Two 40mm Carbs Questions (can this work?)

[garfunkle55]

I'm honestly just taking a shot in the dark with this. I've read about carbs in this forum and online random places, so all of my knowledge of carburetors is purely interpretation. So here's my idea in a nutshell, tell me know what you think and if enough people agree that it will work I'll most likely end up doing this to my car.

So anyways...

I was thinking yesterday when I saw one of those four motorcycle carb setups on a prelude. Since the weber 32/36 is a 32mm primary and a 36mm secondary, right? If that's true then, would two single barrel bike carbs at 40mm apiece be able to run a BS1 with a few performance mods? And if so, would there be any performance increases? I'm guessing a better throttle response, but that's all I can think of without getting into the numbers of it all.
I have a spare intake I'm working on for either a weber carb preferably the 38/38 but if this works out, I guess it would be kind of like having a 40/40 setup...maybe?

Any ways, I'd really appreciate any ideas or input about this. And let me know what you think of the idea.
Thanks for reading.

[turabaka]

or you could just run a dcoe 40 or 45 weber. Most people run a pair of them.

[lostforawhile]

it's been done already

[garfunkle55]

I thought about doing that but I'm looking for a way to put on a carb without having to do any welding or flange work. With the duel carbs I was thinking of just cutting the intake in half (horizontally across the middle if you're looking at it from the front of the car) and using the two holes left on the intake I would clamp the carbs on with some hose and hose clamps. That's a really quick overall run through of what I'm thinking.

[turabaka]

I thought about doing that but I'm looking for a way to put on a carb without having to do any welding or flange work. With the duel carbs I was thinking of just cutting the intake in half (horizontally across the middle if you're looking at it from the front of the car) and using the two holes left on the intake I would clamp the carbs on with some hose and hose clamps. That's a really quick overall run through of what I'm thinking.

If you're thinking what it sounds like you're thinking then that'll never work. Hose clamps will never hold a carb on tight enough. Unless you've done some serious work to your car I'd just go with a 38 weber. Plenty of power, and easy to tune.

[2oodoor]

it's been done already

Two SINGLE barrel 40 mm carbs? who was that?
two twin barrel 40 mm would suit the motor better. You have to figure the two cylinders sharing one one barrel may cause a problem with vacuum for the entire rpm range. Driveability issues for regular driving. That is the sweet thing about the weber design, it can run on the idle jet up into 3K rpm (and more) as the transition stages with those are unique.
SU carbs would be a good choice for this though, despite the single throat, it has variable venturi and would require no jet experimenting, .
A lot of carb combnations would work, but only some of them would perform effecient under all conditions, not just nads out wide open racing:lol:
Why not use four anyway?

[garfunkle55]

Well, from the sound of it I'll probably just stick with the 38/38 cause this would end up being my every day driver. So I can't take chances on something that won't do well in day to day driving. And the reason I decided not to do a four carb set was because I don't have the resources or 'know how' to make an intake. Plus I figured 'hey if i could get this to work with minimal effort, right on' Either way, thanks for the info.

[cygnus x-1]

What you're talking about is a twin carb setup like the stock Preludes, but to fit a 2.0L style head instead of the 1.8L head. I could swear someone started on a project like this but I don't remember if it was ever finished. There were pictures posted of a stock intake cut off half way. Was it A20A1 maybe? Hell if I could actually find it.

The idea could certainly work but it wouldn't exactly be plug and play. Multi carb setups are tricky because you have to synchronize the carbs. A Weber 38/38 will have no problem feeding even a moderately modified 2.0L. And it's a fairly easy conversion. And there is plenty of jetting information in the Weber sticky threads.

C|

[lostforawhile]

What you're talking about is a twin carb setup like the stock Preludes, but to fit a 2.0L style head instead of the 1.8L head. I could swear someone started on a project like this but I don't remember if it was ever finished. There were pictures posted of a stock intake cut off half way. Was it A20A1 maybe? Hell if I could actually find it.

The idea could certainly work but it wouldn't exactly be plug and play. Multi carb setups are tricky because you have to synchronize the carbs. A Weber 38/38 will have no problem feeding even a moderately modified 2.0L. And it's a fairly easy conversion. And there is plenty of jetting information in the Weber sticky threads.

C|it might be mine,the twin 38 mm sidedraft SU's? it's waiting on money to be finished.

[Zufer]

you all fail

#1: Turabaka you are wrong about hoseclamps not holding carbs on. My quadcarb setup i held on by hose clamps and has run for a year like that.

#2: If you are goin to go through the trouble of doing anything custom like this you might as well goall out and run 4 bike carbs or 2 dcoe's

#3: Regardless of what anyone says you still have to mess around with jetting on SU's to make them run properly.

