The Cal-look Lounge

All you Weber tuning experts, can you make me understand something I have been wondering about for a long time?

Why do some IDA (2bbl and 3bbl) applications run air corrector jets that are SMALLER than the main jet size? And then other applications run air jets that are LARGER than main jet size?

according to "books", the Weber rule of thumb is venturi x 4 is main and add 30-50 to get air corrector. Of course books don't make cars run, people do. But if you look at various jetting applications for cars that run IDA's (2 and 3bbl) you'll find some that require air jets SMALLER than main....obviously to make high rpm mixture rich... but why are some applications jetted that way? Which way "works"? Porsche 906 motor....46IDA3C.....42mm vents, 175 main, 145 (approx) air....
Old 904 motor, 46IDA, 170 main, 130 air jet....
But all VW guys seem to run 42mm, 175 main, F7, 210 air....etc...   why?
Jets are jets, venturies are venturies, etc.... did specific gravity of fuel change or something or?

Could it have to do with the fact that we don't run air cleaners. You would think that at high rmps, the air cleaner would restrict airflow.

--louis

906 didn't either

i am not sure, but can it be that the aircorrector is used to balance the quantity (air AND fuel) that gets sucked into the carbs, in relation to the vacuum that is created into the shafts.
 and that the fuel jet is responsible for the quantity of fuel in that. the percentage of fuel and not the rate...

One thing to keep in mind is that probably only half the IDAs out there are tuned right.

--louis

Have you tried "square jetting" ?
 ???

yeah 155 x F2 X 155

check out this info from some Cobra guys..... see what i mean?

http://www.clubcobra.com/forums/archive/index.php/index.php?t-74594.html

Soo many factors to look at - large cam - small cam - duration - lobe center - comp. ratio - head flow....... and like you say Jim - why ? I have had very close engine sizes but different cams - and the a/c jets were still close - But on our race motor - we used 210 mains and 180 ac  - just how it worked out ;)

I wonder how 160 x  F2 x 130a/c would work

what amazes me is they are using very small vents to feed a 427! it's like if we used 40mm chokes on a 3,5 liter 4 cylinder engine!

I'm pretty sure the emulsion tube you are running contributes to sizing of AC and Main jetting. The Weber Tuning Guide (Black Book) has a good section on E tubes and characteristics...

you're right.
874cc per cylinder "by the calculator" should need 49mm vents to turn 7000 rpm

I think a 7-liter V8 must pull so MUCH air through the carb that maybe the setup needs such a rich top end mixture to keep A/FR where it needs to be....  reminds me of watching the fuel flow demonstration at NHRA museum.

But then again.....   what about the little 2000cc 906 motor?  ::)

I thought this post was rather interesting.


Is the Cobra IDA intake IR in design or is it plenum? This line really interested me.


I had this really long post about the different engines and why that would produce differing amounts of vacuum, but it basically all boiled down to different engines, different air flow characteristics, different power bands & different A/F needs. Short explanation, FE Engine = big motor, horrible head design (FE was a truck motor afterall.), power at lower rpms, tree trunk snapping torque, sewer pipes for ports, etc. I ended up thinking myself into a box and as my friend always says when I do that, KISS.

I think it all boils down to AirFlow@RPM and desired air/fuel to achieve your goal. I think I would be looking to engines that preform more like our engines for a guide to tunning carbs. (Motorcycles?)

I wouldn't get too hung up on what the book says. I doubt who ever wrote "the book" ever bolted 48s to a tea kettle er VW flat four. We could get into a theoretical discussion about carb mechanics and air flow characteristics but I am not sure if that is what you are looking for here. ANd of course, once the rubber meets the road, most theory goes right out the window.

--louis
 

if an engine is running carb throat per cylinder, it seems to me it would almost HAVE to be IR. I don't think Webers would run right on one big open hole under them. No sense in the expense of 4 IDAs dropped on a plenum Vicotr Jr thing. Just use two Holleys and try and make it run half as good as a IR'd Weber motor.

The Porsche engine charateristics.......

