EGT temps dyno headers
12-25-2010, 01:56 PM
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EGT temps dyno headers
when i dynoed my engine they used headers with egt sensors
in each header. will ke marine headers change the temps.
engine is a 540 and was able to run 37 degress timing with decent egt temps. but after talking to a few people they dont run there timing that high.
in each header. will ke marine headers change the temps.
engine is a 540 and was able to run 37 degress timing with decent egt temps. but after talking to a few people they dont run there timing that high.
12-25-2010, 03:34 PM
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Ignition timing
Ignition timing is one of the most important adjustments to engine performance. In early days of automotive and marine engines there was a lever on the steering column of the boat or car that allowed the driver to set the ignition timing where the engine ran the best. Just what I need, some bubble headed blond in bikini adjusting my ignition timing while driving.
An engine dyno will tell you what are the maximum timing numbers because the engine will go into pre-ignition and horsepower will go down and overheating go way up. An oxygen sensor will read this overheat in the exhaust temp also.
You would be surprised how easy it is to dial spark timing on antique engines. One 1929 racing engine I ran you could manually set the ignition timing while racing. Tough race you always had the opportunity to kick the timing up one up another notch - might win or loose on the adjustment because power always goes way up with timing increases until - you hit the detonation then its like hitting a horsepower loss wall.
Some modern fuel injection engines have a knock sensor or crystal mounted on the engine to tell if it knocks. The engine will self adjust ignition timing depending on the quality in the gasoline because they will retard the spark when you run bad fuel and will advance until the engine starts knocking on good fuel - my Chrysler 300 had this - don't think the Mercruiser has it though. But does illustrate the point. More timing is better until you hit the detonation. Because this adjustment is so critical most engine tuners set the max timing safely below the usable max to ensure engine life. All these settings are best determined by engine dyno testing or manufacturer experience with a particular engine design.
An engine dyno will tell you what are the maximum timing numbers because the engine will go into pre-ignition and horsepower will go down and overheating go way up. An oxygen sensor will read this overheat in the exhaust temp also.
You would be surprised how easy it is to dial spark timing on antique engines. One 1929 racing engine I ran you could manually set the ignition timing while racing. Tough race you always had the opportunity to kick the timing up one up another notch - might win or loose on the adjustment because power always goes way up with timing increases until - you hit the detonation then its like hitting a horsepower loss wall.
Some modern fuel injection engines have a knock sensor or crystal mounted on the engine to tell if it knocks. The engine will self adjust ignition timing depending on the quality in the gasoline because they will retard the spark when you run bad fuel and will advance until the engine starts knocking on good fuel - my Chrysler 300 had this - don't think the Mercruiser has it though. But does illustrate the point. More timing is better until you hit the detonation. Because this adjustment is so critical most engine tuners set the max timing safely below the usable max to ensure engine life. All these settings are best determined by engine dyno testing or manufacturer experience with a particular engine design.
12-26-2010, 10:11 AM
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a dyno is far from running in a boat when comes to timing...no long pulls...bet you dyno pulls were only full throttle for a very short time...my advice back the timing down unless you have EGT real time on the boat...Rob
12-26-2010, 02:22 PM
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Keep in mind that reducing the total timing raises the EGT. While on the dyno did they get the fuel curve correct and then play with timing last, or where they adjusting both at the same time. Was it an automotive shop that did the dyno work? Are you basing your timing selection on getting the last bit of power shown on a peice of paper. Finally, you should be concentrating on the torque number not the horsepower. All this is just my opinions, good luck.
12-27-2010, 11:03 AM
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ignition timing
Your question is a fairly basic one and I guess we have been coming at you with some complex answers.
Iginition timing is about the same for all engines - Chrysler, Ford, Chevy all will run about 34* full timing because it is the same engineering problem - the gasoline charge takes x amount of time to burn and the piston/crankshaft is moving so fast that the spark is fired early - before the top dead center position - in order for the combustion to occur at the desired moment - faster the engine goes more timing is needed.
With this in mind - all big block chevy engines are timed roughly the same from the low performance passerger car engines to the race motors - changing your exhaust has little to do with the entire problem.
Timing you engine or any engine out to beyond the 37* standard amount may give you a little more power but the danger of engine destruction is just not worth it - unless you are going for some kind of racing record and want to sacrifice the motor.
Iginition timing is about the same for all engines - Chrysler, Ford, Chevy all will run about 34* full timing because it is the same engineering problem - the gasoline charge takes x amount of time to burn and the piston/crankshaft is moving so fast that the spark is fired early - before the top dead center position - in order for the combustion to occur at the desired moment - faster the engine goes more timing is needed.
