i have a 87 740. whats the stock boost and what can i safely turn it up to on stock internals. how do i up it if so. i see there is a wastegate under the turbo and then another type of valve to the right of the intake. do i have to adjust both or just the wastegate?

 

If you are going to mess with the boost you need to do it right.
1st install and aftermarket boost gauge.
Get a base stock boost level I will bet between 5 to 7 PSI.
Then you can by and install a Manual boost controller. Then turn it up to between 10 to 12 PSI safely.
Some people adjust the waste gate as well to make the boost smoother.
But like I said first install a boost guage to prevent overboosting and hurting the engine.

 

do i need a mbc or can i just adjust the rod to say, 10 psi. do i have to adjust the other valve that returns air to the intake too? and if i do need one where can i get a mbc.

 

I would do the MBC before the waste gate adjustment. This way you will be safer.
http://cgi.ebay.com/ebaymotors/NXS-M...spagenameZWDVW
Running one like that on the white car in my Sig. I have a different one in the yellow car.

 

Sorry no adjustment needed on the bypass valve.

 

doesnt the mbc have the same effect as if you adjust the rod, just more on the fly.

 

The MBC will stop high boost spikes the adjustment of the waste gate will not. Which could overboost and throw a rod or something like that.

 

ok. thank you tech. another thing, why does it not spool at all when the motors not under load such as in neutral. does a bov replace a wastegate and would there be any gains other then the tssssssssssssst sound. i could tear apart a motor and put it back together with ease but turbos i am new to and have yet to understand.

 

Im not 100% sure why they don't spool when in park. But it is something about haveing the load on them that makes them boost.
The BOV would replace the bypass valve not the Waste gate.
No gains to having BOV over a bypass they both do the same thing.

 

so the bov/bypass valve is extra protection? could i just make the bypass valve blow off to atmosphere instead of backinto the intake to get a louder sound?

 

It is part of the turbo. If you make a cold air kit for the car it will get louder. Or run the bypass and a BOV.

 

On a 740 with the B230FT engine, upgrading to a 2.5" cat back exhaust with a single free flowing muffler is worth a solid 2 psi of boost as well.

Regards, Andrew.

 

Exhaust gas speed and pressure help the spinning of the turbine. That comes when your under load, and more exhaust is coming out of the motor because more gas and air are coming in the intake...

Does that help make sense??? If you tap the throttle really fast, you will see some small boost.