Well, I Am Going To Add Triple Webers To My 3.0L M20…

[digger]

Thank you for the details Digger. I have reached out to Rama, and they do not have anything to do with carbs any longer. I am about to pull the trigger on some 45's Webers. My options are between a 5 progression hole vs 3. The cost is about $1000 more for the 5-hole. The seller/tuner (based in England) says the 3-hole setup would be fine since I have a SOHC. I can understand how a 5-hole would work more smoothly, but it would require more tuning etc. I dont mind spending more, but only if it makes sense. Any advice between the two?

Does anyone know is Andrew (SkiFree) is still around? He seems to have all the answers I may need, but he hasnt been active on any of his accounts in 5-years. I recall him being a regular on this form in the past.

Sorry, i cant provide any informed comments about progression holes

try contacting Adams Autosport https://www.instagram.com/adamsautosport/?hl=en if you haven't already. Someone else might have other contacts

[TobyB]

You'll be able to make either 40's or 45s work, and the difference will be mostly in mixture control.
It might not even be all that hard to get either to work in similar circumstances.

However, this has been my experience:
I bought a 2L race car that had 40s with 32mm chokes per the rules of the class.
It ran fine, made 150 solid horsepowers, and pulled to a 7000 redline, falling off starting about 6700.
Long runner Canon manifolds.

The rules changed. Now 45s were ok, and chokes were unrestricted.

I went to a 34mm choke, and then a 36mm choke, and the redline went to 7500 with absolutely no falloff.
Idle SHOULD have gone to shit with 36, but the car metered well from 2000, and pulled strongly
(as in, solid a/f ratios) from there. Horsepowers were never measured, but lap times said they went up significantly.
Doing the straight maths, probably to 180.

I then got me some Spanish 45's, and lap times went to hell. After some EGT gauges, it turned out that one
jet well of one Weber was machined too deep, and there was no real fix for it.
Then I got me another Weber, and stuck 36mm chokes in, and after some more tuning, got back to my
40 lap times. Went to 38 mm chokes. Didn't go noticeably faster, and tuning wasn't any more difficult.
The jet combinations made more SENSE than they did on the 40s (larger mains, smaller air correctors)
but the lap times stayed roughly the same. This was on the same type Canon manifold, but opened
up for 45s. All the other variables factored in, the 45's weren't good for more than tenths of a second
on the straights. Which in a race car is all well and good, but on a street car, silly.

So here's my limited opinion: with a smaller cylinder M20, I'd stick with 40s on the street. Then the throttle
plate will open further at just-off-idle, and the progressions will have a chance to work. If you start
on a 34mm choke, tuning will be easy, and your carburetted top end will probably be over 7000, based on what
I experienced with the 2l engine. You WILL be giving up just a titch- but unless you're planning on
tuning at Bonneville and running tracks with long straights, you're REALLY not going to notice all that much.
What you get in return is better mixture control at idle.
Is it a big deal?
Prolly not. So if 45's make you happier, do that.

As to progression drillings, I've always been frustrated by the Weber method. If I was to spend real time
on street development, that's where I'd start filling and drilling....

For spark, it's not going to matter. I used a 6MSDal for the limiter with a rusty Accel coil
and never had any blowout problems.
If you already have the 'squirts, I'd use it for its tunability. There's both power and driveability in a good,
load- sensing spark timing system.

I found DBilas' opinions to be... opinions. And their products to be... heavy. They certainly go fast, though.

t
opinions are like Miatas...

[E30-TourZing]

You'll be able to make either 40's or 45s work, and the difference will be mostly in mixture control.
It might not even be all that hard to get either to work in similar circumstances.

However, this has been my experience:
I bought a 2L race car that had 40s with 32mm chokes per the rules of the class.
It ran fine, made 150 solid horsepowers, and pulled to a 7000 redline, falling off starting about 6700.
Long runner Canon manifolds.

The rules changed. Now 45s were ok, and chokes were unrestricted.

