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Fantastic Dogbox for RX7

Old 02-21-02, 06:27 PM
  #76  
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Dog gears don't make noise.... Straight cut gears make noise! For proof go into your RX-7 or just about any other car and drive around in Reverse. Almost all cars have straight-cut gears for Reverse, that's why they whine like that.

I should really take some pics of my tranny guts
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Old 02-22-02, 03:10 AM
  #77  
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100% Correct, that is where they great sounds comes from, Straight cut gears

Have a look at the size and thickness of the gears on the Guru tranny, no wonder they are so much stronger than most other dog-boxes (excellent for street, drag & circuit).

That is also why they have the ratio's set so well to keep your in the powerband when you change gear. They have stayed away from trying to squeeze 6 smaller size gears in and stay with the 5spd configuration.

The next race meeting here for me is in 3 weeks time and I cannot wait!


www.gurumotorsports.com
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Old 02-22-02, 03:51 AM
  #78  
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Everything looks very good but there's a weak link in the setup that's going to fail every time no matter how strong the gear sets are made! THE STOCK CASE!
Anything that's making over 450 RWTQ is going to send that countershaft right out the bottom of that case. This been tried many times before and the results are always the same. That tranny would only last in a low power/torque, road racing setup. In a drag racing or full power shifting enviroment it's going to fail. I've seen TurboII's with 550ft-lbs of Torque at the wheels destroy the stock case by just stepping on the gas pedal in 3rd or 4th gear!
The problem is that the stock case is not rigid enough and flexes to the point that will cause the counter shaft to be pushed or seperated from the main shaft resulting in the upper and lower gears not meshing properly leading to gear breakage. That's what I've found to be mainly the cause for gear breakage in the stock tranny. When you put a stronger gear set in place of the stock ones guess what next is going to happen? The main bearing secton of the case that holds the countershft in place is going to break and send it straight out the bottom of the tranny! Been there done that and I'm not the only one!
Another problem is with the number of main bearings in the stock case design. Basically there are only bearings in the front and rear of the gear set! If you were to take a look at any of the racing trannies from Liberity, G-force, Jerico etc. you would notice that there are many bearings and many main straps or caps that bolts directly to the case that holds the upper and lower gear sets in place. That eliminates most of the flexing that goes on inside of the tranny!
Just my opinion based on actual experience!

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Old 02-22-02, 04:05 AM
  #79  
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Hmm, I've heard of girdles for Mopar FWD trannies, they have flex problems from trying to put 200+++lb-ft through a trans designed for 85lb-ft! Does anybody make a girdle for the RX-7 tranny? I'm picturing a simple 2-piece strap that goes around where the bearings are, with a bolt on each side to cinch it down tight...
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Old 02-22-02, 04:35 AM
  #80  
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I must say that Guru Motorsports seemed to have very good products and have actually made an attempt to deal with the case flexing problem. I've seen all type of girdles made and designed to help with the problems but as power went up it just kept breaking. The Mazda cases were just not designed to hold the power people are producing presently.
Take a look at the countershft main bearing in the front and you'll notice that it's just about one inch away from the lower cover bolt surface. There's just not enough material in that area to support the shaft.
The Guru motorsport oil cover/girdle combination design should provide better support than the stock cover.
There's a picture from a very old fast fours & rotaries that featured a tranny I believe from Wayne Dyson's drag car at the time that had a lot of trick stuff done to it that sent the counter shaft right out the bottom of the tranny!

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Old 02-22-02, 05:36 AM
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No problems have been experienced with the Guru set-up. As stated by the previous post, they have made changes that will prevent this occuring.
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Old 02-22-02, 05:40 AM
  #82  
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what kind of power do cars you've seen the guru tranny on have? I'm guessing mainly road racers (cars that turn), and some badass street legal cars perhaps.
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Old 02-22-02, 05:51 AM
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Originally posted by Node
what kind of power do cars you've seen the guru tranny on have? I'm guessing mainly road racers (cars that turn), and some badass street legal cars perhaps.
hi, circuit cars (mine for example) are producing about 350hp at the flywheel (non-turbo), 13B, EFI, Guru Torsen Diffs (Stronger than any LSD etc) that really gets the power down.

