intake & exhaust systems = synergistic effects?
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From: Johnson City, TN
Being an engineer, I'll try to sum up what your saying. The end result of an intake and exhaust WILL be more than the effects of adding the results by themselves as you said. BUT the downfall of your logic is saying an intake or exhaust gives you xx.xx amount of horsepower. The reality of it, is that these modifications free up a percentage of power. So if you put an exhaust on a truck by itself, and it gives you for instance 5% gain on a 300hp motor, that might equate to 15 hp, but if that truck has other mods, then that 5% is going to be more, for instance if that truck has 400hp then it would be a 20 hp gain. I ran a supercharged mustang for several years, and just like you are saying. Many people put exhausts on there mustangs and got around 10 hp, but with the supercharger on mine, that same exhaust setup gave me about 40hp. The actual number of horsepower gain is going to seem synergistic, but it's those percentages that are staying the same. That percentage is just bigger because the number you are taking that percentage of is bigger.
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From: ND
Originally posted by CarlJ
Being an engineer, I'll try to sum up what your saying. The end result of an intake and exhaust WILL be more than the effects of adding the results by themselves as you said. BUT the downfall of your logic is saying an intake or exhaust gives you xx.xx amount of horsepower. The reality of it, is that these modifications free up a percentage of power. So if you put an exhaust on a truck by itself, and it gives you for instance 5% gain on a 300hp motor, that might equate to 15 hp, but if that truck has other mods, then that 5% is going to be more, for instance if that truck has 400hp then it would be a 20 hp gain. I ran a supercharged mustang for several years, and just like you are saying. Many people put exhausts on there mustangs and got around 10 hp, but with the supercharger on mine, that same exhaust setup gave me about 40hp. The actual number of horsepower gain is going to seem synergistic, but it's those percentages that are staying the same. That percentage is just bigger because the number you are taking that percentage of is bigger.
Being an engineer, I'll try to sum up what your saying. The end result of an intake and exhaust WILL be more than the effects of adding the results by themselves as you said. BUT the downfall of your logic is saying an intake or exhaust gives you xx.xx amount of horsepower. The reality of it, is that these modifications free up a percentage of power. So if you put an exhaust on a truck by itself, and it gives you for instance 5% gain on a 300hp motor, that might equate to 15 hp, but if that truck has other mods, then that 5% is going to be more, for instance if that truck has 400hp then it would be a 20 hp gain. I ran a supercharged mustang for several years, and just like you are saying. Many people put exhausts on there mustangs and got around 10 hp, but with the supercharger on mine, that same exhaust setup gave me about 40hp. The actual number of horsepower gain is going to seem synergistic, but it's those percentages that are staying the same. That percentage is just bigger because the number you are taking that percentage of is bigger.
I'd still like ChrisAdams to chime back in on this one and let me know how this would REALLY work though...that guy is wicked smart!
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I typed this up today and wasn’t going to post it, too many good ideas flowing. But what the heck.
I think the problem in any analysis of these changes, is the premise itself is flawed.
Everyone tosses out figures, doesn’t mean the figures are right.
Even a dyno is subject to interpretation.
Useable horsepower has nothing to do with ‘dyno’ horsepower.
The 4.6 engine makes 231 horsepower at 4750
Torque is 293 at 3500
The 5.4 engine makes 300 horsepower at 5000 rpm.
Torque is 365 at 3750
You do not want to be exceeding 5000 RPM on these motors for any length of time.
An aftermarket part may advertise lots of additional horsepower, but it’s always weasel worded, or to be nice, it’s always filled with ‘disclaimers’ or statements that range from,’ Power achieved on test engine (hand built on a stand, not production in a truck), or the ever popular ‘your results may vary’.
Even more important, is power curve.
Look at any chart of horsepower or torque for any engine. It starts low, goes to a peak, then drops away.
Now look at our trucks. The maximum horsepower is at the top of the usable RPM range. Right before the red line.
Now look at any aftermarket horsepower improving component.
Ignore the fact that it is being tested on a ‘special’ engine, and in special conditions.
Look at where the most horsepower gains occur. Usually at or above the maximum you can attain in the real truck in real road conditions.
Sometimes (often with cams, high rise intakes, larger fuel systems, headers) there is an actual power decrease at ‘realistic’ RPMs. This is common.
