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???

depends on rev range and all
40s to 46's

3.2 - DME ALL THE WAY...
3.4... KEEP THE DME IF YOU CAN TWEEK IT

40s are fine for most engines, unless your making an all out race engine, then you would want 46s

I sold a pair of 40idas a few years ago for $1000, I have one set left collecting dust on a shelf ( im going to hold on to these though).

46 Webers cost quite a bit more, they are getting pretty scarce.

even with 40s you can get pretty large venturis in them,

I go with FI at all costs.

Sorry, I just hate carbs.

Arron what is dme???

DME is Motronic digital FI.

so a set of 40s would be more than enough for a hot 2.5...eh?
joe tell me.....why don't you like em???

getting them set up can be a pain....dirty jets and the such...

On the other hand I do have a set of 46's that came off of my 2.5.....they might be available??

Most folks that hate em do so for one or more of the following reasons:

1) they stink
2) gas milage goes down the tubes
3) often hard to start
3a) they can't get em to work right
4) they *think* they have to dick with em' constantly

Most folks like them do so for the following:

1) they make power
2) they make more power with the bumpstick of your choice
3) the sound
4) the throttle response
5) the alternative EFI(if you wanna make power) cost more than twice as much
as a new set of PMOs....at any cost indeed.

Mr. Anderson's book (amongst others) has the formula for figuring venturi size for an engine. From venturi size you work backwards to carb size.

The old fart's are just scared of programable fuel injetion.

They think just because it says PORSCHE on the valve covers they need a high end system with all the bells and whistles (most of which they'll never use) that they cannot understand.

Granted, a Moteck (or equivilent) ITB system would be a new challenge, but if you give me one, I'd be a happy camper.
I know where to go to find a guy that could make it work and it would give another 20-30 ft lbs of torque across the curve.... I'd watch to learn.

I hear a local shop had developed an EFI system
using a reworked later style TB set-up that does allow radical cams, etc .......but the cost is similar to the above. I haven't gotten a look at it, but will at the Parade.

The problem with my car now (and has been) is that there is more car than this old fart can deal with. For me, more power is not cost effective whereas more talent would be a boon

Good question,


The question is actually much more involved than you initially think.

First: Do you possess the technical ability to install/program an aftermarket FI system. If not, you will be stuck with a factory system, which is fine. But as someone else pointed out, somewhat limited you may be with cams.

Second: Regardless of the engine size, what is the intended use of the vehicle, if it is only a track car, and you have the technical know how, and the class allows it, I would run FI aftermarket, I like the Motec or Haltec or the like. If this is a street car only, then put a 3.2 liter in it with stock injection and forget it. You love the way it works and when it starts and idles perfectly everytime, You wife might even go for a ride.

Third: If you don't care about the start ability and just want one fast street ride or track ride. heres my recommendation.


2.5 liter 40mm webers 34 mm venturis. 2.2 T heads. Small ports 46x40 valves, GE 60 cams, and the right exhuast, not heat exchangers. Exhaust 6into 2 into 1.

2.7 with 2.4 T heads (ported but not overly ported) velocity is very important to this combo, 40mm webers with 36 mm venturis, Exhaust again 6 into 2into 1

3.2 with 46mm webers and 38mm venturis, again with the proper exhaust 6into 2into 1.

These are my favorite combos for a nasty street engine. You mileage may vary.


Erik Madsen

Erick,

which exhaust do you have in mind for the above combo's?

any brand name you can throw out?
or custom, on the back of standard headers?

brant

And there you have it!!! Why do you need a Motec…because the local tuner shop says so…because some PCA snobs say so??
Of course they’re going to say Motec or Auditronic BECAUSE they make their money on the tuning and dyno time!



I imagine people get sick of me harping on the SDS system I use, but I like it because anyone who can zip up their fly, without getting their beans and franks caught in it, can tune this system. NO dyno time…NO expensive tuning sessions!

All you would need is the biggest stock intake you can fit on it.

Again all the bells and whistles that they will say you need on are of no use to our “antique” cars. About the only reason for going to a high end system would be if your car needed to pass emissions. Although the SDS will still be cleaner than any carb engine and have the exact same power as any other system.

Yeah, I've heard that.....but *show me the dyno* on a 9eleben motor.
All the talk is free without the numbers. Better still, come stick it on my car and I'll use the butt dyno.

As I mentioned a local shop has developed an EFI system
based on a (I think) modified DME intake.....these guys are VERY good ( and expensive). I haven't seen the set-up nor do I know what they are using for a controller, but talked to the car owner & driver.....got no details other than it was worth a bunch of torque and a bit of hp on the graph from an engine dyno...these guys do supply the numbers.

Carbs are nice in that you can do a reasonable tune by ear and plug readings. A butt dyno supplies the rest. No flat spots in my set-up, but it ain't clean.....one step hotter plug helped some this year due to the rich mixture..... all without the expense of a laptop.

I'm with JP on this.

I can't get enough Weber song...

With the MSD it always starts right up, quick warm up.
I clean the idle jets about once every 4-6 weeks in 10 minutes.

That's it. Good power.


KT

No laptop with an SDS




Here ya go!

3.3L turbo, dyno chart shows 420 hp and 456ft-lbs at the wheels with approximately 0.9 bar (13 psi) of boost.
http://www.sdsefi.com/features/jan03934.htm

240hp 3.2
http://www.sdsefi.com/features/may01911.htm

3.3L, 254hp between 6700 and 7400 rpm. The torque curve was very flat from 3500 to 6000 with a peak torque of 220 ft./lbs at 5400 rpm.
http://www.sdsefi.com/features/june00911.htm

3.2 turbo no dyno but reports that this car will suck the windshield out of the new 993 twin turbo
http://www.sdsefi.com/features/mar00911.htm

If you got one I bet you'd soon be looking at turbochargers

Erik,

Why such small intake ports with the seemingly large venturi's? While I like small intakes for drivability (I'm keeping the ones on the 3.0 at 36mm) I've never seen that combo before.

i bet it for higher air velocity above the intake valve which helps with the right cam and air pressure pulse stacking.

yes? =-)

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

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

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