I contemplated the Sam James plenum but in the end ended up going with the standard Van's baffle. I am running the standard Vans baffles with the Oil cooler mounted on the baffle behind the #4 Cylinder. Here are three different flight pics I have taken over the years flying LOP. Most of the time my CHT temps range anywhere in the 275 F to the 320 F range while flying LOP. The 4 cylinders usually are within 10 deg F of each other when doing so.

The numbers may be hard to see but this pic shows flight at 9500ft, OAT 29F, CHT's 261-273F:


And another flight at 11500ft, OAT 37F, CHT's 292-297F:


And one down low at 3000ft, OAT 42F, CHT's 268-275F:

Sam James plenum, IO-320 ...
 

My Sam James plenum has cooled wonderfully from Day 1. I spent a reasonable (i.e. not excessive) amount of time sealing up the front edges where it abuts the engine case, and have a soft gasket across the aft edge at the rear baffle(s). My oil cooler is behind Cyl#4, and despite my pre-flying concerns about high oil temps given that location, my problem is too much cooling when air temps are under 40 to 45F. In these winter months I have 80% of the oil cooler blocked off to get oil temps of 175 to 180; my CHTs running LOP are very close to 300 depending on OAT. Quite honestly, I couldn't be happier with the plenum arrangement.

Build the cowling the way Van asks you to and it will always work just fine, in my opinion a separte plenum is a total waste of money and building time and weight.

Waste of time and money is in the eye of the beholder....also in the eye of the fuel receipt holder.

I took off last of 4 RV's heading to OSH last year, but landed 15 minutes in front of everyone at the first fuel stop. I also took less fuel then anyone else(even the 320).

YMMV, but I like cruising fast. 8.5gph is 178kts TAS at 9500' CHTs 340-350.

Jamie, you should be saying if you climb slower than 120+ knots, you are only using 100 on initial climb out.

And at 29LPH, despite the Dynon being confused there about ROP, the CHT's should be down around 295-310, exactly as others report. I have had a few PM's on this thread, all agreeing but not having taken the time to photograph it. I hope they do.

Experiment for sure, but don't settle for something less than optimal is what I am saying.

Tim sure thing, but where was I holding the superstition? Please point it out if I have. We as humans are all guilty of it at times. We will justify the indefensible for hours despite the data, just because we have a pride issue with the purchasing decission we made. I am just as capable of this as anyone.

Now how about you define the "zero cooling issues" a little bit. You may well have a Sam James plenum that is set up well and works as effectively as the standard baffles. I would like to see the evidence, and I would be really pleased if you did achieve it. I would like to see others with plenums have success. But so far I have not.

Why go to all that trouble and expense and have higher CHT's? Unless you gained 10+ knots in cooling drag reduction I would argue it was not worth it.

They also make it harder to get to the top of the engine, plugs etc. Despite looking cool! ;)

Down here in OZ its pretty warm a lot of the time.
As David says, almost all of the RVs here with plenums that I know of, run significantly higher CHTs than those with stock setups. This seems counter-intuitive, I agree, but thats the data set we have.
I have a standard baffle setup and never see higher than 380 in climb on very hot (40c+) days Cruise ROP around 330-350 dependent on ambient, and 310 or thereabouts LOP.

One theory we have kicked around here is that the plenum removes a lot of the Al baffle material which undoubtedly acts as additional heat sink for cylinder heads in a stock setup. Im not sure how one would quantify that though.

Its also hard to make apples/apples comparisons of how much air is flowing throught the different setups. All things being equal, hotter = less air which should equal less drag - which is the selling point of aftermarket cowls and plenums in the first place. So one would expect a plenum to be hotter and quicker. Or if you talk to someone with a plenum cooler and quicker! ;)

my 2c

Cheers

Richard,

Funny your data set or experience is like mine.

The unfortunate part is I wonder if some plenums are not just hotter, but hotter and slower.

DanH is probably the VAF guru on this topic and I would suggest he has helped many folk succeed in getting cooling right.

So far I have never seen anyone with better cooling results and a faster plane than one with standard baffles using the better seal material.

Heck, mine have leaks in the corners and around the front near the crankshaft.

Tufting an engine and lots of camera's is the answer! I know folk who did this to STC Beech baffles, and they learned a whole heap of stuff that defied commonly held beliefs that even they had. The data changed their minds, even if it was hard to swallow at the time.

This is external testing http://www.youtube.com/watch?v=QbMQWPTzS3M

I looked for some pics, but can't locate many with enough info.

This was taken about a year ago during race testing. I was running about as hard as possible. 2600rpm, 150ROP, 24.7"mp. OAT 2C. CHTs under 350. 190KTAS


Then in April I ran the Hill Country 150 at similar power settings but OAT was about 21C. CHTs were under 395. I was making max power for the conditions and still below 400. :)

Coming back from OSH'12, we were at gross weight and ramp temp in South Dakota was 33*C. It was still 27C at 8500', I kept climbing looking for some relief of the bumps and heat. CHTs never got above 390. I like my plenum.

To be fair, I did have a cooling issue the first summer after phase 1(jan-feb11). When summer rolled around I had to step climb several times to keep oil temp and CHTs in check. I found many "leaks" in plenum and plugging them was the fix.

Not bad, but not as good as or better than the standard baffle results, but to be fair, you are operating at a different MO than the normal cruise. It would be interesting to see what you get operating at a DA of say 8-9K and WOT and 10-20LOP.
By the way your % power is wrong, some engine settings are not entered right. It should be showing about 79% power.

Just to thro the can among the pidgeons a bit, here is 29.6" MP (yes high QNH) and 2450RPM, about 80dF LOP and a genuine 79% power This was S&L in the cruise at 1000'AMSL. It is true that the denser air helps.