80mm x 66mm
10.3:1
45mm intake x 39mm exhaust valve
intake cam timing/lift: 388' duration x .481"
exhaust cam timing/lift: 360' duration x .414"
210hp @ 8000 rpm
46IDA 3C: 42mm venturi, 170 main, 145 air, F24 e tube, 70 idle

All the Cobra Weber manifolds I've seen have been IR.

what I'd like to find out is: WHY?

A carburetor works off of simple principles of differences in pressure. Sure, more air might get yanked through a Weber on one motor over another, due to displacement, rpm, flow characteristics whatever

But WHY are two Otto-cycle motors using such different, almost opppsite...jet stacks? I am wondering, do the "method" of running 170 main x 205 air in a F11 or F7 tube is "leaving something on the table"? What makes it "right" for one motor to run at one extreme end of spectrum and one motor to run at other extreme end? Just sheer air volume being ingested? Well, guys, again, look beyond the 427 Ford then and look at the 2.0L (120c.i.) 6 cylinder Porsche.....ONLY 332cc per cylinder.

Maybe the VW way of jetting is simply based on "IDF's are jetted like.... 140 main, 200 air....bla bla bla....so IDAs are the same..."

What makes us VW guys, who truth be told, tune by seat of pants in variable conditions, right on....and when we seem to be so different from "other" IDA guys? Do laws of physics make a left turn for VW guys?

Sorry, but I really want to get it. Somebody give me a dyno and a month to do this.

I'm not sure I agree. Theory has its place. And specific examples of how other set ups have been tuned, running similar, if not SAME carbs I don't think so much as theory. Reading that Cobra post, OBVIOUSLY some of those cats know what's going on with their Webers. They don't seem to be the type that say "well joe blow said run a XXX main and since I don't really know HOW it should run....I think it runs great."

Too much of that in the VW world that I have seen in last 17 years.

Thought I had... would bore vs stroke play into this?

When i had my old 1914 (w130  -  1,25 rockers  - 10.8:1CR  - 40mm dells - 1-5/8" header, 40-37,5 heads  etc. etc.   ), I used 37mm vents and on the dyno we came out with 160/160 jets (57 idle),  can´t remember what E-tubes we used.
We tried switching to longer stacks and the mixture leaned out at topend and the powerband moved further up rpms.

The height of the stacks definently has something to say.
I would think that the height of the stacks, lenght of the manifold and E-tubes are what makes all the difference... off course together with differences made by big cams, ccm etc. etc.

I think the VW has had a lot of stuff bolted to it that was never designed specifically for a VW in order to go fast. My guess with the F7 or F11 tubes, the carbs originally came with F7s right? Back when people first started bolting them on, there probably was not a whole lot else to use. So they went with what they had, made it work best they could, and it sort of became the standard. Not to many people stray from the norms. I bet if most peeps knew what you were running in your IDAs they would be surprised. I do agree that I think there is room for improvement. However, you may not be able to find that improvement without optimizing the whole package. I don't think the limitation is the flat four design. That is evident from the other thread. I think the limitation is that we take stuff, throw it at an engine and then try to make it all work together. Not much you can do with a cam, header length and intake length as they are sort of set. (long or short, 1 5/8 vs 1.34 etc, FK-8, FK-45, Web86c. Not to mention most were designed 30 years ago.) Even most "custom" head porters use a few basic designs with minor variations. So the carb becomes the crutch to try to make it all play nice.

As to the problem with theory, unlike the theoretical world, the real world is not perfect. I think it can lead you in the right direction, but it won't get you perfection.

The Porsche 904 may be similar in size but I still don't think you can make a comparison. Still too many variables. bore, stroke, valve timing and overlap, rod ratio (if you put any stock into that, I do), IR length/size, valve size, port size/length, exhaust setup, intended rpm range. If you built a VW engine with everything the same as the Porsche engine then you end up with a Porsche engine, minus 2 cylinders. And it would probably run with the Porsche jet stack.



