|
|
|
I would like to upgrade my single piece intake & exhaust manifold from a B18 to the separate manifolds used on the B20 that is in the car.
The exhaust manifold is the two pipe version. Are there separate exhaust manifolds with the same two pipe set up? I got the impression that the separate exhaust manifolds are all single pipe.
Dennis
|
|
-
|
|
|
Opinions are (obviously) divided on this one as to which way is "best."
The parts you want are out there, look in 140-series rigs Late model (non-us import) 122/123/etc and pre-FI p1800 in the junkyard. Early 140-series had carbies so you can find the aluminum intake from one of those. It will also (perhaps obviously) have the appropriate exhaust manifold. Later D-jet exhaust manifolds from the 140-series have larger diameter down-pipes so grab those too.
You may find after all that the exhaust manifold is a "unit" manifold that was cut in half at the factory and a patch welded over the hole!
As stated, the FI manifolds are thinner at teh mounting flange than the carburated version. Carbie manifold thickness is 9/16" and FI is 11/16" no biggie as the washer pockets can easily be spot-faced or hand-ground down an appropriate amount.
People that argue over the relative merits tend to dwell on one thing. Aluminum conducts heat better than cast iron. This is argued both ways by whomever is arguing... The aluminum conducts the heat to the carbs making them tend to "vapor-lock" The aluminum absorbs more heat from the exhaust manifold. The aluminum doesn't heat up enough leading to carb icing. The aluminum conducts heat from the head better so keeps the fuel better atomized. etc. ad naseum.
Aluminum is easier to machine and puts less stress on manifold studs. Aluminum is easier to cast into complex shapes. Aluminum is sexier. Some of those reasons are the ones Volvo went to aluminum intakes. Oh, the FACTORY did it???? well, that must make it OK, huh?
Unless you have the "dual butterfly" manifolds and they are in poor condition (esp. at the shafts) or mal-adjusted, then the intake style isn't going to make the engine "run bad" by itself.
Tired carbs, warped surfaces, b18 needle, etc. will have a definite adverse impact on running an otherwise healthy b20! Also are much more likely.
Always suspect intake issues last, however. Ignition and valve lash are first two things to investigate folowed by false-air (leaks). Monkey with carbs last.
--
Mike!
|
|
-
|
|
|
Dennis,
I don't know that the separate intake is an upgrade. It's one of those things you hear once in a while, but I haven't seen any test data whatsoever. My tendency is to default to the way Volvo did it, barring quantifiable evidence that there is a better way.
You are correct that the earlier exhaust manifolds that went with the separate intake were all single pipe, and you should avoid those. However, the '70-'73 B20s with D-jet injection had separate dual pipe exhausts, although these are hard to find uncracked.
It's not that hard to cut the intake off the exhaust manifold you have, if you must have a separate intake.
|
|
-
|
|
|
All the FI exhaust manifolds and a few from 68-69 carbed varieties are like
what you are looking for.
--
George Downs Bartlesville, Heart of the USA!
|
|
-
|
|
|
When I had the B20 installed, they installed the one piece intake/exhaust manifold that was on the B18. The engine has never run/idled right dispite rebuilt carbs and other adjustments, PCV rebuild, etc.
It was suggested by the shop that put in the B20, that changing to an aluminium intake manifold that the B20 had from the factory would help. OK, but seeing that I have the one piece, I also need an exhaust manifold and somewhere I got the impression that the double pipe exhaust was only on the one I have.
From what Phil said, it looks like they do exist so I can start searching.
Know where one is???
|
|
-
|
|
|
They are pulling your leg. They don't know WHAT the problem is so they
are grasping at straws. Changing manifolds won't help UNLESS you happen to
fix the real problem. Now there are a couple potential problems that MIGHT
be realted to the manifold. They are:
1. A crack in the intake portion of the manifold
2. The cover plate in the middle of the manifold that might have a blown
gasket. (never happened to me but it's possible)
If there are secondary butterflies in the manifold it could be that their
throttle shafts are leaking. What I did for that was to remove the secondary
butterflies and their shafts and their shafts and plugged the shaft holes
with some permatex on some cut-off 5/16" bolts.
But if don't have those particular problems, changing manifolds will NOT help.
Usually bad idle is caused by vacuum leaks so you should check out any hoses
attached to the manifold and associated valves, etc.
Make sure everything is good and tight.
--
George Downs Bartlesville, Heart of the USA!
|
|
-
|
|
I think Phil is right, there never was a separate intake manifold for the carbed B20, but there were several versions, with only minor changes, of the alloy type used on B18s, and they work well on B20s. I certainly wouldn't dare gainsay Phil on the matter of your problem not being the intake manifold, unless you haven't dealt with those gates they have inside. That said, if you want a dual pipe exhaust manifold, your best bet is to cut free the exhaust portion of the integrated type. The casting is beefier where the two pipes join and less likely to split than the ones used on the FI B20s. I rejected a pile of cracked ones before I finally found an almost new one for the FI B20 in my 142E. I hadn't much luck trying the weldthe cracked ones either. Be aware that if you combine the alloy B18 intake with the B20 exhaust, cut free or born free, you'll have to deal with a difference in the thickness of the flanges where they attach to the head. I solved that with a drill and a Dremel Tool. BTW, I have a sneaky suspicion that the cracking of those exhaust manifolds has a lot to do with the downpipe not being securely bracketed to the block, bellhousing, or transmission so they vibrate in unison, rather than being wagged by the ret of the exhaust system.