You can kill your launch or take-off by decreasing the backpressure till the mix is over scavenged at idle. This will help you, but mostly above redline…
An over duration cam does the same thing. The engine has poor idle, poor ‘launch’ but by the time you get the RPMs up into the new higher power-band, you are really moving. And the tach is really above redline.
When building a ‘racing’ motor, this is not a problem. You put in extra lift on the cam, so that at high rpm you get more fuel. You put in more duration on the cam so that you get more fuel to the cylinder, and have more time to push exhaust out of the engine at higher RPM. This is bad at low RPMs but that doesn’t matter. You launch at higher RPM, and hold them up in the power-band at all times.
You improve the bottom end of the engine, improve the oil volume, etc. so the engine can support the higher RPMs where you are now making huge horsepower. You lower the gear ratio, actual, not just to compensate for bigger diameter tires, to take advantage of the higher RPM power band.
The further you move the power band up the RPM scale, the more potential horsepower.
Big horsepower ain’t gonna happen from true bolt on parts. Superchargers, turbo-chargers, Nitrous, are not true bolt on parts. They all put enough strain on the components, that a proper install involves a heck of a lot of work on the whole power train. Sure, you can jack more horses out of the motor, but not for very long, unless you improve the oil flow, the bearing strength, the balance in the motor, etc. etc. etc.
Not relevant to 99.9 percent of the people driving these trucks.
Guys like Fatherford do this, but notice he is already having to rebuild his transmission… and that’s without going full gonzo, blower etc.
Now back to the wonderful world of ‘bolt on’ stuff that most of us do on our street driven, everyday used trucks.
A fresh air intake is NOT an ‘intake’. The intake manifold is untouched. All you are doing is playing around with air temps. This is called ‘working on the margins’.
You can get great sound, you can get very small real-world horsepower gains, you can get a really cool looking thing under your hood.
You are not going to get a 20 horsepower gain at cruise RPM.
Forget it. Not gonna happen. Nope. No way. Look at the graphs, many of the ‘cold air intake’ systems give you LESS horsepower at 2000 RPM.
If the maker says it can get ‘up to’ 20 horsepower gain, it is true if it gets 1 extra horsepower at 5900 RPM.
UP TO means a gain from 0 to the up to number.
That could even legitimately mean 10 horsepower LESS at 2000 RPM.
Some of these cheap ones probably lower the horsepower at every point in the curve.
Most of the makers make a good product, and will not hurt your truck at normal RPMs. My point is that the advertising is not saying what many of the readers mean by more horsepower. Read the fine print. Look at where the meaningful gains are located.
On a 4.6 you are going to get 1-3 more horsepower at cruise from a good cold air intake.
On a 5.4 you are going to get 2-5 more horsepower at cruise from a good cold air intake.
Page 1
I think the problem in any analysis of these changes, is the premise itself is flawed.
Everyone tosses out figures, doesn’t mean the figures are right.
Even a dyno is subject to interpretation.
Useable horsepower has nothing to do with ‘dyno’ horsepower.
The 4.6 engine makes 231 horsepower at 4750
Torque is 293 at 3500
The 5.4 engine makes 300 horsepower at 5000 rpm.
Torque is 365 at 3750
You do not want to be exceeding 5000 RPM on these motors for any length of time.
An aftermarket part may advertise lots of additional horsepower, but it’s always weasel worded, or to be nice, it’s always filled with ‘disclaimers’ or statements that range from,’ Power achieved on test engine (hand built on a stand, not production in a truck), or the ever popular ‘your results may vary’.
Even more important, is power curve.
Look at any chart of horsepower or torque for any engine. It starts low, goes to a peak, then drops away.
Now look at our trucks. The maximum horsepower is at the top of the usable RPM range. Right before the red line.
Now look at any aftermarket horsepower improving component.
Ignore the fact that it is being tested on a ‘special’ engine, and in special conditions.
Look at where the most horsepower gains occur. Usually at or above the maximum you can attain in the real truck in real road conditions.
Sometimes (often with cams, high rise intakes, larger fuel systems, headers) there is an actual power decrease at ‘realistic’ RPMs. This is common.
You can kill your launch or take-off by decreasing the backpressure till the mix is over scavenged at idle. This will help you, but mostly above redline…
An over duration cam does the same thing. The engine has poor idle, poor ‘launch’ but by the time you get the RPMs up into the new higher power-band, you are really moving. And the tach is really above redline.