I find this part interesting. The cam specs, the max rpm and the valve size. That is a pretty big intake & exhaust valve for an 80 bore. Wonder how that effects the flow through the heads?

The Ford 428 FE has a 105mm bore, 53mm intake & 42mm exhaust (Edelbrock heads) . That site was down so I couldn't find cam specs.

I am betting that their IR length is shorter than the one we typically use.

I don't know. I think I am well past the limits of my meager capabilities here.

--louis

I know it is!   ;)

Jim do you know which emulsion tubes were used in the 904?

I have various books that give jetting for 906, 904, 356 4 cam

that's interesting....longer stacks made it run leaner

I would think the taller stack would contain the standoff better and the engine would ingest it, keeping af/r in the correct realm.

I think in the 1970's, most IDAs came with F2 tubes. When I bought mine (2nd hand, had been stored for 15 years or so) they had 37mm chokes, 150 main, F2 tubes and 130 a/c. To be honest with you, I don't think they had ever been run, as they were surgically clean, no stains, all the nylox were clean, etc. Of course, I chucked the 37 chokes in a box and went straight to 42mm....dumb. I think I then tried all kinds of stupid jet stacks, not making them work right until I went to 40mm, 160 F2, 195 air. Anyway it 'felt' right....who knows if it was.

Yeah the Porsche ran very generous valve diameters, but were angled as they are in hemi-design chambers, not side by side like neighboring twins in our antique VW chamber heads. Eventually I think they went 49mm intake, so if that tells us anything how they made more power... the RSR cams got even hotter than these 906's too....imagine that.

Yep I think you are right, louisb, there are many variables in carb setup, and most certainly (when just comparing CYLINDER to CYLINDER..... since each venturi, main, air, emulsion... could care less what it's neighboring counterpart is doing when on IR manifold....unless you have way crazy standoff) the lowly VW and the mighty Porsche are clearly different. But-  again, carbs work on depression, so air goes into void, depression in vent tells fuel to flow, it does, gets aerated with air from a/c jet...etc. What makes the Porsche, Cobra, (and take a look @ Sarge's jetting from '70's) "wrong" for todays big cc motors? Or are they in fact wrong?
Seems like every other "hi po" Weber model on Ferrari, Alfa, etc.... little 30 or 32mm vents....130 main, F11 tubes, 210 airs...
But not the IDAs.

You know Jim, you had me up half of last night turning this problem over in my head lol. Unfortunately, I didn't have any great revelations to add. I do however, think that today's practice in jetting VW engines is a result of Cargo Cult Engineering. (See something work for someone else, don't know why it works, mimic it anyway and hope it works for you.) But I think that is common in a lot of hot rod car cultures. (The other being Voodoo Engineering. Its all black magic so send it to some Witch Dr. that works some Voodoo and they work.) Without a dyno and a bunch of spare brass I doubt we will know the answer anyway.

--louis

good point man....

for what it is worth.... I ordered a 4th 160 main and a set of 130 airs. I have a nice flat straight section of road, and a stopwatch. If I can find the time, I am going to check my thoughts.  ;)

good topic jim and louisb  who knows? all that air at 7000 rpm plus needs alot of fuel in mixture

F14

40mm vent, 160 main, F2 emulsion tube, 130 air, 65x120 idle/air, idle-mix screws out just past 3/4 turn

car runs clean to 6800

no timed runs back to back with large air yet for comparison

here is some jetting from 587/2 Carrera 4 cylinder 4-cam 1966cc motor, as in 356 or Abarth, running sports-style "stinger" exhaust

40mm vents
60 idle
165 main (175 for Le Mans)
F11 emulsion (F20 with standard two-outlet muffler)
240 air!!
3.00 neddle valve

I have 1 F20 tube around my garage somewhere....

here are F20, F4, F11...left to right
F20 and F4 share same 7mm diamter but F20 has 4 fewer holes (at bottom), top holes are same
on the right is the F11 "IDF" tube 8mm diameter and much fewer holes than F4 or F20
I didn't pull the F2's from my car for the post or picture.
who is good at deciphering diameter and hole locations?

