Why my RB20T drop boost when high RPM? Please HELP!

[kelvin_goh999]

Guys,

Can anyone help me the problem above?

Im driving a Cefiro with Skyline GTS engine RB20T. The problem that I'm having is when I test my car on the straight road (DRAG), 1st gear when I press full on the fuel pedal, it goes up to 0.8bar & when it reaches around 5k-7k rpm, the boost drop slowly until 0.6-0.7bar. It sames goes to 2nd gear, 3rd gear, 4th gear & 5th gear. (I try it in d afternoon & night as well).

Anyone experience this before or can help me to figure out what is the problem? I think a normal turbo car should be maintain the boost. Am I right?

By the way, my RB20T is standard. I just modified air-filter & exhaust only.

Your help & advice would be appreciate. Thanks.

P/S: Got a friend told me that the actuator spring is not strong enough anymore, so it opens more & the boost drop when it reaches high RPM. Do you guys think so? He ask me to modify & add additional spring on the actuator.

Kelvin

 

[.S K A G E E.]

IF the problem is turbo related ,there could be two possibilites of why you are experiencing boost drop at high RPM. A) You have exceeded the turbos flow capacity or B) Your wastegate actuator's spring has weaken ( as you have mentioned).
Being that you are running on only 0.8 bar I suppose the best bet would be the latter. I would strongly do not recommend that you modify the springs as the actuators as readily in abundance in workshops that work on RB20s. The RB20 turbines , due to its age and material used , are fairly fragile and broken turbines are common. The actuators on these turbo are usually in good working condition. So get these workshop to sell it to you at a steal.

Other than that there could be a possiblity that the intercooler hoses and pippings are leaking.Inspect their conditions amd also check that the clamps are properly tighten.

 

[cmng]

HI Darling

 

[.S K A G E E.]

Hi sweetie...hahahahhahahaha

 

[kelvin_goh999]

When we open up the engine hub, we saw the actuator is being pull aside. So what my foreman do is straighten the actuator back to straight line & modify a spring outside the actuator.

Now my car runs up to 0.9bar but it stills boost drop till 0.7bar-0.8bar when in high RPM.

One of my foreman said that the problem will solve once I install a boost controller or wastegate. Is it true? Please advice. Thank you.

Kelvin

 

[kaminari]

This call overshoot boost, consider normal once u full throttle it (<5000rpm).Stock boost for RB20/25 should be 0.6bar only. Overshoot boost difference would be arnd 0.1~0.15bar.Boost controller can help u maintain the peak boost and response, as well boost limitter function to prevent overshoot boost. Wastegate can hold bigger boost pressure n more stable compare to actuator.