Carb Education

cr_bobcat

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So all this talk about the aluminum head lately and that Matt is getting the triple SU and triple DCOE intakes set up, I'm starting to get the itch on figuring out how to get my Lynx triple SU setup for the cast iron head figured out. I don't know much about these carbs, but I see that this thing is supposed to work with SU HS-6 or the Stromberg CD175. Are there significant performance or reliability issues between SU and Stromberg?

Thanks!
 
I would wait to see if it performs any better than a direct mount with a 2100 or a Holley carb.
 
I have 2 small log heads in the garage. One of them had a cracked exhaust flange on the #1 location. I figure this is a good one for me to learn on. I was going to get the log lopped off and start making some measurements and mocking up a pattern.
 
sayhello.png


Are you referring to these carbs? The image I used for the graphic above was found in the CI Archives, I don't know if this actually exists anywhere. Has Matt has substantiated this is configuration is going to happen?

ci/WeberDCOE.html

tripledcoe.jpg


Sorry if this config isn't a true statement... But if it is - Cool! :D

- Perry
 
He has the availability to get both of those manifolds. The triple SU and the triple Weber DCOE. I have a Lynx triple SU manifold that I got from Rocklord. It is designed to mate up to a log head where the log has been milled off. I started to read up on the differences between th SU and the similarly designed Stromberg.
 
Did you find a sorce for the carb's yet? My guess is that the SU's maybe a bit harder to find, work on, and get parts for here in the states. The Strombregs were great carb's and somewhat easy to work on as far as the old ones they used on the early Ford Flatheads. Either way you go should be a fun setup! Good luck :nod:
 
The cupboard was bare a few months ago. I tried looking again last week and they are all over the place. Go figure.

This will actually be a long build process so I've got the time to do some research. I've only had the direct mount 2bbl on for a little while too, so I need to finish working the kinks out there before I get too excited about a multi-carb setup. Eventually I want to be able to change heads if I feel like it :)
 
cr_bobcat":edk2oobz said:
So all this talk about the aluminum head lately and that Matt is getting the triple SU and triple DCOE intakes set up, I'm starting to get the itch on figuring out how to get my Lynx triple SU setup for the cast iron head figured out. I don't know much about these carbs, but I see that this thing is supposed to work with SU HS-6 or the Stromberg CD175. Are there significant performance or reliability issues between SU and Stromberg?

Thanks!

Yes, the Zenith Stromberg CDS 150/175 are not as reliable as the SU carb due to the diaphram in the dashpot. Very unreliable with todays fuels, and the supply is not up to scratch. US Armed forces bases always ditch the Freight Rover or LandRover twin CDS175's with a good old Holley 390 4-BBL.

The SU carb has any early fixed needle, not integrated float bowl version that has to be handed to fit a Ford Six. Getting two or three the same is hard

Then they went to the better bias/swing needle version, but there were then versions versions with new Zentih Stromberg CD style integrated float bowls, or the old handed float bowls, and three jet sizes and a bizzilloin different needles.

Then the went to metricated versions in 1986, as Austin Rover then owned the Skinner Union plant and patents. However, Zenth Stromberg still made carbs untill the very late 90's. All the DAF and Sherpa based 3.5/3.9 trucks with the Rover Alloy V8 were appallingly unreliable with this carb.

Again, to fit the earlier side float bowls on a Ford Six is harder.

The set up and operation is easy, as long as you follow the basics.


There is a fully elecronic US made throttle body EFi conversion to the Zenith Stromberg CD 150 used in Triumph TR6's, GT6s, MG "Bee's" and "Midgets".

It has been used with some sucess.

In Australia, the ZS CDS 175's got bored out to 1.875", and used in 350 hp Turbocharged Falcon's by Mike Vine, but that was in the non oxygenated, non ethonal gasoline era, so the diaphram reliablity issue wasn't an issue with low aromatic gas and it was the mid 90's advent of those fuels that created the problems.

Webers are much more expensive, but cheaper long term, and require only a little extra work to pound the SU and ZS CDS carbs, but they don't fit well in an early Round body. Post 1966 wide body cars and Mustangs, pretty easy.

CFM rates area 265 cfm at 1.5 "Hg for 2" HD8 SU's (1-8/8" carb, what the "8"stands for).
HIF 47 or HIF 7's, 265 cfm (1-7/8" carb)
HIF44 or HIF 6's, 245 cfm (1-6/8" carb, what the "6" stands for)
HIF38 or HS4's, 165 cfm stock to 205 cfm gas flowed (1-4/8" carb, what the "4" stands for)
220 cfm for CDs 175'S (1-3/4" carb)
185 cfm for CDs 150'S (1-1/2" carb)
125 cfm for CDs 125'S (1-1/4" carb)

American Mikuni make some really nice SU replacements in the HS 42 size, I'd use them.