Bob S.
|
|
-
|
|
|
If the manifold came off a B18, I don't think it would have those nasty secondary butterflies... or did they start that in '68? Not sure myself. Dennis, if you do have one of those, by all means do replace it with something better.
Bob, I was just looking at an exhaust manifold from a K-jet B20, and it sure looked like it was a once-unified casting that had been cut up. I can't vouch that it was the original one the factory had on that car, though.
I've seen the unified manifolds crack in the center of the exhaust side as well as the separate ones. On my 1800, there's a brace that goes from the rear tranny mount to the exhaust pipe to prevent any flexing of the manifold or headpipes. Cameron tells me these should be found on other models as well... but I generally don't find them in place (I suspect the older cars with single downpipe may not have had this feature). Maybe that explains why there are a lot of cracked later manifolds???
|
|
-
|
|
|
Phil,
On my PV, that bracing attached the down pipe to flywheel housing. Like on most of them, it was worn out, and when I swapped in the B20, I neglected to make up a new one and then sort of forgot about it till I started to deal with the cracked manifold I found on the 142E. At that point I made up a sturdy brace -- for the PV, that is -- to go from the tranny support to the exhaust. I was stunned at how that quieted the whole car down . Six inches of angle iron and eight of flat bar changed the whole personality of the car.
Dennis,
One more thought, probably an idle one, but with all the ideas tossed at you, one more item won't bother you: are you sure your accelerator and carb linkage is moving freely and returning everything to the normal idle position after a run? Please, let us know what the problem turns out to be. This sounds like one of those simple, stupid things that can totally ruin your driving pleasure (the whole point of owning a PV) and that we can all identify with.
Bob S.
|
|
-
|
|
|
Dennis, I ran a B20E with SUs and the B18 unified intake/exhaust for years and had no problems with it. The format of the manifold is not the source of your problems, so a change of manifold is unlikely to fix them.
I wasn't aware that there was ever a separate carb intake for B20 ???
|
|
-
|
|
|
Phil
Thanks for your candid reply. I am trying to solve a very persistant problem with the idle / running that rebuilt carbs (needed anyway), installing a correct PCV system, distributor rebuild, valve adjustment has not fixed. It is over a year now. I don't drive it much but this is partly why. I may be shooting in the dark on the manifold but at this point I am willing to try almost anything.
The problem is:
After a drive at 50 to 60 mph, the idle is very high, around 1500 or more is my guess.
When it is turned off and restarted a few minutes later, the idle is so low, it is hard to keep running.
On the other hand if I start out with just slow stop and go driving, the idle holds where it should and restarts OK.
The fuel consumption is pretty bad and I have had to clean / replace the plugs a few times in the last six months. If I lean back the carbs, then it misses at 50 - 60 mph pretty bad.
Dennis
|
|
-
posted by
someone claiming to be cdu
on
Sun Apr 3 19:59 CST 2005 [ RELATED]
|
|
Sounds to me like you might want to check for a stuck
advance weight in the distributor.
It is easy to find a vacuum leak -- squirt some water or
starter fluid around on the hoses and manifold and if
there is a vacuum leak the idle will change. Just take
care not to blow yourself up.
chris
|
|
-
|
|
|
Now THIS description sounds like you might have one or more loose throttle
butterflies. When the screws get loose, (before you lose them into the engine)
the butterflies move around and won't close right. You might want to pull
the carbs and make sure the screws holding the butterflies are good and tight.
--
George Downs Bartlesville, Heart of the USA!
|
|
-
|
|
|
That's easy enough to check. If it turns out to be something this simple, I will consider it very lucky and be eternally grateful.
|
|
-
|
|
|
Dennis, do you know what needles are in the carbs? I don't know what version of B20 you have, but the original ZH needles from the B18 are definitely wrong and would tend to produce at least some of what you describe.
You're in Eugene, right (I looked it up in your profile). You know you're only 100 miles away from Shayne and/or Cameron in SE Portland... they would surely be able to sort all this out for you straightaway. I don't suppose you'd care to come up to Whidbey Island, or I'd be glad to do the honors.
|
|
-
|
|
|
Phil,
In an earlier post you said:
"If the manifold came off a B18, I don't think it would have those nasty secondary butterflies... or did they start that in '68? Not sure myself. Dennis, if you do have one of those, by all means do replace it with something better."
I have one of those with the nasty secondary butterflies, that are no longer there.
Dennis
|
|
-
|
|
|
I believe it is a B20E, and the needles are KD. If I thought the car would make it, a trip to Whidbey Island would be a good getaway.
|
|
|
|
|
