Boost issue???

[tomsuch]

Hi guys.
Just bought my 3rd G40 a week ago. My previous 2 had toothies and stage 4 charger plus a few little other bits. They both seemed to boost at around 15psi 1bar. My new one is also on toothies, stage 4, cam, 1341cc fmic and a few other bits but it seems to only boost at 10psi, doesn’t matter if I’m wot at 2000rpm or 7800rpm it’s still at 10psi. Could this be a faulty boost gauge? It seems to go very well.
It’s plumbed into the vacuum line from the fuel pressure regulator so the correct place. The pipe is fairly small though, could that be the issue?
What’s your thoughts?
Cheers
Tom

[sleag40]

Over bore + longer duration cam will both reduce back up of pressure  - it just means the engine is using more of the charge than a standard lump would. 

[hayesey]

doesn't sound far off to me too for a 1341 with a cam (although you don't say what cam, I'm assuming something like a 252/276) on a 65mm pulley.  There'll always be a bit of variance between different boost gauges though, they're not mega accurate.  If you've got another spare gauge around you could try it and see if it's any different.

[ereeiz]

Boost is only a fair comparison on like for like (identical) engines. Everyone quotes boost, it's actually the quantity of air that gets rammed in which is important.

Blow through a straw and it's quite hard, blow through a hose pipe and it's easy. Just because the (boost) pressure is higher through the straw, doesn't mean as much air is being delivered.

It's a handy indicator though, especially if you learn what it makes at what RPM, then if anything begins to fail you may notice before it fails completely!