stroking and compression ratios

[barryogen]

I understand the principle, and how it works basically, but where can you find info on stroking particular engines?

From googling I've found that the 2zzge can be stroked by using the crank from the 1zzfe, and then grabbing a set of rods and pistons from someone hawking them... but my thoughts are, the rods in the 2zz look to be the same as the ones that get sold with the kit and are pretty beefy anyway, and custom pistons are on the agenda for my car for adding a bit of boost... so why not add another 200cc while I'm at it for the cost of a 1zz crank(~700 last time I checked).

Now changing the stroke would presumably change the static compression, so even low compression pistons for a stock 2zz, due to the much longer stroke, would probably end up being rather high compression ratio when using a much longer stroke?

So... is there a calculator online, or even just a formula where I can feed in my current engine details, that will spit out compression ratios if I change x, y and z?

FYI
1zz is 79 x 91.5(BxS)(10:1 stock compression ratio)
2zz is 82 x 85(BxS)(11.5:1 stock compression ratio, 8.8 and 9{assuming stock stroke} readily available)

[fivebob]

The comp ratio will change if you use the same rods and the pistons. Normal practice is to either move the pin further up the piston (preferable but not always possible), or use a shorter rod (which results in a poorer rod/stroke ratio).

[barryogen]

Thank you fivebob, I realised that it would change, I was just wondering if it is an easy to calculate thing or not.

Just to overly simplify it, if I used the 1zzfe crank, the stock rods with pistons that would have a comp ratio of 9.0 with the stock crank... what would that mean using the new crank... or is it not easily "work-out-able"

[TRD Man]

Assuming that the stock CR is 11.5 to 1 and that you use the same cylinder head, gasket & piston crown, and that the piston reaches TDC at the same point as with the 2zz crank, you will have approx. 12.3 to 1 CR.

If you started out with 9.0 to 1 CR you'd have 9.61 to 1 after the same mods.

[barryogen]

that sounds like it would make a fun machine assuming that it is still happy enough to rev to 8300...

[fivebob]

It's not so much a case of it can't be worked out, more that it won't work.

If, like most engines, the stock one has the pistons at the top of the block at TDC, the engine will self destruct in a few revolutions as the pistons try and push through the head.

If you move the piston pin position, or used shorter rods, and kept the same combustion chamber volume then it's easy to work out. Simply put it's New Stroke/Old stroke * current Compression Ratio. In this case that works out as 91.5/85* CR or 9.69:1 for an existing 9:1 CR

[barryogen]

If, like most engines, the stock one has the pistons at the top of the block at TDC, the engine will self destruct in a few revolutions as the pistons try and push through the head.

hahaha, thanks for that, just managed to draw myself a mental picture of it... I guess they will be using the Rods for the 1zz then as someone else who had done it said they used the stock ones... but he 1zz stock rods look like pencils compared to the 2zz rods.

ahh well, continue the research then

Thanks for that guys.