Rod Ratios

[TCJBOLDIE]

Obi has started a crankshaft thread and in it I have mentioned "ROD RATIO " so I thought that it should have it's own thread as it was something that many have overlooked when building a performance motor

http://spicerparts.com/calculators/rod-ratio-calculator

 

[thexav]

Interesting, were getting really tecky now!

How would you reduce compression ratio in an engine with rod ratio or can't you?

 

[TCJBOLDIE]

Rod ratios is more about the ability of the engine to be able to rev with the least side thrust on the piston skirts.

Rod ratios have nothing to do with raising or lowering the static CR

The best way IMO to reduce the CR is by installing pistons with the right dish/hollow in the crown/top that adds volume to the combustion chamber at TDC.

I would not advise machining the piston crowns as that weakens them and in a turbo car increasing the boost raises the combustion pressures way above the NA static advertised number and can break.

If building a hi performance motor there is only one way to do it if you want it to last and that is by using the best parts you can afford IE forged rods,pistons and crank along with a MLS head gasket plus ARP or stronger bolts and studs where possible.

 

[TCJBOLDIE]

Interesting, were getting really tecky now!

How would you reduce compression ratio in an engine with rod ratio or can't you?

Yes it is possible by installing slightly shorter rods to the std pin height pistons which would prevent the piston crowns being level with the block deck @ TDC BUT why would you

Here is another link that explains tt whys and why-fores a bit better.

http://www.motoiq.com/MagazineArticles/ID/1996/PageID/3226/Does-Length-Matter.aspx

 

[SLEEPER]

there isnt one magic ratio for rods as it depends on so many things all engines are different

I only know RB26DETTs but at 2.6 they rev for england with the right parts and you can keep the revs with a 2.7 and maybe with a 2.8 .both are just stroked.
When you go for more ccs you need to bore the motor as well as stroking the motor to 3 litre limits the revs too much (piston speed).
Then you have safe serious power with the right upgrades and with a much quicker spool up

 

[wizzer]

Sorry for the noob question.

So what is a stroker kit? Does it include pistons, rods and Crankshaft or just one of those items?

 

[TCJBOLDIE]

https://www.ebay.com.au/i/252638018542?chn=ps&dispItem=1