#4: The hardest part of your idea would be the throttle linkage.... how are you goin to connect the two carbs together. For my setup i used the factory mechanism that came on the carbs but without that my car would never have run.

[lostforawhile]

you all fail

#1: Turabaka you are wrong about hoseclamps not holding carbs on. My quadcarb setup i held on by hose clamps and has run for a year like that.

#2: If you are goin to go through the trouble of doing anything custom like this you might as well goall out and run 4 bike carbs or 2 dcoe's

#3: Regardless of what anyone says you still have to mess around with jetting on SU's to make them run properly.

#4: The hardest part of your idea would be the throttle linkage.... how are you goin to connect the two carbs together. For my setup i used the factory mechanism that came on the carbs but without that my car would never have run.um SU's don't have jets, all you have is a single needle and seat, and the ones already on this setup are for an engine size close to the one on the three g. they will run a range of engine sizes on a single needle. as far as the linkage, it's already figured out and works. i used factory keihin parts to build a linkage that works in reverse when you pull it, it works perfectly, it hooks right to a factory keihin carb cable. the factory linkage setup on the carbs was set for a push rod that worked in reverse of what i wanted. i already have a half of a factory cable connected to the setup. pull it and the throttles plates open. it's not mickey moused eithier, it's just as high of a quality as a factory linkage. many many hours figuring it out. as far as needing four carbs, they run these same carbs with different needles on road raced datsun 280 z cars. if they can run a full out prepped race car,they can run my street car just fine. the hose clamps aren't a bad idea,not much different then i've seen on bikes, but you need an aircraft type clamp that puts 360 degrees of pressure on the fitting. they look like large fuel injection clamps,with the clamping mechanism on the outside of the band. as far as the carb project,as soon as the money situation gets better, i will finish the project, it's sitting almost in front of me. believe me after all this work,it will get finished.

[Zufer]

Ok lost lets take a look a couple things. I work a race shop and am at our local race track almost every weekend during the summer. Can you explain to me why some z's run way better than others if one needle is all thats needed for a range of engines? Oh wait thats because there are people that have spent years tinkering with their carbs to get them right.

As far as the linkage... yes i knows its possible. Is it worth the time...in my opinion no. I also want to point out one fatal flaw in your little deal about SU's. Everyone i talk to that races a 510 or a z says that switching to DCOE's is a very good option. the reason you don't see it at the race track isn't that the SU's are better. Its that most classes require stock carbs and manifolds. So if all these guys that have SU's running properly say that switching to DCOE's is better. And we have to build a custom manifold to do either SU's or dual DCOE's or 4 bike carbs. Why would you choose the one that racers wish they could upgrade from.

And until your car runs and is tuned... I don't think you should be preaching that the SU's are the way to go.

[lostforawhile]

Ok lost lets take a look a couple things. I work a race shop and am at our local race track almost every weekend during the summer. Can you explain to me why some z's run way better than others if one needle is all thats needed for a range of engines? Oh wait thats because there are people that have spent years tinkering with their carbs to get them right.

As far as the linkage... yes i knows its possible. Is it worth the time...in my opinion no. I also want to point out one fatal flaw in your little deal about SU's. Everyone i talk to that races a 510 or a z says that switching to DCOE's is a very good option. the reason you don't see it at the race track isn't that the SU's are better. Its that most classes require stock carbs and manifolds. So if all these guys that have SU's running properly say that switching to DCOE's is better. And we have to build a custom manifold to do either SU's or dual DCOE's or 4 bike carbs. Why would you choose the one that racers wish they could upgrade from.

And until your car runs and is tuned... I don't think you should be preaching that the SU's are the way to go.
i've been messing with these carbs for years,since I was a kid, don't try to sit here and run me down like I don't know what i'm talking about. as far as the old z cars, most of them CAME with these hitachi SU's factory. this set came from a 510 sss, not the 510 here which was really a sentra,but the 510 bluebird. A lot of guys who have run these carbs love them,this is the pre emissions set that everyone wants. I was in a bidding war with 40 people for these. the ones a couple of years later suck. If you are griping about the amount of time it takes to build a custom manifold or something different,then you really don't get it. when you custom fabricate your own manifold and linkages,and air cleaners,and all the lines and fittings, and get it to the point where these are,then you can run down my project. I have countless hours in this, don't think I just threw someting together. There is a lot of research and figuring behind these. and there is nothing wrong with running a street car with two side draft carbs. it's been done for decades on brittish cars, I guess there is something wrong with all those MG's and other brittish cars that have dual sidedrafts. you probably aren't old enough to remember all those cars .