Interesting reading so far. Wish I could scan some emulsion tube pages from my weber manual. Can anyone tell me if the idle jet holder meters fuel or air?

F4 and F20 are practically identical. The f4 provides a slightly richer mixture during slight acceleration or low rpms because of the 4 more holes( .100mm) above the angled holes (.250mm).

The f11 has many holes towards the top, which makes it ideal for mixture weakening at low rpms and slight accelerations.

thanks Lawrence. I get that smaller diameter tube = richer
larger = leaner

hole amount? Location? and the "step" comes into play too.

update:

spent some good quality time with car and box of jets, tubes etc.

started with: 40mm vent, 65 idle, 120 air, 3/4 turn out on mixture screw, 160 main, F2 tube, 130 air
ran well except for loading up @ idle and faint trace of richness (surging) at 2500-3500. Turning mixtures in after load up cleaned and raised idle, but after driving it would get rough and pop in muffler.

next step was 60 idle, but initially to get smooth idle, took 1 full turn out.
Car had lean hiccup at top of idle/progression range, still with 160 main, F2 , 130air

next step was increase main to 170, everyhting else same. Still had hiccup lean spot, and midrange got soft. Top end same

next step was to ditch F2 tubes, go back to 160 main, but this time with F4 tubes.  So the combination now was 60 idle, 120 air,
1 turn out on mixtures, 160 main, F4, 130 air
No more lean hiccup in at top end of idle/progression, no rich surge at steady rate cruise, no hesitation in accleration, still very strong top end. I drove car for about an hour, all kinds of rpm and conditions, and brought car back home, and tried mixtures once more, and found, now just a bit past 3/4 out smoothed idle even further and after more driving, stayed more consistent.

I wish I owned one of the high dollar AFR meters to test my impressions or had access to my friend's dyno up north. I can say though, after the time spent, the car has a new sound and response to it.

Cool stuff, Jim. Did you happen to see what the plugs look like through out the process?  I need to play with my jetting a bit. My car has the same symptoms as yours. My first step will be smaller air corrector(currently 180) thinking about a 165-170. Ill see what happens then go from there.

no I have not pulled plugs yet, as I was all over loads, rpms, idling.... and letting it idle and then pulling plugs would have thrown the plug reading out the window.
Maybe this weekend I will go make some country road passes and clean cut and look @ plugs

Finally got time this afternoon to tinker with the IDAs. The motor would stumble and the carbs would pop when the throttle was barely open, so basically steady cruise around town and sometimes on the highway. Thought it was the airs but that does not jive with the symptoms.

I remembered that my 120 idle jet holders were enlarged when I had the motor dynoed. I was running a 60 idle jet at dyno time and currently have a 50, so I assume the guy drilled the holders out to lean the mixture. Not the best move. I borrowed unmodified idle holders that my friend has and put them into my carbs. The motor is much more civil now. Im stoked!!

Reading and re-reading the post with the old Dean Lowry and Motion Minicar stuff brought me back to this old post.
If you scan the material posted from the 1977 book, you'll see that the jetting was much like we discussed here (i.e. large fuel jets and small (er) air correctors.

Did we ever determine why the trend from this jetting evolved away from the small air corrector? I bet somebody reading this knows... 

I'm kind of obsessed about getting this answered. Put me out of my misery...

Jim,
I got my "new in the box" Italian IDA's back in 1982 and they came with 37's and F7's.  Like you, I switched out the 37's for some 42's before ever bolting them on.   ::)   Somewhere along the line I bought a set of F2's, but wound up always running F7's.

Not trying to go off topic, but what's the general "rule of thumb" thinking regarding emulsion tubes?  As mentioned, I've run F7's forever, and was recently told on another forum to toss them in the garbage can.  In their place, I needed to get some F11's.

What's the number system F2 to F11 (and higher) mean?  Lean to rich?
 ???

The emulsion tube number doesn't mean anything.  The numbers were applied in order of when that particular tube was designed.

