Why is the B18 manifold recommended so often when putting a B20 (with SU carbs) in a 122? Based on postings from this board a few years back, I once cut the intake off a B20 combo manifold just to get a dual-port exhaust: I was advised the intake was "junk". Now rethinking this for new engine. . . Volvo engineers must've had a good reason for adopting combo design: this is a difficult casting to mfr.!! B20 style seems to have much better flow porting. The intake manifold was seperated from exhaust again in 1970s only after dropping carbs and going to FI. . . right?

Is there anything bad about the cast iron B20 combo intake (the one with carb mounts)? How does the cast arn one run in the summer: if timing/mixture is correct will it still run hot and promote vaporlock more often (with the carb heat shields installed), or is this just junkman logic? Was there some issue with an intake balancing baffle. . . .? Curious. . . how many versions of the cast iron combo manifolds were used on the B20 . . . which years are considered best (if any)?

Gotta choose soon. . . . advice?

Suggest you look up Rhys's comments on this subject in the archives. Dates are April 26 and 27, 2002. Thread name is "B-18 Cast Iron Intake...vs. Alum..."

Based on his (and other people's) views I bought a combined all-iron manifold from Topi of TRS USA when he was clearing out all his Volvo stuff. My main interest was in going to the twin downpipe exhaust, since the single downpipe exh. system on my 544 was all shot anyway. Turned out the non-butterfly manifold Topi had was cracked, "junk" he wrote, and with my permission he supplied instead, at less cost, a butterfly type with the butterflys newly removed and the holes nicely sealed with brass pipe plugs. Topi wrote that the separate FI exhausts and non-butterfly integrated carb manifolds are more likely to crack than the butterfly types.

Topi added:
"PS. Since you're in hot California do as I did; Use longer studs and TWO
insulators per carb (between the carbs & manifold) = Carbs run cooler=More
HP and no stalling/hot start problems. I also had better heat shield (custom
made from Toyota cat converter baffle!) under the carbs."

I have no experience yet using this car or any Volvo, so no personal testimonials. Mental contemplation suggests that heating of air/fuel in the combined manifold with butterflies removed will be greatest at low air flows and low engine rpm, when air slosh in/out of the heated crossover plenum would likely be a greater part of the total intake air flow. This should help with cold weather and cold engine, low-speed driveability. It's a rare carbureted car since the 1920's that was not provided with exhaust-heated intake manifolds, with water-heated being a substitute. Exhaust-heated intake air came in with the 60's in most carbureted cars. I suspect that a cold air feed to the SU's in the summer will overcome any unwanted residual heating effects of the combined manifold at high rpm and full throttle, when the air/fuel zooms right past the crossover openings on its short, nearly straight route into the cyl head.

Charles Greenlaw, Sacramento Cal.

Hi its been 30-38 c ( hot and dry )around here lately and my cast iron combo manifold has been working fine, much the same as an alloy one on a previous car.
However if I could find an alloy manifold I would fit it if only because it looks nicer ( minimal chance of fiding one in NZ )
When I was building up the last car I had a number of exhaust manifolds to choose from, they did differ in internal size but there seemed to be no plan to it, I had late FI, early FI, B18, B20, etc, the best ( biggest ) one turned out to be from a 1971 B20 combo originally with strombergs so I cut that one off.
Hans

Yes! What everyone said!
Use the aluminum if you live in a mild climate.
Use the cast WITHOUT extra flaps if you live in frigid temps(yer still gonna hate it in the Summer).
Do not use the cast arn one with the extra flaps unless you get rid of them or BE SURE they are tight and not going to leak air (and you have those carbs that will open them at WOT).
This last manny was the reason my Mom's 145 only got 144,000 miles on it before the motor was ruined- leaky manifold butterflies:o)
Best,
Shayne

Everyone,
I'm in PA. I lost my last 122 to rust, but drove it daily (summer-winter) for 5yrs. with the aluminum intake so I know how that works. It drove fine, but I got very tired of losing splitwashers/woodruffkeys - that repeated "clink" when one drops is aggravating: these are such a pain to install!!

