Am I Crazy: New but Quick Turbo/Supercharger Math?

[zguy36]

Hmmm... which numbers were fudged? All of them!!

 

Your method of finding an equation doesn't start from any theory, from any laws of physics or thermodynamics. You have taken a start number and an end number and come up with a simple equation that takes you from point A to point B for a small set of numbers. Apply this to a set that is different from your initial set and your equation doesn't work.

 

To sit and dwell on the fact that these numbers seemed to have worked out for such a small set, and an equation based on no theory is a bit naive. Do some searching on amazon and find some automotive engineering books. It won't take you long digging into these to learn a few more tools to play with.

[OlderThanMe]

Maybe if you want to just brag while you are building a motor about how much power you are going to make...

WHY do you need to estimate power within 10hp before you build the thing? Just build it until you are fast enough.

 

I would rethink your math logic and try to find out a proper way to determine your numbers if I were you.

If you were to find a mathmatically sound way to find horsepower numbers then please by all means share it with us.

rant mode off

rule #6 might be nice to read:

Click:

 

 

Olderthanme

[Kinked_Chrome]

Wow, it seems like you have put a lot of thought into this. I think you guys are trying to make this more complicated that it actually is. With out any units attached to anything it took me a little while to figure out what was going on, but here is my take on things.

 

The first equation

 

CFM flow x cylinders x .257 = HP

 

I think this one is great, in about to seconds you can guess the HP of a high performance engine. the constant .257 i assume is determined with the energy released in gasoline at max power rich formula, an average rpm, and an average efficiency of a high performance engine, constant air intake temp, yada yada. basically a "guess" of what all other variables are gonna be.

 

The second part

 

Boost in PSI x 14.7 = additional horsepower. All this means is that you are assumming that on average you gain 14.7 HP per PSI of additional intake pressure. Which is why your numbers are different for intercooled and non intercooled setups. i'd be willing to bet for non intercooled lower boost (3-6psi) you're only going to see gains of 12-13 HP/psi and on the much higher performanace applications (intercooled and what not) your more likely to see 16-17+. I think that your equation would be more useful for determine how efficient a turbo setup is, rather than guessing HP. Instead of guessing HP you turn it around and solve for HP/psi

 

For example:

 

start with a 300 HP NA engine

 

and you get 450 HP turbo charge with 10 psi

 

450-300 = 150 HP/10psi = 15HP/psi

 

now let say we add an intercooler and get 460HP and our boost drops to 9psi

 

460-300=160HP/9 psi = 17.8HP/psi

 

Does anybody see what I'm gettting at or am i just rambling on?

[Z-8]

Kevin,

I just read your post, and I'll look at my mag, which I think is an "engine masters", and should have another post tomorrow sometime. I'm glad to help out anyone who has a new equation that might pan out. It's kinda cool when you think about it, at the cusp of discovery, finding a new way to do something. I wouldn't use this until a real answer is found, but since I didn't win the lottery this year, and hence, am not going to buy every engine piece I can think of(still dreaming of that moment), I would use little equations to see what piece's might work best for my budget. I say go for it, and the nay-sayers should read rule #6. I hope I'm not pissing anybody off with this, I really do enjoy this site.

[Kevin Shasteen]

Z8, looking foward to your ideas.

 

Thank you kinked chrome. I never even thought of it that way; but I do believe you have nailed it, which is why I posted the thread.

 

If you get more brains attacking an idea it is merely a matter of time before someone comes up w/the solution.

 

Why, try to get as close to a HP rating as possible? Have you not ever read an article where the authors of the article and the builders of that engine state before they put the engine on the dyno that said engine should make [x] amount of hp; and once the engine is put on the dyno they are w/in 10 to 30hp of their guestimate?

 

I personally like the idea of knowing, within as close a proximation as possible, what an engine will make prior to that engine being put together.

 

The purpose is to make sure I dont, and to make sure any other performance engine enthusiast doesnt, OVER BUILD/OVER CAM their engines.

 

I ran into a guy (never met him before) who had built a twin turbo SBC engine. He had it entirely build, spent a lot of time and money; yet couldnt get one of the turbos to spool. He said the cam company couldnt give him any answers, his cylinder head company couldnt help him and none of his friends could help him. He told me his tt engine has been sitting now for about 6 months and he was thinking about pulling it and putting in a BBC.

