Boost numbers and opinions needed
10-01-2018, 09:18 PM
#41
Registered
One interesting take away from engine masters was that engines tuned to make the most power are pinging and knocking. That’s why I’m skeptical of the “give it what it wants” mantra.
10-02-2018, 06:27 AM
#42
Registered
iTrader: (3)
a carbed old big block, not so much. That being said, i dont buy into the old rhetoric of make it fat, yank timing , and hope for the best.
in one of my research books, they illustrate a graph of flame speed vs lambda. Peak flame speed occurs around 13.2 afr, while max power is 12.5. Its easy to see how detonation can be induced when flame speed is at its fastest. Its also easy to understand, how being on the rich side of max power, with slightly retarded spark , would net the safest setup, with a minimal power loss %.
example, afr in the 11's in boost, with 32* of spark, is prob alot more detonation resistant, than afr at 13, and 32* of spark, and also make more power. Of course if you experience knock at 13afr and 32*, you can retard spark to make it stop. However, the power loss would be greater theoretically.
of course, if youre running a bbc with a single carb , the afrs from cyl to cyl vary by a mile, so you really gotta tune around the leanest/hottest cylinder.
10-03-2018, 11:35 AM
#43
the modern car tuners have it made. Being able to tune and monitor things live, tons of safety parameters to keep things in check when knock shows itself. Its easier for them to keep the engine running at peak performance and efficiency without melting things.
a carbed old big block, not so much. That being said, i dont buy into the old rhetoric of make it fat, yank timing , and hope for the best.
in one of my research books, they illustrate a graph of flame speed vs lambda. Peak flame speed occurs around 13.2 afr, while max power is 12.5. Its easy to see how detonation can be induced when flame speed is at its fastest. Its also easy to understand, how being on the rich side of max power, with slightly retarded spark , would net the safest setup, with a minimal power loss %.
example, afr in the 11's in boost, with 32* of spark, is prob alot more detonation resistant, than afr at 13, and 32* of spark, and also make more power. Of course if you experience knock at 13afr and 32*, you can retard spark to make it stop. However, the power loss would be greater theoretically.
of course, if youre running a bbc with a single carb , the afrs from cyl to cyl vary by a mile, so you really gotta tune around the leanest/hottest cylinder.
a carbed old big block, not so much. That being said, i dont buy into the old rhetoric of make it fat, yank timing , and hope for the best.
in one of my research books, they illustrate a graph of flame speed vs lambda. Peak flame speed occurs around 13.2 afr, while max power is 12.5. Its easy to see how detonation can be induced when flame speed is at its fastest. Its also easy to understand, how being on the rich side of max power, with slightly retarded spark , would net the safest setup, with a minimal power loss %.
example, afr in the 11's in boost, with 32* of spark, is prob alot more detonation resistant, than afr at 13, and 32* of spark, and also make more power. Of course if you experience knock at 13afr and 32*, you can retard spark to make it stop. However, the power loss would be greater theoretically.
of course, if youre running a bbc with a single carb , the afrs from cyl to cyl vary by a mile, so you really gotta tune around the leanest/hottest cylinder.
10-05-2018, 03:04 PM
#46
Platinum Member
Platinum Member
What is the squish clearance on your motor? If you are running a tight squish (.035-.045") then you can run more boost and timing before detonation than you can if you are running an open squish (over .055"). This, and intake charge temperature are the 2 main things to focus on when trying to raise your boost level and power output. Since your motor is assembled, you can't change the squish clearance - but you can change timing, boost, fuel ratio, and cooling parameters (block cooling, exhaust cooling, and intake charge cooling).
mc
mc
10-05-2018, 03:33 PM
#47
VIP Member
VIP MemberThread Starter
Not sure on that...I have .005 piston to deck clearance, .041 mls head gasket, stock stroke, dart iron eagle heads?? is that enough info?? does that mean the .005 plus the .041 head gasket so .046 squish??
