How is boost pressure controlled with no wastegate??? Please don't give me a crazy answer like engine rpm controls it. That's like asking how an alternator works and saying it is controlled by electric. I know exhaust has to be removed to prevent overboosting but how without wastegate?

 

these trucks do not have a wastgate

 

I know that but it's doesn't control itself magically?? does it??

 

well not to be a smart *** but it is controlled by rpm and engine load in our trucks. the turbo is physicly large enough that a wastegate is not needed.....
for instance, in a 24 valve cummins the turbo is under full boost at a lower rpm but the wastegate is dumping the excess exhaust to prevent overspooling. this is due to the physicly smaller turbocharger.
in our trucks the stock 7.3 cannot dump enough fuel to overspool the turbo at lower rpms. if you hook a gauge to your truck you would see the boost start at "0" and slowly rise to its peak at 3300-3500 rpm and then drop at every shift. while its not the best for max power stock it does leave you alot of room to play with chips before you get into dangerous egt's and overboost conditions. we complain because after a big chip goes in that we are hitting 1200 degree egt's but my buddies cummins would hit 1600-1800 just by running through 1st gear on the stock turbo with a chip. the smaller turbos are not good when you start throwing more fuel at the trucks

 

what should normal boost pressures be?

 

there is no normal reading, peak boost is measured over 3000 rpm under full load conditions and stock spec is 12-14 psi

 

with my little mods, it should be 12-14? under load?

 

Unless the turbo is electronic i don't see how a chip would control it besided giving engine more fuel to make more exhaust. It can be said all turbos work off engine RPM the more rpm the more exhaust lol Too much air= detonation.

Why are the smaller turbos not good if throwing more fuel? The more boost the more fuel the engine will need. If u are at boost and u run out of fuel good chance head gasket is going to blow and huge backfire. I know this will happen in gas engines .Pretty sure same in any combustion engine

 

its not just exhaust pressure, but the heat from the exhaust that makes it spin. think of a hot air balloon. its heat, not the pressure of the flame

 

the chip controls the amoutn of fuel, boost is a byproduct of the hot air coming out of the cylinders and into the turbo, which is directly proportional to how much fuel you are putting into the cylinders. the key is how much fuel goes in with the diesel.

the amount of boost pressure is relative to the size of the exhaust turbine housing to the compressor turbine housing in relation to the turbine wheel diameter. in layman's terms- the more hot air you can get to the exhaust side of the turbo to spin it then the more boost air you will output, the larger the turbo housing the more potential for maximum flow. the wastegated stock turbos have smaller turbines and housings so they take less hot air to spin up to max pressure. however, while they take less to spin up they also reach their max potential sooner. this means that you are dumping all of that potential energy out the wastegate instead of utilizing it thus making the turbo less efficient.
also, you cant rate your turbo based on its max boost output. your stock turbo at 25 psi is not putting the same amoutn of air into the engine as an h2e turbo does at 15 psi. (numbers throw out for sake of arguement) my point is you are not after boost pressure, you are after air volume. the engine doesnt care what the pressure of the intake charge is, it cares about how much air is getting into the cylinder for combustion.

another drawback of the smaller turbo is the easy rise in egt's. again, for arguements sake, when you throw more fuel at it you have the turbo as a restriction in the exhaust. you will have higher back pressure readings with a smaller turbo and as a direct result you have higher egt's, and also the waste of energy from dumping exhaust through the wastegate.

i'm not trying to say that wastegates are a bad thing, the key is finding the perfect combination for your engine and its mod's

 

that's kind of what i thought. But a wastegate i believe is solely for controlling the boost the engine will get. I guess with the bigger turbos it will never spin fast enought to detonate the engine,unless increasing fuel thus exhaust gasses will do it.

Anyway hpw much more power can a chip give these trucks? like a 97 powerstroke??

 

You're confusing gassers with diesels.

Gassers have problems when running too lean or too rich.

Diesel's don't have a set air/fuel ratio. It can run richer than a gasser, or as lean as 50:1. It doesn't care.

So no, too much air in a diesel will not equal detonation.

Running out of fuel will not blow a head gasket.

Diesels are a completely different animal. So to answer your original question... your right foot controls boost in a diesel.

 

the wastegate does not control the boost to the engine, it limits it, big difference.

the bigger turbos can still be overspun, it just take alot more fuel to do it.

the 94-97 trucks are limited to chips because of the size of our injectors. you can buy whatever chip you want but on the max settings you will see 80 hp gains at best. to get the full power from a chip you have to be able to move the fuel the chip is commanding. the stock injectors are way underrated. slap a set of stage 1 injectors in it and you can see 352 rear wheel hp and 731 ft pounds of torque! thats what stroking stach dynoed with only a few of the basic upgrades- stage 1's, an intercooler and a superduty styled high pressure oil pump. thats over 400 flywheel hp and 800 ft lbs of torque

 

Man I like the sounds of those numbers since I'm putting all those mods in except the hpop.

 

Coon, nicely handled with great info. Green beans sent.