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shelby4130

Carb Question...Entertain Me

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I am sure this has been covered before but here it comes. (Searching through this forum isnt always easy) Anyway, I am planning my build and want to hear the pros, cons, and differences between something like a 38dges carb or dual sidedraft 40s.

I know thats probably a big difference in setup, but my question is how big is the difference in performance, driveability? This is my daily driver and currently has a 32/36 that I like. It's zippy, but who doesnt want a little more?!? Maybe a lot?

My goal for the whole thing is about 150hp. Would the 38 do it or go to dual 40? Ive heard not to do the dual route on a daily driver. But then I see quite a few of you doing it. Someone help me out, let me know who runs what and how it has worked out for you so far.

Thanks in advance.

Michael

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Michael-

besides the carb what else has been done to your engine? is it stock, recently rebuilt, compression numbers, etc?

i think that will really tell the story of where you can get more power from.

dave

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I am currently gathering the parts for a rebuild. But planning on keeping existing pistons (unless I can find a good cheap set before I go through with it all), 292 cam, new rockers/shafts, rings. It will be a mild rebuild, mostly touching the basics I think. Again, this could all change but I am going this route to keep costs to a minimum.

Cost is another reason for my main question here regarding the carbs. It is obviously much more to go with dual 40s. So I am also curious if the dual 40 route is cost effective (performance-wise).

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Spend your money on high compression fresh pistons, oil pump, all new timing parts, new Genuine BMW rocker arms, and a 38/38.

With stock compression pistions, you'd be wasting a perfectly good set of sidedrafts for mere "wow" factor under the hood.

9.5 or higher pistons would be my biggest suggestion. You'll FEEL that money.

Paul Wegweiser

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Thanks Paul, this is the kind of advice I need. Ive kinda been thinking along the same lines, I was just hoping I wouldnt have to dish out the piston money. I suppose I should wait it our for a good deal and go from there.

Now what about the sidedrafts? Can you obtain 150hp without them??

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With stock compression pistions, you'd be wasting a perfectly good set of sidedrafts for mere "wow" factor under the hood.

a quick ride in my car will change your mind there. even with a stock tired motor, the 40 DCOEs make a huge difference, and I'm not going back to the 32/36.

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do ya really think that more than doubling the airflow, as well as subtracting the big intake manifold, is gonna result in no power gain?

sure i'd be making even more power if i had a built engine and hot cam. but the cam would also shift my powerband higher up.

right now im loving the bottom end torque and easily spinning the tires in most gears.

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Now what about the sidedrafts? Can you obtain 150hp without them??

...not without spending substantial cash and effort. You can always bolt on carbs, but how soon do you plan on opening up the bottom end again after this build? Think long term, get hi comp pistons, and save up for the intake system later.

As for sidies on a stock tired motor as KFunk states...been there, done that. The biggest improvement was in throttle response, the thrill and drama of hearing them roar, the fun of tinkering with them, and visual impact they had....sheer HP? probably not that much if dyno tested. (anyone have paperwork on this?) I don't like the 32/36 carb for my own cars either, though...I want all barrels open at the same time...that progressive linkage always bugged the hell outta me. They're reliable, easy to find, easy to service and tune, but I much prefer synchronous carbs over the 32/36 progressives (38/38 DG series or 40/40 DFAV downdrafts)

And my 45 DCOEs will go with me to my grave (or at least be installed on every car I ever own) - with my current powerplant - they are my favorite part of the car!

Paul Wegweiser

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....sheer HP? probably not that much if dyno tested. (anyone have paperwork on this?)

IIRC, a lil company called BMW added sidedraft solex carbs to a 2002, and added a quoted 20hp. did those engines have any other mods?

probably not ideal, no. but the increased throttle response is the key to me. you hit the gas and you get more power instantly, isn't that the idea of what you want? why should it matter what the peak HP is, as long as you get more power when you hit the gas pedal?

also, isn't having fun the basic point of owning these cars? i sure thought it was.

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Where'd that angry wind come from?

YES!! - fun it 'tis...If it isn't, we should all buy Kias! I'm in it for the visceral: smells, sounds, feelings that these cars give me. I'm merely pointing out that internal parts (such as those added to the "ti" model you just mentioned (hotter pistons, larger intake valves) helped those carbs work to their potential. ti pistons are 9.3:1 I believe - vs 8 or 8.5:1 aren't they?

My advice is just to say that he should build the inner guts of the motor so that he can add all the upper/outer easy to install stuff later when budget allows. If I had $600 +/- and had to choose between brand new 9.5:1 / 10:1 pistons or a set of used eBay / swap meet DCOEs for the same price ...it's be an easy decision for me, personally, that's all.

Here's a link to Richard Stern's site that perhaps proves us both correct :-) :

http://www.bmw2002.co.uk/History/alpina.html

Alpina's 15 extra hp for just adding Webers and manifolds ain't bad, (in fact it's very good, as long as the carbs are reasonably priced and don't need extensive rebuilding, linkage, etc) but look what all that other (internal) stuff gets ya'!

Peace Out -

Paul Wegweiser

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