Piston Size - 20 Valve Blacktop

[Trekka273]

I am looking at various options to upgrade a 20 valve blacktop engine.

I have one question in regard to oversize pistons. I believe the largest made by TODA, and also as oversize pistons from Toyota is 82mm. If I were to get some pistons made, is there anything stopping me from going to 82.5 mm pistons? Is the bore able to be bored enough out to suit these pistons?

If I go this option, I cannot go to an engine greater then 1650cc, and with the standard stroke of 77mm and an 82.5mm bore I would get a capacity of 1646cc. I figure that every bit of counts and this might be a good way of getting a little extra power, provided of course there is enough meat left around the bores.

Thanks for your help.

[Sam_Q]

anything greater than 82mm is considered risky buisness, there was a thread on it a while back. People usually increase the stroke for extra cc, but I guess that's not a real easy option for you for such a small increase. Are you sure it would make 1650cc? doesnt sound right to me

[Trekka273]

Yep, I am sure that an 82.5mm bore with the standard 77mm stroke would produce 1646cc. The 82mm bore works out around 1624cc approximately (I don't have exact figure here with me at work).

If it will cause problems then I won't go the extra 0.5mm, but I thought it would be good if I can get it.

What about if I were to get the block bored out further and sleeved, woudl that make it any safer?

[Sam_Q]

sorry I dont know anything on this topic, however I found the link for you:

http://toymods.net/forums/showthread.php?t=14130

[Trekka273]

Hhhhmmm an interesting read.

There really wasn't a definitive answer there one way or the other. Would 0.5mm piston diameter, over the largest that Toyota make, really make that big of a difference to the bore? I don't know. I wouldn't have thought so, but after reading that other post I am not not sure I want to take the risk.

[oldeskewltoy]

Hhhhmmm an interesting read.

There really wasn't a definitive answer there one way or the other. Would 0.5mm piston diameter, over the largest that Toyota make, really make that big of a difference to the bore? I don't know. I wouldn't have thought so, but after reading that other post I am not not sure I want to take the risk.

Are you sure of this??? My expereince is with 16V slugs... but all the 20V information I have says the largest Toyota goes in O/S is .5mm from standard... making their widest offering 81.5mm Do you have other info????

[Sam_Q]

also raises the point: if a 82.5m piston isnt even available then why are we talking about the possibility of using one

[Trekka273]

Are you sure of this??? My expereince is with 16V slugs... but all the 20V information I have says the largest Toyota goes in O/S is .5mm from standard... making their widest offering 81.5mm Do you have other info????

Well, I am not sure of "normal" Toyota pistons, but I know that Toda make some 82mm pistons. From what I have seen on their website, they make them in 81mm, 81.5mm and 82mm.

[Sam_Q]

82mm is the general acccepted cut-off point