a new way to rate engine power

Interesting thread..... My brain hurts now , ill be keeping an eye on this though

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Measuring CFM ,,,
There are a few ways to do that I know of but I'm not very familiar with any.
One way that I hadn't thought about was the way that EX mentioned earlier, by measuring the fuel flow and Air fuel ratios , that should give a pretty close calculated measurement of CFM.

Here's what's important about the CFM
(Rpm/2 )displacement x 1728 = CFM intake of engine theoretically. The theoretical CFM and RPM would be direcly convertable. This would reflect 100% VE and some engines will never come close yet others can achieve 100+% in the sweet spots.

If the engine being looked at doesn't come close to 100%, well the theoretical cfm will be higher leading to a predicted power output much higher than actual. On the opposite side of that an engine reaching or surpassing 100% will have a higher output than predicted because its taking in more air than expected.

 

Pontiac 8-350-2bbl-hp 255@4600 Tq-355@2800- B/S 3.867 x 3.75-8.8:1
Chevy 8-350 lt1 - Hp 353@ 5600 Tq - 292 @ 4,100 rpm.

So comparing those two powerplant configurations from 1970 you'd come to the conclusion that they are very different.
I'd also say that the Pontiac makes better use of the fuel because its producing much more power at a much lower RPM than the Chevy. I'd venture to say the Pontiac gets a shit load better milage to move the same load. However in the peak HP war the Chevy spanked it pretty hard but how hard? At what cost? And when those are factored in did it really win or loose and by how much.

Right now there's no easy way to factor or comparison the two.
Even more difficult would be the comparison of widely different engine displacement.

 

Actually HP is a myth or maybe better said it is an abstract idea based on Torque at a given RPM.

I like the idea of torque @ CFM. I am not sure that it would be entirely accurate either is can change by a simple carb or exhaust change. And again it is RPM dependent. For instance I have an engine of a given cubic inch displacement that reaches max torque @ 4800 that I tune for another fella. But we have played with exhaust and induction a little bit and we can move max torque by simple exhaust or intake changes. Last time we did any checking we were able to move max torque to 5200 by changing the carb and ignition timming, a little more lead and a carb rated 60 CFM more than what we normally used. Same engine, no change to lower end or valve train just a carb and timming change.

If not for ignition timming being part of the equation I guess that is one way to compair max torque per CFM but we still reach max torque @ a different RPM than say the same engine in stock trim.

I'm just thinking out loud here.

 

Max torque RPM is, by definition, the peak of the VE curve for a given engine. Beyond that point, the cylinders can no longer be filled as effectively by that engine combination. So torque (or "instantaneous" output) will fall off at any higher RPM. So Vicky, that may BE the answer to your question right there...although we still can't find the actual VE at that RPM without measuring airflow and/or fuel flow.

Here's the magic of Watt's horsepower equation: HP shows us how FAST the torque begins to fall off after peak torque RPM is passed. We could say that the more "efficient" engine will continue to build horsepower to a peak RPM that is much higher than peak torque RPM, therefore giving us much more useable output...(less shifting required, etc.)

 

Maybe on a dyno that would work to a point.

Her is my logic on that statement, if you torque drops off too much in the real world you cannot not continue to pull past a given RPM where as on a dyno you could theoretically continue to rev and build HP as you are not pulling anything but the dyno.

Let me try an extreme example, say you have a 3500 lb car, your peak torque is 375 @ 4800 but drops off to 325 right after that. Unless your tires break loose it is not going to continue pulling into the higher RPM range. On the dyno it may very well rev right up to 6K.

I know it is not much for numbers but to really compare engines you need to swap them into the same body with the same driver and let fly.

Again I am just thinking our loud here.

 

Wow.
Do you really believe that torque readings from a WOT dyno run can predict fuel mileage in real world conditions with the throttle nearly closed?

 

I ]know it is not much for numbers but to really compare engines you need to swap them into the same body with the same driver and let fly.