With this in mind - all big block chevy engines are timed roughly the same from the low performance passerger car engines to the race motors - changing your exhaust has little to do with the entire problem.
Timing you engine or any engine out to beyond the 37* standard amount may give you a little more power but the danger of engine destruction is just not worth it - unless you are going for some kind of racing record and want to sacrifice the motor.
12-27-2010, 07:37 PM
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engine was dynoed at a car shop. engine was not run long at peak
rpm. it looks like the ke headers have a provision for for 2 sensors. im not sure if this area in the header is dry or not. im thinking i will run a dual egt gauge to tune in the boat.
thanks for the input
rpm. it looks like the ke headers have a provision for for 2 sensors. im not sure if this area in the header is dry or not. im thinking i will run a dual egt gauge to tune in the boat.
thanks for the input
12-28-2010, 08:02 AM
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I'm sorry but NOT all engines run about the same timing...has more to do with piston dome size and combustion chamber shape, I have 2 565 top sportsman race engines, 1 sonny's w/coventional heads, 15-1 comp...run 37-40 timing, the other is a R/M w/big chief heads, much less piston dome, much smaller chamber and only run 26-28 in that, over 1000hp, so there is a BIG difference in what a specific engine wants...
12-28-2010, 02:24 PM
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your wrong EZ
I disagree - ignition timing lead is primarily designed to adjust the amount of time the combustion takes to occur with the decreasing miliseconds required for the piston to advance past Top Dead Center - this time effect is standard across all engines.
The phenomenon you are noting that some highly tuned engines require less timing is an effort to hide the fact that they are over designed for the gasoline they are using - in effect you are hiding the too high compression by backing down the timing.
In the days of the gasoline crisis in the 1970's there were many high performance auto engines with 10:1 compression and backyard mechanics were retarding the timing and running cold thermostats to kill the heat production in the engine and get away with high compression using poor gas. This game can only go so far - another situation of too high compression is an engine that will need timing and jetting for running on the power peak and then not function at too low or high rpm - in effect the thermal efficiency of the cylinders at max torque cannot be matched to the engine tuning demands at max power.
You got to get it all right - octane - compression - timing - fuel ratio - engine operating temp - or you just going to get a bronc you cannot ride or live with.
Very few people manage too high compression and get away with it.
The phenomenon you are noting that some highly tuned engines require less timing is an effort to hide the fact that they are over designed for the gasoline they are using - in effect you are hiding the too high compression by backing down the timing.
In the days of the gasoline crisis in the 1970's there were many high performance auto engines with 10:1 compression and backyard mechanics were retarding the timing and running cold thermostats to kill the heat production in the engine and get away with high compression using poor gas. This game can only go so far - another situation of too high compression is an engine that will need timing and jetting for running on the power peak and then not function at too low or high rpm - in effect the thermal efficiency of the cylinders at max torque cannot be matched to the engine tuning demands at max power.
You got to get it all right - octane - compression - timing - fuel ratio - engine operating temp - or you just going to get a bronc you cannot ride or live with.
Very few people manage too high compression and get away with it.
12-29-2010, 08:18 AM
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Really ?? well I think sonny's and reher & morrison race engines might know a little more than you or I and having and running both their engines and having long dicussions with them on tuning and the spec sheets that were giving me with the engines I will stand behind what they have told me and what I said...example a hemi heads requires less timing as the spark plug is right in the center of the combustion chamber..so less flame travel=less timing needed, a B/B chevy with conventional heads w/domed pistons has to fire all the way across the dome= more timing, as I said big chief heads with little dome and sparg plug moved does not need as much timing as the distance and dome height not as restrictive(why big cheif sets ups make 100H/P over conventional heads) and thus needing 8-10 deg less total toming to get the same results..now if you don't beleive me give david reher a call @ RM race engines
Last edited by ezstriper; 12-29-2010 at 08:26 AM.
12-30-2010, 12:01 PM
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no intention
EZ - No intention of stressing you out.
Will grant you the time difference between hemisphrical combustion chamber and wedge chamber and the older L - head combustion chamber as well as modern chambers with pop up piston tops all may require a timing increase or decrease to either prevent knock or give time for the complete combustion to occur. This requires some variation in timing.
It is also an issue that I was trying to make of - too high compression giving major tuning problems and requiring timing to be retarded to hide this. I have personally seen engines on the dyno that have too much "volumetric efficiency" and "thermal efficiency" superimpose these two engineering factors at the engine torque peak requiring timing retardation. These same engines at horsepower peak where the "volumetric efficiency" has declined require a completely different ignition timing.
