Here goes:
1.7 & 1.8 have 66 mm cranks, 55 mm rod journals,
127 mm long rods.
2.0 have 50 mm rod journals, and 131 mm rods
T1 has 55 mm rod journals, 137 mm long rods
2" Chev. journal = 50.8 mm
Rabbit/Golf = 48.76 (Don't have the length handy)

stock rod ratios:
1.7/1.8 =1.92
2.0      = 1.84
T1       =1.98

Stroker rod ratios:
T4 w/78 and stock 2L rods = 1.68
T4 w/78 and 135.26 (5.325") rods = 1.73
T4 w/78 and 137 mm (5.394") T1 rods = 1.76

Note: T4 has 24 mm gudgeons, T1 has 22 mm

When stroked to a 78 mm it is possible to use T1 rods (T1 rods bearing are narrower than T4 so this also needs to be addressed by the crank grinder) and will basically drop into a T4 case. The rod ratio is good with either T1 rods or Eagle 5.325 rods.

To offset grind a T4 crank, use Rabbit rods, this gets a 1.5 mm increase in stroke, a longer rod, and 22 mm gudgeons. This works with 94 mm 'B' pistons from a T1. By going this route, you drop a lot of weight off the rod and piston which really helps acceleration of the piston/rod mass. The minus is you have reduced the strength of the crank a little bit, but the T4 crank is much stronger than a T1 due to the bigger main journals and slightly thicker cheeks.

For street motors that will be built with a reasonable compression ratio, use pistons for 80 or 81 mm stroke on a 78. This will help you get your deck height and compression ratio goal when using longer than stock rods. This will also (usually) give you 22 mm gudgeons. Go the extra money for forged pistons, they are lighter and stronger.

This is NOT the bible on T4 motor enlargements, just some facts and opinions that I have ran across in My research to build my 2650 cc T4.  I will also be listing some (As I find and have time for) resources and links for parts, technical info, and whatever else I find that is relevant.

Tom Hansen

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