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single to dual carbs, how much of a difference?
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busmania
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PostPosted: Mon May 23, 2011 7:30 am    Post subject: single to dual carbs, how much of a difference? Reply with quote

I am driving a 67 bus. I believe it has a 1500 or 1600 single port currently but without opening it up, it is anyones guess. I am going to be building a 1776 or 1951 (maybe I mean 1915?) at some point but not just yet because my engine runs great. In the meantime, I was thinking of switching to dual carbs and then using those carbs on my new engine when it comes time to build it. So, how much of a difference will going to duals make? I was thinking webber 34 ICT because I have used them in the past on a type IV engine and was happy with them. Or, maybe webber 40's (but they are double in price).

Would the 40's be too much for my current engine?
I think the 34's would be perfect for my current set up, but will they be good for a 1776 or 1951?
How much of a difference in performance could I expect going from single to dual carbs? I am most concerned with being able to maintain some sort of speed going through the mountains.
Performance wise, where will i notice the difference with dual carbs? Low end torque? High rpm's?

Thanks for hte help.


Last edited by busmania on Mon May 23, 2011 8:09 am; edited 1 time in total
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PostPosted: Mon May 23, 2011 7:37 am    Post subject: Reply with quote

IMO the biggest difference you'll find is in the response quickness of the power! Single carbs tend to "lag" in response to accelaration versus that of a dual carb set up. You may not go any "faster" but will definitely get "up to speed" much quicker! Cool
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aryue
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PostPosted: Mon May 23, 2011 8:27 am    Post subject: Re: single to dual carbs, how much of a difference? Reply with quote

busmania24 wrote:
I am most concerned with being able to maintain some sort of speed going through the mountains.



In the Rockies there is definitely no replacement for displacement when comes to a non-turbo motor.

At 8,000 feet your cylinders are only drawing in about 77% of the air molecules per liter as would at sea level. So, it goes. On a non-turbo 1776cc at 8,000 ft. , you are basically running the equivalent of a 1367cc at sea level.

Build a 1904cc and it becomes a 1466cc engine at 8,000 ft. It still will be slow going, but noticeably not as slow and will pull many uphill grades in third rather than second.

If I recall, ICTs have 29mm vents, which will in addition to bumping the the torque curve past 4K plus RPM - should also make for better low-end torque on a 1776cc, than the 26mm venturi on the more restrictive single Solex. In short, if you look at an engine as air pump, the dual ICTs will be less restrictive throughout the usable RPM range.

Looking at the carb swap from a horsepower perspective on 1776cc - even if it is 8 to 12 hp bump starting at 2,500 rpm - at 8K above sea level - you'll be running 77% of 75 hp motor versus a 65 hp.

My problem is that I live at 500 ft. and going up to 8K to 10K really necessitates changing the idle/pilot jets along the way. Question: which set of duals is it easiest to swap idle jets on?

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Last edited by aryue on Mon May 23, 2011 8:32 am; edited 2 times in total
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PostPosted: Mon May 23, 2011 8:28 am    Post subject: Reply with quote

In general - you may notice a little difference with the dual carbs. But to gain the most you need to complete the "system" (heads, exhaust). I have seen posts where folks say duals help a bit, but have never seen any dyno data to verify.

As far as using the same carbs - I like Kads - I run the same model (different jetting) on a 1600, a 1776 and a 1914.
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PostPosted: Mon May 23, 2011 8:28 am    Post subject: Reply with quote

You should wait until you get the new engine built to change carbs. Your current setup is a single port and you aren't going to get Weber 40s on that without a head change unless you are thinking of mounting it as a single two throat. The only advantage a single centered two barrel has over the dual one barrels is it never gets out of sync - linkage is easier to putz with.

You can put ICTs or Kadrons on it but there won't be any big difference in power. After you build the new engine and get it going you will notice a difference when you put a pair of ICTs or Kadrons on. A 1776 with single port heads and ICTs or Kadrons would be a good choice for a bus. Forget the 94s for your bus - the cylinders are too thin for a bus application unless you live in or near the arctic circle. Same goes for the 1835 (92mm) unless you use the thick wall cylinders. A 74 or 76mm stroker with the 90.5s or 92 thick wall cylinders would be even better.

Speed cost money - how fast do you want to go?
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PostPosted: Mon May 23, 2011 8:40 am    Post subject: Reply with quote

OLD VW NUT wrote:


Speed cost money - how fast do you want to go?


AKA - how fast do you want to spend?
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PostPosted: Mon May 23, 2011 9:27 am    Post subject: Reply with quote

Here's my 1776 Single Port, Engle 100 Cam, with Dual Kadrons on original Kadron steel single port manifolds:

Image may have been reduced in size. Click image to view fullscreen.

I love this motor. Plenty of power & torque for my needs and great gas mileage.
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PostPosted: Mon May 23, 2011 9:29 am    Post subject: Reply with quote

dmilla wrote:
Here's my 1776 Single Port, Engle 100 Cam, with Dual Kadrons on original Kadron steel single port manifolds:

Image may have been reduced in size. Click image to view fullscreen.

I love this motor. Plenty of power & torque for my needs and great gas mileage.


Nice Cool
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busmania
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PostPosted: Mon May 23, 2011 9:30 am    Post subject: Reply with quote

Well, Currently I run about 60-65 on the highway which is OK. 60 feels better with the current set up, but I would like 65 to feel better. This is on flats with ocasional hills. I dont live in the mountains but frequent them often. I want to be at a better rpm range while cruising. I would rather have my foot half way on the gas rather than floored all the time like it is now.

