SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: freshmeat on December 08, 2018, 06:30:53 AM
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In my 454 with speedpro pistons how much clearance should I have between cylinder and piston. My machine shop isn’t very familiar with marine applications and I need to know what to tell him.
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My guy Eric says run them on the high side of the tolerance .0028-.003
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In my 454 with speedpro pistons how much clearance should I have between cylinder and piston. My machine shop isn’t very familiar with marine applications and I need to know what to tell him.
Forged, cast, hyper?
What piston and what cooling system?
Also, compression ratio comes into play if in the low range.
GT
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Forged pistons, compression around 9.5 to 1. Using fresh water for cooling.
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Forged pistons, compression around 9.5 to 1. Using fresh water for cooling.
You don't need to go crazy.
The issue is that the block temperature will be dreadfully cold, especially cylinder number one and two whilst the pistons will be extremely hot under wot conditions.
When we build them, forged pistons will get an additional .001" over and above what the piston manufacturer recommends for an automotive application. If boosted (turbo, roots, centrifugal) we go as high as .002" over the OEM application.
The ring gaps should remain fairly snug, there are times we would order file to fit rings if the gaps on the stock rings end up wide (in all honesty, shouldn't).
I hope this helps.
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It does help. The rings say to be .004 per one Inch If bore and it’s a 454 bored .30 over. What should I set the ring gap at?
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It does help. The rings say to be .004 per one Inch If bore and it’s a 454 bored .30 over. What should I set the ring gap at?
Are you sure you read that correctly? What rings?
GT
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I will read the box again when I get home. What should they be?
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I will read the box again when I get home. What should they be?
I actually put it together wrong in my head.
The word "if" in place of "of" derailed my brain... Lol
This is correct, .004"- .0045" per inch of bore is spot on.
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Food for thought on ring end gaps....
I was just at SEMA 2018 talking about this exact subject with one of the reps from United Engine Machine (ICON, Kieth Black, etc). He mentioned he used to work at Perfect Circle so I asked him what he thought about larger ring end gaps as I've always added a few thousandths to the recommended spec for safety and have never had a problem with blowby. He said PC actually ran tests on end gaps and in a dynmaic running engine they could not measure any difference in blowby from a 0-gap ring on up past .040" gap. Static leakdown tests will disagree, but in a running dynamic engine there was ZERO measurable blowby difference. Honing technique (pressure, speed, final finish, etc) has a much greater affect on ring seal and blowby. The take away for me, and he concurred, was that larger gaps have no performance drawback but will save your motor if it gets hot. I thought it was interesting the way I was taught by the "old timer" jived with a manufacturer's test.
I've always set pistons a hair on the loose side as well. When I say hair I mean +.0005" or so. Same rationale, building durability and a little wiggle room into the clearances. I probably would be more conservative on a short skirt piston but Speed Pros have a long skirt and are much more forgiving. I wanna say we put .0055" into my buddy's 429 Ford, but his compression was up over 11:1 and he runs it HARD.
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Food for thought on ring end gaps....
I was just at SEMA 2018 talking about this exact subject with one of the reps from United Engine Machine (ICON, Kieth Black, etc). He mentioned he used to work at Perfect Circle so I asked him what he thought about larger ring end gaps as I've always added a few thousandths to the recommended spec for safety and have never had a problem with blowby. He said PC actually ran tests on end gaps and in a dynmaic running engine they could not measure any difference in blowby from a 0-gap ring on up past .040" gap. Static leakdown tests will disagree, but in a running dynamic engine there was ZERO measurable blowby difference. Honing technique (pressure, speed, final finish, etc) has a much greater affect on ring seal and blowby. The take away for me, and he concurred, was that larger gaps have no performance drawback but will save your motor if it gets hot. I thought it was interesting the way I was taught by the "old timer" jived with a manufacturer's test.
I've always set pistons a hair on the loose side as well. When I say hair I mean +.0005" or so. Same rationale, building durability and a little wiggle room into the clearances. I probably would be more conservative on a short skirt piston but Speed Pros have a long skirt and are much more forgiving. I wanna say we put .0055" into my buddy's 429 Ford, but his compression was up over 11:1 and he runs it HARD.
One point to take this one step further.
The second ring is typically more of an oil control type thing.. As such, it's not uncommon that the gap on the number two ring is set slightly larger.
About the only negative with larger end gaps is increased carbon deposit potential contaminating the crankcase oil and causing potential ring sticking is the tune isn't quite dialed in...
Anyone that has experience with two stroke engines (apples and orange to a point) knows or has seen what I am referring to.
Just to further the food for thought.
GT
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Thanks for all the info I do appreciate it.
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It does help. The rings say to be .004 per one Inch If bore and it’s a 454 bored .30 over. What should I set the ring gap at?
A ring essentially corresponds to the circumference of the cylinder bore. As the individual components heat, they expand. If you were to straighten out a piston ring, you would have a long narrow piece of metal
As that long narrow piece of metal heats, it expands. The greatest amount of expansion occurs over the greatest cross-section, the length. The thickness and width do expand, but it is the length that grows the most.
The ring manufacturers have taken the expansion rate of the material AND the assumed operating temperatures into consideration when providing that number (.004 per inch of bore diameter). That way, end gap is easily calculated by the end user rather than providing a list of every possible bore size.
To directly answer your question:
A .030 over 454 has a bore of 4.280
4.280 × .004 = .01712 or .017 end gap
You might also find factors for additional clearance, to be added to the .004 for nitrous oxide, pounds of boost, etc.
Keep in mind that these numbers are based on an automotive application. Marine applications are under much greater loads.
If the ends of the rings butt against each other, it can cause a catastrophic engine failure.
I would contact your ring manufacturer for their recommendation for your specific application.
Some videos you might find helpful:
Watch "CP-Carrillo Ring Gap Instructional Video" on YouTube
https://youtu.be/Liq5EI7W8oc
Watch MAHLE Motorsports "Filing Rings" on YouTube
https://youtu.be/2YidK0UPWDw
Watch MAHLE Motorsports "Advanced Ring Filing Techniques" on YouTube
https://youtu.be/IoGjqtWVvqs
Cheers,
Joe
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Key word in your post: Assumed. Any number of things can cause the engine to exceed that assumed number. In practice (IMHO) it's better to build in a safety margin. Running the minimum clearance on any application is just waiting for disaster. Sure, if you can keep the engine within a specific parameter 100% of the time it'll be fine. But we all know "sh!t happens" In the real world. Something clogs, something goes out of adjustment, whatever, and now you're outside those assumed parameter. Now what? That comes down to personal preference: Would you rather the engine have a little extra clearance and have a chance at surviving when said sh!t occurs, or do you run the minimum spec and run a much greater risk of major engine damage?
People get so tied up on having too much ring end gap when reality is isn't all that critical. There are at least 2 studies I've heard of from industry people that prove the same. That's good enough for me :)
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Thanks for the replies guys. I will take it all into consideration. This is the first engine I’ve built in years and I mean years. My son and I are slowly getting it figured out and defiantly taking our time.