Who has broken a 6 speed? - Page 8 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 05-31-2011, 11:39 AM   #141
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Quote:
Originally Posted by bbundy View Post
Well I am the one who started this thread a little more than a year ago because of strange rattling noises at high revs and finally something in the 6 speed decided to derange itself on a short drive this evening. It popped out of third by itself and now makes loud gear whine noises in everything but 5th.. The shift **** goes back and fourth a whole lot if you go on or off torque in 3rd. It is not like stripped out teeth on a gear though, no metallic pop corn sounds just gear grind-whine in every gear including neutral and not as much in 5th.

A few weeks ago I broke a clutch fork pivot ball and when I drained it there was a pretty good chunk of a gear tooth on the magnetic drain plug. And then it developed a tick idling around in 1st gear but seemed fine in all the others.

Seven five speeds have succumbed to my power and track use and now one six speed.

Bob
By now you could have just bought a quaife gearset for as much time/cash you've spent. If my 5 speed goes (which I know it will at some point) I'm straight for a quaife gearset.
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Old 05-31-2011, 11:33 PM   #142
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Beware numbers and math involved:

Lets assume that gear efficiency is 97%. Meaning 3% is wasted and is converted into heat. So letís assume a car is making 275HP @ 6500 RPM peak, and the HP slope is linear, and torque is constant in the range that we care about of letís say 4000 to 6500 RPM. So, using magical formula, the average HP that is put into transmission would be 222 HP. ((275*4000/6500)+275)/2 aka [[HP @4000 RPM+HP @6500 RPM] /2]. From those 222 HP, 6.66HP is made into heat, or 4.96kW=~5000W [converted by google]. So, to keep fluid at constant temperature, basically 5kW of heat must be extracted. Compared to your radiator that has to deal with 66.6HP, this is not much. FYI if you have automatic car radiator on a manual car you already have the heat exchanger that you can use, not sure about the exchange rate. Anyways, letís assume that oil temperature is at 100C, cause its nice temperature. Lower better, but 100C is reasonable in my opinion and exit at 60C. So average temperature of oil would be 80C aka average of the cooler. Lets say you race at moderate high temperatures of say 30C. Heat capacity of air is 1 J/gK and density is 1164 g/m^3 and driving at 50mph, which is 22.35m/s, also J/s=W. Simple math follows, (mass flow rate)mair=density*area(A)*speed=1164*A*22.35=26015 *A [g/s]. Air in and air out we know, so q=1*(80-30)=50 J/g so Q=mair*q=26015*A*50=1300750*A [W]. Lets assume 60% air efficiency, so Q=Q/%=2167916*A. So, Q=Heat, means whatever cooled is whatever generated, keeps temps constant of the fluid. So A=5000/2167916=0.0231m^2=35.8 in^2, letís assume that oil to cooler exchange happens at 90%, [should have done that before hand], so the A would be 39.7=~40 in^2. Overall efficiency would be 54%, whoever wonders. So 50 in^2 heat exchanger should be sufficient.

So now lets wonder how much oil must pass through the cooler to cool it. So we need to know the oilís heat capacity best guess I found is 2000 J/gK. So it takes 2000 J to raise/drop temperature of 1 g of oil by 1 deg C/K. Assumptions from before, 100C in, 60C out, temp drop is 40C. So 2000*40=80000J/g. For sake of trying to keep this practical, lets assume that Flex-A-lite Part# 4110 is used, which is 5x12x3/4 core, which is 60in^2 cooler, letís assume that temp drop and heat exchange the same as before, too lazy to redo for a specific cooler. I know that 5000 W or J/s must exit, so 5000/80000 =0.0625 g/s, density of oil is 840 kg/m^3 =840000g/m^3, so flow rate must be 0.0625/840000=7.4E-8 m^3/s=1.95E-5 gallon/s, or 0.0012 gpm, feels too low, but thatís what math says. Lets assume temperature drop is only 10C, so it becomes 20000 J/g, blah, blah blah, 0.0048 gpm, k, it work, I hope (simple check). So, lets use higher flow rate, 0.003gpm sounds nice, so thatís like 1.92E-7 m^3/s, lets assume about 10 psi needed pressure to drive at the flow rate, 68000Pa, so thatís 0.013 W, pump at 70% eff, thatís 0.019W. So a small 12V motor, if geared properly can drive PS pump and not blow up. For cooling transmission.

For my jet engine, I use .5gpm= with 0.065Ē orifice @ [email protected]= 8.7W. If you wondering, I will try running 1Amp motor, or 5Amp stall current motor, and see what I get. I will measure and see if I got this right or not.

Lets see Wayne 1/6 HP 2,000 GPH Oilless Submersible Utility Water Pump 1/6HP motor, 20Ft head height = 8gpm, 0Ft head height=21gpm(due to pressure differential in a hose), 20ft=240Ē H2O=8.67psi=59786Pa, 8gpm=5.1E-4m^3/s, P=31W=0.042HP, good similar to example http://www.mcnallyinstitute.com/07-html/7-2.html GPM x TDH / 3960 = WHP=0.0404

Lengthy, yes
Waste of time typing, YES
Haters hate, YES YES

Anyways, if you see a problem let me know.
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Old 10-31-2011, 12:44 AM   #143
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I exploded my 4th gear a couple weeks ago. I clutch kicked 4th into the bank at Irwindale. It is my 1st 6 speed break.
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Old 12-03-2011, 10:44 AM   #144
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Default Which tranny for 350 plus RHWP?

