rebuilt engine knocking?, engine builder says its normal for big bore 4's? Options

[narino]

Alright I understand these cars don't have the quietest, smoothest runnning engines made, but does this doesn't sound right to me. There is a knocking sound at startup until she's warmed up. Then it smooths out, not completely though still can hear the knock.

The engine builder, who builds racing type IV engines says that the noise is typical with big bore type IV engines. Here is a link to a video, what do you guys think?

video
http://www.narino.com/images/914-knocking.wmv

Here is what the engine currently has inside it: (originally a 1.7)

103 mm x 78 Stroke
2.0 H beam 5.325 (? no idea what this is was on the paper)
G - Cam
44 x 38 Heads

Thanks in advance!

(IMG:style_emoticons/default/beer.gif)

[narino]

Ok bringing this one back. After paying off some car debt and driving the car around it's still too loud for me.

I've talked to the engine builder and he says he'll swap out the forged pistons for cast iron pistons with tighter tolerance. He is not charging for the piston swap and would only charge labor to do the work, which is about $650.

Does this price sound reasonable? Also, are cast iron pistons really more quiet and worth swapping out the forged pistons for a more quiet no-track, non turbo'd engine?

(IMG:style_emoticons/default/beer.gif)

Thanks in advance.

[rick 918-S]

Ok bringing this one back. After paying off some car debt and driving the car around it's still too loud for me.

I've talked to the engine builder and he says he'll swap out the forged pistons for cast iron pistons with tighter tolerance. He is not charging for the piston swap and would only charge labor to do the work, which is about $650.

Does this price sound reasonable? Also, are cast iron pistons really more quiet and worth swapping out the forged pistons for a more quiet no-track, non turbo'd engine?

(IMG:style_emoticons/default/beer.gif)

Thanks in advance.

Is he going to balance the assembly again? Heavier pistons, Not cast iron though... more likely cast aluminum?... (IMG:style_emoticons/default/confused24.gif) Heavier = more stress on the rotating assembly. But the piston expansion rates should be more equal with the cylinder material.

[karlo]

Forging eliminates metal porosity and improves ductility. With the extra strength, forged pistons can be made a little lighter. The improved ductility will allow them to handle knocking a little better.

Whether or not forged is needed depends on compression ratio, max rpm, power output, etc.

Most forged pistons expand more than cast, so need to run greater clearances when cold, and will be noisier on startup.