Onan Spec's

Rich Gillen


I was mainly interested in the Onan Spec's, Weight, HP@rpm, CC they were, since I have never seen one. I wanted to compare them against these Newer Honda/Briggs and about 25 different Clones out there being used in Cart Racing today with many HD Racing parts. The Singles and the Big V Twins are viable Engines for Part 103 and Kitplanes with a few Mods. You can get the V Twins in 43hp@3600rpm with EFI today. Once you strip off what's not needed they are at a reasonable Weight. If you can use some of the HD Racing parts, and some of them are much lighter than the Stock part you can save some weight. I haven't dug into the V Twin Mods as much as I have the Singles. On the Singles, the Biggest Bore Available is 96mm and the Highest Stroker Crank is 86.5mm. But the Engine blocks can be Big Bored to 100mm, there is just no off the shelf pistons for that yet. So (96mm x 86.5mm) 626.3cc, a (100mm x 86.5mm) 679.6cc. 679cc at 5500rpm could probably make about 55-57hp. The Big V Twins can also probably be Big bored to 96mm-100mm.

A Briggs 993 (85.5mm x 86.5mm) 993.6cc.

(100mm x 86.5mm) 1359.2cc  <== Could make around 100-106hp@5500rpm

(96.0mm x 86.5mm) 1252.7  <=== Could make around 93-97hp@5500rpm

And there maybe some Stroker Cranks out there for them. I haven't looked at them that hard yet.

Be interesting to see if a Big V Twin could fit in a Q2.

Compression Chart. Stock 8.0cr  Head is 46cc.

Re: Quickie(Q1) Onan Engine Spec's?

Sat Dec 1, 2018 4:07 pm (PST) . Posted by:

"David J. Gall" davidjgall


The 16 hp was 46 ci and the 18 hp was 48 ci. Onan called them the B46M and B48M, respectively. The Performer Series (P220, etc. that you listed below) were a later generation engine, potentially better but also larger and heavier. I think one experimenter was adapting the P220 but I never saw a full write up or successful test report.

On the B48M, QAC shaved the 18 hp heads and opened up the carb throat and claimed 22.5 hp. Onan designed a new head and rated it at 20 hp. All were direct drive flat head side valve horizontally opposed two cylinder engines, having two crank throws (that’s important for vibration and equal intervals between power pulses). All ratings at 3600 rpm (think 60Hz AC electricity generator engine).

QAC machined the cooling blower vanes off of the flywheel, removed half of the throttle butterfly shaft, and bypassed the built-in governor (but did not remove it).

QAC’s engine mounting scheme was poorly engineered and led to engine oil leakage and gradual failure of the intended vibration isolation, so after some hours in service, engine vibes went directly into the airframe.

I don’t know why you’re interested in this; the engine is obsolete and much better alternatives are available.

David J. Gall
Quickie kit number... oh, hell, it’s been 37 years and I forgot the damn number! ;)

Rich Gillen


You can make you 447 run better by using the Different Engine Coatings available today. Use the Moly Coated Sidewall Pistons with the Ceramic Coated Tops. Ceramic Coat your Heads Combustion Chambers and use the Heat Dis-percent Coating on the Outside. Have your Cylinders Exhaust Ports Ceramic Coated and the Outside Coated with the Heat Dis-percent coating. Have you Wye Pipe Ceramic Coated Inside & Outside. Your Exhaust will last Longer if you also have it Ceramic coated and will lower your Engine compartment temps, if you use all the Coatings your can reduce you Temps by 20%. I would also run the Full Synthetic Oil either Hirths Blue Max or Amsoil Saber at 100:1 Premix. You can do the Coatings yourself in a Free Electric Stove off Cragslist.

Your 447UL is 436cc, 40hp@6500rpm using 9.6cr with a Muffler. A 377/380HO is 368.4cc Stock 48hp@7000rpm with only 30mm Carbs using 11.2cr, and with a better Tuned Pipe dynoed 57.26hp@7000rpm. So your 447UL can make even more HP.

I was interested in the Onan Spec's to compare, account I have been looking at the Honda/Briggs/Clone Singles which are used in Cart Racing today, so lot's of HD Racing parts for all of them. With Big Bores up to 96mm and with Stroker Cranks they go up to 626cc using a 86.5mm Crank. I was mainly looking for a Single that can make 25-35hp for Part 103 that don't need to be turned to high of rpm. A Honda GX340 can make 25hp with not to much work, and a Honda GX390 can make 35hp with not to much work. Even the Honda 270 can be Big Bored and Stroked to about a 360, so the are many Options out there on what you can build. Racer's run these engine's up to 10,000rpm using up to 14.0cr, were thinking 5000-5500rpm Max and Max 11.5. There are 3-4 different Belt Drives out for them.