Again I am just thinking our loud here.

Yep think out loud session.
And have some way rate and compare engines by some yet to be determined coefficient that equates to swapping as you said

 

Please say where I said this ? I didn't but...
Since you've mentioned it maybe it would give some insight into things - hummm?

 

The Buick torque rating was when gross power was used? What would it make on the same dyno used for the BBC? I bet 10 percent less but still more than the BBC at 2800 rpm...

In the bike world,hi rpm power always beats big low rpm power in a standing start drag race.Kawasaki Z14 makes about 180 real HP at 9500 rpm and 113 torque at 7500 rpm,runs 9.7 1/4 mile stock with a good rider.
This works with cars too....
The HP and torque figures currently used gives a good idea of all around engine performance in my opinion.

 

Depends on what you are comparing I guess.

Fuel consumption would need to be compared over a given amount of time and miles and it would only be average. HP or torque although not anything that you could actually measure could be measured on a track but all you would really be comparing is how well the engine performed and then engine weight would become a problem as it would effect handling or how the specific car hooked up. But you would be able to measure which was the better choice I suppose.


This brings me back to dyno pulls, you could tell on a dyno which engine was more efficient per what was measured on the dyno but the dyno does not take into account weight and packaging constraints.

For example lets take your hemi and compare it to a high winding small block. In your car as you already have the hemi in your car, handling wise you car is going to handle all together differently with the added weight of the hemi in front of the rear axle than it would with the lighter small block. Now lets take it a step further, your hemi is going to catch more wind. Both of those add up to a less efficient engine in the real world even if your hemi proves to be more efficient on the dyno.

That is not to say that either is the better choice or that either engine is better than the other, just a real world comparison.

I have to ask a question on the original formula/idea. When you look for max torque:CFM aren't you just compairting volumetric efficiency and not really compairing power at all?

 

Doesn't quite work that way, Benno... The dyno can actually load the engine harder than anything we can do on the road. Usually a dyno test is set up to "allow" an engine to gain revs at a certain rate (say 200 rpm/sec), and measure torque output at that rate. It's possible to load the engine to "stall" at any RPM (like being on a transbrake at the strip), but there isn't much point in that.

Not disagreeing with your point about torque falling off, but the dyno will find that fairly accurately...

 

Agasin it is dependent on the dyno operator and not on real world usage though isn't it?

I am not agianst dynos, I have dyno numbers on engines that I have kept, they are a useful tool, just being the devil's advocate here.

 

How could they? At anything less than full throttle you are not measuring VE, but a whole bunch of other factors like mechanical efficiency, pumping loss, etc.

Ideally, what we would really like for efficiency is an engine that starts out as a single (KEY: with no pumping loss on the other cylinders) and adds a cylinder at a time as required output increases past the limit of one cylinder.

 

damn you guys are getting to deep for me! lol ill just keep building my engines with the parts i know make them go fast>..lolscrew numbers, when i win in a drag race i know i did good!!!lol

 

You seem pretty eager to piss in everyone's wheaties. First the iPod thread now on this thread talking about hp ratings. For a guy who spends most of his time posting in the intro section you sure seem to think you know what's best for everyone. As for this thread, it surely is making for some interesting reading.


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Uh... How about your post I quoted?
Maybe not word for word, but that is exactly what you are driving at, as most other posters seem to agree.

Unless you know the exact fuel consumption at the different rpm's you've posted, it's just useless info as far as efficiency is concerned.

Do you really believe that a carburetor delivers exactly 14.7 to 1 throughout a dyno pull? At all RPM's and loads?

No engine can burn 100% of the fuel in the cylinders so all engines need a slightly richer FA ratio to make peak power.

And what does it matter what the fuel efficiency is at full throttle?
If you're racing, unless it's an endurance race, you won't care, and if you are trying to get the best efficiency out of an engine, you would never be at full throttle. Therefore, full throttle measurements are totally meaningless as far as real world efficiency is concerned.

