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This should give you an idea...
5th gear pull from just above idle.
Never mind the boost dip at 3K rpm. It's long gone.
That's not the whole picture with regards to low RPM torque though. A stock engine can run a MAP of 100kPa at 2000rpm, but it's making a lot less than peak torque, and that's with a NA tuned runners.
Mhm... The car makes 1 bar of boost at 2000rpm, whats the problem here? I don't get it... If he wants more power, what I don't think he needs in normal driving, he can shift to fourth and park everyone.
Mhm... The car makes 1 bar of boost at 2000rpm, whats the problem here? I don't get it... If he wants more power, what I don't think he needs in normal driving, he can shift to fourth and park everyone.
Obviously I have no problem with the performance of the turbo setup, it's clearly impressive. The point I am trying to make is, it doesn't seem worth it to me to reduce the flexibility of the powertrain and compromise the race track performance just to achieve a marginal fuel saving. A 2% efficiency improvement could likely be achieved with some part load MBT optimisation.
Obviously I have no problem with the performance of the turbo setup, it's clearly impressive. The point I am trying to make is, it doesn't seem worth it to me to reduce the flexibility of the powertrain and compromise the race track performance just to achieve a marginal fuel saving. A 2% efficiency improvement could likely be achieved with some part load MBT optimisation.
He is making so much low end torque that having too short a first and second gear IS currently reducing the flexibility of his powertrain.
The current first gear is more like a "granny" gear in a truck than a usable gear. He said it was basically "useless"
The 3.15 chart showed that both first and second are shorter (a tiny little bit) than the current "useless" gearing he has. This will make the problem worse, not better.
Any change below the 3.15 will only IMPROVE the race track performance until the gearing gets so low (the 2.56) that it does start to slow the acceleration.
I bet his current setup can "blow" the tires away at far less than WOT in 1st and 2nd. Maximum acceleration becomes an exercise in wheel spin control.
The Cayman GT4 is my dream car, someday I will own one.
Porsche "hobbled" that car for 1 reason alone.
It was NOT for fuel economy or because it was an "old" box that didn't have room for the gearing.
If Porsche had put the proper gearing in the car it would "show tail" to many of Porsche's 200K+ 911s.
NOT good to have some 100K "wannabe" whip the flagships...
**** expensive customers OFF!
It has the first gear that Godless Commie wants...
What that bad to the bone Cayman doesn't have is Godless Commie's significant low end torque.
A Cayman GT4 and GC's Miata would be an interesting race. My money would be on GC...
I would NEVER suggest these ratios for a normal turboed Miata. A 3.3 is as deep as pretty much any 4 cylinder blown Miata needs.
His is NOT normal.
His might be the coolest however.
It's probably the most complex as well.
As far as I know, starter engagement depth, distance of ring gear from engine block, and flywheel surface to crank distance is the same across all years and models in NA and NB Miatae, right?
I am definitely not talking about diameters and such, just the above distances.
I have a 1992 1.6 torn apart in the garage, and it gives me a chance to measure and design a flywheel that will work with the E46 gearbox behind my engine.
If the above specs are same on a 90-93 1.6 as my 99, I will be able to postpone engine + trans removal for measuring purposes, and it will give me a chance to drive the car around that much longer to source parts and stuff.
Flywheel: Direct fit on a 94-97 1.8. Also fits a 90-93 1.6 if used in conjunction with 94-05 clutch pressure plate and disc.
Clutch Pressure Plate and Disc: Direct fit on a 94-97 1.8. Also fits a 90-93 1.6 if used in conjunction with 94-05 flywheel.
Starter: Fits any manual transmission NA, but will only use two of the mounting bolts instead of three. We've used this starter in track cars and modified street cars with no adverse effects.
Last edited by Godless Commie; 01-10-2021 at 07:53 AM.
I don't have time to look over all your data. But in my experience, The lower you gear the rear end, the more exciting the car is. There is definitely a cross over point where the goal to reduce cruising RPM makes it a boring car to drive. Likewise, lowering the gearing to make it more exciting makes it too buzzy while crusiing. I like to use stock 6-speed gearing as reference. 4.3, bit buzzy, 4.1 less buzzy and peppy, 3.9 has some legs but still tolerable. Anything above (below?) a 4.3 is going to get more exciting, but increase shiffting and buzzyness, anything below 3.9 is going to be great on a freeway, but a bit boring when you're driving aggressively.
