Engine Vac at Cold Start VS Full Warm

[vristang]

I have noticed that my Cold Start Engine Vac signal is 14". Once the engine if fully warmed up (a good 15 minutes of driving), the vac will be steady at 16.

Just looking for theories as to why, I don't think anything is wrong.

Mine
Forged Al pistons fit smaller in the bore when cold, so vac increases with piston temps.
Oil temperature/viscosity influence ring sealing (but I have a hard time seeing it have this much of an impact).

I look forward to hearing your thoughts.

jason

 

[Black1987Stang]

I have noticed that my Cold Start Engine Vac signal is 14". Once the engine if fully warmed up (a good 15 minutes of driving), the vac will be steady at 16.

Just looking for theories as to why, I don't think anything is wrong.

Mine
Forged Al pistons fit smaller in the bore when cold, so vac increases with piston temps.


jason

I agree with that one also, aluminum pistons do expand alot. I have a weird deal with mine. Mine used to be at a consistent 14 at idle and then i drove on the parkway for 20 minutes and ive never driven on the parkway since the motor was put in and now the vacuum at idle is 15 where it used to be 14 haha, its like it was fixing itself or something.

 

[HISSIN50]

Also since metal expands, two mating surfaces (upper to lower, for instance) can fit a little tighter once warm.

 

[vristang]

One bump to see if there are any other theories out there.

The pistons/intake having to heat up would explain alot of cold start issues.

:Word: