Avstar Aircraft of Washington, Inc.

10415 172nd St. E., Hangar A1
Puyallup, WA  98374
office (253)770-9964
or (253)770-0120
email:  avstarair@att.net

04-10-2008 Ask Mike! Archive Page
Discussion on upgrading the engine in a Bonanza

(The following is an engine conversion discussion, edited and placed in order for easier reading.)
I saw the pictures of the M35 Bonanza engine conversion you did, and am interested in a rough estimate of the cost.

I have a 59 K35 Bonanza, with the original IO470C and Beech 278 prop.  I’m considering upgrading to the IO550B, but am having difficulty finding a shop that has done this conversion, so I can put the numbers together and see if it would be economically feasible for me.


Hi Marvin;
For planning purposes, look at approx. $38,000.00, plus the cost of the engine.  That would cover the "normal" engine change items (labor, governor, exhaust, air pump, hoses, etc.) plus the baffles, STC, prop, engine gauges, with air box and nose bowl change.
(It would not make economic sense for me to sell you the engine, as we would both pay the same price.)
The nice thing about a K35 is it already has the upgraded structure to handle the extra ponies.
If you would like a definitive estimate for this project, I would need to see the airplane first.  Naturally, we would be happy to assist you with this project.  Call if any questions.
Gear Green,
Hi, Mike,
Thanks for the quick response to my question.  I don't think I can swing the IO550, but I appreciate you giving me a realistic cost estimate.  I have my K35 equipped the way I want, and my only desire is to have more power on the summer days here in Colorado when the density altitude is 8000+.
I'm going to look at other options, including the Chuck Ney STC using 520 cylinders on my 470 case.
I'm sorry I'm not closer to your shop.  The pictures on your web site looks like you have a very professional operation there, and your customers are fortunate to have you to look after their aircraft.

No problem Marvin.  We installed S/N 2 conversion of a Chuck Ney engine in a J35 last spring.
Things to consider during the installation:

  • Put in the 520/550 air box; that will gain you about an inch of MAP.  The J we did this to needed an air box anyway, and it made sense.
  • Don't let him sell you the 'large' oil cooler; although it will fit the airplane, you will have to bastardize the engine baffles to make them fit around it.  And, you won't need it.
  • Get the D'Shannon engine baffles anyway; if yours are original, they are probably very tired.
  • If you run it according to the book, it's still only 260 HP.  (Granted, more of the 260 will be available to you at 8000 feet.)

The gentleman we did that installation for put about 230 hours on it last year, we just finished his annual for this year.  He likes the engine, but has commented that if he was to do it again, he would have done a 550.
If you're ever in the area, swing by; the coffee pot is always on.
Gear Green,

Thanks for the invite.  I have one more question about engine conversions.

Do you have experience installing a IO520/550 in a H thru P Bonanza without changing the nose bowl, leaving the engine straight, not canted?

I've seen some Bonanzas with the IO520 installed straight, but am not sure if that saves a lot of money, or if it creates too many problems aerodynamically.

Thanks again for your suggestions on the Ney conversion. 


The 520 and 550 are both approved in the H thru P Bonanzas on the straight mounts.  However, you need to limit MAP on the 550 installations (by the book) so you only have 285 HP unless you cant the mount, which necessitates changing the nose bowl.  At your elevation, shouldn't be a concern, but something to keep in mind when visiting the low-lands.  A couple of years ago, I met a fellow that has a J with the 550 on straight mounts; his eyes got real big when he told me you never use full throttle on take off with a right cross wind.  Runs out of rudder.  That said, yes, we have installed the 520's on straight mounts in both the V-tails and the Debonairs.  This will require the aircraft to be properly rigged to start, then some tweaking on the trim system to compensate for the yaw.  A little time consuming, but worth it.
Gear Green,