"I did the IO-470N conversion on my C35 Bonanza back in 2017. The surgery is major, but not as bad as taking the keel off.  The pieces that are needed to make my C35 into essentially a P35 from the firewall forward are the horseshoe piece in the wheel well and the front "rack" just behind the nosebowl.  This lets me use all the power the mighty IO-470N has to offer subject to airspeed limitations. Below are some photos.

The performance change is dramatic.  Climb is great and it really shines on longer legs at 8-10K.  I can get low 160's ktas at around 10GPH and have seen 172ktas in go fast mode.  The big payoff for me is not having to worry about parts anymore.  I grew up in this particular airplane, so my rationale for making such a financially indefensible decision is somewhat unique.  I plan to fly this airplane until I hang it up.  I think I have a lot of flying left in me.

There are MANY variables that will affect the cost.  Baffles, new or used exhaust, control cables and of course the cost of the engine and prop.  Do not underestimate the value of a running E-series engine.  I had mine sold in less than 24 hours and got many calls after it was sold.  Working electric props are valuable, too.

Admittedly, I went all in with the 'might as wells' such as the BDS baffles, new exhaust, new control cables and painting the engine bay.  I had been collecting E-series parts for a long time so my NET cost was well under $60K. We don't talk about what those parts cost me because they were bought so long ago, so I guess they were free.

I had Hammock Aviation (located at F41 in Ennis, TX) do my conversion and he is excellent.  He has his sterling reputation for a reason.  I consider him a friend and still go to visit when I fly from CT to my inlaws in KC for the holidays.  He has also done at least 15 of these, so he knows the ins and outs.  He also has jigs to get things lined up.  He is also the STC holder for the upgrade.

I don't think there is an option for a straight 35 except for the ARS IO-470N cylinders on the E-225 case STC.  I think you have to use the Hartzell prop in that case.  You also haven't really dodged any E-series parts issues because you are still using the same case, crank, cam, etc.  Nice claimed performance boost, if you can use it (mostly up high).

Doug G.

C35 Bonanza Owner