Mustang and Ford Performance Forums banner

1 - 4 of 4 Posts

·
Registered
Joined
·
332 Posts
Discussion Starter · #1 ·
just wondering what would be the right ring end gap on a boosted engine street strip. sometime this year i do plan on raising the boost to around 20#s.

i have around .018-.020 now on the top ring, my concern is that blowby at idle is considerably more now than when the engine was stock. as the revs climb it goes away and seeing it on the dyno it is not excessive at 7k, hardly noticable at all, just at idle. i am asking cause i might be pulling the engine for some head work this year and while it is out i might change the rings.
 

·
Registered
Joined
·
151 Posts
.022 on both top and second rings on Speed Pro.Some will say less on the second ring but heat and tension issues negate any loss.Most importanty, deck plate hone to make sure there is little variation in the cylinder and insure the correct cylinder finish hone is used.

The blowby issue you mention is likely due to cylinder variation,finish rather than the .018 - .020 which is fine IMO.:cool:
 

·
Registered
Joined
·
332 Posts
Discussion Starter · #3 ·
so your saying that the rings are not seated teh same in all cylinders, or that the cylinders are not all the same concentricity?

the engine runs well and feels very strong. its just annoying to see the valve cover breathers emit vapor when it is idoling. rev it up to around 2k and its gone. when the engine is cold it doesn't do it at all only after it has came up to operating temp.

i thought the stock gap was around .013, my thinking was the extra .007 on all cylinders was causing it at idle. when the engine gets a little heat the gap closes some and it goes away.
 

·
Registered
Joined
·
151 Posts
It would be my guess that you have vented the crankcase by using a breatheable cap, if you are seeing crankcase vapor.The stockcrankcase evacuation/ recirculation system is designed to pull these vapors so they are not seen or emitted into the atmosphere.All engines have blowby but a healthy engine will only have a little.The only way to see what is really happening in the cylinder is to do a leakdown test.

Several things affect ring gap needs,but most importantly heat and material of the rings expansion rate.So your main concerns are ring manufacturer reccomendations, piston design and intended use.

The reason for concern in piston design is the position of the ring groove,the more toward the top of the piston,the more heat the ring is exposed to so it expands more.


:cool:
 
1 - 4 of 4 Posts
Top