The carbs below are HIF6's or 7's off a Jaguar XJ-6 3.4 liter (Mark III, 1979 to 1986) or Austin Rover Montego 2.0 or Maestro 1600. They went metric and electronic in 1986, and the bimetallic strip used for float bowl control sometimes goes haywire in hot underhood environs, and the replacement parts need to be proper Dupont plastic, not the awfull old replacment parts.

Lots to consider for an install that has to deal with ethonal gas and oxygenated fuel in a hight heat, non cross flow environment.
 
Thanks X! I'll try to process all of this in the next few days. My goal is to get one of the weber side draft manifolds from lynx as well. I want to create a mounting plate that will work with both so that I can swap and play.
 
again mit der:
six " 'American Mikuni' ( make some really nice...")
one per cylinder
 
I've had years driving behind HS4's and HS6's, nice carbs, but as time moved on, even the last HIF44 was still good, just 1996 created a fire propne, leaking carb, and the parts backup isn't there anymore.



I've seen some mighty nice set ups made from junked SU carbs...like this six H6 set up made from old Austin Westminster A90 carbs, found in land fills...



and these special HD8 based carbs used on the Vanwell 2.5 liter race car, an OHC conversion of a cut down Rolls Royce Six engine.




Any old log can take two HS6's, but the float bowls can't clash...they often need to be "handed", and they leak. Often.


The Austin Montego 2 liter Turbo used an HIF 44, and it was awesome. All SU'S, ZS CDS's, Mikunis....they can hack a lot of boost for a carb that only likes 2.5 to 4.5 pounds of fuel pressure. 9 psi of boost is easy without any modifications.






But then so would three HSC 2300 Ford CFi Throttle Body injectors and a MSII




These days,


HSR 42, 45 or 48 American Mikuni carbs.

Buy three HSR 45's, job done.



As replacements for one HS2/HS4/HS6/HD6/HIF6/HIF7/ HD8 SU or Zenith Stromberg CDS 125/150/175 serving two cylinders or one serving Four cylinders.

HS2/ CDS125 = 1-1/4", or 31.8 mm
HS4 /CDS 150 = 1-1/2", or 38.1 mm
HS6/HD6/HIF6/CDS 175 = 1-3/4", or 44.5 mm
HIF7 = 1-7/8", or 47.6 mm
HD8 = 2", or 50.8 MM

The Mikuni HSR series (in my opinion) better than Weber DCOE/DCO build quality, and way more adjustablity and longeivity compared to the Skinner Union and ZS CD/CDS series carbs.

http://www.v-performance.com/articles/m ... ions_.html
Tech Articles
Mikuni Carb Installation and Tuning Instructions

2_28_09_VPD%20014_s.jpg




Mikuni Carb Kit Installation and Tuning Instructions - Updated 8/22/15

These instructions are primarily for the dual carb kits as used on Volvo 544, 1800, 122, and 140, MGB's, TR4's, etc. where they are used as a direct replacement for SU or ZS carbs. Most of the information is applicable to any dual installation and much of it is also relevant to single, triple and quad installations. For all applications, be sure to read the tuning instructions located after the installation instructions below.

The HSR Mikuni carbs were originally designed to replace SU carbs on Harley Davidson motorcycles but are now widely used to replace SU's on a wide range of cars. The Dual Mikuni Kit contains carbs modified to allow them to be used in tandem to replace dual SU's (or Zenith Strombergs which were themselves an SU replacement) in an automotive application. These modifications include replacement of the original throttle shafts and the installation of a smaller float needle and seat. In addition to the Dual Carb Kit, Single, Tri-carb and Quad carb kits can also be ordered. An installation on a 68 Volvo 1800 is shown below. Note how the linkage provided with the kit hooks up to the orginal SU linkage.
 
Airflow is irrelevent on independent runner (IR), port on port (POP) intakes, then venturi size governs performance because each carb sees the duty cylce of one cylinder, and are able to pulse tune and supply a huge amount of fuel with no wettined perimeter or puddling, and does so with very little vacuum.

IR set ups are far better coping with big cams and idle and often perform 25% better than a normal 4-bbl carb, although there are many exceptions if the intake manifold is really good. Some 4-bbl or twin carb manifolds work exceptionally well, and the reason is the flow distribution and efficency at wide open throttle.

Weber DCOE's and ID series carbs, correctly sized, make 10 to 15% more power than a correctly sized multiple SU or ZS CD carb system.


