Forged Vs. Hyp. Pistons in 4.3 V6

[OMARiverRat]

Fellow boaters:<br /><br />A long time ago in a place far far away, someone told me that engines designed for marine applications should have forged pistons regardless of size, compression, and power add-ons (blower, nitrous, turbo). Recently I've been told that Hyperutectic pistons work just fine in smaller engines, such as GM's reliable 4.3 V6. Can anyone shed some light on this?<br /><br />I recently purchased a new 4.3 V6 Long block for my 89' Four Winns, OMC Cobra outdrive (pre-vortec engine). The engine came w/ hyperutectic pistons. The engine is bone-stock with absolutely no modifications, and is breathing through a 2bbl rochester. <br /><br />My main question here is if hyperutectic pistons are OEM Equipment on the GM 4.3 marine engine. Additionally I'm curious to know if anyone has experienced any detonation problems with this type of set-up. <br /><br />Thank you all!

 

[John_S]

Re: Forged Vs. Hyp. Pistons in 4.3 V6

I don't believe that forged pistons were used in any standard mercruiser production motors. Maybe in their race versions??? hypers have been used since around '97 with the into of vortecs. Think there was a rod change, as well, but not forged. Shouldn't have any problems as long as you are staying at stock WOT rpms, and stock compression ratios.

 

[Bondo]

Re: Forged Vs. Hyp. Pistons in 4.3 V6

Ayuh,......... Chevy,+ Mercruiser haven't seen the need for Forged Pistons,.........<br /><br />They used Cast pistons for Years,.... They maybe using Hypers now,..... Don't really Know.......<br />I Do Know that Merc saw fit to use Whatever Chevy was dropping into their Trucks, for their Standard Production motors........<br /><br />The stuff from the High-Performance shop is No Doubt a Different Story.......<br /><br />Detonation is the product of either Too High a Compression Ratio,.. Or Too Much Timing.... Or a Combination of Both......

 

[paulie0735]

Re: Forged Vs. Hyp. Pistons in 4.3 V6

If your going to use the forged pistons, (personally I wouldn't bother on a stock 4.3) than you must ensure that the block is bored and honed to suit the pistons that you use, especially if you choose the forged as they require a lot more clearance than cast and more again than hypereutectic. As for the detonation issues, its generally accepted that hypereutectic pistons will not cope with detonation or 'ping' anywhere near as long as forged or cast pistons will, for that reason alone and given the unreliable fuel quality over there I would stay with the standard cast pistons.

 

[John_S]

Re: Forged Vs. Hyp. Pistons in 4.3 V6

As for the detonation issues, its generally accepted that hypereutectic pistons will not cope with detonation or 'ping' anywhere near as long as forged or cast pistons will,

Probably why or at least partially why, all merc vortecs comes with knock sensor and to auto retard the timing when it occurs.

 

[coalbucket]

Re: Forged Vs. Hyp. Pistons in 4.3 V6

The hyper. pistons also need a wider top compression ring gap than normal. If using the piston in a application such as marine or racing on a 4" bore I normally gap the top around .038-.043". If not you run the risk of welding the ends of the ring together under heavy load.

 

[Buttanic]

Re: Forged Vs. Hyp. Pistons in 4.3 V6

I have used Keith Black hypereutectic pistons in my circle track race car and in my boat with out any problems. They recommend .008 top ring gap in marine applications. Hypereutectics are stronger than cast but not as strong as forged. They expand less than forged so they can run smaller piston to cylinder clearences than forged. <br /><br /><br /> http://kb-silvolite.com/article.php?action=read&A_id=32