How to ID a B20 vs a B18?

[DaWhole9]

So I was googling on the 'net and actually ran across an ad of my car. Looks like a scammer actually got their hands on an old ad. I chuckled because there are pics I did not see of the car. Description looks to be copy and pasted from the old ad...except the engine...it says B20 engine, when my car is a 1964 Wagon (estate) which came standard with a B18. Hold on...does my 1964 wagon have a B20 in it. It also says (and the previous owner said) it has a 4 speed with overdrive. The owner said the OD wasn't hooked up and he didnt know much about it, it was the way he bought it. Now wondering how I identify the motor....

[Natedog]

It’ll be stamped b18 or b20 on the cast red block high on one side.

[Derek UK]

It's actually cast in as part of the block. A quick id looking down on the head, if you see Volvo just above the manifold it's a B18 head and if it doesn't show it is under the rocker cover and is a B20 head.

[Uncle Benz]

Just under the number 4 spark plug

[DaWhole9]

What a nice surprise!! Its a B20. Its got a Weber on it..was that a good performance upgrade over the twin SU's? Looks like a Weber 38 or a 32/36...anyone know what the normal upgrade was for the B20?

[Derek UK]

The downdraught Weber conversion is common in the USA. It was offered by IPD and others. It's rarely jetted correctly for the best combination of good running across the whole rev range with both good performance and fuel consumption. IPD at the time offered a jet kit against a returnable deposit so that you could tweak it to suit your car. Moving the running characteristics from good to excellent took both time and patience. You just paid for any jets you didn't send back. Not surprisingly changing the jets without the necessary knowledge made many run worse than when it was first fitted!
SU's are better but to Americans they were something they weren't used too. After about 100k miles the wear around the throttle shafts made tuning difficult so they got a bad reputation as always being in need of adjustment. When in good condition they keep their tune very well and shouldn't be messed about with if you don't understand them. This bad reputation led to good sales of the Weber conversion.
If you car runs well with the Weber and you are happy with it that's fine. The SU's will be better at the top end but only if in good condition. If you find a good looking set with worn spindles and are prepared tp pay quite a lot to get them properly refurbished then it's worthwhile. You will need the correct inlet manifold for them and some bits to get them up and running, linkage, filters etc. Needles for B20B spec needed too.
Take care. Stay safe.

[Clan]

Originally Posted by DaWhole9

What a nice surprise!! Its a B20. Its got a Weber on it..was that a good performance upgrade over the twin SU's? Looks like a Weber 38 or a 32/36...anyone know what the normal upgrade was for the B20?

The next step up in efficiency from twin SU or Strombergs should be 2 x 40 or 45 DCOE webers or similar Solex carbs , a twin choke downdraft ( like yours ) is half way between a single choke carb and twin SU/Stromberg so not really worth spending on .

[DaWhole9]

My other car is a modded BMW 2002. For performance the carbs normally used are...

Stock solex 1 barrel. Not great for performance.
Weber 32/36 - A nice boost in performance and retaining fuel economy
Weber Dual 40 Sidedrafts - A boost in performance over 32/36, would need cam and exhaust to take full advantage of the extra fuel.
Weber 38/38 - A boost in performance over the Weber 40s, especially on the low end. at the extreme top end the Weber 40s can equal or maybe give a tad more power but ho lives at 6500 rpm?
Weber Dual 45s - Big boost on the top end, but maybe a little sluggish down low. as with anything over the 32/36 a can amen exhaust and ignition upgrades are needed to get full benefits.

So I am wondering if that is similar for the Volvo. Looks like the 32/36 and SU's are similar in performance.
Dual 40s may be an upgrade but if I have a basically stock motor would I see those gains? Is it worth dropping over $1k for maybe 10-20 more hp over the 32/36?
Then there is the Weber 38...it has the ability to flow more than the Dual 40s and its easier to tune. In some cases its difficult to get the initial jetting correct for an engine. Too lean on the top end and too rich on the low end or vice versa but hard to get good all around, until the 123 Tune Dizzy came along and the timing was able to be manipulated to help keep it in tune and then bam...the 38 is a beast. I have had that combo on the 2002 with a modded motor, cam, high comp pistons, exhaust, 123 Tune Dizzy and weber 38/38. Peppy and angry.

the Volvo runs GREAT at this point so my focus is going to be brakes and suspension, then cosmetics. It does have an electric O/D I will have to sort out as well. I do have a set of Weber DCOE 40s sitting on a shelf that I was going to put in the 02...hmmm....maybe I drop those in the Volvo...

[Derek UK]

The Volvo twin carb engines were designed to use SU's. Each SU feeds equal length inlet tracts for best fuel balance. The inlet manifold lengths for these downdraught carbs aren't equal even if some of them are better designed than others. They will always be a compromise. Side draught Webers and Solex carbs are best left to the performance end of the market. Yes they used to be standard on a lot of Alfas but the factory had a lot of experience with them racing and had a dyno to get the best jetting before releasing those cars to the market.