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EM7 upgraded inj and turbo


Brandt
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I have a '91 EM7 300 Maxidyne that has 2 or maybe 3 failing injectors.  This was a transitional year and it is all mechanical except for the elec fuel pump.  I was told that I could upgrade the injectors and turbo (at the same time) and possibly achieve 400 HP.  I have lost contact with this source, but am ready to do the upgrade.  Where do I find out what part numbers I need for the inj and what model turbo.  The truck works at 4900'-5900' elev and I plan on adding a pup to it.  Gross will be around 88-91K depending on how long my pup tongue is.

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You do understand that this engine is a maxidyne.If i had a maxidyne i would not want it to be in the 400 

hp range.If it was a not a maxidyne then i would use a 400/427 Vmac injector and turbo plus max out the rack on the pump and set timing at spcs for a 400.

Edited by theakerstwo

glenn akers

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OK, 400 is out of reach.  I am not familiar with the differences between the Maxi, Econo, Thermo power curves.  I can live with 350.  I'm just wanting to gain as much as I "reasonably" can due to the increase in weight that I will be pulling.  I have a 12 spd behind it with 4.42 gears.  I think the 12 psd is a 1050TX???

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I didn't know you have a 12 speed! With those close ratio gears you can use some of the more "peaky" power curves. But I'd still be conservative with the HP increases- This is a 27 year old truck and one has to allow for some wear and age in the engine and drivetrain.

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There is only 225K miles and 12K hours on this truck.  It was a county plow truck and seems to have a lot of idle hours.  I do have to remind myself that it is not a Series 60 and won't go for a million.

The build sheet shows:

EM7-300L-4VH  1425 lbs-ft

TRTXL1070B - 12 spd w/.78 OD

CRDPC92 & CRD93 diffs with SS440C axles

 

I would much prefer 4.17 gears, but I don't think I'll ever recoup the cost in fuel savings.  With Dayton hubs, I'm kinda stuck with 11R-22.5 tires

Edited by Brandt
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Sounds like nice powertrain specs- You've got the low RPM Maxidyne with peak torque at only 1020 RPM and a broad enough power curve that you can shift just the main box. Or to keep the revs up for engine braking split the main box gears, or just split top gear and use it as an overdrive. As for adding a pup and pushing the GCW up to around 90K#, the truck will move it, but not all that fast.

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  • 2 weeks later...
On 4/4/2018 at 9:23 AM, Hobert62 said:

I have 12r-22.5 on my B.     they are the same height as a 11r-24.5

Can I run 12Rs on an 8.25" rim or does it need a 9" rim??

 

The OEM injector # is 736GB343P3.  I have a Turbo #, but Google turns up zero info on it.

 

When I'm empty I run the low side of the gears until I reach the top on, then split to the high side.  When loaded, I might run the low side for the first shift, then I split them all the way up.  I generally shift around 16-1700, as I am conditioned to shift low due to the 1.5 mil electronic engine miles I've done.  I don't know what this engine is governed at as I've never ran it up that high to find out.

 

Found the old shop info, it is Antrim Diesel in western PA.

Edited by Brandt
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I think Antrim diesel is of I-81 in southern pa around green castle area.       As for the 12r 22.5 I read one place that said 9" wheel and another place that said 8.25" - 9" wheel.   I have them on a standard 8.25" wheel and they fit nice with no excessive bulging or anything. 

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  • 1 month later...
  • 2 months later...

Finally got the high flow injectors (ADSKBAL137P26HFEX) and turbo (SCH174828) in.  The truck runs a bunch better!!  Before, my empty mpg was 7.4 to 7.5.  Now my mpg is 7.2, but that is 50% empty and 50% loaded at 62K.  The most boost I saw was 27psi, but 22 psi seemed the norm.  Empty I was pulling 9 psi to maintain 60 mph.  EGTs ran about 800, but did spike at 1000 on a 4 mile grade. These are after the turbo readings.

 

I still have 2 problems with it.  Before it reaches operating temp, it still sputters and stamers.  Once the temp gauge hits 180 it goes away.  I thought this was injectors, but after the new injectors the problem remains.

The other problem is that in a long pull while loaded, I hear pops and sputterings from the exhaust. I also watch the boost go from 25 to 18, to 23 to 20 and bounce around synchronized with the pops and sputtering.  I have done nothing to the fuel pump. I even hesitate writing this because the truck is due for a fuel filter change and it might just be filters.  If it is not filters - Am I over fueling it??  Under fueling it??   I have driven electronic engines 98% of my life - what does a fuel pressure gauge tell me and do I need one??

Because I am kinda ignorant on mechanical engines - yesterday I was tooling around at 62K on the flats at low rpm (1000-1300).  Does this over heat the pistons?? Cause pistons to crack??  Anything bad?  I was pulling 15 psi boost and 800* exhaust temp.  My load point and dump point were about 4 miles apart , I wasn't on the throttle very hard as most of it was on a dirt road and there was no traffic that I was holding up.  I don't think I made it into top gear all day.

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  • 5 months later...

Update on the sputtering? Did fuel filters fix it?

Our 1995 did a sputtering miss kind of thing this last year, new fuel filters cleared it up. Came back a week later, another set of filters, been running like a champ since. It had acted like one or two injectors would momentarily stop working then clear up. Sounded almost like the Jake brake operating, but I pulled the wires off the heads and it'd still do it. Seemed strange, normally a clogged fuel filter results in feeling like the engine hits the governor at a noticably lower rpm. 

 

All our trucks are mechanical.  A 1976 endt676 (just retired due to frame rust) and a 1979 endt676  (285 hp maxidyne) stock governed at 2100 rpm, pulls strong from 1200 rpm all the way up. Pyrometer says to downshift at 1125 degrees. Mack got away with such a broad power band by putting out a lot of oil pressure at low rpm to help lubricate a crank making so much power at low engine speeds.  Our 1979 makes 90+psi on the oil at low rpm. Our Maxidynes have oil spray nozzles that spray the underside of the pistons to keep them cool, no idea what newer engines (read as anything newer than that 1979) have. We have never had the oil pan off our 1995 mechanical 350 hp mack in the 10 years we have owned it. We've had one valve cover off once. =D. It's no Maxidyne, but it's proved itself to be reliable, if a little weak.

 

It's a diesel, it's governed where it's supposed to be. Load it up, run it hard and see how it wants to work. Don't grind gears, don't overspeed the engine going down hill, don't throw your back out on the potholes.  You've been driving mechanical engines your whole career, some of them just had computers in them too. About the only hurt you can do to it us run it out of oil or coolant. 

Edited by JoeH
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  • 1 year later...

Sputtering is still there when the engine temp is low. It seems to go away after the gauge hits 160*.  Fuel issue went away after I changed the nearly 30 year old fuel lines. Seems they were collapsing under a load.

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Ok... first let me say this. I know of an em7 with a 460 turbo and pump on it with a lot if fuel added to it. Probably too much fuel BUT.... LET ME TELL YOU. THAT THING IS AN ANIMAL. I will also tell you it us headgasket time. It ran well for a few years. I do not feel this is the setup for you. Especially when you make these long pulls. It works here in N.Y. because one it does a lot if local work. We have hills but just not enough to over work her. With that being said. Some of the torque curve is produced in the pump. If I'm understanding things right. It has something to do with how governor works inside pump. I dont think he changed cams but im sure pump timing is different.  It was a Canadian em7 from what i was told. I only can verify its definitely an em7. Like I said before. Very fun for what its used for. I think you would blow it up.

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