Boost question

[Kombat0001]

Have a stock 91 gts-t and it has a aftermarket boost gauge when im accelerating hard it makes about .8 -.9 bar then slowly drops to .5 ... is this normal or is it a boost leak somewhere?

[Nismo_line]

no thats not normal. i dont think a boost leak as you probably wouldnt be able to build that much boost. my guess is a actuator on the way out.

[Skym]

Usually not normal. But stock BOV can leak due to getting oil deposit's around the valve or BOV gasket leaks which can cause a drop in boost level at higher rpm. Check fuel pump, fuel system as well, as parts like FPR, fuel pump could be on the way out.

Sometimes it's just the BOV itself that leaks. Aftermarket BOV usually fixes the problem.

Can test internal wastegate actuator spring by adding compressed air to actuator bulb via vacuum hose with T'd in boost or compound gauge. When the internal wastegate actuator arm moves, that is the spring pressure and should be around 12psi. If failed it should be lower than around I think was 11psi.

[Kombat0001]

I have heard that it should only make .5 bar not as much as .8... is that right?

[Skym]

Stock is around 7-8psi.

[Kombat0001]

I cant find a controller of any kind for the boost levels however I am Making .5 bar in second gear so 7 psi. Then in third it scrambles to .8 bar then levels at .5 bar. .8 is around 12psi I believe. In fourth it makes .8 bar all the way. What would control this to be higher than stock? ECU looks stock from the outside. No Boost controller electronic or manual.

[Skym]

Removing restrictions. Just freeing up exhaust, intake is enough to make the boost level rise.

Rear of exhaust = 0.2bar
Frontpipe = 0.1bar
Dumppipe / turbo outlet pipe = 0.08bar

Podfilter is 0.1 bar, but stock airbox is better (bigger airfilter thus less restrictive) and would just change the intake pipe to airbox. The stock intake location just under under headlight is the restriction.

Intercooler (tube N fin, stock intercooler is bar N plate) is another 1-1.5psi.

It should be able to reach up to 1bar, 330hp at engine once all the restrictions are removed and turbo, engine are in good condition, with ECU tune, etc.

Stock ECU can pull ignition timing, adjust fueling to suit (knock / low octane maps), then not to adjust the boost level slightly. If see a big V in torque graph (on dyno), then it's the ECU playing with ignition timing, fueling (knock / low octane maps).

A dyno run would be the best way to check if fueling, etc is ok.

[Kombat0001]

thanks so much that helps... will try to get a dyno test done to see what it looks like