I think it would be a hot idea is to make a chart or spread sheet, list the engine size(s), compression, cam, valve size, headers, heads, etc, and then the jetting combination that is being used.

Get to work on it , Dean.

Who cares how you get there, the goal is to get the A/f or lambda line as straight and as flat as possible throughout the rev range. To me jetting charts are only a rough starting ponit.

Huh? ???

The numbers were assigned at random. Looks at the scans, to see what Bruce means;

(http://i146.photobucket.com/albums/r260/cam_shaft/WeberEmulsionTubes2.jpg)
(http://i146.photobucket.com/albums/r260/cam_shaft/WeberEmulsionTubes1.jpg)

Edited to make the pictures a bit easier to read.

Well, I don't think an engine wants a "flat" a/f curve through the rev range. An engine runs at a different a/f ratio @ idle than it does @ light cruise or under full throttle full power


don't you guys wonder what happened (it almost seems like some guy discovered Weber made air corrector jets larger than 155).... how can a jetting pack at two extreme ends of the spectrum (talking air jets here) be "ideal"? Or maybe we can deduce that since some guys found ultimate jetting to be 150m x 130a and other guys found that ideal was 165m x 210a (in same application, same vent diam), that maybe there really are TWO ways to feed a motor the ultimate in mixture? I doubt it though
Where's Roger Crawford? I'm sure he could answer this for all of us.  8)

OK, then I'm missing something then...  What's the difference between a F2 vs. F7 vs. F11, etc...  If the numbers don't mean anything, then why run one over the other?

David, the emulsion tubes differ in diameter and orafice orientation. I posted some info a little further up the page and Jim posted a picture, which shows the differences. I would post more data, but don't have my weber manual here at work ;D

I think guys run what they know worked for other guys, hence the F7 tube. I have tried them in my car with various engines and they did not respond as well as F2's, but I also only changed tubes. I didn't change jetting, nor somethign else that works hand-in-hand with emulsion tubes, the float levels.
About 8-9 years ago a friend and I were dyno-testing a 2276 IDA motor @ Heads Up in Fullerton. It was a street motor for a manx-style buggy, and we initially ran it with F7's, and made 207hp. We were told by Roger to change to F11's, not to touch timing or jets, and try again. We went to 213hp (best pull of the day). Knowing this, I tried F11's in my car last year, just for a spin around town, and it had a hiccup that I was too lazy to chase, so I just put F2's back in. But very interesting that the F11's woke the 2276 buggy motor up. I wonder if VW guys had access to more than the F7, F2, F11.... what developments would be found?

Good topic Jim....

I have found that for most street/strip motors with IDA's in the 40-45mm vent range alway seem to make more HP with smaller than recommended air correctors.
Most applications use the F7 tube, but I have a set of F11's in my 2276 race motor (with 45vents) that I get to play with alot.

I have a couple sets of 190 and 200 air correctors in my tuning kit.
I have never ended up on a combination that worked best with them for any motor/application that I have had the honor of tuning on.
(I even took out my rod bearings once trying to run a 200 air combination at the track once.)
I always seem to land in the 160-175 range for most motors (for both air and Main jets). (square jetting, or there abouts)..

I have a buddy who runs F7's with 180 mains and 210 airs.. and it rips...
Go figure...

Hi Tom (get Mike's oil pump?)
I have a close friend up in San Francisco/Oakland area (Pinole actually) that does race/hot-street 911 stuff, and he also swears by the air corrector being smaller than main on the 46IDA3C stuff he does for the hot Porsche stuff. He just dynoed a 3.4L motor with 50mm PMO carbs (Weber IDA3C copies) with 45mm vents and found best hp and a/f ratio running 185 main x 130 airs! Not sure which tube. We've gone around and around discussing "why" this works and we can't seem to understand "why"
He keeps offering for me to drag my Bug up to him and we'll spin it up on the dyno and see just what my thinking does or doesn't do.

My ex boss told me you want to lean out the top end fuel curve, and that is why you'll see some guys running 230+ a/c jets.

