BOP (Buick/Oldsmobile/Pontiac) Aluminum V-8's for Aviation Use
I have seen so much interest and so much mis-information about this engine in RAH (the Rec Aviation Homebuilt) newsgroup that I thought it time to compile what I know in hopes of keeping others from error.
Much of the history of this engine happened before I learned to read. I have never built driven, or flown behind one of these engines, but I have been researching them intermittently for over ten years. For more hands-on experience, Corky Scott's given me permission to post his comments to a Rec Aviation Homebuilt Newsgroup inquiry, and CONTACT! magazine has lots of articles in their back issues that detail the true life experiences of brave auto engine experimenters.
The story of this engine's automotive development, including it's illustrious racing history (drag, Formula 1, road racing), and present status is well-told by other experts.
From the very start of it's life, the high power to weight ratio of this engine attracted people interested in using in airplanes. Much of the following is better documented in Richard Finch's book, Converting Auto Engines for Experimental Aircraft, and in CONTACT! Magazine, issues 11, 19, 25, 36
Oldsmobile's Advertising Stunt
Oldsmobile put one of their turbo engines in a Cessna 175 as an advertising stunt, and made both TV commercials and print ads using it as a prop. It's pretty well detailed in Hugh Macinnes' Turbochargers
Steve Wittman's Direct Drive Conversion
Back when the engine affordability crisis first hit, the redoubtable Steve Wittman spent several years adapting his Tailwind design to use an inverted, direct drive conversion. A larger airframe was used (W-10, the original Tailwind is the W-8). I believe this airplane still exists, it was apparently at Steve's Florida home as late as 1995. He had two forced landing in this airplane, one of which was ignition related, the other due to detonation.
The engine ran inverted to put the prop in the right place. The stock oil pan replaced by a shallow aluminum cover for the crankshaft, and oil drained out of the valve covers to a new external sump. The existing oil pump intake was removed, and replaced with a hose fitting that connected to the new sump. An aircraft updraft carb bolted to the original intake manifold via an adapter. The distributor got an oil slinger and a seal so it could run upside down without filling full of oil. Exhaust went out a simple log manifold, the radiator was horizontal on top of the engine, air exited through the top of the cowl. A transmission bell housing supported a Cadillac front wheel bearing, with a hub for a cut down aluminum prop. The engine ran about 3600 RPM at take off. Aircraft Spruce and Specialty sells plans for this conversion.
The biggest problems were ignition and pistons. At the time (the plans are dated 1978, much of the work was done earlier than that), spark plug wires that had low noise, a hot spark, and long life could not be found. That has changed, as more electronics got into cars with higher performance and high underhood temperatures. Magnecore looks like the best ignition wires, but any of the speed shop brand spiral wound wires are head and shoulders above anything Steve had to work with. They found better pistons, but it also sounds to me like the compression ratio might have been a tad too high to start with.
There is a lot more detail in the conversion plans, and anyone who wants to use this particular engine, or this inverted configuration, should immediately get them from Aircraft Spruce. There is more than enough there for a competent mechanic and/or a machinist with a lathe with a 6 inch swing, and 20 inches between centers, plus a mill or shaper for keyways, to produce a reliable conversion.
Beachner V-8 Special
This self-taught engineer put over 900 hours on his low wing tandem retractable gear design before being killed in it. The engine quit just after takeoff, but started to run again just before his 180 back to the airport resulted in a hard off-field landing. He lived through the crash, but the resulting fire (fuselage tanks) got him. His direct drive conversion used the engine upright, but with an outboard bearing mounted on a bellhousing much like the Wittman conversion. He also tried a mechanically driven supercharger, turbocharging, and a reduction drive.
Morse Aviation/Auto Aviation Development Company/Prowler Gear Drive
This beautiful 1.66 to 1 helical reduction gear conversion featured a complete aircraft style accessory case on the back (front in the car) of the engine for mounting the dual distributors, alternator, vacumn pump, oil pump, hydraulic pump, and starter. Development work was done on a Skybolt, once the engine was sorted out (including aerobatics), it was fitted to an original design all-metal tandem low wing plane that looked like an amalgam of the best of all the WWII fighters. My information is that the developer, George Morse, has passed, and the project, both the engines and the plane, is moribund. Apparently a few engines were sold, and used.