In this situation a timing retardation is programed into the computor or the if they are equiped with mechanical timed distributor where this cannot be done, they will detonate at max torque and or not produce full power at horsepower peak depending on how they are timed. Some won't run very well at all and become very ill tempered engines to drive.
This is the reason that Merc Racing and Mercruiser almost always refuse to use compression ratios over 8.75:1. It is to prevent the "thermal efficiency" from causing detonation.
With better gasoline the compression could go into the 9.5 or 10:1 range or even 12:1 with huge across the board power increases at all engine operating ranges.
"Thermal efficiency" is the engineering term used to describe the heat value realized by efficient combustion - higher the "thermal efficiency" the more energy from each combustion - on the order of 30% of the power in the gasoline used for work. Compresson of 10:1 getting considerably more work from the gasoline than 8.75:1. Aluminum heads also lower this whereas the iron heads keep the heat in the combustion chamber - one manufacurer tried copper heads to offset detonation and could not get the engine to produce horsepower increase in the engine because they sucked so much heat from the combustion.
"Volumetric efficiency" is the engineering term used to describe the cylinder filling from exhaust and intake designs. Usually it is difficult to completely fill an engine cylinder when it is running - owing to the speed at which the engine operates. Usually maximum cylinder filling occurs at engine torque peak - this is why the torque is the highest at that point because the cylinders are fully filled. Exhaust design - header etc. port shape and capacity, fuel system design all effect this. With tuned headers, good camshaft events, tuned runner intake system it is possible to fill engine cylinders to over 100% capacity at torque peak and the same engine will fall off to 80% at max power or idle even less.
The Hemi (Chrysler) is famous for being able to overlap the torque and horsepower peaks - occur at the same time - this is very desirable and is on reason they such great aircraft and race engines. The wedge engine (BBC) design has the advantage of mechanical octane in the combustion chamber design but usually has torque and power peak separation. These two discriptions are general.
Best to you my friend - interesting thread.
Will grant you the time difference between hemisphrical combustion chamber and wedge chamber and the older L - head combustion chamber as well as modern chambers with pop up piston tops all may require a timing increase or decrease to either prevent knock or give time for the complete combustion to occur. This requires some variation in timing.
It is also an issue that I was trying to make of - too high compression giving major tuning problems and requiring timing to be retarded to hide this. I have personally seen engines on the dyno that have too much "volumetric efficiency" and "thermal efficiency" superimpose these two engineering factors at the engine torque peak requiring timing retardation. These same engines at horsepower peak where the "volumetric efficiency" has declined require a completely different ignition timing.
In this situation a timing retardation is programed into the computor or the if they are equiped with mechanical timed distributor where this cannot be done, they will detonate at max torque and or not produce full power at horsepower peak depending on how they are timed. Some won't run very well at all and become very ill tempered engines to drive.
This is the reason that Merc Racing and Mercruiser almost always refuse to use compression ratios over 8.75:1. It is to prevent the "thermal efficiency" from causing detonation.
With better gasoline the compression could go into the 9.5 or 10:1 range or even 12:1 with huge across the board power increases at all engine operating ranges.
"Thermal efficiency" is the engineering term used to describe the heat value realized by efficient combustion - higher the "thermal efficiency" the more energy from each combustion - on the order of 30% of the power in the gasoline used for work. Compresson of 10:1 getting considerably more work from the gasoline than 8.75:1. Aluminum heads also lower this whereas the iron heads keep the heat in the combustion chamber - one manufacurer tried copper heads to offset detonation and could not get the engine to produce horsepower increase in the engine because they sucked so much heat from the combustion.
"Volumetric efficiency" is the engineering term used to describe the cylinder filling from exhaust and intake designs. Usually it is difficult to completely fill an engine cylinder when it is running - owing to the speed at which the engine operates. Usually maximum cylinder filling occurs at engine torque peak - this is why the torque is the highest at that point because the cylinders are fully filled. Exhaust design - header etc. port shape and capacity, fuel system design all effect this. With tuned headers, good camshaft events, tuned runner intake system it is possible to fill engine cylinders to over 100% capacity at torque peak and the same engine will fall off to 80% at max power or idle even less.
The Hemi (Chrysler) is famous for being able to overlap the torque and horsepower peaks - occur at the same time - this is very desirable and is on reason they such great aircraft and race engines. The wedge engine (BBC) design has the advantage of mechanical octane in the combustion chamber design but usually has torque and power peak separation. These two discriptions are general.
Best to you my friend - interesting thread.
