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Old 11-15-2001, 01:04 PM   #1
MINDGAME
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No, it's not a WRX...

Default Is there a REAL way to calculate HP?

I see a lot of posts where people add the "advertised" horsepower gains from different bolt on mods together and say "So, this should get me over 200hp right?". Since different mods, effect the hp and torque curves at different places, how does one calculate real gains before spending their money?

Example: On paper the Cobb intake shows the best gains. However, it is conceivable that a Ganzflow or a Weapon-R intake mated with a Brullen exhaust could give you more power than a Cobb intake mated with the same exhaust, because different mods affect the powerband differently, and when you start mixing and matching I'm sure that those advertised gains end up being much different. This is just an example of combining different mods in a calculated way, I have no data to support that "this" product works better than "that" product when used in conjunction with "this" product. But I am suspect of it. So, is there a way to calculate this type of information before buying parts and then getting on a dyno? Am I the only one taking crazy pills around here?
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Old 11-15-2001, 02:33 PM   #2
JGard
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there is only one real, and accurate, way to do it... put the car on a dyno.
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Old 11-15-2001, 02:43 PM   #3
MINDGAME
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So, your telling me it is just a crapshoot? You have to actually buy the parts to get an idea how they perform with other parts. There's no equation or formula you can use to predict how two different mods will kick in on the curve together?
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Old 11-15-2001, 02:56 PM   #4
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No, there are no equations. There are forums where people post about what parts they are using and in what combination and how well they work together. If only we could locate such a place...
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Old 11-15-2001, 03:19 PM   #5
MINDGAME
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Better yet, it'd be cool if there were a place where people could ask questions about things they didn't have knowledge of, and receive straight forward answers (instead we have to settle for sarcasm). I think there should be a new title under the specialist's names called "Scooby Snob"....haha.
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Old 11-15-2001, 03:24 PM   #6
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The sarcasm arrives when you don't pay attention. You are posting in a forum FILLED with information on how well different parts work. You sense that the vendor provided power increase numbers are fishy (they are) and want some sort of mathematical model into which you can plug numbers (from where? who knows!) and get out the hp of the car. If that were possible, who would need dynos? You just plug in the numbers for all your mods, and PRESTO! Crank hp!

Now, I'm sure that with a sufficiently complex system of differential equations you could actually get a moderately accurate model, but just the modelling of the modifications would be an incredible chore, even for a well funded company. So, "put it on a dyno" really IS the answer, and "read the forum in which you are posting" really IS what you need to do.


Ben
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Old 11-15-2001, 03:29 PM   #7
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G-Tech Pro
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Old 11-15-2001, 03:43 PM   #8
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Quote:
Now, I'm sure that with a sufficiently complex system of differential equations you could actually get a moderately accurate model, but just the modelling of the modifications would be an incredible chore, even for a well funded company. So, "put it on a dyno" really IS the answer, and "read the forum in which you are posting" really IS what you need to do.
Not only that, but how do you prove that the model is correct? That's right, put the real thing on a dyno and test it. You would only have to test a few combinations, but development of the models would cost more than buying the parts, a car, and a dyno (not just renting it).
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Old 11-15-2001, 03:53 PM   #9
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I agree paying attention is important.

From my original post:
"So, is there a way to calculate this type of information before buying parts and then getting on a dyno?"

The key word here is "calculate" and "before".

From my post it is plain to see that I know what a dyno is, and what it does. I know what this forum is, and I don't think I over-stepped any rules by asking a question I have never seen posted before.

I wanted to see how a Compass intake would fair with the new Brullen headers without being the guinea pig. If that's an impossibility, then I can live with that. It just seems you can't ask a question here without getting a reply with a bold 24 pt. SEARCH as an answer or some know-it-all trying to make you look like a simpleton.
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Old 11-15-2001, 03:58 PM   #10
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I ask again: if it could be simply calculated, why would anyone use a dyno?
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Old 11-15-2001, 04:41 PM   #11
MINDGAME
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To see what you were getting at the wheels.

I was looking for an accuate flywheel calculation. The car is 165hp stock and I assume that what most aftermarket manufacturers' advertise as gains are at the flywheel as well. But we agree that simply adding one gain on top of the other does not work...I was looking for a way that did work. I apologize, as I did not mention flywheel in my original post.
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Old 11-15-2001, 04:47 PM   #12
bsquare
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Even the stock numbers are questionable. Unlike air-cooled Porsche motors that would all post almost identical dyno numbers from the factory, Subaru (and most other manufacturers) have surprising variations in the actual power output of a given factory motor. If you are looking for a specific hp number from your car, plan to visit the dyno. If you are interested in making your car feel as fast as you'd like, then the subjective opinions expressed on this board are exactly what you need.


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Old 11-15-2001, 05:12 PM   #13
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Quote:
Originally posted by MINDGAME
Better yet, it'd be cool if there were a place where people could ask questions about things they didn't have knowledge of, and receive straight forward answers (instead we have to settle for sarcasm). I think there should be a new title under the specialist's names called "Scooby Snob"....haha.
i second that...
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Old 11-15-2001, 05:17 PM   #14
Squeege
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Default Estimating gains

Well, if you had a bunch of dyno sheets in your hand comparing stock to stock+[insert bolt-on part here] then you could figure out roughly how much hp and/or torque you gain at a given rpm point. You COULD use this and figure out your theoretical peak hp at a given rpm or gains at specific rpm points, but you would be ignoring the interaction of parts when installed together.

Of course, this is just a repetition of what the others have said.

Bottom line is you would need to measure the engine's output/car's performance somehow, be it dyno, G-tech, drag strip, etc. and compare with stock numbers.
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Old 11-15-2001, 05:27 PM   #15
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Quick answer is no.

The best you could hope for is a theoretical maxinum. Say they spec that a part flows, X CFM at STP and you know you injector flow rate, etc you can give an estimate at least. Likely its going to be so far off as to be worthless though.
Oh, there are engine modeling tools out there, but thats more for camshaft design and such I think.
-B
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Old 11-16-2001, 10:06 AM   #16
Longshot
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Get a Blitz Power Meter and a G-Fake pro and you can make educated guesses.. also, doing a drag run will help, but that comes down to driver skill.

Korey
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