It can be done by a crankshaft reconditioner, but only if your willing to go to a different conrod with a smaller bigend. Exactly how much depends on many components, and what your trying to do.
I destroked a 1600 to build a big bore 1300 race engine, then CAMS changed the rules 😂😂😂.
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I was thinking of a race engine at 60 (stroke)x92 (thickwall) (bore) which would be 1595cc which is ok for class C tarmac rally cars, where I want to put the car eventually
The rules state that for Class C (i think i was class c) that you can go up to the limit for the original class your stock motor falls into, ie 1300cc in the 0-1600 class can go up to 1600cc.
Shaun... what sort of events are you planning on running in ???
Tarmac Rally regs are a bit fluid to say the least, and realistically unless you're going to do something like Targa or Classic Adelaide then you're likely better off sticking with 3J. Also Targa is now run under AASA, so as far as I know the CAMS classes are only used as a reference.
My advice would be work out what events you want to run (specifically), identify the guys/cars that would be good to compete with, then build a car to suit that class. Going up to 1999cc like Dave has suggested for example is a 3J Improved Production trick. BiX did it with his engine, Marcus also, and pretty sure that Grant Cook's beetle also is a 72mm stroke.
👍
EDIT : Sorry - just realized the "not a combo discussion" at the start... ignore me.... 😊
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VWDCQ vice pres & web dude - vwdcqinc.org.au
Join a car club - get car peeps
My toys
'70 Hillclimb Bug 'Jezebel' w/- Haltech EFI - http://bit.ly/VwTNtQ
'60 KG Coupe - resto kinda started
01 New Beetle - gf's car, but I turn the spanners
you really need to read the regs cause most say an overbore of 1mm max dunno bout your class but if you wana be competitive they may ask you to prove your combo!!
Sides wrote:Going up to 1999cc like Dave has suggested for example is a 3J Improved Production trick. BiX did it with his engine, Marcus also, and pretty sure that Grant Cook's beetle also is a 72mm stroke.
Not really a trick.......the trick is about building a winning combo that fits within the cc range for the class. Most of the under 2lt class winning cars were never close to 1999cc.
VW 1100 used a 64 mm stroke crank (and 75 mm cylinders). Only sold in Australia in the early months of 1954 so you won't see any around.
VW 1200 36-hp (1954-60) also used 64 mm stroke, with 77 mm cylinders. The 1200 40-hp (1960-66) was dimensionally exactly the the same but redesigned.
VW 1300, 1500 and 1600 all used 69 mm stroke.
You can increase or decrease the stroke of a crank by offset grinding. A crank's (half) stroke is measured from the centre of the main bearing journal (that is, the crank centre-line), to the centre of the big-end journal. To decrease the stroke, you have to move the big-end journal centre closer to the crank centre.
To use an example. Let's say your crank is a 69 mm and you want to make a custom version with a 67 mm stroke. You measure the diameter of the big-end journal, and let's say it's 50 mm across. You have to move the centre of that big-end journal 1 mm closer to the centre of the crank (since half of the stroke - the complete circle - is the radius). So, you machine the big end into a new circle with its centre 1 mm closer to the crank centre. You end up with a 48 mm diameter big end, offset 1mm closer to the crank centre than before. And there you have it - a 67mm stroke. The change in big-end diameter is the same as the change in stroke. Of course you'll need custom rods with smaller big ends and bearings to go with them.
Volkswagen did this trick in reverse with the Type 4 motor when they went from 1800 to 2000cc in 1975. It's the same crank but the big ends have been offset ground outwards to go from a 66 mm to a 71 mm stroke. The 2000's big-ends are 5 mm smaller than the 1700 and 1800.
Do a Google search on 'crankshaft offset grinding' - it's a pretty common hotrodding trick but probably not financially viable for VWs, given the ease of swapping cylinders and pistons instead.