Jess Meyers Belt drive
Jess built a belt drive, bolted it to a Buick, and flew it in his Swift for the next 15 years. It fit under the original cowling. KITPLANES had an extensive article on this project in the Jan. 1987 issue, p. 10, and again in 1989, June, P. 72. Jess is now working with the GM 4.3 litre V-6, and is moving away from this engine, he was kind enough to comment for me:
From: BELTEDAIR@aol.com Date: Fri, 24 Dec 1999 16:56:24 EST Subject: Re:BOP V-8 Ryan, our philosophy from the very beginning has been to keep the engine as stock as possible, We believe that this was our key to success with this engine. We are not at present building drive units for this engine due to the cost of parts that must be obtained from BMW. They are now the owners of the engine. Finding a competent shop that can resleeve the older Buicks was also a problem, other than that it was a great engine. Jess
Shirl Dickey's take off on the Long-EZ uses a drag boat gearbox and a flexible coupling in it's drive train. This installation also had it's teething problems, including at least 2 forced landings. One was due to exhaust heat kindling a little fire in the engine compartment, I think the other was electrical. Issue 28 of CONTACT! has a lengthy article on this design and engine installation. The prototype has been fitted with a Nissan V-6, and I believe it now has a Chevy V-6, although I'm not sure if it's the iron block 4.3L or the smaller 60 degree V-6. Shirl is also moving away from this engine, he sent me this interesting E-mail:
From: Dorothy Dickey Sent: Monday, January 24, 2000 8:46 PM To: Young, Ryan Subject: Re: Engines for E-racers There is nothing wrong with the Buick engine it's just that I no longer favor auto engines for aircraft applications. This is because it is not possible to achieve equivalent reliability and performance of an aircraft engine for the same or less money... So why do it. Shirl -----Original Message----- From: Young, Ryan Date: Tuesday, January 04, 2000 11:52 AM Subject: Engines for E-racers >I seem to recall that you are inching away from the BOP aluminum V-8. What >auto engine are you currently recommending for your design, and why? > >I'm working on a web article on the BOP/Rover V-8. > >Highest Regards, > >Ryan Young
There must be others. E-mail me if you have any details
Things to consider today
First off, the original BOP engines are, by this time, scarce. The last US models were produced over 30 years ago. Junk yards don't hold on to cars forever, the F-85's, Buick Specials and Tempests that held these engines have gone to the crusher a long time ago. Chances are, if you could find one, it would be un-usable due to corrosion, wear, etc. There are exceptions, but they are just that, exceptions.
Rover engines are available, but they are going to run you some money, due the cachet of "British", "Foreign", etc. I see lots of Range Rovers and Discovery's here in Northern California, I'm sure there are plenty of them in junkyards having been "on the roof" or driven into trees, etc. Rover is now owned by BMW, which is not likely to decrease parts cost.
It's tough to get these engines re-sleeved, if they need it. Probably better to throw that block away, and look for another one.
Any junkyard engine should be rebuilt, with a new cam, lifters, timing chain, composite head gasket, no lower head bolts, and Rpi's main bearing stud kit, see their web page.
The Rover engines after 94 are much improved. 3.5 liter before '94, might be okay, but avoid like the plaque 3.9 or larger engines prior to 1994, the blocks WILL crack, it's just a matter of when.
Displacement is your friend, particularly in direct drive installations, which need power at lower RPM. RPI can get you up to 5.2 liter, which will produce 230 hp at 3500 RPM and 310 HP at 4500 RPM. Of course it also cost about 3 times as much as the biggest stock block (4.6 liter, 188 HP at 3500 RPM, 220 at 4500) and about 6 times as much as a rebuilt 3.5 liter.
Watch your compression ratio and deck height, particularly if you are using the Buick 300 crank. These engines were pretty high compression to begin with, and stroking them increases the CR unless the pistons are changed, the block shaved, or both. If you didn't understand the previous paragraph, you have no business trying to fly one of these engines.
It is absolutely crucial to use the best shielded plug wires sold (Magnecor looks pretty good), and use seperators and/or looms to eliminate cross-firing, both Steve Wittman and Jess Meyers reported trouble with sparks jumping from one wire to another at altitude. This can lead to a broken crank, and surely a scarey, rough running engine.
Specialist in this engine
East Coast Rover The chief US agent for Rpi, and very knowledgable in their own right. Located in Maine.
Rpi Engineering These Brits have all the demon tweaks and a VERY informative web site.
Rimmer Engineering Based in Colorado Springs, they have rebuilt engines, and Eaton mechanically driven supercharger kits.
Dan LaGrou (D&D; Fabrications) 8005 Tiffany Almont, MI 48003 810-798-2491 Sells blocks, heads, cranks, anything you might need to build up this engine.
They don't make engines like this anymore - light weight, with relatively large displacement, with a torque peak at RPM low enough to use for direct drive, produced in reasonably large numbers. I don't think there is a more suitable engine in this horsepower class for a direct drive conversion.
But if you are going to use a reduction drive anyway, I believe you are better off chosing a more modern engine. You can get more horsepower per pound, better systems, better fuel economy, etc, and the higher RPM of most modern engines has only moderate marginal impacts on PSRU design. And you can get this for the same, perhaps less money, with an engine that has better parts support.