Engine Temps

[Charles Perdue]

Marty, I am always curious. When the temp readings were taken, what type of water pick-up were you using?

If it was the pick-up in the rudder blade, which side of the rudder was the pick-up hole on?

Charles

 

[Mike Rappold]

Marty,

During the time frame the temperatures were recorded, what was the engine rpm doing? Is it holding steady through the turns or up/down? Also what is the time interval between each successive reading?

Thanks in advance.

Mike

 

[Marty Davis]

Marty,

During the time frame the temperatures were recorded, what was the engine rpm doing? Is it holding steady through the turns or up/down? Also what is the time interval between each successive reading?

Thanks in advance.

Mike

There was a 500 rpm drop in the turns and the boat was doing 33.5K in the Straights.

Not sure of time between samples. Can you determine a pattern based on the data to the left of EGT?

We had a data logger that was measuring rpm, so that was documented.

The boat was running 73mph in the straights, so you might be able to back into the time increments.

 

[Marty Davis]

Marty, I am always curious. When the temp readings were taken, what type of water pick-up were you using?

If it was the pick-up in the rudder blade, which side of the rudder was the pick-up hole on?

Charles

Charles:

Water pickup was in the rudder and was on the inside.

You are moving toward a conclusion that I thought might be valid, that there was a little bit less water than optimum to keep temps steady. There was some elevation of temps as the run progressed.

 

[Marty Davis]

Don Maher please sign up again for the tech forum. I hit the wrong button and rejected your entry. SORRY.

TchedOff you need to register using your real name, not a screen name.

 

[Charles Perdue]

Marty, I am always curious. When the temp readings were taken, what type of water pick-up were you using?

If it was the pick-up in the rudder blade, which side of the rudder was the pick-up hole on?

Charles

Charles:

Water pickup was in the rudder and was on the inside.

You are moving toward a conclusion that I thought might be valid, that there was a little bit less water than optimum to keep temps steady. There was some elevation of temps as the run progressed.

Marty, I have several different thoughts to the changing temps as the run progresses.

The first is I am an old carburetor man, motorcycles, real outboards, racing Go Karts, automotive engines, racing/ daily transportation and about everything else that has a carb on it. ALL of the carbs with a float and float chamber are sensitive to fuel levels, sensitive to as little as .010 of an inch for consistent performance.

On our fuel systems, the fuel tanks themselves act as the fuel float chambers in relation to the fuel level differences between the carb spray bar and the fuel level in the tanks. This level difference as the fuel burns in our boats are measured in INCHES. Even taking into consideration that we are using pipe pressure there is still a leaning out effect on the engine as the fuel level drops in the fuel tanks. Leaner mixture, higher EGT. Whew.......get to the second one later.

Charles

 

[Marty Davis]

Marty, I am always curious. When the temp readings were taken, what type of water pick-up were you using?

If it was the pick-up in the rudder blade, which side of the rudder was the pick-up hole on?

Charles

Charles:

Water pickup was in the rudder and was on the inside.

You are moving toward a conclusion that I thought might be valid, that there was a little bit less water than optimum to keep temps steady. There was some elevation of temps as the run progressed.

Marty, I have several different thoughts to the changing temps as the run progresses.

The first is I am an old carburetor man, motorcycles, real outboards, racing Go Karts, automotive engines, racing/ daily transportation and about everything else that has a carb on it. ALL of the carbs with a float and float chamber are sensitive to fuel levels, sensitive to as little as .010 of an inch for consistent performance.

On our fuel systems, the fuel tanks themselves act as the fuel float chambers in relation to the fuel level differences between the carb spray bar and the fuel level in the tanks. This level difference as the fuel burns in our boats are measured in INCHES. Even taking into consideration that we are using pipe pressure there is still a leaning out effect on the engine as the fuel level drops in the fuel tanks. Leaner mixture, higher EGT. Whew.......get to the second one later.

Charles

Charles:

Very well could be that (gradual leaning out), or could be cooling. Hard to know without split testing both.

Callahan always has said that our carb system is archaic.

I personally use a carb with a low speed mixture to give me at least some range.

Have you ever thought of using a pop off valve on the tank to vent pressure at a set pressure? I made several pop off valves to vent at different pressures.

 

[Tim_Duggan]

Marty,

Sorry for the confusion. TCR = Trapped Compression Ratio.

 

[dwilfong]

Yes I have seen some of the setups on hear. But if you hook it to the rudder servo with a linkage I don't think it would add that much.

A lot more KISS than soft wear and programing.

And you could find a happy medium with the pipe.

You could also slide the fat section and not the throat.

David

It would be nice if it was as simple as attaching a linkage to the rudder, but I can't see it being that simple. There Has to be provisions in the mount of the pipe and not compromising the rigidity of the mount if the boat should happen to come unstuck and roll. In a word - weight. In the larger classes, not such a big deal, but in the smaller classes - vital.

From an electronics perspective, the programming aspect may be tricky, but once it is set it would be more reliable than more moving parts - no question. Unless it gets wet! Ideally, the function would happen with little to no input at all once set up.

Therefore, "fooling" the pipe into acting longer rather than physically making it longer has real merit in my opinion.

Why mechanically change the pipe length? Why not use water injection to do the same thing?