 

I asked him what his cam specs were and in two minutes I suggested his cam had to much overlap in it. He told me Comp Cams had sold him a cam according to his wishes. I told him I dont know what he asked Comp Cams for and I dont know what Cam they think they sold him - but, if his cam has as much overlap in it as he says it does....his cam is the problem.

 

He told me that, if the cam were his problem, that I had solved his problem in two minutes that no one else has in the past 6 months. He had even called the turbo company and cam company multiple times trying to figure out why his one turbo would not spool up.

 

He came by my work a few weeks ago and told me that Comp Cams had on their computer sold him a turbo cam, yet somehow someone had grabbed the wrong cam in the warehouse and sold him the wrong cam by mistake.

 

Comp Cams gave him the right "Turbo Cam" with the correct overlap in it. Now he has a TT SBC that kicks but. Why couldnt anyone else help this guy? Why did it have to be me? I dont know - but I like the idea in knowning that my efforts helped some guy out there that was about to give up on his tt engine becuase of an accident at the cam company.

 

Why do we spend so much time staring at our computers utilizing an engine simulator trying to decide which combination is best. Doesnt anyone realize that these simulators are based on equations? I like the idea of knowing what an engine will make before that engine is put together; that is just me and so when I read an mag that has a well written article in it - I buy that article and put it thru a lot of scrutiny in an attempt to further my understanding. This scrutiny adds to my past knowlege base.

 

Anyway, that is why I go to such exstremes.

 

This anomaly being discussed on this thread is identical to the 1/4 mile equations where if you have a time slip of any car going thru the 1/4 mile trap, you also will have the speed of the car, get the car weighed w/the driver in it and then you can solve for the amount of RWHP needed to make that 1/4 mile trip. With any equation you can transpose those variable if one variable is missing and all others obtained.

 

With that 1/4 mile formula in mind - the end answer will give you RWHP. Then you can add the usual assumed 15% loss of power due to drivetrain inefficiencies to obtain FWHP.

 

Now that you have the FWHP you pretty much know how your engine stands performance wise; yet this 1/4 mile formula in no way dictates which car should be used, it in no way dictates which engine/trans/cam/heads/suspension...or anything else should be used.

 

If you didnt even have a car you could still utilize the 1/4 mile equations to know how much FWHP is needed to get a theoretical car down the 1/4 mile if you had car weight of [x] and wanted to go thru the traps at a speed of [x] you could determine how much FWHP is requred of your engine (you have not yet built) in order to perform at that level.

 

So, if you dont have a car yet you can use the 1/4 mile formula: what good is it? By itself, nothing; yet it is good in giving the end user ideas of how to get close to their desired objective. From there good ole research and development takes over. I believe this anomaly - if it plays out falls into this same category.

 

For those of you who think the numbers are fudged; I do have a process for normally aspirated engine analysis; and I can work it forwards or backwards depending on which variables are known or not known. You dont have to know everything in order to come up w/reall #'s. You need to know a lot, w/common sense; but the mfg's take care of most of the intangibles.

 

I always try to concentrate on three relationships:

1) DCR to SCR relationship

2) Peak Power to Displacement relationship

3) Peak Power RPMs

 

This is how I approach every well written performance article.

 

The very first thing I do is determine the relationship between cylinder heads and the cylinder. This relationship gives me a constant that after you have done this a few hundred times you will begin to see patterns. The qualifier you will begin to identify by doing this will determine if the cyl.heads are mild, medium, or maximum for the level of performance you have chosen.

 

The second thing I do is determine the overlap of the camshaft. Anyone who has been researching engines will recognize the cam overlap chart that has been around for years. This further indicates patterns; of which further allows the researcher to understand the category of performance that engine will fall.

 

The third thing I do is locate a cylinder head CFM chart of the cylinder head(s) used in the article. Once I have that CFM chart I then determine what cfm is required to make the hp the dyno dictates.

 

Again, after you have done this a few hundred times you will begin to see patterns and these patterns will allow you to know what an engine will put out before you actually ever look at the dyno.

