The Tool Shed (s/n 1013 rebuild)

[BRS]

... on a car that passage is blocked BELOW the heads, by a deflector that is almost never included with new heads, and is omitted by far too many aviation conversions.
....

I only added those deflectors as a result of one of the posts (& link) on this forum. The top one does little as the head is open on the side of the fins. It's really there to give a place to safety wire the one on the bottom to.

[karmarepair]

... on a car that passage is blocked BELOW the heads, by a deflector that is almost never included with new heads, and is omitted by far too many aviation conversions.
....

I only added those deflectors as a result of one of the posts (& link) on this forum. The top one does little as the head is open on the side of the fins. It's really there to give a place to safety wire the one on the bottom to.

That's a good thought, particularly since the CB Performance heads I have don't have the center rib in that area that would have been a convenient place to safety wire the bottom deflector to. I've been trying to fabricate a top deflector that DOES seal that area, but I think a top and a bottom wired together will be easier to fabricate and install.

[BRS]

Last week I flew for the Tool-Shed for the second time. I did a low pass near the end of a 20 minute flight. Mixture was full rich and EGTs I believe were near 1300˚. When I pushed-in the throttle the engine sputtered badly, pulling back some then slowly re-advancing the throttle smoothed it out.

Q. What's the likely hood of the sputtering being due to advancing the throttle too quickly?

I have a video but it's kinda gruesome, with the sound turned up, considering how badly this could have ended had the engine quit.

[GraemeSmith]

Last week I flew for the Tool-Shed for the second time. I did a low pass near the end of a 20 minute flight. Mixture was full rich and EGTs I believe were near 1300˚. When I pushed-in the throttle the engine sputtered badly, pulling back some then slowly re-advancing the throttle smoothed it out.

Q. What's the likely hood of the sputtering being due to advancing the throttle too quickly?

I have a video but it's kinda gruesome, with the sound turned up, considering how badly this could have ended had the engine quit.

On the basis of limited information and assuming the carb is tuned correctly and not in itself over-rich. Sounds like you were too rich for the Density Altitude prevailing. Sudden full throttle in a high DA will over rich the engine before it can pick up RPM. Either lean for best power or advance the throttle more smoothly. Both are good practice anyway.

[BRS]

...a low pass near the end of a 20 minute flight. Mixture was full rich and EGTs I believe were near 1300˚. ...

On the basis of limited information and assuming the carb is tuned correctly and not in itself over-rich. Sounds like you were too rich for the Density Altitude prevailing. Sudden full throttle in a high DA will over rich the engine before it can pick up RPM. Either lean for best power or advance the throttle more smoothly. Both are good practice anyway.

Thnx Graeme for the reply.

After some thought I've come up with the following. An EGT of 1300˚ is not what I would consider rich and the DA was only 300'.

My primary steed is powered by an IO-360 with electronic fuel injection. As such there never is any hesitation when pushing in the throttle, as fuel is added at the heads. So getting used to a carb seems to be the adjustment that needs to be made. It's the pilot not the engine that needs adjustment.

Since the fuel is added to the intake some 4' (apx intake tube length) from the heads it takes a bit of time to get from the carb to the cylinder, yet air flow increase is instantaneous when opening the throttle. I'm convinced (for now) that the engine leaned-out as I too quickly pushed in the throttle thus increasing the available air before the fuel had yet arrived to the cylinder. At least that is the assumption I'm going with.

So to restate my original question: Have others observed poor response to rapid throttle opening on the aeroVee and RevMasters.

[WesRagle]

Hi Brock,

So to restate my original question: Have others observed poor response to rapid throttle opening on the aeroVee and RevMasters.

I have no recent experience with a slide carb so I can't answer your question.

Since the fuel is added to the intake some 4' (apx intake tube length) from the heads it takes a bit of time to get from the carb to the cylinder, yet air flow increase is instantaneous when opening the throttle. I'm convinced (for now) that the engine leaned-out as I too quickly pushed in the throttle thus increasing the available air before the fuel had yet arrived to the cylinder. At least that is the assumption I'm going with.

Just some comments. Until recently I hadn't given much thought to exactly how the air and fuel get mixed during induction. I had envisioned a fine mist coming from the carb that instantly evaporated into the air and then headed for the cylinders.

Based on what I've been reading, with carburetors and throttle body fuel injection, much/most of the fuel ends up on the wall of the induction plenum (intake tubes). When the experts try to model a throttle body injection system they even have a name for the fuel deposit. They call it the Tau puddle. The fuel gets mixed with the air by evaporating the fuel off of the intake plenum wall. Under rapid acceleration the Tau puddle gets depleted resulting in a momentary lean condition. If the guys modeled the Tau puddle correctly, they will implement acceleration enrichment (accelerator pump) correctly, and the momentary lean condition will not be noticeable. Of course we don't have an accelerator pump so what you experienced could well be a momentary lean condition but I really don't know.

A question for you. Did your cylinder wraps reduce your CHTs? Inquiring minds want to know :-)

Wes

[sonex1374]

...[snip]...Have others observed poor response to rapid throttle opening on the AeroVee and RevMasters.

Brock,

With the AeroInjector, yes, this can happen. If you rapidly open the throttle, the airflow increases right away, but the fuel has momentum, and it's not moving that fast to start with. It takes just a bit of time to increase the flow rate to match the airflow. If you go to WOT too fast, the engine will stumble momentarily, and that can be annoying. The solution is to advance the throttle slowly to give the fuel time to "catch up". My standard practice is to take 1-3 seconds to go to full power and this keeps the engine from stumbling.

This stumbling only seems to happen under certain conditions, and sometimes not at all. In any case, it doesn't seem to be a problem, more of an annoyance really.

Jeff

[Scott Todd]

I've posted this before but will again here for completeness. I'm on my 3rd AeroVee. I've been flying one in a little Biplane for 15 years. They are ALL rich on the low end. If you don't lean for taxi, it will stumble on full throttle as it burns out the excess fuel. Its quite repeatable in my Biplane and my new Onex that now has 20 hours on it. I go to full rich for run-up and then again as I pull on the runway.

[bvolcko38]

The Aero Injector is quite similar to the old Posa slide carb. The old guys had the same problem with the Posa being very rich at low end. They drilled a small air bleed hole (1/8")? in the slide to allow extra air and thus lean the idle mixture.

[BRS]

Hi Brock,...

A question for you. Did your cylinder wraps reduce your CHTs? Inquiring minds want to know :-)

Wes

Wes et All,

Yes, I'm happy to report that adding the wraps as well as blocking a few spots did take care of my cooling issues, so it seems. CHT's on my last flight were in the 350-360˚ range while oil never exceeded 150˚, which means I might be blocking some of the smiley which will in turn improve CHTs.

Granted, it was a short flight and the OAT was cool.
BTW - in the end the wraps were easy to make. Just took a bit of effort to fit them the way I liked.