The problem with IR set ups is that each carb venturi has to be very big to ensure the jet functions correctly. Everthing must be in perfect conformance with the Weber IR sizing chart, and the jets have a 20 to 25:1 venturi to jet ratio.

In any IR set up, downsizing to a too small venturi creates a major loss in power right through the rev range, and a deap noticable loss in peak power rpm, with an inability to over spead past the power peak. Its only noticable by comparison. Such set ups still operate with typical docile idle, but progressively loose torque and power through the truncated rev range.

Any time you go back to one venturi serving two cylinders, the duty cylce is increased, the pressure drop increases, and the whole engine no longer responds to large carb venturis. Staged Offy Weber ICT/ICH's, Autolite/Holley/ YFA's are like this.

Simulatanoues Triple SU's and ZS CD's are midway between an IR set up and an Offy Tripower. They like a little more venturi area, and it won't hurt to go bigger. Going smaller doesn't give an improvment in off idle torque, its jetting and venturi size that govern most.


Something like a Triple progressive Weber ICH/ICT with 27 or 29 mm venturis works fine with very undersized carbs... its not independent runnner, not port of port.


Common SU carbs and how they rank at 1.5" Hg or 20" H20----->Industry Standard varies 1.5, 2 or 3" Hg is times 13.56 to get " H20, but they round to down nearest whole number.

1.5"Hg -----> 20"H20
1.83"1Hg ----->25"H20
2.0"Hg -----> 28"H20 (27.2 really)
3.0"Hg -----> 40"H20

Holley 4bbls, 1.5"Hg
Holley 1 and 2-bbl, 3.0"Hg
Holley Weber 2-bbls, 3.0"Hg
Some Autolites were reputed to be rated a 2"Hg, BUT I doubt this, its normally 1.5" for 4-bbls, and 3.0"Hg for 1 and 2bbls.
Propane carbs are rated at 2"Hg.

To convert, the square root of the difference.

Ultimately, engines work by having the least amount of fuel to give the most amount of power. IR/POP systems do this just like an EFI set up, some needing only 3 cc per second of fuel to make 100 hp, or 6 cc/sec to make 200 hp, or 12 cc/sec to make 400 hp. Having three or six carbs doesn't use three or six times as much fuel.


1.83"1Hg ----->25"H20


Common other carbs and how they rank at 0.75" Hg or 10" H20----->Industry Standard varies.

Multiply by 1.41 to get 25 "H20



Chapter 4 SOHC Pinto Carb Modification

Rated pressure drop stated as 25 " H20, but actually 1.83" Hg----->Industry Standard varies.

 
Now you're talking!

So what I think I'll do in the meantime is go ahead and get the log milled. Next step will be to get a piece of plexiglass cut to size to fit over the mill. Tape it on, and start drawing on the geometry. I can then cut it out and do some test fits. That ought to keep me going for the next 6 months.
 
You've fairly much got the roundhouse punch on multiple carb info.

The most important work done on six cylinder carb sizing and calibration is the Argentina Six cylinder engines, specfically the old OHC conversion to the Nash in line 232 six. When it got OHC, it got sent to South America, and the wild Southerners played with the 5000 rpm rev limit engine, and were able to resolve venturi sizes for engines in our rev ranges, 3500 to 5000 rpm.

Chrylser Australia too made some 260 degree cam, 265 sixes that reved only to 5000 rpm, and the carb venturi sizes were screwed down to serve a 248 hp engine. Its in this area that Weber DCOE 45's impress the most. Similar issue was the 1960'S DCOE 42 Maserati GT3500


(Not listed below, but I know that the 32 mm 42 DCOE carbs flowed more than the 33 mm venturi 40 DCOE; Vizard noted that DOCE 45's with 32's also flowed better than smaller carbs with 33 venturis. The Argentine and Italian and Australians used Weber Italy to help them really unlock those lower rpm in line sixes.

"Weber Carb Edjumakashun" from Sat Feb 20, 2016


viewtopic.php?f=34&t=74494
/viewtopic.php?f=5&t=31668

That ideal size graph for venturis on a IR/POP system again...

EWVSCexDV10F2.jpg

EWVSCexDV20F2.jpg


I got the lower rpm range line sorted back in 2003 after some slueth work from Alfa Romeo and one French carb tuning site where they used a 5000 rpm Weber IR/POP line.

I haven't plotted that line, but its four 5000 rpm points are at

400, 28
475, 31
525, 31
550, 33
600, 34.

At 475, 525 to 550 cc per cylinder, the carb venturi size is rounded to the nearset mm, and they program uses the emulsion tube to control best fuel trim. When plotting, 525 should be 32 mm.

