Questions for those using forged pistons and stock ecms

[GNVAIR]

Are any of you guys having problems with false knock?
I was told recently by someone that I should stick with a cast piston if I am going to use the stock ecm as the looser forged pistons can set off the knock sensor. I have built many engines and agree that forged require looser tolerances, but my question centers around the sensitivity of the knock sensor. I am planning to install a set of J&E's in my new engine as well as an engine I am building for a friend. Should I be concerned with piston slap setting of the knock sensor? The same person that recommended the cast pistons said that the only Buicks that should be running forged are the race cars using DFI/Fel Pro set ups.
Lets here some stories guys.

 

[Red Regal T]

I'm no expert but I never heard that before. If it were the case, the many people who use forged pistons would have brought it up many times.

 

[bruce]

Gm in their SBC marine applications use a 45d male to female coupler to change the plan of reference.

The J+S Knockguard has a tunable threshold.

Nothing beats sneeking up on the tune to make sure your not in detonation by plug reading.

Any thing electrical is subject to error, hard to beat looking into the chamber via plug readings to see where your at.

The stock ecm allows for tuning the attack rate, the limit, the decay rate, of detected knock, and then allows for taloring the Burst Knock Retard parameters.

The stock ecm has lots of stuff few explore.

 

[TType85]

I'm running J&E forged pistons, no false knock here.

 

[turbojimmy]

I have forged pistons, too. No false knock.

Jim

 

[turbosam6]

Well, I've got J&E's, and I've got some noise, but not sure what it is. Could be slap. It sounds like a bad lifter, only taps sometimes, and you have to drive for awhile to get it. You can drive on the highway, every 5-8 miles, I get some false knock, then it goes away. No metal in filter, good oil pressure.

 

[KendallF]

In general, forged pistons are set up with looser bore clearances because they expand more when they heat up. So...if they're set up correctly any noise should be gone in a few seconds when they come up to temperature anyway. Once warmed up and running, a forged piston should not be any noiser than a cast piston. In fact, it could be considerably quieter when it doesn't blow chunks like a cast piston under detonation! (just had to throw that in for our resident hypereutectic freak or two... )

 

[tc86gn]

TRW forged. No false knock.

 

[kenmosher]

BRC forged ... no knock.

 

[Intercooler]

Originally posted by KendallF
In fact, it could be considerably quieter when it doesn't blow chunks like a cast piston under detonation! (just had to throw that in for our resident hypereutectic freak or two... )

I have pictures of some forged chunks too

 

[GNVAIR]

Thanks guys! Looks like it will be the J&E's. I guess someone was very WRONG!

 

[Intercooler]

Any thoughts on using the Diamond pistons like Ron's Custom Auto uses? Cost a little less, same material and looks decent too. I think it is www.diamondracing.net

 

[ragenssjgohan]

Im no expert in anything but I had a false Knock when my Flex Plate Came Loose... Sounds sorta like that ::Shrugs::

 

[325DR]

J&E's here. No false knock.

 

[Steve Wood]

Diamonds are good pistons...no problems

 

[turboman38]

30 over TRW forged and no knock.

 

[qtr@atyme]

Diamond and trw raw forgings are made by the same company.
up to a little while ago the trws had the diamond logo inside of them

 

[750H.P.V6]

False Knock

Lee,

I read your post as well as the responses and I personally don't think you've been misled. If you were told that you would have false knock all the time then whoever said this exagerated. However all the people chiming in saying that they don't have false knock don't know where and when it occurs.

I responded to a post several days ago that was to do with knock at light throttle cruise. False knock due to excess piston clearance usually occurs on decel believe it or not. This will vary from application to application and depend on how much skirt clearance you run on your pistons.

The more H.P you are shooting for the looser the pistons need to be and the ring gaps as well. If you end up running less than .004" clearance on whatever pistons you use then you should be fine. If you're planning on making over 600 H.P. you will need more clearance and false knock can be a real possibility.

Just thought I'd put my 2 cents in.

Good Luck
Neal