I went to a 34mm choke, and then a 36mm choke, and the redline went to 7500 with absolutely no falloff.
Idle SHOULD have gone to shit with 36, but the car metered well from 2000, and pulled strongly
(as in, solid a/f ratios) from there. Horsepowers were never measured, but lap times said they went up significantly.
Doing the straight maths, probably to 180.

I then got me some Spanish 45's, and lap times went to hell. After some EGT gauges, it turned out that one
jet well of one Weber was machined too deep, and there was no real fix for it.
Then I got me another Weber, and stuck 36mm chokes in, and after some more tuning, got back to my
40 lap times. Went to 38 mm chokes. Didn't go noticeably faster, and tuning wasn't any more difficult.
The jet combinations made more SENSE than they did on the 40s (larger mains, smaller air correctors)
but the lap times stayed roughly the same. This was on the same type Canon manifold, but opened
up for 45s. All the other variables factored in, the 45's weren't good for more than tenths of a second
on the straights. Which in a race car is all well and good, but on a street car, silly.

So here's my limited opinion: with a smaller cylinder M20, I'd stick with 40s on the street. Then the throttle
plate will open further at just-off-idle, and the progressions will have a chance to work. If you start
on a 34mm choke, tuning will be easy, and your carburetted top end will probably be over 7000, based on what
I experienced with the 2l engine. You WILL be giving up just a titch- but unless you're planning on
tuning at Bonneville and running tracks with long straights, you're REALLY not going to notice all that much.
What you get in return is better mixture control at idle.
Is it a big deal?
Prolly not. So if 45's make you happier, do that.

As to progression drillings, I've always been frustrated by the Weber method. If I was to spend real time
on street development, that's where I'd start filling and drilling....

For spark, it's not going to matter. I used a 6MSDal for the limiter with a rusty Accel coil
and never had any blowout problems.
If you already have the 'squirts, I'd use it for its tunability. There's both power and driveability in a good,
load- sensing spark timing system.

I found DBilas' opinions to be... opinions. And their products to be... heavy. They certainly go fast, though.

t
opinions are like Miatas...

Thank you for the time spent explaining these details. I have a few specific questions.

It seems running 40mm carbs but having 36mm chokes can cause some drivability issues around town. At least I have been told this. I get the impression 30mm-34mm is ideal for 40's but bigger than that 45's make more sense. Do you think doing an initial setup with a 36mm choke/45mm would make my 3.0L hard to tune?

Are you referring to a stock m20 as a 'smaller cylinder M20?'

My local weber supplier (redline) says that the FJAS carbs are better quality than the Spanish Webers. They are also half the price. Thats quite an impressive claim. Especially when the Weber forms I have recently signed on seem to say the same thing. Anyone here have anything to add about the FJAS carbs?

I am looking pretty seriously into the iBooster setup. I am doing some deeper dives with this, but it seems like a better compromise considering the vacuum isn't the best with carbs, and it allows even more space. My daily has an iBooster setup and it works quite well. Any thoughts on this conversion for my touring? It would be nice to setup the canbus, but I feel a bit out of my comfort zone sorting the electronics out. (perhaps I am over-thinking the difficulty)

Thank you all again for your help!

[TobyB]

It seems running 40mm carbs but having 36mm chokes can cause some drivability issues

Yes, anecdotally it makes sense, as a 36mm choke only provides a 4mm restriction on the 40mm bore.
In THEORY that's not very much 'depression' for metering.
I really do think that 40's with a 34mm choke will be enough if you're not planning on holding the throttle
open for minutes at 7000+ rpm. But then, 45's ARE bigger...

