I am going to file my own rings this time because the machine shop screwed them up royaly.
I am going to purchase some speed pro moly rings. I know the technique I just need so help on the actual gap for 306 ci. NA motor with a forged piston.
What ring gap should I use if I plan to install a 6 psi supercharger? It's a 331 and I'm using Probe pistons and file fit rings. The instructions with the pistons aren't very good.
I've read in Ford Muscle articles:
.0045" per inch diameter for the top ring = 4.030" x .0045" = .018" and
.0035" per inch diameter for the second ring = 4.030" x .0035" = .014"
But I think this is for non-boost engines. I thought I saw something that said up to .0024" and .0020" for the top and second ring. Anybody know what I should gap them to? Any suggestions would be great! Thanks...
Also, do you have to check the oil rings and the zig-zag spacer in between the oil rings? The gap on the oil rings seems pretty big, but the spacer ends but up against each other when they are in the bore.
[ This Message was edited by: sweetstocker on 7/10/03 11:51am ]
SCOTT
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Joined: Feb 2, 2001
Posts: 1036
From: All over
Posted: 7/10/03 11:39am
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Since most 6psi kits bolt on factory 9-1 motors with no problems...I would run factory type gaps. I think the .018 & .014 that the piston company recomended would be just fine with that small amount of boost. The bigger gaps are for engines that will see major amounts of combustion chamber heat thus needing more gap to keep the ring ends from pinching and breaking in the bore. Unless your ring lands are very high on the piston they wont get too hot.
[ This Message was edited by: SCOTT on 7/10/03 11:46am ]
sweetstocker
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Joined: Jun 01, 2003
Posts: 23
From: FL
Posted: 7/10/03 11:50am
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The grooves are a lot higher on the 331 pistons than on the stock pistons. Also, because of the increased stroke and the 60cc combustion chamber heads, the compression ratio is closer to 10:1.
sweetstocker
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Joined: Jun 01, 2003
Posts: 23
From: FL
Posted: 7/10/03 9:40pm
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maybe I should go .020" and .016" to be safe? or more?
SCOTT
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Joined: Feb 2, 2001
Posts: 1036
From: All over
Posted: 7/11/03 11:00am
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Quote:
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On 2003-07-09 23:50, sweetstocker wrote:
The grooves are a lot higher on the 331 pistons than on the stock pistons. Also, because of the increased stroke and the 60cc combustion chamber heads, the compression ratio is closer to 10:1.
Yes, but your new rings are skinnier 3/64" right? they will streach less with heat than the thicker type 1/16" rings.
Still sounds like the .018 will work for you. Once your motor is broke in the ring gap will increase on its own a small amount, I'd hate to see you have problems with excess blow bye "too much crankcase pressure" from your boost going past the large gap in your rings which will blow out your rear main seal and others. Unless you plan on hours of road racing and constance "doging out" your motor which will produce high combustion temps, I wouldn't gap past .018
Have you called probe and asked them their thoughts?
sweetstocker
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Posts: 23
From: FL
Posted: 7/11/03 11:45am
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The rings are 1/16, 1/16, & 3mm. I emailed Probe and haven't got a response yet.
n2omike
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Joined: Apr 4, 2001
Posts: 2526
From: West Virginia
Posted: 7/11/03 1:36pm
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I was using 0.019" for the top gap... and my pistons had a very high ring groove. I was also using 200hp worth of nitrous. (0.019" was really pushing it for that engine)
No bottle, I'd go with 0.016" top and bottom.
Mild to moderate Bottle or blower... around 0.020" with a forged piston. Hypereutectics require significantly more.
Nastystang
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Joined: Jan 1, 2001
Posts: 1942
From: Vancouver WA
Posted: 7/11/03 1:52pm
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I just got off the phone with a friend and saw this topic and thought I would chime in. I have no expertise in this area but Ron1 is running .028 gap ( dont know if that is all or which one ) with his 347 using 200 HP shot. That is what the piston manufacturere reccommened.
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fasteach
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Posts: 77
Posted: 7/11/03 7:57pm
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honestly, i wouldnt get my panties in a twist worrying about endgap...a few thousandths isnt going to lose anywhere near the power that butted gaps will cause. if there was alot of power to be made in super-secret endgaps, the market would be flooded with zero-gap type rings! wait for the MFGR's rec. gaps, and dont worry about 3 or 4 hp...if youre really worried about crankcase pressure, you could always fabricate a pan-evac setup, or run a vacuum pump. david reher has some interesting thoughts on the subject at rehermorrison.com . but what do i know...food for thought. Duke
sweetstocker
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Joined: Jun 01, 2003
Posts: 23
From: FL
Posted: 7/11/03 9:47pm
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Here is the reply from a tech at Probe:
"I'm doing the same thing you are. I'll gap the top at .021 and the
second at .023. I know this flies in the face of magazine publishing.
But, if you allow more pressure to be built up between the top and
second ring than is present in the combustion chamber, the top ring
comes off the wall. That makes the second ring your first
compression ring. This is baaad!"
He also said to add .001" to each if not using an intercooler.
Anybody ever hear of gapping the second ring more than the first like that?
SCOTT
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Joined: Feb 2, 2001
Posts: 1036
From: All over
Posted: 7/12/03 12:26pm
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Quote:
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On 2003-07-11 09:47, sweetstocker wrote:
Anybody ever hear of gapping the second ring more than the first like that?
sweetstocker
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Joined: Jun 01, 2003
Posts: 23
From: FL
Posted: 7/13/03 12:37am
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Thanks for the help!
n2omike
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Joined: Apr 4, 2001
Posts: 2526
From: West Virginia
Posted: 7/13/03 8:08am
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The instructions that came with my Speed Pro rings said to gap the top and bottom rings the same amount for the reasons stated above. Before, they used to recommend the bottom one be tighter.
Just a little FYI from out piston ring buddies at 'Speed Pro'. Take it for what you want.
A car that sees 'sustained' boost for significant periods of time will need more ring gap. Short boosted or nitroused periods won't get things quite as hot. If you plan on road racing the car, and plan on hammering the engine repeatedly, open up the gaps a little. If it will see mainly street duty, or the occasional pass down the track, leave them a little tighter.
sweetstocker
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Joined: Jun 01, 2003
Posts: 23
From: FL
Posted: 7/13/03 9:14am
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Wow... there are alot of different opinions to choose from. I think I'll mix them all together and make up my own!
The one thing I have consistantly read is for supercharged engines the ring gap factor (what you times your bore by) goes up a little bit. Since you can't turn the supercharger off like you can nitrous, you are always adding some amount of boost and some amount of heat.
Like SCOTT said, .018" is probably fine, but because the ring landing on a 331 is a lot higher than stock and because I will have a supercharger, I'm going to go with .020" for the top ring.
For the second, I'm going to go with .018" because it won't see as much heat. Also, I don't want it to be the same or higher than the top ring.
By the way, the service manual for my car (1989 5.0) says the Top and Second ring should be .016"-.020".
SCOTT
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Joined: Feb 2, 2001
Posts: 1036
From: All over
Posted: 7/13/03 11:54am
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Not wanting to step on any toes, but......
FACT: top ring is hotter than second ring
FACT: when at running temp top ring gap will close up more than second ring gap
FACT: "example only" top ring .018 bottom ring .016
FACT: when at running temp both rings will have nearly the exact same gap.
Question??? So how will compression get buit up in there and get stuck????? It wont happen unless there is a BIG difference in the gaps....like .025 top and .016 bottom.
Ok I'll quit posting on this topic
[ This Message was edited by: SCOTT on 7/13/03 12:36pm ]