I call BS to the general idea of what's been said here. (and by the way, so much was
said I'd have to pick through it, line by line......I ain't gonna do it)
This I will tell you (and I've been in the aftermarket and high performance aftermarket
my entire working life), most distributor curves are not even close to accurate and
they're absolute crap for any kind of performance use. That's truth #1.
Truth #2- most people cannot eliminate the variables and thereby tune distributors
and carburetors to their max potential. Yes given an infinite amount of time and
effort they may get close, but.....
Truth #3- without a dyno, a distributor machine and possibly an exhaust gas analyzer,
you're just dreaming if you think you can optimize a custom tune.
And the difference in performance is pretty great- it's not all hype and snake oil.
This is one of those cases where spending $150 with the right person who has the
skill and the right equipment will save literally hundreds of dollars of wasted time
and effort.
So you have looked at the aftermarket/replacement junk that someone else either likely bought, adjusted or just threw in....and using that for the basis of saying that using common mechanical skills and tools (such as a timing light, vacume gauge, tach & the specific cam specs ie power band) that it can't be done.......hate to tell you this, but that's exactly what the sun bench does except it does it with meters versus understanding the readings that you are getting from these other tools.....off the engine instead of on the engine......
You must be part of the 30 or early 40 something crowd who is just unfamiliar like many with the previously taught distributor tuning standards...which every mechanic even in high school shop class was taught (which I know all of which went away in the late 70's early 80's). Yes, I do not doubt the output of a dyno....but for most street engines (not super modded), there are still mechanics out there (very gray haired) who can literally rest their hand on the engine, listen, feel and tune that engine easily to within 2 or so hp of what a dyno will do.....with regards to recurve a distributor, this is just a basic skill of mygeneration- even HRM did a big challenge write-upback in the 70's...what was better tuning by ear or with a dyno...using a relatively stock engine.....guess what, it was as close to a dead even heat as you can get......even the editor at the time wrote..."it really brings to question if you have a mechanic who has old school skills, if you really even need a dyno if you never plan on seeing a race track". Yes, these skillsets are becoming lost.
There are few parts that can't be fine tuned...if you just have someone show you how (because much of this information was never printed in a book, it was taught as part of the industry standard- which hasn't existed for decades)
BTW....when our family & Ed Eskenderianwere running faltheads at 200+ mph at El Mirage in the early 50's on oem distributors (points, etc) do you really think they had "dyno's" back then- or did they use their hands, ears and touch to tune the engines....and mind you, we are talking about cranks, cams, etc that were not off the shelf bought, but either made from scratch or created from junk yard parts......and there was nothing even close to QA that we have today..............and those engines were oem rated at around 80 hp.
i love it when people who do not remember the past, fail to recognize the most common tools that can be used with a little smarts to do the same job...............
I agree, with proviso. #1- Factory settings on non-performance engines were for driveabilty, and maybe economy. Of course, I've never seen a distributor that was even friggin' close to factory specs. Used distributors are usually a mess, and reman distributors are worse. I have not tested aftermarket distributors, such as the Pertronix, for advance spec. Adjustment of distributors is quite easy, with proper equipment, and power improvement is dramatic.
#2- Using 289HP spec for centrifugal-only distributors and BOSS 302 spec for dual-advance is an excellent starting point, or even ending point if you are not going for-
#3- A chassis dyno tune. Unless the engine is analyzed on a chassis dyno, under load, and timing, advance, and carb/injection operation is optimized, you're essentially guessing. A friend of mine has a dyno built into the floor of the service bay in his shop for just that purpose.
It boils donw to this...if you are unfamiliar with how to properly tune an engine (including recurving the distributor which any and everybody did back in the 50's, 60's & 70s), and you are not willing to try, then I agree, pay someone to do it for you ....just like replacing spark plugs....I can not tell you how many people think you just unscrew the old ones & screw the new ones in.......yes, another 15 minute class that can also increase the hp by 5 or more....but some actually started paying people with osciloscopes back in the late 70's & 80's $ to install their spark plugs...because it was sooo much better, accurate and ...gosh, you don't understand Mr. Jeff!
