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EM7 300 Good or Bad?


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Just been offered an EM7 300 from a 1993 CH 600 at a very good price and would like to open it up to around 350hp to put into my R series.

Are they a good motor or am I better rebuilding the E6 315 and sticking to it?

Any comments/help is greatly appreciated.


If anyone needs any workshop manuals let me know.

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Let me tell you about the E7 mechanical.If it is a Em7 it is a maxidyn and goes good with a 6 speed but if it is a E7 it is good for a 9 or 10 speed.The maxidyne can be changed over by a fuel pump builder.If it is a 300 just set the fuel out about .090 and time to 16 to 18 degress BTDC.The engine that I run is a replacement for E6.It was a 300 but I had the pump cal to 350 and timed it from 9 degress to 18 using a turbo from a Vmac 400.it is set to 1900 max but needs to to run from 1100 to 1700 for best fuel burn.It will pull down lower than the E6 and still run smooth.If you time it to specs which is 9 degress for a 95 year engine It will pull down as low as a gas burner but will burn more fuel.Some one has done stated that they have more grunt than a E6 and that is caus.e it has a 1/2" more crank stroke

glenn akers

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Thanks for the replies guys. Been around trucks all my days but am a very recent convert to Mack, we don't have many of them in Scotland but since coming down to NZ have been pretty much surrounded by them. I have been working mainly on Kenworths, Internationals and what the Japanese call "trucks" (Nissan, Isuzu etc). Cummins, Cat, Volvo and Scania are my speciality so I dont know much about the Mack motors, hence my questions. I only recently bought the R series and am growing rather fond of it, once I get it the way I want it I will hopefully be using it most days as a working truck so want a good strong reliable motor in it.

I do prefer a "mechanical" motor but have no issues putting an "electronic" motor in as long as its a good one. I was looking at a 454 but was told to leave it where it was as they are bad for heads. Ideally I would like around 400hp but would settle for 350hp in the mean time! I do have an idea concerning a 450hp Scania V8........


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  • 3 weeks later...
  • 7 years later...

As an owner of a 92 EM7 300 motor with a T2080 transmission and 5.05 rears. I have turned up the pump and upsized the injectors to increase power. The changes are very worthwhile. Articles on this site have stated to get to 350hp you need to change pistons and cam? So it would seem it more cost efficient to start with an E7 motor. I  have not put my truck on a dyno yet, so horsepower now Im not sure. My only complaint is the huge jump to the top overdrive gear. But it drive 65 to 70 fine.

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