NON-Interference Pistons!

[jamiesibley]

How would this work:

Ordering custom pistons from ross, wiseco, je ect.. with a thicker top surface and have deep eyebrows cut into it. Deep enough to let the valves clear even if the timing belt broke. I think this small investment would be a god-send to anyone who breaks a timing belt.

Thoughts?

 

[Enigma_Man]

It's been gone over before, someone figured this out.

You'd either need to cut releifs in the piston that are deeper than the piston is thick (IE drill holes through it), or you'd need to reduce your compression ratio to something like 4:1.

It's not a viable solution to a problem that doesn't really exist if you maintain the car correctly (in most cases, other than the occasional freak what-have-you)

-Jesse

 

[GRNDSM]

I asked this question of Archer Brothers during Shootout ’96 (back when they were still racing DSMs). He said that they worked with JE for a while to see if that can happen and the answer was a definitive NO!!!

Leon
RR

 

[GSXanimal]

I know its probably not possible but yes it would be great.

 

[autronicDSM]

Forget Wiseco unless you want to order at least 12 pistons.

 

[talon1979]

That is a cool idea, but I am sure the car would loose a lot of power. The whole reason cars use interference motors is because they are more efficient and make more hp.

 

[josh long]

Why?

The valves will still run into each other.

Josh

 

[Brian Nutter]

Hi there, I don't get to this site often enough, but I develop the sport compact pistons at Wiseco. The non interference idea is nice, but the negatives are: valve pockets that are so deep that the deck surface of the piston must be thickened to compensate (heavier) :and: due to the proximity to the ring lands-the top ring would have to be moved way town to maintain proper thickness. Even then, the area between the valve pockets and the outer diameter of the top land area can be so thin radially, that cracking could occur w/out proper hand-massaging of that area w/ a die-grinder and cartridge roll. I'd agree with one of the earlier posts,- this is all possible, but I think proper maintenance of the belt is probably the better way to go.

 

[92GSXBaltimore]

if you dont care about your compression ratio, then the answer is yes.

 

[Mirage2LTurbo]

Originally posted by josh long
Why?

The valves will still run into each other.

Josh

 

[1LE]

Originally posted by talon1979
That is a cool idea, but I am sure the car would loose a lot of power. The whole reason cars use interference motors is because they are more efficient and make more hp.

I'd think so too, but compare the 4g63 to a 3s-gte... Same size, roughly same power output, same compression, one is non-interference 3s builds up just as well as a 4g without sacrificing the non-interference design... Just food for thought...

 

[josh long]

Why does it matter, without redesigning the head so the valves cannot hit each other? If your motor loses time and your pistons don't munch the valves, the other valves should make sure they are fully bent.

This is why in the FSM they give you specific directions to turn the cams when installing the timing belt.

The only benefit I can see from this exercise is the chance the valve guides might not crack as much. Due to the valve stem deflection under impact would likely be much less.

Josh

 

[Defiant]

Originally posted by josh long
Why does it matter, without redesigning the head so the valves cannot hit each other? If your motor loses time and your pistons don't munch the valves, the other valves should make sure they are fully bent.

Not usually. Unless both cams are rotated the right amount and mis-timed just right, you'll play hell getting the valve edges to touch. Piston damage is much more likely.

However, making an interference engine a non-interference engine is practically impossible.

So, what say we move along now?

Good.

 

[jamiesibley]

Thank you guys, I feel this was very well dicussed.

I totaly agree that if the valves are going to touch anyways, changing the pistons doesn't make sence at all.