Engine Index Ratings (EIR) By Cyrus

[crazy280]

I think 240jz has the right idea with the "Riemann Sum". We should use that technique to estimate the horsepower in an engines useable powerband, which is usually the area between peak torque and peak horsepower, but in real life it's actually determined by what rpm your transmission drops you into when you shift into each gear. So we need to know the gear ratios of the tranny attached to the engine to figure the powerband of each gear, then use the Riemann Sum to get the area of the horsepower for that powerband, then multiply that number by the gear ratio, seperately for each gear. You'd end up with a sort of mathematic "map" of that engine's total real-world power. You would list the power as "total horsepower x rpm for each gear". This method takes into account not only "mechanical advantage of gearing" for high revving engines, but also "horsepower under the curve" for beefier engines. It would look something like this:

1st gear: 10,000

2nd gear: 7,000

etc.

I would love to calculate an example for this but my brain is tired now ........... Anyone?

[BrandonsZ]

To compair complete cars try this:

 

(Area under the curve HPXRPM from 0 to Redline)*Gas Mileage

-----------------------------------------------------------

Weight

 

-The HP Curve over the entire RPM range takes into account the torque bonus for bigger engines (higher HP at lower RPMs) and RPM bonus for higher revving engines (HP at Higher RPMS).

-The Average Gas Mileage takes into account body shape and gear efficiency.

-The Weight is self explanitory

 

This could be a back of the envelope calculation before you bet your pinkslip with that Ricer on Saturday Night. If you research well, you could be the proud? owner of a 1993 Acura Legend with a Turbo sticking out of the hood and a rat's nest for wiring under the dash.

 

I'd like to add something about octain rating requirements because of course you have more energy in 107 octain than 87, so it's an unfail advantage to this calc, but it's not as simple as penalizing Rating/87 because this is a virtual percentage of octaine as compaired with pure octaine, but if we looked up the heating value of the fuel you use in either car we could use that for compairison it's a little variable that messes with the fidelity of mileage.

 

This is very subjective, but is gives you a warm fuzzy or a well founded respect depending on which number is bigger. Too bad it's not a simple number with simple units. We need a unified theory of automotive engineering here.

 

I like it but it's not perfect by any means.

[Scottie-GNZ]

Just curious. Why is RPM a factor and a factor that gives a bonus or penalizes a combination? Is an engine that makes 400hp at 6500 RPMs "better" than an engine that makes 400hp @ 5200?

[BrandonsZ]

It was explained earlier and quite nicely I may add, but not by me, I couldn't do it justice.

[dr_hunt]

I dunno, you can size up the competition any way you want, and they can size you up any way they want, math or no math, formula or no formula. But I've put faster cars on the trailer cause I tree'd them or they broke, or they broke out or they red lighted, or the best of all, cause I'm faster. I like the old tried and true method of racing to see who's the fastest, which combines driver skill and a good consistent car.

 

My buddy Joe Saavedra runs a blown alky dragster on a 7.70 index, typically he can run a 7.70 right off the trailer or at least in the 7.70's no matter where he runs. He's tough to beat and so is anybody on any given day. It has been said, repeated by myself, "It's better to be lucky than good".

[cyrus]

After much soul searching and sleepless nights I have found a refined formula that seems to hold true for example. I may move it from a theory to a law...

 

(Quarter mile trap speed / Cost of Swap) X Bling = Coolness factor, Cf

[BrandonsZ]

I made an excell spreadsheet with wheel torque vs. RPM for every gear and graphed it in an area graph. Then I compared the original engine and original gearing from a dyno and normalized it with my newe engine. Then I took an estimated drag coef. based on the alleged maximum speed of a stock z-car using CX^2. And graphed that too. I got a pretty cool picture. It's a warm fuzzy.

 

http://album.hybridz.org/showphoto.php?photo=3252&cat=500&page=1

[rudypoochris]

this is how i woudl do it... assuming a max performance run with mpg at say crusing (i know this isnt accurate the crusing mpg part but hey it will offset the always going full throtle part)

 

the HP value woudl eb the HP under the curve between lowest practical rpm and highest practile rpm... so between say 3000-6000, because lets face it if we are trying to go fast we are not going to be using 750-3000 rpm....

 

NOTE: cars will have different interval to measure from but if we keep them all 3000 rpm it should provide for a relatively decent application.. for instance a rotary maybe would be best between 6000-9000 while a v8 is best 3000-6000 and a diesel from 2000-5000... lets not worry about diesel though....

 

so using the original formula:

 

EIR = (HP under the curve at the given interval stated above)*(mpg at crusing)/(Weight of the engine)

 

now this is how id do it....