Today everyone looks at that equipment as antiquated (although it did actually have a bit of a purpose)..its just a matter of perception and looking at "can I accomplish my objective in other ways"............for some, it's just easier and much better PR to say...i paid Mr. XX to dyno tune my engine"...and my hands are clean, my polo shirt has no marks on it & I have only touched an engine with gloves on...oh if I break down on the raod, I call someone to tow me to a mechanic versus saying...I fixed it myslef on the roadway....
and lets take the opposite end of the spectrum.......todays ultra high performance 1/4 mile engies...many if not all of the top performers engines are exceeding the "scales" by which todays engine & chassis dynos can "read'......how do you think they tune their engines...yes, they use technology when & where they can, but the final, is based upon experience because that is what is ultimately left when you exceed the dynos capabilities.
nobody has tuned the curve or knows the process used for a chassis dyno?
The term "dyno tested" is used a lot these days, and most people tend to accept dyno results as absolute truth. Unfortunately, dyno results are no better than the testing equipment and method used to get the results. In other words, unscrupulous operators can make the results come out to be almost anything they want.
The real purpose of a dynamometer is to measure changes in performance and to tell the user whether modifications helped or hindered performance. In other words, a dyno is like a bathroom scale. It tells you whether you're gaining or loosing. Almost any dyno can tell you whether you're gaining or loosing, provided you make your comparisons using the same dyno, under identical conditions, or corrected to the same standards. You also need to use the same dyno operator, but that's another story. The problem comes when a dynamometer is used to determine a peak power level. Just like bathroom scales, different dynos are likely to yield different results. So, which results are accurate? Do you want a fudged result to make you shine or do you want to know the true horsepower your car puts down on the road. Those that wants a dyno figure for bragging rights beware, some one with a dyno sheet indicating 20 - 25 % less power might hand you your breakfast.
Both acceleration and sustained-load or Eddy Current chassis dynos measure power delivered by vehicle's drive wheels. In theory, this makes more "real world" sense than simply measuring the net engine power output on an engine dyno. After all it is not the crank that's on the road but rather the wheels.
An acceleration chassis dyno, such as the Dyno Jet really ought to be named a "calculating dyno" since it attempts to measure power output by calculating power based on the amount of time required to accelerate the dyno rollers from one speed to another. This is possible when the weight of the rollers (actually the moment of inertia) is calculated into the equation, and mathematically it sounds good. The problems come with actual application and a number of inconsistent variables that cannot be built into the computation.
By its very design, a power test on an acceleration dyno is a very short test, lasting only a matter of seconds, and during the test, the vehicle's engine and drive train are in a constant state of transition. By its nature of transitioning from one speed to another, gear changes are usually required. This creates torque spikes when the shifts occur. At anything other than a direct 1:1 ratio in the transmission, the engine torque (power) is being multiplied, and an acceleration dyno has no way of ascertaining the transmission gear ratios of the vehicle being tested. If the vehicle has a manual transmission, there's the problem of gear changes that momentarily remove the drive force from the rollers, or worse yet, initiate some momentary tire-to-roller slippage. Automatic transmission vehicles also have the problem of the torque converter clutch being unlocked during acceleration. The amount of slippage in the torque converter, being a function of stall speed and load, is another inconsistent variable.
While the weight of the rollers and their resistance to acceleration must be known to calculate the power required to change the speed of rollers on an acceleration dyno, just as important is the mass of the vehicle's drive train, especially the drive wheels and tires. Obviously it takes more power to accelerate the wheels and tires on a dually than it does to accelerate single wheel/tire configurations, but an acceleration dyno has no way of accurately computing the moment of inertia of the vehicle's drive train. Consequently, the peak power number generated may be inaccurate.
