Tuesday, March 10, 2015


You might have noticed that things are slowing down a bit and that posts are less... focused... than when we began a few weeks ago. Things are still moving forward, but given that I only have one or two days a week to put into the car (and I'm working alone right now), the project isn't exactly moving blindingly ahead.
Also, sometimes things don't go very well and I end up burning up a whole day on a task that I really thought would take a couple hours. Today was such a day. One of the days last week was, too.
Anyway, here's a refresher of what things under the hood used to look like. Of note is one pair of SUHS6 carburetors, which are [if I may say so] one of the most elegantly designed and highly functional carburetors in the history of engines. Presto:
Those carbs are now sitting on the shelf in the garage, where they'll wait for some other project, or maybe I'll hear from someone interested in buying a professionally rebushed set with proper needles for a B20 and K&N elements tucked into the original filter housings.
SUs like that are just dandy for engines that produce up to something around 140hp, and for engines that produce more than something around 140hp, larger carbs are warranted. And as terrific as SUs are, they're British, and British things are considered kind of stodgy (which, of course, is absurd). Italian things, on the other hand, are considered really sexy and also functional, though perhaps a little finicky. My wife is Italian, so she's probably an expert but I haven't decided to ask her about the finicky part.
My friend with the Fiat summed it up nicely, "It's Italian. If I can start it, it will WIN!"
Enter the legendary Weber 45 DCOE.
A guy I used to work with told me that DCOE stands for "Double Carburetors On End." That's not quite right, but it's close enough for us Americans. Doppio Corpo Orizzontale something something. I'd run a pair of 42 DCOEs on this car when I first put it together, which I later sold, but managed to come up with a pair of 45s more recently which were, sadly, not being used. Neglect is a real problem for DCOEs. Horrible waste.
The first thing to do was to test fit the forward carburetor. The intake manifolds that are being used are much longer than the old Warnerford piece that I'd used before, so I anticipated cutting a hole in the inner fender.
With the inner fender removed:

Yep. Gonna cut.

If we'd stuck with the old manifold, cutting wouldn't be necessary. But that intake has a couple fairly sharp bends that the fuel mix would have to navigate on its way into the engine, which doesn't help fuel atomization and can lead to an increase in turbulence (which is a good thing in some places but not in the intake charge. At least not to this degree. Er.. it works pretty well, it's just not ideal, and we want ideal).

The other thing that's preferable about a longer intake manifold is that there's a whole science behind optimizing the fuel mixture beyond just 'reducing turbulence.' Smart people have measured how well a Volvo engine will run with different length intake manifolds as the variable, with carbs and engines as constants. In short, there's an ideal distance between the carburetor and the intake valve, and those short manifolds come up... uhm... short.

There are a few long manifolds on the market that are functionally excellent - TWM and MISAB come to mind - but the Holy Grail (far as I'm concerned, anyway) are the VCS [Volvo Competition Service] intake manifolds. Back before Volvo came up with the R-Sport line, they offered factory made race car parts through their VCS Catalog, which hardly anyone knew about and dealers did little to promote (thus, the rarity of all the bits they offered). No other intake manifold is as appropriate as these. Functionally excellent, and genuine Volvo.

I'd owned a pair of such manifolds [NOS, no less] some years ago (actually, two pairs) but had sold them when finances were dire. As this project was coming together, I contacted the fellow who'd bought one of the sets and he very graciously agreed to sell me another NOS pair he had on hand.

They're only NOS until someone installs or alters them, after which their market value decreases. They become "used." I happily committed this travesty and stuck 'em on the car.

Once the manifolds are fitted with the carbs, the carbs have to connect to the gas pedal. Most of the racers I've seen use a really sweet dual cable assembly that does an excellent job, but I wanted the old school rods and levers setup.

One real benefit to the cable setup is that the effective throttle input doesn't change if or when the engine rocks. Even so, we're going with rods and levers. Sexy billet aluminum levers fitted to industrial strength stainless steel rod. It looks like this:

One nice thing is that the setup is really adjustable, as all the little arms cinch down on the shaft that runs back to front. As long as you line everything up super carefully, it works very well.

