BlacknRedGT

Anyone race the 944/951 with one of these?? Is it possible and are the cost outrageous??

Not looking to do it myself but would love to watch a video of one

333pg333

What 'box are you thinking of? Usually a sequential box has these.

gt37vgt

well I'd love to have taller 1st and 2nd strait gears then the noise is gone once you hit third but it would be great for big launches. also you can convert to dog engagement without going sequential

333pg333

Yes but don't you have to custom order all straight cut gears? In other words there's not actually a 'box with this as an option?

gt37vgt

yeh but the plus is strait cuts are cheaper from the gear man when i go to see rohan at extreme rotaries please look at the web page Pat do get my custom full length studs made( that i emailed you about ) i can ask him

333pg333

What's the advantage of s/cut gears anyway? My guess is that it's more for race teams that need to pull down box's all the time, change out gears that as you say are cheaper to buy, no syncros. What else?
Oh, and I kinda like the noise but I'm guessing that would get tiresome after a while.

BlacknRedGT

I know alot of race teams use the straight cut tooth gears (spur gears?) because it allows faster acceleration with almost zero shift time. (Kind of like sporttronic/tiptronic) I hear it is also easier to tear down and replace gears (Quessing a crew could do it in 10/20 min) to change the ratios. I just didnt know if it was possible with our cars or cost effective? Im suprised to see no one has tried, Ive seen alot of BMW's with this.

Ian Carr

With some thing like a dog box, all gears are spinning at the same time, compared to normal transmissions which use syncros to match speeds when shifting. Its pretty cool actually I went for a ride in a STI that had a full dog box race set up, and the only time he uses the clutch it to get going, other than that your are supposed to power shift. Plus they are stronger in general, and allow for better acceleration and more power to get to the ground.

BlacknRedGT

So could that type of application be applied to our cars is the question?? I know there are some gurus out there who know

Van

Straight cut gears have less frictional losses - so more HP makes it to the wheels.

Laust Pedersen

The only justification for helical cut gears is noise reduction. More teeth are engaged simultaneously (due to the cut angle) and the engagement starts more softly as a point (lower noise) than for straight cut teeth full line contact (noisier). For the same diameter the tangential forces are the same for straight vs. helical, but helical cuts also have to deal with axial (thrust) forces on both the tooth and gear cluster (need for high load thrust bearings).

Not only are helical teeth exposed to higher forces (vector sum of tangential and thrust forces), but the surface contacts are also point vs. line contact (helical vs. straight cut). Although the point and line contacts expand to small ellipsoidal and rectangular contact areas under load, the summed engagement areas are quite a bit less on helical gears i.e. much higher surface stress, with a chance of pitting (more need for surface hardening).

In other words for a given size (and therefore weight) straight cut teeth are strong and noisy (good for racing) and helical cut teeth are much less noisy, but not so strong, which can be compensated for by size and weight (good for the streets).

Laust

gt37vgt

and dog engagement instead of sycross is a completely separate thing . And as for some trivia the Citroen symbol represents them pioneering opposing helical agles with double gears to neutralize the thrust caused by helical cut gears.
excellent explanation Laust

BlacknRedGT

this is all good info but has anyone done it on a 944?? It sounds like it would be worth it if you mainly use your car for the track. I have also seen the dog boxes that have 1st 2nd and 3rd gear with striaght cut teeth while 4th and 5th gear are helical cut.

gt37vgt

were have you seen those ?
a hewland trans axle is an option but expensive. also dare i say how about a corvette trans axle ???lol

daigo

http://www.mendeolatransaxles.com