Equally important regarding realistic acceleration chassis dyno results is to have the roller inertia weight closely equal the weight of the vehicle. If the effective weight of the rollers is 4000 pounds and the vehicle weighs 8000 pounds, obviously the vehicle's engine can accelerate the rollers far faster than it can accelerate the vehicle on the road or vice verse. Calculations can still be made when there are such large variances, but the more unequal the roller moment of inertia and vehicle weights, the more removed from a "real world" simulation the test becomes. If the moment of inertia of the rollers is substantially less than the weight of the vehicle, it is questionable whether the rollers can fully load the engine the way the vehicle would load it. On a turbocharged vehicle, full boost may never be achieved on an acceleration dyno, and that of course, results in lower power output. On an acceleration dyno, you simply can't duplicate the load a vehicle encounter on a continuous uphill grade etc.
Exactly where peak power occurs is another problem with an acceleration dyno. Because everything is in transition during a test, the RPM where peak power, or even changes in power, occurs can only be approximated. Still, in apples-to-apples comparative testing, an acceleration dyno can reliably indicate whether changes to the vehicle result in performance gains. Similarly, if multiple vehicles are tested on the same acceleration dyno under similar conditions, that dyno can usually indicate the relative power differences between the vehicles. The reason we say "usually" is that recognizing and quantifying tire slippage on an acceleration dyno is difficult to impossible. The real problem with an acceleration dyno is putting any faith in the calculated peak power number. These problems escalate in itself when tuning a vehicle for everyday driving conditions. Anything other than wide open throttle and the tuning results are very questionable. In many cases what appears to be a safe tune on an acceleration chassis dyno is every thing but that. It is virtually imposable to do a cell by cell tune on an acceleration dyno and in most cases the full midrange and under the curve potential of the engine can not be fully optimized.
A sustained-load chassis dyno does not calculate the test vehicle's power output. Instead, it measures power output directly by imparting an electrical load or water absorption load on the rollers and measuring torque. It can sustain this load indefinitely to allow conditions to stabilize on the test vehicle. It can take readings at any desired engine speed or roller speed to exactly determine a power curve and the peak power output RPM. The test vehicle can be locked in direct, 1:1 drive with the torque converter clutch (on automatics) locked to eliminate any torque multiplication or slippage. Similarly, engine RPM, wheel speed, and roller RPM can all be monitored simultaneously to immediately identify any tire slippage on the rollers. A sustained-load chassis dyno is simply more accurate.
On a sustained-load chassis dyno, the weight of the rollers has no significance since the load is usually measured at a steady speed with the load imposed on the rollers. This also means the weight of the test vehicle is insignificant. It could be a Geo Metro, Supra, Viper, Corvette, Ferrari, one ton pickup or a dually it makes no difference.
Perhaps the best way to explain the differences between acceleration and sustained-load chassis dyno operation is to envision the way they load a test vehicle compared to actual road loads. An acceleration dyno is like a drag strip, deriving its power rating from how fast the dyno rollers can be accelerated. A sustained-load dyno is like an unending uphill grade, measuring the power necessary to climb that grade at any given speed. Performance engine tuning is more complete and accurate on a sustained-load or Eddy Current chassis dyno.
So why doesn't everyone use sustained-load chassis dynos for performance testing? There are many reasons, but there are two reasons that are important when it comes to testing tuning and aftermarket power products. First, a sustained-load chassis dyno is mechanically more complex and expensive because of the load generators and load-measuring units that must be connected to the rollers. These things, taken together, mean that the sustain-load dyno, and sometimes the permanent installation facilities required for it, is substantially more expensive than what's involved for an acceleration dyno. In fact, the total costs of a sustained-load chassis dyno may be more than five times as much as for an acceleration dyno. Second, many of the power products produced by various manufacturers for the performance market generate their best results during short tests. Let's put that another way; these manufacturers of quick and dirty power modules and programmers really aren't interested in revealing the problems their products cause under a sustained load.
