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su versus weber carbs


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So I have a stock engine in my 1974 260z with SU carbs from a 1971 240z.  Is there really a significant performance difference by switching to Weber carbs and is there and difference between the Weber dual carb set up versus the triple carb set up?  I'm trying to decide if it's really worth the money to change.

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Not if you are going to hook em up to a stock engine IMO. Now if you add all the other performance goodies, it may be worth your money and time. But for me, SU’s are cheap, easy to tune and provide plenty of juice to put a smile on your face.......especially if you add the other mods that work with them.

 

 

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Ask any red blooded male, the triple DCOE carb look and sound is frankly pornography and a mating call!!!!

However, bear in mind that DCOEs were designed for racing / high performance applications. They will flow great at the top but you will lose low / midrange torque on your stock engine - unless you choke them right down, which imho defeats the object of installing a high flowing carb. Diseasd said it perfectly.

Much like adding too big an exhaust / header, you lose gas velocity low down where the mass of air is, relatively speaking, small but the DCOE choke area is the same regardless. Less air speed = less fuel atomisation. The SU is designed to keep the air velocity constant across the jet by constantly varying the choke area. This means you get better atomisation low down / mid range (think torque / drivability). The carb opens itself wide when you put the hammer down at high revs / high load conditions to give you flow.

That’s why for a stock engine SUs work so well. Last dyno session on ZTherapy SUs (with custom needles) my modified L28 touched 245bhp @ 6400rpm (where the operator ran out of balls). On the road, she pulls hard to about 6700 rpm without losing enthusiasm! So yes, they can also produce good power if properly set up. I’m sure a set of DCOEs can give me a few more ponies at the top but the cost per BHP equation doesn’t make financial sense. A big advantage of DCOEs is of course the lovely mangoletsi intake manifold with near straight runners to the head - great for flow!

But if performance is not the concern and your objective is sound and looks, then there is no substitute for that intake roar of triple DCOEs!!

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Here’s a perfect example. Eiji and I race once each year in Dinwiddie. In this race, he’s running a stroker with trips, larger valves and taller cam. I’m running my usual .080 cut, Isky Stage III with a .040 over bore. It’s pretty close till top end. On May 14th we run again.....this time I’m also running a stroker still with SU’s.....we’ll see how that comes out LOL. I love my SU’s. Turn up the volume.

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So what are you running in the quarter... My guess is 13's or 14's, oh, and the sound is awesome in the video.

Edited by w3wilkes
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Eiji ran low 14’s I ran high 14’s. I hope to crack into the 13’s in two weeks with the new Stroker motor. It feels much fadter, but you know how that goes.

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And then, there is the DU6

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Not without their challenges from what I’ve read. A company in the UK has started making them again though.

Or this crazy set up on a V12 Jag ....

066ba957e9ea10f58f2a8b68578ce148.jpg


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  • 3 weeks later...

Ah, so the SUs pulled ahead a 1/4 a second. I assumed it was Guy's quick mind ove Eiji's?

Power beats the lights. :ph34r:

I can't figure how to watch the video! Old arse laptop only plays sound.

 

Edited by siteunseen
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3 hours ago, w3wilkes said:

Looked like the ZX had you off the line which you more than made up by the end of the run.

Absolutely....Caught me sleeping, but caught up and passed him at finish line. The 336 rear does better than his 410 top end, and the SU’s once agIn proved they can play with the big boys!

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