Ring gap discussion.

[DolSVT00]

Not that I plan on really changing anything, but I read this both ways.

Now I know the formula's for compression/bore for ring gaps and I know you would want to loosen it up on the top ring especially for boosted and nitrous applications

I typicly set my gaps at .023 top ring for a 3.572 bore and .015 for the bottom ring. (plasma moly construction)

But I have heard and read that there are advantages to setting the bottom ring gap larger (as in larger than the top ring gap) and making more power in boosted applications (the Import scene does this often). On to the theory... Supposedly the pressures are built up between the top ring and the bottom ring and create more heat on the piston and by filing the bottom ring larger, you allow for a bit more blow-by and thus make more power from less heat.

I'd like to hear some opinions on ither method.

[slowgreen99]

spray it

[BAD BOB]

i would feel that blow by is a boosted engines enemy but i dont know anything about boost

[Derek]

I was told that a good engine builder hones cylinders to fit a certain power adder. but know nothing of rings. will admit moderate knowledge.

[DolSVT00]

Originally Posted by BAD BOB

i would feel that blow by is a boosted engines enemy but i dont know anything about boost

Thats the way I alwayse thaught about it, but the more I read... The more I wonder.

Originally Posted by Derek

I was told that a good engine builder hones cylinders to fit a certain power adder. but know nothing of rings. will admit moderate knowledge.

Not necesserily for certain power adders, but mostly for ring type and in ring type selection you select for the power adder.

And it has more to do with the rings construction than anything and the cyl wall finish should fit that ring type. (Medium, Fine,Coarse) Example for cast iron chrome rings you would want about a medium finish (around 280 grit) for Moly rings, you would want a fine finish (around 400 grit)

[Derek]

Ahhhhh!

[Pesce Nero]

your top ring gap seems big for your size piston. my engine is built for spray and i'm only at a 24 gap for mine. i cant see taking your second ring larger than 15.

filling the engine with blowby without a vaccuum pump on the motor also seems like a bad deal but i really dont know either

[WWhittle]

Increase blow by??? New to me.

[slowgreen99]

spray it

[DolSVT00]

Originally Posted by SIXPACKGUT

your top ring gap seems big for your size piston. my engine is built for spray and i'm only at a 24 gap for mine. i cant see taking your second ring larger than 15.

filling the engine with blowby without a vaccuum pump on the motor also seems like a bad deal but i really dont know either

.023-.025 Is commonly what I do with our rings and is typicly a general consensus from every builder I have talked to in the past about mod motors (and what chrisheltra's and my first build was). I know on N/A motors you would tighten them up for our bore size.

Now the bottom ring I agree I usually woln't go larger than .013, I pretty much agree with you.

But I keep reading these articles about a larger bottom gap and it goes against everything I know about building engines.... I figured it would be a pretty good discussion topic.

[DolSVT00]

(from a discussion Board)

Most piston ring manufacturers recommend a minimum end gap of .004 inches times the bore diameter for the top piston compression ring. So for a 4 inch bore, the standard end gap would be .016 inches.

For the 2nd compression ring, the standard end gap recommendation for most stock engines is typically .005 in. x the bore diameter. So for a 4 inch bore, the minimum end gap on the 2nd ring would be .020 inches.

For a modified street performance engine that generates more horsepower and heat, the end gap should be opened up a bit to compensate for increased thermal expansion. The recommendation would be a minimum top compression piston ring end gap of.0045 to .005 inches times the bore diameter. For a 4 inch bore, the ring end gap on the top ring should be increased to .018 to .020 inches.

For the 2nd compression ring on a modified street performance engine, the recommendation is typically open up the end gap to .0055 inches times the bore diameter. For a 4 inch bore, the 2nd ring would be gapped to .022 inches.

For a nitrous or blown racing engine, the top ring end gap sould be opened up to as much as .006 or .007 inches times the bore diameter. Now we're looking at a 2nd ring end gap of .024 to .028 inches in an engine with 4 inch bores.

For the 2nd ring on a nitrous or blown motor, the recommended ring end gap is even wider: .0063 to .0073 inchestimes the bore ( or 0.025 to 0.029 inches with a 4 inch bore).

The recommended ring end gap for oil rings regardless of the engine application is typically .015 inches.

The real Kicker

Some racers believe that opening up the 2nd end gap even more (say an additional 10%) can improve overall ring sealing by allowing trapped gases to escape before they blow past the top ring and cause ring flutter at high rpm (say above 5000 to 6000 rpm).

[WWhittle]

I can't relate to that because they consider 5-6000 rpm to be "high rpm". LOL.

[DolSVT00]

Originally Posted by Wes Whittle

I can't relate to that because they consider 5-6000 rpm to be "high rpm". LOL.

Well, it is for turtles and big blocks......... like us

[WWhittle]

Originally Posted by DolSVT00

Well, it is for turtles and big blocks......... like us

That would be REALLY high for my diesel!

[DolSVT00]

Originally Posted by Wes Whittle

That would be REALLY high for my diesel!

[Pesce Nero]

i was mistakin, im 34 top 36 second

[1998ta__1991rs]

spray it

[WWhittle]

spray it.

[Matts94Z28]

spray it.

[bwelch]

^^^What they said!