 

I assure you there is no hidden agenda of hidden meanings. If its not word quote I didn't say it. You are welcome to your assumptions but please don't make them mine or anyone else's reality. Fair enough ?

Perhaps the term "efficient" automatically conjured visions of sparingly also. Forget about the cost and quantity of fuel used and look more at what you get for the amount of fuel.

Another way to look at it might be this:
A company spends x and makes y
Another company spend 100x and makes 99y.
99y is certainly greater than y but first company is more efficient.
A third company spends 300x and makes 302y
This third company consumes far greater x and certainly isn't more economical than the first but it produces more y for each x.

If you think its useless, great. Providing some solid info on that may lead the discussion to more fruitful path and one that's not useless.

 

Aircraft piston engines were rated for fuel burn per hour . Unlike cars, aircraft engines run under high load all the time..Gasoline engines fuel burn per HP is only efficient at nearly or wide open throttle . Generally around .5 pounds of fuel per HP per hour being the most common for well designed gas engines. Part throttle uses less fuel but more fuel per HP.
Flathead engines faded away in aviation very early on because they consumed more fuel per HP than OHV types.

 

What about just using Kilo-Watts like the Ausies do?

 

Sorry, I wasn't trying to rile you up. However, to keep this about engines and efficiency, I still think that without knowing precisely how much fuel is consumed for each engine at it's peak torque RPM, it is meaningless.

The problem I have with your theory is that you seem to think that CFM's VE and FA ratios and everything else that applies to an engines efficiency don't change as the RPM's change. There is nothing in your theory that is repeatable or reliable to be able to predict the efficiency of on engine at any rpm.

Maybe you could better define what you mean by efficiency or whatever you're trying to get to.

 

The op seems to want to combine power with efficiency somehow.

 

I would think with all the sensors on a modern engine (MAF, O2, TPS, etc.), you could get the info to make about any caculation you wanted.

I'd also bet that there isn't any kind of calculation of HP/efficiency at idle/partial throttle/full throttle that hasn't been done by the factories when they were developing modern fuel systems.

 

Some good points here.

I'm not an aviation expert but I have flown some friends planes (Cessna's mostly) and after take off and climb out I close the throttle to about half to get the best cruse (most efficient) speed setting. Can any more experienced pilots confirm this?

 

The problem I have with your theory is that you seem to think that CFM's VE and FA ratios and everything else that applies to an engines efficiency don't change as the RPM's change.

Really ? The whole point of this is to determine these changes based on RPM and the calculated theoretical CMF.
Of course all of the things you mentioned all change with rpm range.


I'm beging to think you have not read what's here or perhaps a preconceived assumption about your thoughts on my thoughts. Or your ideas about what "I'm driving at" or that what you think about what I seem to be thinking is fucking correct.

Now FNGs will get some basic respect from me, because I don't know them. That could be mutual

 

My head go boom.




O.K., I think you are on the right track to be looking more closely at torque when searching for more efficiency. If that IS what you're doing. (Who Knows?) Like you, (I think), I came here to learn.

 

The HP is comparable yes. 100 HP is 100 HP.
The 2000 rpm vs 6000 rpm is not comparable .
We can assume that the 2k rpm engine is exactly 3x the displacement size of the 6k rpm and then they COULD be comparable again. Not because of the cubic inches, but because of the theoretical cfms being equal.
But a 95 cubic inch twin @ 6k to a 285ci 6/8 @ 2k isnt going to be comparable unless the max torque is there at those rpms too.

 

This thread is a waste of space.

 

Why? Just because the OP can't explain the meaning or value of his fundamental equation and doesn't have any effective measure of one of its key parameters?. He did warn in his sig that he's looking to fit a breathalyzer to his keyboard!

 

I'm a newbie on this site, so could someone explain to me if this thread is really a form of trolling, or are these guys writing about stuff they just don't understand and this "black and white fact claim" is an example of the way it comes out? Sorry if this sounds offensive porkbeaner, but I just don't get it.