10-05-2018, 03:57 PM
#48
Registered
What is the squish clearance on your motor? If you are running a tight squish (.035-.045") then you can run more boost and timing before detonation than you can if you are running an open squish (over .055"). This, and intake charge temperature are the 2 main things to focus on when trying to raise your boost level and power output. Since your motor is assembled, you can't change the squish clearance - but you can change timing, boost, fuel ratio, and cooling parameters (block cooling, exhaust cooling, and intake charge cooling).
mc
mc
10-05-2018, 04:26 PM
#49
Registered
the modern car tuners have it made. Being able to tune and monitor things live, tons of safety parameters to keep things in check when knock shows itself. Its easier for them to keep the engine running at peak performance and efficiency without melting things.
a carbed old big block, not so much. That being said, i dont buy into the old rhetoric of make it fat, yank timing , and hope for the best.
in one of my research books, they illustrate a graph of flame speed vs lambda. Peak flame speed occurs around 13.2 afr, while max power is 12.5. Its easy to see how detonation can be induced when flame speed is at its fastest. Its also easy to understand, how being on the rich side of max power, with slightly retarded spark , would net the safest setup, with a minimal power loss %.
example, afr in the 11's in boost, with 32* of spark, is prob alot more detonation resistant, than afr at 13, and 32* of spark, and also make more power. Of course if you experience knock at 13afr and 32*, you can retard spark to make it stop. However, the power loss would be greater theoretically.
of course, if youre running a bbc with a single carb , the afrs from cyl to cyl vary by a mile, so you really gotta tune around the leanest/hottest cylinder.
a carbed old big block, not so much. That being said, i dont buy into the old rhetoric of make it fat, yank timing , and hope for the best.
in one of my research books, they illustrate a graph of flame speed vs lambda. Peak flame speed occurs around 13.2 afr, while max power is 12.5. Its easy to see how detonation can be induced when flame speed is at its fastest. Its also easy to understand, how being on the rich side of max power, with slightly retarded spark , would net the safest setup, with a minimal power loss %.
example, afr in the 11's in boost, with 32* of spark, is prob alot more detonation resistant, than afr at 13, and 32* of spark, and also make more power. Of course if you experience knock at 13afr and 32*, you can retard spark to make it stop. However, the power loss would be greater theoretically.
of course, if youre running a bbc with a single carb , the afrs from cyl to cyl vary by a mile, so you really gotta tune around the leanest/hottest cylinder.
I’d bet adding timing usually makes more power right up until blows. So “giving it what it wants” in that scenario doesn’t work.
10-08-2018, 06:25 AM
#50
Registered
iTrader: (3)
There really is only one correct time to ignite the spark plug. Finding that number, is the hard part. You can have an engine that makes a very high peak cylinder pressure , but doesnt make the most power. The way to accomplish that is with incorrect timing. You want the spark to ignite at the proper time, not so that it makes peak cyl pressure, but so that combustion takes place at the right time, and puts the most leverage on the crankshaft. Too much timing is negative work, reduced power, and dangerous. Too little timing, is wasted efficiency, and in a boat can melt things.
was watching a webinar the other day from the hp academy. They had an import car on the dyno. They did steady state pulls, focusing on one area of the fuel and timing maps at a time. They ran an afr of 13.0, 12.5, and 12.0. There was very little power difference.
timing, they adjusted live while in steady state on the dyno. It was easy to see the torque rise as timing was increased , and once they crossed the line, the torque began to fall off again. I dont remember the exact number of degrees, but its irrelevant since every engine is different.
im sure the crew at mercury racing tunes in a fairly similar manner. I doubt they are doing 300-600 rpm per second sweep pulls on their modern efi engines in order to get a tune.
Gasoline seems to make its best power in the 12-13 range. Going a tad richer than 12, doesnt seem to kill power much, at least from what ive seen on supercharged stuff. I think id rather stay on the richer side of max power, on a boat engine. Timing wise, for me, its not the peak timing that worries me nearly as much as the low to midrange area.
heck, even the carb engines from merc with the thunderbolt 5 used to add timing while at a cruise state, sensing for rpm increase. What is was actually looking for was to see if the engine was making more power with the extra advance, if it did, it stayed there. If it didnt, it backed it down. Sort of a similar concept. Without pressure transducers and fancy monitoring eqiipment installed, finding the optimal point of ignition is impossible. Thats why most use the MBT method, which imo is still better than just guessing at numbers of what one might think is good on paper
squish? On a forced induction engine? Many forced induction pistons dont even have quench pads these days.