When building a ‘racing’ motor, this is not a problem. You put in extra lift on the cam, so that at high rpm you get more fuel. You put in more duration on the cam so that you get more fuel to the cylinder, and have more time to push exhaust out of the engine at higher RPM. This is bad at low RPMs but that doesn’t matter. You launch at higher RPM, and hold them up in the power-band at all times.
You improve the bottom end of the engine, improve the oil volume, etc. so the engine can support the higher RPMs where you are now making huge horsepower. You lower the gear ratio, actual, not just to compensate for bigger diameter tires, to take advantage of the higher RPM power band.
The further you move the power band up the RPM scale, the more potential horsepower.
Big horsepower ain’t gonna happen from true bolt on parts. Superchargers, turbo-chargers, Nitrous, are not true bolt on parts. They all put enough strain on the components, that a proper install involves a heck of a lot of work on the whole power train. Sure, you can jack more horses out of the motor, but not for very long, unless you improve the oil flow, the bearing strength, the balance in the motor, etc. etc. etc.
Not relevant to 99.9 percent of the people driving these trucks.
Guys like Fatherford do this, but notice he is already having to rebuild his transmission… and that’s without going full gonzo, blower etc.
Now back to the wonderful world of ‘bolt on’ stuff that most of us do on our street driven, everyday used trucks.
A fresh air intake is NOT an ‘intake’. The intake manifold is untouched. All you are doing is playing around with air temps. This is called ‘working on the margins’.
You can get great sound, you can get very small real-world horsepower gains, you can get a really cool looking thing under your hood.
You are not going to get a 20 horsepower gain at cruise RPM.
Forget it. Not gonna happen. Nope. No way. Look at the graphs, many of the ‘cold air intake’ systems give you LESS horsepower at 2000 RPM.
If the maker says it can get ‘up to’ 20 horsepower gain, it is true if it gets 1 extra horsepower at 5900 RPM.
UP TO means a gain from 0 to the up to number.
That could even legitimately mean 10 horsepower LESS at 2000 RPM.
Some of these cheap ones probably lower the horsepower at every point in the curve.
Most of the makers make a good product, and will not hurt your truck at normal RPMs. My point is that the advertising is not saying what many of the readers mean by more horsepower. Read the fine print. Look at where the meaningful gains are located.
On a 4.6 you are going to get 1-3 more horsepower at cruise from a good cold air intake.
On a 5.4 you are going to get 2-5 more horsepower at cruise from a good cold air intake.
Page 1
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If some of the makers can show more horsepower gains at 2000-2300 RPM they should post about it, showing real truck results.
And giving outside air temps, and altitude. Both of which make a huge difference to any horsepower.
Mind you, they are not selling these as cruise improvers, they are selling them as ‘top end’ power increasers. And why not? A good one does give you a nice edge in the next street race.
Ditto on the exhaust. Look at their claims. When they post charts, notice that most or all the claimed horsepower gains are at the top end, again, above where you drive unless you are beating the truck to death.
Now if we are not talking bolt on stuff, you can match all the components when you build the motor.
To find proper power curve enhancing components for building a high performance motor, you take the power curves of each component and match the ranges.
With bolt-on parts, the power curve is already determined by the cam/piston/valve etc.
So you are not going to move the power curve up very far. So you are not going to produce many more horsepower at any given RPM.
What you are doing is trying to minimize the losses from the factory equipment.
Putting an air intake on that gives you 30 more horsepower at 5700, but your shift point is 5000 is not too useful.
These trucks don’t take well to manual shifts…
Putting on an exhaust that has almost no back pressure, and is optimized to give you 30 more horsepower at 5500 RPM, well, see previous sentence.
Underdrive pulleys might give you ‘free horsepower’ but at the cost of less alternator, less power steering (sorta important if you have big tires), and less A/C on hot days at idle.
I am told there is no gain from the water pump and the fan. These are your two biggest horsepower drags.
E-fans might be a great idea. But the reason Ford doesn’t put them on the trucks turns out to be because they didn’t think the trucks would cool well enough in a hot climb with a load, so they would have to lower the towing etc. rate on the trucks. By a large factor.
Three e-fan vendors I talked to told me not to put them on my truck, as I live in a very hot climate, and climb hills.
If I lived in Michigan, they would be great. Again freeing up factory load, not making more horsepower.
