Nope...Again...BTDT...Two rear heads.. one on front turned 90 Degrees... n ow Intake is Intake/..Exhaust is Exhaust... If ya put it On or mock it Up...It becomes Obvious..
But.. just because me and Ron did it...Don't mean y'all should...do it Yer own way...OK with Me!!!
BTW The XR method Been Done ...to Death...Not the best Way at all!!!

 

Slipped out and took a Picture of our "extra" rear head, Simply placed on top of Normal set-up..
Does that Help??
Why isn't it on there?? Simple More Complicated...But Not Faster...Not slower either...Simply Different!!!


FWIW
The Only real Modification was to the Rocker Box...two spots!

 

Yes, it does help, thank you! You meant to say 180 degrees--a half turn. You had typed 90 degrees--a quarter turn--hence my confusion. Now I got you!

 

Thanks, Paul. Yeah, that's what I had thought, too, re: using two front or rear heads just set on in usual fore-aft orientation: you'd need to mess with the cams somehow, just hadn't sat down to work out precisely how.

That's what is intriguing about Racepres's suggested solution: with two rear heads and the no. 1 head turned 180 degrees (valve cover and rockers oriented as per normal), the intakes and exhausts end up actuated by the existing, respective cams. No machining or mods needed to the bottom end, and easy-peasy to buy hotter Sporty cams from the usual suspects.

 

Yea...My Bad...Type faster than I Think!!! 180 degrees...
I still believe the two fronts will work...turned 180.. (yea Not 90) buit..We surely tried that at the time...and there was a Reason we went two Rears..I simply do Not recall the "Why's". Could have been as simple as Exhaust Options...tho we have always had a Mountain of Exhaust Pipes!!

 

No worries. I was just confused as hell and wondering what the bejesus is wrong with me.

So, as I said earlier, the mods to the rocker box don't daunt me. Though if it isn't obvious when I start fiddling with it, I may ask for a clarification.

Yes, I'll almost certainly have to improve my welding skills to fabricate a custom exhaust. Seems like the best option to avoid the cost of sending pipes out for chrome would be stainless, as that can be sanded and polished very nicely (as I recently found out on another bike). But with argon (?) inside the pipe sections you're welding, per a video I watched on this subject, seems like you can get pretty smooth inner joints that require a minimum of sanding before moving on to the next joint...

As for 'not faster,' I respectfully beg to differ. I suspect that twin Dellorto 40mm carbs would net better mid-range/roll-on and upper-end WOT performance than any pick-yer-poison single chuffer. A single carb in my experience hot-rodding the A-Series engine for Spridgets yields better lower end torque and certainly better mileage--and (reason I fitted one to the 'test mule' shown on the Creative Spridgets blow-through supercharger overview and installation pages) means greatly simplified snorkels for the intercooler and bypass circuits. No balancing, too (though balancing two carbs is simple; never figured out why it daunts people so much).

And, yes, I know 2 versus 1 carb is an endless debate--as it certainly is among A-Series enthusiasts. But all the (naturally aspirated) open class A-Series racers fit dual carbs, whether single- or double-throat (Webers), because from the mid-range rpms and up to redline, it's just no contest. The Super Sporty linked earlier pretty much proves that to me...

Am I fixin' to race this bike? Not at my age. This project is as much about something fun to do as anything else. But I'd be lying if I didn't admit that the prospect of twisting a throttle grip attached to a pair of Dellorto 40s bolted to an Ironhead engine, and listening to that ancient, four-cam power plant roar through the canyon singing a song like no other bike on the planet (or at least in these parts), makes me look forward to getting out of bed in the morning.

Now, if this guy will just drop that price a grand or so...

 

Oh: the intake manifolds, and carb placement and positioning is a fascinating challenge. Certainly on the A-Series--and a lot of other engines I've read about and played with over the decades--longer intake runners actually yield better performance at certain points in the rpm range. In this case, if I were to go with Racepres's X-head configuration, I'd have the no. 1 cylinder's carb aimed aft on the L/H side, and the no. 2 carb aimed forward on the R/H side... correct?

If that's right, then slightly longer intake runners would allow the carbs to be tucked in closer to a fore-aft alignment parallel to the V... and as regards the forward-facing no. 2 cylinder's carb, out of the way of my R/H knee. Obviously, fuel line and throttle cable arrangements are no big problem to work out--just fun fiddly stuff, with the main challenges being aesthetics. Regardless, my recollection is that longer intake runners actually give you back some lower- and mid-range responsiveness you lose with dual carbs. So, avoiding carbs jutting out to the sides could conceivably net dual benefits...?

But what I do not want to create is a nightmarish routine maintenance setup. Perhaps my favorite thing about the '51 FL is that adjusting the valves takes me 20 minutes, and is actually a relaxing process that I enjoy. An Ironhead is basically the same process, correct? If so, I don't want the no. 2 carb setup complicating that.

 

Alot of Concerns
The Carb Thing first...I assure you we had all the Carb we needed..with a Bored G on a 75 cu in Ironhead. Figured the 44 Mikuni to be easiest to attach while allowing almost enough air.. The Numbers proved that the Modified G was Best (ET and MPH) the D and Bored D worked about the same as the 44 Mikuni.. plenty of air...But Zero tolerance for small hiccups.
The carb orientation is as you envision!! and we Ran quite long Intake runners.. (hose)
My partner and our Head Man did the calculations for the length..approximating the volume of the Existing Manifold as if it were a plenum! As I recall! Note that there are plenty of Misconstrued Notions on Various Carburetors magically Creating Hidden Horsepower... We Found None...once optimal, for our Setup, was Discovered.. again Bored G with a Full Radius, Short, velocity Stack.
Exhaust...Made more Difference that going to Bigger Carbs...by one Heck of a lot!!
Reason we have Mountains of Pipe!!! Seems to my feeble mind it was fairly simple to "break" our existing front pipe somewhere mid down and twisting (turning if you like) to match angle required to exit left side vs right...
Finally...This was Not Folly
we raced Heads up Nationally.. By Rule, stock displacement was 84 inch Big Twins, and 75 cu inch Sportsters..
we ran a Best, 9.80 and our MPH was 135.05. Neither with the X-Head setup..tho it was Plenty Competitive to keep us in the Points. But, Since we were points Racing...More Complicated was Not Desired.. back to Conventional setup for Pure Business!!
Dont know of any Nearly stock displacement pre Evos..that could run with us..ATT... Maybe Ever

 

The 90 degrees confused me too. But it was getting late and I was tired so didn't worry about it. But that setup does look much easier.

Paul

 

e is MEasier...Certainly..
when it comes to the Dual is Better/Worser, than single???? I call a Draw...with Proper Manifolding of course!!
One Aside..we obviously had opportunity to try to Balance the Carbs when dual...
With such a Setup..on our Harley Twingle..more is simply Always More..take all you can get...if one gives More...again...More is More Better...Take it and Run!!! An HD is after all,... a Twingle!!