Rod and levers and a support and a lockring:

Another view, from a different angle. The excess rod has been cut from the forward end (see the black line? Right there):

... and from the front. The inner fender is now in place, with a big honker of a hole in it. The splash shield isn't in place (actually, it hasn't even been made yet). Also please ignore the crap that's laying across the top of the carbs:

These last two pics illustrate the difference in length between the VCS manifolds (top photo) and the Warnerford (lower pic). Sorry the scale is so completely off:

The benefit of the Warnerford is that you don't have to cut away your inner fender. No big deal on a PV, as these are replaceable pieces, but if you have a 122 or an 1800, you might think twice about it. I'm told that the Warnerford is the only option for a right hand drive Volvo, so if you're in Australia, that's probably the one you'll want.
The other benefit to the shorter manifolds is that the carbs aren't hanging way off in space away from the engine. We'll devise some kind of support. Probably.
And that's about it. We're nearly caught up with the car's current state, which is kind of cool. I'd hoped to take a test drive later this week but it's not looking promising with recent setbacks. We'll see how tomorrow goes.
Cheers -


  1. There are plenty of induction tract length tools and calculators and you know the interesting thing is, the engine doesn't care the location of the butterfly. Meaning, if you have to run a shorty intake you can make up for it on the other end (sharp, turbulence causing, bends and edges aside).
    Looking at the narrow angle Colombo V12 with carbs mounted low but with tall velocity stacks poking into the hood. Or the Alfa GTam or GTAs racing engines with these same 45 DCOEs and a stubby manifold (nearly mounted to the head really) overcoming the space between the fender issue while giving needed intake runner length with curved velocity stacks. Or the 6 inch air horns on some SPICA setups.

    Anyway, I like it. Next I would like to see what you got under the air filters and how you are planning on feeding them cold air.

    Good to note about the Warnerford having sharp bends, I had thought about using that style myself. (something about lots of Webers sitting around and "horrible waste" :)
    Case may be that the DCOE is just not a great fit for the B20 head; Chokes are too far apart in comparison to the intake on the head. Your second to last photo illustrates that pretty well. Couple of 2" SUs maybe, or, oooh... DCNFs...

  2. I'm no expert on this, so much of what I'm doing is based on what I've heard from others... who (presumably) are experts. And I've certainly heard a lot of conflicting info. For example, one thing I've been told by a number of people is that the engine really does care how far away the throttle plate(s) is/are, and that this plays a role in manifold length. Maybe that's not true. If it's not true, then I'd assume the only real benefit to the longer manifold is to smooth out the curves, so to speak. Maybe that alone merits the design.

    I've also seen dyno sheets from Volvo engines that run DCOE carbs that show a *decrease* in power output with velocity stacks versus without. Certainly not in all cases. Probably not even half. Even so, if we get to the dyno, we'll certainly try with and without to see what works best... but I have only one set of stacks on hand, and I'm not keen on buying several more to experiment with. This effort is a balance between what we can reasonably accomplish versus what we can afford, and there are lots of necessary things that will take priority.

    The other thing is that all out horsepower isn't the top priority - the engine will need to produce a good amount of torque, run on pump gas (so CR will be at or below 11:1) and be able to sustain 6000 (or more) rpms for long periods of time (we're not allowed a 5 speed nor overdrive). So, like the rest of the car, the choice to use DCOEs is (hopefully) a balance between performance and making use of what we've got on hand when possible.

    SUs would be a much better choice in some ways. For one, they're a whole lot easier to adjust for elevation changes (and we'll be traveling from sea level to 9000 feet and back). On an SU, you simply adjust the jet. On a pair of DCOEs, you swap out 2 main jets per carb, possibly air correctors, and possibly emulsion tubes.

    Thanks for the note.



  3. On a Volvo, when you are comparing those two intake manifolds, yes, that alone merits the design! I suspect a lot of said comparisons were X manifolds vs Y manifold given the same stock Weber (e.g. same pre-carb filter/stack arrangement/length).

    re with or without stacks
    Keep in mind that changing the intake length and flow (a good velocity stack should smooth out the incoming air. Less turbulent air, remember? Result in a higher flow rate) by installing stacks will almost certainly require jetting changes. Dyno sheets where someone simply added or removed the stacks while at the dyno are less than helpful.

    There are a lot of fluid dynamics models on what effect a bell-mouth will have on income air/fluid at ever increasing rates. I suspect the 1 or 2 hp gain (given proper re-jetting) is only seen at higher RPMs with your common or stock length stacks that will fit in your filter housing.


    Good point about altitude. Are you going to carry alternate jets or shoot for a good middle ground? compromise != ideal

  4. I'm not going to spend a whole lot of time worrying over velocity stacks. Some are better than others, for sure. But tuning the length of the stacks is very likely a level of detail we aren't going to visit.

    There'll be more about the engine and how it's formatted in the future. The one currently in the car is, for the most part, a placeholder that allows me to fit everything together and drive the car while getting other things sorted out. We'll be using a different engine for competition, and may end up with 48 DCO carbs in place of the 45s. We'll see.

    I don't want to get too far ahead of myself just yet. Right now I'm just going to focus on the basic 'car assembly' stuff.

    We'll have alternate jets on hand. I don't think we'd be able to find a happy medium given the altitude changes we're looking at.

    Cheers -