In all fairness, the fore-going reasons why many manufacturers and tuning shops choose acceleration chassis dynos may reflect the old "chicken and egg" syndrome. If a company is unable or unwilling to invest in a sustained-load chassis dyno, then they also will lack the facilities to more fully develop their products for safe operation under sustained loads. Who knows which came first, an inadequately developed product or the inability to develop a safe, reliable product? Either way, let the buyer beware.
The term "dyno tested" is used a lot these days, and most people tend to accept dyno results as absolute truth. Unfortunately, dyno results are no better than the testing equipment and method used to get the results. In other words, unscrupulous operators can make the results come out to be almost anything they want.
The real purpose of a dynamometer is to measure changes in performance and to tell the user whether modifications helped or hindered performance. In other words, a dyno is like a bathroom scale. It tells you whether you're gaining or loosing. Almost any dyno can tell you whether you're gaining or loosing, provided you make your comparisons using the same dyno, under identical conditions, or corrected to the same standards. You also need to use the same dyno operator, but that's another story. The problem comes when a dynamometer is used to determine a peak power level. Just like bathroom scales, different dynos are likely to yield different results. So, which results are accurate? Do you want a fudged result to make you shine or do you want to know the true horsepower your car puts down on the road. Those that wants a dyno figure for bragging rights beware, some one with a dyno sheet indicating 20 - 25 % less power might hand you your breakfast.
Both acceleration and sustained-load or Eddy Current chassis dynos measure power delivered by vehicle's drive wheels. In theory, this makes more "real world" sense than simply measuring the net engine power output on an engine dyno. After all it is not the crank that's on the road but rather the wheels.
An acceleration chassis dyno, such as the Dyno Jet really ought to be named a "calculating dyno" since it attempts to measure power output by calculating power based on the amount of time required to accelerate the dyno rollers from one speed to another. This is possible when the weight of the rollers (actually the moment of inertia) is calculated into the equation, and mathematically it sounds good. The problems come with actual application and a number of inconsistent variables that cannot be built into the computation.
By its very design, a power test on an acceleration dyno is a very short test, lasting only a matter of seconds, and during the test, the vehicle's engine and drive train are in a constant state of transition. By its nature of transitioning from one speed to another, gear changes are usually required. This creates torque spikes when the shifts occur. At anything other than a direct 1:1 ratio in the transmission, the engine torque (power) is being multiplied, and an acceleration dyno has no way of ascertaining the transmission gear ratios of the vehicle being tested. If the vehicle has a manual transmission, there's the problem of gear changes that momentarily remove the drive force from the rollers, or worse yet, initiate some momentary tire-to-roller slippage. Automatic transmission vehicles also have the problem of the torque converter clutch being unlocked during acceleration. The amount of slippage in the torque converter, being a function of stall speed and load, is another inconsistent variable.
While the weight of the rollers and their resistance to acceleration must be known to calculate the power required to change the speed of rollers on an acceleration dyno, just as important is the mass of the vehicle's drive train, especially the drive wheels and tires. Obviously it takes more power to accelerate the wheels and tires on a dually than it does to accelerate single wheel/tire configurations, but an acceleration dyno has no way of accurately computing the moment of inertia of the vehicle's drive train. Consequently, the peak power number generated may be inaccurate.
Equally important regarding realistic acceleration chassis dyno results is to have the roller inertia weight closely equal the weight of the vehicle. If the effective weight of the rollers is 4000 pounds and the vehicle weighs 8000 pounds, obviously the vehicle's engine can accelerate the rollers far faster than it can accelerate the vehicle on the road or vice verse. Calculations can still be made when there are such large variances, but the more unequal the roller moment of inertia and vehicle weights, the more removed from a "real world" simulation the test becomes. If the moment of inertia of the rollers is substantially less than the weight of the vehicle, it is questionable whether the rollers can fully load the engine the way the vehicle would load it. On a turbocharged vehicle, full boost may never be achieved on an acceleration dyno, and that of course, results in lower power output. On an acceleration dyno, you simply can't duplicate the load a vehicle encounter on a continuous uphill grade etc.
