Piston skirts

I have a Blown 400 sbc that i just tore down and my pistons look good top and bottom but the skirts look like they come out of a cirkle track engine. The cylinder walls are scuffed also. Ive only put about 25 1/8 mile passes on this engine and everything else looks to be fine so im wondering if its tuneup or something im overlooking.

Brian

 

check your bore. Dave

 

What lenght of rod are you using? Short rods will hammer the pistons on the skirts.

Corey

 

Havent checked bore and clearances yet , just got it apart tonight. My rod length is 6 inch.

 

Did you say 25 passes on you first disassembly. Doesn't that sound like a lot.
How much power,what blower, etc I guess
My 2 cents

Corey

 

Pitons

Sorry Blwn400, I've had a long day,didn't wnt to come across like an ass. What I wanted to say was, how much boost are you hitting this thing with and if you want a good answer we need more back story. There is a super human amount of info on this site, the boys will take care of you.

Cheers
Corey

 

Not sure on horsepower but it went 4.30 in the 1/8 mile weighing 1700 lbs. Its a 10/71 standard helix 23 degree heads. This is my first blown engine im usually nitrous but went this way looking for more power and less headache.

 

22 pounds of boost at 30 percent over.

 

Pistons

If this is your first blown engine the skirts may be ok. A blown engine will always (sic) show some scuffing because of the pressure and hamming a blower can put on them. Maybe you are not used to the look of a piston out of a blower motor. Do you have a person that can advise you or maybe put up some pictures.


Corey

 

Blower pics

You may be right because i havent saw any used blower pistons. If anyone could send me some pics of a blower piston with normal wear or scuffing on it would be great. My email is bandlnapier@yahoo.com
THANX Brian

 

Bore

As far as bore goes i think its a little loose. Measured piston skirt and cylinder and come up with 6.5 to 7 thousandths difference. Seems loose to me but not sure if blown application is supposed to be run looser than nitrous engine or any engine for that matter.

 

Are you measuring 180 across from the wrist pin for clearance spec.? or at the bottom of the skirt? Roots blower I always used .010 clearance 180 across from pin. yours might be to tight.

 

Clearance is fine as long as the skirts aren't collapsed.
Coating the skirts will improve the skirt life and appearance.
Change oil more often?

Dave Koehler
http://www.koehlerinjection.com

 

If it scuffs one side of the piston, in rotation on the load side of it, it's probably tune-up related.

If it's scuffing both sides it's probably piston to wall. Check the skirts to make sure they aren't collapsed.

Small block-solid block-blown motor you should call the piston manufacturer, but a company like JE might want .006 to .007 at the balance pad. They may even tell you no less than that as a minimum.

But I'm a hemi guy...insert standard disclaimer here.