Turbo Boost & RPM
 

My Dad, a retired High School teacher, used to say, "If you don't stand up and ask a question...it just means that there's at least 25 other guys sitting in the same classroom wondering what the answer is!" :humm:

My question pertains to the correlation between engine RPM and turbo boost pressure. I just bought a 1996 12V 5 speed...admittedly, the first turbo-diesel I've ever driven. I am a little perplexed at the lack of low RPM pick-up, after earlier hearing so much about the Cummins reputation as a pulling work-horse. My boost gauge does not seem to come to life until the engine reaches at least 1500 RPM.

To better paint the picture, I'll describe my first dump run...

Starting from a stop sign and turning up a steep grade, I'll wind the engine up to about 2,250 RPM in 2nd gear before making a smooth civilized shift into third. With the engine RPM dropping down to about 1,100 RPM on the shift, I cannot seem to get any turbo boost as I struggle up the hill. Zippo on the boost gauge...regardless of the amount of persuasion by my right foot! Unfortunately, I find myself back in 2nd gear and grinding up the remaining mile long hill at 20 MPH!:argh:

To add insult to injury...half-way up the hill, an Isuzu NPR 4 cylinder turbo diesel comes charging up behind me loaded down with two chagrined-looking guys in the front seat shared with a couple of large dogs and a shed load of lawn equipment in the rear. According to my dump receipt, I had only 420 Lbs of branches on board plus an Australian Dingo mix riding alert shotgun. Comparatively, this is a grade that I used to routinely pull in 3rd gear with my old 88 Dodge 318 with it's accompanying 400+ lbs Greenlee toolbox.

Is it normal not to get too much turbo boost below 1,500 RPM? What are the rest of you fellas experiencing? I earlier read a post suggesting a differently configured fuel plate would help with low RPM torque, however, are you not just sacrificing total overall fuel economy for a specific power need? Revoke my Diesel Bombers membership, but I'm decidedly standing in the reliability and good fuel economy line.

Any suggestions would be most appreciated...

Regards,

Steve

first of all check air filter and fuel filter then all piping and connections between turbo and intake manifold for leaks and or restrictions and during this pulling of the hill did it smoke at all should have been smoking in there somewhere. and when you get a chance look up the definition of diesel bombers on this site and it might help you find the answers your looking for in the last paragraph of your thread good luck hope you find the answers you were looking for:humm::rocking::rocking:

don't get confused with RPM and turbo boost.
It is normal to have the boost kick in that late.
But- this is not what makes boost.
You get boost when the engine is under load.
Hot exhaust air moves the turbo- the hotter the better. Remember: hot air expands and moves very quickly.
The exicted air molecules bring a lot of air movement. That also develops a lot of boost-and power!

When you have done what Arizona already mentioned you will recognize a lot of power.
Some turbos aren't that good in developing boost during low rpm. It depends on turbo size. The smaller the turbo the quicker the response- the bigger, the less but more boost in high rpm:jump:

Yup, swap fuel filter, air filter, run some kind of fuel treatment (always) to keep fuel system clean. Check for leaks in the intercooler, If its a bad one, you can hear the air coming out, but only under load.

Boost is fuel related and like said above hot air spins it faster.....so the hotter the air the more fuel you need to heat it up and make it expand and spin that wheel. Do the AFC mods listed in the Performance forum stickies and you'll have a whole new truck. My cousin worked with a kid that was complaining about this very thing, my cousin gave him my number and we talked and he came over and I tuned his AFC and he couldn't believe the difference.

Need more fuel:rocking:

needs to be :bomb:

you only had 420 lbs in the bed and could not get out of 2nd gear?

Can any one say boost leak?

No, I was rather fuming but alas, the truck was not! Neither black nor white smoke. I might add...acceleration in say 3rd or 4th gear [I know...never touch 5th!] starting with engine RPM of at least 1,500 results in a rapid boost pressure upwards of 20psi. and decent acceleration [at least for an ol' guy! :tu:] It's the lower RPM settings [1,100 to 1,400] where load acceleration is weak and boost pressure needs Viagra!

Thanks for your advice. Though the K&N air filter indicator is reading in then 'green', I'll, nonetheless, take it out for a look as well as checking the fuel filter.

Regards,

Steve


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Thanks...very good explanation. :tu: The boost pressure rises adequately under a load starting from 1,500 RPM and up. Below 1,500 RPM, however, it just lugs with no corresponding rise in boost pressure. Many years ago, my only other diesel truck was a little non-turbo 4 cylinder Nissan. With the Nissan, I just learned to stay on the upper RPM 'power-curve' and it, in turn, rewarded me with an honest 32 MPG at the pump!