Still losing sleep...

To further explain, I was talking about jetting an engine on a Engine Dyno, such as a superflow 902 or a DTS like Rogers, where you are able to accelerate the engine under full load , from anywhere from 50rpm per second to 1000 rpm per second. We normally test at 200rpm per sec to simulate a 4th gear pull.
Why would you not want a flat lambda line? Isnt that why fuel injection is superior? I know you will never get it completly flat, due to the limitations of the adjustments you can make, mains, airs, emulsions etc, But it still remains the aim of the game. I will scan a lambda line off a formula ford engine i dyno'ed last week to show you what i mean. We even turn down emulsion tubes to adjust the fueling at a particular rpm.

Dyno testing as such allows you to check actual throttle response under load, opposed to just a flat "pull" at peak hp rpm right?
Throttle response was something i was thinking about last night after re-reading this post.

Is jetting for max hp in a drag race situation different than setting up IDA's (jetting) for throttle response?

I'd guess the answer is "yes." What do you see on the dyno, as far as improvements in throttle response, by changing air correctors?

I see three "ways" to get an engine to see a "too rich" curve, aside from too much fuel psi or incorrect float levels:
1. go too large on idle and main fuel jets (obvious)
2. go too small on Venturi Diam (increasing signal too far to jet circuits)
3. go too small on air corrector jet, in turn, swaying the ratio of air/gas ratio in aux vents to a overly rich condition.

Most people know ideal a/f ratio for hp is 12.5-12.8, but does an air cooled motor live (at full power/load) at this a/f-r? Being the air cooled motor relies so much on it's "rich" fuel curve for cooling, I think we (air cooled guys) need to think in different terms than the GT40 or Cobra or DCOE (Alfa, Lotus, MG's, etc) guys.

Overall, aside from worn linkage eyelets on my Berg linkage, my car runs fairly well as a 95% daily driver, 272 @.050" cam, 9.7:1, large oval port heads, 42mm vents 170m x 175a IDAs, but I wonder where something is being left on the table.  ::)

Having tried to apply all the stuff I learned in my time racing V8s, I can say for certain that the VW defies common race motor logic in almost every way. Most drag race V8s at the sportsman level use ROLLER cams shorter in duration to your street motor Jim, and smaller primary tube headers than most VWs use.

Do you thing the air corrector might be related to the intake tract pulse?


Anyway, I've found that it's best to just not to argue with the motor about what it wants!

I'm sure the intake pulses/reverson affects which emulsion tube and air corrector is optimum.

Something else I thought about this afternoon, though I really wonder how valid this thought is (as far as the change in jeeting theory in last 30yr), manifolds for IDA's, generally, have gotten longer than they were in the past, haven't they? Most of the 70's IDA motors we see pics of have the short style manifolds with the carbs reversed from the Skat Trak tall style we all know today.
Plus...
Look at some of those cam specs shown in that old 1970's book that was posted, some of those cams are advertised with 342 degrees duration... much wilder than the K8, FK87, stuff that is run today (and usually on much bigger displacement motors today than yesteryear).
I'd love to know what was done to get the over 200hp from Bad Company's 1800cc motor (carburetor wise).

Hey Jim. Yes I got Mike's oil pump. Thanks...

His 2110cc motor is gonna be super nice.
The rotating assembly is at the balance shop currently. Case work is done, just wating for the rotating assebly to come back so I can do a final clearance check.
K-Roc does real nice work...
Thing should ripp...

It never gets old building hot VW motors.. I love it...

My best run to date (108.9 MPH) was with a 70/110-170/F7-180 stack. A tad fat but runs smooth and cool. The LM1 w. data shows all the info pretty clearly, addictive really. IIRC Alan Uyeno started running 170/170 years ago with excellent results.

