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Whats better 38mm Su's vs 38/38 weber for torque and power??


Lozer

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One thing that a 2 barrel downdraft has over dual single barrel side drafts is a plenum. The plenum provides an area for the fuel to atomize and the pulses to equalize before it enters the head. With a couple simple mods to the plenum and carb adapter, the downdraft offers more power and torque over dual SU's. To be clear, we are talking about a L series 4 cylinder.

 

You can make a side draft manifold that has a common plenum. It's actually not a lot of work.

 

Another reason I like the Weber, it's got an accelerator pump. The SU's do not. Starting is easier with a Weber and throttle response is quicker.

 

Webers down drafts are a lot more flexible when it comes to tuning as well.

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I wouldn't wish SUs on anyone..........

Used to tune them for people, 311s, MGs, and other euro trash.

Damn things would never stay in sync more than 6 months.

 

I'd do the Weber, but only if you can find a nice aftermarket down draft manifold.

Stock is really restrictive.

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The SUs are probably better for all-around drivability whereas the Weber would be more performance based.

 

 

Going with the 38/38...yeah, mo power.

 

I really like my 32/36. Plenty of throat when I need it and runs great when just cruising. Decent mileage too.

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I liked the Su's that I had on my car, but then again, I only had datsun experience with su's and one 32/36 that never ran right. So.. Either you can ask for everyone's opinion, or drive two cars with different carbs. Personal experience and opinions differ for people. Maybe you like the su's, maybe you like the weber. 

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Most people never get the Weber tuned just right.  Setting the idle mixture screw is about as far as they get. There's the emulsion tubes, pump nozzles, power valve, auxiliary venturis, needle and seat, and then the fuel, air and idle jets. Playing around with all those until you get a good understanding of how a Weber works will allow you to get the most out of any carb.

 

To be clear, I'm not just talking about full throttle performance. When I built engines for a living, top of my list was a good driving experience. Smooth idle, seamless acceleration without lag or pops from the carb, those things are all important to me, and the Weber is far more tunable than the SU's in that regard.

 

In addition to carb tuning is the all important distributor advance curve and cam timing. Add the mods to the intake and you've got a smooth ride.

 

SU's are neat looking and sound cool, but I would take a down draft any day. If you want to talk about dual Mikunis, now that's another subject. I'll gladly swap a Down draft for a pair of dual PH44s.

 

Mileage with a 38/38 is going to be worse than with a 32/36, and performance won't be that much greater to warrant the additional venturi size.

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So reamed out my l16 intake and slammed the 38/38 on and tuning was quick with a wideband (correct needles off the batt as it was installed on this motor originally)

 

and WOW what a difference. so much smoother and feels substantially more torqey everywhere.

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90 degree bend in intake tract doesn't matter. Not at that point. As I stated earlier, the bend, which is the plenum, helps atomize the fuel and equalize the vacuum helping the air get distributed more evenly.

 

A 90 degree bend at the valve is more detrimental. That's where it matters.

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