The International Cessna^® 170 Association

The cowls on my 48 are fairly worn and almost beyond economic repair. I have a set of 53 cowls, they are slightly different. Question, can they be switched out and is that approved? Yes the 53 has both access doors on the upper cowl.

I’m fairly sure the newer cowl would fit the airplane and engine, but you’d also have to change the baffling too. The cooling system changed completely between ‘52 and ‘53.

cessna170bdriver wrote:I’m fairly sure the newer cowl would fit the airplane and engine, but you’d also have to change the baffling too. The cooling system changed completely between ‘52 and ‘53.

My thinking as well. The early versions had the internal cylinder wrap around baffles and the sealed area is located at the front by the cowl by the two inlets. On the later models (with no internal pressure covers) it seal up tight against the rear where the accessory case mates to the engine. As long as the new cowl fits the same near the front it would make no difference? Not sure...

Sealed area at front.

Does anyone have a picture of the later versions they could share?

The IPC would illustrate it fairly well. You’ll need that IPC if you plan to do this conversion anyway.

gahorn wrote:The IPC would illustrate it fairly well. You’ll need that IPC if you plan to do this conversion anyway.

I have both IPC’s. I guess I didn’t ask correctly, as long as both cowls close off the airflow at the front either will work. Just wondering if anyone has done this before.

Poncho73 wrote:

gahorn wrote:The IPC would illustrate it fairly well. You’ll need that IPC if you plan to do this conversion anyway.

I have both IPC’s. I guess I didn’t ask correctly, as long as both cowls close off the airflow at the front either will work. Just wondering if anyone has done this before.

Cessna did it...
(can’t find that smartazz emoticon).

gahorn wrote:

Poncho73 wrote:

gahorn wrote:The IPC would illustrate it fairly well. You’ll need that IPC if you plan to do this conversion anyway.

I have both IPC’s. I guess I didn’t ask correctly, as long as both cowls close off the airflow at the front either will work. Just wondering if anyone has done this before.

Cessna did it...
(can’t find that smartazz emoticon).

OK, got it. I’m going to see a 53 barn find tomorrow. We will see what that brings.

The original 170,s and 170a all had the plenum chambers over the cylinders and the later 170b,s went to the pressure cowl.
I had a 170a with the plenum chamber and couldn’t wait to go to the pressure cowl when I fitted the 4 banger. That was a big mistake . The plenum chamber is the most efficient system . In the end I have rebuilt the plenum system and fitted the plenum in a form . It’s the most efficient system. It proves that I make mistakes .

ghostflyer wrote:The original 170,s and 170a all had the plenum chambers over the cylinders and the later 170b,s went to the pressure cowl.
I had a 170a with the plenum chamber and couldn’t wait to go to the pressure cowl when I fitted the 4 banger. That was a big mistake . The plenum chamber is the most efficient system . In the end I have rebuilt the plenum system and fitted the plenum in a form . It’s the most efficient system. It proves that I make mistakes .

Just like my 48, I would leave the plenum system too.

ghostflyer wrote:The original 170,s and 170a all had the plenum chambers over the cylinders...

The last year for the internal plenum was the '52 B model.

Bruce is correct, of course. The ‘53 B-model introduced the pressure-cooling cowling and improved cabin heat/ventilation. (And after SN 25612 changed the gear-legs to the handed “lady legs”... no longer interchangeable left/right.)

It is arguable which cooling system is better. Cessna never went back to the previous.

Poncho73 wrote:The cowls on my 48 are fairly worn and almost beyond economic repair. I have a set of 53 cowls, they are slightly different. Question, can they be switched out and is that approved? Yes the 53 has both access doors on the upper cowl.

To get back to the original question, you may be plowing new ground here. I don’t recall anyone saying they have done it and Cessna didn’t ever mix pressure cowls and plenum cowls as far as I know, it was either one way or the other. The first thing to check would be if the pressure cowl has the same screw pattern where it attaches to the boot cowl.

I don’t see why you couldn’t leave the plenum in place and install a pressure cowl as long as you get a good seal around the intake area up front between the plenum and pressure cowl. If you leave the plenum in place and use the pressure cowl, make sure there is no interference between the two which would rub holes in one or the other.

The pressure cowl uses a different rear bulkhead than the plenum but if you wanted to change out the entire cowl/baffle system it might just work.

Approval is another issue I can’t reply to. It might be like changing landing gear, either style is ok?

With my STC for the 4 hangar there isn’t any mention of change of cowling but there was A kit of baffles to be fitted .they had to be modified slightly due to engine differences. Both the baffles and plenum chamber work well. I have had issues with the regulator on this as they are under the impression the plenum should go . Ok show me the paper work where it says I have to. Gee, I love the rules when they go my way.