Ring gap/forced induction recommendation ***carnage pics inside***
03-21-2012, 12:40 AM
#51
I'm actually opening mine up (top ring land) to .024-.026 for a little bleed off and heat. I believe it was a article where Duttweiler recomended it for boosted motors. If your going for more boost like you mention, I would do it. My opinion it looks like detonation was your problem. The gap from the top of the piston to the first ring land is defiantly a weak point in the pistons. Also did you change out your pistons to flat tops?
Detonation may have been the problem. But I'd have to attribute that to the fuel, as no pinging or KR was noted during my tuning sessions. I'm only running 16* timing for the 90 octane. If that's the problem, it should have blown up a long time ago.
I pushed my LM7 harder than I've pushed this L33. It also had alot more miles on it, so I'd bet the cylinders are worn "larger", and the ring gaps are wider too. Are the LM7 pistons made of a stronger material than the L33 pistons? I thought they were basically the same, aside from the flat top vs dished part.
03-21-2012, 01:01 AM
#53
They are made of the same material. I believe the gap( top ring land to the top of the piston) is bigger on the lm7 then the l33 or lm4 flat tops since the rod length was different on the flat tops. The flat tops where made for the 4.8 which had to raise the top ring land up on the piston. That was my dilemma when I had to choose the flat tops and dish. I went with the dish since I hope to be running higher boost.
03-21-2012, 01:02 AM
#54
Maybe take this as an opportunity to throw some Wiseco K474M96 pistons in there? Then let us know how it does on 12-14 psi??? ARP rod bolts as well maybe? Try some thermal coating on top of the pistons to reduce chance of detonation and help keep the piston structure's temperature down a few degrees.
As far as ARP rod bolts, it's not a certain boost level, or hp level, that makes ARP rod bolts a good idea. It's rpm that kills them. Below 7000 rpm, I feel that the stock rod bolts are just fine.
03-21-2012, 01:10 AM
#56
They are made of the same material. I believe the gap( top ring land to the top of the piston) is bigger on the lm7 then the l33 or lm4 flat tops since the rod length was different on the flat tops. The flat tops where made for the 4.8 which had to raise the top ring land up on the piston. That was my dilemma when I had to choose the flat tops and dish. I went with the dish since I hope to be running higher boost.
I guess I can measure the spacing on the ring lands on the L33 while it's apart. I have a LM7 in the shop, but it's not apart yet. If you have a LM7 piston handy, take a minute and measure it too. I wonder if they're the same or not?
c Also nothing about my statement was incorrect neither was yours. Open up that top ring gap.... Also If I ever get my twins going. I would like for you to tune it. Would you be up for it?
03-21-2012, 01:50 AM
#58
Hahaha, ya I'm not stressed about this at all. Probably the cheapest breakage I've had in a long time. I just have a week of waiting for parts, so I figured a discussion was in order. I like to hear lots of different opinions, put some thought into all of the different ideas, then make a decision. Helps keep me open minded & learning. 
As for your project, I'd like to check it out sometime.
As for your project, I'd like to check it out sometime.
03-21-2012, 02:19 PM
#59
They are made of the same material. I believe the gap( top ring land to the top of the piston) is bigger on the lm7 then the l33 or lm4 flat tops since the rod length was different on the flat tops. The flat tops where made for the 4.8 which had to raise the top ring land up on the piston. That was my dilemma when I had to choose the flat tops and dish. I went with the dish since I hope to be running higher boost.
Ak, have you tried contacting them to see what they gapped the pistons to in the article?
03-21-2012, 02:38 PM
#60
You're partially incorrect here. The LM7 and L33/LM4 pistons have the same pin height. The 4.8 rod is shorter than the 5.3 rod, but that's because the 4.8 has a shorter stroke.
I guess I can measure the spacing on the ring lands on the L33 while it's apart. I have a LM7 in the shop, but it's not apart yet. If you have a LM7 piston handy, take a minute and measure it too. I wonder if they're the same or not?
I guess I can measure the spacing on the ring lands on the L33 while it's apart. I have a LM7 in the shop, but it's not apart yet. If you have a LM7 piston handy, take a minute and measure it too. I wonder if they're the same or not?
Honestly I wonder if it was bad gas... Unfortunately thats something you find out in the worst way possible.