more carb options

[comet66]

I've been reading about multi carb induction using motorcycle carbs ie. Ak Miller's 170. I also have read alot about the tri power setups and their ability to keep in tune so I started to look at the european sixes.
So to my point has anyone ever used the Zenith 3 barrel ? It might be the answer and it would have the WOW factor. They came on Porsche and some other cars.

It is very similiar to the old Ford Boss 4 barrel and the new Dominator. I do have a picture but do not know how to post it.
This would be on a 200 with a 250 head, headers and dura spark.
Thanks for any input.
Jim

1966 Comet 202

 

[ludwig]

That's a real interesting idea. I checked it out. That's also a cool looking carb. You could do a three-hole thing on the hood for a one-of-a-kind looker. What do they flow? I'll bet you could do a mounting block thing with a billet of aluminum. Hmm.

http://www.motormeister.com/html/carb.html

 

[lyonsy]

i whouldent mind trying the slide carby's off bikes on a 250
id go the webber carby off the porsch but and use both porsch did on a 3L

 

[xctasy]

PMO does a US made repro of the Zenith.

Like the Weber IDC3 that was used in the 911T's and early Ferrari 365BB's. An awesome carb with an awesome price.

http://www.pmocarb.com/

The dual triples are simply better than any other carb you car to name, if sized to suit.

Using the Weber jet sizing chart, the Venturi size in mms to the volume of one cylinder

(144 = 394 cc
170 = 463.5 cc
187 = 510.6cc
188 = 512.5cc
200 = 544.9 cc
221 = 603.1 cc
250 = 681.5 cc


240 = 656.4cc
300 = 819.6cc)

Pick you rev range 6 grand to 10 grand, and whamo, you've got the correct carb size. For most of us, 6 grand is the upper end of what we would ever use on an I6, so follow the blue line, and the cc per cylinder, and there is your venturi size for any independent runner carb ever made.

You have to guess the likely curve for power at 3500 to 5500 rpm, if your 'dumb' enough to use a stock cam. I am!

Get it right, and it'll work in a way that exceeds any fuel injection system. Mathematically, it gets about 25% more than an EFI system , and about 60% more power than a stock log head. All the bends are gone, and each carb feeds three cylinders more of less directly, as its spacing is about 3.7 inches between each venturi.

Purely Magic Optimisation!

 

[lyonsy]

whould they work better then a throttle bodie setup like the webber with injection weather throttle bodie injetion or multipoint?
so on a 250 reving to 6000 you want around a 40mm webber

 

[Anlushac11]

8)

Im leaning more and more towards using some sort of TBI over a carb.

I have a Offy 3 x 1 for my log head I still havent used and Im thinking more and more of 3 TBI units.

 

[mutt]

0Check out the S&S Super B fixed jet side draft. Its obsolete now, you can snag them at Harly swap meets for 50-75 bucks, if you are patient.
Three of them would be quite nice on a 300, with all jets, etc readily available, as they are identicle (float, too) to the carbs that superceeded it....long buggers, which is why they went out of favor on harleys......

 

[comet66]

Thanks for the posts with the pictures.

I found and bought a set on Ebay for under $300.00 with the manifolds. I haven't recieved them yet, but with some of the comments I'm wondering about mounting both on the log. A six shooter.
I have a 200 in the car now, but have a 250 waiting for a rebuild. Maybe one on the 200 both on the 250.

This forum is great, I got more info about the carbs and specs in this post than a couple of day of surfin the web.
How do I share pics?

Thank you all again.

 

[XPC66]

What are the engine CCs and guesstimated peak power revs? If you can give me the intake valve size and intake port size even better. Cam specs?

 

[xctasy]

XPC66 might have a much better model than my corporate raids

whould they work better then a throttle bodie setup like the webber with injection weather throttle bodie injetion or multipoint?
so on a 250 reving to 6000 you want around a 40mm webber

The peak power rpm is the key. Peak power rpm is often 5 to 25% less than the maxiumim likely revs. Bigger the cam, the less over rev potential.

