Safe to swap pistons?

[gkent]

With the minimum info provided, the solution could be as simple as backing off the timing.

 

[66Satellite47]

Thanks Wild, in those motors I was at 12.2 -12.4 CR static & running 110 Union with pretty big cams. Guess I can see how a lower CR street motor could see the advantage

 

[33 IMP]

Laugh out gaskets has what you need. The gasket they have can lower your compression Rachel about one full point

Why do you think his name is Rachel?


LOL!

 

[Bladeruner69]

So as far as gaskets, I have the Felpro .040. The heads are Eddy alum. Guess I should have added that I am limited to California grade 91 octane. Thanks for the speedy and thoughtful replies. You guys rock.

 

[Bladeruner69]

This is my cam. Timing is already pretty tame. 36 total with the lighter springs so it comes in pretty late.

 

[66Satellite47]

Actually I think the lite springs make the timing advance sooner. Looking at the timing lite will tell you. Back the timing down to 34*, see if that works. Otherwise you're stuck with mixing fuel, or thicker head gaskets, swapping pistons. Depending on what ignition setup you have. Some ignition tinkering may help.

 

[Fran Blacker]

If you put in much thicker head gaskets you'll need thicker intake gaskets.

 

[66Satellite47]

If you put in much thicker head gaskets you'll need thicker intake gaskets.

Good point, but the .010, .030 are readily available. I think even .060.

 

[gkent]

Gaskets are cheaper than pistons !!! And a lot less work too !

So you lose quench - big deal. Loss of quench doesn't do damage - ping does !!

 

[beanhead]

Actually I think the lite springs make the timing advance sooner. Looking at the timing lite will tell you. Back the timing down to 34*, see if that works. Otherwise you're stuck with mixing fuel, or thicker head gaskets, swapping pistons. Depending on what ignition setup you have. Some ignition tinkering may help.

This is correct. Could be a simple timing issue.
You've got a decent size cam. I would do a compression test to determine how much pressure is there. Then dig in to tuning, starting with the ignition curve--plot it from idle to total. Verify it's not too much too soon. Go through the carb settings and make sure your mixture and float levels are good.
You may very well end up swapping gaskets or going into the engine, but start with the free/easy stuff first!

Man this is starting to give me deja vú...
@Kern Dog fought a similar battle with his 493" some years back.

 

[Curiousyellow71]

Answering the initial question. I wouldn't be afraid of reusing rings on new pistons with only a 100 miles on a normal build....BUT...if it's been detonating this is not normal, It is possible you have already lost some ring tension. It really depends on how you were driving it and how hard you were on the rings. Eventually detonation will remove the ring tension completely and you will be prying on the rings trying to get them off. If it were mine I would not switch pistons. Every other option is better.
I think there is likely multiple problems, piston style, rod length and engine operating temp and the plug heat range and carb...etc...all are important details not mentioned.
A hughes cam with a lsa on 108 with a steep ramp is building compression and not helping, It looks like that is a older hughes so it's hard to say what seat timing is as Hughes doesnt consider seat timing important. But since Hughes uses Howard's cam profile's your current cam has been replaced and is listed as 284/288 @ .020 lift. It's a good sized cam at.050 and is going to make power, but Imo...not a pump gas cam at 10.5 ...my guess is it will struggle to run on pump gas until scr is below 10:1. A different cam with a wide lsa and more seat timing is needed for your present compression, but there are to many details missing in the build to really say what all is going on. Too hot of plugs can even cause a engine to detonate. It's often overlooked but it's the first place to look.

 

[dvw]

What plugs? Is the ping on tip in only or all the time? Try slowing the timing curve. Tighten the lash .004". Next back the cam off to 108 if its really in at 105. To be honest true 10.8 with a Eddy head should fly. What is the cranking compression?
Doug

 

[eldubb440]

why not try retarding the cam? would this not bleed off some compression due to intake closing later on the compression stroke?

