I want to replace my 300,000 km injectors on my 94 6.5 GM diesel - I have a
brand new motor with less than 5000 km on it. I see claims of 40 hp gains
being made by companies selling marine injectors for the 6.5. Is there any
truth to these claims?
Yes, injectors will help get you extra HP, but you should realize a few
First, the reason why marine injectors give improved performance is that
they let you use that much more fuel and are not regulated for federal
highway emissions standards. You could get a whole lot of extra power but
that doesn't mean your mileage will be all that great or you will pass a
smog test. Remember, the claim of +40hp is probably not from installing the
injectors alone, but is seen with a host of other modifications as well (or
at least a few others).
Second, in order to take advantage of marine injectors, you need a way to
improve your fuel flow and engine management - which translates into
spending money on something like a chip. In fact, since it's your fuel
solenoid driver (FSD) that controls the fuel output of your fuel injection
pump, you will need a higher numbered calibration resistor for it to get you
more fuel. Your truck came from the factory with a #4, 5 or 6 chip (9 is
the highest for on-highway vehicles) but you will need a resistor from a
marine FSD of around #15 or more to get you the fuel delivery you need.
Good news and bad news - the good news is a new calibration resistor only
runs about $20.00. The bad news is if your FSD is still mounted to your
fuel injection pump then it's incredibly difficult to remove the old
resistor (which lives inside the wiring harness connector to the FSD) and
replace it with a new one. There is still some debate as to when the ECM
looks at the resistor value, so you may have to perform a calibration on
your fuel injection pump in order to take advantage of a new resistor and
increase fuel flow.
Third, if you want to increase your power you will also need to install an
intercooler. An intercooler takes the compressed air from the turbocharger
and cools it down, which increases the density before it enters the
cylinders. The more air you can pack into the cylinders, the more efficient
you will burn your fuel and the more power you will get. Unfortunately, an
intercooler is NOT cheap, but if you're adding more fuel with marine
injectors you will want more air in the cylinders as well to be able to burn
it, and while possible it's not simply a matter of increasing the PSI from
Fourth, adding power means generating more heat. Pre-'97 motors had
problems with burning through head gaskets in the rear-most cylinders from
too much heat, so you should also consider installing the post-'97 high flow
water pump with dual thermostats and crossover. This water pump increased
coolant flow through the motor and helped solved the burn-through problem
with the gaskets.
Fifth, more power means more stress on your tranny, especially if you have
an automatic. If you do, the 4L80E is a great tranny but increasing the
input power will stress it and you will need to consider beefing it up as
And lastly, I recommend going to www.thedieselpage.com as it's a great
resource for info about light-duty GM diesels. Much of the info I've gotten
over the years keeping my former '95 Chevy in top shape came from them.
Cheers - Jonathan
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