[Zufer]

Uh... before you start bashing on me for my age... I have spent countless hours looking at british cars for just this reason. What did i stumble across... most of the fast ones street or not ran 4 bike carbs or dual dcoe's. your right i probably don't know as much about SU's as you. But from what i do know about custom things in general... its not plug and play with the tuning no matter what. I had probably 50 hours plus into tuning my DGEV weber and it was well worth it. Also i built my own manifold. I built my own intake adapter that was setup to let me run a CAI for my four carbs. Your missing my point if you think i don't realize why people build custom stuff. All i'm saying is if you are goin to spend the time and money why not go for the best you can no what was the best for some 60's or 70's stock car.

[lostforawhile]

Uh... before you start bashing on me for my age... I have spent countless hours looking at british cars for just this reason. What did i stumble across... most of the fast ones street or not ran 4 bike carbs or dual dcoe's. your right i probably don't know as much about SU's as you. But from what i do know about custom things in general... its not plug and play with the tuning no matter what. I had probably 50 hours plus into tuning my DGEV weber and it was well worth it. Also i built my own manifold. I built my own intake adapter that was setup to let me run a CAI for my four carbs. Your missing my point if you think i don't realize why people build custom stuff. All i'm saying is if you are goin to spend the time and money why not go for the best you can no what was the best for some 60's or 70's stock car.hoping by summer i can raise the money to finish these then i can silence a lot of people

[Zufer]

ok... if you really want to silence the subject i guess you'd have to put the same amount of time and effort into building a DCOE setup and dyno them both. but since your not gonna do that i'm sure. i guess you won't ever win.

[2oodoor]

you all fail

#1: Turabaka you are wrong about hoseclamps not holding carbs on. My quadcarb setup i held on by hose clamps and has run for a year like that.

#2: If you are goin to go through the trouble of doing anything custom like this you might as well goall out and run 4 bike carbs or 2 dcoe's

#3: Regardless of what anyone says you still have to mess around with jetting on SU's to make them run properly.

#4: The hardest part of your idea would be the throttle linkage.... how are you goin to connect the two carbs together. For my setup i used the factory mechanism that came on the carbs but without that my car would never have run.

you F A I L
why would you say this?

I can contradict every one of your observations just as easily.
Turabaka misunderstood most likely, that these were going to be rubber isolated carbs.
There are many aspects to look at in carb choice, one being financial. Of course having the resources is just as important and reflects on the $$ part as well.
Derr, SU have no jets. Just needle size and depth adjustment.
The hardest part of garfunkle's idea is not the linkage, but the aluminum manifold fabrication. Of course that is an opinion as is anything here is going to be until you can show how much effort it takes to build any of them. Then again you would have to compare the skill level of the person doing it, wanna go there? Pointless to do so for the sake educational value of this thread dude.

[lostforawhile]

he has to have something to start trouble with, now wasn't this thread about whether two carbs can be run on this engine? :uh:

[2oodoor]

you should both post links to your manifold build threads. I happen to like both of them.

[lostforawhile]

you should both post links to your manifold build threads. I happen to like both of them.i need to rehost a lot of the pictures since imagestation went FAIL! I do have them all though.

[Zufer]

if its about cost... my setup is well under a 100 dollars. however i had access to an aluminum MIG gun.

My point is not taht it can't be done.... more so that its not worth your time to only do two carbs... for the same amount of effort you can go for a quad carb setup.

Oh and if we want to compare skills sure... i can do that.

[lostforawhile]

if its about cost... my setup is well under a 100 dollars. however i had access to an aluminum MIG gun.

My point is not taht it can't be done.... more so that its not worth your time to only do two carbs... for the same amount of effort you can go for a quad carb setup.

Oh and if we want to compare skills sure... i can do that.who's buisness is it of yours to decide what someone elses project is worth? who do you think you are to tell me my project isn't worth the time? I don't trash your project, quit running everyone else down.

[A20A1]

or you could just run a dcoe 40 or 45 weber. Most people run a pair of them.

From what I've read, most engines get better results from Dual webers with smaller chokes vs a single weber with larger chokes. If you're not modding your engine a whole lot just stick with the smaller carbs. If you feel like going bigger you can always sell the smaller ones. Webers usually sell well, especially the DCOE's.

Anywho the least trouble would be the 32/36 or 38.
There are some interesting mods for both carbs out there. some mods make the 32/36 synchronous and others swap booster venturies from other webers into the 38 for added response. I really hate vacuum leaks so to play it safe, since we have so many plates and thus so many gasktets, the adapter plates should be welded if you can do it, but it's not required.

I liked the idea of Quad Bike carbs or Dual Webers but those are IR setups and I'm traveling a different route mainly because I like using downdraft carbs and having secondaries to tap into. Aside from the power valve and other linked passages in the base of a 4bbl, my carb via the manifold will be divided in two and will hopefully work like two seperate 2bbl carbs. So yeah it's not as good perhaps as a quad or dual carb IR setup but with the secondaries it shouldn't suffer as much in the low end as a single larger dcoe.