Exactly where peak power occurs is another problem with an acceleration dyno. Because everything is in transition during a test, the RPM where peak power, or even changes in power, occurs can only be approximated. Still, in apples-to-apples comparative testing, an acceleration dyno can reliably indicate whether changes to the vehicle result in performance gains. Similarly, if multiple vehicles are tested on the same acceleration dyno under similar conditions, that dyno can usually indicate the relative power differences between the vehicles. The reason we say "usually" is that recognizing and quantifying tire slippage on an acceleration dyno is difficult to impossible. The real problem with an acceleration dyno is putting any faith in the calculated peak power number. These problems escalate in itself when tuning a vehicle for everyday driving conditions. Anything other than wide open throttle and the tuning results are very questionable. In many cases what appears to be a safe tune on an acceleration chassis dyno is every thing but that. It is virtually imposable to do a cell by cell tune on an acceleration dyno and in most cases the full midrange and under the curve potential of the engine can not be fully optimized.
A sustained-load chassis dyno does not calculate the test vehicle's power output. Instead, it measures power output directly by imparting an electrical load or water absorption load on the rollers and measuring torque. It can sustain this load indefinitely to allow conditions to stabilize on the test vehicle. It can take readings at any desired engine speed or roller speed to exactly determine a power curve and the peak power output RPM. The test vehicle can be locked in direct, 1:1 drive with the torque converter clutch (on automatics) locked to eliminate any torque multiplication or slippage. Similarly, engine RPM, wheel speed, and roller RPM can all be monitored simultaneously to immediately identify any tire slippage on the rollers. A sustained-load chassis dyno is simply more accurate.
On a sustained-load chassis dyno, the weight of the rollers has no significance since the load is usually measured at a steady speed with the load imposed on the rollers. This also means the weight of the test vehicle is insignificant. It could be a Geo Metro, Supra, Viper, Corvette, Ferrari, one ton pickup or a dually it makes no difference.
Perhaps the best way to explain the differences between acceleration and sustained-load chassis dyno operation is to envision the way they load a test vehicle compared to actual road loads. An acceleration dyno is like a drag strip, deriving its power rating from how fast the dyno rollers can be accelerated. A sustained-load dyno is like an unending uphill grade, measuring the power necessary to climb that grade at any given speed. Performance engine tuning is more complete and accurate on a sustained-load or Eddy Current chassis dyno.
So why doesn't everyone use sustained-load chassis dynos for performance testing? There are many reasons, but there are two reasons that are important when it comes to testing tuning and aftermarket power products. First, a sustained-load chassis dyno is mechanically more complex and expensive because of the load generators and load-measuring units that must be connected to the rollers. These things, taken together, mean that the sustain-load dyno, and sometimes the permanent installation facilities required for it, is substantially more expensive than what's involved for an acceleration dyno. In fact, the total costs of a sustained-load chassis dyno may be more than five times as much as for an acceleration dyno. Second, many of the power products produced by various manufacturers for the performance market generate their best results during short tests. Let's put that another way; these manufacturers of quick and dirty power modules and programmers really aren't interested in revealing the problems their products cause under a sustained load.
In all fairness, the fore-going reasons why many manufacturers and tuning shops choose acceleration chassis dynos may reflect the old "chicken and egg" syndrome. If a company is unable or unwilling to invest in a sustained-load chassis dyno, then they also will lack the facilities to more fully develop their products for safe operation under sustained loads. Who knows which came first, an inadequately developed product or the inability to develop a safe, reliable product? Either way, let the buyer beware.
Courtesy of Banks Power.
i'm more than aware of these things. i just want to hear from someone who claims they have "tuned" a distributor curve (by curve i'm talking about the mechanical advance, vacuum advance, initial) on a dyno to understand what they are doing because i don't personally believe it or have NEVER seen someone post data from the tests.
todays ultra high performance 1/4 mile engies...many if not all of the top performers engines are exceeding the "scales" by which todays engine & chassis dynos can "read'......how do you think they tune their engines...yes, they use technology when & where they can, but the final, is based upon experience because that is what is ultimately left when you exceed the dynos capabilities.
yes, a whole new generation................
at the end of the day don't race cars tune based on things like measured performance (i.e. timeslip) with experience probably being a starting point?
