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Hyper pistons and timing issues
Has anyone else experienced this problem with Hypereutectic pistons chipping caused by a bad distributor?
I had my 351C M code motor professionally rebuilt late 2012. The builder chose KB177 pistons which actually are .020" taller (1.67" compression height) than stock. The distributor was a new reman. that was supposedly the correct spec. The only change was to go with PerTronx III. I wanted to keep it all stock appearing. On running the motor in the car, spark knock was immediate. Too high compression for 91 octane fuel was my first thought as the pistons put the ratio close to 11.0:1 static, taking head and block truing into consideration. I could go on and on, but after several discussions with the builder, he agreed to put the car on a dyno in late 2014 and 4k miles of spark rattle under load at 3k rpm, it was seen that the distributor timing was drifting up to 39 deg. and not constant. Oil consumption was up too. I used an inspection camera in #1 cylinder and saw vertical oil streaks above the piston and the top edge of the piston appeared rough. Scored bores obviously, but why? I emailed UEM, makers of the KB pistons and was told that "hyper piston do not do well in a bad timing environment" such as I've experienced. I also contacted the distributor re-manufacturer and it would appear they only build to a 'middle of the road' setting. Springs and weight curve kits are not available, although a tech did send me some that 'may' be different.
I am now faced with pulling the original date correct motor, which may be junk and build a new one.
My question is: Has anyone else experienced this problem and what pistons and distributor would be recommended for my strictly street M code Mach 1 to avoid this happening again? If I do go back to hyper pistons, I'll not be using a stock distributor for sure, but I will lose my stock appearing engine compartment.
4,000 miles of knocking is enough to destroy any piston, let alone the more brittle hypereutectic pistons. My question, why bump the compression on a street engine? Usually compression increases are accompanied by increasing the cam duration and lift, effectively reducing the dynamic compression ratio and pinging potential.

“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
I have a 351C-2V with some KB Hypereutectics (9.5:1) running normal timing (16* BTDC @ idle & no vac - running up to 36*). My distributor is a Cardone with a 'stock' appearance running a Duraspark ignition module. It looks pretty stock, actually (well, the Accel Super Coil, not so much), and with the Duraspark module hidden behind the passenger side shock tower, it's a fairly well concealed mod.

The reason I went that route is to fit the factory (repop in my case) Ram Air air cleaner without having to modify because of clearance issues with MSD or other HEI-type distributors.

So far, so good.


[Image: mach1sig2.gif]
i had the same issue, builder used Hypereutectic pistons in my engine with open chamber heads, he might of tried to use the taller pistons to increase compression.
Engine knocked majorly from day one.

some things that might of saved my engine, first there were so many issues the car did not get driven much.
next i had a high efficiency core rad made which made my engine run cold.
i had a Massive carb backfire issue so the first change was installing a 50cc accelerator pump from the stock 30cc
next was drop 2 heat ranges on the plugs to see if that would stop the knocking, it didn't

I limited total timing using a piece of rubber hose on the end stops in the the distributor. again no real change.
ditched the mr gasket spring kit that the engine builder installed for oem and retarded timing.

i then spent years farting around with the carb increasing fuel delivery and retarding timing and distributor curve until the engine became tolerable.
in that time i had a massive oil consuption issue which turned out to be the teflon seals for the valve stems failing, switched to Vitron seals.

basically Hypereutectic pistons are crap, and never combine them with open chamber heads and a retarded engine builder.

the detonation was horrible in my car, marbles in the mufflers, flames blowing out of the carb from lean misfire. all that on a new rebuild and the engine went on a dyno before getting to me so it was turn key,, turn key my butt!

I've told myself if there is scoring in the cylinder heads and my pistons are messed up i don't want to know unless the engine grenades then i'm junking my 72 and calling it a day.
Thanks for your replies. To answer the question, " why bump compression on a street engine?" it was NOT the intent. The aim was 9.5:1, but I can only assume the builder either made a mistake, happened to have a set of KB177's on the shelf, or simply did not know that the 177's were .020" taller. Either way, with closed chamber heads and the use of fuel additive, it should have handled the higher compression. A bad distributor is the issue. ( I didn't mention the company's name, but someone else did)
The 4K miles between first finding out the problem and where I'm at now, is the result of many "discussions" with the builder and actually finally diagnosing the real issue. If driving normally, avoiding too hard accelerations, this engine still has loads of power, so I was not too concerned about putting the miles on it. Should I have pulled it earlier, yes, but it is what it is now.
I appreciate all your comments which will no doubt help me decide what I need to do for a better reliable motor. I am hoping that the bores are not that damaged and can be honed to .040" with a new set of pistons................, but I could be holding my breath a loooong time!!
I would run a set of forged pistons on your next build. Other than being minutely heavier, there's no reason not to run forged in a 351C.

You can have your stock appearing cake and eat it too, by using a Duraspark distributor. The only giveaway is the two wires exiting the housing, vs one on a points setup. You can bury the box behind headlight or shock tower, or step up to an MSD or similar ignition.


ok, good info above . . this is incredibly simple.

run whatever pistons you want . . as mentioned, the pistons were NOT your problem . . even if you put 2618 material pistons in it and let it ping for 4,000 miles, those will blow up too . . your engine was telling you something was very wrong for 4,000 miles ad you simply ignored it.

set your timing CURVE in your stock distributor so it does not ping . . I or someone else will tell you how to do this if you want.

since you have to rebuild it, use lower compression, if you tell us what your cam is we can suggest a decent compression.

octane boosters are basically useless . . the best ones like torco only raise the octane by 2 points . . the best one is caled real led and has real tel [lead] in it but it is pricey and you dont want to be using boosters anyway.

your engine EASILY could have been saved if you ran the temp at 180, ran a spark plug that is 1 step colder than stock, jet it a hair rich, and reduced your timing.

if it were me, i would set my quench/squish clearance to around .035 . . this will also square the block deck to the crank if it is done properly and will reduce the potential for detonation with closed chamber heads.
I would have suspected that the spark plugs would have looked like hell and been the first real indicator of the engines detonation ills. If your engine still has good even compression, one solution would be to install a camshaft that would lower the dynamic compression ratio effectively making the engine something that will run as you expect it to. You would need to contact a company that can build you a custom camshaft to effectively make the best of your particular combination.

