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Author Topic: 8V71 Injectors - What are the different types? (Best pick for 4106 with V730?)  (Read 2406 times)
technomadia
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« on: June 25, 2013, 08:20:00 PM »

I've been reading the forum archives trying to understand the different injector options that have been used on the 8V71 over the years - and so far I haven't found a particularly clear answer that explains the difference between the 7E, C, N, and S prefixes on the various injectors I have seen mentioned.

The number that follows is the sizing - 55, 60, 65, 70, 90 -- this is the amount of fuel injected in each stroke, right?

Looking over an old 4106 GM part book, it indicates that the 4106 originally shipped with S60 injectors. And according to our manual, the engine was governed to 1650 rpm's and 235hp.

That was a long time ago.  I'm curious what the best choice injector setup is today, for a non-turbo 8V71 mated to a V730 transmission (instead of the 4-speed manual). Our engine is governed at 2,100 rpm now.

I've seen a lot of mentions of using an A-timed N65 setup for this configuration, but other threads have mention N60's and even 7E55's as being preferable.

Is the A-timed N65 optimal for fuel efficiency? Hill climbing? Clean exhaust / minimal smoke?  Driving around at altitude?

I did see one old thread say: "BTW the 'A' timing is a disaster in a GM bus because the torque peak is moved from 1200 RPM to 1600 RPM, results very disapointing hill climbing, even though the peak horspower is higher."

But others contradicted this. 

When paired with a V730 automatic, what is the ideal torque peak?

Are there any other injector / tuning options we should be considering during our rebuild?

Cheers,

   - Chris
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Cherie and Chris / www.technomadia.com
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luvrbus
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« Reply #1 on: June 25, 2013, 08:29:29 PM »

N70 with standard timing since you have a new radiator that will put you in the 300+ hp range if the shop if the shop doesn't know the setting I give it to them  If you use the G's don't advance the the timing when using 4 letter injector it's built in to the injectors
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technomadia
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« Reply #2 on: June 25, 2013, 08:43:38 PM »

If you use the G's don't advance the the timing when using 4 letter injector it's built in to the injectors

G's?  Thats a new one to add to the list.

So just what is the difference between a S, C, N, G, and 7E injector??

Are there any other variants?

Cheers!

  - Chris
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« Reply #3 on: June 25, 2013, 08:45:43 PM »

The guy I used recommend exactly what Clifford recommends;  N70s standard timing, 2300 to 2400 no load RPMs.  From what I understand this setup will smoke a bit in the hills.  How much, I haven't any idea.  The same guy told me use propane in the hills to eliminate the smoke and add horsepower!   I decide to go N65s A timing 2450 RPMs no load.  I get no smoke at all so I wonder if the N70s STD timing would have been acceptable.  

I agonized over this issue for a month btw.  It was horrible.  No one had experience, but the opinions abounded!
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OneLapper
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« Reply #4 on: June 25, 2013, 08:58:06 PM »

E's and C's are emission injectors stay away from those Mark I putting a 8v71 together now and I am going to use the 70's I changed his over to a high capacity blower there wont be any smoke the 70's are a fire engine injector they can have a wide range he wants the full 318 hp and that is what he going to get 
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« Reply #5 on: June 26, 2013, 04:34:46 AM »

I have a complete set of N65's that came out of my old engine that were running fine when I took them out.  Let me know if you want them, we can make a deal.  They were installed with A timing.  The book shows timing pin settings for both A and S timing for those injectors.  If you look at the torque curve for the N65 A-timed vs say the 60 with standard timing, yes the torque peak moves to 1600 rpm from 1200 rpm, but the torque at 1200 rpm is still higher for the N65 A-timed engine than it is for the other engine.  More torque is still more torque...

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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« Reply #6 on: June 26, 2013, 05:41:33 AM »

Where's the peak torque on the 70's?  The curious want's to know!
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« Reply #7 on: June 26, 2013, 06:06:15 AM »

You are going to be around 900 lbs  @ 1400 rpm ideal for your gearing the N65 with A timing was for trucks with a 10 speed it's not much good in a bus unless you have more than 4 gears
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dellisor
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« Reply #8 on: June 26, 2013, 06:25:03 AM »

Let me know when you choose which injectors you want, I have a guys number that sold me a great set of rebuilts for 187 shipped and he will give you two weeks to return yours without charging a core. Mine is a 6-71 so only 6 for that price. 
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« Reply #9 on: June 26, 2013, 06:31:50 AM »

I doubt the DD dealer will use anything but a authorized DD injector because of warranty they don't cost that much more  

Chris like others was just trying wrap his head around what all the numbers meant and there is a ton of them and he didn't even mention the tag color 

I am going to PM my injector guys number to Chris that can give him his answers as it all over the map with people on these boards
« Last Edit: June 26, 2013, 06:35:53 AM by luvrbus » Logged

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« Reply #10 on: June 26, 2013, 09:35:11 AM »

I had standard timed N65's in my 8V-71 with V730. Worked well, but would smoke at altitude above 5,000ft. Upgraded to turbo with 7G75's putting out 375hp and 1125lb/ft torque-now it is a pleasure to drive. Good luck, TomC
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« Reply #11 on: June 26, 2013, 11:59:45 AM »

Sorry I assumed that the injectors run about 125.00 each and mine was for a set, I also assumed you where doing the work yourself. My mistake   
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technomadia
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« Reply #12 on: June 26, 2013, 12:01:46 PM »

I still have no idea what the actual difference is between the S, C, N, G, and 7E injectors other than that C and 7E are for better emissions, which Clifford says "stay away from" but which actually sounds like a good thing?!?

What is the downside of these emissions injectors?

Looking over archive threads and talking to some folks - it seems that without a turbo a N70 will be prone to smoking (how much?) - especially at higher elevations, the N65 with standard timing will smoke some, but the N65 with A-timing should have essentially no black smoke at all.

Does this seem to match people's experience?

I certainly don't want to end up with a bus that belches black smoke while driving through National Parks, or while puttering around a campground.

Cheers,

  - Chris

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« Reply #13 on: June 26, 2013, 02:59:22 PM »

 I had N65 Brown tag injectors in mine with "A" timing,, It would not smoke at 10000 feet at 10% grade if your life depended on it. I often wondered if I was getting the horsepower that I should have expected with that combo. I devised a propane mixing system that made a large improvement on grades.>>>Dan (Clifford and I agree on few things, but one thing is agreed, that regardless of the injector size  (within reason) the timing of said injectors will make a major difference in power.
« Last Edit: June 26, 2013, 03:04:56 PM by Utahclaimjumper » Logged

Utahclaimjumper 
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« Reply #14 on: June 26, 2013, 03:06:40 PM »

Emissions injectors means they are for emission-controlled vehicles. They won't make your engine run "cleaner". Proper maintenance and adjustments will. I say go with the 70's.

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Rick A. Cone
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