de-lip, open piston bowl?

mech2161

mech2161

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I'm in the process of doing a conversion. When I pulled the head to have it 0-ringed I found a cylinder that had some piston damage. I need to replace it and wondered if I should pull them all and open the piston bowl. I'm doing full cuts, 5X22's. 5k GSK, MAX SPOOL 2.5 cam and mild head port. Is this a good idea or not? If so how much should they be cut before their rounded? Anyone have a picture of one that's done?

96 12v 215 pump.
 
no its not a good ideal cause then the spray would not be in the bowl and would hit and score the piston walls.
 
LOL That's why you open the bowl. To keep the fuel in it and not hit the top. I'm not cutting the top off.
 
well you say de-lip i think making the piston surface flat. you mean like what the 04.5 -07 pistons are like with the wide bowl like this:
P9130174.jpg
 
Yes that's it. Any idea how much to cut back on a 12v piston?

The injectors are 5X20's, I listed them wrong in the original post.
 
no matter what you spray pattern will be the same unless you change tips. changing the bowl design you change the flame propagation in the cylinder. if anything the most i would do is remove the lip and make the bowl come straight up at the edge. test one first thou to make sure there is not an internal oil passage in the piston
 
I don't want to go crazy and lower the compression too much. I understand the spray pattern is the same. If the bowl opening is larger you can get the fuel in it easier with more timing.
 
true you just have to watch how much you change the bowl because it will affect the way that the flame propagates.
 
Understood, I don't want to change anything in the bottom or the center. I have the bad piston I took out to cut on as a test. I know it has a rather large lip. I don't think I need to cut all of it out, but how much would be acceptable?
 
I can post a pic on a stock piston when I get to the shop later.
 
Does it have a larger opening? I'm asking because I've never built a Cummins.
 
mech2161 said:
Does it have a larger opening? I'm asking because I've never built a Cummins.
Click to expand...

Marines have the bowl that you would want. If you open the stockers up try to get them as close to the same size as a marine bowl.
 
Thanks! I did a search and found some good pictures that AsTroSS posted in another thread. Looks like compression ratio drops pretty fast when opening them up.
 
doesnt anyone offer an aftermarket piston with a larger shallower bowl?

dont know if that is a word but you know what i mean...

keep the burn in the bowl (w/ some compression and timing) w/o req 120° spray pattern

i like your idea of opening up the stockers but yeah...think about the volume you would be removing

would kill the comp quick style...not to mention who knows what it would do to the strenth of the piston?
 
I don't think it would compromise strength to remove the lip. I read the thread with the pics of the Mahle and 370 Marine pistons. The Cummins 370 Marine piston would be comparable to removing the lip in a stock piston. The comp ratio of that piston was stated to be in the 15... range. That's probably lower than I want to go. But... that's what I think the opening should look like. A piston with a bowl that wasn't as deep would be sweet.
 
I see a part # under each picture. Are they off the shelf Cummins pistons?
 
I'm open to suggestions. I was thinking with a stock piston 20*. This is all new to me. Remember I ran a Ford up till this build.
 
LOL They chose me, as in free. With the 12mm pump I would think it may be easier to get the volumn of fuel out with a larger tip. I think something in the .015-.017 would be better.
 
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