A 265 E49 Hemi runs a 40 mm venturi with power at 5400 rpm or so.



There is an old Jetting.Exe program I've got which is 1997 Dave Andrews from the Datsun 24 Ounce forum, its only written around 4 cylinder cars up to 2.4 liters, and nothing below 5000 rpm.

There are issues with intake runner length (what the Chamberlin brothers called 'distance to air'), the volume, and the ratio of contraction. Phil Irving gives examples.


TBI set-ups don't work as well as port injection or the very best independent runner carbs, but you can make anything work brilliantly if you build it an tune it yourself.

In Datsuns, the L16 and L24 have similar jetting in Weber Form. This selection is similar to a 144 Ford

In Datsuns, the L18 and L26 have similar jetting in Weber Form. This selection is similar to a 170 Ford

This selection is similar to a 187 or 188 Ford. A four cylinder 2.1 engine is the same as the Ford 3.1

This selection is similar to a 200 Ford. A four cylinder 2.2 engine is the same as the Ford 3.3

This selection is similar to a 221 Ford. A four cylinder 2.4 engine is the same as the Ford 3.6. There is no ability to select a 2.7 four in this program, or less than 5000 rpm, so a stock 250 with just carbs added can't be assessed.

 

[simon]

about three years ago, I was toying around with the idea of dual inline ZENITH 40 TIN porsche carbs. Then the prices for salvagable cores exploded in Germany, and now with USPS not offering international ground shipping anymore, even eBay.com isn't an option anymore.

So the Kraut is out of the game; but for US residents, it might still be a very interesting option.

 

[XPC66]

xecute the go with the L20 running something like a works cam (e.g. 76°) is a set of DCOE48s. This is a pic of the unlapped bigger valved peanut head, I unshrouded and ported for one of my current projects, which runs the aforementioned carbs:

Mind you this setup runs well into the 8000 rpm range and makes a lot of power because of it.

 

[xctasy]

This is all Law of the Machine stuff from physics. You know, when you get a load of data, and then run a linear regerssion, and find a line of best fit. Thats what the equations are on the graphs... natural log functions from real world data, an unbeatable combination of emprical data verses scientific fact!


Oh man. Okay, I've gotta admit it, I used to read Fast Fours and Rotories, and each time there was a wicked little cammed and carbed Ricer, I took stock of the venturi sizes. What got me in a 1990 copy was a wicked blue Datsun 1600 with an all out L20 four, and DHLA 48's and, gasp!, 40 mm chokes/venturis. I did a real quick cubic inch to venturi area equation, and got 0.063 sq inches per cube. It reved up to 8000 rpm. I then did a 265 Hemi E49, with DCOE 45 and 40mm chokes, and got 0.044.

I then looked at all the 3.2 to 4.5 liter engines from DB5 Aston Martins, Triple Weber B -head E-types to Maserati GT 3200's an even the Talbot Largo, and saw that they got similar power as the 265 Hemi at revs proportional to the veturi size. An LP400 Countach had 8000 rpm power band, but the Charger E49 had 5400 rpm, the difference was how much carb venturi area was carried for each cub of engine.

Hondas I then got all the carb configurations from Dell Orto and Webers in SOHC Cortinas from David Vizards books, and then looked at Dave Emmanual's Weber carb manual. They listed aftermarket instillations for triple Weber 240Z's, US Triumph 250 (GT6/TR4), Big Healy's and all of a sudden, I got the curves as listed above.

I realised that in an idependent runner port on port carb scenario, the peak power rpm apes the venturi size to the nth degree.

I then found that way back in the day, the Eurpoeans (Weber, Dell Orto) and the British (I think Amal was British) and the Americans (Lectron etc) all used the same tuning method. Best co-oberation was Bob Chamberlin of the Chamberlin Engineering out fit...he and Phil Irving used the curves to lock down ideal power for a small engine that Bob prototyped in the early 60's. They used the Conventry Climax Amal carb curve, which is similar.

It's all on the net in French, with the same dynamic formulae.see http://pboursin.club.fr/bonus/weber/weber.htm

I thought this was all hidden until recently!

