Wrist pin/skirt exposure at BDC on 408
12-09-2009, 04:58 PM
#1
TECH Addict
Thread Starter
iTrader: (29)
Join Date: Apr 2005
Location: Margate, FL
Posts: 2,269
Likes: 0
Received 0 Likes
on
0 Posts
Wrist pin/skirt exposure at BDC on 408 Hey guys, I have PMed a few of you with the same question- but I also wanted to put this out there to see what others think.
I have in my possession an iron 6.0L block in which I would like to use to build a 408 stroker (for boost). I spoke to a local engine builder who mentioned that the wrist pin sticks out too low at BDC and that he felt this compromised reliability, especially under a lot of boost (say 10-12 psi).
How many here have any knowledge about this kind of thing? Is this true in all cases? I read that I could have some custom pistons made to order that may help to reduce exposure at BDC...is that true?
In other word's, what are my options at this point?
Thanks in advance for everyones' time!
Erik
I have in my possession an iron 6.0L block in which I would like to use to build a 408 stroker (for boost). I spoke to a local engine builder who mentioned that the wrist pin sticks out too low at BDC and that he felt this compromised reliability, especially under a lot of boost (say 10-12 psi).
How many here have any knowledge about this kind of thing? Is this true in all cases? I read that I could have some custom pistons made to order that may help to reduce exposure at BDC...is that true?
In other word's, what are my options at this point?
Thanks in advance for everyones' time!
Erik
12-15-2009, 05:46 PM
#5
a 4" crank with the RIGHT piston is just fine with a 6 liter. Your engine builder is correct that it can be an issue, but only if the piston company has failed to take into account cylinder length when designing the skirt taper. In this case, as long as the skirt is still at full diameter at bdc and doesn't break into a taper until a bit higher than that, the piston will ride nicely in the bore and the engine will live just fine. What is often (mistakenly) described as "poor rod ratio" when a piston skirt looked like heck is actually due to the piston manufacturer not designing the part correctly.
12-16-2009, 09:46 AM
#6
a 4" crank with the RIGHT piston is just fine with a 6 liter. Your engine builder is correct that it can be an issue, but only if the piston company has failed to take into account cylinder length when designing the skirt taper. In this case, as long as the skirt is still at full diameter at bdc and doesn't break into a taper until a bit higher than that, the piston will ride nicely in the bore and the engine will live just fine. What is often (mistakenly) described as "poor rod ratio" when a piston skirt looked like heck is actually due to the piston manufacturer not designing the part correctly.
Also, a longer than stock rod helps this issue.
Trending Topics
12-17-2009, 01:56 AM
#8
FormerVendor
Yes you should still be fine as we have some 1000-1500 hp deals with the 6.0 block and 4.000 crank but so far only the Wiseco and Diamond pistons were made correctly for that application. These engines have Turbos which are easier than say NOS on pistons.
MAC had a case with a larger bore piston I think that had more rock as at that time most companies assumed a sleeved engine or LS7 block so they had lower break point designs than the smaller bore stuff. All his points back then were and are still very valid and pistons have even evolved a lil more now.
If you go to crazier and crazier power levels you probably should run an even shorter stroke to allow a stronger piston with thicker ring lands and more skirt in the bore at BDC with the limited cylinder length in the 6.0 like MAC and ATVracer are saying.
MAC had a case with a larger bore piston I think that had more rock as at that time most companies assumed a sleeved engine or LS7 block so they had lower break point designs than the smaller bore stuff. All his points back then were and are still very valid and pistons have even evolved a lil more now.
If you go to crazier and crazier power levels you probably should run an even shorter stroke to allow a stronger piston with thicker ring lands and more skirt in the bore at BDC with the limited cylinder length in the 6.0 like MAC and ATVracer are saying.
