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???

[Aaron Cox]

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

[TimT]

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,

[Series9]

I go with FI at all costs.

Sorry, I just hate carbs.

[pete-stevers]

Arron what is dme???

[Series9]

DME is Motronic digital FI.

[pete-stevers]

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???

[d914]

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??

[J P Stein]

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. (IMG:style_emoticons/default/biggrin.gif)

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.

[Mark Henry]

The old fart's are just scared of programable fuel injetion. (IMG:style_emoticons/default/happy11.gif)

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.

[J P Stein]

The old fart's are just scared of programable fuel injetion. (IMG:style_emoticons/default/happy11.gif)

Granted, a Moteck (or equivilent) ITB system would be a new challenge, but if you give me one, I'd be a happy camper. (IMG:style_emoticons/default/biggrin.gif)
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 (IMG:style_emoticons/default/biggrin.gif)

[Thorshammer]

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

[brant]

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

[Mark Henry]

The old fart's are just scared of programable fuel injetion. (IMG:style_emoticons/default/happy11.gif)

Granted, a Moteck (or equivilent) ITB system would be a new challenge, but if you give me one, I'd be a happy camper. (IMG:style_emoticons/default/biggrin.gif)
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.

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!

First: Do you possess the technical ability to install/program an aftermarket FI system.

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.

[J P Stein]

The old fart's are just scared of programable fuel injetion. (IMG:style_emoticons/default/happy11.gif)

Granted, a Moteck (or equivilent) ITB system would be a new challenge, but if you give me one, I'd be a happy camper. (IMG:style_emoticons/default/biggrin.gif)
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.

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!

First: Do you possess the technical ability to install/program an aftermarket FI system.

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. (IMG:style_emoticons/default/biggrin.gif)

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. (IMG:style_emoticons/default/biggrin.gif)

[Trekkor]

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

[Mark Henry]

No laptop with an SDS

Yeah, I've heard that.....but *show me the dyno* on a 9eleben motor.

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

[Mark Henry]

If you got one I bet you'd soon be looking at turbochargers (IMG:style_emoticons/default/wink.gif)

[Eric_Shea]

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. (IMG:style_emoticons/default/confused24.gif)

[Dr. Roger]

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

yes? =-)