The rationale is that when gas flowed on a flow bench, there is a point when running larger venturi is offest loosing the venturi signal. Apparetly, a 48 DCOE and DHLA or DHRA, or IDA flows better with 40 mm chokes than does a 45 mm carb with 40 mm chokes.




A more English freindly site, missing a lot of the info, but that articulates the details of Dave Edwards script file is

www.fordcaprilaser.co.uk/weber_dcoe_carbs.htm

 

[XPC66]

All that effort and I could have just given you a simple formula.

 

[xctasy]

Well, if I had been given it, I wouldn't have understood why! You can't premedicate for intellegience or for hunger or thrist. The horse has gotta want to drink, you can't give 'em a drink untill he's thirsty.

Here a test for ya.

Make a function of a function which satisfies the equation from 10 000 rpm to 4 000 rpm.

Input x, the volume of one cylinder in cm3, and m, the maganitude of rpm (any number from 4000 to 10 000 rpm) and solve for y, the ideal venturi size in mm.


The seamless equation has to have a linear input, and satisfy the flowing Ln equations which have been determined from all the data below.

They are

10 000 rpm, venturi size is equal to 17.858 Ln(x) - 58.894
8 000 rpm, venturi size is equal to 17.117 Ln(x) - 59.572
6 000 rpm, venturi size is equal to 13.884 Ln(x) - 48.934
5 000 rpm, venturi size is equal to 12.500 Ln(x) - 41.822
4 000 rpm, venturi size is equal to 11.507 Ln(x) - 44.311

That is the one formulae I've been waiting for all my life!

 

[XPC66]

You factored in VE?

 

[xctasy]

No, Volumetic efficency drops out of the equation. The cam builders set the maximum power rpm on an assumed VE. Go to Crow cams, and see how the power rpm and maximum engine speed change as you go up engine VE and cam stage.

Hence, the whole engine is assumed to have the power at the rpm given.

Eg, an XF EFI Falcon has a cam of about 264 degrees, and 162 hp at 4000 rpm, with an rpm maximum of 4500 rpm.

If it was saddled with a 2V carbed or EFI or independent runner set-up, the peak power band would still be 4000 rpm. pOWER WOULD BE ABOUT 150 with a carb, 162 hp with EFI, and about 185 hp with triple DCOE 45 or 40 Webers and 34 mm venturis or chokes. So VE may improve 15% with triple Webers over an LE-jetronic style EFI, but the power peak RPM stays the same. The cam sets the heartbeet. Looking at Hot Rods old 350 engine with any type of carb system proves that.

Anytime VE improves, and you do nothing else, the engine gains power. Its a David Vizard rule, and rpm is not a factor unless you have improved VE by the cam.


One of the reasons I like IR systems is that you get VE for free, with no cam or head mods, just a triple carb intake with the right sized chokes.


Put another way, the Indicated Brake Effective Mean pressure improves at any given speed if the VE improves. I can prove that by taking any given engine and do this

Take maximum power peak, and multiply it by any cubic capacity, and divide it by maximum power rating.

The result is an Aspiration Ratio. Any time VE improves, the engine makes more power per cube, without automatically needing more revs.


Eg (249.5 cubes times 4000 rpm)/162=6160, a pretty lame indicator of a very low stressed engine.

Stock EFI cams on XF engines with no other changes show 150 hp or so with ease,
so Aspriation Ratio is (249.5 * 4000)/150 =6653

Triple Webers, (249.5*4000)/185 = 5395.

By inspection or proportion, if a stock 250 with 2-bbl and EFI cam has a VE of 75%, then with EFI, its 81%, and with triples and no changes, its likely to be 93.5%. No change in peak power revs because the carb is pulse tunning the intake charge hard into the cylinder. So this is where I get the 25% gain minimum for an IR set-up on a 2-bbl set-up, mainly becasue all the bends, the time of concetration from the centre branch of the engine to the out ends is no equal. Compared to EFI, you get shortened intake runners, and more power due to the fourth order ram tuning, were gas speed is no longer super critical, but is able to operate in alternating current wave in a partial fuel standoff situation, where the gasses are pulse tuned like on a big tunnel rammed Prostreeter. If you've seen videos of IR cars (like Mazda rotaries or Mini 1275's with IDA's, or Harley motorbikes with Mikuni 42's), at wide open throttle, the fuel stands above the venturi in a haze of hydrocarbons. Its a hall mark of the right tuning at or near wide open throttle. This is why velocity tubes and stubstacks, or adding metal plates 3/8" from the carb mouth help maximum power by containing the fuel standoff in carbs.

