difference between 33 and 35HP OMCs?

[adam1961]

Does anybody know where the two horsepower went when they brought the 40.5 cubic inch bigtwin block back as the 33 in the late 60’s? Was there an actual change, or just a rating issue?

Adam

[chinewalker]

Marketing… You’d be hard pressed to find any real world performance difference between the two…

[garry-in-michigan]

I believe it was a reduction in compression ratio to make it easier to crank and give it a smoother idle. It allowed them to eliminate the starter compression relief valve in the head and evened out the horse power range (20 to 33 to 40) . . . 😉

[1946zephyr]

Yep, just like Garry said. Funny thing is too, the 33 still has the same head. Just the casting was changed, to remove the compression relief feature.

[adam1961]

Great!
Thanks for the information. I had a feeling this was the case.
Does the 33 have the larger crank top end like the ’62+ 40 HP? or is it the same as the late ’50s 35HP bigtwins?

[chinewalker]

Bigger crank.

[billw]

Nice runners. Mine always reminded me of a giant 18.

Long live American manufacturing!

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