I never had the opportunity present itself...mainly because I'm a cheap S.O.B., but here is how I WOULD do it, given the chance....
First, I'd determine my optimum total advance over my normal operating range (with vacuum advance disconnected).
Next, I'd determine my best initial advance, based on warm cranking speed and idle quality.
Using the data collected in the successive pulls to determine optimum total advance, I'd plot the advance that produced the best power numbers at each rpm increment to a piece of graph paper (my idea of best power would be to add torque + hp and divide by 2) and then try to duplicate that advance curve through the selection of plate, springs and stops.
By "plate", I mean the advance plate that contains the slots that determine the span of advance (in distributor degrees) that can be applied. If my optimum total advance is 34* and it starts and idles best at 10* then I need 12* of distributor advance. I'd probably pick a plate with a 13L (26* advance).
I'd expect the advance curve to ramp steeply from 1,000rpm to about 2,500rpm so I'd select a "short" spring to control the advance from idle to 2,500 rpm, making sure to bend the spring post to hold tension on the spring to keep the advance at 0* at idle. We need to have a "steeper" curve from idle to 2,500rpm so we'd pick a lighter tension spring for one side. The curve needs to be wider from 2,500rpm to redline. To do this, we'd select a "long" spring that would be slack from idle to 2,500rpm, then provide tension from there up to redline. It would need to be heavier in tension than the other spring and we'd install that one on the other side, adjusting the post to fine tune the rpm where tension starts to be applied. This will now override the light spring.
Now we need to "tweak" our curve based on real operating conditions. If we get pinging under load right off idle that gets better with rpm, we'll move up to the next heavier spring for the "low" rpm portion of the advance. If we get pinging under load approaching 2,500rpm, then we'll take a little slack out of the other spring so it limits the travel allowed by the first spring at a lower rpm. If we get pinging under load above 2,500rpm that is fairly consistent, we'll move up to a bit heavier "high" rpm spring, and if we get pinging under load approaching the upper end of our operating range, we'll push a plastic "washer" over the limiting pin (stop) that controls the amount of advance so that we lower the total amount available. Conversely, you can also grind the "slot" in the plate wider to allow it to provide MORE total advance.
Finally, we'd reinstall the vacuum advance and fine tune the vacuum adjustment so as to prevent any pinging under light loads/high vacuum.
If it still runs like crap then don't blame ME, I'm just telling you how I'd do it, not the RIGHT way to do it.
IMHO, 95* of people would be happy having their distributor recurved to B302 specs while the other 5* of anal-retentive people like myself would want "perfection". I believe that there is enough difference between variables (altitude, temperature, compression ratio, camshafts, exhaust systems, valve train, etc) to make such a spec as the B302 a "catch all" for the majority of applications. That's not a bad thing... heck, how many people do you know that experiment with their camshaft timing or modify their carburetor circuits? Same diff if you ask me.
If you really think that you can really vary an advance curve that much...meaning getting 100% in at 2500 or 2000 rpm is easy & can be done (verified) with a timing light.....if you really think there is going to be that much variation of input between 1500 and 2000 rpm (a whole 500 rpm range) to require a Sun Bench and its really going to produce that much of a result, well.....
Now this is just ridiculous. Distributor curving machines are just needless doodads, luxurious baubles, the lack of which can 'easily' be worked around 500rpm, give or take makes no difference
One comment with regards to expertise...the 'experts' I've encountered in any field never felt the compulsion to convince others of their status through self promotion or similar effort. It was either known, or it was not.
Apologies to the OP, whose question was never whether or not the professional service has merit, but merely who to go with...sorry my little commentary is of zero use there. Good luck
Thanks, the conversation went a little sideways, but I did get a couple of leads to follow up on. I'm not up for doing it myself, so I'll inquire to those listed that are close by.
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500rpm, give or take makes no difference
