Top speed run with B1 26 pitch
Yesterday, 11:08 AM
#31
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1. Replaced the failed lifters port engine #5 cylinder.
2. Re adjusted all the valves both engines for proper pre load. I was in both engines over the winter aligning the rockers and not sure I did the pre load correctly meaning the valves in the correct position plus comp says 1/2 turn of pre load and I did 1/4.
3. Got the carbs and the AFR numbers dialed in better.
4. Advanced the timing on both engines to 35 degrees from 33. From what I've read this is probably helping out the afr readings at least at idle where like I said I was in the upper 9's and low 10's.
Yesterday, 11:09 AM
#32
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hpmaniac (Yesterday)
Yesterday, 11:26 AM
#33
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Is the rule of thumb about adding or subtracting 2" of pitch equaling approx 400 rpm linear?? From my almost "$2,000.00 now experience" it's not. I am wondering if the jump to 28" pitch props is an exponential jump in the boating world.
Last year I borrowed a set of 28's and a set of 26's both B-1's and both sets of props didn't really match each other as a set whether different years and Mercury changed the style of the blades or maybe some repairs were made to one and not the other. The point is both sets were used, visibly different from each other and unknown history. Both sets ran fine in fact, both of these sets rendered better top speeds than these new ones.
Based on last years performance and my goal of running a WOT of 5k rpm I bought 28" B-1's. Seemed like a logical move because I was running around 53-5400 rpm with the 26" and the speed was 78mph. I was really hoping to bury my speedo at 80 with the new setup. I finally get out on the water with the new props and my speed is down to about 73 and the rpm is 44-4500. My disappointment at that moment couldn't be measured....
The first question is always about trim and I know there are variables so this is just FYI. I have the mechanical indicators for drives and I am just above 7 out of 8 so it's trimmed out pretty far and feels like it too. I don't have any problems getting on plane with the 28's and the mid range cruise is fantastic! At 3600 rpm I'm running 60 mph. That used to be my wot speed! Carbs are mechanical secondary's and are opening fully. I did bump the timing from 33 last year to 35 degrees all in this year. Normally that makes the engines run stronger right? AFR's are in the mid 11's. Last year with the carb issues I think the AFR's were in the 10's. It was pig rich everywhere.
So my question is whether its better (good idea) to have these 28's changed to 27's or just buy the 26's? Maybe a new set of 26's would run at the 5k rpm I'm looking for?
Neither will happen this season because the 26's were out of stock till the fall and I'm hoping to get some actual boating in this season and don't want to wait for these 28's to get altered.
As always, I appreciate your help and input.
Last year I borrowed a set of 28's and a set of 26's both B-1's and both sets of props didn't really match each other as a set whether different years and Mercury changed the style of the blades or maybe some repairs were made to one and not the other. The point is both sets were used, visibly different from each other and unknown history. Both sets ran fine in fact, both of these sets rendered better top speeds than these new ones.
Based on last years performance and my goal of running a WOT of 5k rpm I bought 28" B-1's. Seemed like a logical move because I was running around 53-5400 rpm with the 26" and the speed was 78mph. I was really hoping to bury my speedo at 80 with the new setup. I finally get out on the water with the new props and my speed is down to about 73 and the rpm is 44-4500. My disappointment at that moment couldn't be measured....
The first question is always about trim and I know there are variables so this is just FYI. I have the mechanical indicators for drives and I am just above 7 out of 8 so it's trimmed out pretty far and feels like it too. I don't have any problems getting on plane with the 28's and the mid range cruise is fantastic! At 3600 rpm I'm running 60 mph. That used to be my wot speed! Carbs are mechanical secondary's and are opening fully. I did bump the timing from 33 last year to 35 degrees all in this year. Normally that makes the engines run stronger right? AFR's are in the mid 11's. Last year with the carb issues I think the AFR's were in the 10's. It was pig rich everywhere.
So my question is whether its better (good idea) to have these 28's changed to 27's or just buy the 26's? Maybe a new set of 26's would run at the 5k rpm I'm looking for?
Neither will happen this season because the 26's were out of stock till the fall and I'm hoping to get some actual boating in this season and don't want to wait for these 28's to get altered.
As always, I appreciate your help and input.
While all f my prop tweaking experience comes from racing model boats, I've got a number of friends who have made the transition from models to full size hydroplanes, and they indicate the dynamics are the same, even I they don't scale perfectly. Physics is still physics. In a lot of ways, learning from the tiny little props (respectively) we use for model boats translates into better understanding of how our larger props work.