I was playing with some tune pipe soft wear and it seams that the only parameter that changes with ex temp is the header length.

It seams to show with the range of temp change sowing in your data that a 1/2" of change in length would do the trick.

Making a slip pipe with a bimetallic spring around the pipe at the header would move the pipe out with the temp change.

Would be pretty simple and not add to much weight. Just put a bushing on the stinger mount.

The pipe would react to temp no mater what you are doing.

David

 

[Kim J]

In Europe using a float chamber are common in the FSR V and also the O class - never seen it used in the H class.

Also keeping the low speed needle intact gives you more driveability.

With a noise rule - max 82 DB - a extra muffled pipe is required. Performance and heat problems are easily affected by this.

 

[Marty Davis]

May I be so bold as to ask;

What was the effect of TCR on EGT with all other variables fixed?

TD

Tim:

I have arrived at the TCR that I find works best for me on my .21's. That is 10.25:1. So, I have not split tested TCR in this regard. What effect do you think that would have?

 

[Tom w]

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[Tom w]

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[tnrcboatracer]

I have been watching this thread with interest. Please allow me to interject some thoughts.

Regarding the constant tank pressure: constant tank pressure will not compensate for head loss. The constant pressure will still need to lift the fuel higher to get to the spray bar, the head loss is still the same regardless of the static pressue in the tank. The only way to compensate is to increase the pressure as the tank level lowers (by the same ratio). The key here is a contant fuel pressure at the spraybar. A simple way to do this is the float chambers popular in Europe. Adding a sump tank will not affect this (as discussed previously).

Harry Byrne used to make the pipe Maximizer. It was a telescoping slip coupling and linkage that allowed the pipe length to be adjusted, or coupled with other functions. A bimetal spring with sufficient force to move the pipe will be too slow to react to the temperature changes shown here.

The leaning of mixture due to G-forces will have to be accomodated. Perhaps the finer atomization of the Zoom carbs can minimize the g-force effect. But until nitro motors go to direct combustion chamber injection, we will always have the potential for fuel droplets being pulled out of suspension by G-forces.

Putting the TC at the mid point of the pipe makes sense to me, especially if you are interested in the effect on sonic velocity. This is the area where the waves are doing their avearge propagation. Placing the TC near the port (in a gasoline engine) will tell you if the temp is getting critical for meltdown of components, or for better controlling mixture. The exhaust temps of MeOH/Nitro fueled motors are much lower than their gasoline counterparts. In this case, I think the mid point of the pipe is a good compromise; it allows for visibility of the effects on pipe length as well as mixture (though mixture may be a little compromised).

Overall a very good discussion. It makes me want to come up with some sort of constant pressure fuel delivery system. Perhaps boosted by pipe pressure with a pressure regulator at the carb.

 

[BB Mods's]

Scrap that, let's work on a secondary direct injection system, the motor would have to retain it's stock carb location (and a portion of the overall fuel mixture) if for nothing else then to lube the bottom end, but the bulk of the fuel could be applied directly to the combustion chamber as Jon suggested.

fuel pumps will be a must, FPR's will be critical to insure we can hold a constant flow of fuel.

 

[Marty Davis]

Marty,

Have you logged RPM's to coincide with the temps?

If you have what are your RPM's doing when the temp rises?

A change in RPM will change your optimal pipe length.

Tom W

Tom:

No I didn't have the ability to coordinate both.

 

[tnrcboatracer]

Scrap that, let's work on a secondary direct injection system, the motor would have to retain it's stock carb location (and a portion of the overall fuel mixture) if for nothing else then to lube the bottom end, but the bulk of the fuel could be applied directly to the combustion chamber as Jon suggested.

fuel pumps will be a must, FPR's will be critical to insure we can hold a constant flow of fuel.

Mist oil into the bottom end and inject fuel into the top end. We mist lube our machining spindles all the time. Works great. Getting equipment small enough to do it in our application may be tough.

 

[Charles Perdue]

I saw that the Europeans were using float chambers and I built one and played with it in a 21 Seaducer, it worked very good. A small float chamber could be built into the fuel tank of a rigger.

To build a direct fuel injection system for our applications in the boats running on nitro would be a REAL challenge. When you guys get one built, I will be glad to test it for you, maybe for free.

Charles

 

[camaroboy383]

jon,,,, thank you for touching on the TC location... for sure makes more sense now....

alden

 

[Tim_Duggan]

May I be so bold as to ask;

What was the effect of TCR on EGT with all other variables fixed?

TD

Tim:

I have arrived at the TCR that I find works best for me on my .21's. That is 10.25:1. So, I have not split tested TCR in this regard. What effect do you think that would have?

Marty,

I have seen examples where the temp of the pipe goes up as the engine gets older / loses the ability to burn the mixture as effectively in the engine, and as a result burns it in the pipe. I was curious to know if Compression ratio gave a similar result from a controlled test, rather than theorising or assuming.

If lower TCR = Higher EGT at a stoichiometric mixture(not lean), it would go some ways to explaining those cases often heard of the "freak" engines that run the best they ever have with a poor seal or fit of the piston and sleeve...... possibly due to the pipe length or shape was not compatible with the lower EGT when the motor had a good seal.