anyone stroke this puppy out?, I thought i remember sometime reading the 1.8 is the euro-destroked 2.0 turbo disel? so why not swap crank and rods etc and have a 2.0T. upgraded the turbo to T-28 / stg 3 / k04 / T3/T4 etc whatever you want and youd have some more grunt (trq) and the displacement would help out the spooling not like we really lag anyways, compared to other Turbo cars.

just food for thought

 

Someone asked the question two weeks ago, do a search on this board.

Note that more displacement won't help with the lag one bit because although you do put more air into the turbo you also require more from it, so it evens out.

It will of course help with torque.

 

but I'm poor

The TDi has a 79.5mm x 95.5mm bore and stroke,
the 1.8 has a 80.0mm x 86.4mm bore and stroke.

If the bore spacing and crank journal diameters are the same, the TDi crank and rods may work, but would probably require custom pistons (not a big deal).

However, before mucking about with the engine dimensions, there are some things to keep in mind. The rod/stroke ratio for one, and the stroke/bore ratio for another.

In theory, a longer rod makes for a more undersquare motor, great for torque, bad for revs and top-end power.
From a website: "A short stroke relative to bore size is beneficial because of less piston drag. A large bore relative to stroke allows larger valves to be used with less cylinder shrouding."
However, a larger bore is harder for the ignition to get a complete burn, which will cause increased emissions and possibly a greater chance for detonation. The center mounted spark plug will help against this though.

I found this on Rod/Stroke ratio:
"This ratio determines the maximum piston inertial loading and the optimum crankshaft angle (the number of degrees after TDC at which the crank throw and connecting rod are at right angles). The greater the R/S, the less the maximum inertial piston loading and the more reliable the engine or the greater the red line. The greater the R/S, the further past TDC the optimum crank angle occurs and the higher rpm at which the same maximum torque will occur with resultant higher horsepower (remember HP = torque x rpm)"

In theory anyways. I have no idea what the rod lengths are for the two motors.

 

because you have more exhaust gas going to the turbo at any given time.
More gas sooner = quicker spoolup.

But I wonder at what point does the stock exhaust manifold pose a restriction?

 

As you alluded to. The rod length isn't really the largest factor, you select it after you select the stroke if you can. The stroke is twice the journal offset of the crank.

The big deal is the journal offset or stroke length. Doubling the journal offset gives the rod more leverage on the crank and so increases torque. This might seem good, except that the rod had to move farther to produce the same amount of rotation on the crank. Thus it also reduces RPMs.

You can select whichever you'd like to emphasize. Luxury usually equals torque and low revs, since it makes the car seem like it isn't working very hard. However, to produce more power you actually need to go for the rpms. It's a wash at first glance, but as was mentioned by xr4tic, longer rods produce higher inertial loading.

Essentially, that means that at the same power output, the pistons actually have to move faster in the larger stroke engine. This happens when the rod is all the way to the side, i.e. the piston is halfway between top and bottom.

This is why F1 and motorcyle engines use incredibly short strokes and high revs. Cars would like to use it, but apparently as the strokes get shorter and the revs get higher, scavenging becomes a problem and your emissions go to pot, at least in an engine the size of a car engine. I'm sure someone will beat this soon, probably Honda or Toyota.

10K revs, here we come!

 

VW has a propensity to use similar bores. The 2.7T and 1.8T have the same bore. Does that mean one is just a modified version of the other? Obviously not.

I think this is all you see with the 1.8T and 2.0 diesel, just a propensity for similar bores, no shared heritage.

 

of like the small block Chevy history. If you look in the back corner above the oil filter it still has a distributor hole, they just blocked it off.

 

just that larger displacement will help with lag.

Although there are rumors that the 2.8 and 2.7 are the same block, just machined differently.

 

I know you weren't saying that, but the original poster implied it was so