Guys,

What really is the upper limit of engine power/torque before a T1 gearbox starts getting into the 'self destruct if given a bootful' zone?

Having looked at a few things with this Corvair engine and with the upgrades planned as i go (cam, headwork, carbs etc) its likely i think ill be in the region of 120-130hp. Torque is very likely to be up from the std 160lb/ft due to the cam. Powerwise, thats perhaps approaching 3 times the power of my current engine and id guess at least double the output of whatever VW ever bolted to it......Ive already been told to pretty much forget first gear if im running a 'Vair engine as it will eat it for breakfast.

Which brings about the question of is it even worth running a T1 box? The kits to fit a corvair transmission into a vw (transvair) havent been available for ages and hardly ever appear second hand, so they're out. Considered a Porsche 914 (915 or 901 code) gearox as they are 5 speed etc but apparently equally as chocolate as a T1 box, only with porsche repair prices....

Other than a custom built bears or Rancho box, the only other option i can see its a 6 rib 091 gearbox, which will take a little work to fit. The only thing im not sure on its if you can flip the diff in the bus gearbox, which ill need to do as at this juncture with which ever gearbox i go for (unless its the Porsche 914 gearbox which rotates the right way), im not reversing the rotation of the corvair engine.

Appreciate its not a common conversion and that hardly anyone (if anyone at all?) here has done. Ive tried contacting the northern guys with the conversions but had no response....

I do not know the limits but silly abuse with a standard 1600 lump will kill a box, both my standard boxes handle the 114BHP and 157Nm  torque of the twin cam alright it will also depend on your tyre grip I have 225/70 on the rear with a lot of weight and they will break away when floored in first just after starting moving.
I never do 3000rpm and drop the clutch launches but as soon as it is moving it gets floored on a regular basis the first box got me past 100,000 miles before the bearings got noisey the present box has 80,000 miles of my use plus whatever it did between 1967 and I guess around 2000 when I brought it.

during the late 60's to late 70's they were the favourite transmission for modified jalopy racers or as they are today auto grass racers who used to put allsorts of engines on them unitl FWD became the norm for cars and better stuff became availiable.

Keith,

Thanks, thats useful to know. Im trying to get a guesstimate from the corvair guys as to what the torque would be with the mods ive got planned. I know the Isky 260 cam improves the bottom end and the 110 engine (the one ive got) develops all its torque by 2600rpm. Coupled with the flow/port work on the heads and possibly different carbs, i know its going to go up....

Im already thinking ill be needing an uprated pressure plate as well, been looking at the Kennedy range. The stage 2 will handle 220 lb/ft, the stage 3 will do up to 260 lb/ft of torque. Ill probably go for a stage 3 unless the torque numers come back suggesting differently or anyone else can tell me not to?

GTMIKE runs a 2.3 Turbo Injection in his LWB GT 

The last I heard he had it mapped to 325bhp, and the box is still going I think....

Amazing

Ben I have never had an uprated clutch just a bog standard 200mm beetle one but it depends how you launch off the line I guess.
Mikes figures are impressive for a buggy power plant.

basically BHP gives you top speed the Torque gets you there.

Indeed they are impressive figures..........

There is always the element of the 'traffic light grand prix' to consider........

Ive only just realised that ive got the Crown conversion kit so for now, ill stick with a T1 box for now. Im reasonably familiar with them by now....

All depends on how much you intend to abuse the gearbox and how much grip you have in your tyres.

If you are going to drive sensibly, then a stock gearbox will handle a lot of horsepower and torque.

If you are going to drag race it and launch at 7000rpm, then a stock box probably won't last much past the start line.

I have destroyed several race built gearboxes with super diffs and 4 spider gears, cracked multiple 3.88 Ring and pinion sets and shattered reverse gear (it sits over the join in the output shaft), this was with a 180BHP 2332cc type 1 engine and either 305/55R15 road tyres or 28x25" slicks, dropping the clutch at 7000 rpm to launch or at 5000 rpm for a burnout.

Conversely Ritchie Webb is currently running 8 second quarters on 091 box with a Berg mid section and bug nosecone on his turbo/nitrous 2332cc 600bhp+ engine in his cabrio running slicks and having no issues (he also used to destroy type 1 boxes).

Cheers Zeb.

Im not planning on full throttle, rev limit hitting launches everywhere.

Tyres wise, i guess ill be running the 275/60s by then, so a reasonable amount of grip. I dont plan on doing much, if any in the way of drag racing. It most likely the most action it will see is the occasional spirited drive somewhere!

I had considered the 091 gearbox as i know they are pretty strong. Just not sure how you would mate a corvair engine to one, unless bellhousing is the same as a T1 box?

old standard gearboxes seam to be stronger than modern aftermarket ones,mates running 240 bhp scoobie lump though a gt type 1 gearbox and shes holding it.
not destroyed mine yet and I let rip at 4300 rpm oops

I would tend to agree that the old standard ones probably have better components than many of the aftermarket ones.

The breaking point of a 3.88 Ring and pinion is round the 180bhp mark for a standard type 1 style engine, a 240bhp Scooby lump will almost certainly be turbo charged, turbos place a lot less stress on the gearbox than normally aspirated engines - the power tends to be applied less aggressively.

Paul 'Botch' Venners used to run a 300bhp+ type 1 turbo rail on a standard gearbox and never broke it, firstly because he couldn't afford the replacements and secondly because he launched gently - turbos make their power at the top end of the strip, normally aspirated closer to the start line.

I regularly dumped the clutch at around 4500 with my 2021 powered cabriolet and the gearbox was fine.

Dumping the clutch at 7000rpm at peak HP from a 2332, with 28" slicks is a different matter - this places way more stress on the gearbox, the hp being at the breaking point for the R&P anyway, it is just a matter of time before something snaps.

It is all about knowing where the weak points are and what it takes to break them, then staying inside those boundaries if you don't want it to hurt your pocket.