Reducing CR by skimming Pistons or new con rods

[Crafty_]

• sigh*

In the case of the engine put together that I saw, yes it did.

To put it very simply for you, an original rod and reworked one, put on to a screwdriver shaft by the small end resulted in the 2 rods being a different length to the centre of the big end.

Completely agree this was a compromise (as did the owner/builder) and doubt it would survive in a competition engine long, but it was done and it did work, in conjunction with a reworked piston to drop CR slightly.

[mtrehy]

Thanks for keeping it so simple for me.

There was me thinking that it was the crank that dictated stroke... Glad you cleared that up.

[Crafty_]

Of course you can change the CR by the crank, you can do it with shorter rods (which has other effects too). The easiest way is to change the piston though.

[mtrehy]

Crafty

" I've seen a set where the small end was machined and moved up the rod to shorten the stroke, only a small amount mind."

Me

"No you haven't."

Crafty (picture of modified rod)

"I forget how much the one I saw was done, but there you go, thats an MR2 rod apparently."

Me

"And you think that changed the stroke?"

Crafty

"In the case of the engine put together that I saw, yes it did"


Changing rod length does not change stroke. End of story.

[Boosted LS1]

mtrehy said:

No you haven't.

Oh yes he has and it shortened the stroke :-)

[Crafty_]

In that case I apologise, I didn't answer correctly.

[stevieturbo]

A stroke of genius...eh ? lol or maybe madness

[MaxRothery]

Huff said:

I'd have thought (as a layman in these matters) if you bolt the thing together as-is at 11:1 and run it in at 2bar+ the rods will very quickly be adjusted to a more suitable length automatically...

. I was more or less aiming to lower the CR to make it more boost friendly. I did a bit of the calculations to work out how much more volume is needed above the cylinder and it comes out a 2.2mm to reduce the CR from 11.1 to 8.5. The engines I'll be using are the M13a block from a Jimmy and the hardened internals from the M16a from a swift sport. Hks do a 4psi kit with stock internals so I'd just be reducing the stress on them. Seeing as other 1.6t are running a CR of 10, a thick gasket and something like half a millimetre off the piston would do that. £700 on some forged Pistons would work as they are stronger and I could take said material off and still be relatively strong

[stevieturbo]

MaxRothery said:

I was more or less aiming to lower the CR to make it more boost friendly. I did a bit of the calculations to work out how much more volume is needed above the cylinder and it comes out a 2.2mm to reduce the CR from 11.1 to 8.5. The engines I'll be using are the M13a block from a Jimmy and the hardened internals from the M16a from a swift sport. Hks do a 4psi kit with stock internals so I'd just be reducing the stress on them. Seeing as other 1.6t are running a CR of 10, a thick gasket and something like half a millimetre off the piston would do that. £700 on some forged Pistons would work as they are stronger and I could take said material off and still be relatively strong

You do realise the difference between 4psi...and 36psi boost ? Like...seriously ?

And whilst you will need more than your calculated 2.2mm to achieve the CR drop you seek, really....have you actually given this project serious thought ?

It seems like a nonsensical question given the end goal you seem to be wantng. Either that or the end goal is nonsensical.

[MaxRothery]

stevieturbo said:

You do realise the difference between 4psi...and 36psi boost ? Like...seriously ?

And whilst you will need more than your calculated 2.2mm to achieve the CR drop you seek, really....have you actually given this project serious thought ?

It seems like a nonsensical question given the end goal you seem to be wantng. Either that or the end goal is nonsensical.

Yeah, I do realise the difference, and I have given it some half decent thought. From what I've found, swift sport internals are relatively strong, and there are forged kits out there for a decent price. There is one or two people running high boost through these engines but the bore it out and make it smaller, doing this makes it s 1.8 with 9.5 CR. And that 2.2mm is to drop it to 8.5 CR, it doesn't have to be as drastic, 1.6mm drops it to around 9.8 which will still be better to turbo than 11.1.

And it's probably both a nonsensical goal and a nonsensical question

[Stan Weiss]

There are many ways to lower the CR. One that I have not seem anyone bring up is to "Open up the combustion chamber".

Stan

[ShiningWit]

Stan Weiss said:

There are many ways to lower the CR. One that I have not seem anyone bring up is to "Open up the combustion chamber".

Stan

We have these modern multi-valve heads now here you know, you'll be lucky to get 1cc out of a combustion chamber without resorting to major work and risk of messing it up or failure.

[davepoth]

MaxRothery said:

davepoth said:

what engine is it?

. I'm looking into using a jimmy with a 1.6 internals. The M13A with M16a crank, rods and Pistons, creating a 1.6 in a 1.3 block. Only reason for doing this is that the regulations state that it must have a production variant but the engine can be modded to increase engine size. Otherwise I'd be swapping engines over

Here's a bit of info I found.

