I'm looking at the Empi dual down draft carb kits and had a quick question regarding differences in the carbs themselves.

It looks like they have HPMX or Dual D carbs available.

Which one would you choose?

Should I lean towards real Webers or Dellotos?

The intention here is to use the kit in its stock form initially and later change to port fuel injection using the carbs as throttle bodies much like MB911 is doing with his EFI conversion.

http://www.914world.com/bbs2/index.php?showtopic=363246

Being able to remove everything in the bores is critical for me. No fixed boosters or venturis is a requirement.

I'm planning on starting with an 8.5-9.0 compression 2056 with a webcam #86.
I am planning on having the final engine as a 96mm bore/78mm stroke, but this will be in the future.
I believe I should start with 44 mm carbs instead of 40.

Suggestions, tips, and opinions would be greatly appreciated.

You will notice more support for webers over time.

You may notice some of the small parts for the knockoff are not easy to come by and that things like gaskets don’t necessarily fit the same as Weber / Dellorto

Buy quality - not price

I have been running twin Webers on a 356 for 20+ years and on several 914's and have had good luck with them

Choose a 40 IDF combo for the 2056 914. I hear the Empis are pretty good for the $$ and can be set up to run well. If you can get the Weber or Redline the parts all fit well and the jets and such interchange as they should
Unless the engine is reving over 6k headers and head work you will not be needing the 44 and may be more than necessary and can be a bit more on the tuning and possible less throttle response

That said I LOVE my 44's on my 2056 but she live in the upper RPM range most of the time

I see the 40mm as at top of its range on a 500cc cylinder.
It should have better low and midrange fueling vs the 44mm.

But, I will not stay 2056 very long.
I'd prefer to start with 2270 if I could.

I am on a very tight time schedule as I am building this car with my 82-year-old father (who is the REAL Porsche nut in my family) and he has Multiple Myeloma...

He got this shit from exposure to agent orange in Southeast Asia...

It will not be long till he goes "wheels up" for the last time and I have to get this car to a usable status rapidly.

I'd rather start with a stroker, aftermarket FI, and a bunch of extra stuff but time dictates this will start carbureted, COP, and small (2055).

I believe I should spec out 44mm carbs as these have more "headroom" over 40s

Thanks for the replies everyone.

I was hoping to use the cheaper Empies as I don't think they will be delivering fuel for very long and they will end up being simple butterflies in the throttle tract.

Brand new Webers are $350 more. Strangely PMB says "Made in Spain" and back when I was screwing around with DCOEs the real Webers were made in Italy...

A Datsun L28 has 460cc cylinders and they definitely preferred 44s.
The very best carbs were Mikuni 44PHH. I've had multiple sets.
I saw a nice Z-car set sell on BAT for $6,666...
UNBELIEVABLE!

I'm also planning to profile the ports, (minor porting) CC chambers, run maximum quench, fly cut heads, Replace everything but the seats in the heads.(if I can keep them-unknown right now). Ceramic coat piston crowns, combustion chambers, valves, exhaust ports, etc.

So worked heads, balanced rotating assembly, normal hot rod stuff...

I am starting with a near perfect 73 2.0 core that I purchased from 914Sixer.

He is a foundation point for this forum IMO.

The original 2.0 heads are near perfect, no cracks that I have found yet. The intake guides are still usable. The exhaust guides are NOT!
One exhaust valve #4 show tip damage.

I haven't yet decided to use them as new stuff is cheap, but if I was going to start a project that used an original head these are the types of cores I'd be hunting.

See what Venturi’s you can get off the shelf for 44mm webers.
You can get a few sets (I would) as you plan for your future expansion goals.
I don’t think you can get 48mm venturis small enough for a 2056.
Anything can be made….but it’s just easier to stick with the product that still has support.

Don’t spec out carbs for headroom. Spec for what you have.

You can get up to 36mm venturis for IDF40s which will be big enough and will still retain driveability.

When you get to the point that your pushing 600cc / cylinder and it’s being choked at above 6000 rpm, then you could justify 44s but you’ll end up choking those down to 38 vents.

This is the standard chart for Venturi sizing vs Displacement and RPM. This chart is all about top end flow and top end HP assuming headers and open exhaust. This chart does not reflect the what is best for street driveability.

Click to view attachment

https://www.cbperformance.com/product-p/6356.htm

44s = 32,34,36,38
40s = 32,34

The 44 are CNC machined in USA for everything except the 36 which is stock Weber.
The CNC stuff looks better IMO and those are budget friendly.