 

[Kern Dog]

I agree with Wild, which heads have you got? my 500" EDE RPM head motor worked fine on pump 93. Timing was a conservative 36*, all in at 1200 RPM, just off idle. Which gaskets are you using? Seems like 10.8 would be tough with iron heads. Even with iron heads & head gasket thickness, the right cam could help.

I have a few comments on this.
Why does the timing have to be "All in" by 1200 rpms? Why should it be so aggressive when you surely have a converter stall speed of at least 2500 ? With a manual trans, do you release the clutch at idle and floor the loud pedal?
It is a fair question and one that I started wondering about while dealing with the problems I had.
REgarding the cam, and this revelation only came to me recently:
The concept that a bigger cam "helps" may not always be entirely true. The bigger the cam, the less efficient it is at cylinder filling at low rpms. It becomes much more efficient to do so at high rpms. THe cylinder filling is where the problem occurs. THe more pressure in a cylinder, the more power as long as it does not detonate. A bigger cam may help at low to mid rpms but get it up to 4000 and above where the cam starts to really make power and the detonation will likely be back.

 

[Bladeruner69]

You guys are a wealth of information for a guy like me with limited shop class knowledge.I am going to pull some receipts and do some tuning tomorrow(on quarantine) and see what I come up with.

 

[BSB67]

What plugs? Is the ping on tip in only or all the time? Try slowing the timing curve. Tighten the lash .004". Next back the cam off to 108 if its really in at 105. To be honest true 10.8 with a Eddy head should fly. What is the cranking compression?
Doug

This!

If its only has detonation under load you might be able to tune around it.
1) Slow the timing curve
2) bring the total timing back to 32°
3) try a -7 or -8 NGK plug
4) 160 ° thermostat.
5) Jet/transition slightly richer, maybe,
6) back the cam up to 108 like mentioned,
7) tighten the intake lash up 0.005" (cold lash setting of 0.006"-0.007")
8) then try the head gasket.

Check your cylinder pressure.

I run 10.8 in mine. Cranking cylinder pressure is 190 psi. I run 93 octane. I'm at about 1000 ft elevation. I'm not sure I could run on 91 octane. But I would try pretty hard at making what you have work before I'd be thinking pistons.

 

[66Satellite47]

I have a few comments on this.
Why does the timing have to be "All in" by 1200 rpms? Why should it be so aggressive when you surely have a converter stall speed of at least 2500 ? With a manual trans, do you release the clutch at idle and floor the loud pedal?
It is a fair question and one that I started wondering about while dealing with the problems I had.
REgarding the cam, and this revelation only came to me recently:
The concept that a bigger cam "helps" may not always be entirely true. The bigger the cam, the less efficient it is at cylinder filling at low rpms. It becomes much more efficient to do so at high rpms. THe cylinder filling is where the problem occurs. THe more pressure in a cylinder, the more power as long as it does not detonate. A bigger cam may help at low to mid rpms but get it up to 4000 and above where the cam starts to really make power and the detonation will likely be back.

Kern, in my application it was a drag race motor, not for street. Although I use the same distributer with my "streetable" 500" & 512" motors. Yes I have fairly loose converters. Cam is a complex isscam ue. My "guess" is more ignition tuning & carb tuning is needed. Also retarding the cam ICL may help. Plug range could also be an issue. Many unknowns.

 

[33 IMP]

Well @Bladeruner69 excellent tuning suggestions from some really smart people ( not including myself) that may solve your problem for little to no effort. And if tuning doesn't quite solve it, solutions much easier and cheaper than tearing the engine apart amd putting high-dollar pistons in it. All happy to help.

 

[wyrmrider]

if you have quench thicker head gaskets make it worse
if you don't then dose'nt matter
you can get 5cc deshrouding the valves out to the bore- NOT gasket size
some head chambers overhang the block deck so deshroud accordingly

 

[HEMI-ITIS]

You have the typical example of the need for water/meth injection starting at 75% throttle!