Changing surface texture for fuel fallout issue

[BradH]

I wasn't sure if I should piggyback this onto the current thread on burr finish, but I wanted to put this out there for people's thoughts.

Long story short, I ended up pulling off the heads after my engine's dyno last session. The engine ran very well and met or exceeded the expected performance, even though we never got a solid tune on one of my carbs (we tested 3 different ones, plus member PRH's own Holley HP that he uses sometimes as a dyno mule).

Once the top end was apart, I saw there was a consistent indication of raw fuel in the intake bowls, since every cylinder had the same staining directly behind the intake valve guides. At some point I decided to rough up the 60-grit finish in the runners and the bowls, hoping that this would help with what I saw.

So, some "before" and "after" pics...

First, two shots showing the view from the runner entry and the staining (fuel wash?) pattern in the bowls.
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The after shots after hitting the majority of the intake runners w/ the carbide and the "chatter" that I added to the bowls themselves.
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Finally, since the manifold itself had been left as-cast when tested, I sized the exits to match the intake port entries and tried to leave a similar finish as seen in the intake ports.
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I'm interested in hearing if others think this was the right approach to addressing (or mitigating) the fuel wash issue shown above. Or, for future reference, what other steps could / would have been taken. Thx - Brad

[RevTheory]

Hey, no matter how your testing goes, your first pics show where your epoxy guide vein needs to go

When are you going to be able to test it again? I'm really curious to see how it goes. I would certainly *think* that the chatter you did above the seats will kick that fuel back up into the wind.

[hysteric]

Smaller Carb?

What did the plugs look like?

[swampbuggy]

Were the Air to Fuel ratio numbers close to correct for the type of fuel? being used ? Mark H.

[BradH]

Re above questions...

Yep, a guide wing certainly looks appropriate for that location... but I don't trust my ability to build one from epoxy that will stand the test of time. Already had an issue w/ a "fix" I did to an intake in the past that -- despite my following all the recommendations -- either came off or was in the process of loosening up when I pulled it off later that year.

"Smaller" carb is kind of relative, IMO. The engine makes in the high 600s HP (680-ish best on dyno) and one of the best pulls towards the end of the session was with PRH's Holley HP 1.38 v x 1.75 t. None of the carbs I brought to the dyno were well sorted out at the time; the "bigger" carbs that "should have" made more power were all on the lean side from what I recall of the test data. My smallest carb now is 1.42" v x 1.75 t, and I have a few larger ones with different venturi & booster configs to try out.

Air-fuel ratios during testing were in the acceptable-to-lean range, depending upon the carb & the given tune tested at the time. IIRC, PRH's Holley HP was in the mid-to-high 12s; the two of my carbs that we spent any time trying out (1.50 v x 1.75 t w/ down leg boosters and a 1.58 v x 1.75 t w/ annulars) were in the high 13s. However, simply adding more jet to those didn't necessarily result in an improvement; there were some config & tune issues that I hope to have addressed when I get a running car again. Oh, the fuel on the dyno was 50/50 93 E10 and 110 leaded; we wanted a margin of safety w/ the fuel cuz the CR was close to 11.5.

[hysteric]

What's the rest of the combo?

Did you look at the plugs?

[GARY C]

I would say your first two shots show were the valve and guide blocked fuel from the back of the bowl, a guide vein/fin that induces swirl may get rid of the stain but only back to back dyno testing would show if it helps or hurts power.

As clean as the port is I would not be to concerned about it's previous finish.

[David Redszus]

A rough surface finish will increase the boundary layer thickness thereby reducing cross sectional area
and reducing air flow. If the affected area is a flow separation area, then the rough surface may delay
flow separation and improve air flow. That's for dry air.

For wet air flow, a rough surface will increase the wetted surface area, allowing greater heat transfer to
improve fuel evaporation. My guess is that it could be defined by some Reynold's number.

Fuel evaporization is a function of time, temperature, and turbulence. Seems like a burr finish in the
right locations could assist with all three.

But, considering the constantly changing engine parameters, a dyno or flow bench might be much
too inaccurate to properly measure the effects being evaluated.

[Mummert]

You will have some fuel fall out between the guide and valve job no matter what. There is negative pressure behind the guide. Looking at your valve job could help as a last chance to break up some of the fuel that has fall out of suspension. Old Dodges have the chamber very biased toward the exhaust flange as well. Sharp defined underseat angles are good no blending, one of those time when the last couple of flow bench numbers don't help.

[steve cowan]

20210126_094321.jpg

This is a recent valve job i done on my 182cc cast iron dart heads.
The bottom cut is 82 deg and throat is 89% of a 1.94" valve
I did a burr finish on throat area only,I hand finish the SSR smooth as I believe the boundry layer will be very thin in this high speed area.
These heads are on an engine now and will be run soon,not saying my way is THE way but just something else to look at.
Darin Morgan has a couple of new YouTube videos
Wet flow
Air speed.
Amazing information that is a must watch for any engine guy,we are extremely lucky to have people like Darin Morgan that will share there hard earned knowledge for free

[BradH]

Interesting comments and observations above. I'm considering what I did per the pics above as something in between a "If it makes you feel better about things" and a potential Band-Aid.

There won't be a follow-up engine dyno session, but at some point the top end will come back off the engine and I'll be looking for any signs that it made a difference over a longer amount of use.