Better than making more horsepower, as taking a load off your engine gets more gas mileage.
Of course the extra draw on the alternator on a warm day probably means you break even many days a year…
It’s all trade off.
Exhaust means more noise, less smooth power, maybe a tiny loss at the bottom, lots of increase at the top. (OK, most of us LIKE more noise.)
Air intake, maybe less at idle, less filtering of dirt, more noise, nice increase at high RPM. (OK, more noise, well it’s mixed on the intake, half like it, half don’t.)
Under-drive, better throughout the power range, better mileage. Less noise. Less power for your electronic toys, less power for your power steering. Less power to the A/C. A bear to install.
E-fans. If you live in a cold climate, all good. In a hot climate, use at your own risks.(That’s a quote from two vendors). Improvement in response, better mileage, quicker warm up (these trucks warm up pretty fast stock). A little hard to install, and pretty expensive for the recommended ones. Ford knows all about e-fans as they are stock on lots of Ford made cars. They had a reason to not put them on…
Combining. Combining the e-fans with the Underdrive pulleys makes a lot of sense, if you don’t have oversized tires, over powered stereo and are in a reasonable climate. Say temps seldom go to 100, and/or it’s pretty flat. Helps if you don’t tow big stuff.
Exhaust combined with intake has a certain logic, but it’s not really relevant.
If you increase the air flow, increasing the exhaust will work together.
If you increase the scavenging, (lower the back pressure) and then add more air, then again you have got a system working together.
Caveat;
We are not talking about increasing the air flow more than a tiny amount. We are talking about cooling the air slightly. Cooling the air has nothing to do with the exhaust.
So there is no actual reason to ‘combine’ the various bolt-ons. No reason not to, but no magic gestalt is gonna happen.
The cold air intake is not going to flow more air than your actual intake is going to flow. Take the dang thing off, and take the hood off, and it’s still only getting a couple percentage points more than stock. We are talking air flow, not temperature in the posts about more air in, more air out. Nope. Barely enough to measure.
They don’t claim it either.
And giving outside air temps, and altitude. Both of which make a huge difference to any horsepower.
Mind you, they are not selling these as cruise improvers, they are selling them as ‘top end’ power increasers. And why not? A good one does give you a nice edge in the next street race.
Ditto on the exhaust. Look at their claims. When they post charts, notice that most or all the claimed horsepower gains are at the top end, again, above where you drive unless you are beating the truck to death.
Now if we are not talking bolt on stuff, you can match all the components when you build the motor.
To find proper power curve enhancing components for building a high performance motor, you take the power curves of each component and match the ranges.
With bolt-on parts, the power curve is already determined by the cam/piston/valve etc.
So you are not going to move the power curve up very far. So you are not going to produce many more horsepower at any given RPM.
What you are doing is trying to minimize the losses from the factory equipment.
Putting an air intake on that gives you 30 more horsepower at 5700, but your shift point is 5000 is not too useful.
These trucks don’t take well to manual shifts…
Putting on an exhaust that has almost no back pressure, and is optimized to give you 30 more horsepower at 5500 RPM, well, see previous sentence.
Underdrive pulleys might give you ‘free horsepower’ but at the cost of less alternator, less power steering (sorta important if you have big tires), and less A/C on hot days at idle.
I am told there is no gain from the water pump and the fan. These are your two biggest horsepower drags.
E-fans might be a great idea. But the reason Ford doesn’t put them on the trucks turns out to be because they didn’t think the trucks would cool well enough in a hot climb with a load, so they would have to lower the towing etc. rate on the trucks. By a large factor.
Three e-fan vendors I talked to told me not to put them on my truck, as I live in a very hot climate, and climb hills.
If I lived in Michigan, they would be great. Again freeing up factory load, not making more horsepower.
Better than making more horsepower, as taking a load off your engine gets more gas mileage.
Of course the extra draw on the alternator on a warm day probably means you break even many days a year…
It’s all trade off.
Exhaust means more noise, less smooth power, maybe a tiny loss at the bottom, lots of increase at the top. (OK, most of us LIKE more noise.)
Air intake, maybe less at idle, less filtering of dirt, more noise, nice increase at high RPM. (OK, more noise, well it’s mixed on the intake, half like it, half don’t.)
