8 replies to this topic

[Java_Green]

I am building a supercharged A+ engine and looking for advice considering choice of pistons. Since I am about to put in new cylinder liners I would prefer STD dimension, i.e. 70.60 mm in diameter. The aim is approximately 9.5:1 in compression ratio with a compression chamber volume of 23cc, so some dish is needed.

[Steve220]

I'm not sure about classic mini cylinder liners, but on bigger blocks if they're press fit, they need to be bored and honed anyway - Do they come undersized to bore to 70.60? You are severely limited yourself to piston choice at 1275, at 1293 (+20) you open yourself up to both cast and forged options. As well as lowering your CR with size alone.

 

9.5 CR is quite high for boosted - why have you chosen that?

[mini13]

the liners are basically at 1275 size, but they will at least need a hone, and probably a light bore

 

also bigger bore will raise the compression not lower it

 

 

https://westwoodcyli...0-1380-engines/

 

[Java_Green]

I'm not sure about classic mini cylinder liners, but on bigger blocks if they're press fit, they need to be bored and honed anyway - Do they come undersized to bore to 70.60? You are severely limited yourself to piston choice at 1275, at 1293 (+20) you open yourself up to both cast and forged options. As well as lowering your CR with size alone.

 

9.5 CR is quite high for boosted - why have you chosen that?

I know that 9.5 in CR is considered as high for a boosted engine. My guess is that a CR of 9.1-9.5 is suitable for the application and set up (other opinions and knowledge is more than welcome). This is roughly my thoughts; the ERA run a CR of 9,4 and with a fairly similar combustion chamber design, about the same boost level, ECU controlled ignition and fueling (X-flow head with injector in each runner), with a better heat dissipation (Aluminium head) and lower intake temperature (in the front and not "turbo heated"). 

[Java_Green]

I am thinking that the liners needs to be bored out to 70.60 mm (std dimension) when fitted into the block. It would be good to not go for +20 directly as that would make it possible to at least rebore the block once without replacing the liners.

[Steve220]

the liners are basically at 1275 size, but they will at least need a hone, and probably a light bore

 

also bigger bore will raise the compression not lower it

 

 

https://westwoodcyli...0-1380-engines/

Yep, you're right. Had a mind fart this morning

[Steve220]

 

I'm not sure about classic mini cylinder liners, but on bigger blocks if they're press fit, they need to be bored and honed anyway - Do they come undersized to bore to 70.60? You are severely limited yourself to piston choice at 1275, at 1293 (+20) you open yourself up to both cast and forged options. As well as lowering your CR with size alone.

 

9.5 CR is quite high for boosted - why have you chosen that?

I know that 9.5 in CR is considered as high for a boosted engine. My guess is that a CR of 9.1-9.5 is suitable for the application and set up (other opinions and knowledge is more than welcome). This is roughly my thoughts; the ERA run a CR of 9,4 and with a fairly similar combustion chamber design, about the same boost level, ECU controlled ignition and fueling (X-flow head with injector in each runner), with a better heat dissipation (Aluminium head) and lower intake temperature (in the front and not "turbo heated"). 

 

Oh, you're going 7 port?

[Java_Green]

I'm not sure about classic mini cylinder liners, but on bigger blocks if they're press fit, they need to be bored and honed anyway - Do they come undersized to bore to 70.60? You are severely limited yourself to piston choice at 1275, at 1293 (+20) you open yourself up to both cast and forged options. As well as lowering your CR with size alone.

9.5 CR is quite high for boosted - why have you chosen that?

I know that 9.5 in CR is considered as high for a boosted engine. My guess is that a CR of 9.1-9.5 is suitable for the application and set up (other opinions and knowledge is more than welcome). This is roughly my thoughts; the ERA run a CR of 9,4 and with a fairly similar combustion chamber design, about the same boost level, ECU controlled ignition and fueling (X-flow head with injector in each runner), with a better heat dissipation (Aluminium head) and lower intake temperature (in the front and not "turbo heated").

Oh, you're going 7 port?

That is correct!
7-port it is... Front mounted supercharger feeding a plenum from where a runner goes to each port.

[Steve220]

Ah, you'll be fine with a high CR then. The alloy will help remove the heat from the combustion process better and you'll have greater control over fueling. I've got 9.5 and full send! Although, be careful if you're not running an intercooler/chargecooler, inlet temps can rocket!