Crank off setting .... does any of you's know anything about it ... was speaking to some tech guy and he was saying i could regrind/offset the big ends on the crank by about .50thou ( max bearing size ) this in turn would be like stroking the engine now i know this would drop the Piston TDC by about 1>2mm and decrease the com .. and to over come the comp drop the block can be skimmed/decked to bring back the comp or even raise it a little. does this sound a sound right and any one done such thing ?

thanks again

Mark

i find it strange that the stroke is increased as per normal then reduced by maching, so back to square one plus the oversizes on the crank have been used up:confused1: or am i missing something here?

well thats what i was trying to get my head around ... the only benefit i can see by it is the increase in torq as the bigger the rotation of the cycle will make it easier for the piston to push down on fire .. in turn give u a increase in power output ...

 

does it make sense or i'm i sprouting a load of shit ? haha

Generally you only grind the crank if you have spun a bearing and it's damaged the crank in the process, the engineers will tell you how much they've had to take off to get it smooth, then you fit over sized bearing to compensate for the ground crank putting you back to the thickness you started with, acl do .25 ect over size,

 

The only way of stroking the engine is bigger pistons and using stroked crank n rods,

 

You can lower the compression with either custom pistons or fitting a thicker Headgasket, this means you could run more boost safely on standard fuel

 

But back to the original question no fitting over sized bearings will not stroke the engine

ok dont think u understood what i asked ... ... Its not just regrinding the big end .. its all so about Off setting them by 50thou

in turn it will have a Larger rotation radius

Another factor is a long stroke does not like rpm unlike a "square" stroke....stroking is a fav mod in big V8,s as peak power is produced more by the size of the bang and not rpm,s as on turbo motors so i can see increases from bore size increase but i cant see the + side of stroking these motors myself.

Yea I did but what I'm saying is that's the only reason you would fit oversized bearings,

 

If you fitted bigger bearings to a standard sized oem crank then when fitting the caps back to the crank and rods it's not gonna tighten as it sould as its designed for a certain sized bearing

The only + on stroking is increasing the displacement say if you made it to a 3.2 it would be ever so slightly less laggier when fitting bigger turbos as there would be more air to spool them up quicker

The only + on stroking is increasing the displacement say if you made it to a 3.2 it would be ever so slightly less laggier when fitting bigger turbos as there would be more air to spool them up quicker

 

you can increase displacement by bore width without changing the stroke..thats my argument:winkiss:

Yep I'm not saying you can't just saying cant be done with bigger bearings lol

 

Yep bore width is the easiest way of doing it, and done by most when fitting larger pistons than standard

well thats what i was doing anyways ... jumping up to 89mm ... it was only when talking to some one that he explained this way of getting more power and displacement

thats why i'd thought i ask the Q

 

i can see how it would work but in practice ... will it

 

89mm pistons and 85mm stroke takes it up to 3173cc all most 3.2l

Yep I'm not saying you can't just saying cant be done with bigger bearings lol

Yep bore width is the easiest way of doing it, and done by most when fitting larger pistons than standard

 

yep i cant see this too just by increasing bearing size:confused1:

well thats what i was doing anyways ... jumping up to 89mm ... it was only when talking to some one that he explained this way of getting more power and displacement

thats why i'd thought i ask the Q

 

i can see how it would work but in practice ... will it

 

89mm pistons and 85mm stroke takes it up to 3173cc all most 3.2l

 

theres not much clearance from the bottom of the piston skirt to the block so does it include shorter pistons in the equation?

That's right mark just stick to fitting a larger piston and the will increase as you want, I'd just forget about what the other guy said lol

not sure of that but theres ppl fitting 89.5/90mm pistons with out any problems other than treating the block

any updated pics on the build Mark??

The Americans are way ahead of us in building these engines they often get a lot more power out of most makes of engines than we do,

 

The only risk of course would be cracking the thinner bores under extreme heat, but if its be done before why not try it,

 

On another question before I get my block rebored if I'm fitting 1mm oversized pistons will the machine shop know how much to take off the bores or will I have to specify this, as I know different makes of pistons have different clearance/ tolerances?

by forged 87.5mm engine is fitted and running ...

 

but just sorting out my shopping list again

 

Bigger pistons

Cams

Pulleys

The Americans are way ahead of us in building these engines they often get a lot more power out of most makes of engines than we do,

 

The only risk of course would be cracking the thinner bores under extreme heat, but if its be done before why not try it,

 

On another question before I get my block rebored if I'm fitting 1mm oversized pistons will the machine shop know how much to take off the bores or will I have to specify this, as I know different makes of pistons have different clearance/ tolerances?

 

when i used to build bike motors mate i bought the pistons 1st and after reading the clearance specs then gave this to the machine shop to drill the holes...i used a lot of wiesco forged slugs which required a big clearance.

Yea I know cp use a small clearance and sometimes accur piston slap when cold,

 

I just wanted to get the block sorted while I'm saving for parts, could email z1 and ask them what the clearance would need to be

yep what he said ...

little research and then buy pistons .. then off to machine shop