Under-drive, better throughout the power range, better mileage. Less noise. Less power for your electronic toys, less power for your power steering. Less power to the A/C. A bear to install.
E-fans. If you live in a cold climate, all good. In a hot climate, use at your own risks.(That’s a quote from two vendors). Improvement in response, better mileage, quicker warm up (these trucks warm up pretty fast stock). A little hard to install, and pretty expensive for the recommended ones. Ford knows all about e-fans as they are stock on lots of Ford made cars. They had a reason to not put them on…
Combining. Combining the e-fans with the Underdrive pulleys makes a lot of sense, if you don’t have oversized tires, over powered stereo and are in a reasonable climate. Say temps seldom go to 100, and/or it’s pretty flat. Helps if you don’t tow big stuff.
Exhaust combined with intake has a certain logic, but it’s not really relevant.
If you increase the air flow, increasing the exhaust will work together.
If you increase the scavenging, (lower the back pressure) and then add more air, then again you have got a system working together.
Caveat;
We are not talking about increasing the air flow more than a tiny amount. We are talking about cooling the air slightly. Cooling the air has nothing to do with the exhaust.
So there is no actual reason to ‘combine’ the various bolt-ons. No reason not to, but no magic gestalt is gonna happen.
The cold air intake is not going to flow more air than your actual intake is going to flow. Take the dang thing off, and take the hood off, and it’s still only getting a couple percentage points more than stock. We are talking air flow, not temperature in the posts about more air in, more air out. Nope. Barely enough to measure.
They don’t claim it either.
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Page 3
So do you get more usable horsepower at 5000 RPM from each of the mods? Yep, a good exhaust will flow much better at the higher RPM than a stock quiet one.
Small gain from lowering the temp in the cold air intake, larger increase from the low restriction air filter. Big increase in ‘power sound’.
So no real extra increase from adding them together, no compounding. I wish it would.
To get the compounding, we would have to build it from stock, with a game plan.
Sorry about that
Chris
So do you get more usable horsepower at 5000 RPM from each of the mods? Yep, a good exhaust will flow much better at the higher RPM than a stock quiet one.
Small gain from lowering the temp in the cold air intake, larger increase from the low restriction air filter. Big increase in ‘power sound’.
So no real extra increase from adding them together, no compounding. I wish it would.
To get the compounding, we would have to build it from stock, with a game plan.
Sorry about that
Chris
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Hey, what you said ... Chris ... you explain my .02 domino reference effect quite synergistically while deflating if not negating gestalt! Most excellent work!
Though ... I'll soon re experience long slow tows in relatively hot conditions making a real life test of the tow/heat theory! I have a few places that I go that gets our trucks quite hot while pulling. A couple are slow bumpy steep grades where my theory is that the engine driven fan just doesn't pull enough air to cool things down... I would think that electric fans could cool or pull more air than the engine fan in many conditions. This is slightly contrary to what I got from what was just said.
Care to shed some additional wisdom or elaboration in this area of thought?
Though ... I'll soon re experience long slow tows in relatively hot conditions making a real life test of the tow/heat theory! I have a few places that I go that gets our trucks quite hot while pulling. A couple are slow bumpy steep grades where my theory is that the engine driven fan just doesn't pull enough air to cool things down... I would think that electric fans could cool or pull more air than the engine fan in many conditions. This is slightly contrary to what I got from what was just said.
Care to shed some additional wisdom or elaboration in this area of thought?
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Originally posted by tycreek
Hey, what you said ... Chris ... you explain my .02 domino reference effect quite synergistically while deflating if not negating gestalt! Most excellent work!
Though ... I'll soon re experience long slow tows in relatively hot conditions making a real life test of the tow/heat theory! I have a few places that I go that gets our trucks quite hot while pulling. A couple are slow bumpy steep grades where my theory is that the engine driven fan just doesn't pull enough air to cool things down... I would think that electric fans could cool or pull more air than the engine fan in many conditions. This is slightly contrary to what I got from what was just said.
Care to shed some additional wisdom or elaboration in this area of thought?
Hey, what you said ... Chris ... you explain my .02 domino reference effect quite synergistically while deflating if not negating gestalt! Most excellent work!
Though ... I'll soon re experience long slow tows in relatively hot conditions making a real life test of the tow/heat theory! I have a few places that I go that gets our trucks quite hot while pulling. A couple are slow bumpy steep grades where my theory is that the engine driven fan just doesn't pull enough air to cool things down... I would think that electric fans could cool or pull more air than the engine fan in many conditions. This is slightly contrary to what I got from what was just said.