Turbo street/drag cars currently running these boxes are up to 600hp and certainly give them a hard time without drama! Rohan (from Guru) will know more cars than what I do, I just run one of his boxes and love it!
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Old 02-23-02, 07:29 PM
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Here is a nice HTML tool to compare gear ratios and speeds for the different gearboxes out there.
Remember, the comparisons have nothing to do with power capability of the boxes.
http://www.geocities.com/rotarymoe/Top_end_mph.html
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Old 02-23-02, 09:59 PM
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Strength is not a problem!

One of the things you will notice on the pictures of the Guru transmission is the billet bottom plate on the case; this not only makes it look cool it also adds substantially to the strength and reduces the flexing of the 'standard' case.

Now I am not saying it is designed for full on 1000hp drag cars (if you want that go to an air-shifter etc) but road, race, street-drag Guru is the go.

Check out their updated webpage.

www.gurumotorsports.com
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Old 02-23-02, 11:50 PM
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Anyway, one other important point about the Guru boxes would be the gear ratios.
Here is a link that would show what these ratios do.
Note there is a box TFC11...


http://home.att.net/~rotarymoe/Top_end_mph.html

Note the colors remind you of this forums new look.
http://home.att.net/~rotarymoe

Last edited by moespeed; 02-23-02 at 11:53 PM.
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Old 02-24-02, 01:01 AM
  #87  
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twister: what kinda rwhp do you think to actually consider more of a drag tranny over the guru?
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Old 02-26-02, 02:34 PM
  #88  
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Question

Does anyone drive there car around on the street with a 1:1 5th gear? Cruising on the freeway that puts you over 4K RPM with the stock rear end.

Maybe I am to picky, but I would have to have a 6th gear. Not to mention speeds at LSIR in California put me real close to 5th gear (stock tranny/rear end) with stock suspension and the old turbo. For sure I would need more that 1:1 on a track like that.

Anyone else reach speeds over 150MPH on tracks? I thought I heard people running 180MPH or so on a couple east coast tracks. Plus you add in the better gearing and you will most likely be reaching those speeds faster.

Just thinking out loud.
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Old 02-26-02, 04:00 PM
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Originally posted by Styk33
Anyone else reach speeds over 150MPH on tracks? I thought I heard people running 180MPH or so on a couple east coast tracks. Plus you add in the better gearing and you will most likely be reaching those speeds faster.
Why i wondered about 6th gear, high speeds, low mpg on highway, and yeah, east coast kicks ***
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Old 02-26-02, 06:25 PM
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Oh come on, people used to cruise thei musclecars around with 4.11 and shorter gears with 1:1 high gears, similar size rear tires, and huge engines that top out at only 6500 or so RPM.

Do this. Drive without using 5th gear. No problem.
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Old 02-27-02, 01:45 AM
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You do not need 6 gears, but of course if you want a weaker set-up go for it! In the standad casing, look at the pictures of the guru set-up, they go for strength! Hey, if you want to keep on replacing broken gears go for something else, I know what I prefer. Strong gearsets for street, drag and circuit! Have a look at the guru website ,they do have an overdrive box, i.e. 4th = 1:1 !!
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Old 02-27-02, 09:42 PM
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I WANT ONE!! but all i can do is (for right now)
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Old 02-28-02, 12:00 AM
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Originally posted by twister
You do not need 6 gears, but of course if you want a weaker set-up go for it! In the standad casing, look at the pictures of the guru set-up, they go for strength! Hey, if you want to keep on replacing broken gears go for something else, I know what I prefer. Strong gearsets for street, drag and circuit! Have a look at the guru website ,they do have an overdrive box, i.e. 4th = 1:1 !!
Twister. Do you know the ratios for the rest of the gears?
Notice this information is left out on their Web site.

Have you seen a 6-speed straight cut gearbox with broken gears?
Has anybody seen a 6 speed straight cut gearbox being broken and how?
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Old 02-28-02, 03:57 AM
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Ratios, I will find out re the overdrive box from Guru, the engineering shop is not far away. Have to be this weekend, I am busy until then.

