Thread: spiking boost

ok somewhat new to the turbo scene... i have a 240sx with a sr20det.. the car has been running amazing it spikes 11psi and holds 9psi...yesterday i upped the boost a little now it spikes 14psi and hold 11psi....im on a stock t25..my question is spiking boost that high bad? im kinda concerned i really dont want to mess anything up spiking boost, a buddy told me as long as its NOT holding 14psi im fine...input on the situation? thanks in advance guys

As long as your air to fuel ratios are fine, you will be fine. You are running a DET, which has a fairly low compression. Your only issue is that T25 running out of breath, but even then I heard of them running to 18psi...

ok so im in the clear as long as AFRs are good...i also heard several people state that the det ecu is self leaning? which means if i up boost it also ups fuel? i have a nismo adj fpr on my fuel rail..? correct me if im wrong please

Like mentioned above if your fueling is on point a healthy DET will take anything a T-25 can throw at it.

OK AWESOME..thanks guys

Our ECU's are self learning but not in Open loop. And even if it was self learning in open loop, by the time it would self learn, you would melt your engine .

Open loop = O2 sensor feedback is not used. Closed Loop = ECU uses the O2 sensor to tune itself to 14.7. When in Open loop, the ECU does not know what your AFR's are.

Maybe you have a blockage in the wastegate source line or youre using a crappy mbc. Do you have the wastegate line run properly?

I'm sure what he meant is that the ECU adjusts fuel and timing based on airflow. Unlike MAP sensor based cars that require a retune after upping the boost.

But self-learning isn't really a function of these computers, like you said. Fuel trim is the only thing adjusted in closed loop.

we have plenty of slightly modded s14 silvias here and they all have the DET inside so your question is a common one :-)


There are two problems/risks for you that could lead to engine knock which is bad.

1. the stock injectors are 370cc and are maxed out at appr. 12 psi above 6000RPM. So if you have a short boost spike above 6000RPM it could lead to a lean mixture for that short moment.

2. all the parts of the stock fuel system are old and worn (if not replaced) and especially the pump and the AFM are known to fail slowly with age. So even if you stay on the save side boost wise a worn afm for example could lean out your mixture and lead to engine knock and harm your engine.

My advice: stay with the current situation and buy a knock monitor. Or at least buy a AF-Gauge and learn to use it. Simple rule to start with: Under full acceleration above 6000RPM the AF-ratio has to be in the 10th, if you don´t reach 10th something is starting to wear.

thanks for the info..car has a walbro 255 and a nismo fpr im getting a wideband soon...let me rephrase my ? sorry....my car was holding steady 8.5psi with no spiking what so ever....i turned boost up some it holds 11psi and spike 14psi...my question is....can harm be done with spiking boost if its only holding 11psi and not holding 14psi?