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Will work for Supra parts
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Discussion Starter · #1 ·
I'm still very new to the world of Supras, and while surfing Powerhouse Racing's website I took a look under their clutch and transmission page only to find a PPG High Performance Gear Set for Getrag six speed available. I read with more interest and suddenly I realized this gear set allows clutchless upshifts! Man, that's cool. I've heard of straight cut gears before and I know they can be shifted without clutching, but I never thought such a thing would be available for a street car.

Has anybody ever purchased one of these transmissions? How's it drive? I've never had the chance to see something like this before, but you hear about them on a lot of race cars. Would I be correct in assuming these would not be that great for running on the street? Without synchronizers, these must take some getting used to and a lot of rev matching. What do you guys think? Does anyone here actually own a transmission like this? When shifting, do you simply let of the throttle altogether briefly enough to grab the next gear, or do you back off slightly to drop the rpms down to the point where the next gear would engage?

Must be a bit similar to driving a semi tractor? From a dead stop, you must need to let the gears spin down to a stop, and downshifts must require some skill or double clutching?

Even if it might be impracticle for street use, I'm just really interested to learn more about the technique required to use one sucessfully.
 

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Your best bet to find more info on this would be to contact Obiwan at PHR directly. I know Jeff Watson has a set of these in his Supra but haven't heard of anyone else with them.
 

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1400rwhp/8 Sec Club
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I thought that was a awesome idea and "damn, i should of done that." Until i saw the $7,600 price tag! Man, you could go through 3 getrags for that!
 

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Driver Down
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I wouldn't want to run straight cut gears in a street car...

talk about whine. They'll hear your gears whining over your open wastegate :bigthumb:
 
G

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not a flame but you should go find out how a gear box works
straight cut gears has nothing to do with clutchless upshifts
or shifting at all
 

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PPG are a great outfit, but a straight cut, dog engaged gearbox will take a bit of getting used to, and you'll need a firm hand to shift it into gear. Big bucks for the mod, I wouldn't get it unless you have bucketsd of money to burn, or are really going to put that transmission through some punishment.

Its the dogs that let you do the clutchless shift, not the straight cut, yes, you want to rev match very well.
 

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Getrag Gearhead
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I want to see the insides of the HKS sequential shift gearbox for the 2JZ. That would be worth investing into if the price is right but currently isn't it like around $20k ?

Yeah, the dogs will allow for clutchless shifting if controlled with a standlone and shift ignition interrupt. It is still not streetable. Synchroniser shifting is about the best you can do for the street.

Straight (spur) cut gears are cut that way to increase efficiency. They normally have about 95% efficiency vs. the 80% of a helical cut gear set. The helical cut gear's teeth slide into each other. This causes more drag but reduces noise and they always have about 2-3 teeth in constant contact. The spur cut gears pivot over each other at their contact points. Comparing efficiency would be like saying the spur gears have 5% loss vs. the helical 20% loss. This also equates to a 75% reduction in LOSS over the helical cut gears.

While it is assumed that the straight cut will allow for clutchless shifts the dog gears are what really make this happen. On certain transmissions one can get a set of gears with either straight cut or helical option or dog or synchro engagement or combination for different gears. The PPG gears are probably the first replacement gears for the getrag we have come across.

Joe.
 

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Will work for Supra parts
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Discussion Starter · #10 ·
Thanks for the info. I wasn't aware that it was the dogs that allowed the clutchless upshifts. Guess I'm not a transmission tech, but I do understand how conventional gearboxes work. Dogs engage the gearset, the synchronizers bring the gearset you are about to engage up to the proper speed for a nice smooth shift, and the gears transfer the power.

Excuse my stupidity, I guess, but what is it about the dogs that are different and allow you to engage the next gear without clutching? Does anyone have any pictures?
 

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Getrag Gearhead
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Synchronisers use a cone that presses against another cone. The cones are usually made of a brass or aluminum alloy and can be coated with a carbon/graphite or molybdenum sulfide coating. This coating is used to reduce heat while providing friction and enhance lubricant retainment on the friction surface. The cone acts as a brake during upshifts to slow the input shaft speed and a speed enhancer during down shifts. Downshifts are usually harder for synchro and thats when double clutching is useful. Synchros also have small teeth that act as the interlock mechanism for the shift sleeve and the gears. These teeth will wear out every time the gear grinds. When ever your transmission synchro is worn and makes a grind the gear is being chewup. Think of it like brakes once your pads lining is worn out and there is nothing remaining the metal backing of the pad will grind onto the rotor. Every time you use your brakes the pads will damage your rotor even further. Gears are the same case. When the synchro is worn the gears will grind and eventually the teeth will be so rounded out that the gear not remain engaged. The shifter could get kickout into neutral byitself. In the severest case, the gear can jamb up and not allow you to shift out of that gear even if you come to a full stop and the engine is turned off.

