Lock all the forums you want...

[Alfred1]

Here's an insult free argument.

I found an equation that describes the air-drag on an object as it falls through the air fast enough so that the air behind it is turbulent and I’m going to use it to try to estimate the drag on Jake’s 912 relative to the drag on a modern economy car.

C is a dimensionless drag coefficient that depends on the shape of the object, p is the density of air, A is the cross sectional area of the object and v is the speed of the object.

Drag = ½*C*p*A*v^2

Now I’m going to make some assumptions. I’m going to assume that a Porsche 912 and modern economy car have approximately the same frontal area (A), that the 912 has a drag coefficient of 0.35 and a modern economy car has a drag coefficient of 0.30 and that the EPA highway mileage test simulations are done at 65 mph.

Using the equation above to estimate the drag on the 912 at 85 mph I get

D1 = ½*0.35*p*A*(85^2)

And the drag on the modern economy car at 65 mph

D2 = ½*0.30*p*A*(65^2)

D1/D2 = ½*0.35*p*A*(85^2) / ½*0.30*p*A*(65^2) = (0.35/0.30)*(85^2) / (65^2) = 2.0.

That is, Jake’s 912 travelling at 85 mph would have twice the air-drag on it as a modern economy car travelling at 65 mph. Do I believe that his 912, powered by a carbureted, pushrod 2056, gets 38 mpg while travelling at 85 mph when according to the EPA a 2004 Suzuki Swift gets 35 mpg on the highway? No I don’t!

[BigD9146gt]

I don;t think its appropriate to assume the coeffient of anything. Assuming is like guessing, and guessing is for horse shoes and hand granades. I think the best i got out of my 914 with a 2.0 lower end and 1.8 heads, 40IDF webers, on average 75mph was low 30's...maybe 35mpg and a ZD fifth gear.

But then agian, thats only when i'm going north, when i'm going south, i get much better mileage

[Alfred1]

Modern cars have drag coefficients around 0.3 and older cars have coefficients around 0.4.

[Bleyseng]

Originally posted by Alfred1
Wow, Geoff, it never occurred to me that you would want to "kick my ass". You have to be careful with your assumptions because I have no history of getting my ass kicked. And, I use the Engine Analyzer software, not desktop dyno.

I think Jake's own dyno graphs of his "stocker" and "stock update" motors show that what I was saying is true. Gaining 15 hp from a 95 hp motor by just adding a cam with more lift/duration will cost you bottom-end hp and torque.

I just guessed that since you never have shown up even after I pm'd you inviting you. I make all kinds of ass umptions and I get in trouble all the time. You should show up for the events down here as all of us learn a hellva lot from each other.

Of course, large changes in a cam can or will move the hp/torque curve around or up. I am not real experienced with that software but like Jake rely of real world experience. Type 4 motor's exhaust is the weakest point of the head design and the cam is set up for running pretty warm for emissions. Thats why either a longer exhaust duration/lift or a bigger exhaust valve to a point gets you some hp Porsche left on the table. They were shooting for 100hp out of the motor to replace the 2.0 110hp six. Economy also figured into the design as the 2.0L gets about 25 mpg vs the 1.7L at 30mpg.
A flat torque cuvre is (IMHO) more desirable than a peaky one. A nice hp curve without peaks and valleys is nice too.This winter I am tearing down my motor after 5 years of abuse. Gonna try different cam for fun.
I am not interested in the least of trying to prove Jake or anyone else wrong. I do things my way, they do theirs their way.

Best mileage I have gotten was 30 mpg with my 2056 FI going 80-85 all the way from Portland Ore.
Geoff

[Dave at Pelican Parts]

Originally posted by Alfred1
...Now I’m going to make some assumptions. I’m going to assume that ... the EPA highway mileage test simulations are done at 65 mph.

That is not a valid assumption. The EPA tests are done at specific load/RPM/temperature/etc. conditions, and take into account some specific assumptions about how long a trip will be taking place. You can easily do better than the EPA figures for a car by driving for a while (warming the engine up fully), then filling the tank and driving for a steady speed (usually in top gear) for however long that tank lasts. I do, on every L.A. trip I make in my Honda.

I will not address the 38 MPG @ 85 MPH question, because I don't have anywhere near enough data to be able to do so.

--DD

[ws91420]

Alfred your avatar tag says 914 VR6 why are you so concerned about or flat fours? If your not happy with your VR6 then maybe you should of had a (pardon the cliche) V-8.

[Alfred1]

Originally posted by Dave at Pelican Parts
That is not a valid assumption. The EPA tests are done at specific load/RPM/temperature/etc. conditions, and take into account some specific assumptions about how long a trip will be taking place. You can easily do better than the EPA figures for a car by driving for a while (warming the engine up fully), then filling the tank and driving for a steady speed (usually in top gear) for however long that tank lasts. I do, on every L.A. trip I make in my Honda.

I will not address the 38 MPG @ 85 MPH question, because I don't have anywhere near enough data to be able to do so.

--DD

What is the speed limit on US highways? I thought it was somewhere around 65 mph and since the EPA gives highway mileage ratings it seems reasonable to assume that their tests would simulate a car travelling at or near the speed limit.

[schosh]

The speed limit on most of the controlled access roads around here is 70 mph... real world most traffic between cities runs at 75-78... my 2.0 Webber 40 is lucky to get 26mpg ...

[Alfred1]

I did some research and found this info on the EPA site:

The test to determine the highway fuel economy estimate represents a mixture of "non-city" driving. Segments corresponding to different kinds of rural roads and interstate highways are included. The test simulates a 10-mile trip and averages 48 mph. The maximum speed is 60 mph. The test is run with the engine warmed up and has little idling time and no stops (except at the end of the test).