Care to shed some additional wisdom or elaboration in this area of thought?
My info on the heating comes from the vendors, and Ford. And I hope your truck cools great, no problems, and you will keep us posted.
I want them to be wrong.
I just don't expect them to be wrong...
A thermal clutch fan, when hot, can pull a wicked amount of air. The clutch freewheels when you don't need the extra air.
You don't get something for nothing. If it takes 15 horsepower to move 20,000 cubic feet of air, then it takes 15 horsepower to move 20,000 cubic feet of air.
That means that it takes 15 horsepower to spin a mechanical fan, or 15 horsepower in electricity to spin two electric fans.
If you can find where this doesn't apply, I would be very interested.
The gains are from warm up, where you don't need the fan, and from light usage, where the fan stopping has no effect on the rig.
In cold weather, the mechanical fan is a liability. There you get great gains from the electric fan.
Cruising around town in 35 degree weather and the electric will save you the big bucks on gas.
But under towing, 100 plus degrees, etc. to cool the motor with the electric will take about as many horsepower as to cool it with the mechanical.
No free lunch.
Still, if your usage/ conditions allow it, it's the best gas saver, mod that I know off. It's also reduces engine wear, and is environmental friendly.
Again, my warmest regards, and I hope you prove the vendors, etc. wrong wrong wrong.
Chris
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Originally posted by MikeF150
Chris... I understand your logic, but any insight into how the addition of just the AF One from Troyer gets an extra 25 HP at the rear wheels @ 3000 RPM.... ?? AF One
Chris... I understand your logic, but any insight into how the addition of just the AF One from Troyer gets an extra 25 HP at the rear wheels @ 3000 RPM.... ?? AF One
Tuning was never brought up in the discussion. Too many variables.
Also look at the air filter in the pics. I don't think I have ever seen a K&N style air filter that would flow more air. That's not the intake, that's the filter we are talking about.
Snipped quote from Mr. Toyer
Quote
Now in terms of PEAK power gains at 5000 rpm, there the gains are smaller - about 10 HP or so, in round numbers, and this same pattern is seen with all intake kits for these vehicles - meaning the few that actually gain *any* power gain most power down low, and then a little bit up top.
Quote
So at the point where an exhaust makes most of it's gains, the 'intake' makes the least of it's gains, if any. As the man says, the few that actually gain *any*.
So going back to the point of this whole over long thread, is there is no 'adding' or 'adding plus' in the result.
For those who don't want to total it up, taking the vendors word for it, (why not, he's a good guy, and despite making a living selling these parts, he tries very hard to give us the straight stuff) the best unit on the market might give you 3% increase at the shift point. Most brands won't give you much, if any.
As to his lower range increased numbers, I presume the 5.4 has a god-awful factory intake/filter. That’s what he is saying, in plain English.
I have only messed around under the hood of a couple of 5.4 engines, so I don’t have that knowledge. I’m sure he does.
The 4.6 intake is pretty adequate. The factory air filter is about like breathing through a ten foot piece of garden hose...
With a K&N filter I got 1 mile better gas mileage, but by switching to the AEM brute force, no gain in mileage, only a gain in power above 3500.
Remember, 4.6 to 5.4, apples and pears.
Chris
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[QUOTE]Originally posted by J-150
[B]I would say in real life 15 plus 25 equals 20 for HP gains.
How about 'claimed' 15 at 3000 plus 'claimed' 25 at 5000 equals
actual 5 at 3000 and 15 at 5000.
And when combined, 6 at 3000 and 16 at 5000.
I hate claimed figures.
I also hate it when they won't give a nice clean graph on a regular engine, showing the curve, so you can match it with your other components.
Oh well, they don't make a living selling graphs....
Chris
[B]I would say in real life 15 plus 25 equals 20 for HP gains.
How about 'claimed' 15 at 3000 plus 'claimed' 25 at 5000 equals
actual 5 at 3000 and 15 at 5000.
And when combined, 6 at 3000 and 16 at 5000.
I hate claimed figures.
I also hate it when they won't give a nice clean graph on a regular engine, showing the curve, so you can match it with your other components.
Oh well, they don't make a living selling graphs....
Chris