 

The one floating variable that can not be known is the volumetric efficiency of that engine. For most do it yourselfers, it can be assumed as most do it yourselfers build a normally aspirated engine in the 1.05 to 1.35 hp per cu.in. and in the 1.45 to 1.65hp per cu.in. for turbo/supercharged engines. Yet when a master engine builder puts together an engine and has utilized all of ther resources - the VE% can not be assumed as they know things you and I will never know.

 

So, for the average engine build you and I read in any performance mag or how to build engine books, the pattern I have seen regarding the:

 

CFM x .256 x #cyl's = HP

 

formula, is this. For a [normally aspirated] engine you CAN NOT use the maximum valve lift number. You have to deduct .125" to .150" from the full valve lift number and take the CFM from the cylinder head chart that matches the full lift minus 125-150"; and input that valve into the hp formula. VE% not withstanding, you will be within 10 to 35hp of what your engine actually makes about 95% of the time.

 

Other patterns I have noticed regarding the VE%, relative to the

 

CFM x .256 x #cyl's = HP

 

formula is this. If your normally aspirated engine is utilizing an 8.5:1 to 9.25:1 SCR, then you can assume an .85 VE%. If your normally aspirated engine is utilizing a 9.5:1 to 10.0:1 SCR then you can assume a .90 to .95 VE%. If your normally aspirated engine is utilizing a 10.5:1 to 11.0:1 SCR then you can safely assume a .95 to 1.00 VE%...., all this is assuming your cylinder head to cylinder relationship is proper (with all other components being properly fitted...even in the mag articles sometimes the components are mismatched)

 

Vizard thru all of his books will say, "Providing the other components are properly matched"..., so if he can assume properly matched components - then so can we when making calc's for a paper engine not yet built.

 

Regarding the turbo/supercharged engines, the valve lift per cfm chart number needed to get close to actual output is usually .100" less than full valve lift...but, my exposure to a turbo/supercharged engine is limited; which is again why I posted this thread.

 

Other patterns I have notices is the DCR to SCR relationship regarding performance engines. This relationship further ties into the cam overlap to engine-car intent relationship, which further falls into the cylinder head to cylinder relationship.

 

DCR will usually be in the 8.25:1 to 8.5:1 for engines utilizing an IVC of 55 to 65 degrees ABDC which allows somewhere in the 80% to 85% cylinder filling once that intake valve has closed.

 

DCR will usually be in the 7.75:1 to 8.0:1 for engines utilizing an IVC in the 70 to 75 degrees ABDC which allows somewhere in the 70% to 75% cylinder filling once the intake valve has closed.

 

DCR will usually be in the 7.25:1 to 7.5:1 for engines utilizing an IVC in the 75 to 80 degrees ABDC which allows somewhere in the 70% to 65% cylinder filling once that intake valve has closed.

 

With this you can utilize the DCR to decide which optimum SCR is required to overcome the harmful side affects of the cam overlap being used.

 

All this can be confirmed through the

 

DCR^1.2 x Atmospheric Pressure = BMEP equation

 

You can utilize this equation to confirm what cam IVC spec is required if you want a particular BMEP relative to Atmo your engine will be operating in. And if you know BMEP then you can further qualify things thru the,

 

PLAN / 33,000 = HP,

 

or the IMEP - FMEP = BMEP eqution.

 

How many ways one decides to qualify hp depends on that persons personal understanding of hp.

 

I have a process - many may not understand it, but I do have a process that works and is repeatable.

 

If I ever run into a person who has desiged software for an engine simulator, my first question will be to have them show me how they have calculated IMEP.

 

I know how to calculate BMEP and I can calculate FMEP..., but I can not seem to come up w/anyone who can show me how to calculate IMEP. The IMEP calc's are very proprietary.

 

Again, how one decides to qualify HP depends on their personal understanding of hp.

 

I believe I am well read on most subjects and I have built a number of engines in my past so I have experience in that dept as well. I would not call myself an expert as I am not an engineer nor do I have access to the indicators and propieriatry equations those engineers have access to; but I can hold my own .02c's worth when needed.

 

The process is an equation that can be transposed, extrapolated, and done forward or in reverse; as long as you understand the equations.

