injection pump timing

Where is a good place to start with timing for a prostock truck? mine is at 36 degrees (ag gov 13mm p7100 6.7 bore and stroke)

Depends on the piston bowl and spray angle of the injectors more than anything

Well said marine style pistons take a lot less timing than say Ross pistions

Mine has Ross centered bowl pistons and 145 spray angle


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khales said:

Mine has Ross centered bowl pistons and 145 spray angle


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We've tested two essentially identical engine builds and one liked 36 degrees and the other liked 40 degrees for no apparent reason. If you don't have access to a dyno, you're just going to have to play with it but it's hard to compare results from different events, different sleds, different tracks, etc.

I'll say this, on lower HP trucks, I've had some 500 to 600 HP trucks that made within 15 HP with timing set from as low as 18* to as high as 32* and it really didn't make a difference other than shift the peak power a couple hundred RPM higher.

One time with my Junker Drag Truck, after it blew a headgasket and was on a fresh once-torqued gasket, we started with low timing to do a couple of retorques. At the time it had a maxxed Farrell 215 pump 650 cc's with a 60mm over 83mm HT4B compound setup. With 18* timing it was WAY down on power, like 625HP at the tires. After a retorque on the dyno, I bumped the timing up 4* and it picked up like 160 HP. Added 2 more degrees and it picked up another 75 HP. I stopped there because it was enough power to run the drag race class and was tired of losing head gaskets so didn't want to push my luck. Some setups respond incredibly well to timing, and others not so much.

I remember a couple years ago we were playing with Todd's Triple Turbo'd Street truck AKA Frankenstein. It had a 13mm Northeast Pump and a pair of cheap S475's feeding a GTX4202. At 24* timing it made very close to 1000 HP at the tire, bumping timing up to 32* would pick up a little over 300 HP with no other changes.

The small trend I've seen is setups with excess air or HP numbers low vs. amount of turbo seem to respond extremely well to timing whereas setups that are producing good power numbers vs. turbo size/available airflow don't see the large gains from timing changes. This is most likely a result of poor tuning to begin with and therefore the large gains with more timing.

Another trend I've noticed with larger power setups, if there is enough airflow to "clean-up" the fuel, there is very little to zero power gain with added timing. Case in point, on PDD's UCC truck with the Farrell 16mm pump and a pair of GTX5533 (98mm) feeding a GTX50 (88mm) we made just shy of 1200 HP to the wheels with 400 cc's of fuel at 26* timing. A timing bump to 32* picked up zero HP, but it was 100% clean on both runs at full boost and appeared to be fueling-limited. 3RWHP per cc is borderline unbelievable yet when you turn all of the 400 cc's into clean nearly 100% complete combustion it's possible I guess. With the super fast injection rate of the 16mm vs the 13mm, it took much less fuel (cc's) and timing to achieve the same power numbers. 1200 RWHP required almost 800 cc's on the 13mm pump and 32* timing minimum.

Big Blue: Are you guys using an adjustable pump gear to play with timing on a dyno? I absolutely hate having to change timing when it comes to p-pumps. It's such a long process unless you have a adjustable pump gear. Didn't know if you had a quicker process

When I was on MassDiesel's dyno it was 15 minutes between pulls when I moved my timing, it isn't that hard when you have a system down. I also backed up my settings with the timing light from tinytach

9 LIVES said:

Big Blue: Are you guys using an adjustable pump gear to play with timing on a dyno? I absolutely hate having to change timing when it comes to p-pumps. It's such a long process unless you have a adjustable pump gear. Didn't know if you had a quicker process

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Yes, adjustable timing gear is a must. To be honest, once you go 13mm, it's so easy for timing to slip, a keyed adjustable gear is a standard requirement in my opinion.

What would you guys consider to much timing with marine style pistons with 145° angle injectors?

I have an adjustable gear on my truck (with 13mm pump) I've yet to change the timing. I'm anxious to see the time saving.

It takes about 5 mins, I just keep a big wrench on the pump nut and hold it while I pop the bolts loose in case it wants to turn, bump it to the next hole 2* at a time. Whose gear did you get?

I got mine from eat soot website