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glenn654

Well Known Member
My -4 always runs cool except on the hottest Georgia days,then its normal. I have been thinking of experimenting with reducing the size of the cooling air intakes to reduce drag/more speed and more normal temps. Has anyone already done this? What have your results been? Comments?

CAVU,
Glenn
N654RV @ OKZ
 
Yes sure

Yes I did it temporarily with high density foam and speed tape for races. I reduced the inner edge, near the spinner. The plug had a nice curved surface. I can't say how much speed I picked up but recall the temp went up a little, but it was hard to tell how much was from the inlet mod, since I was racing in a warmer climate at full throttle.

I suggest you make temp plugs, tape them on and flight test before permanent mod. I recall the plug at the thickest point reduced the inlet width about 2", but don't recall. I did not play with the height since the baffle and top of the cowl where internally faired in but that is doable as well.

I did not make the mod permanent because the cowl was painted and pretty. If the cowl would have been unpainted I would have incorporated the mod. I spent a MINT on the paint job so I could not bring myself to making the Mod. At some point you say enough is enough and just want to fly.

Separate from the cowl inlet mod, I did other mods to get temps higher, mostly oil temp which was my biggest issue. I always had low low oil temp, which I solved by installing a smaller oil cooler and reducing the airflow to it. I made other baffle mods and got the CHT's balance. Like I put a large block plate on the #1 cyl (front right) and got it in the lows 300's, which was fine.

As far as reducing the inlet area and a new shape, keeping the basic look I would start with the inner corner as I did, followed by reducing the overall height. By making the inlet thinner, less tall probably is much easier than filling in the inner edge of the inlet, where there are fasteners or the hinge pin. The old RV-4 cowls had more leeway when installing them. Some builders made their inlets too tall anyway. You will see that at airshows, where you see inlets that look huge and others narrower.

Measure your current inlet area and start with a 10% decrease in area. Remember shape is important. Don't forget smooth curved shapes and no
abrupt transitions or discontinuities as it enters the baffle if possible.


My ultimate suggestion is try to replicate the Sam James style cowl and plenum. You could do this to a stock cowl. Buy some round inlet rings and fiberglass those in. This would also require you change your baffle to make it a complete "dog house" or sealed upper plenum. Using your existing baffles add a top to it and some transition to the round cowl inlets in the front (made of fiberglass). The round inlets and plenum connect with round flex duct. You may raise the temp a little, but you are sure to gain some speed.
 
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Get the best

I had a O320 and took off a large 9 row Stewart Warner 10599R, which was really for a IO360 or even a 540. Hey I did not know. The RV-4 runs cool any way and this made it even cooler. Blocking air alone did not increase the oil temp enough.

I replaced it with a smaller 6/7 row cooler, I think it was Harrison P/N 8526250. That is the same as a SW Stewart Warner 8406R. I sold the plane, so I can't verify but fairly sure.

I kept the SW 10599R I removed and now using it on my RV-7 with a O360. If you are running a bigger hot setup, like a RV-8 with a IO360, suggest the SW #8432R. It is similar to the SW 10599R but is a double pass. Anyway you want hotter not cooler. SW is my number one choice for any cooler because they cool better and are better quality and design.

Van's sells CLONE coolers, like the "EA OIL COOLER 4211", which I assume is a Positech P20002C (*new part number*). This is a Harrison/SW clone I believe. The 4211 had problems and supposedly Positech made improvements and changed it to a P20002C part number. I would make sure you get the new improved model. Actually I would pass on Positech altogether and get a SW first or one of better brands of clone like Aero Classic or Niagara second.

Notice in Van's catalog also sells a Harrison/Stewart Warner "STYLE" cooler. Not sure what those brand those "STYLE" coolers are, but they are NOT Harrison or SW.

These are the equiv part numbers (to my best knowledge):

- SW #8406R
- Harris #8526250
- Aero Classic #8000075
- Niagara #20002A
- Positech #4211**​
**(Note: new improved 4211 cooler part number 20002C, like the Niagara P/N to add confusion.)

I'd rather have an old SW or old Harrison rebuild/overhaul/cleaned than a clone, but that is me. You will end up still spending more than a new clone but cheaper then a new SW. If you don't have a critical cooling scenario like a RV-4 with a 320 than a clone I assume is fine.

Here is spruce's list of coolers :
http://www.aircraftspruce.com/menus/ep/oilcoolers.html

If you have cooler questions call Pacific, they know RV's and coolers and can point you in the right direction.
http://www.oilcoolers.com/
 
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George - thanks. I was picking up on the point that for most of us these things end up with the oil overcooled, not that many folk appear to hav thought about that. Here in the UK, except for glider towing I rarely see oil temps above the absolute minimum for keeping the oil dry. Small oil coolers are scarce.

Thanks
 
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