1978 201J model

[Daryl DeBetta]

  My partner and I own a 1978 J model and in a couple of years (maybe sooner depending on flying times) we will need to overhaul our io360 A3B6D and prop.  My question to all out there is : what would performance gains be verses dollars spent for upgrading to a 210 hp io390 non turbo, also with adding a power flow exhaust system (which will be needed at time of overhaul)?  We currently have every LoPresti speed mod on the aircraft now and we cruise at 153 kts @ a planned 10gph (exact is 9.7) 50 degrees ROP

[Bartman]

I considered the IO390, but its a big chunk of change. There may be other reasons to upgrade such as roller cam followers, but I don't think top speed performance is one of them. My 77 J will do 159 knots and except for the Powerflow it is stock straight out of the box on a 1900 hour engine with stock injectors, and others are a few knots faster without any modifications. If you are only doing 153 then I'd check rigging and gear doors to ensure complete closure.  As far as the Powerflow, I'm not convinced I see any increase in speed, but probably do see some improvements in climb power.  Most people don't run 50 ROP as this is the highest cylinder pressure fuel flow. I'm usually 10 deg LOP on about 8.6 gph, or if I'm ROP then I go for 125 ROP and if memory is correct that's about 11 gph but I don't run there much. 

For me, I have decided to keep running my 1900 hr engine and when the time comes we will rebuild it. I have been blesssed to have an IA who has run a high performance engine shop for racing engines who became a pilot then an IA. We have discussed it and since I will likely keep the plane, I will have him rebuild it and send out what we have to. If I was thinking of selling I would go for a high profile shop or rebuilt exchange, or maybe even the IO390. 

[Bob - S50]

In theory, I think a 5% increase in power (200 --> 210) would give you about a 2.5% increase in speed.  That would bump your 153 up to about 156 or 157.

However, I agree that you should probably be getting more speed than that, especially if you have the LoPresti speed mod.

I've found that our '78 J will do about 162 - 164 KTAS (147 KIAS) at 7500' DA, at 75% power (10 GPH/barely LOP), with just me on board (2140 lb gross wt).

Of course your true will depend on your altitude.

[Vance Harral]

32 minutes ago, Bob - S50 said:

In theory, I think a 5% increase in power (200 --> 210) would give you about a 2.5% increase in speed.

Airspeed is proportional to power cubed, not squared.  A 5% increase in power only gives you about a 1.7% increase in speed, i.e. 153 KTAS becomes 155.6 knots.

There may be some good reasons to go with the IO-390, but cruise speed isn't one of them.

[jetdriven]

It’s only 7.5 HP at altitude. 75% of ten HP. 20-30k is a lot of Money to pay for 2 knots. 

[bradp]

What about your engine is saying it needs to be overhauled right now? Besides time of course??? Bad compressions? Making metal?  Long periods of non use? Etc.  if there is nothing wrong with your engine keep flying it until it starts telling you it wants to be overhauled, but you need to have the ability to listen to your engine.  I’d be more confident in a 2000hr engine that has been listened to and cared for over a newly overhauled.  

Do you have an engine monitor with download capabilities?   That will do more for your flying enjoyment than either an exhaust or 10 HP upgrade.  

Someone I met last summer said he got maybe 1-2 kts from the lopresti cowl.  I just parked my standard J next to what I think is an E with a lopresti cowl tonight.  If I run into the pilot tomorrow I’ll ask their experience with the cowl.

You should be getting a higher TAS if you are running in that power range of 50 ROP.  

Please do your engine a favor and prolong its life by either going richer or LOP.  Where you are running now is right in the red box.  

If Inwas overhauling a 78J id keep the 200 HP and convert to a single mag each side (A3B6) instead of the dual (A3B6D)  

[carusoam]

Put it in the category of the fancy cowling on your bird already...

The fancy muffler you have...

The extra HP and fancy roller tappers are expensive improvements...

The only other way to get these improvements is to get them with the plane when you buy it...

Are they real improvements...? Yes.

Worth It? Depends who is paying for it...

Are you building the best example of an M20J..? Go for it...

Would you be more interested in a turbo normalizer for that?

quick review...

1) improved aerodynamics is a great way to improve Cruise speed.

2) improved power is a great way to improve T/O run and climb rate.

3) more power is an expensive way of going a little faster. Increased FF to go with that.

PP questions and ideas only...

Best regards,

-a-