i have a quick question regarding the boost on a 1981 280zx turbo.. if i remove the pop off valve and plug it will that increase boost more than 10lbs.. and what is the max boost pressure for the stock turbo.. thanks

 

No. It won't increase the boost at all. The WASTE GATE controls boost.

12-13psi is about the max that the stock turbo will be efficient.

Two books you should read:

 

no it will not jump up in boost, but allow you to build more than 7lbs of boost i believe. not an expert. but did you google it? and max boost for the stock t3 turbo is more than 10lbs so if thats your goal just intercool boost control it and you should be fine notsure about the injectors though.

 

Definately. Turning up your boost is a great way to blow up your engine.... if you don't know what you're doing. So if you don't really care about blowing your car up go for it...

In a nut shell to answer your question and to clarify...

The Pop off valve is something you don't usually see in a modern turbo charger system. Superchargers have them but they aren't really necessary on a turbo charged system that has a properly functioning blow off valve. The difference is that a Pop off valve is after the throttle body and acts as a safety device. It will vent excessive preasure to atmosphere to prevent over boost conditions. The blow off valve will vent to atmosphere or recirculate (better but infrequently done with most Ricers) before the throttle body. This prevents a presure differential on the intake/output side of the turbo compressor which will cause the turbo to suddenly stop and causes excessive stress on the turbo.

Without a Pop off valve you are trusting that your wastegate will maintain correct boost levels. Since the stock Pop off valve is set for around 8lbs of boost you'll need to modify it so that it doesn't blow off until higher than your max normal running boost levels.

If you want to run over the stock boost levels most people say up to 10lbs of boost. Personally I wouldn't run that high with the J-Pipe but if you are going to risk it make sure you run at least 91 octane. I would run an intercooler if you are going to run anything above stock boost levels. Above 14lbs the stock turbo is going to be super inefficient and you'll be dropping off in power.

Don't forget your fuel injectors will only supply so much fuel. If you put more air in than the fuel can keep up with you'll start to run lean. Lean is mean until you melt your pistons....

 

the stock pop off valve is a joke. its 30 year old technology. If you have a GOOD boost gauge, not the stock one, all you have to do is pay attention and let your foot off of the throttle if it ever over boosts. What is supposed to happen when the POV fails closed and you just happen to lose the line going to the wastegate, same thing. Ditch the POV, its a piece of junk. I did the whole modify it with washers thing, and it eventually failed and wouldn't let me run full boost. There's a reason you don't see any fairly modified turbo cars out there running a pop off valve. Unscrew it from the manifold and go to home depot and buy a 1" pipe plug, screw that thing in. Once you've done that. Go on hybridz.org or Zcar.com and SEARCH to see how to raise the boost properly and not blow anything up. But as posted above, generally 10psi on the stock system running 93 octane will do just fine. Stock as in stock fuel pump/jpipe/injectors. You can go up to 12psi with a walbro 255 fuel pump and a good front mount intercooler. Anymore than 12 and your injectors no longer flow enough fuel. But anywho, those are just the basics, do some actual searching and you'll learn all you need to know.