I am just completing my Miata build and the car should put down around 350 rwhp. I will be track daying the car exclusively. I currently have a freshly rebuilt 6 speed in the car but it sounds like if this is the tranny I plan on running it i just a matter of time until it blows. Is the consensus get a five speed and do the Quaife gearset? Thanks
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Old 12-03-2011, 12:14 PM   #145
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Quote:
Originally Posted by Buzz View Post
I am just completing my Miata build and the car should put down around 350 rwhp. I will be track daying the car exclusively. I currently have a freshly rebuilt 6 speed in the car but it sounds like if this is the tranny I plan on running it i just a matter of time until it blows. Is the consensus get a five speed and do the Quaife gearset? Thanks
At 350whp, it will let go eventually. At my modest power level I'm still going strong.
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Old 12-04-2011, 08:45 PM   #146
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Default who has broken a 6 speed

Sav was TDH's failure when he was running a turbo (and as I recall more than 250 ftlbs torque) or with his current Rotrex setup with "only" makes ~ ~ 250 ft lbs (albeit at 7k)?
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Old 12-04-2011, 11:38 PM   #147
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Quote:
Originally Posted by Buzz View Post
I am just completing my Miata build and the car should put down around 350 rwhp. I will be track daying the car exclusively. I currently have a freshly rebuilt 6 speed in the car but it sounds like if this is the tranny I plan on running it i just a matter of time until it blows. Is the consensus get a five speed and do the Quaife gearset? Thanks
Not many people put down the money for a Quaife.
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Old 12-12-2011, 11:57 PM   #148
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Problem is there are no Quaife gear sets anywhere for our cars. I was told knowone has them and they are not going to produce more unless there is significant demand. Does anyone have any other options? Any other high HP guys want to chime in? Thanks!!!
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Old 12-13-2011, 12:06 AM   #149
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What happened to the gear sets FM was selling?
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Old 12-13-2011, 12:13 AM   #150
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Quote:
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What happened to the gear sets FM was selling?
They have not been selling them for a while. I think with the cost, they were not selling enough. I believe you can still custom order them from quaife.
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Old 12-13-2011, 12:37 AM   #151
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Sav, i've seen and heard of guys with t5s blowing through them (albeit behind a 400 ft/lb tq v8) very quickly. Im wondering what kind of testing you have been doing if any to maybe try to squeeze one in a miata. i mean i have an extra t5 world sitting in my garage and size wise they seem damn close. however i think more of us miata guys would rather see our beloved 5 speeds with their smooth shifting be beefed up with maybe some sort of cheaper quailfe alternative
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Old 12-13-2011, 12:39 AM   #152
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V8R is using the T5's to reduce weight with great success behind built L33's.
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Old 12-13-2011, 12:44 AM   #153
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there are a few shops that are making very strong wc t5 boxes, they are about 1300 bucks for the gear sets can be made straight or not, dog engagement or not, and i think that is a very viable option for guys like sav and feaflora making 300+ ft/lbs
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Old 12-13-2011, 12:48 AM   #154
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something like this, a 2500 dollar trans that can handle about 500 ft/lbs plus a cheapish adapter set up for about 500? make the whole thing run about 3k could be a good place to start

http://www.jegs.com/i/G-Force-Transm...ductId=1343711
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Old 12-13-2011, 05:28 AM   #155
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There is no such thing as a cheapish adapter setup.
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Old 12-13-2011, 08:53 AM   #156
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Does anyone have an adapter set up for tranny like this?
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Old 12-13-2011, 09:12 AM   #157
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Nope - or all us high hp guys would have them. Market for it? Possibly, but you still have to get over the +2000 price tag over a 6spd, just like the Quaife, and many are simply not going to pay that much. Now if the 6spds were as weak as the 5spds, I think that'd be a different story... we'd be forced to look elsewhere.

IF you really wanted to know an estimated price tag, call V8 roadsters and get his input. I'm sure he could build you one.
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Old 12-15-2011, 09:15 AM   #158
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V8 roadster had no help for our application. I called the US distributor for Quaife and they are going to let me know today if Quaife will make more gears for our cars. If this does not pan out I am going to go with Quaife gear set from FC RX7 as I know they will fit. The input shaft is a little longer but I can work with that. I already had another friend do it with his boosted Miata and he has had no problems. I will keep you posted.
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Old 12-15-2011, 12:28 PM   #159
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I believe many of you are looking @ the Quaife gear set as just being "stronger" than the OE 5 and 6 speed. It is but it's also a whole lot more. Less parasitic driveline loss due to the gear tooth pitch, better gear ratios for FI and high strung NA Miata's and arguably better shift feel/engagement than the 6 speed could ever hope to have.

Is it expensive, yes. However for a quality part you need to pony up the dough. I did the initial R&D and gear selection for the gear set (option 1) and provided the trans for Quaife to work with. It was up to Quaife for pricing. All in all, $2600.00 for a full gear set (not including new OE wearable items and labor) isn't a bad price for what you get, IMHO.
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Old 12-15-2011, 02:44 PM   #160
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has anyone successfully welded a BP engine side bell housing to a T5 tranny side housing and used a custom clutch disc? ive been kicking this idea around for a bit cause i plan on 500whp out of a built BP in my 72 spitfire and i dont wanna be replacing trannies constantly like some of my friends turbo miata projects. i figured T5's are everywhere and very cheap all i would need is a bell housing and i would be able to swap it from trans to trans if there was a failure.

i figure a custom clutch disc is maybe 300, good used T5 is maybe 300, diy custom mounts 150 max, new drive shaft yoke 300, put you around 1050. leaving 1550 in the budget for making an adapter bell housing. which may or may not be doable depending on your local welding/machining prices. and if the trans were to fail you would only be out the 300 for a new trans.

Last edited by fastivab6tg25mr; 12-15-2011 at 02:55 PM.
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