six question, again hypotheticly speaking, what size carbs would one by if....... Options

[pete-stevers]

one was building a 2.5?
or
if one was building a 2.7........
or.....
if one was building a 3.2
or........
a 3.4.....
of course my next question is
what are they worth???

[Thorshammer]

Eric,


I just lost my long explanation, Thanks B (you beotch).

Anyway, many people think they must strengthen the pulse at the carb, when the real problem is the lack of inlet port velocity to produce a strong signal in the first place.

About 25 years ago, someone stopped developing these engines. Now, technology has changed significantly, and very few are revisiting the 6 cylinder engines. One good example of this is Jake Raby, he has applied and developed the type four engine very nicely. I don't really feel anyone is doing this for the smaller 6's, there just isn't any money in doing it.

So, what you get is a cookbook engine, this cam, this venturi etc......
kind of what I have done, but with a different spin. Cylinder filling makes power. You get intake pulse signal from a properly designed engine package.

Good volumetrics will make power everywhere, small venturis will only enhance a piss poor package in the midrange and hinder what the top end potential may be.

Take race engine packages for example: building a 2.0 six to race: Use the 906 cam, 46mm int 40 mm exh, tall manifolds, 46 webers and 38 venturis, with 32-34 inch primaries and megaphones. How many times have you heard this shit. My 2.0 EP race motor has none of the above, and I assure you it makes more than most. People just have to do the research and apply newer technology to these engines and they will respond.


Erik Madsen

[Thorshammer]

Oops,


Need to clarify one more thing. The exhaust system is custom, 6 into 2 into one, with the best collectors you can find.

NO FLAT COLLECTORS, they suck, and you don't have to have them. Call burns and order what you need, you WILL be satisfied.

Try this: 1.5 inch primaries near 29-30 inches to a triangle shaped collectors (standard 3 pipe collector) with a 2.0 inch outlet, using a 2.5 inch transition and then bringing the two tubes together to a 2 into 1 collector and then to a spintech muffler 17 inch. After that, just a turn down tip works great. You may be able to buy these in the near future from a well known 914 exhaust manufacturer, I'll keep you posted.

Erik

[Thorshammer]

Found my long post:

Eric,

In the Porsche world it is very common to run a fairly small venturi in the carb for good throttle response, the most given reason I have heard is: you need a good signal at the carb for atomization and this is what the factory has done.

Problem, is most tuners use the idle air bleed to balance and not really to tune. It has some nice effects to the main circuit and with the right emusion tubes the "strong" signal is not as important as it once was. Also, camshaft technology has changed significantly which leads to a different intake pulse.

Also remember, with a strong pulse stated at the inlet port, and the proper valve overlap the signal at the carb is very strong.

My contention is, along the way, people stopped developing these engines, oh about 25 years ago. Only a very small few have continued, and the result is some new thinking. When I started, I was a cookbook thinking type of guy. ie... 906 cam, 46intx40m exhaust 35mm intake ports, tall manifolds, 30-32 inch flat collector exhaust, with megaphones?????? I can tell you that after alot of development, not of the above mentioned stuff is in ANY 6 engine I am involved.
BTW the traditional Weber velocity stacks that everyone has, are really not ideal, the sharp lip near the top of the stack causes some major turbulence.

Also consider this, Motorcycle engines are making almost 120bhp per 600ccs and use 36-38 mm throttle plates with no venturi. So if we consider they are displacing 150cc per cylinder, and the standard 2.4 liter porsche engine 400cc, what do they have that we don't..... Alot, but suffice to say our heads flow alot less due to having 2 less valves and we don't spin our engines to 15,000 rpm. But the major improvements in motorcycle engines started coming with increasing inlet port velocities to the extreme, and then focusing on inlet flow at low lifts, this may clue a few people into what I do with my race motors.

In my testing, the combinations I have indicated in my previous post only perform well as a package. The porting of the heads is critical. The cross sectional changes are absolutely everything. They must be correct.


Erik Madsen