NitroDann's Long Awaited Garage Thread

[little decks]

Much of the driveline issues come from running fairly big (for an MX5) slicks, once we started putting the stickier Michelins on the cars went quicker but the traction loaded up the driveline

[NitroDann]

This poor car has 17x9 with carrera cup slicks.

I dont have high hopes after all of this reading haha.

thankyou for the input

Dann

[little decks]

yeah she is gonna struggle, it's also more of an issue with the torque rather than the peak power, when you have the turning moment from the crank opposed by the tractive effort all that load will every now and then find a weak spot in the driveline to give way which is either 3rd or 4th gear or an axle.

[NitroDann]

Custom axles are easy enough.

6 speeda arent, good opportunity to do an RX7 trans/diff swap though.

Dann

[hks_kansei]

Just run OEM daisys on the back with some Nankangs.

I guarantee they won't allow the diff/box to load up.






Would it be worth the effort to get/make an adapter plate to mount other gearboxes to the engine? (ie: stronger boxes than the RX7, I know Supra/Celica boxes used to be a common swap for V8 holdens back in the day)

[NitroDann]

Well....

I dont know enough about it, here in Australia people talk about breaking drivetrains all the time, however in the USA a few mods are made and everything seems to go ok by all accounts.

No offence to anyone on either side but Im just a bit confused as to what the facts are, or perhaps no one really knows and whether stuff breaks comes down to luck.

On the upside, this will have some pretty clever boost control so we can tune out the big torque ramp it has a little to give it an easier time, without sacrificing any performance hopefully.

You will see it at South circuit next trackday, it will slaughter the huge slicks dont worry, no need for daisys to drift.

Dann

[Sean]

Would it be worth the effort to get/make an adapter plate to mount other gearboxes to the engine? (ie: stronger boxes than the RX7, I know Supra/Celica boxes used to be a common swap for V8 holdens back in the day)

There was one machine shop here in Aus making custom adapted kits for the RB25 box. I contqcted him earlier this year and he claimed to have thrown out the jig and no longer be interested in doing such work for a couple of reasons (not related to power etc).

I know a couple of people here run his set-up, and CT had one is his race car too.

There are also plenty of guys in Aus making good power in race cars and street cars who don't seem to break them, and guys making not so much who break lots - I suspect driving like a spasticated monkey helps break them, and having either a little bit of mechanical sympathy or a dwindling bank account seems to make them last a bit longer.

The mounts etc seem to have solved a lot of the problems though - which makes sense really...

[little decks]

Yeah I've seen Dad rebuild RX7 boxes and MX5 boxes and the RX7 isnt a great deal stronger, Dad was looking at a tremec conversion but it was too expensive to engineer it properly and then got into the NC stuff anyway which has some more options out there to strengthen the thing up... the axles werent really a huge issue, it was more of having too much camber which every now and then screwed the CVs.... just get yourself an SE drive train to start off with, its much much cheaper and shouldnt be a huge problem, a lot of the issues that are had are related to pretty abusive driving like dumping the clutch and compression locking the thing with the good tyre... ive seen Dad do two 6 speeds side by side... one went in a car with a little over 220rwkw and the thing lasted over a year running michelin 17x225 r8b compound slicks on the rear... the other box went into a car running about 180rwkw with 16x205 in the same compound and wont last 2 meetings, so obviously if you are a bit more sympathetic on the machinery that isnt a problem...

[little decks]

also... ive never understood how solid mounts make a difference? I've never asked many questions or anything but the gearbox is bolted to the block and not the chassis.. so it moves with the engine anyway, the rear is independent not a banjo and the diff isn't solid mounted... so its already designed to effectively almost float in unison, so if anything solid mounting would be detrimental... any bumps and vibrations to the car start stressing the driveline wouldn't they?

[Black_Penguin]

Me and my Dad also play with Lotus 7 replicas, a popular gearbox is the Toyota T50.
I've known guys to break these with a 16v 4AGE (around 100hp) on the street, I know of one behind a 300hp 3SGE in a slick-shod race car that has survived for many years.
Mechanical sympathy is key.

[Boyracer]

I have a SE diff conversion for sale.

[gslender]

also... ive never understood how solid mounts make a difference? I've never asked many questions or anything but the gearbox is bolted to the block and not the chassis.. so it moves with the engine anyway, the rear is independent not a banjo and the diff isn't solid mounted... so its already designed to effectively almost float in unison, so if anything solid mounting would be detrimental... any bumps and vibrations to the car start stressing the driveline wouldn't they?

It stops torque twisting and fixes the changes in the gear selector, which if the seat and driver rotated with the engine/gearbox, then yes solid mounts wouldn't be needed.

G

[little decks]

I understand that it stops torque twist but i kinda think solid mounts will do more harm than good, in regards to the gear selection... the box has synchros and is designed so that you dont have to put it in the right place, so long as you provide minimal force it will move across the gate where it needs to go from gear to gear, if you have problems with that its because you are forcing it to go where you think it should go and no amount of elbow grease will ever help the situation... just destroy your box... where you are seated relative to all this shouldnt matter the angular rotation of the gearbox in terms of degrees of rotation one couldnt imagine it would be more than 10 degrees

[gslender]

I understand that it stops torque twist but i kinda think solid mounts will do more harm than good, in regards to the gear selection... the box has synchros and is designed so that you dont have to put it in the right place, so long as you provide minimal force it will move across the gate where it needs to go from gear to gear, if you have problems with that its because you are forcing it to go where you think it should go and no amount of elbow grease will ever help the situation... just destroy your box... where you are seated relative to all this shouldnt matter the angular rotation of the gearbox in terms of degrees of rotation one couldnt imagine it would be more than 10 degrees

no. the issue is that under extreme torque acceleration you can accidently select 2nd->5th and miss 3rd gear because of the twisting that is occurring at precisely the same time the gear change is occurring. When you are racing you kinda want to avoid any subtle issues. many folks who have fitted them have reported less occurances of miss gear changes due to the gearbox/engine not torque as much. MazdaSpeed even sell stiffer mounts so I'm confident it is ok. Some people even fit solid mounts that are even stiffer still !!

[little decks]

I understand what you are saying and I have experienced what you are talking myself, but once I was more comfortable in the car and more relaxed I wasn't trying to force the gears so much and then the twisting wasn't an issue for selecting gears... I can see how it would be more of a problem with a dog box though.