More Holman Moody Volvo Outdrive Questions?

[Craig]

Noting the other HM Volvo Outdrive entry, I have noticed in my shop manual that the AQ250 had an option for a lower, so I assume faster, gear ratio than the 270 (the 270's best being 1.61:1). Is the reasoning accurate that boats with the 250's are going to be a little faster (all other things being equal)? The old Powerboat Magazine articles (discussed previously) from March 1970 that critiqued the Donzi 18-2+3 and the Cobalt XV-200 (the Donzi 16 copy) detailed both of these boats equipped with a 302 HM Ford and HM outdrive. They call the drive for both simply the "B Unit" (i.e. they don't say 270, etc.) but while they mention that the B unit had 1.61:1 gears, they also mention an available "A Unit" with 1.35:1 gears. I don't think the 270 had that gear option. Did the 250 and 270 overlap in production years? I love the little "Holman Moody Marine" outdrive plates, but it sure is easier to know what old Volvo drive you have if just says 270, 280, etc. on it like "non HM" Volvos!! Anyway, just for fun, here's the performance of the test boats: They both had, as said earlier 302 Fords (235hp), the "B unit" with 1.61:1 gears, a 14x21 medium cupped 3 blade prop (assume aluminum back then) and a Holley 600 CFM carb. Given all that info., they both ran 51 mph at 5000 rpm's and 4700 rpm's respectively. Not as impressive as nowadays, but not too bad for aluminum props! Back to the 250, 270 thing, are those drives fairly interchangeable??

[mattyboy]

TYPE 250A 1.35:1
TYPE 250B 1.61:1
TYPE 250C 1.85:1
TYPE 250D 2.15:1
out of the volvo book

the 250 is older than the 270, then came the 280, 280t with trim and then the 290

all parts seem to interchange I believe the internals are stronger as the series progressed
H/M might have bought in bulk or had an agreement for so may units that's why they all seem to be 250's you can also tell by the serial numbers start with the model number 250 XXXXXX

Matt

[Craig]

Matt,
I took a look at my book again and have the same info. you posted. Still I was wondering about the 250 being able to get the boat moving faster due to the gear ratio. I guess it would involve horsepower too. I would think it would take more power to get the same boat going "X"mph with 1.35:1 gears than it would with 1.61:1 gears. But it seems that if you had adequate HP, the 1.35:1 gears should be able to go faster. I didn't know, MOST of the HM's are 250's? Seems like I've seen a lot of 270's in the registry. Interesting. Looking at the shop manual drawings a 250 and a 270 look awfully similar, and as I said, if you had the HMM plate on the drive you wouldn't be able to tell what drive it was "quickly." I guess, as you noted, you'd have to check it by the serial #. I've never heard that Holman Moody actually changed any part of the drive other than to put their name plate on it, I guess just to let people know that "their" brand of marinized engine was inside.

[Craig]

What was the deal with the Volvo speedmaster? Did HM ever have their name on any of those? They look cool, but wonder how they act besides probably good speed? Don't look too good for water skiing!!!