pcrussell50
Petty Officer 1st Class
- Joined
- Sep 21, 2008
- Messages
- 296
so far, i've had my "fast little boat" for about a year. it's a stripped down 16 footer with a classic performance hull, [bass boat'ish proportions], and it's powered by a 1975 v4 crossflow, 135hp evinrude. i don't have a single problem with this motor, and i love it!
i post about this boat and motor over on the "fast outboard boat " forums, [screamandfly.com]. and a few of them over there have this motor too. the senior members who ought to know, almost universally recommend that i use more than the 91 octane pump gas we have here in the southwest. they say this motor has a high ring stack and doesn't stand up well to detonation. sounds reasonable to me.
here's what's been going on: i've been using this boat just fine for the last year using the wimpy 91 we have around here, [unknowing about the requirement for high octane fuel], and things have been fine. BUT, the boat has been severely under-propped. i can't run it at full throttle once it's up on plane because it will easily go way past 6000rpm, so i throttle back a good deal to keep it at 5800 rpm. so this motor has never really seen a heavy loading scenario, where the octane of the fuel is put to the test.
here's what's about to change: i got a coarser prop that will hopefully allow me to realize some more speed and also be able to finally run it at full throttle. if i chose the prop right, i will get 5500rpm or so at full throttle, and that WILL put the octane of the fuel to the test. it'll be a couple of months before i can try it out because my wife is due with our first baby in 3 weeks, so i have time to ruminate and figure out how to find race fuel to mix with pump gas in between needles, ca and bullhead city, az.
anyway, what do you all know about the requirement for early v4 crossflows to use higher than 91 octane fuel?
also, in the car hobby, one might also back down the WOT spark timing advance a little. i'm new enough to this, that i do not know if there is a way to leave the idle timing as-is, but lop a little of the top? how involved is it to set the timing on big two strokes? i've got all the automotive tools for this, but don't know what i need to do an outboard.
peter
santa barbara, ca
i post about this boat and motor over on the "fast outboard boat " forums, [screamandfly.com]. and a few of them over there have this motor too. the senior members who ought to know, almost universally recommend that i use more than the 91 octane pump gas we have here in the southwest. they say this motor has a high ring stack and doesn't stand up well to detonation. sounds reasonable to me.
here's what's been going on: i've been using this boat just fine for the last year using the wimpy 91 we have around here, [unknowing about the requirement for high octane fuel], and things have been fine. BUT, the boat has been severely under-propped. i can't run it at full throttle once it's up on plane because it will easily go way past 6000rpm, so i throttle back a good deal to keep it at 5800 rpm. so this motor has never really seen a heavy loading scenario, where the octane of the fuel is put to the test.
here's what's about to change: i got a coarser prop that will hopefully allow me to realize some more speed and also be able to finally run it at full throttle. if i chose the prop right, i will get 5500rpm or so at full throttle, and that WILL put the octane of the fuel to the test. it'll be a couple of months before i can try it out because my wife is due with our first baby in 3 weeks, so i have time to ruminate and figure out how to find race fuel to mix with pump gas in between needles, ca and bullhead city, az.
anyway, what do you all know about the requirement for early v4 crossflows to use higher than 91 octane fuel?
also, in the car hobby, one might also back down the WOT spark timing advance a little. i'm new enough to this, that i do not know if there is a way to leave the idle timing as-is, but lop a little of the top? how involved is it to set the timing on big two strokes? i've got all the automotive tools for this, but don't know what i need to do an outboard.
peter
santa barbara, ca
]*then i do a couple of speed runs while she's gone, then recover the boat. 1.5 gallons. maybe 20 minutes of running/day.