Custom Cam Company I Use

Custom camshaft Q&A

If you contact that company and talk with Mr Curtis, he can design a cam for your exact engine that should cure your ills, as long as there are no other underlying issues with the rest of the engine combination. I have ordered and installed several custom camshafts over the years. Please feel free to ask me any questions that you may have if you decide to give this option a try vs building a new shortblock.

You can try other tuning tricks to try and stem the symptoms of detonation, but ultimately they all have an affect on overall engine performance. If you change the camshaft to cure the main issue, then all of the standard engine tuning practices will remain traditional and you will not need to compromise timing, temperature, fuel, etc.

Just my thoughts.

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I don't know why hyper Pistons get such a bad rap as I've used them in many engines over the years with zero problems. These Pistons have been in everything from street driven everyday engines, street/strip engines and 7000+ RPM burnout engines, all without a single piston failure because of its design or materials used in making them. As for brands though I've only used the KB's (customer supplied) in one engine I'd built, which was a SBC but seemed to be alright and the engine still runs and still makes the occasional trip to the strip. I'd heard of claims about the KB hypers not being up to par and the set I seen seemed OK, so I really can't comment too much about them. The hypers I've had a lot of success with are the Dynotec ones and have seen first hand and heard many compliments on what these things handle, heck I've got a set still on rods that had well over 100 passes on them, plus a few burnout comps, we were even running N2o (150 shot) on these for atleast half of that time, yet the Pistons themselves are quite fine, one rod on the other hand has a big S in it from a casting fault in the head allowing water into the cylinder, but all 8 Pistons are quite fine and if replaced the bent rod, would have no problem running them again. As yourself and many have said your biggest problem was the distributor, but allowing the problem to continue for that many miles was just asking for troubles, plus the fact your engine builder knew of this happening and allowing it to continue tells me that he doesn't really know what he's doing or just didn't care. I wouldn't let this problem continue for 4miles let alone 4000 and as Barnett said it wouldn't matter what piston you were using, the results were never going to be favourable. Reading the spark plugs should've told someone that something bad was going on inside the engine, let alone the pinging noise of it detonating its head off. An ignition curve would've solved atleast some of the problems (maybe not all) and without knowing what camshaft you're running, using one as Mike suggested to let off a bit more dynamic comp may've been needed to get make everything right for your engine. As has been suggested a custom camshaft by a very reputable camshaft grinder (Ed Curtis as recommended) will help a lot for a desirable outcome. Hopefully your block is salvageable and may get away with a rehone and new Pistons, or maybe able to hone it to .030 over. In any case don't blame the piston for what was ultimately an ignition problem and running it that way for far too long, because if you were to take that much punishment for that long, you wouldn't be real healthy either. Anyway all the best with the outcome and remember, there are many people on here only too happy to help you if needed so problems like these don't happen again.
The piston issue first. The following was lifted from a post made by Barry Robotic, owner of Survival Motorsports. It sums up the matter well, in my opinion. "Its not at all about ultimate strength. In a lab environment the hypers may perform better in tensile and deformation testing to the point of failure. Its about the failure mode.

Forgings generally fail in a plastic fashion - they'll deform and crack before coming apart. Hypers fail in an explosive fashion - all the silicon nodules in the alloy are inherent stress points, and failure will sometimes result in "cup o' pistons" where no part is bigger than an inch in diameter.

Since performance applications in a non-OE environment are subject to unpredictable and uncontrollable conditions - such as over-rev from missed shifts, or broken driveline components, or marginal fuel systems, or overeager drivers, or....they are a lot more likely to get into the faiure/stress mode. Nobody ever intends to break an engine - but "are you feeling lucky?"

Difference in weight between aluminum alloys is nominal. You can do things in a forging that are more difficult in casting. You can do things in castings that are more difficult in forging. At the end of the proverbial day weight is almost entirely dependant on cross sections. The stronger forged alloys can be machined to thinner cross sections hence they can be lighter.

Similar situations and comparisons exist for the clearance variances in materials and castings vs forging. The piston design has a greater impact on clearance than does the alloy etc." If oil consumption is up and compression is down, it is likely that one or more ring lands have been damaged.

The distributor issue. The problem did not occur because the distributor was "stock". The distributor did not have the proper curve for the application, too much advance, and too much compression for the cam used, as Don C said.
I have seen several rebuilt distributors have in excess of 50 degrees advance including the vacuum advance. It doesn't matter who makes the distributor, what matters is having the correct curve for the application. The "right" curve is determined by a great number of variables; compression, cam overlap, octane, gear ratios, weight, vehicle use, etc.. Most of the time it is not just a matter of changing springs. It usually requires mechanically limiting the amount of possible mechanical advance by narrowing the advance slot and limiting the amount of possible vacuum advance. While it can be done by trial and error with a timing light, it is a lot easier to have reputable shop do it for you. While the number of people who can and will do this have declined greatly, there are some still out there. Here is one. http://428cobrajetcars.com

Obviously the octane of the fuel being used plays a large role in determining when detonation or pre ignition occurs. Octane differences of one or two points can make a significant difference in the likely hood of detonation occurring.

I hope you get it all sorted out and can save the numbers matching block.

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