It's been my experience that depitched props are far less efficient that a pitched-up prop of the same resulting pitch. Pitch progression is a large part of how well a prop actually moves water. Depitching also decreases the progression ratio, while increasing pitch typically also increases progression. Think of rolling a ball against a wall or up a quarterpipe. The ball will just bounce off a wall while it will roll up the quarterpipe, eventually rolling up a vertical wall. The water sees the same dynamic when the prop slices into it.
I'd have to think that Merc has the proper progression pretty well worked out (for each model line, anyhow), and I tend to believe that starting with the right pitch and the proper progression is ideal, but, if I had to choose one way over the other, I'd probably go with pitching up to your ideal pitch, as opposed to down.
My 2-1/2 cents, anyway....
Thanks. Brad.
Yesterday, 11:32 AM
#34
crank engine and watch vales with a remote start.
As the exhaust valve just starts to open adjust intake on that cylinder, as the intake is closing adjust exhaust. This is 100% the best way to do it. On hydraulic roller bbc engines i like 1/2 turn preload.
Yesterday, 11:38 AM
#35
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Thread Starter
Put on a polymer 1 inch carb spacer, Every engine i have been on dyno with has gained 12-20 hp with these spacers. Look them up. Also the best way to adjust valves is this, and this is how nascar and prostock do it.
crank engine and watch vales with a remote start.
As the exhaust valve just starts to open adjust intake on that cylinder, as the intake is closing adjust exhaust. This is 100% the best way to do it. On hydraulic roller bbc engines i like 1/2 turn preload.
crank engine and watch vales with a remote start.
As the exhaust valve just starts to open adjust intake on that cylinder, as the intake is closing adjust exhaust. This is 100% the best way to do it. On hydraulic roller bbc engines i like 1/2 turn preload.
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hpmaniac (Today)
Yesterday, 11:41 AM
#36
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Rob,
While all f my prop tweaking experience comes from racing model boats, I've got a number of friends who have made the transition from models to full size hydroplanes, and they indicate the dynamics are the same, even I they don't scale perfectly. Physics is still physics. In a lot of ways, learning from the tiny little props (respectively) we use for model boats translates into better understanding of how our larger props work.
It's been my experience that depitched props are far less efficient that a pitched-up prop of the same resulting pitch. Pitch progression is a large part of how well a prop actually moves water. Depitching also decreases the progression ratio, while increasing pitch typically also increases progression. Think of rolling a ball against a wall or up a quarterpipe. The ball will just bounce off a wall while it will roll up the quarterpipe, eventually rolling up a vertical wall. The water sees the same dynamic when the prop slices into it.
I'd have to think that Merc has the proper progression pretty well worked out (for each model line, anyhow), and I tend to believe that starting with the right pitch and the proper progression is ideal, but, if I had to choose one way over the other, I'd probably go with pitching up to your ideal pitch, as opposed to down.
My 2-1/2 cents, anyway....
Thanks. Brad.
While all f my prop tweaking experience comes from racing model boats, I've got a number of friends who have made the transition from models to full size hydroplanes, and they indicate the dynamics are the same, even I they don't scale perfectly. Physics is still physics. In a lot of ways, learning from the tiny little props (respectively) we use for model boats translates into better understanding of how our larger props work.
It's been my experience that depitched props are far less efficient that a pitched-up prop of the same resulting pitch. Pitch progression is a large part of how well a prop actually moves water. Depitching also decreases the progression ratio, while increasing pitch typically also increases progression. Think of rolling a ball against a wall or up a quarterpipe. The ball will just bounce off a wall while it will roll up the quarterpipe, eventually rolling up a vertical wall. The water sees the same dynamic when the prop slices into it.
I'd have to think that Merc has the proper progression pretty well worked out (for each model line, anyhow), and I tend to believe that starting with the right pitch and the proper progression is ideal, but, if I had to choose one way over the other, I'd probably go with pitching up to your ideal pitch, as opposed to down.
My 2-1/2 cents, anyway....
Thanks. Brad.
Yesterday, 01:00 PM
#37
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was there a big temperature change between your top speed last year and this year? As the weather gets hot and humid they all slow down.
Yesterday, 02:25 PM
#39
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Yesterday, 02:26 PM
#40
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I dont think thats it. My first run the temp was in the 90's and still better than current and It wasn't quite as hot this time around.