 

Again, thanks Kinked Chrome for your input. I think your comments are a bullzeye.

 

This was an anomaly that by itself means nothing; but I still like it.

 

Kevin,

(Yea,Still an Inliner)

[X64v]

Boost in PSI x 14.7 = additional horsepower. All this means is that you are assumming that on average you gain 14.7 HP per PSI of additional intake pressure.

 

Bam, that's my problem with all of your theory, right there. In my opinion, that is a horrible assumption. So if you take one of the original 36hp VW Beetle engines, boost it to 10psi (assuming the motor holds together), you're magically going to add 147hp, for a total of 183hp?

 

Your equation seems only to work on v8's around 400-600hp, because those are engines and power levels where adding 1psi may indeed add 14.7hp, but that is merely a coincidence.

 

Boosting my 120hp L24 to 10psi gave me what I could best guess to be 180hp. It was certainly no 267hp...

[Z-8]

Kevin,

Do the articles in the mag have to be about turbo/supercharged engines? I flipped through it, and none of them are.

[Kevin Shasteen]

Z8,

 

I would say yes, the articles anyone presents needs to be a turbo/supercharged engine for us to further prove/disprove this anomaly.

 

Along the lines of x64v's following questions, I would more than welcome non V8 examples in an attempt to see if the 14.7 constant changes w/engine displacement.

 

Bam, that's my problem with all of your theory, right there. In my opinion, that is a horrible assumption. So if you take one of the original 36hp VW Beetle engines, boost it to 10psi (assuming the motor holds together), you're magically going to add 147hp, for a total of 183hp?

 

Your equation seems only to work on v8's around 400-600hp, because those are engines and power levels where adding 1psi may indeed add 14.7hp, but that is merely a coincidence.

 

Boosting my 120hp L24 to 10psi gave me what I could best guess to be 180hp. It was certainly no 267hp...

 

I wouldnt say horrible assumption.., I would say "Not yet qualified" assumption. Hence the purpose for this thread.

 

I would agree w/you in that the only articles I have are from American V8's; as the European crowd is horrible in not giving complete parameters in their magazines and they, the Euro mfg's seem to be leading the way in regards to turbo engines; yet if they are leading the way then why are they so non-revealing when it comes to their engine paramters in their performance mags.

 

That is one element I really appreciate about the American magazines - they are about the most complete articles of all others.

 

In an attempt to qualify the anomaly's process relative to your VW and L24 engines; my first question would be:

 

1) What does the cfm charts for both the L24 head indicate and

What does the cfm chart for the VW head indicate

 

2) Secondly, if you were going to use a turbo on the L24 or the VW; then you would want to utilize a cam lift whose max lift was .100" higher than the cylinder heads cfm required to make that hp per the cfm hp equation.

 

If someone can come up w/a cylinder head chart for the L24 or VW engine I believe this would be an excellant example to further qualify this anomaly.

 

Kevin,

(Yea,Still an Inliner)

[Kinked_Chrome]

Bam, that's my problem with all of your theory, right there. In my opinion, that is a horrible assumption. So if you take one of the original 36hp VW Beetle engines, boost it to 10psi (assuming the motor holds together), you're magically going to add 147hp, for a total of 183hp?

 

Your equation seems only to work on v8's around 400-600hp, because those are engines and power levels where adding 1psi may indeed add 14.7hp, but that is merely a coincidence.

 

 

this is what i was trying to get at. It is merely a coincidence. It is not an anomaly.

[X64v]

1) What does the cfm charts for both the L24 head indicate and

What does the cfm chart for the VW head indicate

 

Honestly, I don't know what the flow charts look like for those two heads, but as far as your original process goes, I don't see where it matters. You only used head CFMs as a method to predict the horsepower of the normally aspirated engine before it was built, and we already know the normally aspirated horsepower levels of these two engines.

 

All I'm getting at is that in your equations you've been using 14.7hp/psi, which is, to say the least, very unqualified.

 

 

I think you're going to be much closer with the pressure ratio method, though it will be a bit of an overshoot, because it does not take into account the flow restriction the turbo presents on the exhaust side, or the drag the supercharger places on the crankshaft.

[Kevin Shasteen]

x64v, how did you go about guessing at the hp of your turbo L24?