I just pop that into Excel, and it gives you a linear regression to solve for any cylinder capacity between the ranges in the graph.

The ranges for a big 635, 688 or 725 cc cylinder 232, 250 or 265 aren't on the charts I've seen.

Chrylser Australia had the the 248 hp at 4800 rpm E37 265 (38 mm venturis),
or 280 hp at 5000 rpm E38 (40 mmventuris )
or 306 hp at 5600 rpm E49 (40 mm Venturis )

http://bringatrailer.com/2010/10/16/cyl ... mi-6-pack/

listed as having a 5000 rpm power peak, and being a 38 mm venturi at 725cc. The Gran Routier Renault Torino with 232 and reving to 4700 rpm at the power peak, 35 mm. So there is evidence to establish the 5000 rpm line pretty accurately.

EWVSCexDV30F4.jpg
EWVSCexDV40F4.jpg



The lower blue line is for our Fords with IR/POP system at the 6000 rpm power peak rev limit, but Alfa Romeo has the 5000 rpm rev rang worked out


I've used the following Weber call size jets from another website application. Each graph is a generic one for 1.6, 1.9, 2.1, 2.2 and 2.4 liter DOHC Alfa Romeo engines.

Twin DCOE 40 Weber with 28 mm chokes for a 1.6 liter DOHC Alfa Romeo engine= 144 cid Ford Falcon six reving to 5000rpm. 115 micron Weber =152 cc/min=115 microns is a 45.28 thou jet. 400 cc per cylinder at 5000 rpm = 28 mm ideal venturi size



Twin DCOE 40 Weber with 31 mm chokes for a 1.9 liter DOHC Alfa Romeo engine= 170 cid Ford Falcon six reving to 5000rpm. 125 mircron Weber = 201 cc/min=125 micron is a 49.21 thou jet.475 cc per cylinder at 5000 rpm = 31 mm ideal venturi size



Twin DCOE 40 Weber with 31 mm chokes for a 2.1 liter DOHC Alfa Romeo engine= 188 cid Ford Falcon six reving to 5000rpm. 125 mircron Weber = 201 cc/min=125 micron is a 49.21 thou jet .525 cc per cylinder at 5000 rpm = 31 mm ideal venturi size





Twin DCOE 40 Weber with 33 mm chokes for a 2.2 liter DOHC Alfa Romeo engine= 200 cid Ford Falcon six reving to 5000rpm. 135 micron Weber = 251 cc/min=135 microns is 53.15 thou jet. 550 cc per cylinder at 5000 rpm = 33 mm ideal venturi size
.


Twin DCOE 40 Weber with 34 mm chokes for a 2.4 liter DOHC Alfa Romeo engine= 221 cid Ford Falcon six reving to 5000rpm. 140 micron Weber = 275 cc/min=140 microns is 55.12 thou jet. 600 cc per cylinder at 5000 rpm = 34 mm ideal venturi size





Here are flow figures for Triple DCOE carbs with the best trumpets fitted to the ends. Its based on flow through two carb barrels.



40 DCOE , 24 mm, 202 cfm at 1.5" Hg = 286 cfm at 3.0" Hg
40 DCOE , 26 mm, 241 cfm at 1.5" Hg = 341 cfm at 3.0" Hg
40 DCOE , 28 mm (Fiat 2300S), 279 cfm at 1.5" Hg = 395 cfm at 3.0" Hg
40 DCOE , 30 mm, 316 cfm at 1.5" Hg = 447 cfm at 3.0" Hg
40 DCOE , 32 mm, 336 cfm at 1.5" Hg = 475 cfm at 3.0" Hg
40 DCOE , 34 mm, 346 cfm at 1.5" Hg = 489 cfm at 3.0" Hg
40 DCOE , 36 mm, 350 cfm at 1.5" Hg = 495 cfm at 3.0" Hg
45 DCOE , 32 mm, 324 cfm at 1.5" Hg = 458 cfm at 3.0" Hg
45 DCOE , 34 mm, 376 cfm at 1.5" Hg = 532 cfm at 3.0" Hg
45 DCOE , 35 mm, (Torino GR) 397 cfm at 1.5" Hg = 562 cfm at 3.0" Hg
45 DCOE , 36 mm, 418 cfm at 1.5" Hg = 591 cfm at 3.0" Hg
45 DCOE , 38 mm (E37 Pacer), 438 cfm at 1.5" Hg = 619 cfm at 3.0" Hg
45 DCOE , 40 mm (E49 Charger/Tornino 380 Motor w TC), 444 cfm at 1.5" Hg = 628 cfm at 3.0" Hg
 
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