Dog gears simply remove synchro sleeves and the gears are redesigned to have deep grooves to engage the dog teeth into. These teeth are a lot larger and deeper but are a lot less in number. While they are used a lot on racing and also in some motorcycles you have to have a high amount of effort to engage them. Upon engagement a shock is also sent thru the vehicle. This is due to the sudden RPM change. How the dog gears are shaped will determine if they are designed for full throttle up shift or not. Some would prefer the acceleration side to have a bevel cut onto them to allow the hub to slide with the full throttle upshift (i.e. drag application). While others would rather have the dogs cut straight for dependability. If the accel and decel are bevel cut then the gear will not remain engaged and can come out of gear. Normally the parts used in the entire assembly is case hardened and heat treated high carbon steel gears. They are normally able to with stand the harsh racing environment easier than brass or aluminum synchronisers.

Joe.
 

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I have a set of PPG gears in my WRX.

While I am sure the designs are very different in alot of ways, they too must be similar in alot of ways.

Sooo... this is what I think:

I have 1-4 helical cut doggears with an upgraded STi synchro'ed 5th and reverse. I have never tried clutchless shifting, but flatshifting I regularly do at the track.

With flatshifting set-up properly (via engine management of some kind), shifts are seamless and quick and DONT send massive shockwaves through the drivetrain. Its actually VERY smooth, IMO. I rev to 8200 currently, so I have my UTEC's launch control/flatshifting parameter's set to 6200 rpms. From gear to gear I drop 2000 rpms, so its best this way.

You can shift this dogbox soo fast that you need interlockers to prevent the shifter lever from slipping between the 1-2 and 3-4 shiftforks when shifting WOT from 2nd to 3rd. This would never happen on a synchro'ed box simply because you CAN'T shift them as fast. Period.

My set-up is very streetable and easy to get used to. Its good to master double clutching and rev matching as it will make it much easier to live with. But, by having a synchro'ed 5th gear, I can go 1-2-5 and cruise with little effort or thought.

Upshifting, you don't NEED to double clutch or rev match,... but you'll need to shift quicker and more concise if you don't to avoid grinding. I don't recommend downshifting AT ALL without learning how to rev match and double clutch in conjuntion with oneanther.

All in all it took me about a month to get it down pretty good. After dragracing this tranny though... I'll NEVER go back to a synchro box. Just in quicker shifts alone you can drop a couple tenths. Coupling that with flatshifting, my 1-2 shift almost feels non existant!! Seriously.

The helical cut gears aren't very loud at all for me. 4th is probably thee loudest, but still not bad.

I've ran 11.3 @ 125 on multiple occasions, thanks to this gearbox... no thanks to the crappy clutch I was running :dunno: (soon to be replaced with something that MAY get me into the 10s! Probably 11.0-11.2 though...)

The gearset retails for $4100, figure another $1000 for the billet shift forks and interlockers and lastly about $1000 for assembly and you have yourself a $6100 transmission.

I got mine new with all the options, plus some for $3300 assembled.... so I consider myself lucky! :) It was worth every penny, and I would have paid $6100, too.

Hope this helps. BTW- Last I knew Jimmy P. and Matt M. were thinking about getting a set of these. I hear PPG had discontinued them, but will re-manufacture them if they get a group-buy. I plan on letting Jimmy P drive my car just to try them out.... I hope he doesn't think my ride is too slow! lol!

def
 

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Will work for Supra parts
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Discussion Starter · #13 ·
Wow, I couldn't ask for a better reply then that. Thanks! That helps a lot, coming from someone who actually runs one. I appreciate the time you took to reply to post your impression of the gears. Nice.
 

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I Solve Problems
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There was a video on this site a while back with a skyline with this gearbox. It was so freaking loud, sounded like each gear was grinding at each shift. You would not want your street car sounding like that.
 

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lis2k said:
There was a video on this site a while back with a skyline with this gearbox. It was so freaking loud, sounded like each gear was grinding at each shift. You would not want your street car sounding like that.
Maybe they were grinding? If you don't take care, grinding is easy and WILL happen every gear change. With a little practice however, not so bad at all.

I guarantee that I could drive most people around for a good while before they'd realize something was amiss with my tranny. :bigthumb:

def
 

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Getrag Gearhead
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Enzox said:
I was told that a straight cut would sound like this

http://www.espritfactfile.com/videos/racing/GT1-1.ASF
That is exactly how they will sound. Notice at the very end on the video the driver looses control of the car from too many downshifts causing a lot of sudden and violent changes in shaft speeds. This change reflects upon the output shaft and input shaft even with the clutch disengaged. When he was at the limit of his tires grip a simple gear change with dog gears caused his tires to loose grip and spin out. This one of the prime reasons not to run dogs gears on the street.

Joe.
 

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Mine are not nowhere near that loud. So go with helical cut if you can.

To say he loss control BECAUSE of downshifting is abit presumptious, however.

Without knowing brake bias or tirer wear just for starters, you cant say it was JUST because of the gearbox.

At any rate, would I recommend this gearbox for road/circuit racing? not likely, but for dragracing and daily driving... not an issue.

You say this example is a prime reason not to use them on the street... where would you be driving like that ANYWHERE on the street????

Most of the cars on this board that would need this gearbox are making in excess of 900 whp+... I don't imagine ANY of those people wanting to take that much onto any course and expect for it to stick regardless of gearbox.

def
 
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