Same goes for exhaust. The louder it is, the lower you'll rev it if you've got more than 5 brain cells. For example, my car was naturally aspirated for a short while, but with 3" turbo exhaust. I removed it, and installed 6-speed at the same time. Car felt like a rocket ship because I could use entire rpm range, and had shortened the gearing.
I don't have time to look over all your data. But in my experience, The lower you gear the rear end, the more exciting the car is. There is definitely a cross over point where the goal to reduce cruising RPM makes it a boring car to drive. Likewise, lowering the gearing to make it more exciting makes it too buzzy while crusiing. I like to use stock 6-speed gearing as reference. 4.3, bit buzzy, 4.1 less buzzy and peppy, 3.9 has some legs but still tolerable. Anything above (below?) a 4.3 is going to get more exciting, but increase shiffting and buzzyness, anything below 3.9 is going to be great on a freeway, but a bit boring when you're driving aggressively.
3.636 in mine and it's definitely not boring with a 6-speed. 300+ rwhp takes care of that.
Note that 6-speed w/ 3.636 has very similar ratios in 1-5 as 5-speed w/ 4.3.
I just found out a cool thing, and it clarifies the diff grouping I had mentioned earlier in a previous post..
While it is true 3.xx and 2.xx ratios are not interchangeable, meaning, they require different cases and internal parts, 3.07 is an odd duck, and is interchangeable with the 2.xx gears.
And that means I can switch just the gears out between 3.07 and 2.93 if I need to for whatever reason.
One of the reasons I am looking into lowering my cruise rpm is because of the pronounced vibration my engine develops at around 3600-4000 rpm. It is OK to blow through that range while accelerating, but staying there in cruise speeds is something I am trying to avoid.
The said vibration is largely due to the large hunk of extra mass hanging off the exhaust side of the engine. I am also working on that issue to mitigate the vibration.
Also, I will be able to install the larger turbine and the corresponding bigger turbine housing (still sitting on my shelf) for "better" top end power with the new drivetrain. Wouldn't even dare do that right now.
I run a miata 6 speed and Mfactory 3.3. I also have very similar low end performance (250lbft by 2800 rpm, 1 bar off idle). I would recommend going with the 3.xx ratio. I still have to use boost by gear in 1st and 2nd with 225 45 R15 R1Rs, but I wouldn't want it to be any slower in 3rd and 4th. The sub 3k cruising speed without any need to downshift in high gear is choice though. A 3rd gear that has power from 35mph to 90mph (limit of traction) is a real hoot.
While short gears are fun/peppy and you can impress all your friends, longer gears are faster from lets say 0-100mph. Plus the advantage of lower cruise rpm AND (in most cases) less fuel consumption.
When I'm on the Autobahn and go from like 60-120mph in fourth (5 speed/4.1, next year 6 speed/3.63), my car is pretty damn quick and I would be slower with 1 or 2 shifts.
I must admit, that I wish shorter gears for fun sometimes, but in reality I know I'm faster with longer gearing, have more traction and don't end up in the barrier that fast.
The real problem here is the fact that the BMW transmission is geared substantially LOWER than the Mazda 5 speed...
This is why the change from Mazda 5 speed with 4.10 to the BMW set up with 3.15 gear DOESN"T change the total gear ratios in the first 3 gears.
If he used the BMW trans with the Mazda 4.1 rear it would be ridiculously short.
In this application 2nd might be SHORTER than first (Mazda trans) and he would have 2 "granny" gears.
In an ALL OUT drag application with slicks and a prepared surface this might be the way to go.
In a street or track application it would suck.
It's the total gear that matters, not just the final drive.
I'm still suggesting a ratio lower than 3.xx for this set up due to torque available and the gearing in the BMW transmission...
If he was staying Mazda transmission it would be 3.3 or 3.6 and for the most part I would suggest 3.6 as the 3.3 parts are all aftermarket and can have noise issues.
