Prop VS Motor: Airgator, LS2 6.0, Sensenich NEED ADVICE

[sarros2004]

Hi All,

Need some help. Not sure if I have an engine issue or prop.

I finally have my rig mostly assembled and in the testing phase now, Thanks largely to a post I previously had here and all of your valued input.

Here is what we got. I am running a 14 ft Airgator, 2.38 rotator, and an 80 inch 3 blade R prop. The power plant an LS2 6.0 aluminum block running a standalone ecm with fuel injection. It also has an upgraded cam, and long tube headers. I am estimating the hsp conservatively around 500.


I have been told the sweet spot on this prop is 2200-2400 rpms which with the reduction is have should put the engine around 5200-5600.

Our testing has been on dry ground, as ultimately the intent is to get in the sweet spot to get it moving on the dry before we hit the water.

The our first attempt we had the prop pitched at the 2 mark. We couldn't get over 3100 engine rpms. We backed down the pitch all the way to 1 over gradual adjustments finally achieving around 3700 engine rpms.

We gave up on that and switched to a 2 blade hub, using the same 80 OA blades. Again we started pitch at 2, and achieved an rpms in the 4000 range. We backed the 2 blade pitch down to 1, and got around 5000 rpms, just on the cusp of wanting to make the boat move.

I have read many of these forums, and received many suggestions. I do not feel I have a bad prop, gearbox, motor ratio. It just strikes me as odd that I appear to be ha ing so much trouble getting the prop to turn. Leading me to believe that I may have an engine issue. It runs well and sounds strong.

Not sure what I need to ask here, just looking for some input and some advice.

[unforgiven11B]

I would suggest you get live/real time data on your engine and see what’s going on.

[OneBFC]

My opinion is your engine is not producing the power you think it is.

Start with giving the engine a close look tune and mechanical wise.

Good luck!

[SWAMPHUNTER45]

Have to agree with both of the prior posts.

When you say upgraded cam do you know the specifications or part number?

Once you check all the quick and easy data related to the tune I suggest a compression test of all 8 cylinders.

Often little things can catch you, is the engine getting air? Does it have fuel pressure? Is the ignition functioning properly?

[One Eyed Gator]

With a cam and head work, and at around 10.6:1 my ls2 carbed is around 400hp. With a 2.68 and 79.5" 3 bld R set at 2.5 motor turns 5500.

Sounds like something is wrong in your tune.

Tune it self
Fuel Pressure
Injectors to match Estimated Hp
Correct length push rods
???

[GeeLeDouche]

Agreed with all the above posts. Either something is wrong in the cam or possibly something is hurt in the motor. It should spin that sucker a lot harder than what it is. I would get some live data from the motor if you can..

[digginfool]

Look to see if all injectors are firing. Get yourself a set of noid lights and make sure all the injectors are getting the signal to fire. It's a real simple test and the kit is under $40 on the high side. Make sure you're getting spark on all cylinders as well. I've had both issues with my LS; bad coil pack, bad injector. I've also had a couple issues along the way with the wiring. The factory wires are very light gauge and they have failed with no external sign of damage. Also, get yourself a good thermal gun to check temps on each runner on the exhaust. That will help you find the cylinder(s) that are not firing.

[CarMotorBarge]

Also not a bad idea to pull the plugs and look at them. Might give you some info to solve the problem.

[sarros2004]

Thanks to all. Seems to be unanimous that I am pursuing an engine issue. I will begin troubleshooting this week starting with a compression test, and injector balance test. Plugs are new but will reinspect during compression test. Fuel pressure tested fine during initial priming of the system. Injectors are factory and should have the flow characteristics for 500-600 hp. After engine health is confirmed I'll get my tuning guy out and we will trouble shoot for that. He suspects that because we had a leaky exhaust system it may have skewed his air fuel ratio sensor. I'll keep you all posted. Thanks again for all the input. Deffinitely have a direction to go now.

[CarMotorBarge]

It is also a good idea to install a wideband O2 sensor so that you can keep an eye on the AFR while you are driving.

[sarros2004]

Funny you mention that carmotorbarge. My tuning guy uses a wideband sensor to check af ratio and adjust the tune. We found exhaust leaks at the mufflers and suspect it may have skewed the results enough that the fuel trims are way misadjusted. We are going to run it again now that we have the leaks corrected. Hope to do that this week. I may add an additional o2 bung just for a wideband o2 as you mentioned. I'll keep yall posted.

[One Eyed Gator]

Are your sensor bung holes in the collector?

[sarros2004]

Yes, One Eyed, O2 sensors are in the collectors (headers). And also, We have made some progress tonight. Got my tuning buddy out, and he began some troubleshooting. He noticed his Air/fuel ratio readings were off the charts when the prop speed came up. He deduced that the the air movement from the prop was washing out the readings from the mass air flow, and also his wide band we had in the exhaust pipe. We got in touch with another tuner out of Texas who was working on the tune with us remotely. Moved the wide band sensor up in place of one of the o2 sensors and began tuning using speed density rather than mass airflow curves. Before we got rained out we had achieved 5k rpms, with the 3 blade back on and pitched at 2. A MAJOR improvement. Basically using speed density we found we are running short of fuel at the higher rpms. Started pouring the juice to it, and she's running better We are gonna hit it some more tomorrow if the weather holds. And do some more diagnostics and check some peripherals. Hopefully be out sliding soon.

[SWAMPHUNTER45]

Curious did you have a curved type air induction with a KN element or more open set up to filter your air. I have noticed many use a curved intake and wonder if that may be why for some reason.

I do know that GM and Chrylser use a ram air system so it must be possible to have a straight shot in but they may have sensors and software more able to manage the turbulence.