I have had a 6 speed fail in my very race car! But I am not going to say what brand! It has already been mentioned here.

Look, I go for quality that is why I go for Guru, I tried most other brands amd found they let me down, Guru Motorsports products do not!
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Old 02-28-02, 03:15 PM
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Originally posted by twister
I have had a 6 speed fail in my very race car! But I am not going to say what brand! It has already been mentioned here.
You should mention the name not unless you work for Guru.
Did you see a reason why this box broke?
What failed? What happened?
What kind of clutch setup did you have?

The more info you give would be appreciated.

Last edited by moespeed; 02-28-02 at 03:18 PM.
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Old 02-28-02, 07:35 PM
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I do not work for Guru but I also do not bag other manufactures! I have found with my experiences that I would rather pay for strength, quality and reliability with the right ratios in a 5spd box that works better with much faster gear changes! Than go for 'squashed' in 6spd just to get 6 gears!

I use both a twin / triple plate config (5.5") Gen 3, as well as a brass button clutch in my Gen 1 racer behind a 13B EFI with a Guru Transmission and Torsen Diff!
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Old 03-04-02, 09:09 PM
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I sent email to Quaife asking about a tranny for the 20B car.



Mr. Farkas,

Thank you for your inquiry. Unfortunately, while Quaife has a wide range of
gearboxes, nothing is suitable for your RX-7. The smaller, lighter gearboxes for
small GT cars such as your RX-7 cannot withstand your power outputs, and the larger
gearboxes that are designed for big V8/V10/V12 powered cars and are significantly
heavier in weight. These gearboxes are also not suitable for everyday street use.

Regards,

Ralph Hollack


----- Original Message -----
From: [email protected]
To: [email protected]
Sent: Sunday, March 03, 2002 10:04 PM
Subject: Trans for Mazda


Im looking for an all around trans for my RX7
its has a 20B 3 rotor pushing 650HP 480ft-lbs
this is my drive around town car most of the time its
tuned down to ~450hp.
but some times I do take it to the drag strip and run
and some times I do take it to the road race tracks

im looking for 1 trans that can cover doing both.

is a squl trans and option? how streatable would
it be?
I would like 6 speed with nice over drive.

do you have a trans that would fit this need.

thank

Tony Farkas
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Old 03-05-02, 03:46 AM
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The best thing on your market (without reinventing) your car we know (that is why we have produced it) is a 5spd Guru transmission.

As previously discussed the reason we have gone for 5 gears is to enable the strength and relability to be built into the configuration of the original casing (with our billet sump and additional bearing girdle support option) we have run this in cars with similar horsepower without problems.

The overdrive ratio is .85, 5th gear at 7,500 rph you will be doing approx (dependent upon wheel diameter, but these numbers are based on 26.5") you will be doing 162mph. You must have some longer freeways than Australia to warrant a higher overdrive!
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Old 03-05-02, 05:01 AM
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I live and Texas where my compution is vippers and vetts most of the time we race 70 - 140
and we have been know to push it over 165 to see who is going to back down. I just want some 5th or 6th gear that im not backing down becuase of red line.
the stock vipper is good up to Top speed of 192 mph.
450 horsepower at 5,200 rpm and 490 pound-feet of torque at 3,700 rpm.

sure i beat them to 160 but then they pull away from.
thats why I race them 70 - 140

can you trany handle the power from the 20B?

Last edited by 87GTR; 03-05-02 at 05:09 AM.
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Old 03-05-02, 05:16 AM
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As stated a Guru gear-set is a 5spd, but there are good reasons for this, strength and power!

We run this trany in a number of 20B cars producing in excess of 650hp, so yes the gear-set will handle the power.

If you want more top end than 160 mph change your diff ratio or wheel diameter. These boxes are designed to keep you in the powerband at all times so right across the board you will be in a better position.

Obviously nothing is indestructible dependent upon tractive effort and driver capabilities but this is definitely the strongest gearset you will find to fit into your Mazda gearbox.

Last edited by ROHAN AMBROSE; 03-05-02 at 05:22 AM.
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