Ted75zcar, you too have a compounding system and even with the Mazda trans you have gone low (3.3). If you popped a BMW 6 speed in your car your problems would be EXACTLY the same and you wouldn't like it until you lowered (numerically) your rear gear...
250lbs/ft at 2800 is BADASSED!
I bet it EATS tires.
Just imagine a 2nd gear equal to your third...
That's what you need!
For maximum acceleration do you launch in first or second?,
If first I'd bet it's less than 1 second before shifting to second and starting in second might actually be quicker.
Does someone have the transmission gear ratios for both the Mazda 6 speed and the BMW 6 speed to compare?
I'd love to look at the differences between the 2 six speeds.
It gets interesting when specific gear ratios are calculated with the diff ratio factored in.
Also, I discovered I can convert excel files to jpeg, so I can post them here.
I based my comparisons for the total gear ratio of the 5 speed since that is what I have.
The 4.10 at the far right is to see how ridiculous things would be in the case I were to keep the Miata diff.
2.93 is the best ratio for your car with the ratios given.
I would still prefer a 2.8 but it's not available.
That same chart with the 6 speed Mazda gear box with 3.3, 3.63, 3.9, 4.1, and 4.3 would be greatly appreciated if you have the time.
Looking at the Total gear ratios is "The Way" for me...
Thanks for the work...
If all this torque is available at 2,000 rpm, you really do not need very close gear ratios.
From the gear chart in the first post, the engine never sees below 4,300 rpm except when starting off in first gear. Maybe not even then.
You have a light car, a lot of power, and are probably going to be traction limited in first gear anyway.
A bit of an extreme exaggeration perhaps, but think..... Would a Top Fuel dragster be faster with a six speed gearbox than direct drive ? Why ??
Have to agree with Mr Ninja, very low first and second gear ratios are going to be a disadvantage, unless you have a heavy vehicle and a small under powered engine.
2.93 is the best ratio for your car with the ratios given.
I would still prefer a 2.8 but it's not available.
That same chart with the 6 speed Mazda gear box with 3.3, 3.63, 3.9, 4.1, and 4.3 would be greatly appreciated if you have the time.
Looking at the Total gear ratios is "The Way" for me...
Thanks for the work...
Here's the chart with 6 Speed and 5 Speed transmissions:
One pretty important thing to remember:
When comparing different diff ratios with a given transmission (like, the 6 speed) rpm drop between gears will always be the same, just the attained speed in redline (or, a given rpm level) will be different.
At this point, it is just a matter of whether you have enough torque to get to that calculated speed, or, if that attained speed is sensible (like, 20 mph in first gear at redline, etc.) or not.
Last edited by Godless Commie; 01-11-2021 at 06:05 PM.
Redline with my 3.63 and the BMW 6 speed is a breathtaking 150mph in a car that feels really small at that speed on the track. I would not want to go that fast in it on the autobahn or any other open roadway, and I consider mine to be very stable. It stops being about stability and starts being about survivability at some point.
I think the cruising RPM in mine is fantastic for the highway (about 3300 at 80mph if I recall correctly). I think the 3.15 is so much lower it should be very nice for long trips at 80mph and still keep the middle gears close enough to be very peppy. Don't get me wrong, I'm sure the 2.93 would be fine but you will give up some acceleration and sportiness in the middle gears. There are always trade offs.
Speaking of which, high cylinder pressures and low piston speeds will mean excess wear on the cylinder walls and most certainly on the bearings. Keep an oil with good film strength in it.
I think you will be incredibly happy with the BMW ZF 6-speed.
Diff specialist called. He is putting together an "empty" diff housing with no internals for me so I can use it for measuring and prototyping in my car.
I need something light and dispensable to mock up different ideas, because I want to retain the PPF.
Off to measure for flywheel specs for a 240 mm E46 twin disc clutch behind a BP crank.
Rest assured I will invent ways and methods to make this thing as complicated as possible. Just look at my other projects...
01-07-2021, 03:03 PM
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If he wants more power, what I don't think he needs in normal driving, he can shift to fourth and park everyone.
