Max injection times vs rpm?

[GrannySShifting]

Id assume with the DI stuff theres only so much window of time to complete an injection cycle as you cant on the back of an intake valve like we are used to. There should be a rough formula I would think that would take into account rpm (as speed goes up window would have to decrease) and also start of injection timing... The later you start the shorter the window would get, the earlier the longer up to a point. Not sure if higher rpm events would want a later or earlier injection timing for max power as a general

[GrannySShifting]

So...

https://www.hptuners.com/forum/showt...tart+injection

[Higgs Boson]

many threads on this topic

[Robert C Morgillo]

many threads on this topic

Many Higgs is very true, 3 good ones for sure.

https://www.hptuners.com/forum/showt...ion-calculator

https://www.hptuners.com/forum/showt...culation-check

After digesting as much of this book as I could Automotive Spark-Ignited Direct-Injection Gasoline Engines, It is apparent this forum has some of the best minds. The forum looks like it was created to to prove out the book!

Going strictly by the book, looking for Drag race type performance only, in a perfect world it looks to me like if my Gen V was a "Dyno Mule", the cam timing and SOI would look like this.

Cam 3d.JPGCam.JPGSOI graph.JPGSOI 3d.JPG

It would be based on GM's initial "out of the EPA environment" numbers. In other words, It looks like GM knows there is some resonance in the low to mid RPM area. Hence the jagged, but linear SOI.
I am sooo tempted to try this... I think I am going to load it into the Baja Truck right now. Stop me if I am going to blow it up!

[Higgs Boson]

Robert that is very similar to what I do. If you have calculated and adjusted injection timing on GenIII and IV you have a good idea of what you want to do and as long as you know the valve events you can set up when to inject, the older cars use EOI and the GenV uses SOI, the main difference there.

I also generally have been zero'ing the low end of the VVT table since around 2011 or so but lately I have been leaving closed throttle decel areas stock and sometimes I leave in some retard at light pedal cruise cells.....the torque based ECMs can get wonky if you alter too much in the negative value torque cells and I haven't mastered editing those yet. Stock decel is usually the best functioning anyways.

Editing most of these tables is now a lot more strategic and less sweeping. I will also add that I do change a lot in the spark tables to smooth out a lot of decel characteristics and get them to run a lot more traditionally.

[Robert C Morgillo]

Excellent thoughts on decel and, the negative torque areas. Going back into the tune now to re-visit that. Thanks Higgs!

[IARLLC]

Hi Bob,
One quick thought on the cam timing. The cam is so small that I wonder about beginning the retard down as low as 1200 RPM and rolling smoothly on up to 8 or 9 by 6000 RPM. The earlier port injected 6.2s in the Yukons started the cam retard as low as 800 RPM. It is actually not retard (but advance reduction) down there because 0=8.5 advanced if I remember correctly. Real curious to see if you get some low end gains from that.

[Robert C Morgillo]

Jeff,
I think you may have a point. We did retard the ole Small Blocks substantially, when running in stock classes where we had to use stock grinds. The point where they began to pick up power was early. They were really short, low lift cams. like in the low 180's if I remember. The LSA's were usually in the 114 range.

For reference, the cam in the 5.3 Gen V is

193 @ .050 Int
199 @ .050 Ex
.500 lift In
.492 Ex
113 LSA
With 8 lobes ground on a smaller lobe circle to accommodate the larger profile of the DOD Roller.

I think we are chasing just a few horsepower here. It will take a Dyno to be sure. But that is exactly what this is about. Getting the most. I did get a tip from a guy working on COPO. He said the cams they have cross at 3000 rpm. I took that to mean it begins to pick up power when retarded from stock around 3000 rpm. The COPO's are definitely different grinds and motors however. I have to save my pennies. This HPtuner thing is going to cost me a Dyno!

[IARLLC]

Bob,
Interesting to know that the cams the COPO guys use cross at 3000 RPM. I am curious what specs are on those, gotta be bigger. Well even if it yields just a few ponies...the hunt is fun

[Robert C Morgillo]

Bob,
Interesting to know that the cams the COPO guys use cross at 3000 RPM. I am curious what specs are on those, gotta be bigger. Well even if it yields just a few ponies...the hunt is fun

Jeff,

Wow, a big cam! the 6.2L N/A 2016/2017 COPO cam:
242 In @ .050
285 Ex @ .050
.641 lift In/Ex
LSA Unknown

Man there is over 40 deg between the In and Ex duration! A bizarre cam grind. It looks like a blower cam. I wonder what they are telling us here. It is almost like they need a much better Exhaust port. The Exhaust valve is small. If this cam works (and I am sure it does), I would head to the flow bench and "hog" out that exhaust port. I would probably mess it up but, how could you need that spread?

copo-specs-and-stats-chart-2016-2017.pdf

[Higgs Boson]

yes the LTx motors weakness is exhaust flow.

[Robert C Morgillo]

yes the LTx motors weakness is exhaust flow.

Higgs,

Wouldn't that make retarding the cam a good move on the 6.2L? Since the bad effect of the intake valve closing later dropping cranking compression and hurting low-rpm power, should be lessened by the excellent flowing intake port. Also these are 11 to 1 motors. Cylinder filling should be aided by the velocity of exhaust gas in a retarded camshaft, leaving the exhaust valve time to use the velocity of the charge. Seems like retarding the cam should produce a lot on an exhaust restricted port, if you set SOI to compensate for the late intake event. Of course with full exhaust and, stock manifolds, all bets are off. Is this what you see on the 6.2's? Is the 5.3 also exhaust port weak?

I do know however, we never got much after 8 deg of retard. Rule of thumb was always if you needed more than 8, the cam was wrong.

[IARLLC]

A couple quick thoughts:
WOW! Yeah that 40 degree spread is NUTS!!!! And it crosses over as early as 3000 RPM?
I think that your stock cam might cross over much earlier.
I think the cam's park position (0 on the graph) is 8.5 advanced sooo it is not even straight up until you retard it 8.5 (6000 RPM)...I think.

[GrannySShifting]

Those cam specs cant be real, with 105 LSA and 106 ICL, exhaust valve couldnt have enough clearance??

[Higgs Boson]

That's not really that big of a cam for a drag car. I run a lot bigger cam in my 327ci. Goes to 9000 RPM though.

[Robert C Morgillo]

That's not really that big of a cam for a drag car. I run a lot bigger cam in my 327ci. Goes to 9000 RPM though.

Not on the intake I guess, but the exhaust is sure long. Any idea if the 5.3 Gen V is also short on exhaust port flow?