Has anyone tried to fit 2" SU carbs on a B20 engine. The intake manifold openings would of course have to be machined to fit these carbs. Any experience on the additional performance?

I had Joe Curto in New York fit angle float bowls to a pair of HD8
Jaguar carbs so I could put them on my 2130cc B20. I had several problems
with the engine, not related to the carbs, and I think it had a little better
power but used quite a bit more gas. Unfortunately I had a pair of J.C.
Whitewash air filters bolted up with 5/16" hex nuts on the inside of the
filters. Somewhere one of the nuts on the front one came loose and got into
#2 cylinder where it got between the piston and the flat part of the
cylinder head, making extremely traumatic sounds and drastically affecting
both my and the car's performance. Neither the piston nor the head was
seriously damaged but the block was destroyed - the nut caused the piston
to cock in the cylinder, whose wall was pretty thin and the cylinder was
split from top to bottom. I was in Panama at the time so I had some trouble
finding a B20 block, although I finally did find a bare 1975 8-bolt
block without even maincaps. The old maincaps worked fine but could not
find maincap bolts (M12-1.75) of the proper strength till I took a trip to
Dallas over Christmas. Finally got it back together in February. It is now
a stock bore B20 using 2 HS6 carbs. Less power but still OK.

That may be more than you wanted to know......

--
George Downs Bartlesville, Oklahoma

Sven & Ron Kwas

Does the same theory applies to fitting twin sidedraft weber carbs in this instance? Surely the volume of the webers would be more than that of the 2" SU's.

vortex;

Your observation is absolutely valid and correct. ...not to be pickey...but it would be more correct to speak of cross-sectional area and not "volume" (but we all knew what you meant). By fitting Webers (according to my scale, 45mm is just about 1 3/4", so a pair of 45DCOEs, DOUBLES the cross-sectional area and flow capability) you are even MORE "overcarburated", then with two HS8s. You certainly dont need this normally (and at part throttle, it isn't even utilized!), but its nice to have the ability at your disposal...and with their excellent setup flexibility, its the only way when going racing (and where the driver is using the entire throttle range - especially full - constantly).

In the case of a road car, this is analagous to fitting a bigger battery...you don't use it normally either, by its nice to know its there when you need it and call on it (the frequency of "calling on it" depends on your age and need to show off/impress/have fun!).

Cheers

Webers work on entirely different principle than SU's, that being SU's are unique in that they are a constant velocity carb. Webers are so adjustable that they can be tuned very accurately to any engine they are installed on, I have run twin 40 or 45 DCOE Webers on 5 cars in my past, mostly for competition, and to say I really love these carbs. Don't expect fuel economy but power and throttle response will be second to none, if you take the time to set them up and jet them correctly.

Volvord 784VC
http://www.telusplanet.net/public/gilesij/Volvord/

From what I hear (and I've never been tempted to spend the money or
offered a deal I couldn't turn down on them) the side draft Webers or
Mikunis (like on the 122 on ebay - see the pic) are probably better.
I'd think they would probably give better mileage than the HD8s also.
Topi could probably tell you. Try him at TRS-USA.com or John Parker
at jparker3@twcny.rr.com
--
George Downs Bartlesville, Oklahoma

We have also considered this set up. However, SU's seem to perform best with higher air velocity. Have serious doubts that you could get the 2" to breathe properly, even in race conditions.
As a side note, a lot of work was done with multi carb setups on Minis, and in the end a single large carb gave best performance for most situations.
It might be worth the effort to find a single carb B18 manifold and try just one 2" carb. If you are looking for a project, this one might give good results. Will be interested in how it all turns out.
We have a set of 2" as well. Watch for input from Dead Volvo Society (my brother and family). Our 2" are more likely to end up on the 164.

Svend;

Do you mean higher flow volumes...because with the dashpot going up and down as a function of flow, this keeps the velocity at the jet the same at the point of carburation (SUs and similar motorcycle style carbs are called constant velocity designs because of this)?

I also have to wonder about your statement that one couldn't get the HS8s to breathe properly...although not as easy to set up as Webers (and with the SU's simplicity that is arguable...maybe a better term would be versatile), SUs are quite configurable...with different dashpot springs, and hundreds of metering needles available...some years ago, I satisfactorilly set up a single HS8 in suck-through configuration on a turbocharged B18...even though its been a long time, I still remember the howl (and thrust) when that turbine made boost...Jahoo!!! In that case, a bit more carb than the HS8 would probably have been in order, but the SU was available, and a joy to set up.

Cheers

You're right about the physics of that. However as you noted in another posting on this topic, the larger bore SU's tend to "over carburate" for normal on road driving. If I ever get time to try variation, I would like to try the 2", but overall, I can't find enough wrong with the HIF's to make me want to invest the time. Thanks for response.

You may notice a slight improvement in power but probably not enough to justify the effort. In the past I set-up another car (not a Volvo) with four 1 1/4" SU's, this was worth the effort in that it improved performance and throttle response. It was a little bit of a pain to set-up and sync but it was fun to drive and very cool to look at.

Volvord 784VC
http://www.telusplanet.net/public/gilesij/Volvord/

Vortex;

According to the book Tuning SU carburetters, Published by Speedsport Motorbooks, ISBN85113-072-0, the 1 3/4 HS6 were suitable for use from 1500-3000cc displacement engines...and as a reference the HS8s were suitable from 1750-3500cc...you can draw your own conclusions! ...and maybe this is why its not a commonly occuring installation...but if you happen to have some Jag carbs and have this insatiable need to bodge something up, have fun and let us know how it works out...I bet it would look pretty impressive under the hood! I have a manifold you would need to open up...e-mail me off-line if you want it.

Cheers