Weber 46 + 3L + RSR style cams
 

Hi

Any thoughts on how the Weber 46 carbs should be jetted / set up for a 3L engine with RSR style cams?

We have run in to an issue where it runs rich below 4,000 rpm but nicely above.

Short video from first day on the dyno: https://m.youtube.com/watch?v=tT18K1XqvkY

Johan

My only experience is with PMO 46’s, and I think we’re running into similar issues. Perhaps my experience can help you.

What’s rich under 4000? 12.1-12.4? I think there are many of us suffering from a rich condition at light throttle cruise at 3000 rpms for Webers and PMO 46’s.

I’m not sure our cams make a difference, I think that ultimately you have to choose where you want fuel efficiency, top end power or cruising economy.

What happens when you go up a size air corrector? For me I get slightly better cruise numbers but start going lean and running out of power above 6200.

What happens when you go down a size main jet? For me, noticeable loss of power on top end, no change to rich cruise.

A couple of things I’ve done recently have been experimenting with timing using the Bluetooth programmable 123 distributor, including adding advance during light throttle low rpms, using a vacuum signal. And increased airflow using a larger, less restrictive air cleaner and filter. And adding an MSD for better spark. And went to a hotter plug. I believe this has netted about .3 - .6 points difference leaner during light cruise. I’m seeing light cruise AFR’s at 12.4-12.6 now.

And I should add that top end and torque has also increased with the MSD. The motor spins powerful all the way through 3000-7200.

Add me to this list. I'm running PMO 46 on a 3.0 liter ( 3.2 SS, really) with 993SS cams and my idle is so rich it's thinking of buying twitter. My rings haven't seated, I have under 10 gallons of gas through the setup, and the smoke is unreal. I have a twin-plug setup, and I'm using old HPV-1's with crankfire sensors. One mechanic says the spark is being drowned in two cylinders . Crazy stuff.
Ed Mayo is set to have this dropped on his front porch on December 19. We'll see what happens. He was the one that got it running in 2018 for 6 months, he ought to be able to get it running well this time... I hope I hope....

This 123 dist... do they make a twin-plug version?

Yes I believe 123 makes a twinplug dizzy, but I have no clue if it’s any good. I have no experience with their products

Your rsr cam is a pure race cam meant for rpm’s over 5000. If it’s doing nicely up there, then you’re done. If you want it to play nicely with other’s and have street manners, then I think that you have the wrong cam.

I’d still think you’d be able to get the right AFR across the board, even if the cam is happier above 5,000. For ex with ITB it wouldn’t be an issue

If you had a PMO or Weber expert with you , you could get close . It does not seem to be the case ,
the comparison to the ITB is not even close to being a fair one . Find yourself an expert and I am sure you will figure this out . The cam you are running is a full race cam ! not meant to be driven at less than 3,800 rpm EVER , pair that with carbs and there you have it .
The car sounds like it is on song and running well above 4,500 rpm to red line, 7,700-8k?
The data you have provided has been minimal , there are more the 20 variables that must be addressed , so I think you should be thrilled with the way it runs .
Just my thoughts
Ian

We are very happy with how it runs above 4,000, but believe it can be better down low. It’s not an exact RSR cam but similar in the sense that it has high lift and a fair bit of overlap

Fully understand that not much info has been provided. Was honestly mostly hoping for some input on what jetting others have run on similar engines

No redline at the moment. Peak power is at 7,170 where it gives 305hp, with a flat torque curve at 320nm. We pulled it to about 7,800

I'm running 46mm PMOs on my 2.8. Mod S cams, RSR headers with 997 GT3 muffler. Curved distributor. My jetting is 38 venturis,160 mains, 60 idles, 175 main airs, 110 Idle air jets, F16 emulsions. 12.0 - 13.0 AFRs at idle and cruise at 3000. By the way your car sounds like a Beast on the dyno. Love the exhaust

Thank you x2, 911 Slant! This is exactly the info I’m lookin for, it helps when we start trying to work out through

About the exhaust. On her first ride in the car my wife said “it’s not as loud as I’d thought it would be”. Good start I guess! I think it sounds great when revving it out but it is on the loud side.

https://youtube.com/shorts/lix686ceoB0?feature=share

I think that it is highly likely that your motor is much different motor than 911 slants, and you are running Webers vs. PMO’s so his carburetor configuration might not be the holy grail you’re seeking.