                M13A         M15A         M16A         M18A
Power         62.5kW         74.5kW         76.0kW         92.0kW
Torque         110Nm         133Nm         165Nm         170Nm
Bore/Stoke 78.0mm/69.5mm 78.0mm/78.0mm 78.0mm/83.0mm 83.0mm/83.0mm
Compression 9.5:1         9.5:1         11.1:1         9.6:1

If this is correct you want the 1.5 gubbins, not the 1.6. Whatever power you lose from the small capacity you'll more than make up for in boost.

Here are some 9.0:1 Forged pistons for that engine.

http://www.ebay.co.uk/itm/Wiseco-Forged-Pistons-TU...

Edited by davepoth on Thursday 21st May 19:44

[stevieturbo]

davepoth said:

Here's a bit of info I found.

                M13A         M15A         M16A         M18A
Power         62.5kW         74.5kW         76.0kW         92.0kW
Torque         110Nm         133Nm         165Nm         170Nm
Bore/Stoke 78.0mm/69.5mm 78.0mm/78.0mm 78.0mm/83.0mm 83.0mm/83.0mm
Compression 9.5:1         9.5:1         11.1:1         9.6:1

If this is correct you want the 1.5 gubbins, not the 1.6. Whatever power you lose from the small capacity you'll more than make up for in boost.

Here are some 9.0:1 Forged pistons for that engine.

http://www.ebay.co.uk/itm/Wiseco-Forged-Pistons-TU...

Edited by davepoth on Thursday 21st May 19:44

he seems to suggest he has to retain his M13A block.

Either way, how to reduce the CR really is the least of his worries/easiest part of a reliable 2.5bar boost in such a setup.

If he cant get past that small step, he stands little chance of the difficult work.

[anonymous-user]

stevieturbo said:

Either way, how to reduce the CR really is the least of his worries/easiest part of a reliable 2.5bar boost in such a setup.

Pffft, develop a reliable & competitive 35bar BMEP inlet restricted turbo engine? Easy. What is he going to do after lunch?? ;-)

[Stan Weiss]

ShiningWit said:

Stan Weiss said:

There are many ways to lower the CR. One that I have not seem anyone bring up is to "Open up the combustion chamber".

Stan

We have these modern multi-valve heads now here you know, you'll be lucky to get 1cc out of a combustion chamber without resorting to major work and risk of messing it up or failure.

So how are they any different than what is on my FORD 2.5l 16v DOHC?

For each cc he can get out of the combustion chamber that is .2 mm less he has to cut off of the piston. A picture of his combustion chamber would help.

Stan

[stevieturbo]

Stan Weiss said:

So how are they any different than what is on my FORD 2.5l 16v DOHC?

For each cc he can get out of the combustion chamber that is .2 mm less he has to cut off of the piston. A picture of his combustion chamber would help.

Stan

Well...he is full of "Wit" I guess lol

Of course chambers can be modified, 1cc would not be difficult from most, and more is usually easy too


https://www.youtube.com/watch?v=IRAjpx7dMSA

Edited by stevieturbo on Thursday 21st May 21:51

[ShiningWit]

Stan Weiss said:

ShiningWit said:

Stan Weiss said:

There are many ways to lower the CR. One that I have not seem anyone bring up is to "Open up the combustion chamber".

Stan

We have these modern multi-valve heads now here you know, you'll be lucky to get 1cc out of a combustion chamber without resorting to major work and risk of messing it up or failure.

So how are they any different than what is on my FORD 2.5l 16v DOHC?

For each cc he can get out of the combustion chamber that is .2 mm less he has to cut off of the piston. A picture of his combustion chamber would help.

Stan

We got fancy 1 ltr engines, turbos, fuel injectors, ECUs and everything too, no carbs here you know.
Seriously, if the OP had spelled the car properly it would have helped, he mentioned a 'Jimmy' which should be Suzuki Jimny, and the 4vpc combustion chamber for that will look like hundreds of others, they all take the same form, here is one:



Not much room for any removal there.

[ShiningWit]

stevieturbo said:

Well...he is full of "Wit" I guess lol

Of course chambers can be modified, 1cc would not be difficult from most, and more is usually easy too


https://www.youtube.com/watch?v=IRAjpx7dMSA

Edited by stevieturbo on Thursday 21st May 21:51

Aw come on, that's an expensive bodge - how much is it going to cost to program a multi axis CNC mill to do one job? Then what about the valve seat/heads sticking out? Even then you won't take anywhere near 3 points from the CR. A set of forged pistons the correct CR is the only way.

[Boosted LS1]

Why not offset grind the crank journals in the block to lower the crank. Easy peasy, jobs a goodun. Then all you need is a lowering spacer for the sump.