I had expected the race car to change character when I put 36mm chokes in, but it really didn't seem to affect
anything very much, other than top end airflow. Metering did change, but it wasn't more than incremental.
Keeping in mind, of course, that while a race car spends very little time at 'puttering' speeds, I didn't notice
anything unusual in driving out to pregrid...
A 36mm choke in a 45 would provide a very good venturi, and give good metering. Again, the real challenge
will be the tiny throttle angles it'll need to putter down to pregrid at 35mph, and it won' uncover the progression
holes very much, if at all...

yup, an M10b20 has a 500ml cylinder, and an M20b25 has a 416ml cylinder, so each throat on an M20 will be
drawing 83% of what an M10 will at the same rpm...

If FJAS is one of the suppliers from China, I've heard similar- that some Cast in China carbs are very good for what they are.
If you can get a return guarantee, it would probably be worth trying them. When I was having issues,
I put pyrometers in the headers, and for $50 a runner, they were really useful, in combination with a wideband
in the collector, at telling me how close to balanced the carbs were.

When I had a booster on the racecar, with a pretty aggressive cam, I never had vacuum issues.
Closed throttle is closed throttle, and the booster just needs to be evacuated between braking events.
That said, getting rid of the booster is nice, since it's always in the way.

t

[digger]

pretty sure we are talking about a 3L 6 cylinder

[E30-TourZing]

Yes, anecdotally it makes sense, as a 36mm choke only provides a 4mm restriction on the 40mm bore.
In THEORY that's not very much 'depression' for metering.
I really do think that 40's with a 34mm choke will be enough if you're not planning on holding the throttle
open for minutes at 7000+ rpm. But then, 45's ARE bigger...

I had expected the race car to change character when I put 36mm chokes in, but it really didn't seem to affect
anything very much, other than top end airflow. Metering did change, but it wasn't more than incremental.
Keeping in mind, of course, that while a race car spends very little time at 'puttering' speeds, I didn't notice
anything unusual in driving out to pregrid...
A 36mm choke in a 45 would provide a very good venturi, and give good metering. Again, the real challenge
will be the tiny throttle angles it'll need to putter down to pregrid at 35mph, and it won' uncover the progression
holes very much, if at all...

yup, an M10b20 has a 500ml cylinder, and an M20b25 has a 416ml cylinder, so each throat on an M20 will be
drawing 83% of what an M10 will at the same rpm...

If FJAS is one of the suppliers from China, I've heard similar- that some Cast in China carbs are very good for what they are.
If you can get a return guarantee, it would probably be worth trying them. When I was having issues,
I put pyrometers in the headers, and for $50 a runner, they were really useful, in combination with a wideband
in the collector, at telling me how close to balanced the carbs were.

When I had a booster on the racecar, with a pretty aggressive cam, I never had vacuum issues.
Closed throttle is closed throttle, and the booster just needs to be evacuated between braking events.
That said, getting rid of the booster is nice, since it's always in the way.

t

Thank you Toby and Digger for the input!

So my actual CC's are 2926. So 488cc per cylinder. If I am gathering this correctly, you are saying with the 40's, the progression holes will be uncovered and thus assist better than if I run 45's and a 34mm choke? (which is at its min)

I feel inclined to give the FJAS a try based on the reports coming back to me. Its just a bit unusual for me to order 'replica' parts, but smoother tuning is key, and it sounds the FJAS have more consistency. But man, its hard to say. So many differing opinions in this subject. I wasn't expecting this! Haha

Which booster did you use on your race car? Was your setup in an E30? Also, did you run vacuum from the carbs or the manifold?

[digger]

Thank you Toby and Digger for the input!

So my actual CC's are 2926. So 488cc per cylinder. If I am gathering this correctly, you are saying with the 40's, the progression holes will be uncovered and thus assist better than if I run 45's and a 34mm choke? (which is at its min)

I feel inclined to give the FJAS a try based on the reports coming back to me. Its just a bit unusual for me to order 'replica' parts, but smoother tuning is key, and it sounds the FJAS have more consistency. But man, its hard to say. So many differing opinions in this subject. I wasn't expecting this! Haha

Which booster did you use on your race car? Was your setup in an E30? Also, did you run vacuum from the carbs or the manifold?

dont trust anything you read on forums