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Cummins 6CTA8.3 Injection Timing

74M35A2

Well-known member
4,145
328
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Location
Livonia, MI
16 degrees is what the majority of all the 8.3L RV guys run that seek mileage and power gains. They were the largest group of personally owned 8.3's I could find, that tinker with them. Our stock timing is 8 degrees, theirs is 12'ish, and they were noting gains of 2-3mpg by moving to 16, and said any performance mods too much better hold like that. 16 was regarded as the max safe do-not-exceed number for stock head bolts/gasket with no issues. Decreases smoke, decreases EGT. Not really a power gain by itself, but once you add more pump fuel, the results will be further ahead. Should be an instant mileage gain though.
 
Last edited:

simp5782

Feo, Fuerte y Formal
Supporting Vendor
12,120
9,357
113
Location
Mason, TN
That's not yours, it has an $800 electric lift pump on it. Nice fit though, looks stock.
Thats why i used future tense terminology. Im just waiting for the call to head to Texas

Sent from my SM-G935P using Tapatalk
 

brazengoat06

Member
362
2
16
Location
Tulsa, OK
Justbtodaybi installed an egt gauge on a completely stock 8.3 and I was just shy of 1400 on hard throttle trying to keep speed on highway. Keep in mind it's a m934a2 so it's heavy. But still this seemed high for stock. Thinking i should first try and get more air in the engine before doing anything else. Thoughts?
 

MAdams

Active member
380
127
43
Location
San Dimas, CA
I'm trying to wrap my head around this and an stuck. A few months ago I attempted to advance the IP timing 6 more degrees(14 total) but after I was done I kept wondering if I retarded the timing by mistake. After driving the truck I didn't notice any more power and my EGT's seem high, like 900 degrees F cruising down the street at 35mph. I did the EGT gauge and timing at the same time so I have no base line.

Here's the question. The motor spins CW while looking at the front pulley, so does the IP shaft. Once the IP drive gear is removed from the IP shaft, do I rotate the crank pulley CW or CCW? All the gears under the front cover are throwing me off. Worse case I can go back to stock
 

74M35A2

Well-known member
4,145
328
83
Location
Livonia, MI
You'll pop the pump gear off like you did, then back the crank pulley up 6 degrees by rotating it counter-clockwise when viewed from the front. Then cinch the pump gear back on.
 

MAdams

Active member
380
127
43
Location
San Dimas, CA
The gear is bigger than the hole. All you can do is use a gear puller to remove the gear from the taper but not remove the gear from the housing, or loosed the IP mounting nuts and knock the IP back a 1/2" or so.
 

Mos68x

Active member
826
33
28
Location
Seligman,AZ
OK, I wasn't sure if the IP shaft was splined, keyed, or tapered. At least tapered we can adjust timing without removing the whole cover. Now I just have to find the tools since all I have is the standard gear puller, I'll look at HFs steering wheel puller next time I'm in town.
 

Mos68x

Active member
826
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Location
Seligman,AZ
Another easy way (and free) is to measure the circumference of the damper, which is 30.5625 for mine, divide by 360 for the measurement per degree and then multiply by the number of degrees you want to change the timing. I'm just going to do 8* for a total of 16*. That equates to rotating mine CCW by 5/8~11/16 or 17~18mm
 

Mos68x

Active member
826
33
28
Location
Seligman,AZ
Well that was a fail, gonna have to reset it back to what to was and figure out how to set proper timing marks on the crank and then figure out where timing is at right now.
 

Mos68x

Active member
826
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Location
Seligman,AZ
I was rereading the thread from the beginning, does anyone have pics of their timing pins so that I can go back to a referenced point? I'm at least going to undo what I did earlier
 

74M35A2

Well-known member
4,145
328
83
Location
Livonia, MI
The timing pins on the pump and engine gear case rear will only depress in at one point each. Pull the pump gear off, rotate each until the pins can each be pushed in, then bolt the pump gear back on. That will set the timing back to the stock 8 degrees. Don't forget to pull both pins back out before starting the engine!
 

Rmtaunton

Well-known member
1,510
31
48
Location
Smyrna, ga
74 ,, you have all the knowledge on this , and now a new motor and 13 speed , still looking forward to both but nobody has done it yet , I might take the plunge , and document it if you can stand lots of emails and do you still have the 6 speed


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74M35A2

Well-known member
4,145
328
83
Location
Livonia, MI
6 speed and spare 8.3L is scrapped. Got like $62 for all of it. Would have rather one of you had it, but nobody wanted a 1:1 final gear trans, or to ship the stuff.

Sorry I never did this to mine, but I fully understand how to and would be happy to talk anybody through it. Feel free to fill my inbox, I'll give you my cell #.
 

Mos68x

Active member
826
33
28
Location
Seligman,AZ
6 speed and spare 8.3L is scrapped. Got like $62 for all of it. Would have rather one of you had it, but nobody wanted a 1:1 final gear trans, or to ship the stuff.

Sorry I never did this to mine, but I fully understand how to and would be happy to talk anybody through it. Feel free to fill my inbox, I'll give you my cell #.
I musta missed that, I certainly would've taken them both, even if I only used the engine.
 
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