pistons

[twin_c's]

Hi all been looking through the web recently and found that hyundia atos G4HC engine is a 66mm bore and the pistons are a dished piston so they would be good for a boosted motor. the specs are a 25mm comp height and 17mm gudgeon pin dia. anyone have any idea if these would work?

[James]

I might have a city piston at home, I will have a look. The city piston is flat top, you wouldn't want to go any lower in compression than it is already, otherwise performance will suffer.

[twin_c's]

the dished piston would be good for high boost applications (25+ psi) or a longer stoke crank with the dish machined out

[James]

Its already ridiculously long stroke, I wouldn't think you would want to hurt the redline any more.

Even at 25 psi boost with the stock, very low CR of 7.6:1, I would be extremely surprised if you were being limited by detonation, rather than piston / rod strength, especially with the very high octane petrols commonly available now. I'm guessing the city CR is where its at because it was designed to be able to run on 91 RON.

If anything building a modern city engine you would want a slight dome, allowing you to get to 9:1 or there abouts, get even more torque and get the turbo spinning even sooner.

[bmgjet]

Its already ridiculously long stroke, I wouldn't think you would want to hurt the redline any more.

Even at 25 psi boost with the stock, very low CR of 7.6:1, I would be extremely surprised if you were being limited by detonation, rather than piston / rod strength, especially with the very high octane petrols commonly available now. I'm guessing the city CR is where its at because it was designed to be able to run on 91 RON.

If anything building a modern city engine you would want a slight dome, allowing you to get to 9:1 or there abouts, get even more torque and get the turbo spinning even sooner.

Defently agree with not wanting to go longer with the stroke or lower the compression any more.

I measured the compression on a T1 engine Iv got spare as 7.3:1 which is extremely low. That should be sweet up to 30psi on 95 octane if the parts could handle that power. If anything youd want to increase the compression to high 8s low 9s. And a bigger bore would be preferred over long stroke. The sleeves look quite thick from a visual inspection.