Offset crankshaft grinding

[TH Performance]

why would you use 5s pistons since these are weak?!

listen:

live the rods alone, offset grind the crank and make custom pistons, this is the cheapes way to do it, if you wnat to make 2.3L

[Roundy]

Oversquare has (almost) nothing to do with the ability to rev.

It is mostly dependant on the length of the stroke.

A shorter stroke has the ability to rev higher than a longer stroke, basically regardless of piston diameter.

So yes for a given capacity an oversquare engine will have the capability of higher revs, but that is only compared to different geometry engines in the same capcity.

But if you are suggesting that a 3S crank in a 5S block with 88mm pistons has the capability to rev higher than a 3S crank in a 3S block it is just wrong.

[TH Performance]

no it is not, sine the 3s block is shit for higher HP and will crack.

It is always or TTE or 5s block used for racing.

That said, IF 3S block would be STRONG enough for racing/thrashing, THEN it would rev the same.

BUT there is added 0.1L capacity that you can really feel while driving.

So you are right, but not for this particular case of 3s block

[jonathan yee]

why would you use 5s pistons since these are weak?!

listen:

live the rods alone, offset grind the crank and make custom pistons, this is the cheapes way to do it, if you wnat to make 2.3L

should clarify "5s sized" pistons ie 87mm+ with the higher pin height. noone in their right mind would use stock 5sfe pistons.

so did you get custom pins with an even higher pin height than the 5s spec? i didn't think there'd be much room left.......thin crown?

[jonathan yee]

Oversquare has (almost) nothing to do with the ability to rev.

It is mostly dependant on the length of the stroke.

A shorter stroke has the ability to rev higher than a longer stroke, basically regardless of piston diameter.

So yes for a given capacity an oversquare engine will have the capability of higher revs, but that is only compared to different geometry engines in the same capcity.

But if you are suggesting that a 3S crank in a 5S block with 88mm pistons has the capability to rev higher than a 3S crank in a 3S block it is just wrong.

i was thinking that it'd add to it's ability to rev if you change the rod/stroke ratio.

such as 3s crank, 5s block 5s spec pistons with the pin height higher and longer rods. this is what i'm aiming for, this would give me an improved rod/stroke ratio 2070cc with .5mm OS pistons,

if i could get a shorter stroke crank easily and longer rods again, retain 1998cc then i'd consider that. but i think i'd need a custom billet crank for that.

[Roundy]

Yes a longer rod does help a bit, but it is a smaller effect than the difference in stroke.

[TH Performance]

yes u r right

[ed]

yep, agree with everything said avove. all pretty good and correct info

just wanted to chime in with mine, destroked a 1UZ crank from 82.5mm to 78.5mm. same journal sizes as are being talked about (from 52 to 48mm). and if youre cunning you might find, as i did, that the honda 1.888" journal is this size, and suddenly you can start picking rods from SBCs running a honda journal (theres heaps). im managed to squeeze in a 6" sbc nascar rod, and along with a the destroke, did a set of custom slugs, and with the rods, got a rod stroke rati of about 1:1.95 or something!

and just for pics for folks who dont know what it looks like, heres one of my offset ground journals. you can see the remanants of the original journal, and can see how the journal centreline has moved 2mm (4mm destroke)



cheers
ed

[CHB]

ed_jza80,

whats "SBCs"?

[RONA]

Small Block Chevs.

[ed]

that ^^^^^^^^^^^^

[MWP]

Since ill be doing a 5S-GTE build shortly too, im also considering the offset grinding option.

Im wondering if i can use the "standard" CP 8.5:1 5S piston, with a little (1-2mm) machined off the top to bring the pin height down.
Ill end up with higher comp (dont want over 10.5:1 though), but with E85 becoming more common, it shouldn't be a problem.
I havent done the calcs yet to see how much i can actually take off the piston top without increasing compression too far though.

I am worried about the rod/stoke ratio too, and the decreased life-span that will come with it.

[jonathan yee]

i supposse it depends on what HP you want and wether you think an extra 100cc(over the standard 5s stroke) will make much difference.

you wouldn't go extra stroke on the 3s block as you generally only want to bore them out 0.5mm so the bores don't crack which will mean you won't get the full capacity increase of the extra stroke.