That's quite bit of carburetion if using a common plenum, no matter how small. I think you may need to use some very small chokes (venturies) in them to help keep the air speed up. No personal experience with flat motors here, but what I gather from reading some of Speedy Bill's old books it seems the full-race Merc flattys with 4 carb intakes were pretty radical and short on low-speed performance. Four Strombergs are somewhere around 600 to 700 cfm, in comparison your two 48s are going to be close to 1000 cfm. In the late '70s on my street 10.5:1 compression 1835cc VW (please forgive me here) with a pair of 48 IDAs I ran 37mm venturies, it was a daily-driver/street-racer special that could run 13.70s all day long with great street manners. On my 12:1 compression race-only 1835 (12.40s in the 1/4) I ran 42mm venturies. I once put a pair of 48s on a mildly-cammed 1756cc street engine and it had almost no low-end at all . Easing into the throttle slowly felt like I was stomping on the gas and kicking the carbs wide open. It was was essentially un-driveable until I took out the 37mm venturies and put 32mm venturies in those 48s, that's the smallest size they made for the 48 IDA. Good luck with your project, let us know how it goes for you.
Jim Inglese has already stated that it will require chokes that weber does not make. They will be custom made and smaller than 32mm. At this point, he wasn't too concerned about setting them up.
Have been considering a pair of webers on my 260 cu in flathead. What is the difference between ida and idf? Thanks, Harley
IDA is larger in size, somewhat harder to tune for the street but it can be done. IDF's were alot easier to tune for street driven cars. Drilling the third hole in the progression port helps alot when setting up the IDA's. Some of the older race carbs did not have that and it was idle, or wide open operation. I am using these for mock up, just because its what I have and the ports line up from carb to manifold. If science doesn't let it work, well at least I tried.
This ^^^^ Get some 40 IDF's [they were OEM on Alfasuds ,and they are cheap] They look similar to an IDA but the bolt pattern is different
I posted how to do the ir calculations on another thread, as well as the Vizard stuff on the IR small-block he built, but a bunch of guys bitched, so I deleted it. chug the Kool-Aid! Since the only reason to run a flathead is to "kick it ol skool", why would you want to run webers on one anyway? Doesn't make any sense to me, but then, most of what I read on here doesn't make sense to me, so what else is new?
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