T500 piston mods

[dbc105]

I've bought a set of Zookie Stage II barrels from a fellow in Ca. that never installed them. He also had a set of pistons that had been modified only thing was it looked like factory cast pistons were use and I run forged pistons in my bike. I'm trying to find out what the mods are so I can make the same mods to my new Wisecos. He said they were modified on the top and I wondered if the dome was rounded more in order to add to the transfer and the exhaust timing duration. Can anyone help me out? Then also how much would that drop the cylinder pressure?

Thanks,
DC

[Zunspec4]

Hi DC,

Altering the dome of the piston will make no difference to the port timings* but the PO may have done this to set the squish clearance. On my race engines one uses Weisco and the other Wossner and the combustion chamber is profiled to match their particular piston domes.

Cheers Geoff

* - Unless the dome is lowered solely in line with the transfer port opening which is effectively raising the transfers.

[tz375]

It's not unheard of to modify the crown of a 2 stroke piston, but it is unusual. Do you have any pictures so we can see how different they look to stock or to the WISECOs?

BTW, for the street, cast are arguably more suitable. And they are cheaper. But if you already have the Wiseco's it's a moot point.

[dbc105]

No, I don't have any pics or measurements. I've read of where a two stroke piston is modded either on the crown at the locations of the exhaust and transfer ports and it said not to get any closer to the top of the top ring groove than 2mm.

As to the cast pistons, it is not a street bike it is one of my race bikes and everything I've read has said don't turn cast pistons to higher rpm due to skirt problems. So it is just as easy to run forged.

As to the squish, he didn't have squish heads, he just had stock heads which have no squish. i wish I had a set. I save a little money I want to sent a set of heads to RK Tek and get them done.

I was hoping someone here was familiar enough with Zookie's work and would know. I looked at his profile and it didn't look like he has been here in some time and so asking him looks to be a stretch. These barrels look good and he did a fantastic job on them and I'm glad I was able to get them. Always good to be able to depend on someone else's experience that has had good success.

As a side note, looking to get it on the track next weekend at Roebling if all goes well.

DC

[diamondj]

Hey - it's possible the skirts were modified for timing, or they could be balanced so the piston weights are similar, or it could just be the cylinders are bored to match the cast pistons. The most likely mod is the skirt edges are chamfered to not catch on the porting. You realize your piston to cylinder clearance will be wrong (ie too tight) if you switch to the Wisecos, right?

[D&D CHASSIS]

I have heard RKTek is highly over rated....... according to quite a few performance sled guys......