When we were selling new IDA's at Auto Haus in the 70's, they came with 37mm vents and 70/120 Idle, 130/F7/120.  Most of us new nothing of jetting back then and the engines these carbs wound up on were for the most part 1600-1700cc, Engle 110, 1 3/8" exhaust combos.  Seems like we found that 135 main 130 air worked well but the idle was always real fat and tended to load up easily in traffic.  Eventually, someone discovered 65 Idle fuel jets and that helped a bunch.  My 1835 with 125 cam and 1 1/2" exhaust ran a 145/F7/140 stack with 37mm vents as I recall and ran well.  The 2074 in my first rail ran 37mm vents with a 145/F7/170 stack and made 155 hp on Vittone's dyno at 5500 rpm. 

My 2074cc in my old rail, with 10:1, an 125 Engle, Chase Morse 1-5/8, ran 37mm venturis, 145/165 with F7s. Ran 65 idles as well. Made exactly the same power as your's did on F&A dyno (air cleaners and stinger). Ran beautifully, except along the water/beach at Pismo where it used to pop at low rpm, but as soon as I got back in the dunes, it was fine. It would track along in second gear down to a high idle, and then up to about 5500-6000 clean. It was a done deal at 6200.

37mm motors are a lot of fun as drivers. In some ways, they seem crisper and faster than a 42mm motor. I'm sure in an all out drag race, the 42's would win hands down.

I remember being at Roger's shop in the late 1990's and there was a young kid working there that had a clean sedan with alloys, 2276, K8, Roger's heads and IDAs. Roger went somewhere and took the kid's car, and I was impressed with how crisp and snappy the motor sounded as Roger left the parking lot. When he came back he told me the secret was the 40mm vents. He said the kid wanted to go home and put 42mm's in it,  but Roger told him it would make a big hole in the power.

I've spent (wasted?) so many hours going back and forth with vents on the motors I've had in my cars, and I have to say, the 42's run "ok" but overall, I'd have to say the car always ran sweetest with 40mm's and locked up advance.

I ran my last 2165 (FK45) with 37mm's most of the time, and it was really sweet to cruise on freeway with, it just sort of floated along @ 75mph. But it was done at about 5800-6000 if I stomped it.
The 40mm would run thru 6800 in 2nd gear.

Rayburn's car seems to make good use of his 42mm venturies, as his car seems to pull like there's no tomorrow, idle on up to the orbit. Funny, by calculator... that motor could use a 46mm!

Santa, I want a dyno for Christmas.  8)

Thinking back on it, when I built the 2332 for the second rail, I drug that out to Vittone's too.  I was expecting to change jets with the larger engine size and cam (125 to FK89) plus 12.5:1 compression but all remained the same and I think it made 175-180 hp at 6000 rpm.  That motor had 912 rods and would really put you back in the seat down low.  The 37mm vents as well as a heavy flywheel made for very docile low speed cruising in the dunes as well as good "on the hill" starts.



My only experiences with larger venturies has been with my current rig.  This is the only set of IDA's I've ever owned with a third progression hole.  I was never able to make a 37mm / f7-f2 combo work well with these carbs.  Finally, I tried some 40mm vents which solved most of the problem... the rest was cured by fattening the idle air holder to a 115.  Art Thraen recommended the f11 tubes and the 160/210 main stack.  It's all good!  Wait till Carlos sees you want Dyno for Christmas :o.... your in big trouble!! ::) ;D

Dyno Don C. had to razz me about this topic.... maybe we can debate for another year Don?  ;D

If you take a peek in KS' new Cal Look book, check out jetting on Mahaffey's 198hp street motor (1970!)....120 airs?!  :o

Obviously "worked" in his Webers.

yeah, motor sure do get "snappy" when you lock out the advance curve.
Seems to clean up the transition issues.... right now...LOL.
I really like to run hot street motors with locked out dist. They idle great....

No kidding Tom, one of the best things I've done was lock my MSD out. Car became tons crisper off idle, and go rid of a saggy spot off idle. I wired my 6A box so it is fired seperate from starter, to minimize kick back. Yes, and the ilde got that hard-edged, urgent beat to it too.... when you hear that, you know the motor is going to rip. Then that cracking bark when you open the throttles, you know there's more to come.

So have you found your answer Jim?