An average of speed of 48 mph with no stops would seem to me to maximize the fuel mileage figures and that's what it says on this web site:

The Environmental Protection Agency is weighing changes to the way it calculates fuel economy ratings posted on new cars and trucks to better reflect real-world driving conditions.

The review, which comes as concerns rise over escalating oil prices, could result in lower posted fuel economy ratings and potentially impact sales of profitable but gas-guzzling pickup trucks and SUVs.

Since the EPA last adjusted the formula for estimating vehicle fuel economy in 1984, highway speed limits have been raised and urban sprawl has created longer, more congested commutes.

Environmental groups argue that the actual fuel economy for today’s vehicles can be as much as 34 percent lower than the city and highway ratings posted on the windows of new cars and trucks.

So the EPA highway mileage figures are probably themselves too generous and that would mean that Jake's highway mileage figures are even more amazing than they already appear.

[Will98D]

Man, you are spending a lot of energy trying to refute what Jake says. Certainly Jake knows a lot about the T-IV and appears to get considerably more out of them than was originally designed in. Probably a lot of people don't believe the 38mpg thing, but it isn't the end of the world so who gives a damn and why get caught in a flame war. At work we make FI systems, but we used to make 40,000 4-barrel carbs a day and lots of the older guys still laugh about the tales of an 80mpg carburetor that would show up in Popular Mechanics, and how the 'Big Bad Oil and Car Companies were withholding it'. It's easier to chuckle and move on, because quoting formulas and other technical approaches is sure to ignite the whole "Engineers don't know *****" argument before long, and you can probably search the archives and find a dozen of those, some of which I got entwined in. Now I have other things to do, and in fact all of the bickering and sounding like a bunch of hens has dulled my interest in the car.

[Alfred1]

I'm tired of it too now but somebody's got to say something against the constant barrage of hype. I think that's how he advertises - I wish he would just take out an ad in one of the magazines instead.

[Alfred1]

Originally posted by Acox914
buy his engine and tell us the results then alfred! gawd! quit b.itching and drop the personal vendetta on jake

If I paid $7000 USD for one of his 150 hp motors, I would suffer from a severe case of buyer's regret afterwards. You have a '73 2.0? Buy his wunder cam and install it and let us all know if you gain 15 hp and do "NOT lose any HP over any portion of the spectrum". I already know the answer.

[ws91420]

Alfred there is such a thing as book smarts and real world smarts. Any idea can look good on paper but not work in real life. Plus I didn't think that a drag coefficient was dependent of speed. Jake has built these engines for quite a while and I am sure his customers are all satisfied wtih his work. What is your background? Can you rebuild a motor? Machine a case and heads? Reassemble a motor and make it run? If you can't then leave it to the people who can and quit your verbal spars at someone who can.

[Alfred1]

Originally posted by ws91420
Alfred there is such a thing as book smarts and real world smarts. Any idea can look good on paper but not work in real life. Plus I didn't think that a drag coefficient was dependent of speed. Jake has built these engines for quite a while and I am sure his customers are all satisfied wtih his work. What is your background? Can you rebuild a motor? Machine a case and heads? Reassemble a motor and make it run? If you can't then leave it to the people who can and quit your verbal spars at someone who can.

... there is such a thing as book smarts and real world smarts

Book smart people rule the world.

Any idea can look good on paper but not work in real life.

Well, some ideas can look good on paper but not work in real life and that's why you have to test them but countless numbers of things can be proven with complete certainty just on paper e.g., not all numbers are rational numbers.

... I didn't think that a drag coefficient was dependent of speed.

I said "C is a dimensionless drag coefficient that depends on the shape of the object".

What is your background?

A couple years of auto shop in high-school and then a 6 month course at vocational school.

Tech School 1

Tech School 2

Tech School 3

Can you rebuild a motor?

I have rebuilt a half-dozen or so.

Machine a case and heads?

Nope, just grind valves and valve seats and brake discs and drums.

Reassemble a motor and make it run?

Definitely.

[Acox914]

love the PM on 914club alfred

[Alfred1]

Originally posted by Acox914
love the PM on 914club alfred

Huh - I PM'd you? What did I say?

[BigD9146gt]

Originally posted by Acox914
buy his engine and tell us the results then alfred! gawd! quit b.itching and drop the personal vendetta on jake

No offence, but this is what kills these threads. You know, you can just skip over this thread all together, just because it sits at the top of the forum does not obligate you to read it.

I don't want to be the moderator, nor pretend to be. I;ve gotten into it with others in different threads for pages and the thread got on track by those who didn't care about the bickering and kept on typing about the points at hand.

Many of you take Jake's knowledge with a grain of salt, but theres A LOT of new commers who arn't the wiser, and will believe anyone. The nice thing about this forum is you CAN dissagree, and telling others to shut up is WORSE... this is something i realized a few months ago on these forums. So the more input we get, the more we can find a medium.

Jake might be way out in left feild in Alfreds opionions, and vis versa, which in the end, evens out, and HOPEFULLY people ask more questions rather than just beleiving either.

Damn i';m tired, and hungery. Just got finished dropping a 3.0 SC engine for a top end rebuild, came in for a quick chat on the adictive pelican board, and its time to go home. Have a good night everyone! Don.

[Alfred1]

Originally posted by Acox914
Ill ignore your DumbA** PM on the "other site"
i do hope you get banned though you instigate lots of problems.

I didn't PM you on any forum today.

[Alfred1]

That's right. I also got an excellent grade in a statistics course and it's a great tool for proving things with a certain error level and confidence interval. It helps me to know what I'm in the middle of with some certainty.

[schosh]

Time for us all to move on.....