I picked this up from Doc Brown this past weekend. Thanks again! Now to keep an eye out for a roller miata and an RX7 transmission to dismantle...
I picked this up from Doc Brown this past weekend. Thanks again! Now to keep an eye out for a roller miata and an RX7 transmission to dismantle...
Best of luck AWSX1686 !
Below is a photo from my notes. These are the flow rates and dead times for the stock injectors at various fuel pressures.
Last known picture of the B3 powered Miata.
In reply to Doc Brown :
Thanks!
AWSX1686 said:I picked this up from Doc Brown this past weekend. Thanks again! Now to keep an eye out for a roller miata and an RX7 transmission to dismantle...
What do you need an RX-7 transmission for? If you're looking for a roller Miata to stick the B3 engine into, you'd just use the Miata transmission, since the business end is the same as a B6 or BP engine.
If you need an RX-7 trans for other reasons, I have a couple that are in various states of decrepitude internally that I will give away for the price of "take it, take it take it take it"
Knurled. said:AWSX1686 said:I picked this up from Doc Brown this past weekend. Thanks again! Now to keep an eye out for a roller miata and an RX7 transmission to dismantle...
What do you need an RX-7 transmission for? If you're looking for a roller Miata to stick the B3 engine into, you'd just use the Miata transmission, since the business end is the same as a B6 or BP engine.
If you need an RX-7 trans for other reasons, I have a couple that are in various states of decrepitude internally that I will give away for the price of "take it, take it take it take it"
Need the RX-7 trans to steal 5th gear from to put into the miata trans for an extra overdriven 5th. Ideally would like 2 RX-7 transmissions for this, one for the B3 miata I'm prepping for, and one for the current daily.
I'm not 100% sure which years of RX-7 transmissions I'm looking for, I'd have to look back and see.
AWSX1686 said:Knurled. said:AWSX1686 said:I picked this up from Doc Brown this past weekend. Thanks again! Now to keep an eye out for a roller miata and an RX7 transmission to dismantle...
What do you need an RX-7 transmission for? If you're looking for a roller Miata to stick the B3 engine into, you'd just use the Miata transmission, since the business end is the same as a B6 or BP engine.
If you need an RX-7 trans for other reasons, I have a couple that are in various states of decrepitude internally that I will give away for the price of "take it, take it take it take it"
Need the RX-7 trans to steal 5th gear from to put into the miata trans for an extra overdriven 5th. Ideally would like 2 RX-7 transmissions for this, one for the B3 miata I'm prepping for, and one for the current daily.
I'm not 100% sure which years of RX-7 transmissions I'm looking for, I'd have to look back and see.
You'd need one from an '86-91 trans, and '86-88 and '89-91 are different.
To be honest, because the transfer gear ratio is different between an FC trans and Miata, the ratio benefit is not all that great. Yes they have a .711 or .697 5th gear in the RX-7 trans, with its higher transfer ratio, but in a Miata it ends up being not worth all that effort IMO.
aving driven an FC trans with a 12A, it was a hateful experience, and the 12A has much more midrange and low end torque than a B3 could ever hope for. The 4-5 drop is ridiculous and you find yourself wishing for a gear in between the two, because 5th was always too tall and 4th wa always too short. (Ah, that explains the RX-8 gearing)
I didnt mind the high rpm of a miata going 80 mph. You need it to keep from being bogged down.
If the car is too noisy or buzzy, try to address those issues outside of gearing.
Knurled. said:AWSX1686 said:Knurled. said:AWSX1686 said:I picked this up from Doc Brown this past weekend. Thanks again! Now to keep an eye out for a roller miata and an RX7 transmission to dismantle...
What do you need an RX-7 transmission for? If you're looking for a roller Miata to stick the B3 engine into, you'd just use the Miata transmission, since the business end is the same as a B6 or BP engine.
If you need an RX-7 trans for other reasons, I have a couple that are in various states of decrepitude internally that I will give away for the price of "take it, take it take it take it"
Need the RX-7 trans to steal 5th gear from to put into the miata trans for an extra overdriven 5th. Ideally would like 2 RX-7 transmissions for this, one for the B3 miata I'm prepping for, and one for the current daily.
I'm not 100% sure which years of RX-7 transmissions I'm looking for, I'd have to look back and see.
You'd need one from an '86-91 trans, and '86-88 and '89-91 are different.