 

Why do I need the cfm chart? My need for the cfm chart is the same reason any pro engine builder will utilize the cfm chart. Engine builders will use that data to prove their required paratmeters [on paper] before they build that engine.

 

I always like to ge a cfm head chart of any engine build as it futher proves the cfm hp formula does work (not including this anomaly), in the real world if you know how to use it.

 

This process takes the full cam lift x rocker ratio to obtian full valve lift. With that full valve lift the process then deducts .125" to .150" from the full valve lift; and whatever that value is - we can then go to the cfm chart and obtain the cfm required (according to the cfm hp formula) to determine what the theoretical cfm is required to obtain that hp output. For turbo/supercharger engines the full valve lift minus .100".

 

The cfm to full valve lift minus the appropriate .125" to .150" for normally aspirated engines to .100" for turbo/supercharger engins is the cornerstone of the process. That is why I need the cfm charts for any cylinder head as well as the cam profile specs; as those two are interacting.

 

I know this anomaly/coincedence (whatever you want to call it) has no real sicence to it (as we know at this time) I just find it interesting. You gotta admit it raises an eye brow! Believe me, I am very methodical when I examine an engine build. I understand the pressure ratio math. I still find this anomaly interesting and when I come across something that has repeatable resultes (even if it only occurs on v8's at this time), my mind does not let it go until I am satisfied that I have approached the oddity from every possible angle.

 

I would really like to get as many non v8 turbo/supercharger engine build articles, in my hands, to analyse as possible.

 

I've tried reading the non American V8 engine mags for data but they never give parameters for their cylinder heads and rarely will they give all the spec's for their cams they use; I have a good idea of what their cam specs are. I would really like to know their cylinder head parameters.

 

BTW: since the VW issue came up, I bought a Performance VW book in the early 90's where KRE was claiming type 1 VW engines putting out an easy 250+ hp engines w/a turbo on mild boost, 400+ hp on that same engine w/more boost. In that same book at that time KRE had a methonal burning type 1 VW enigne putting out 600+hp using a turbo. Kre says prior to the 70's you were lucky to get max 180hp. With the advent of cylinder head tech the 180 hp engine is an easy one.

 

Of course they never gave a dnyo in the older book, never gave a cfm chart for their cyl heads: they did give cam specs for the 250 and 400 engines. KRE since then has been know for 1000+ hp for full race type 1 VW engines.

 

Can anyone point me in the right direction for turbo/supercharger articles that offer as complete as possible data regarding engine parameters for a non V8 engine?

 

Kevin,

(Yea,Still an Inliner)

[Kinked_Chrome]

I hate to be so critical, but i think that you are wasting your time. I'm not exactly sure what you are trying to figure out with all this engine building data. Are you just trying to come up with a way to estimate horsepower output? Or looking to see how cam and cylinder head profiles affect output? I'm sort of lost at what your trying to do.

[X64v]

x64v, how did you go about guessing at the hp of your turbo L24?

 

Why do I need the cfm chart? My need for the cfm chart is the same reason any pro engine builder will utilize the cfm chart. Engine builders will use that data to prove their required paratmeters [on paper] before they build that engine.

 

For the N/A side, I have an old dyno graph. For the boosted HP, it's a seat of the pants guess. I was able to do 141mph with a bit of throttle left at about 7psi, and comparing my aerodynamics with that of the tests run in the aero forum, I came up with a required 150hp for that. I also used the pressure ratio method, which said 180hp at 7psi. I figured after additional losses it'd be about 165 or so at 7psi, and 180 or so at 10psi, but again, those are just guesses.

 

As to your use of the cfm numbers, I totally understand how you use them in the first part of your calculations, I have no argument with that. What I mean is directed solely at the added HP from the turbo/supercharger. The part where you guess added HP isn't 'based' on cfm, or anything else for that matter.

[Kevin Shasteen]

Its okay to be critical. I am probably the biggest critic of myself.

 

My agenda? About 7 years ago I began researching the engine behavior to an nth degree. Since then, crunching #'s to identify patterns has become a past time for me if/when I have the time.

