Think my injectors are too small?

[Chevelle]

Engine Specifics:
-Chevy 350
-1.94 heads, RV cam
-DUI HEI distributor
-NOT a race engine by any means
-Holley 2Barrel Projection Throttle Body
-85lb per hr Injectors
-MS2

Problem:
Most of the time engine stumbles and pops around 4800-5200 RPM. On some occasions I've gotten it to 6000 RPM without a problem. In the attached log see duty cycle around 1372, 1435, 1478, 1487 Seconds. Just checking to make sure you agree or if there is something else to check. Unfortunately my fuel pressure gauge is under the hood so I can't view that when the error happens.

[elutionsdesign]

Yes I do, you are technically out of injector at 4200 rpm.

[Chevelle]

Just to be sure... Megatune calculates duty-cycle based on the actual physical time the injector driver is open and closed irrespective of the injector characteristics settings in Megatune such as "req fuel" correct?

[elutionsdesign]

Duty Cycle is strictly the percentage of time the injector is squirting fuel, correct, and once you get to 85% and above you are loosing the ability to reliably control fuel. Doesn't matter what ECU is being used, OEM or MS, the calculation is not a function of injector size. In your log you hit 85% around 4200 rpm and it maxes out above 120% at 6 grand or so.

[jsmcortina]

It does sound like the injectors are too small. If the duty shows above 100%, then that's just not happening.

James

[billr]

I have no argument with the DC discussion, of course, but am surprised the 85# injectors aren't big enough. I think of an "RV cam" as being pretty mild, intended for good torque at lower speeds. Considering that, a 350 cid engine (this one is up to 360 now?) making the 300+ hp that the 85's could provide fuel for seems about reasonable. Is this engine using gasoline, or E10, E85, something else? I would hate to see the OP going to the trouble to change injectors if the problem is fuel pressure or simply the tune.

[bradyzq]

Well, if you switch from 4 squirts to 2, assuming your deadtime is correct, you will gain 2ms of headroom on the injectors, which would bring you down under 100%.

But we don't know what AFR you're achieving. We can see the target in the msq, but no AFR data in the log. If you're running way too rich, you may have lots of room with those injectors when it's tuned correctly.

Your VE table looks a bit odd too. As mentioned above, 300hp should be doable on that injector setup.

More tuning, and more complete logging are needed before we can tell if injectors are too small.

[Brian]

You can always get a little more flow by upping the pressure. I think those old projection throttle bodies have an adjustable regulator.

[kaeman]

I was looking at your required fuel calculator settings, shouldn't you have 170 lb/hr. 85 x 2 or should it be 170/8 = 21.25lb/hr? I am used to my ms1 and ms3 fuel calculators. your required fuel just seems hi to me. 6.7 (13.4ms) I put in the injector flow rate of 85lb/hr and it gave me a calculation of 5.4 (10.8ms) you could be flooding the engine with the current settings, the ve table at idle and 100 kpa shouldn't be that large a number... but a rich miss fire using autotune will add fuel where the engine cant burn the fuel it already has. the highest ve values in your table should be at the max torque rpm 100kpa bin. but your tables seem to be reversed.