Not sure if you may have read but us old carburetor people deal with a air flow issue and need to cap off the back of our filter box to prevent air flow from pulling our fuel out. I would think fabricating a remote filter would be a potential remedy. Glad to hear your on to the problem and it is no longer a mystery.

[GeeLeDouche]

What fuel delivery system are you running? obviously not a self learning one if it is not performing at higher rpms?

[sarros2004]

I THINK WE HAVE IT

But first to answer the last 2 posts.

Swamp hunter, it is a very short intake, it is pretty much a 90 degree right out of the throttle body. I have it angled down sort of in an attempt to keep rain water from dripping into the engine. The filter is a cone type oil bath, though not K&N brand, clamped right to the end. I got it and the pieces I needed for it from siliconeintakes.com. Excellent source if you guys are looking for air intake parts. As for the reason for curved intakes you mentioned, I'm not not sure. My filter really is not in the direct path of airflow from the prop, it's more or less directly in front of the engine. Either way tuning using speed density eliminates using the mass airflow readings for initial setup. As I understand it, Now that we have the tune established the MAF is turned back on and the computer will make its adjustments based on that (within a certain range of the base tune). Side note: I've got mad respect for you old carberator guys, tuning one properly is a skill that always seemed to evade me, granted I am a fuel injection baby. If it doesn't have an OBD2 port, I'm pretty much guessing.

Geeledouche, the fuel delivery system is essentially factory. I'm using the factory injectors, factory harness ,and factory ECM that came with the motor out of SS Trailblazer. The only differences are that I'm using a Bosch 044 fuel pump with a fuel filter/regulator assembly from a C6 Corvette. The ECM is of course tuned with different software but it has all of the control over fuel, it uses readings from a mass air flow and O2 sensors to make fuel trim adjustments. However you have to tune in the "base" fuel curves that it will make adjustments based on.

THE RESULTS SO FAR

So we have the tune dialed in now. Air fuel ratios are excellent across the entire rpm range. It raps to 5000 rpm with almost no delay.

With the 3 blade and pitched at 2 (100 degrees) we were able to get 5200 max rpms out of the motor, which puts us just under the 2200 - 2400 optimal rpm for the prop.

I plan to run it Saturday morning to get a feel for it, and then possibly make small adjustments to get us into the 2200-2400 prop speed bracket.

Given the info I have read on these forums, I still feel like the motor as built should be able to push the rpms higher, given the propeller is only pitched at 2, but then again air fuel ratios tend to tell all. I believe to get any higher rpms I'm going to have to back the pitch down a wee bit.

Any one have anymore thoughts or input regarding my rpm range and prop pitch settings? Am I off base in my reasoning or method here?

[SWAMPHUNTER45]

I say run it and let the system learn your needs and see how things go.

As long as your not overspinning the prop you should be good for some testing.

Keep an eye on the temperature we have some hot days coming.

[One Eyed Gator]

One thing to look at is if you have an LS2 out of a TBSS it should have the 411 injectors which are 36lbs at 58psi good for around 450hp at 80% duty cycle. Also a few GM setups run at 40 psi not 58 and the TBSS had several different injectors depending on the year.

Just a few thing I would verify.

Depending on the cam you may be pushing the injector above its duty cycle .

I would read up on the MAF sensor if you going to run with it I believe for the best performance you 3" of straight before and after the MAF

Sounds like your getting there

[sarros2004]

Thanks all. Swamhunter, I will be running it tomorrow morning to see how she does.

One eye, ill have a look at the injectors tomorrow, I believe I'm good as we have achieved the correct fuel ratios without running out of injector, but deffinitely wouldn't hurt to look. As for my mass airflow, I dont have much room to maneuver it without it being in the way. I'll see how she runs and go from there.

I'll post some results of how she runs.

[sarros2004]

Well the saga continues. My low rpm issue has returned. Cant get her over 3100 rpms. I now entirely believe this not a prop issue. We had it cracking 5k easy the other evening. Now right back at it. This go round however we had erratic fuel pressure, and the pump is not sounding healthy.

My fuel system is a Bosch 044 pump with C6 Corvette regulator for pressure control. The Tank is 40 gallon with the bung and pick up coming in from the top. I know these pumps are NOT designed to "suck", which is why I mounted it at the rearward base of the cell. No leaks.

Thoughts?

Recommendations.?

[OneBFC]

Monitor fuel pressure while you are running the engine under a load on the trailer. I bet you will find you are losing pressure as load increases.

That's my guess anyway based on the availab info.

[SWAMPHUNTER45]

Is tank vented properly

Most likely bad pump or regulator.

Some systems run 2 pumps but I am not well versed on when or why.

[sarros2004]

Vents are good. And fuel pressure is erratic, but like you indicate under load it is most noticable. I believe with my current set up I need to try lift pump. However I am concerned that most of the "lift" pumps I am finding are similar still in line pumps like the Bosch.

I did find a facet lift pump that will do 50 gallons per our. The o44 is rated at 87 gph. Not sure if the facet will work or not, but cant seem to find anything close to that 86, that is a true lift pump.

[Slidin Gator]

How much fuel can you burn in an hour? If you are burning 50 gph at WOT you need to get off and run, cause it's leaking bad and about to burn flat up.

Put a Facet 50 gph gold flo on the tank to feed your HP pump and you will be golden, at least until one of them shifts the bed. The facet will pull good suction and your HP pump will be happy, just keep your filters clean. Keep a spare of each in your emergency box.

[OneBFC]

https://www.onallcylinders.com/2013/05/ ... -answered/

Plenty of automotive engine boats out there will need more than 50gph. Your may not, but without a dyno you should build in plenty of extra capacity.