I am having a dilemma. Could someone please confirm / advise on the following…
Boost Gauge fitted (Apexi, not Standard useless thing)
When the engine is off what boost pressure should I be showing?
It is currently showing 0 Bar
When the engine is on tick-over what should it be showing?
When I start it, the gauge shows -0.5 Bar, then goes to -0.6 Bar, sits there for 2-3 seconds then goes to -0.7 Bar and stays there.
Stationary reving:-0.7 Bar to 0 Bar (sometimes it gets to 0.1 Bar)
Driving (Hard):
-0.6 Bar through to 0.5 Bar then drops to 0.4 Bar when flat out and stays there.
Other factors…
The car is a 1992 Mk1 GTO (import). I have removed the restrictor plug from the lower prong on the boost solenoid. Before I did this the car would boost to 0.4 Bar Maximum but just stay there. Now it goes to 0.5 Bar but drops of after 3-4 seconds.
I have done the fuel relay mod. Made car better of line.
I have a HKS twin Mushroom filter with a HKS pipe. (no centre cat).
Is there something wrong with my car? Am I leaking Boost?
Orpington GTO thinks my gauge should read 0 Bar on tick over. Is this right? His gauge reads 0 Bar on tickover but his pick up pipe is in a different place to mine. I have checked the Apexi web manual and mine is connected to where they say it goes.
What max boost should I be showing with the restrictor out?
I do not have a boost controller of any sort.
Standard recirc dumpvalve.
On tickover, you should be showing vacuum, so -.6 > -.7 bar is correct.
On cruising, without accelerating you should also be in negative figures. On light acceleration you should be around 0.
On acceleration your figure of .5 and then .4 bar is probably also correct (I think thats about 7-9psi) although if it is dropping then that could mean you are loosing boost (check pipework, adjust bov)
yeah, engines draw a vacuum at idle (my guage is in PSI and Hg (inches of mercury) so my readings are a little different)
I read about 17Hg at idle (the dropping with warm up will be where the idle control valve is having to be a little more open when you first start her up - your engine revs will be higher too)
I’ve installed a boost controller, so I get 14 psi for a few seconds and then 9psi to redline
when the engine is switched off you get neither vacuum nor boost (funnily enough), so 0 is correct
if Orpington GTO’s guage reads 0 at tickover then his boost guage is plumbed in somewhere before the butterfly (which in my opinion is the wrong place, after the throttle body gives you a truer reading of what the engine is seeing in terms of boost)
Conversion factors:
1 psi = 0.06895 bar
1 bar = 14.50326 psi
1 psi = 6.8948 KPa
When engine is off you should see 0 Bar
When it’s ticking over you should see negative pressure of around -0.5 to -0.7 .
Stationary revving should see your lowest negative pressure to 0 bar
Driving (Hard) If your cars running 0.5 bar that’s around 8 PSI which is about right. You say that you get around 0.4 Bar when flat out and stays there. O.4 = 6 PSI and that’s what your actuators are set to run.
Before i installed my boost controller this is what i was running. Mine never held 8 PSI for long, before dropping back to around 6 PSI.
My boost gauge is mechanical and reads 0 with the engine turned off and get about the same boost readings as you so would assume this is normal as Dave previously had the same prior to fitting a boost controller.
I thought I was right about it showing a negative presssure on tick over, it would have to as the engine runs a vacum before boost! Also, why would a boost gauge have minus figures on it if they were not used?!?!
I will let orpington GTO know that he needs to replum his pick up.
It would also apeer that removing the restrictor doesnt make that much diffrence? Eitherway im fitting an E-Boost within the next week so I wil be running 0.95 Bar untill I get my new injectors and pump.