Piston Problems?

[Hall's Racing]

OK here's my problem. I am having problems with 2 of my blasters. Both are stock bore, both have vito performance +5 pistons. The only other mods. is the FMF Exhaust. We took them out last weekend and the pistons broke in both motors. When we took the heads off both pistons were broken out on the intake sides in the exact same spots. Any sugestions?

 

[blaster99]

yea DO NOT I REPEAT DONOT BUY VITOS PISTONS THE ARE CRAPPY AND RUINED MY WHOLE MOTOR,stick to weisco or namura too lol

 

[88BamBam]

they were cast pistons. only buy forged they last longer. vitos have a forged set but only wiseco makes them

 

[Hall's Racing]

I feel the same way now. I just hope the insides of the case's are not broken.

 

[ruthless_one3k]

Yeah vitos cast pistons have a real bad rep. I would just get a Wiesco or like bambam said the vitos forged (made by Wiesco) if you really want the +5. Honestly, I think the +5 claim is a little high, and I believe it would lose a little power on the bottom. They put a little notch on the exhaust side of the piston to simulate a higher exhaust port, which generally moves the power band up and lets it rev higher. But I think that would lower your compression ratio and rob your low end power. I'm not sure how much though.

 

[Wildcard2]

Ruthless, you are absolutely right about it moving the power band up and loosing some bottom end power. I never have been a fan of this type of duration mod as the port floors will not line up at BDC and the material removed affects your compression in 2 ways 1)more open port duration 2)less material to the piston crown which also lowers the compression ratio. If you want your port durations altered there is only one good way to do it right...have it ported by a reputable builder, that way it will be matched to your pipe and other mods as well as elevation, rider weight, fuel and riding style.

 

[gonzo]

I have a friend that is a personal friend of Vitos and asked him about the lower comp. and he says if you do a volume test on the dome of a super stock piston (+5) it is the same as a stocker so there is no comp. difference, thats an old Yamaha racing trick from the 70's, but again if you've raised the exhaust on your motor stay away from those pistons

 

[pittboss45]

The reason that they broke was most likely due to too much clearance between the cylinder and the piston. You probably needed to bore the cylinder out to the next size.

 

[Hall's Racing]

I had already decided to bore the cylinders. I agree with all of you. The new pistons will be wiesco and I think it would be best to bore up a size or two to take out any wear in the cylinders.

 

[Wildcard2]

Only bore up to the smallest increased size possible if you need a bore job. Have a competent machine shop check the bore to let you know if it's necissary. Pitboss brings up a very good point, loose bores are the most common cause for breaking skirts on unmodified pistons.

 

[FLOTEK]

another thing to consider on these super duper turbo nitro power pistons is by changing the port duration on the exhaust by means of a custom cut piston you are also effectively changing the blowdown of your port timing ,in this case it wont hurt anything ..on a ported modifed motor this can really screw things updue to the builder already setting the appropriate durations to their desired times,...in other words the power pistons can screw up a ported motor