Thoughts on Compression

[Mike M]

As some of you know I have been building a new engine for my MM. I have tried to buy the best parts to go into my brand new aluminum block, CP pistons-Manley Rods-Forged stroker crank (5.0) billet oil pump etc. I took it to a reputable builder experienced in these engines. I installed the engine and immediately heard loud piston slap. Long story short the engine is back out, and I am probably going to have to send out the pistons to have them coated. I did some measuring and it seems there is about 3 to 3.5 thousandths piston to wall, spec for these pistons are 2.

Anyway these pistons will raise my compression to 10.4:1, I usually use about 100+ octane exclusively but running my 12lbs of boost do you think I could have it safely tuned for 91 octane with that type of compression? I probably won't be running 91 but I would rather have it tuned to the 91 octane out here just in case I can't get my hands on the good stuff.

[babbage]

A 170 Reishe stat and a rear head cooling kit (Reinhart) with an EMP pump may allow you to run it on 91. Perhaps add a Fitch fuel catalyst. With that setup I'd shoot for 93 as you can get it anywhere - except California.

Did you do offset wrist pins? - I hear that helps reduce the slap. Not sure on the tolerances though. Good luck.

[musclemerc]

Let me get this right. You think that a cooling mod and a EMP WP will assist him with running 91oct fuel on a high compression/stroked motor???

Maybe I'm missing something here.

Anyone else?

[Joe Walsh]

Mike, I don't think that coating the pistons will make up for the incorrect bore diameter.
Those coating are considered" sacrificial".
Have you asked the engine builder....WTF?

[Mike M]

Only 91 in this state (don't know why)

These pistons are pretty but they are not offset.

I was hoping piston coating would last 60k+ (the coating on the stock pistons looked really good after 47k).

Yes I had the machinist come and listen to the engine and he concurred that it is piston slap, we will see how much I pay for him to make it right. :-(

If I buy another set of pistons what seems to be the brand or model # that people have had no sound issues with?

Also what compression is the highest for a blown engine. I like to be on the higher side for drive ability.

I would like to use these existing pistons if possible hence the coating.

[Joe Walsh]

Only 91 in this state (don't know why)

These pistons are pretty but they are not offset.

I was hoping piston coating would last 60k+ (the coating on the stock pistons looked really good after 47k).

Yes I had the machinist come and listen to the engine and he concurred that it is piston slap, we will see how much I pay for him to make it right. :-(

If I buy another set of pistons what seems to be the brand or model # that people have had no sound issues with?

Also what compression is the highest for a blown engine. I like to be on the higher side for drive ability.

I would like to use these existing pistons if possible hence the coating.

The piston's coating should last for a fairly long time assuming that all the clearances are correct.

I wasn't sure what the thickness is on those skirt coatings....:dunno:

I thought that their final applied thickness was negligible in regards to piston->cylinder wall clearances.

I've got Diamond forged pistons in my engine and I've heard good things about Mahle pistons.

.

[RacerX]

Did he just hone the block or actually bore it over at all? Or did the block come standard bore and honed from factory?

[Mike M]

Standard bore, I assume he did a light hone.

[RacerX]

Standard bore, I assume he did a light hone.
I'd ask him. I assummed MMR would tighten all my fasteners down with correct torque...

[TooManyFords]

Is this only cold or when fully warmed up?

[Mike M]

Cold and Hot, never ran the engine for more then 10 minutes but it was unacceptable.

[TooManyFords]

If it does it for more than 2-3 seconds from cold, there is a problem. My MMR with aluminum pistons and an iron block have a small rattle for just a couple seconds and then it's good to go.

[Mike M]

So what is the consensus on max compression with 12lbs boost.

[RacerX]

10.4 with 91 octane, you'll need to watch timing. Should be fine if you pull enough timing though and keep the engine/air temps cool.

[SpartaPerformance]

Let me get this right. You think that a cooling mod and a EMP WP will assist him with running 91oct fuel on a high compression/stroked motor???

Maybe I'm missing something here.

Anyone else?

10.4 isn't high compression i.e. the 3v is 10:1 and it runs on 87 octane.

[FordNut]

I have CP Pistons. Diamond is also good.