[Zufer]

Well lost as far as i know there are only 3 people that have made a sidedraft setup on an A20 work on this board. Phydeux... some guy from prelude power that has bike carbs... and me. So i feel like i have a bit of say in whether or not this is worth it. And as far as i'm concerned it isn't. I Got a gain... but at the loss of drivability. So if you are goin for a complete race setup ok it might be worth it. But as far as dailying... Just run a downdraft weber. Its cheap... simple... and bolt on.

[lostforawhile]

Well lost as far as i know there are only 3 people that have made a sidedraft setup on an A20 work on this board. Phydeux... some guy from prelude power that has bike carbs... and me. So i feel like i have a bit of say in whether or not this is worth it. And as far as i'm concerned it isn't. I Got a gain... but at the loss of drivability. So if you are goin for a complete race setup ok it might be worth it. But as far as dailying... Just run a downdraft weber. Its cheap... simple... and bolt on.why would i lose driveability with SU's? they self adjust to the particular airflow needs of an engine,they have been used in some form or another on engines since the 20's, do you think even those cars had driveability issues? the only reason they stopped being used was because the tiny bit of oil that can seep down past the piston in the dome,can affect emissions. for crying out loud,rolls royce used a dual sidedraft setup on some of their cars. do you think they would put up with driveabilty issues? do some research,they are some of the smoothest operating carbs out there, all the crap added to a standard carb is to try to make the best of a compromise on the airflow through it which can't be ideal under all conditions. An SU type carb,or in technical speak, a variable venturi carb,adjusts itself to all operating conditions of the engine. in other words the cfm of the carb changes depending on the engine load. a standard carb needs things like idle jets,and power jets, and accelerator pumps, etc. etc. to try and do the same thing,even then it's always a compromise.

[Zufer]

ya... i'm aware... I have variable venturi carbs. However being that i haven't put in thousands of hours into developement as rolls royce would have. Therefore being that all of these setups are custom they have little quirks.... Mine is ridiculously sensitive to whether conditions. I had a weber that was very well tuned and although it need to but upped to a 38/38 due to the large cam i was using it was a much more reliable and consistent setup.

[2oodoor]

Well lost as far as i know there are only 3 people that have made a sidedraft setup on an A20 work on this board. Phydeux... some guy from prelude power that has bike carbs... and me. So i feel like i have a bit of say in whether or not this is worth it. And as far as i'm concerned it isn't. I Got a gain... but at the loss of drivability. So if you are goin for a complete race setup ok it might be worth it. But as far as dailying... Just run a downdraft weber. Its cheap... simple... and bolt on.


If you used a stand alone ignition I think you would get more out of the quad set ups. You could program you timing to smooth out the carbs transition stages. Also some kind of cold start enrichment system would help too.

[lostforawhile]

if anyone does do carbs that clamp on,these are the kind of clamps you need, they put 360 degree pressure on the fitting http://i220.photobucket.com/albums/dd158/lostforawhile/S4020041-1.jpg

[accordion89]

wow this is an intense thread

[Civic Accord Honda]

wow this is an intense thread

word brotha , just realized i must of missed this

[Hauntd ca3]

i kinda like these threads, just to see what sorta ideas are being thrown around out there.
a few additions i would like to add.
su carbs do have a jet.
that brass tube that the needle slides in and out of is the jet.
they come in many various sizes to suit fuel the motor needs.
chances are, that if you keep modding a motor running su's, you'll run out of flow in the jet eventually , so you just get the next size up.
the needles arnt a straight taper in most cases.
if you could scale a needle up by a huge amount, you'd find that the degree of taper changes quite a bit over its length to suit the amount of fuel needed at that dash pot opening.
jaguar didnt stop using su's until they went racing with the c and d types and that was just because the dcoe linkage for 3 carbs was easier and more reliable than linkages for 6 su's.
oh and once they entered the usa market they swapped to stromberg cd series carbs for that oil leaking reason stated earlier.
as for the bike carb bit.
the poms started out using amal smoothbores, coz they were cheap, plentiful,compact and easy to tune. and they have no butterfly being a round slide carb.
syncronising them to all open at the same time is a shit tho.
i think that using bike carbs is a good idea to.
as most are similar to a cd stromberg in design they are a nice smooth carb and simple to rebuild and tune.
a manifold is piece of piss to make, a flange with a tube per carb and you are set.
just need a linkage needed then.
am looking forward to see how the lost mobile goes when he's all done
and i say give it a go garfunkle, what you got to loose apart from time