Cummins 6CTA8.3 Injection Timing

[Bigchevy383]

What should be the stock in gear rev limit be?

 

[74M35A2]

Mine is 2150rpm which gives 67mph in top gear. Can reach almost 2300rpm on a freeway downhill, but no more. A GSK (Governor Spring Kit) from a 5.9L will increase it. The 8.3 goes up to 3000-3400 range from Cummins in marine apps.

 

[Bigchevy383]

Mine does 2200 on flat ground and will touch 2300 downhill. Still stock as far as i know, has seizing wire still on nuts and looks as old as the engine.

 

[patracy]

Mine is 2150rpm which gives 67mph in top gear. Can reach almost 2300rpm on a freeway downhill, but no more. A GSK (Governor Spring Kit) from a 5.9L will increase it. The 8.3 goes up to 3000-3400 range from Cummins in marine apps.

While the 8.3 is a lot like a 5.9 in design, they will not rev to what a 5.9 will. I'd recommend staying under 2800rpm. Bad things happen in a cummins 5.9/8.3 when overreved. Mainly the valves try to occupy the same space as the piston. Which is compounded by boost.

I spun my 5.9 up to 4K routinely, but it had valve springs, studs, rocker studs, exc.....

 

[74M35A2]

Yep yep. Heavier rated valve springs are available for those interested.

 

[Bigchevy383]

Tell me more....

 

[74M35A2]

Higher spring pressure rated springs are available for the marine versions that spin faster. Blue-Ox aftermarket exhaust brake systems recommend heavier valve springs when using their product on the 8.3L, so that means they are available. I don't know the part number off hand. The faster spinning 8.3's also use a different harmonic balanced though too, I think.

 

[nevrenufhp]

Found some HD valve springs :
https://puredieselpower.com/class-8...duty-valve-spring-4936076.html#/product/15347

 

[74M35A2]

Thanks. Some specs would help, I'll see what I can come up with this week.

 

[Bigchevy383]

I was lookin at them springs earlier. Doin springs might as well do oversized valves, port polish and oring the heads while your doin. Change lifters, rockers, heavy duty push rods. Big cam, ceramic coat the pistons, change rod and main bearings while your there.... it would be so easy to get carried away if we knew where we could get parts

 

[patracy]

I was lookin at them springs earlier. Doin springs might as well do oversized valves, port polish and oring the heads while your doin. Change lifters, rockers, heavy duty push rods. Big cam, ceramic coat the pistons, change rod and main bearings while your there.... it would be so easy to get carried away if we knew where we could get parts

Not a lot of room in a diesel to install larger valves. And it's almost pointless in a forced induction engine. O-rings/Fire-ringing the head, yes that's worthwhile. Studs, even better. Wouldn't change the tappets unless I did a cam. Rockers are fine too. Pushrods would be a worthwhile upgrade. Cam, in all honesty, you're not going to be able to justify it in this engine. Coating the pistons? Maybe for a little more insurance. I'd only inspect the rod and main bearings. I've had 5.9's apart with over 100K on them and not any visual indication of bearing wear on the mains/rods. Parts are easily located.

 

[74M35A2]

I was simply going to do the GSK, increase the fuel rate, bump the timing, and see how it felt. Some here are reaching nearly 3000r's with just the GSK. If so, that is plenty enough to increase top speed and stronger fueling during up shifts. Not sure what is left to be gained with an even higher top rpm. If suspect valve float, I was going to upgrade springs when I do valve seals this spring (already purchased). Per the Cummins dealership and Cummins service manual, you just bring each piston up to TDC and remove the valve spring retainer locks, retainer, and spring. No need to inflate the cylinder with compressed air as with a gasoline engine. Can do it on the truck without taking the head off. The valves are pretty much resting on the piston crown on a diesel when at TDC. I don't want to run more spring pressure than necessary, due to fear of wiping out the flat tappet cam. Oils are just going to have less and less zinc in them going forward. Almost everything today is roller lifter or follower already.

 

[patracy]

You typically don't get to "suspect" valve float. You realize it happened during the tear down.

And yes, that's the same trick I used to do springs on 5.9's. I also did studs without replacing head gaskets. But that's a little more involved than just swaping bolts.

 

[Csm Davis]

I don't want to run more spring pressure than necessary, due to fear of wiping out the flat tappet cam. Oils are just going to have less and less zinc in them going forward. Almost everything today is roller lifter or follower already.

The 8.3L has flat tappet lifters? I haven't dug in to one yet. I would have figured that as new as they are they would have rollers.

 

[74M35A2]

Diagram showed it to be flatties, and it is an older design. I have not had mine apart yet, and hope not to! It is a low cost, high volume, medium duty production engine. I have heard it is the highest volume engine Cummins has ever produced, but maybe that was before the Dodge Ram unit.

Here is the only spring ad with ratings I can find yet. Still want more description of stock vs x....

http://shop.dieseltuff.com/Pacbrake-C14010-Exhaust-Brake-Valve-Spring-Performance-Kit-C14010.htm

 

[74M35A2]

Bumper for anybody wanting to advance timing on their 8.3L. I just got off the phone with Industrial Injection, and they quoted $126 to "calibrate" the pump, meaning check/adjust on a flow bench, including altering the timing to your #. If one does not want to advance the timing via the crank damper degree method I posted earlier, this is another option to do so and then just re-install it via simple push pin alignment of the engine and pump. I am considering this simply to have them check and confirm pump health before I do mods.

 

[74M35A2]

Sorry for my tardiness on this. I was going to mark out some masking tape for the diameter of my balancer, but I instead got lazy and bought the Cummins magnetic timing tape kit with magent pointer. Fits a variety of balancer sizes. Getting ready to finally take some base line data and then do this via the spill port method.

 

[74M35A2]

This will be a great one for everybody to armchair quaterback:

To do the spill port method of setting injection timing, which is supposed to be the most accurate, I need to remove the delivery valve contents, and then put a short tube in #1 injector output pump fitting, block the injection pump return port, return port, and then pump diesel fuel into the injection pump at a pressure of 300-450psi. I have come up with 3 ways to be able to do this. (1) 300psi liquid pump, which I don't really have, (2) use compressed nitrogen bottle regulated down to 300psi over diesel fuel in a fillable pressure vessel (add pressure slowly to not heat), or (3) use an electric pressure washer. I know, not superior, but with the bypass regulator adjusted down to 300psi or so, I don't see why this would not work. Use a pressure gauge on the outlet, feed the pressure washer pump diesel fuel instead of water, and regulate it down to 300psi or so.

Unless somebody has an electric pump rated at 300-450psi to loan, which I would loan the magnetic timing tape kit in exchange, then otherwise I will soon be feeding diesel fuel into my pressure washer. Will attempt to turn the pressure down tomorrow using water as an initial feasibility study.

 

[Jbulach]

Look into airless paint sprayers. If I remember correctly they will do some fairly high pressures (low volume of course, not sure how much you need).


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[nevrenufhp]

Are you sure that's not 300-450KPA? That would put it at 45-60 psi, which is typical good fuel pressure.