 

EIR = (HP under the curve at the given interval stated above)*(mpg at crusing)/[(Weight of car)-(the original drivetrain)+(the new drive train)]

 

the whole drivetrain and car weight part gives a more realistic representation of how the engines weight effects the whole scenario. An engine weighing 400 lbs compared to a 200lb one is 100% heavier when put into a 240z lets say it is 2100 lbs with the 200lb engine and 2400 lbs with the 400lb engine (the big boy has a beefed up drivetrain too) so, the increase instead of being 100% would be a much smaller effect thus reducing its overal effect in the formula. Because in real life even though the 400lb engine is twice as heavy its not THAT big a deal once in the car. Btw this thread should be made sticky and someone should figure out a standard HybridZ EIR. YAY

[Jsquared]

What, all you guys ever do is go in a straight line?

 

the whole drivetrain and car weight part gives a more realistic representation of how the engines weight effects the whole scenario. An engine weighing 400 lbs compared to a 200lb one is 100% heavier when put into a 240z lets say it is 2100 lbs with the 200lb engine and 2400 lbs with the 400lb engine (the big boy has a beefed up drivetrain too) so, the increase instead of being 100% would be a much smaller effect thus reducing its overal effect in the formula. Because in real life even though the 400lb engine is twice as heavy its not THAT big a deal once in the car.

It's a big deal if the heavy engine doesn't have a significant increase in power, and it will noticeably throw off the way the car handles dynamically.

 

Engine Index Ratings

 

I just came up with EIR to evaluate the best possible engine availble. Tired of specific out put balonney, etc. Well to rate an engine overall: EIR = (HP x combined mpg)/weight

 

 

ie...

EIR of Stock LS1 = (325hp x 21 mpg) = 17.06

----------------

400 lbs

 

Lets run some more motors to see what is best.

mpg can't be used to judge an engine, mpg is heavily reliant on transmission gear ratios, final drive, and vehicle weight. Put a second stupid-high overdrive on any engine and it'll get good economy on the highway. And when is specific output "baloney"? It tells a lot about the amount of engineering that went into an engine and how well that engine is designed. Then again, a high specific output engine that is still too small doesn't do anyone any good

I thought of this when comparing a "little" 4.6 mustang engine "big" 5.6 LS1, the ford look about double the size and make way less power. So I want to be able to quantify that. I was reading an article automotive engineering and GM looks at MPG x HP = index

 

from page 100

car hp x mpg = index

c6 400 x 22.6 =9040

GT2 porsche 477x 18.2=8981

viper 500x 15.5 = 7750

911 turbo 415 x 18.2 = 7553

911 3200 x 20.6 = 6592

murcielago 580 x 10.8 = 6264

s2000 240 x 22.7 = 5448

z4 225 x 23.6 = 5310

360 400 x 12.7 = 5080

Leave it to GM to make up some baloney formula to make it look like they can build something well. The modular Ford engine looks big because it has DOHC heads. True, the center of gravity is marginally higher, but the ability of those heads to flow significantly more air is a much larger benefit than the problem of the raised Cg. Of course, you can't really compare those two engines in a DOHC-vs-OHV argument since neither of them is what would be called a top-notch design. Add to that the fact that mpg of the LS_ engines would be significantly less with a normal transmission.

Car 2 has a higher peak and narrower powerband and will require a higher 1st ratio to get the torque to the road and more frequent shifting (more gears) as a result which wastes time.

incorrect. You can't judge this just because the engine is smaller. My little factory forced-induction 2-liter 4-banger has a wider powerband than a stock NA LS1. It doesn't make as much power or torque, but it weighs about 100 lbs less. Only 5 gears, but a shorter rear end, lighter car, etc. Too many factors to judge.

So to truly compare one car to another we need weight, gear ratios, final drive ratio, the complete powerband curve, what tires they are using (size, brand and model), their aerodynamic signature including downforce and drag (assuming drivers are equal), and one heck of a complex empirically based formula taking all these into account.

 

This could be done and we could make a simple number to tout your ride, but with unequal drivers, you could still lose.

Well said

After much soul searching and sleepless nights I have found a refined formula that seems to hold true for example. I may move it from a theory to a law...

 

(Quarter mile trap speed / Cost of Swap) X Bling = Coolness factor, Cf

excellent! We have a winner.

You guys have gone from comparing engines to comparing whole cars. To simply look at the engine vs engine, all you need is displacement, a dyno graph, and a weight. HP/L, TQ/L, powerband, HP/LBS, can all be found from that. To decide what to use in a car... well that requires a whole new set of variables, most of which are focused more on budget and the car's use than the engine itself.

[BrandonsZ]

So my chevy Sprint from 1986 was... say 90hp and got at it's high 60+mpg

5400... I beat a Z4??? Wow no wonder why I liked that car. Damn thing wouldn't pass smog in 97, GROSO POLLUTER, how does a freekin 1.0L engine getting 50-60mpg have gross polluter? GMAFB!@