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... If both gears are the same width, the helical actually has more surface area so it would have greater torque capacity...
One nitpick, and this is one that I didn't find out until I came across some guy from X-Trac talking about it. If both gears are the same and have the same pitch, this is true... but the limit on automotive gears tends to be fracturing at the root of the gear tooth and not contact stress on the faces. And because of geometry and manufacturing you can have a bigger pitch (which is to say less teeth per inch of diameter) on the spur gears than the helical gears, which means much bigger roots.
There is also another huge advantage with spur gear: misalignment tolerance.
Helical gears dont tolerate gear misalignment (case flex, shaft flex) anywhere near as well as spur gears do.
Originally Posted by emilio700
The helical vs spur (straight cut) debate depends on whether they are the same size or not and dog vs syncro engagement.The spur is usually a dog engagement, Helicals usually syncro which requires the gear to be a bit narrower. Narrower - less torque capacity. If both gears are the same width, the helical actually has more surface area so it would have greater torque capacity. This is assuming the resultant thrust loads are dealt with adequately. In the case of the QBE60G, the case is designed with bearings to accommodate those thrust loads. In the case of the QBE60G, the helical box is also dog engagement. So in theory at least, has greater surface area than the same width spur gear thus greater torque capacity and less noise. Everything else being equal, spur gears transmit torque more efficiently and run cooler as Dave mentioned. This is the reason I chose spur. Also because it sounds bitchin.
When doing gear analysis using the AGMA design methodology, spur gears usually end up having about 98% efficiency, which means put in 200HP of power, you get 196HP to the output shaft and 4HP of goes to heat. That's about 10,000 BTU. Helical gears usually have about 96% efficiency, so for the same 200HP in, you get 192HP to the output shaft and 8HP of heat, or 20,000BTU. That's something to consider.
If you can afford the Quaife, you could consider a transmission cooler setup cheap insurance if your approaching the HP rating. I would absolutely run a cooler if you are putting more than the HP rating through this awesome beast. With that said I will probably never be able to justify such a large expense on a miata trans. The video has some serious drool value though, and will be much better when you get your ***** shift **** working properly
Now that's what I am talking about! The rev drops (lack of really) between shifts are amazing! I can only imagine how sweet that marriage would be in my setup with the narrower powerband of the Rotrex.
I have the ign cut set at 100ms right now and we're running our Supermiata B6 Sportclutch and light flywheel. That's fast but we might be able to trim that down. We just received some very promising prototype organic discs for our twin. Those will go in which will lower MOI quite a bit. Then we'll start dialing back the ign cut interval and see where the limit is. The engine hasn't been tuned yet and isn't actually pulling all that hard on top. Dyno tomorrow.
Very interested in riding in this at mrls. Sounds awesome. Also interested in organic discs. I just had mine slip the other day. And want an extra set on hand for swapping.
I have the ign cut set at 100ms right now and we're running our Supermiata B6 Sportclutch and light flywheel. That's fast but we might be able to trim that down. We just received some very promising prototype organic discs for our twin. Those will go in which will lower MOI quite a bit. Then we'll start dialing back the ign cut interval and see where the limit is. The engine hasn't been tuned yet and isn't actually pulling all that hard on top. Dyno tomorrow.
I have the ign cut set at 100ms right now and we're running our Supermiata B6 Sportclutch and light flywheel. That's fast but we might be able to trim that down. We just received some very promising prototype organic discs for our twin. Those will go in which will lower MOI quite a bit. Then we'll start dialing back the ign cut interval and see where the limit is. The engine hasn't been tuned yet and isn't actually pulling all that hard on top. Dyno tomorrow.
Can I keep my current twin 5.5 clutch with the sequential? It's VERY light and would help with shifting.
I looked at the exchange rate yesterday after seeing your video. It's still very favorable. Once my next big deal closes I am going to pull the trigger.
Got it to the dyno yesterday. Was hoping for 180whp on pump gas. Fell a bit short. I want to fiddle with the intake pipe set up and spend a bit more time on the VVT table above 5000rpm. Motor only has about an hour on it so it's still a bit tight.
Still, lots of fun
08-24-2016, 01:52 PM
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