…and watching your videos indicates that you have a very smooth and rapidly accelerating motor…but that doesn’t tell us specifics. You haven’t provided data. Perhaps it’s a secret?

For reference F16’ E-tubes on my car didn’t work, they went extremely lean across the whole spectrum.

Moving forward with an analysis and a prescription for your set up requires more information about your cars AFR’s and the carburetor attributes, to include; e tubes, chokes, venturies, main jets, idle jets, idle airs etc.

Camshaft attributes? Timing?

Also where is your distributor timing at various points and max?

Any discussion using a broad range of AFR’s isn’t helpful, narrow down the AFR’s to 10’ths.

For example my motor is a 3.2 Short Stroke, 9.5:1 CR, 1.5” ID headers with 2/2 muffler, making 265 hp,

46 PMO’S, 38 Venturies, 55 Idles, 130 Idle Airs, F11 Etubes, 145 mains (yes, 145 mains), 170 airs, 45 pump jets.

Synchronized at 5 on the STE synch at 950 rpm, and at 3000 RPM’s 7.5 on the STE, all exactly within a tenth.

Idles warm at 950 rpms with AFR’s at 13.6 to 14.2.

At light cruise (less than 10% throttle, 3000 rpm’s, 3rd gear) it is rich - AFR’s 12.4 ish.

Getting on the gas from any rpm (IE 2800 rpms) gives a 12.8 AFR to the point of max torque (5700 rpms) and then transitions to 13.4 AFR’s on its way to max horsepower (7000 rpms) and to redline 7200 rpm’s.

The reason for the decreased AFR #’s is that the volumetric efficiency decreases after achieving max torque at max RPM, therefore less fuel is required to keep the engine spinning at its highest efficiency.

Getting my carburetors tuned to this level has taken many hours of tuning, testing, troubleshooting and experimenting to under the watchful eye of my friend Ian who posted above in this thread.

In the interest of this forum and the many people who want to learn or help, please provide all camshaft specs, all carburetor jetting variables, ignition timing numbers.

No secrets as such (except for the camshaft specs). More a case of me being an amateur, not fully understanding all of this, acting middle man. Hence my original question :)

What exhaust you have? Headers or heat exchangers? What ID? Equal length? Short pipes or long pipes?

Headars are equal length with 1 3/4” primaries, going in to 2 1/2”, finally merging in to a one-out at 3”. Collectors are from Burns and we use two shorter mufflers in sequence, which are straight through (perforated tubes).

Primaries are right around 40cm in length

1.75 primaries for 3L seems a bit to much IMHO. That might not create enough „suction” in the lower RPM range (chimney effect) and therefore you’re overly rich in that range. Big diameters and short pipes are good for high RPM, but not for the low end. Would you be able to change headers with 1.5-1.625” diamater for primaries or so and check the result? I’m not an expert, just an idea…

It might be on the larger side as you say, think 1 5/8” is more common

We don’t have smaller headers handy, but that could be arranged if needed

I'm using 1.625" and it's still really rich.

How Rich is Really Rich?
 

I’m really interested in comparing AFR’s because that might be useful information for the OP. Here’s a template for you, please consider filling in the blanks;

Idles warm at _____ rpm with AFR’s at __.__to __.__

At light cruise (less than 10% throttle, 3000 rpm’s, 3rd gear) the AFR’s are__.__.

Getting on the gas from 2800 rpm gives a __.__ AFR to the point of max torque ______ rpm and then transitions to __.__ AFR’s on its way to max horsepower at _______rpm and to redline at ______ rpm.

I'd love to supply AFR, but I have no way to measure it right now.

Oh, well then that’s a problem. So you’re reading the plugs? Smelling the fumes? Any other symptoms?