MEFI Burn Tuning for idle.
08-22-2015, 10:15 PM
#11
I didn't want to go there but since you did I was wondering if that 5 blade Maximus is simply loading the motor up at idle where there is no power/torque for that cam as you alluded to. Conjecture on my part but that's where I'm leaning right now.
08-24-2015, 09:18 AM
#12
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The cam was spec'd out by Erson, I would assume they would know more about cams and motors than all of us, he just said use dry exhaust. Right now, I have seen 75mph in a 02 38 Powerquest that has every single option(AC, Bathroom, shower, full stereo, generator, ETC) with 5 blades at only 5100rpm, so it can't be that far off for that heavy of a boat, and I haven't even adjusted the timing at the top end yet, still only 32 degrees I beleive and somewhat rich(12.0:1).
No load, 60ish KPa, load jumps to 80 then back. I would have to screenshot the values, but I dump fuel in it when it jumps to 80 and then around 60, its significantly less fuel. Never tried a different prop.
Either way, this weekend, I kicked out the mechanical pump, starboard motor quit running but I hear the electric, will only pop every now and then, so I have to fix this now and move from there.
No load, 60ish KPa, load jumps to 80 then back. I would have to screenshot the values, but I dump fuel in it when it jumps to 80 and then around 60, its significantly less fuel. Never tried a different prop.
Either way, this weekend, I kicked out the mechanical pump, starboard motor quit running but I hear the electric, will only pop every now and then, so I have to fix this now and move from there.
08-24-2015, 05:41 PM
#15
The cam was spec'd out by Erson, I would assume they would know more about cams and motors than all of us, he just said use dry exhaust. Right now, I have seen 75mph in a 02 38 Powerquest that has every single option(AC, Bathroom, shower, full stereo, generator, ETC) with 5 blades at only 5100rpm, so it can't be that far off for that heavy of a boat, and I haven't even adjusted the timing at the top end yet, still only 32 degrees I beleive and somewhat rich(12.0:1).
No load, 60ish KPa, load jumps to 80 then back. I would have to screenshot the values, but I dump fuel in it when it jumps to 80 and then around 60, its significantly less fuel. Never tried a different prop.
Either way, this weekend, I kicked out the mechanical pump, starboard motor quit running but I hear the electric, will only pop every now and then, so I have to fix this now and move from there.
No load, 60ish KPa, load jumps to 80 then back. I would have to screenshot the values, but I dump fuel in it when it jumps to 80 and then around 60, its significantly less fuel. Never tried a different prop.
Either way, this weekend, I kicked out the mechanical pump, starboard motor quit running but I hear the electric, will only pop every now and then, so I have to fix this now and move from there.
The load change from 60 to 80 kPa when going into gear is a big jump. Try a smaller pitch and or diameter prop and change nothing else and see if it still stalls going into gear.
Does it stall going into gear on the trailer and hose?
Can you pull more than 5100 rpm with that prop? If not you likely have too much prop.
08-24-2015, 09:26 PM
#16
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Fascinating to think a 502 could be effected by a prop turning 700/1000 rpm's. I have a little 4.3 swinging a 22-18- or 20 until 1400 rpm there is no difference. Actually the boat does not even begin to create a pressure wave until 1600 rpm.
Last edited by Pliant; 08-25-2015 at 11:03 AM.
08-25-2015, 12:25 AM
#17
Prop pitch, blade size, blade count and drive ratio are all significantly different between your application and his. It can make a difference, especially if the cam is tweaked out for top end power and therefore lacks idle grunt.
08-25-2015, 12:47 AM
#18
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1996 I think 502.
Stock 502 with custom Erson roller cam, roller rockers, , valve springs, Stainless marine dry exhaust.
If I recall correctly, cam specs are 244,[email protected], 114 LSA.
IAC counts no load is under 10.
Bravo 1 running 5 blade labbed Maximus.
Stock 502 with custom Erson roller cam, roller rockers, , valve springs, Stainless marine dry exhaust.
If I recall correctly, cam specs are 244,[email protected], 114 LSA.
IAC counts no load is under 10.
Bravo 1 running 5 blade labbed Maximus.
08-25-2015, 09:09 AM
#19
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Will the motor idle at a lower rpm?
The load change from 60 to 80 kPa when going into gear is a big jump. Try a smaller pitch and or diameter prop and change nothing else and see if it still stalls going into gear.
Does it stall going into gear on the trailer and hose?
Can you pull more than 5100 rpm with that prop? If not you likely have too much prop.
The load change from 60 to 80 kPa when going into gear is a big jump. Try a smaller pitch and or diameter prop and change nothing else and see if it still stalls going into gear.
Does it stall going into gear on the trailer and hose?
Can you pull more than 5100 rpm with that prop? If not you likely have too much prop.
It does not stall on the trailer going in gear, and I am sending the props down to Frank and Jimmies in FL over the winter for a little pitch change since they are the ones that labbed them originally, and they did an excellent job guessing at a brand new combo.
08-25-2015, 02:51 PM
#20
Not really wanting to change the prop, I think that would be going the wrong direction... I can cruise almost 55mph at 3500 with this prop, and not willing to give that up until I have exhausted all other options. Idle with both motors in gear is around 6-7mph.
It does not stall on the trailer going in gear, and I am sending the props down to Frank and Jimmies in FL over the winter for a little pitch change since they are the ones that labbed them originally, and they did an excellent job guessing at a brand new combo.
It does not stall on the trailer going in gear, and I am sending the props down to Frank and Jimmies in FL over the winter for a little pitch change since they are the ones that labbed them originally, and they did an excellent job guessing at a brand new combo.
Two points.
1) I only suggest trying a smaller prop for test purposes only regarding stalling when going into gear. The fact that it doesn't do it on the trailer suggests a propeller load issue.
2) If you can't pull more than 5100 rpm you aren't likely hitting peak HP with those cams. If you CAN pull more than 5100 rpm, does the motor reach peak HP rpm with your current props?