Anyway, the right IR carb venturi creates more power than injection at the same revs because of pluse tuning, and this was observed by Ford in the developement of the 250 Falcon six in both USA and Australia in the late 60's by engineers. We see it today in Toyota TRD race engines. Only reason they run EFI is for tuning and advancement, not because EFI makes more power.

 

[XPC66]

yeah but, you have a chart that just has rpm, nothing to indicate peak power, peak VE, peak anything.

It's no secret that peak torque (peak BMEP) occurs a few hundred rpm below peak VE. This has nothing to do with a Vizard discovery, because it is a give, although he may have been in the right place at the right time to publish the fact to a new audience. The problem of selecting a carb is based on arbitrary peak and intermediate power levels. However, every engine exibits a different characteristic. So 80000 rpm on one brand 2 litre engine will have different fueling requirements for another... that's why tuning is required.

I agree that the cam is like the policeman directing traffic. I'm also very aware that guys with strokers think their increased torque is because of the extra leverage, instead of realising it's the change in BMEP at lower rpm and better overall power production.

I'll have to disagree on the carb versus efi. EFI is far superior because it can adjust for multiple input process variables including instantaneous load, CO, etc, whereas a carb is an analogue open loop, best fit solution as is it 's compatriot dizzy. Carbs do sound great when overfueling at idle however. From my experience EFI gives a significant mean increase under the curve.

I have found, with sidedraughts, selecting both the barrell/horn sizes and the choke sizes is really a ranging issue, not soley a setpoint determination. You may find those ready reckoners have accomodated that ranging and thus the frustration at finding a best fit equation.

 

[xctasy]

On all points raised, I hear what you say. I certainly aggree with you over area under the curve, what you say is indisputable.

The issue is that a cam defines peak power rpm. An ideal venturi size follows that. Two inputs of swept volume and rpm define the ideal venturi size to the mm, without any realtion ship to VE whatsoever.

Just go through all the IR Weber set ups in Phillipe Boursin website, and you'll see that everything is within +/- 5% on my quoted formulae, and the VE's vary vastly. There is an absolute, simplistic, and unfaltering realtionship.

As for fueling requirements, there is a total abilty to seamlesly vary fuel delivery 25% on any given IR carb. If , say, a Torino 230 OHC with 176 hp at 4500 rpm has a 33 mm DCOE 40, the valid jet size can be varied from 132 to 165 with no changes to venturi, and no detrment to power.

Each jet has a fuel metering accruarcy to +/- 2%. An EFI injector cannot even deliver +/- 10%, and uses controlled fuging to vary the fuel table requirements by running an algorithim form the O2 sensor output. It is constantly trimming. Carbs build in the constant trimming based on dyno tuning. Effective distance to air for pulse tuning can be varied by 60% just by velocity stacks.

No, injection is just a great way of getting away form the simple adiabatic facts of engine set-up, and you end up fighting battles on 400 front's rather then 4 or 40 with carbs. Go to any drag race, and see who wins...those who understand where there power peak is, and those who dredge up more questions without isolating the basics.


My back ground is calibration and electronics serve the purpose of responding to a miminum of input. If your able to block diagnose, and then draw down from the whole to the part, well an good, but virtually no one person does it, it takes teams of people. The Weber carb chart is a fight on only 3 or four front's and is pretty much VE independent.

I see not a schread of evidence to the contrary.

 

[XPC66]

Well I'll agree to disagree on the EFI. I have consistently achieved far better results with injection over carburation. The only reason the L20 has webers is for the rules, otherwise it would have an ECU.