 

When you have crunched as many numbers as I have (I dont like the way that sounds because it sounds haughty - and I'm not haughty in any way), you will actually begin to see patterns.

 

I have played w/the turbo math and like the idea of turbocharging an engine - yet have never had the time to actually turbo an engine. All my hot rodding was years ago w/the muscle cars; normally aspirated at that.

 

When I saw the coincidence, as you put it, while crunching #'s, it kind've took me by surprise.

 

Knowing that any IC engine is an air pump and that all components that when factored into the next component it interacts with will create a ratio or create a value, which ever vernacular you prefer; and that this value can then be quantified to determine components as mild, moderate, or maximum..., then regardless of displacement the coincidence should surface on any turbo/supercharge engine.

 

If one accepts the assumption that any engine is prepped or optimized for street/strip use; then the only caveat to this coicidence would be in not knowing VE% and not knowing if/how much the constant (the 14.7 coincidence) changes w/variances in displacements. What I wanted to see, if possible, was any turbo/supercharger spec build to find any meaning at all to this concidence.

 

What am I trying to accomplish? Nothing, maybe nothing more than passing time! BTW, this process (not including turbo/supercharged engines) works very well for the normally aspirated engines running in the 1.00 to 1.35 hp per cubic inches regardless of displacement.

 

Once you get beyond the 1.35 normally aspirated hp per cubic inch, there is more going on than just airflow; which comprimises the close tolerance the cfm hp formula brings to the table.

 

Crunching #'s of any engine build article is kind've a facination of mine. I like to attempt to prove to anyone willing to listen that engine performance is mostly predictable; if you understand how to qualify the variables involved.

 

I was not looking for this coincidence when I came across it. This coincidence that this thread concentrated on was nothing more than a numbers crunching accident that took me by surprise; and I wanted others to offer their input before I moved on.

 

It appears the data on the turbo/supercharged non v8 engines are not as easily obtained as v8 performance is. With that in mind - apparently this thread has run its course.

 

Unless someone has something else to add I think we have beat this dead horse as much as we can. Thanks for humoring me everbody.

 

x64v, Does anyone have a cfm chart for the Datsun I6 cylinder heads? I have searched the net over and can not find them for the life of me. You would've thought someone by now would have posted a cfm chart for these engines.

 

Kevin,

(Yea,Still an Inliner)

[Kevin Shasteen]

I was able to do 141mph with a bit of throttle left at about 7psi, and comparing my aerodynamics with that of the tests run in the aero forum, I came up with a required 150hp for that. I also used the pressure ratio method, which said 180hp at 7psi. I figured after additional losses it'd be about 165 or so at 7psi, and 180 or so at 10psi, but again, those are just guesses..,

 

What trans, differential gears, and tire size were you using at that time?

 

Kevin,

(Yea,Still an Inliner)

[X64v]

81-83zx 5 speed, 3.364 R180, 215/60/R14's. I hit 6600 in 4th, according to the tach in Megatune. Aerodynamically, my car best resembles the #6 windtunnel test.

 

 

x64v, Does anyone have a cfm chart for the Datsun I6 cylinder heads? I have searched the net over and can not find them for the life of me. You would've thought someone by now would have posted a cfm chart for these engines.

 

I don't have one offhand, but I'm pretty sure I saw that 1 fast z has some baseline flow numbers somewhere, and I'm willing to bet if you were extra nice to Braap, he might just tell you as well (I don't know for a fact that he has any, but I'd be mighty surprised if he didn't).

 

 

Edit: Found one. Not sure exactly what head this is, but it's probably either an N42 or a P90. Blue (test 1) is stock.

 

http://forums.hybridz.org/showpost.php?p=745040&postcount=12

[Kevin Shasteen]

A few years ago I made my own Tq/Hp loss due to Aero Drag Calculator and Turbo calculator. With your gearing and the assumed .45 to .49 Cg and 7psi boost; I think your engine was putting out more than 180 hp.

 

My Aero Drag calc does not take turbo/supercharged psi into consideration as it merely takes the Cg, Frontal Area, Gearing, HP, Tires, MPH into consideration but the Turbo Calc obviously takes boost into consideration.

 

The Aero Drag calculator indicates 180 hp at that rpm w/your gearing would be experiencing a -3 to -17hp depending on which Cg of .45 or Cg of .49 you went with.

