Help with piston-sidewall clearance

[jbarlow]

Have to go see my freshly machined motor, and need to ask an intellegent question about side clearance.

The difference this time for me, is that the 2.5 common block has been bored for a set of forged Venolia 2.5 0.030 over pistons (vs. stock cast Mahle I'm use to).

I am planning to use either Speed Pro (which come with) or Hastings (but I'm open to other suggestions).

I know TII 2.2 and T 2.5 specs are 0.13mm - 0.32mm, but what should I check this for??

What about ring gap??

I am intending this motor for primarily street duty, with occasional trips to race.
I'd like to avoid piston slap, which I have heard some guys endure in racing motor spec, in order to account for expansion.

Thanks in advance.
Jeremy

[jbarlow]

Quote:

I know TII 2.2 and T 2.5 specs are 0.13mm - 0.32mm, but what should I check this for??

Asleep at the key board...Again!!


Should have typed...

"...I know TII 2.2 and T2.5 specs are 0.0005" - 0.0015"..."

Also that other forged sets spec at 0.0035" to 0.006".


Some feedback from anyone running this similar set-up now, about positive or negative experience would be helpful!!

Jeremy

[GLHS0658]

That is what I am setting up mine for (Venolia's)

The side wall clearance is determined by the piston manufacturer.

You have to run what they recommend. If you go too tight to reduce piston slap....boom! The piston expands to fit the bore when it is at operating temp.

Just let the car FULLY warm up before you boost

[jbarlow]

I realize that the spec are provided, but what I was really looking for was some feed-back from some experienced TDers runnning these already.

I recall an old post (by Dave Reynolds??) saying that he had to increase his side wall-piston clearance, to get rid of noise, etc.

Jeremy

[GLHS0658]

Wouldn't noise (piston slap) be increased with MORE clearance?

[flybyuin2.2]

i was running Venolias with .003"clearance and after a 5 min. warm up the motor was running as quiet as a stocker, running .006"clearance seems a bit excessive, the pistons will most likely rattle when warm(have that solid cam effect)

[jbarlow]

Quote:

i was running Venolias with .003"clearance and after a 5 min. warm up the motor was running as quiet as a stocker

Excellent feedback...this is exactly what I would think to be the case, but I couldn't figure out why I was reading posts saying that more clearance was being sought?!?!

I also presummed that larger clearance would result in more noise, or potential for "slap".

Is it possible the guys setting up thier engines for racing duty are going with more clearance??

My intent is street, with the occasional race.
Not having run forged pistons previously is why I posted original question.

Jeremy

[crazy1eye]

It depends on what boost/hp your going to be making. With the JE's, they specify .003 / .004 if your running big boost. So, be carefully with those Venolia's, they need more clearance.

[jbarlow]

What are you running?? Are you using Venolias??

The spec sheet is 0.0035", but as you mentioned they may need more clearance.

Some first hand experienced comments / feedback from the list please!!

Jeremy