Honda 75 vs 90?

[Gregw]

I was looking over the Honda marine site this morning, comparing the 75efi and 90efi. They have test results for both motors on the C-dory 22 cruiser. The 75 outperforms the 90 in speed / RPM and MPG up until about 4250 rpm where they are equal at approx. 22mph (the 75 get slightly better mileage). Above 4250rpm the 90 goes faster with a 2.5mph advantage. Seems like the 75 is the way to go, but I'm sure there is more to it, help me understand.

The 75 was tested with a 13 3/4 x 15 in, 3 blade prop, aluminum (3086lbs)

The 90 was tested with a 13 1/4 x 17 in, 3 blade prop, stainless(3214lbs)
and a 13 1/4 x 18 in, 3 blade prop, stainless(3214lbs)- (this set-up did much worse)

Did the weight difference of 128lbs make the difference or the different prop, would the 90 do as well if it had the 13 3/4 x 15 in. prop?

[Sea Wolf]

GregW-

The 75 and 90 are probably the same engine with different fuel injection programing and perhaps a larger air intake for the 90. Most manufacturers make two or more engines out of each basic engine block they make for cost reasons.

The chief advantage of the larger 90 will be if you want to carry heavy loads of persons or gear. It's absolutely amazing how much stuff cruising folks accumulate in their boats over a year or more of time. 300-400 lbs is not uncommon. Also, if you take out four or more persons on a a day cruise, you'll appreciate the extra HP.

I'll guess the chief reason the 75 outperforms the 90 below 4200 rpm is because of the steeper 17" pitch prop on the 90 as opposed to the easier to turn 15" pitch on the 75. The 90 would probably have identical numbers with the 75 with the 15" prop. Note the increased negative effect of the increased 18" on the 90 with that prop switch. The steeper 17" pitch allows the 90 to reach a higher speed at full rpm where the extra HP is developed. Unfortunately, we don't see the chart/graph and cannot tell at what rpm the engines top out with the different props.

I have had 15" and 17" pitch props on two different 90 HP engines on my C-Dory 22. The 15"s turn easier and accelerate better. The 17"s are OK, and go a little faster, but I think they lug the engines a little (top rpm 5000-5300 rpm). Better yet would be a four blade 15" prop which would still use the HP, not vibrate, accelerate very well, and slip less, and therefore reach full rpm and good speed.

128 lbs of weight will make a difference, but probably only 5% or so.

My quick $0.02 on a rainy Sunday afternoon!

Good Luck!

Joe.

[Gregw]

Thanks Joe, Yep, I'm stuck inside today as well.

" Unfortunately, we don't see the chart/graph and cannot tell at what rpm the engines top out with the different props. "

The chart I'm looking at on the Honda Marine site does show this;

90hp WOT (17in) = 5400rpm, 32.9mph, 4.4mpg

90hp WOT (18in) = 5100rpm, 28.5mph, 3.9mpg

75hp WOT (15in) = 5500rpm, 30.36mph, 4.47mpg

The 75 hp test is loaded with 800lbs of people, fuel, equipment etc. on top of the weight of the boat and motor, is that considered light?

[rogerbum]

3 typical american males = 540lbs (or more).
40 gallons of gasoline = 240 lbs.
The contents of my norcold fridge (about 24 cans of soda + food) = 40 lbs.
Other food + pots and pans = 40lbs
My tools, spare parts, extra anchor = 100lb
My fishing gear including 2 down riggers and extra downrigger weights = 150lb
10 gallons of water = 80 lbs

That's about 1200 lbs and that doesn't include my blankets, books and charts, electronics, camera, flares and other safety gear, spare clothes, 2 (or more) bottles of wine, the first aid kit and medicines, the diesel for the stove/heater, the porta-potty, the ice chest, ice, the fish I have on board, the fenders, boat hook and paddle etc. So, yes, 800lbs is light.

