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Author Topic:   60 degree vs 90 degree engines.
JimU posted 03-10-2003 11:26 AM ET (US)   Profile for JimU   Send Email to JimU  
In a previous thread one respondent implied that there was a qualitative differnnce between 60 and 90 degree blocks on the larger v-6 2 strokes. Brand aside, what are the relative merits of the two? Is there one to avoid? thanks jim
kglinz posted 03-10-2003 11:54 AM ET (US)     Profile for kglinz  Send Email to kglinz     
The main thing is that current Whalers, set up for dual engine installation, are designed for the engines to be mounted on 26" centers. Honda says their BF 225s are designed to be mounted on 26" centers though the engines are more than 29" wide. Yamaha/Merc F225 engines, according the Merc installation instructions, are to be mounted on 28.5" centers. Apparently Whaler is mounting them on 26" centers. Both engines are 60 degree.

Kemp Lindsey

kglinz posted 03-10-2003 12:01 PM ET (US)     Profile for kglinz  Send Email to kglinz     
Correction. Just checked Honda website and they now say the BF225 is only 24.6' wide.
lhg posted 03-10-2003 01:26 PM ET (US)     Profile for lhg    
Mercury invented the 60 degree 2.4/2.5 liter V-6 block for outboards in 1976. The engines outperformed anything else on the market, with smaller displacement, and completely dominated the bass boat and racing industry for years. OMC always used 90 degree, as did Yamaha when they copied OMC's blocks. When Merucy brought out the 3.0 liter engines, it also had the 60 degree Vee, and it also outperforms anything else in it's class in conventional 2-stroke configuration.

When Mercury's patent or trademark expired, OMC quickly converted the V-4 and V-6 150/175 blocks to 60 degree, with a huge increase in performance. Now it seems all of the manufacturers are "closing down" the 90 degree vee engines to 76 degrees or less.
Yamaha's new enignes have abandoned the 90 degree V, in favor or 76 or 60 also.
So there must be something right about the 60 degree block, besides a more compact size.

Perhaps an engineer can fill us in on the reasons why the 90's don't perform as well.

JBCornwell posted 03-10-2003 01:42 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
It is worth noting that the OMC and Bomb 60 degree engines are loop charged, the 90 degree Vs were cross scavenged.

The loopers make more horses on less fuel than the old 90s.

Red sky at night. . .

brisboats posted 03-10-2003 07:31 PM ET (US)     Profile for brisboats  Send Email to brisboats     
Hmmm I would really like to hear an engineers take on this . Horizontally opposed Boxster engines such as Porsche, ferrari and even subaru make some serious horsepower in relation to there displacement. Is there really a corrleation in the degree of the V angle or is it more the efficiency of the engine design? The loopers scavenge the intake and exhaust more efficently and therefore out perform the crossflow design. Or is the narrowing V angle trend because of the popularity of twin engine installations? Would a 2.5 liter V-6 60 degree engine out perform a 2.5 liter V-6 90 degree engine with the exact same compression fuel delivery etc.?


JBCornwell posted 03-10-2003 10:08 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
The 60 degree configuration is easier to balance, but harder to do with cross scavenging because of the space needed for bypass in a cross flow.

Boxers are the easiest of all engines to balance. I have run VW and Corvair engines sitting on a couple of sawhorses.

Red sky at night. . .

Bigshot posted 03-11-2003 09:14 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Cross flow is old school reliable but a gas hog. Loopers are the way to go.
Clark Roberts posted 03-12-2003 08:43 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
For harmonic balance there is an ideal angular separation of the cyls determined by dividing no. of cyls into 360 degrees. For 2 cyl you get 180 degrees (opposed}, 3 cyl = 120 degree radial, 4 cyl = 90 degrees (V4 or radial), 6 cyl = 60degree V6 or radial...etc..etc..etc... anything other than the primary balance configuration will require counterbalance features on crank... blah, blah etc..etc.. Happy Whalin'.. Clark .. Spruce Creek Navy
PS> There's more involved than the above but that's the very basic concept...
jimh posted 03-12-2003 08:48 AM ET (US)     Profile for jimh  Send Email to jimh     
As usual, Clark Roberts has given us a concise answer, and thrown in a formula for good measure!

A corollary question: Does the performance of the motor, particularly the torque, vary with the angle of the V-block?

