Cylinder Head Baffle Wrap Gap

[Randy]

Data: RV7A with Aerosport IO-375 and low compression, oil squirters installed. Oil and CHTs will run up over 220F and 400F if I let them but I do not, via running lean of peak. I cannot run at best power mixture very long without busting though those temp limits, but I can cruise all day, as long as I keep it well LOP, burning about 7.5GPH. Also have EZ Cool cowl flaps, it will go too hot even with them open. Baffle seals are not perfect but they seal well and all other leaking areas have been sealed, washer behind number 3 etc. I have measured pressure delta above and below engine, and at the oil cooler and the numbers are good. I have dual Pmags, pulling timing way back makes no difference. Vernatherm is gone and oil plunger installed so all oil goes to the cooler unless oil pressure goes above about 100 PSI. Engine now at about 95 hours, oil consumption normal.


In my quest for lowering my cylinder head and oil temperatures I finally got around to measuring the gaps in the cylinder head baffle wraps. I cannot explain why I waited so long to do this. A conversation at the Reno races got me to check this when I got home. What I found surprises me and I wonder if the following dimensions are possibly by design?

To clarify, these are the gaps at the cylinder heads, not the cylinders themselves.

My gaps.
Cyl. (1) 1-1/2" Cyl. (2) 2-5/8" Cyl. (3) 2-3/4" Cyl.(4) 2"

That seems like a lot of variation. The wraps are held nice and snug to the cylinder fins so that is not the issue. I made my own tapered cylinder baffle wraps, but the wraps for the heads are stock from Van's kit.

Anybody know what the gaps that let the cooling air escape from under the heads should be?

Are these gap dimensions normal?

Maybe this is finally the "smoking gun" I have been looking for that might help explain my persistent high oil and CHT temps.

Randall in Sedona

[BillL]

I don't know if that is an angle valve head or parallel - but a few questions.

1. Did you address the lack of flow on the front of #2 and back of #3 heads where the fins are short and baffles block off flow to the lower fins?

2. If you did address the flow in #1, does the CHT follow the lower gaps?

3. SJ and somewhere I can not recall - says the proper lower gaps are 2 1/4" for the heads, and 1" for the cylinders. 1.5" would, by that measure, be too small.

I am not saying this is the root cause of your issues, but they are a reference point for you.

[rhill]

May I ask What Oil cooler are you using?

[Randy]

I am using Van's stock RV7A cowl without the snorkel so air intake is shared with cooling air intake.

I did address the cooling air to the back side of Cyl.3, but not the front side of Cyl. 2. I will look into that.

My oil cooler is the SW 8432R fed with 4" Scat to a firewall mounted RV10 cooler mount.

Specifically I am hoping to learn what Cyl head baffle wrap gaps others are successfully using, or a Lycoming specification for same. I have this question off to Aerosport also, maybe they will have something for me.

Randall in Sedona

[Bubblehead]

"cylinder head baffle wraps"

I'm having a hard time understanding what we're talking about. Can you post a picture?

[BillL]

Originally Posted by Bubblehead

"cylinder head baffle wraps"

I'm having a hard time understanding what we're talking about. Can you post a picture?

He is talking about the cooling air exit gap at the bottom of the cylinder and head. This area controls the flow through the fins.

Here is DanH's lower pict with wraps, a bit larger than 1" and 2.25" per Kent Paser.

[Randy]

I had a long conversation with an ECI representative yesterday and his recommendation for the gaps was 1-1/2" for the cylinder wraps and 2" at the cylinder heads.

And, they should all be the same.

My cyl head baffle gaps range from 1-1/2" to 2 3/4" so I should open up the tight ones and perhaps see a bit better cooling as a result.

FYI my baffle kit was standard from Van's and they are drawn nice and snug to the cylinder head fins. The variation I experience seems to have come from the way the baffle kit was made.

Randall in Sedona
OP

[Bubblehead]

BillL - that is what I thought too, except this part of the post threw me: "but the wraps for the heads are stock from Van's kit."

OP Randy's later post, after yours, seems to say we're talking the stock aluminum ones, not the ones like Dan uses.

The stock wraps from the Van's kit are formed aluminum, snugged up by the threaded rods and the gap is what it is, but the ECI tapered cylinders can cause some variation.

[Randy]

Bubble Head,

I am referring to the aluminum wraps on the fins on the heads, held to the fins with threaded rod or safety wire.

I keep getting different figures for how much gap their should be between the inter cylinder pieces and the "wraps piece" supplied by Van's baffle kit.

One thing I have learned is that the air gaps are not designed to be different.

I assumed the kit would provide equal size air escape gaps and they do not, at least not on my install, and they are pulled snug against the fins.

Somewhere in Lyc. literature there will be a spec on these gaps...

Randall in Sedona.

[Mike S]

Originally Posted by Bubblehead

seems to say we're talking the stock aluminum ones, not the ones like Dan uses.

As I recall, Dan also has the stock alum shrouding over the RTV/glass units.