Low Presti cowling

[KJB]

Hi all,
I own a PA30C, 1967, Turbo. With Top overhauled engines and after nearly all renovated, like new baffles, gamis, injection, ignition and remove of obstructions, It runs excellent. But I still have a hot CHT, RH,3rd cylinder. Does somebody experienced Low Prestis cowlings and can second his affirmations about better airflow and better cooling.
Appreceate your comments.
KJB

[Zach Grant L1011jock]

Your baffle is too tight on the #3. It is a flat baffle, and the fins are too short on that side of the cyl, and when it is pulled tight up against the cyl, no air can pass behind it and cool the cyl. Simple fix is the bend the baffle so it does not fit tighty agaist the back side of the #3 cyl. The more elegant fix is the box out the baffle allowing more air to pass improving cooling. As far as the Lopresti nose bowls go, I think they may get more cooling air in at speed, but not on the ground or in a slow climb.
-Zach

[N3322G]

Let me add my experience to Zach's regarding baffles. Frequently when someone else puts the cowls back on the engines, the flexible baffle material is bent in the wrong direction and so they don't fulfill their purpose of directing airflow over and around the cylinders.

I've also found that after adding new flexible baffles, there were lots of holes/gaps and once they were filled, the engines temps dropped 20 degrees across all cylinders for the same flight conditions.

With respect to LoPresti cowls and cooling, I have a different perspective. We raced the twin for decades with stock cowls and as the right seat person my job was to watch the one-probe CHT gauges provided by Piper so that when it reached mid-gauge or about 400 degrees, I opened the cowl flaps - obviously, it slowed us down so we only did it to keep from frying the engines. The number of incidents were noticeable and usually occurred on steep climb outs in the summer in mountains.

After Mom got the LoPresti cowls, we found no requirement to open the cowl flaps when racing - no matter how long the steep climb or how hot the temps. So using the same measurement criteria and roughly the same conditions and pilot, I would say the LoPresti cowl cools better than the old stock cowl in all configurations.

Then we added the JPI engine monitor - this gave us a lot more information and we get it a lot faster. With newer faster information, we do open the cowl flaps more often when doing back to back practice approaches or steep climb-outs when the ground temp is 104 on the ramp. I suspect we would have done the same with the old stock cowls but we just didn't have the same quality of speed of information that we get now.

Your experience may vary.

Hopefully, the flexible baffle tip helps.

[KJB]

Thanks Pat + Zach,
Generally I must say this airplane is great and runs fantastic and I`m quiet satisfied.
What I`m trying now is just a kind of fine- tuning. Level 130-150 it runs 165-175kn TAS on 7,8- 8,4 Gal/h, rich of peak. With better cooling the Nº3, it could go with less, or even faster.
On the ramp or on climb I only operate with cowl flaps open, established in cruise I control the CHT with the EDM760, which makes me playing, open to close, with the Cowl flaps.
About the bent of the baffles, that opened a new aspect in my efforts, which I will work out. Your answers helped to me a lot.
If I have no gain in cooling, I `ll contact Mr.LoPresti.
Blue skies
Klaus.
P.S.: Pat, I saw you and your airplane with all the stickers of the world race some 5 years ago on a friendly warm summer day on the ramp in Waco.I stayed in Arlington and I had been around with a 172 from Skymates working on my Instrumental.
When I saw your airplane, I knew that`s the one! a year later I purchased N11YY.
Next time in Texas , I pay the drinks!

[N3322G]

Klaus,

Glad to try and help.

The twin has been painted since you last saw it but we reserved a place for the 1994 world decal. Still used the colors mom selected and it still looks fast - even when its on the ramp.

[N8632Y]

Klaus,
I too own 69 twinky, non T....and have chased 3rd cyl temps for years.
I went to the Lopresti cowls and found they help, sometimes.
The key is the shape of the bowl and the induction air.
In high speed cruise, the plane has a low angle of attack, and this is where the
bowls work, but, by the same token, increase the angle of attack, such as in low speeds, like training and slow flight
steep climb outs, or simply sitting on the ground, waiting for clearance and having the xwind blow "across" the nose bowl,
which will suck the air out of your engines, giving you a reverse benefit of the bowls.
I use my JPI to climb out 150-200 ROP, and at high altitudes, ROP.
I found I'd rather fly 55% pwr, 75 ROP, than
60% at peak, get same fuel flow and speeds, but better temps,,,about...

steve