X-post - Heads are lifting at 1.4 bar of boost. What to do now? (Photos)

[flightlead404]

Originally Posted by Tippy

All 24 at once? I'd imagine the thread peaks would be rounded off, no?

I didn't mean the studs, just barrel nuts, washers, sheet metal screws, other things like that on the engine. Although it probably wouldn't damage the threads either. The "tumbler" doesn't really tumble, its more of a vibration and slow rotation. Things woundn't be banging together hard. I've never had a problem.

[Tippy]

Originally Posted by flightlead404

I didn't mean the studs, just barrel nuts, washers, sheet metal screws, other things like that on the engine. Although it probably wouldn't damage the threads either. The "tumbler" doesn't really tumble, its more of a vibration and slow rotation. Things woundn't be banging together hard. I've never had a problem.

Ah, gotcha. Thanks

[JakobM]

Originally Posted by RarlyL8

I'm sure someone has asked this question but I didn't see it; why so much boost?
You can make power other ways that do not stress the engine so much.

if we leave detonation out of the equation then it is the combustion pressure (when everything else equal) that lift the heads, not the boost. If we add extra NA displacement or flow extra to compensate for X bar of extra boost, the same combustion pressure would still be present and result in same head lift

[JakobM]

proberly a detonation issue

[Tippy]

Originally Posted by JakobM

if we leave detonation out of the equation then it is the combustion pressure (when everything else equal) that lift the heads, not the boost. If we add extra NA displacement or flow extra to compensate for X bar of extra boost, the same combustion pressure would still be present and result in same head lift

Exactly.

For exaggeration purposes, 25PSI of boost through a stock 930 could have lower overall cylinder pressure than an Xtreme headed, DC100 cammed, with ITB engine at 15PSI/1bar.

Purely for making a point, not actual comparos!

[boosted79]

Timing affects cylinder pressure. The more advanced the timing the earlier the pressure peaks and if the piston is still coming up the pressure will be much higher than with later timing which puts peak pressure right after TDC when the piston is going down which is where you want it for max power. So you can have lower cylinder pressure and make more power. Twin plug it and retard the timing, problem solved.

[Tippy]

Originally Posted by boosted79

Timing affects cylinder pressure. The more advanced the timing the earlier the pressure peaks and if the piston is still coming up the pressure will be much higher than with later timing which puts peak pressure right after TDC when the piston is going down which is where you want it for max power. So you can have lower cylinder pressure and make more power. Twin plug it and retard the timing, problem solved.

'Tis the plan

[stownsen914]

For twin plug, I understand that 26 degrees BTDC is a reasonable number for full advance on a normally aspirated engine (some go a couple degrees more, some a couple degrees less). Use the same range for a turbocharged motor?