It looks like my combo is the early type, without the dreaded butterflies (1968-69 only - Stromberg 175CDs were issued these years?) Since I can't stomach driving this next 122 (AZ wagon) in road salt, it'll be an April-November driver. Given all everyone's said about heat transfer issues with the combo intake, I am still wondering just how bad I would hate it in mid-summer. Can anyone report on drivability using this manifold with SUs (not Strombergs)?

thanx,
vovo122

I think the main reason we say you would hate it, is because it would not be as powerful as a car fitted with the separate intake. The mixture of the outside heat, mixed with the heat from the car's exhaust, would make for some lower power numbers. In general though, there won't be any drivability problems(as far as i know).
happy volvoling(i just made that up)
Kyle

I used one in Panama for several years, the 67 model without the secondary
butterflies, and it was fine. It is always summer there.
--
George Downs, Bartlesville, Oklahoma, Central US

No driveability issues whatsoever if the SUs are in good shape and the correct heat shield is fitted. If the shafts are sloppy, you'll have to tune rich and you'll have hot starting problems, but that might apply to the aluminum manifold as well. Don't believe I've tried it in temps over 100F, but up to that, no probs.

One observation, in addition to the others already made: the separate, two-hole, B20 exhaust manifold tends to split more easily than the cast iron in and out combination. This was the main reason for my using the the cut-off exhaust portion of one of the integral units to go with the alloy intake on my carbed B20. I managed to find an almost new exhaust manifold to replace the cracked one on my FI B20E, and plan to fabricate extra bracing for the down pipe in hopes of making this one last a bit longer.
Bob S.

There were at least two different cast arn combined manifolds for the B18/20.
If you are going to bigger carbs or ported heads, the aluminum one is easier
to work. The biggest drawback I have seen is that the later cast arn manifold
has secondary butterflies which are opened by arms mounted on the throttle shafts of the carbs. I put some HS6s on my 164 (when I got rid of the #$%%
Zenith-Strombergs and could not find a way to open the secondary butterflies
so I removed them. The recycle heated balance tube (for low speed operation with the secondary butterflies closed) does wonders for cold-weather idling but if the secondaries don't open you are limited to about 1/6 throttle.

In cold weather (described in detail in my post of a few days ago) on the aluminum manifold, if you start up and run and drive fairly fast, the cooling in the carb keeps the manifold cold and the engine may be cranky for some time. One way I have dealt with this is to go into the Quick Trip and get a cup of coffee. By the time I come back out, some heat has conducted into the manifold and carbs and the car is a LOT easier to drive.

Rather than go to the trouble of cutting up a cast arn manifold to get the exhaust portion, I'd look for a FI exhaust manifold, which has bigger passages also. You do have to use some half-washers on the shared studs to bolt it up because it has a different flange thickness.
--
George Downs, Bartlesville, Oklahoma, Central US

As far as I've heard, the early b18 intakes are suggested because they are aluminum, and mainly because they aren't connected to the exhaust. The cast iron combo manifold (i don't know how well they flow, other people will, and they will also provide more info on what i'm saying...) is good for cold climates because the hot exhaust warms up the intake, which warms up the engine much faster and it is happier in the cold weather compared to a seperate manifold. This is exactly what works against the combo intake in warmer/hot weather. The hot exhaust heats the intake air even more, hotter air = less dense =less power. Definitely not a performance set up. So, it depends on the climate where you live mostly. Or, if you are like me, and care about performance all the time, :-) , i'd go with the alloy manifold any day.
My $.02
good luck
Kyle
--
Kyle - attending Ore. State, while my lil 68 142 (74 b20, broken m40) sleeps...

Kyle;

Well put! The only thing I have to add is that the onepiece flows just fine.

If you install the seperate alu intake, and are unhappy with coldweather performance, just richen jets three faces each, I find that works well for me...OR one could even draw air off the exhaust manifold by constructing a sheetmetal ductwork to do this...didn't the airbox with a single, rectangular filter, used on 140s draw cool OR manifold preheated air based on a valve...one could just install one of those airboxes for the winter.

Cheers

Unless you've got to pass an emission test, go with the old style split manifold.
--
Jim McDonald