My ? is, I installed a boost pressure gauge on my truck and under a good load, it pulled 50 psi. I thought it was incorrect, and since then, I have installed 3 other boost gauges, including a digital gauge and they have all read the same pressure but the digital gauge actually 51 psi. How is this possible with a stock turbo? And what kind of horsepower mite I be makin?

 

It's possible on a stock turbo, but it isn't good. You're over-spinning the turbo, pushing it way out of its efficiency range, because you have so much fuel; your intake and exhaust gas temperatures are likely very high, and your exhaust manifold pressure is probably substantial.

If you properly wastegate the engine it will drop EGT's, boost pressure, back pressure and intake temperature; that will let the turbo live longer and quite possibly give you more power than you would have otherwise. That much pressure out of a stock turbo, and the stock turbo is more detrimental as an exhaust restriction than it is beneficial as a pressure booster.

If you go to a bigger turbo you will also see a drop in EGTs, boost pressure, back pressure and intake temperature, the turbo will live longer, and you will definitely get more power. This is because a larger turbo can move a greater mass of air at a given boost pressure, without heating it up as much.

 

Thanks man. I have another MUCH larger turbo off a CAT engine. I am contemplating doing a twin set-up. After the engine has reached operating temp, my exh temp gauge only shows about 950. So Im really con-fuzzed on what the hell is going on. How am I getting that kind of pressure and not terrible temp?

 

is your sensor before the turbo? if its after,then that would make sense

 

It is after. I got the gauge out of a Peterbilt and the temp probe on it was after the turbo so I figured that I would put it after the turbo on mine.

 

The temperature in the manifold is going to be a lot higher than in the downpipe, and it'll also respond faster.

Semis are more interested in watching trends then tuning for power. They're set up at the factory with a given turbo and a given amount of fueling, so they know what post-turbo EGT's are going to be safe and where it becomes dangerous.

But the more we turn up the fuel, the more of an EGT drop across the turbo there is, and the bigger the turbo the less of an EGT drop. We play with enough variables that it's a lot more useful to have the pyrometer before the turbo.

Chances are that your pyrometer would be maxed if it was in the manifold.

Even if you use the second turbo as a twin, you will still need enough wastegating to keep the little turbo from over-spinning. If your stock wastegate is working right and just not keeping up, an external wastegate is a good idea.

 

My buddy's 95 12 valve w/ just a #10 fuel plate would run 50 psi all the time on a stock charger untill he blew the intercooler apart.

 

yeah x2 get that probe in the manifold, you will notice a very drastic change in the temp. reading, prolly a couple of hundred degrees. if your running that hot all the time, you are just asking for troubles. get a bigger turbo,

 

for sure move the probe... my buddy had his probe after the turbo on an 2006 with a smarty on the 170 setting and he was only seeing 900* and after i talked him into putting it in the manifold he was seeing almost 1300*

 

Yes, there can be anywhere between a 200 to 600 degree difference between pre and post turbo. Post turbo is never a good idea unless you have a preturbo probe as well.