rod/stroke ratio

[krappy]

im building up a celica engine (3sgte) and i wana swap in a camry crank cause it will stroke it to a 2.2L. Problem is, the R/S ratio for the celica is already 1.6 something if i do the swap itl be 1.5 Im worried this might destroy my cylinder walls in high revs and cause reliability problems. Im considering buying longer rods, but how am i supoed to lift the head so that the pistons dont hit the valves. or, am i supoed to be by an even lower compression piston?. for some reason i think iv seen gasket sets that raise the head for this kind of thing. But id be raising it over 5 mm. Any suggestions?

[2.2 Straight six]

are you sure the crank's compatible?

[slideways...]

usually you can contact a company that makes pistons and rods and they make a shorter piston plus move the wrist pin slightly up to give clearance for a longer rod. plus you could get a thicker HG.

[SaabJohan]

First, there is usually no point in increase the stroke so much that you end up with a bad crank geometry. Infact, the main reason to increase the stroke is that it can be done more easy than an increase in engine speed. I would however recommend that you analyze the engine first, what is easier to to, increase the stroke or increase the engine speed? Remember that increased stroke means increased torque, this means a higher load on the tranmission.

If the rod length is increased, this should be combined with pistons with a lower compression height.

[chevy2808]

in the immortal words of smokey yunick, "It is essential to use the longest connecting rod you can possibly fit in the engine!" If the piston dwells longer near top dead center and the ignition is dialed in correctly, the power created during the combustion to press against the top of the piston, which translates into more effort against the piston during the early stages of the power stroke.
There is also a secondary mechanical advantage from a larger rod ratio. since the piston dwells longer near the top of the stroke, the crank arm swings over further before the combustion cavity begins to open. this allows the pressure of combustion to be more effectively transmitted to the crank arm during the period when pressure is the highest. this increased leverage exists throughout the power phase and the end result is a smoother running engine that produces more effective work during the power stroke.

[MillsCarbs]

Let us not forget another benefit to increasing rod to stroke ratio. Cylinder wall side loading coming off BDC is reduced, and therefore frictional losses are reduced. We can see this example when looking at the 302 ford with a rod to stroke ratio of about 1.6, as you look at the rod angularity coming off BDC you will notice it is quite poor. If you look at the 351 Windsor with a slightly better rod to stroke ratio of 1.75 you will see much less cylinder wall side loading.

Regards,
Josh Mills
millscarbs.com