Another "How much will it make?" Project "Special Needs"

[zums]

Was the case being pressurized on the first pull or did it show up after contact
Tom

[CGT]

Was the case being pressurized on the first pull or did it show up after contact
Tom

My guess is pretty much from the beginning. But the piston to head contact wasnt diagnosed till after i got it back home.

I just refused to belief that ring seal had just went away magically since last dyno session.

Leaks down really good, but i got the idea of looking in with a bore scope. Thats when i saw things had been hitting pretty hard and it started making sense what was going on.

So I dont know the extent of the damage yet. But im hoping things arent too messed up.

[GARY C]

What were the results? It seems to have fell into the abyss .

575 hp 491 torque was best. Fighting weird issues over a day and a half. Turns out .027 piston to head is not enough clearance on this particular engine.

SN needs to come apart to assess damage. Pretty upsetting. I now how have found valve spring limitations as well as piston to head limitations on this engine.

Give it some run time, it will self clearance.

[GARY C]

I was thinkin about flying out for dyno session, but I need to bring some big block heads and 2 sets of vortecs and 2 sets of headers and a crank. Then all that home plus a block and a second crank.

All that my be troublesome in a Skyhawk.

Randy

You better do some port work to the head on the Skyhawk first then or hope for a strong a hell of a tail wind.

A tail wind would make me run off the end of the runway. Always take off into the wind. Oh and use check list. LOL

And even if it'd haul the weight, I don't know where I'd fit it all.

Randy

Time to invent the plane trailer.

[zums]

Was the case being pressurized on the first pull or did it show up after contact
Tom

My guess is pretty much from the beginning. But the piston to head contact wasnt diagnosed till after i got it back home.

I just refused to belief that ring seal had just went away magically since last dyno session.

Leaks down really good, but i got the idea of looking in with a bore scope. Thats when i saw things had been hitting pretty hard and it started making sense what was going on.

So I dont know the extent of the damage yet. But im hoping things arent too messed up.

Has to be a pinched land, since last dyno session all was good right?
Tom

[CGT]

Zums, yes no issues with ring seal last time.

[zums]

Should of said deformed, or hopefully lucky enough to just unload the ring dynamically, without land distortion
Tom

[Frankshaft]

For shits and giggles, try it at .050 piston to head.

Are you saying it will make as much power at .050" as .027" ?

It was reduced for compression increase mainly, and thinner gasket was easiest way.
It definitely had ring issues this time that it didn't last time. When we put vacuum on it, it would pull 9"-10" at an idle, but as you rolled into a pull and load and rpm went up it lost vacuum and would only pull 4"-5" at rpm under load. Brought it up to rpm with no load and it'd pull 12"-13" but as you opened the throttle and added load the vacuum went away and it started smoking. It hadn't smoked with no vacuum before.

I've seen evidence that tight quench reduces timing requirements but I can't say it helps power or not.

Be interested in what you've seen in this area.

Seems too much contact reduces power.

Randy

Maybe, maybe not. On high compression, small chamber type heads, 15 degree, sb2, the like, extra clearance doesn't hurt power. On one engine, it picked up power. I don't have dozens of examples. On a 23 degree deal, it may lose some power. I know dyno time is valuable, and its tough to make those kinds of changes back to back. I think if the compression was equal, I don't think it would lose anything. Isn't there a program somewhere that will calculate that?

[MadBill]

Should of said deformed, or hopefully lucky enough to just unload the ring dynamically, without land distortion
Tom

Good point. If the leak down hasn't changed it suggests no pinching, just unseating the ring from the bottom of the groove when high RPM piston/head impact occurs. Is it gas ported with the usual very tight groove fit which would reduce the pressure loss due to the ring lifting off? If not, maybe you can just throw in a set of five thous thicker gaskets and go back at it...

[MadBill]

For shits and giggles, try it at .050 piston to head.

Are you saying it will make as much power at .050" as .027" ?

It was reduced for compression increase mainly, and thinner gasket was easiest way.
It definitely had ring issues this time that it didn't last time. When we put vacuum on it, it would pull 9"-10" at an idle, but as you rolled into a pull and load and rpm went up it lost vacuum and would only pull 4"-5" at rpm under load. Brought it up to rpm with no load and it'd pull 12"-13" but as you opened the throttle and added load the vacuum went away and it started smoking. It hadn't smoked with no vacuum before.

I've seen evidence that tight quench reduces timing requirements but I can't say it helps power or not.

Be interested in what you've seen in this area.

Seems too much contact reduces power.

Randy

Maybe, maybe not. On high compression, small chamber type heads, 15 degree, sb2, the like, extra clearance doesn't hurt power. On one engine, it picked up power. I don't have dozens of examples. On a 23 degree deal, it may lose some power. I know dyno time is valuable, and its tough to make those kinds of changes back to back. I think if the compression was equal, I don't think it would lose anything. Isn't there a program somewhere that will calculate that?

I recall David Redzus in a post some time back relating squish area to squish clearance; more of the latter being optimal with more of the former...

[CGT]

Should of said deformed, or hopefully lucky enough to just unload the ring dynamically, without land distortion
Tom

Good point. If the leak down hasn't changed it suggests no pinching, just unseating the ring from the bottom of the groove when high RPM piston/head impact occurs. Is it gas ported with the usual very tight groove fit which would reduce the pressure loss due to the ring lifting off? If not, maybe you can just throw in a set of five thous thicker gaskets and go back at it...

No gas ports. Im hoping that it will be an inspection of things and can be solved with thicker gaskets. It had .040 pth before .027 now. Thanks for responding Bill.

[In-Tech]

I would bet you are ok and just have to give it some more room like you had before. That instantaneous rattle of squishing the ring land can be compared to detonation or, even worse, preignition as it distorts not just the rings but the heads/valves/crank too.

Back in "the day" my ol' 440 cu in BBC with forged alum SuperRods and heavy ass Manley/(TRW) pistons had .090" PTH clearance and would still lightly remind me of my chamber shape and cyl head surface finish on ~11,000 rpm passes.

[CGT]

I would bet you are ok and just have to give it some more room like you had before. That instantaneous rattle of squishing the ring land can be compared to detonation or, even worse, preignition as it distorts not just the rings but the heads/valves/crank too.

Back in "the day" my ol' 440 cu in BBC with forged alum SuperRods and heavy ass Manley/(TRW) pistons had .090" PTH clearance and would still lightly remind me of my chamber shape and cyl head surface finish on ~11,000 rpm passes.

Ive seen light reminders before. This isn't as light

[CGT]

Isn't there a program somewhere that will calculate that?

The piston to head ring seal elasticity calculator?

[MadBill]

Would it work for the rubber rod variable displacement concept?