SuperHawk, thanks for the chart. Proves to me that the 40mm bores are at their max (34mm venturis) at 5500 rpm.
Too small in my book.
They'd work well with a stock 2.0 running sub-6000 rpm IMO.
For what I'm building and future plans the 44s look like the way forward.
By the time the big motor is in I will not be using the carbs for fuel.
At that point a straight 44 mm bore will not add intake pumping loses until the rpm exceeds 7k

44s with 32mm vents.

36mm Venturi readily available for Weber 40IDF via multiple sourcesClick to view attachment

Don’t forget 44s also have more area at the butterfly that will cause problems at transition since flow slows as a function of area and as a result 44s just have less vacuum signal at the transition ports.

Mike Pierce has several sizes of venturis for our Webers. I have found he is the best source, Pegasus is also good

Yes, I am aware of the issues regarding using a performance carburetor with too large a butterfly. Basic throttle tip in usually requires a progressive linkage to make it more tractable at low-speed operation.

I've also had experience regarding the opposite.
The Cobra replica (on my website) that I wrenched on had a mild performance 460ci engine that the previous shop speced out a 600cfm Holley for it. This is way too small for this displacement. A proper street carb should be 800 cfm and a serious race carb would be over 1000 cfm.
But, the 70 year old customer told me he NEVER ran it above 3K.
For his driving style the 600 cfm carb worked great.
What a waste...

It was VERY responsive down low and had 600+ ftlbs of torque in a 2300lb car.
It's the most violent car I've ever driven. At any speed below 70 in what every gear you want you could turn it sideways with throttle input alone.
Dangerous for the un-initiated...

I expect I will have this changed over to aftermarket FI fairly quickly as I have to use a Microsquirt to control the COP system (or waste spark if I wanted to be lazy).
I will have to spend money on ignition stuff anyway (like an appropriate distributor), so I'll go the full Monty and do the Microsquirt. This will require cam/crank sensors, map sensor and a TPS if I want ignition only.
At this point adding port injectors is child's play.

What would your suggestion for throttle size be regarding 4 ITBs, using port injectors, on a 10/1 compression ratio/300 degree cam. 2270 with a redline of 7K?

I hit your thread regarding type4 oil pump shenanigans...
You, Sir are also a foundation of this website.
Thank you so much for freely sharing your findings.
Saved me lots of "spin up" time regarding oil pumps.

+1 I agree for the initial motor.

I will be employing a WB02 sensor from the start.
The used exhaust I bought has a wonderful spot for it.

Or 32s in 40s. The Venturi size is the key. Save your dough and work the 40s. A wrecked car I bought had 40s. I put the drivetrain in my car. The engine ran well. Ran out of steam at about 5.8 to 6k flat out on I-5 in Northern California returning home from the Camarillo WCR. I was focused on the road not the speedo. So the speed? It was plenty fast for me.

With the ITB setup being the second goal, maybe use eBay clone webers. They cost less than getting a real Weber or Dellorto rebuilt. Maybe they can work as donors for the throttle bodies.
Bought one once just to get a (was running when parked 914) started.
Both real Weber & Dellorto carbs are artworks as carburetors.
Good luck moving forward.

Did the 40's have 32 vents? Currently I am running 28's and she runs ok, but considering going to 32's. TIA

What are you trying to accomplish by moving up in vents? If it is to move the power band then 30's or 32's will work. 28 to 32 is quite a jump. You will lose the low end punch.

1971 vs 2056. Cam? Who knows? A.C.E. did mine. Spoke on the phone first with usage details. REAL customer service. Great out of the box with a Triad linkage.

Superhawk996 has it right for engines below 2100 cc
For a street based car the proper choice is the 40s

It looks like best low-end performance is to be had with 28mm venturis.

Seem damn small IMO but folks on this forum have drivability issues with larger.

I have had a bit of a set back with my 2.0 core.
Both heads have tiny cracks starting from the spark plug threads.
I will not be able to inexpensively build a "euro-spec" 2.0.

I did find these for my final target motor (78X96 now).

Super stubby DCOE flanges...
https://store.jenvey.co.uk/throttle-bodies-...m-vshort-tspxxi

These fit my design better than anything else I have found. Just blades and a place to fit TPS units.

Should I end up building a carbureted 2055 I will stay with 40mm butterflies, but I would order the HPMX Empi carbs. They appear to be a high-quality clone of the Weber IDF/IDA series and have minor improvements over a true Weber IMO.

Webers did NOT work nearly as good as Mikunis in the L-series Datsun world.

Thanks for all of the replies...