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Worth sacrificing rod ratio for extra stroke? Toyota 3S vs 5SGTE

Engine Building Fundamentals

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I am planning out the build of my new race engine for my time attack car. I am going to be using a 5S-FE engine block, which is known to be stronger than the 3S-GTE engine block, and the cylinder head from a 4th generation 3S-GTE with Kelford 272 degree cams.

My main question is around use of the 5S vs the 3S crank. The 5S crank has a stroke of 91mm, the 3S crank has a stroke of 86mm. The rod length is the same on both - it is the pistons which differ with the wrist pin location on the 5S piston being higher than on the 3S piston.

Stock rod length is 138mm, going the 5S crank route gives a rod ratio of 1.51:1 and the 3S crank gives a rod ratio of 1.6:1. I played with the idea of using 5S pistons and a custom longer rod, which would give a rod ratio of 1.66:1, however I think the added expense of going down this path and also the lead time of waiting for custom stuff may not be worth it, as the 3S stock rod length is already a pretty well proven option.

So I guess I'm looking for opinions from those more knowledgable than me with engine building - is it worth using a 5S crank and getting the extra stroke at the expense of the rod ratio, or stick with the 3S crank? To me, 1.5:1 seems pretty low for an engine that is going to spend most of it's time higher in the rev range. I'm not chasing huge power, I just want the thing to be reliable so I can do as many events as I can. Planning on using a Garrett G25-660 on the engine.

Thanks in advance for any feedback.

i was involved in a similar build i went for the 5s crank and block with a 3s head only bord it to .020 and it went very well same cams etc i can't remember the numbers but it was in the mid to late 350-400 wkw area with 30 psi boost . i remember the 5s crank was slightly heavier about 3lbs i think, i do remember going through a few 3s blocks trying to find one with good thick bores with no success, and snapping a few blocks learning years ago,

Regards Ross

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