As far as cost goes. When I build it, i wont be too concerned about that (my salary is seasonal. I have money in the winter, and none in the summer so this project is likely a few months away unless I decide to splurge now. I would like to be in the $2500 range when all is said and Done. (clutch and all the other added parts you dont think about). I have built engines before, but I am thinking this time I might just buy a long block. Would $2000 be reasonable for a GOOD longblock? I would also like to ugrade some of the cooling/oiling stuff. Dog houese etc, deep sump etc. In reality i would probably only save about $4-500 if i built it myself right?

As far as waiting to put the dual carbs until I have the engine. I may do that, but if I buy them now, I have manifolds for both single and dual ports already so that is not a problem....after I find them in my garage. When I buy or build my new engine, I will likely build it as a dual port.

How does this sound? 1776 dual port with 34ICT's? Or stick with single port? I have read, and read, and read about the differences. Everyone has their own opinion and we know what that is like.

Again, I am most concerned with all different aspects of highway driving. I like to road trip, that is why i have a camper. I would say it would be 75% flatland, 25% mountains.
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PostPosted: Mon May 23, 2011 9:34 am    Post subject: Reply with quote

I keep hearing about Kadrons. For a 40mm set, it seems like a nice compromise for a bigger carb. How is the linkage? If I did the webers, I would buy them with the CB performance linkage, which I have also found to be very simple and reliable.

So, I guess now my choices are.
34ICT's with cb performance linkage - $399
40IDF (what is ICT vs IDF?) webers with cb linkage - $779
40 Kadrons with linkage - $560 (good compromise?)

Are the kadrons as simple as the webers?
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PostPosted: Mon May 23, 2011 10:42 am    Post subject: Reply with quote

If you're looking at Kadrons, check out the Kaddie Shack

http://kaddieshack.com/

They offer a "turn-key" kit with rebuilt/rebushed 40 or 44 Kads for $379.00. Add the options you need and you'll be just a little over $400. I've read a lot of good reviews about them here.

Looks like the way I'll go when I build my 1776.
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PostPosted: Mon May 23, 2011 11:07 am    Post subject: Reply with quote

There are plenty of opnions on dual Kad linkage. Here is what I know - I run the Skat linkage and its not expensive. I do a slight modification though, which is to run a larger single spring in the same manner that the stock Kad linkage does.

I am a huge believer in making sure the carbs are synched properly - if you are running wide open all the time, it doesnt matter, but since all my cars are driven on the street, drivablility is very important.

On my first set of Kads, I chased my tail all over the place trying to get them to run right. After finding the perfect synch tool (homemade manometer similar to what bike tuners use), it made life so much easier. But I also found that since I could measure the synch really well, there was too much play in the stock Kad linkage.

There are a couple issues with Kads and I know AJ Simms is aware of them and I would ASSUME that Kaddie Shack is as well (accel nozzle siphoning fuel). Once you get past that and the synching, they are VERY easy to work with. I run them on 3 of my cars.
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PostPosted: Mon May 23, 2011 4:27 pm    Post subject: Reply with quote

After buying my 70 bus, I drove it about two, three times, and then I could not stand it anymore.

Put dual IDFs on there...............ahh, much better!

That darn stock carb runs so crappy it makes me crazy
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PostPosted: Tue May 24, 2011 6:42 am    Post subject: Reply with quote

I found a guy locally that has been "building engines for years". I obviously take that with a grane of salt. However, here is what he is selling. Sounds reasonable to me right? Would teh 8.5 compression be too high in a bus?

Here is what he sent me.
The 1835 is brand new.. and has many upgrades to include engle 110 cam, malhle pistons, Chomoly pushrods, highflow oil pump with external filter and full flowed case, is has 36hp dog house shroud, altenater, the compression was set at a healthy 8.5 to one. I have a dual carb set up for it or a single. The price depends if you want long block: $1100, turn key with dual webers (40's): $1700 and turn key single carb: 1500
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PostPosted: Tue May 24, 2011 7:43 am    Post subject: Reply with quote

In a Bus, I'd rather run a 1776cc with a counter-weighted crank, W100 cam, balanced rods, Mahle forged P/C with pistons balanced and a stockish L3 dual-port head. All of which will exceed $1100, if you are talking about a long block outright.

90.5 mm pistons and cylinders have thicker cylinder walls than the 92's on the 1835.

Also, for a Bus don't go the 36 hp fan shroud route unless you live in Key West, Fla. Stick with an upright dog house fan shroud with operational thermostatically controlled cooling flaps. Trust me, the engine will last a lot longer.

So don't even think of doing the local guy's version of a turn-key. and you'll never know what corners were cut to get an $1100 long block out the door.

Dual Kads will be fast enough, if you are on a budget and can master setting them up properly.

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busmania
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PostPosted: Tue May 24, 2011 8:40 am    Post subject: Reply with quote

aryue wrote:
In a Bus, I'd rather run a 1776cc with a counter-weighted crank, W100 cam, balanced rods, Mahle forged P/C with pistons balanced and a stockish L3 dual-port head. All of which will exceed $1100, if you are talking about a long block outright.

90.5 mm pistons and cylinders have thicker cylinder walls than the 92's on the 1835.

Also, for a Bus don't go the 36 hp fan shroud route unless you live in Key West, Fla. Stick with an upright dog house fan shroud with operational thermostatically controlled cooling flaps. Trust me, the engine will last a lot longer.

So don't even think of doing the local guy's version of a turn-key. and you'll never know what corners were cut to get an $1100 long block out the door.

Dual Kads will be fast enough, if you are on a budget and can master setting them up properly.

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Thanks. Pretty much what I was thinking but I guess I was just looking for reassurance. Sometimes I get excited when I see a price, but I KNOW shortcuts were made somewhere along the line. But because I dont know what most of that stuff means as far as specifics, i dont know if it is good or bad. I figure to do it right, it will cost me at least $2500-3000 total when all is said and done.
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