RPM Spring and Upgraded Fuel Pin? - Diesel Bombers



1st Generation Dodge Cummins 89-93 Discussion of 12 Valve 5.9 Liter Dodge Cummins Diesels with Rotary Injection Pumps

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Old 01-27-2018, 08:28 PM
IHC5.9L's Avatar
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Default RPM Spring and Upgraded Fuel Pin?

After a nice 4,200 road trip I realized I'd like two things from my 1st gen Cummins: a bit more horse power, and to have that power extended through to 3,200 RPM. Some research led me to what looks like relatively simply upgrades paths. A new 3200RPM governor spring and upgraded fuel pin to get the results I'm looking for.

Still have some questions though:

1) When you make these kinds of upgrades is it necessary/wise to also upgrade your valve springs to the 60lb version? People seem to be split on this.

2) Does upgrading the fuel pin, and thus getting more fuel to the engine, actually get you better MPG? Again, people seem to be split about this - especially with 1st gen engines.

Finally, anything else I should consider if I decide to get these upgrades done?

Thanks!

Michael
67' IHC Travelette 4X4 w/ 1990 12v 1st Gen Cummins
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Old 01-31-2018, 12:49 AM
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Originally Posted by IHC5.9L View Post
After a nice 4,200 road trip I realized I'd like two things from my 1st gen Cummins: a bit more horse power, and to have that power extended through to 3,200 RPM. Some research led me to what looks like relatively simply upgrades paths. A new 3200RPM governor spring and upgraded fuel pin to get the results I'm looking for.

Still have some questions though:

1) When you make these kinds of upgrades is it necessary/wise to also upgrade your valve springs to the 60lb version? People seem to be split on this.

2) Does upgrading the fuel pin, and thus getting more fuel to the engine, actually get you better MPG? Again, people seem to be split about this - especially with 1st gen engines.

Finally, anything else I should consider if I decide to get these upgrades done?
I think the 366 spring is fine with stock valve springs. But any more, I'd go with the valve springs too.

The fuel pin only really come into effect on acceleration. Once at cruise, boost should be minimal, and the pin has the least effect.

I would go for a 4" exhaust. Then HX35 and/or injectors.
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Old 01-31-2018, 12:11 PM
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Thanks. Kinda what I thought. I'll check out those injectors as well as a bigger exhaust.
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Old 02-09-2018, 07:39 PM
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A 366 spring, turning the stock fuel pin to its deepest ramp side, 1.5 turns in on the power screw & a PDR Hybrid HX35 to replace your baby H1C, along with 12cm housing for 5 spd or 16cm housing for auto will do what you're asking quite well.

14cm exhaust housing ideal, but $$$.

As far as injectors - you have the slightly larger non intercooled units in there already, no need to upgrade them for the power levels/what you're asking the old girl to do.

Get them cleaned up, checked, and pressures reset to a slightly higher 260 BAR, bump the VE about 3/8" or so, and have fun.

You should also drill a few 2" holesaw circles on the leading edge of your factory airbox, put in a High Volume Low Pressure piston Lift Pump to eliminate the leak prone factory diaphragm lift pump, and do the KDP fix.

Last edited by ofelas; 02-09-2018 at 08:09 PM.
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