[westward]

I may be mistaken on this, but I believe that only the 90 has VTEC, a clear advantage. Given that they're the same weight I'd go with the 90, which I almost did. Mike.

[westward]

Sorry, I just caught that the test 75 had a 2" lower pitch prop than the 90. That alone explains all of the low end performance delta and is further argument for choosing the 90.

[Sea Wolf]

Thanks, Roger!

That's quite a complete list!

My comment of 300-400 lbs was intended to reflect the additional loaded on weight of gear, and not persons, fuel, water, kicker, extra batteries, etc.

I'm sure my CD-22 weighs 3300 lbs or more, just from the weight calculated from the motor and necessary accessories, and the on board list of absolute must-have necessities!

Glad I have the 90 to push things along. Tried to buy a 115, but the dealer wouldn't install it! (Liability issues)

Joe.

[Gregw]

[starcrafttom]

if you are getting a new boat then you can have a 115hp. get the lightest engine that you can. Also of note, was that info for the old carbureted engine or the new fuel injected models?? the new FI 90 honda makes 110 hp not 90 and weighs less then the older model. and c-dory with a new 90 is going to out run a older, last year, 90 with carbs.

[tpbrady]

Greg

I don't think many people are running a 17 pitch prop on carbureted Honda 90. I have used on on my VTEC 90 and it does reasonably well on economy at higher speeds, but not suffers from lack of responsiveness when loaded in heavy seas. The optimum prop at this juncture seems to be either a 15 pitch 4 blade Solas or 15 pitch stainless 3 bade. I have two more props to experiment with and then my collection will be complete. They are a 14 pitch stainless 3 blade Quicksilver and the same prop in 16 pitch. The programmed fuel injection seems to pose some unique problems in prop selection, since it has some operating characteristics that would make running a lower pitch prop an advantage. You trade off top end for more economical mid range cruising (12-15 mph). You could really see it when running a 13 pitch prop but the advantage disappeared after 15 mph. The fuel economy on the 17 pitch prop didn't equal the 13 pitch prop until the speed approached 20 mph and at the low end was a lot worse. The 13 pitch prop also resulted in a little too much RPM at WOT.

So the experiment continues. I am suspecting the 14 pitch might yield the best results given the loading of my boat and the sea conditions I spend most of my time in.

Tom

[thataway]

I didn't find the comparison of the 75 and 90 on the C Dory site--I did find the two 40's vs the 75. On the Honda Site, I did find the C dory with 90 and 75--the 90 in 1999 and the 75 in 1996, Neither of these are the current engine, the EFI engines are newer engines and I believe that both engines are carburated in the Honda site comparison. The efi in the 75 and 90 were introduced in Sept 2006.

I would go with the 90. Almost always we end up with more gear and weight onboard--also if you prop correctly there should be little difference in the mileage between the two engines. These tests with light boats are fair for a comparison, but one has to look at all of the factors. Props are a huge factor, not only pitch, but blade number, cupping etc.

[journey on]

This is similar to the choice between a Honda 135 or 150 for a C-25. The Honda 90 is the same as the 75, with the addition of VTEC (listed under Specifications/Fuel Delivery.) They also have two ignition curves, torque and high end (called Blast.)

The majority of the C-25 buyers chose the 150 and I suspect that the majority of the C-22 buyers will chose the 90. Personally, there have been a few times I was glad that I had the higher HP, even though it's only above 4000 rpm. Cruising boats do get heavily loaded, as do cruising skippers.

The new 75/90 is smaller (1496 cc) and lighter than the older 75/90.

Boris

[BoatLine]

The main difference between the Honda 90 efi and 75 is the variable valve timing (V-tec) which kicks in at 5300 r.p.m. which may not be that useful on a C-dory 22. On the other hand, our price for the 90 is only $481 more than the 75 (check our web site).

[westward]

Seems like I read somewhere that the new generation of Honda VTEC variable valve timing had 3 modes, the first being intended for ultra low emissions while idling. I could be mistaken. Mike.