TonyRich posted 07-14-2006 07:53 AM ET (US)     Profile for TonyRich  Send Email to TonyRich     
The angle of the V does not vary the total output of an engine. Consider a radial aircraft engine of either a 5, 7 or 9 cylinder layout. This can be in banks of cylinders. This would say theat an R2800 cid from Pratt and Whitney would be 2 banks of 9 to give 18 cylinders (DC6 Skymaster by Douglas). 4 banks of 7 would give an R 4360 cid (Boeing B377 Stratocruiser)and 2 rows of 9 would give an R3350cid (Lockheed L1049g constellation). The amount of torque delivered by each design of engine does not matter Inline, V4, V6, V8, V12 radial etc. The ultimate aim is what is best for the user. Some engines are more efficient on fuel than others. If you hark back to the 1950 - 60 era there were reciprocating piston engine aeroplanes flying non stop from California (USA, excuse me I am from Australia) to France on less than 8000gal of fuel. Early Boeing 707's and Douglas DC8's could not fly from Newyork to London without a fuel stop in Gander Newfoundland. It all boils back to BMSFC (Brake mean specific fuel consumption) and what the engine will develop in BMEP (Brake mean effective preasure). Excuse the terms but an engine will use a certain amount of fuel per horsepower hour. This is physics not folklore. I had an OMC Evinrude 2.6 litre V6 crossflow 235 with Boyessen reeds, planed heads, releived crankcase, ported block and it went like what on a 19" boat. Eventually it stopped and was replaced with an OMC Evinrude Looper 2.7L 225. The crossflow would eat any engine for torque and grunt but used much more fuel doing it. The OMC Loopers are much better on fuel but extremely lazy. Mercury's are the same, nothing at the bottom end until engine revs improve the torque pattern. Japanese over head cam engines are typical. You can take a 3.0L Nissan twin turbo v6 that may produce 250hp on unleaded petrol but a 6 litre Chevy V8 will do the same. The Chevvy will still do 600,000 miles but.... The all alloy small engine won't. Physics aside you can't get any better than .5lbs of fuel per horse power hour from an outboard, if it is going to make the horsepower detailed on the cowl. Tunioning aside for special applications as an internal combustion engine is just an air pump.
So if you want 100 HP for an hour you are going to use use 50lbs of fuel (at least).
Mind you the Curtis Wright R3350 Turbo Compound R3350 Radial Aircraft engine on the Lockheed L 1049G Constellation and Prat and Whitney R4360 Turbo Supercharged radial where down to around .4lbs fuel per horse poer hour.
Whaler_bob posted 07-15-2006 10:21 AM ET (US)     Profile for Whaler_bob    
Thanks Tony and Clark!
I always enjoy the tech details and engineering facts.
Regarding old aircraft radials.... it goes to show how ingenious these pioneer engineers were at squeezing every last hp out of and reducing every last ounce of weight while at the same time maximizing fuel efficiency out of the technology of the era. And..... without computers!

pineapplepig posted 07-15-2006 02:57 PM ET (US)     Profile for pineapplepig  Send Email to pineapplepig     
I think one of the issues the original poster was asking about the merits of the two types is why choose a 60 degree over a 90 degree. The question is what sort of boat do you want to mount the engines on as the heavier boat will benefit from the extra 'grunt' and torque of the big block, whereas boats in the 18-25ft range are great platforms for the small block. Take the E Tec range, the great benefit of the small block is that there is a huge weight saving over the big block (110lbs) which in turn means that many boats which cannot take the weight of a pair of 4 strokes or larger block E Tecs, could take the small blocks. I am not sure if this weight saving diference between small and large block equally applies to the heavier 4S?
jimh posted 07-15-2006 07:55 PM ET (US)     Profile for jimh  Send Email to jimh     
Since this discussion began several years ago, there have been other discussions on this same topic. See

for a good discussion. I do not think there is any inherent advantage in a V6 for a 60-degree over other configurations, although the 60-degree configuration does have better natural balance in the design. Here is a good history of the OMC V6 engines, both 90- and 60-degree:

This article cites improvements in casting techniques for making it possible to produce a 60-degree V6 which was introduced in 1991. Also see:

for more discussion of the OMC V6 engines.

Although in the archives you will find many references to a patent held by Mercury regarding the configuration of a 60-degree V6 engine for use as an outboard, there has never been any citation of this patent and its existence is uncertain.

TheHonda V6 also uses a 60-degree block. Suzuki took it a step further and produced a 55-degree V6 engine. Yamaha has a 76-degree V6. I have never heard any explanation for that angle.

an86carrera posted 07-16-2006 11:42 PM ET (US)     Profile for an86carrera  Send Email to an86carrera     
I just did a patent search for this and found nothing. u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=0&f=S&l=50&TERM1=mercury+ marine&FIELD1=ASNM&co1=AND&TERM2=&FIELD2=&d=PTXT

Does Mercury have another name?


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