To be honest, because the transfer gear ratio is different between an FC trans and Miata, the ratio benefit is not all that great. Yes they have a .711 or .697 5th gear in the RX-7 trans, with its higher transfer ratio, but in a Miata it ends up being not worth all that effort IMO.
aving driven an FC trans with a 12A, it was a hateful experience, and the 12A has much more midrange and low end torque than a B3 could ever hope for. The 4-5 drop is ridiculous and you find yourself wishing for a gear in between the two, because 5th was always too tall and 4th wa always too short. (Ah, that explains the RX-8 gearing)
You'd need one from an '86-91 trans, and '86-88 and '89-91 are different.
So, usefulness debate aside, either the ‘86-88 trans or the ‘89-91 trans would work for this purpose?
RossD said:I didnt mind the high rpm of a miata going 80 mph. You need it to keep from being bogged down.
If the car is too noisy or buzzy, try to address those issues outside of gearing.
On my current daily driver, a basically stock NB, I completely agree with you. However, with the B3 engine installed I believe will change it entirely. The torque is at the top end of the stock BP, but much lower in the B3. Also tuning for economy, it doesn’t make as much sense.
It may well end up still that I have the engine running in the car before the 5th gear mod, and then I could do a proper before and after.
AWSX1686 said: So, usefulness debate aside, either the ‘86-88 trans or the ‘89-91 trans would work for this purpose?
Correct.
Let me see if I can dig up an ancient web page...
Found it! http://fm.no-ip.com/Car/tranchrt.txt This is a page that has not just the ratios of the different Mazda transmissions, but also the tooth counts of the gears. This is critical.
The Miata transmission has a 5th gear of 40 teeth on the countershaft gear and 18 teeth on the mainshaft gear, for a ratio of .45:1. (The input shaft has a 21 tooth gear and countershaft's input has a 38 tooth gear, for a 1.81:1 ratio. 1.81 times .45 is .814, which is the final 5th gear ratio)
According to this page, there are three different FC (nonturbo) transmissions, and they aren't Series 4/Series 5 but Base, GXL, and GTUs. Since you are not going to find a GTUs transmission (like three-digit production runs in 1990 and 1991), we'll ignore that. According to the chart, Base transmissions had a 22/52 and GXL had a 17/41, or .423 and .415, respectively. Times the Miata's drop gear ratio of 1.81 and you get either a .765 and .750 5th gear, respectively. A long way off from the FC trans' .711 or .697 5th, because the FC has a much greater drop ratio to the countershaft. Which is probably why Miata transmissions are stronger than RX-7 transmissions.
Now, personally speaking, the difference between a .814 and a .750 final drive is roughly 8 percent. Switching from the stock 185/60-14 to a 195/60-15 is a roughly 6.6% change, and it keeps your ratio spreads happy, and you don't need to buy a 48mm (I think, it's been a while) socket to cut in half and weld in a 2' section of pipe, to make a megadeepwell socket so you can remove and install the gears.
Knurled. said:AWSX1686 said: So, usefulness debate aside, either the ‘86-88 trans or the ‘89-91 trans would work for this purpose?
Correct.
Let me see if I can dig up an ancient web page...
Found it! http://fm.no-ip.com/Car/tranchrt.txt This is a page that has not just the ratios of the different Mazda transmissions, but also the tooth counts of the gears. This is critical.
The Miata transmission has a 5th gear of 40 teeth on the countershaft gear and 18 teeth on the mainshaft gear, for a ratio of .45:1. (The input shaft has a 21 tooth gear and countershaft's input has a 38 tooth gear, for a 1.81:1 ratio. 1.81 times .45 is .814, which is the final 5th gear ratio)
According to this page, there are three different FC (nonturbo) transmissions, and they aren't Series 4/Series 5 but Base, GXL, and GTUs. Since you are not going to find a GTUs transmission (like three-digit production runs in 1990 and 1991), we'll ignore that. According to the chart, Base transmissions had a 22/52 and GXL had a 17/41, or .423 and .415, respectively. Times the Miata's drop gear ratio of 1.81 and you get either a .765 and .750 5th gear, respectively. A long way off from the FC trans' .711 or .697 5th, because the FC has a much greater drop ratio to the countershaft. Which is probably why Miata transmissions are stronger than RX-7 transmissions.
Now, personally speaking, the difference between a .814 and a .750 final drive is roughly 8 percent. Switching from the stock 185/60-14 to a 195/60-15 is a roughly 6.6% change, and it keeps your ratio spreads happy, and you don't need to buy a 48mm (I think, it's been a while) socket to cut in half and weld in a 2' section of pipe, to make a megadeepwell socket so you can remove and install the gears.
Ahhh, the knowledge that the good folks of the GRM forum bring to the table. Thank you sir.
The transmission info is very helpful, as is the math and logic of the gearing vs. tire size. Tire size is definitely something I was thinking would be a useful tool in this endeavor, I'll definitely look more closely at that now.
Thanks again!
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