This is the one I like.

You can buy a Clone Duromax 440 18hp@3600rpm for $289. Take out the Governor and Low Oil Sensor, add a Hi Rev kit $80 (Better Valve Springs, HD Valve Retainers & HD Locks and Chrome Moly Push rods), and add a Bigger 34mm Flat Carb ($34) and a Tuned Exhaust Header ($40), and you got a 35hp@5000rpm Engine. Most people add the Billet Rod and Aluminum Flywheel to cut weigh and if going over 5000rpm. If you go over 5000rpm you want to also use Roller Rockers, which come in (2) Ratio's 1.2 and 1.3 so you get a higher Lift & Dur. Most Racers take out the balance Shaft and just balance the Crank to also Save Weight.

The Big V Twins are also being used 623cc to 993cc, and they can be Big Bored & Stroked also to maybe 1250cc which ca get you up into the 75hp to maybe 95hp range. The Stock 43hp@3600rpm can also come with EFI, some of the Smaller ones also come with EFI. The Highest I have seen turned for Airplane use is 6200rpm.

32.79hp@5500rpm 420cc Engine.


Re: Quickie(Q1) Onan Engine Spec's? [2 Attachments]

Sat Dec 1, 2018 2:20 pm (PST) . Posted by:

"Charlie" oldcolt1972

Hi Rich,
I own one of those. Trust it so much I built my
plane around the 447 that you know I have not flown behind.
I have not seen a dyno curve for the Onan but
expect it has a fairly wide sweet spot but that is far from proven.
My decision to change to the 447 was due to the
Onan's total lack of reliability under load,
especially loads at or beyond the rated power.
As with discussions with you in the past I do not
feel a 447 is the right motor as well to fly
behind especially with a clean plane that will be
in trailing throttle allot during descents.

The Onan was pulling head studs especially with
the shaved heads. I am not sure if problems went
beyond that since back in the '80s word did not
travel very fast if there were "issues".
An engine with the longer strokes might have been
of interest had we known of them at the time but
to me they were still of too little power for
those of us out east on shorter runways.


My 447 is the DC version, the exhaust is full dual stainless chambers. Again never been run. The chambers never got silencers attached to them but utilize mid body outlets which are considerably quilter.

On the 4 strokes there are quite a few 100mm pistons made for single bikes. Might be a proper pin height  to work with.

FWIW all the over 9hp Briggs engines are either Mitsubishi or Dihatsu engines, The larger twins are Dihatsu last I knew. Not sure if this has changed since I am no longer an OEM for them.

I have been working with a few Kohler twins for a few decades, they are pretty damn respectable on their own as well.

David J. Gall


In that case, the specs you found on the tractorforum website for the B43G and B48G (correction to my previous citation) would be the correct specs for the QAC base engines. You should check in at the Small4-strokeEngines yahoo group, and also the Minisport SD-1 sites for the French Briggs conversions.

David J. Gall

Rich Gillen


Ok, Thanks, similar in Size & Weight to the Onan B43G and B48G . I know how to Build these Engines, I was just interested in what CC and if they used Direct Drive or a Belt/Gear Drive originally. These New Singles from Honda/Briggs & these other Clones can make 25-60hp, and the Big V Twins can make a lot more 75-105hp.

I doubt we will see anyone resurrect the Q2 or Q1 as a Fast Build kit unless this 3D Printing Technology comes up with a Cheap Solution, to take advantage of these New Engines. We don't even have anyone making a Good Belt Drive in the USA for these Honda yet.

You can Buy a De-tuned 625 (626.3cc) 23hp Single for $800. ACE makes a nice Belt Drive in India for around $569 for the Singles.  For Big V Twins USD, $ 649 & $ 699.


Ace Belt Drives.



In a message dated 12/4/2018 7:51:33 AM Central Standard Time, Q-Performance@... writes:


Re: Onan Spec's

Mon Dec 3, 2018 9:31 am (PST) . Posted by:

"David J. Gall" davidjgall


In that case, the specs you found on the tractorforum website for the B43G and B48G (correction to my previous citation) would be the correct specs for the QAC base engines. You should check in at the Small4-strokeEngine s yahoo group, and also the Minisport SD-1 sites for the French Briggs conversions.

David J. Gall