question about injectors, turbos and HP...

[bevans6]

Reading the manual last night (I know, I should get a life) a question came to me.  I don't understand the relationship between injector size, turbos, economy and horsepower very well, except that bigger is more and smaller is less...which seems a little simplistic even for me.

I have my new 8V71T industrial engine that I am slowly putting all the bus stuff onto so I can put it in the MC-5c when the weather is nicer.  It has a turbo, I haven't been able to figure out exactly which one.  It has N80 injectors.  We talked about it and what I recall is the suggestion was it probably was 370 hp.  What I was wondering what would happen if I put in smaller injectors?  so I looked in my manual and sure enough there is some mention of 8V71T's with 65, 70 and 75 injectors (and I know some military engines came with 90's or maybe even bigger).  So my thought process came around to "I have perfectly good N65 injectors in the old engine.  I know at least half of the N80's in the new engine are sticky and need to be cleaned if not rebuild or replaced.  What would happen if I stuck the good N65's I happen to have in there and ran them?"

So - what would happen?

Thanks, Brian

My new engine is exactly the same as this one, fwiw:  8V-71T Factory New Engine Model 7083-7395  Ser. 8V445923  Complete With All Accessories from the Jobbersinc web page  http://www.jobbersinc.com/detroitd.htm

[HB of CJ]

You turbo is PROBABLY matched to the big injectors.  If you go back to N65 injectors, less fuel will mean less boost, but only a little bit.

What will happen is that instead of 370 or 400 hp, you will probably end up with around 350 with a little bit MORE air going thru the engine.

This will mean, all things considered, less smoke and better high altitude performance.  Over boosted, under injected means less polution.

Your application would also respond well to a nice, big air to air intercooler.  Lowering your exhaust gas temp will help increase piston life.  HB of CJ (old coot)

[HB of CJ]

Sorry.  With N65 injectors, plus that big turbo, expect around 325 hp or around there with little or no smoke, plus good high altitude performance, especially with a big air to air intercooler.  Whew!  HB of CJ (old coot)

[bevans6]

Well, I'll be honest I was thinking that I would probably be in the 325 hp range.  At this point saving a grand on not putting in rebuilt N80's is well worth while, I can always upgrade later, reducing the HP will ease the cooling load, be nice to not be polluting I guess, and adding an air-to-air intercooler is always a fun project for later...

How can I find out what turbo I have.  I can't find many numbers on it, but I haven't brought it in from shop and looked at it in great light.  Does the engine number or the pictures I posted give anyone a hint?

Brian

[lostagain]

You'll have to look for numbers on the turbo both outside and inside the housing. I found the A/R no. stamped on the inside of the compressor horn on the turbo that's on my 6V92.

I would think the turbo is matched to the injectors? But I don't really know. Like the bigger the inj., the more boost to burn the fuel. I know that my  6V92 has inj. that are problably too big (90), because it smokes black easily if my foot is down too deep. If if were me with your money , I would get the 80s overhauled, and do more research on the turbo and trade for the right one to match your inj.

JC

[bevans6]

I LOVE the way your approach (with my money of course) is to spend the grand on the new/rebuilt N80's AND spend a grand on a new turbo, when my idea was to spend nothing by stealing the injectors out of my old engine and using the turbo I have regardless of what size it is...   

brian

[kyle4501]

I'd consult with someone like Don Fairchild. It is likely that not only has he already been there & done that, he has probably worn out the T shirt. 

[Geoff]

If your N80's are sticky just run fresh diesel through the system and move the racks back and forth until the injectors free up.  They are just gummed up from sitting, and if they are rebuilt/new, they would work just fine with a little work.  I wouldn't put N65's, what a waste of horsepower that would be.

[robertglines1]

Brian you have put allot of work on this project .Might as well go for the most you can get if it don't cost you more! try running fresh fuel through the injectors and see if spray pattern doesn't clear up. No cost there and if they don't then make decision. That engine is set up with them. you would appreciate the extra hp. when all is said and done do it your way!!!!   Bob

[luvrbus]

Brian  8v71 T   

N65 308 hp
N70 335 hp
N75 350 hp

those N80 will smoke up the country side to bad you don't have a aftercooler block HP goes up with the same injectors


good luck

[TomC]

As strange as it sounds, have N65 injectors in a non turbo engine and it will put out 300hp and 800lb/ft torque. Install the same N65 injectors in a turbo'd engine and you'll get 325hp and 975lb/ft torque-a testiment as to the higher efficiency of the turbo'd engine.  If you have the 4 speed manual-they were usually rated up to 1200lb/ft torque.  Detroits last version of the 8V-71TA (with aftercooler) had N80 injectors in them and was rated at 400hp and 1200lb/ft torque.  Yours would be more like 370hp and 1150lb/ft torque without the aftercooler.  Make sure you have a fuel modulator.  It is a hose going from the air intake above the blower to the left head with a small air cylinder that prevents the fuel rack from opening until you have turbo boost.  Otherwise you'll have massive black smoke everytime you accelerate-I know from experience.  Good Luck, TomC