Speedwell Manifold Question

[gimmesomeshelter]

I just received a set of new speedwell manifolds. The good news is that they were promptly shipped, well packed, and look fantastic! My only concern is that the intake ports are 45-46mm wide. I assumed they would be 40mm. I'm thinking of using some DRLA 36s. Will the port mismatch between the Dellortos and the manifolds decrease the air flow? Would it be worth the time/money to have the manifolds welded/ported so they match my carbs?

Manifolds from Speedwell:

Manifolds from Stefi.g:

Manifolds from Mr. Okrasa (in development)

Cheers,

Paul
_________________
"I would rather have questions that can't be answered than answers that can't be questioned."

Richard Feynman

[[email protected]]

I don't see a problem using them as is ..i couldn't find a post that guys were talking about wider intake ports with smaller throttle body and I remember lots of folks were saying that it's not a problem if the manifold is wider ..only problem you would have if the carb was bigger than the manifold than you would have a problem and would have to open up the manifold ...but if you don't want the speedwell ones I'll take them since I need them 🙏

[motofly196]

How the hell did you get a set of Speedwells? I tried for over 6 months, and just gave up finally...

[John Moxon]

[alanhall]

Paul,
Theoretically, from a fluid mechanics point of view, a backward facing step in the flow path (as you would have w/ this manifold) is almost as bad as a forward facing step. But practically it would probably work OK, however, if you had room, a block maybe an inch thick or so where you transition from the carb base diameter (40mm?) to the 45/46 mm diameters might be a fairly easy solution.

Obviously it would be best to have a manifold designed for the size carbs you are using, with afairly uniform flow area throughout the manifold.

How big an engine is this all going on?

[gimmesomeshelter]

"How the hell did you get a set of Speedwells?"

I just sent an email to Ray asking when his next batch would be available. I've had pretty good luck buying items from Ray, but he's never responded to any of my requests for technical help (e.g. "which springs should I use with my ratio rockers?").

My goal to have an engine similar to 356 Super. The displacement will be 1588cc, and the max RPM will be 5000.

Cheers,

Paul
_________________
"I would rather have questions that can't be answered than answers that can't be questioned."

Richard Feynman

[TomSimon]

I've run 48IDA's on manifolds welded and ported out to 52mm. The 2165 engine didn't notice a a bit of difference. I latter added a pr of 52's, and it didn't really pick up in power.

My guess is the engine liked the additional intake runner volume, and maybe the intake tract reversion pulse, said to hug along the outer wall of the intake tract, was being partially stripped off by the mismatch 'step'.

A reversion pulse, present in most race engines with large overlapping cams, is evidenced by this 'fuel fog' that is observable by the naked eye, hovering about 1-2" above the velocity stacks at higher rpms. It's quite a sight.
_________________
2-time NASA Pro Racing Champion, Bonneville 130 Club and 150 Club Memeber, BRS Pro Gas racer