Side drafts

[AJ/FormS]

I was a motorcycle mechanic for over 25 years. I was sorta the go-to guy for carb work. Most 4 cylinders had 4 carbs, and 6s had 6 and so on. Once the factories started putting them on a common mounting plate and a common throttle shaft, life was easy.
But then guys would park them for the winter,and neglect to either drain them or put stabilizer in the system, and the following spring, I got to do it all over again.
Motorcycles have a very narrow window of operation, and most multis are CVs, and generally stay at one altitude, give or take. And the throttle valves are barely bigger than the intake valves, and the intake runners are extremely short. But the thing is; the airbox is a tuned part of the system. If you mess with it, you will have issues. And if you got those bugged out, you invariably introduce a new set of issues. And every stinking change is multiplied by the number of cylinders.
So while I have great confidence that multi-carbs work on motorcycles, there is no way I'd stick a bunch of them on a car-engine that has to operate under so many more conditions, and especially on one that is way under-powered for it's chassis in the first place. I mean most motorcycle-multi's are operating at well under 12 pounds per horsepower, and getting down to 8,7 or even 6. And you hardly ever whack them open under 3000 or 4000 and they have WET-CLUTCHES.
The lightest chassis for a slanty is the early A, and you'd be lucky to get that combo under 20 pounds per horsepower. And it will have a TC in the range of 1600 to 1850. So good luck signaling multi's with that. Then you throw in a wild card like sucking hot underhood air, changing altitudes, and rainy days, and heaven forbid, snow,lol.
Well I might put three duals on the manifold, but probably one or maybe two are gonna be fakes.
I better add that I have great respect for the person who can make a set of them work properly, and I'd be willing to bet he has many,many, hours into the set-up.
Yeah and just to drive a point home, most slantys will be happy with a 250cfm 2bbl, right on up to 3800rpm, And from there on, it needs just a bit more, like 300 at 4500,and about 25 cfm per 500 after that.

 

[kesteb]

When you start running an IR manifold with a venturi per valve, those classic cfm calculations go right out the window. I have an old Haynes manual for webers. It had suggestions for setting up the carbs for various engine sizes. An alternative would be a similar sized production engine. That would get you into the ball park.

 

[slantsixdan]

A pair of HS6 SU's on a mild slant would be a wonderful setup.

Or the more advanced HIF6s, yeah. If one started with a pair of expertly-built carbs, applied appropriate heat shielding, dialled in the jetting carefully and put together the linkage thoughtfully, this would stand one of the better chances of being a good-running, relatively problem-free setup.

 

[C130 Chief]

Dan, never much considered the HIF series, mostly because it seemed like they over-complicated the SU to make it more like a CD175 Stromberg. Mid 70's BL dreck. Always thought the HS series was the most foolproof. Not that I'm knocking the Stromberg, my 2nd favorite multi-carbeuretted DD was a 73 TR6 with Strombergs (1st favorite was a 71 Fiat 124 Coupe with dual 40mm IDF's, but that's another story).

 

[pishta]

My buddy had 2 Jap SU's (Hitachis?) on a Datsun 510 w/1800 SSS motor...in WA. he said he had to push start that thing on really cold mornings. something to do with the damper oil in the carbs? EFI baby.....

 

[Killer6]

My buddy had 2 Jap SU's (Hitachis?) on a Datsun 510 w/1800 SSS motor...in WA. he said he had to push start that thing on really cold mornings. something to do with the damper oil in the carbs? EFI baby.....

Speaking of, how's that coming? I saw where You had Your injector ports & rails set-up & assembled, did You pressure check the head when You finished?

 

[pishta]

work in progress. A 3 year old doesnt accelerate anything in the garage.....