce the best results from 1st all the way through 5th.
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  #50  
Old 9th January 2011
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Originally Posted by 900 aero View Post
Man I really enjoyed this reply. I enjoyed it that I wish i lived close by so I can learn so much more from you. Cheers and thanks. Now i am interested in knowing more about the custom ring/pinion to get my rpm's even lower. I have had much better luck with 89+ gear boxes so i would rather get a custom Gear/pinion made than take my chance on a pre 88 box.
See my above post regarding the transmission as a system. '89/'90 gearset could be used on a 9:33 pinion/ring ('88 and earlier) by either using the smaller bearing housing (fits a chillcast cast without modification) or by machining a custom bearing housing to fit into an '89+ case. A '91-'93 constant mesh gear would also benefit an '89 gearset if 1st feels too tall. If you go to the trouble of completely reworking the transmission, it would make sense to consider every component and how it can be modified to produce a more desireable result on the whole, not just how much more top speed can be produced.

Personally, I think that for most of us an '88 and earlier gearset is plenty good, especially if you take the time to have it cryo-treated and shot peened. I would recommend taking the actual ratios into consideration more so than the slight difference in gear width (which cryo-treating seems to make up for).
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  #51  
Old 19th January 2011
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Count me in for a set. My airflow project is finally scheduled for completion and this was on my list almost 7 years ago!

Any update regarding this group buy effort?
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  #52  
Old 23rd January 2011
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Starting to get some interest now Mike! I think this can be a go!
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  #53  
Old 17th April 2012
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Question Best chance of finding Type 8s...

Obviously, as stated numerous times in this thread, Type 8s aren't produced anymore/hard to come by. Wondering if I went to a junkyard to look for some what year and style of 900 would I have the best chance of finding them in? (ex. 1990 and up T16 4-door) I mention this as when I went to the junkyard recently, I saw 2 4-doors, 1 turbo, 1 not, in the "staging area" (can't pull parts yet). Didn't know if I should go back in about 30 day when they'll be on the lot, to see if they have Type 8s.
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  #54  
Old 17th April 2012
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#8's weren't available for the north american market. So finding them in a junkyard would take a miracle.
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  #55  
Old 18th April 2012
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Originally Posted by dmgb5 View Post
#8's weren't available for the north american market. So finding them in a junkyard would take a miracle.
Ah...well that settles that then doesn't it XD
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  #56  
Old 18th April 2012
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Originally Posted by dmgb5 View Post
#8's weren't available for the north american market. So finding them in a junkyard would take a miracle.
am happy to be contradicted ,,But for whats its worth I stll havent seen a set on an Aussie Market car ..
If you are in OZ .. and you know of a potential source , love to hear of it
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  #57  
Old 20th April 2012
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Originally Posted by AUSSIE900 View Post
am happy to be contradicted ,,But for whats its worth I stll havent seen a set on an Aussie Market car ..
If you are in OZ .. and you know of a potential source , love to hear of it
No sure about the Australian market...maybe only EU and UK markets got #8's in limited quantity.
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  #58  
Old 22nd April 2012
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Quote:
Originally Posted by aerobar900 View Post
What are the effects on normal city driving.
I've been on Type 8s for more than a year now and the experience has been:

1. Improved fuel consumption ~15%, when compared with Type 6s
2. Quieter highway driving: 60mph needing only 2,300rpm, compared with 2,700rpm with Type 6s, and 3,000rpm for auto.
3. Struggling around 2nd and 3rd gear at low speeds. Have to change down to 2nd when 3rd used to do, or even 1st when 2nd used to do, as the gears are more widely spaced now. If your ignition timing is too retard, you'll struggle more at low RPMs.

Don't try it on an LPT - I upgraded mine to FPT and the difference with Type 8 primaries is marked.
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  #59  
Old 28th April 2012
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I would be interested if price is right!
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  #60  
Old 17th May 2012
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Quote:
Originally Posted by dmgb5 View Post
No sure about the Australian market...maybe only EU and UK markets got #8's in limited quantity.
Only way we would probably see one is if it was shipped back by a military move, and it had been purchased and driven overseas prior to shipment to US, but you would have to have a list of applicable VINs' to find one.
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