 

My Turbo Calc uses Corky Bells calculations from his book. His assumption of a low to high hp puts your engine in the 165 - 245 hp range.

 

Since you said you had a little more throttle left at 141 mph, I'm betting your engine was in the 200 hp to 200+ range.

 

I'm betting your engine was making more than you thought it was.

 

When you hit the 141 mph mark did it feel like you could've grabbed 5th w/out loosing speed (or did you have a few other things to worry about - like staying on the road)?

 

Did the engine feel like it had a little more to offer?

 

Its late, I gotta get some sleep. Talk to ya in the morning.

 

Kevin,

(Yea,Still an Inliner)

[X64v]

If I would have grabbed 5th, I would have been stuck right about there I think. However, with my gearing, 5th is very deep (2500rpm at 70mph).

 

I made my own drag calculation based on the aero test. That test for my model showed it took 108hp to push that car 120mph. Obviously it takes 0hp to push the car 0mph, and drag goes up with the square of speed, so with some simple calculation, the equation for my car is found to be:

 

Req. Hp. = .0075(mph)^2

 

Throw 141 in there, and you get 149.xxx hp.

 

Now remember, this 141 was at 6600rpm, probably not at my horsepower peak with a stock head and cam with a T3 turbo. Drop into 5th, and then I'm just under 5000rpm, probably not my peak horsepower either (I was thinking around 5500rpm or so). I could have perhaps made it to 145mph as I was, and proper gearing may have given me maybe 150mph as an absolute top. It takes ~170hp to push my car 150mph.

[zguy36]

Kevin,

 

If you want any respect for your equations, then these equations need to be based on something more tangible than fudging numbers around from just a few sources. You mentioned that your equations are similar to horsepower calculators that use 1/4mile times. Those equations are built from the simple F=ma equation. You have not started from an equation that governs a law of physics, but instead taken two numbers and a couple variables and figured out a fudge factor to get your solution. I am not a naysayer, but someone who holds a degree in mechanical engineering and someone who understands that an equation should be based in something other than just a few small bits of empirical data. Equations based on empirical data are extremely vulnerable to error.

 

I will reiterate why your equation will not work unless you take into account many many more factors.

 

Cam profile: You can take two identical engines, both that have the exact same head flow rates but having different cam profiles. As you can imagine, these engines will not make the same power.

 

Exhaust size: Again, two identical engines but with different exhausts. All of your input variables will be exactly the same, but again, power levels will be greatly different.

 

Turbine size: Again, two identical engines but with different size exhaust turbines. Look at the different power levels that can be had. Take TimZ's engine with the GT42 turbo and replace it with the stock T3 turbo. Think you are going to get the same power level with the same boost pressure? No.

 

Intake design: Again, two identical engines with two intakes. Both heads may flow the same, but depending on tuned runner lengths, you are going to get completely different power levels if one is tuned for low RPM vs. high RPM.

 

 

Fuel type: Depending on the fuel being used, you advance your timing curves and increase power levels, all other factors being the same.

 

 

 

I have only listed here a few variables of which can have an effect of 50+ horsepower differences. I tried very hard to not rain on your parade last time, but I think it is time that some rain starts to fall.

 

Plainly put, there are so many variables involved with modeling internal combustion engines, that it is mathematically impossible to come up with a catch all equation. What you have created is something that fits for a small set, with very few variables. Yes it seems to work, but you can't really say that it holds much merit.

 

You may say that it can be done, since you can purchase programs such as desktop dyno that do exactly what you are trying to do. Well, these programs use a similar approach as you, but pull from a data base of thousands versus a database of a handful. And just the same with these programs as your equation, if you change the variables out of the range of what is mapped in the database, then your result is useless.

[Z-8]

Zguy,

First off, your right. He does need more evidence to back up his claim. And that's the exact reason he's here, talking about it, trying to get more inputs to see if it's right or wrong. He never said(in is extremely long post:mrgreen:) that "his equation/anamoly" was right. I was hoping to help a little, but my resource doesn't have anything on turbo/supercharged engines. I wish you the best in this journey Kevin, and will post anything that I come across that might further your endevor.