[Fot] Weber vs Mikuni

[van.mulders.marcel at telenet.be]

Glen, 
With 1 1/2s carburettors, I suppose you mean HS4? The SU logic is a little weird. 1" + 1/2" = 6/8" so you would think it are HS6s, but when talking about HS carburettors, 1 + 1/2 = 1 + 4/8 and they took the 4 to name these carbs HS4... 
Marcel 


Van: "fubog1" <fubog1 at aol.com> 
Aan: "van mulders marcel" <van.mulders.marcel at telenet.be>, "Mike Harmuth" <ofracer at gmail.com> 
Cc: "fot" <fot at autox.team.net> 
Verzonden: Donderdag 18 oktober 2018 22:39:39 
Onderwerp: Re: [Fot] Weber vs Mikuni 

Well I won't speculate on the cause, but I doubt that it's the SUs. 
My small crank 1300 w/1 1/2s on a eurospec manifold w/Stahls header, "big" valve head, would buzz easily to 9k, still making power, if I let it. 
Normal shift point 7800-8000. 
FWIW... 
Glen 


-----Original Message----- 
From: van.mulders.marcel--- via Fot <fot at autox.team.net> 
To: Mike Harmuth <ofracer at gmail.com> 
Cc: fot <fot at autox.team.net> 
Sent: Thu, Oct 18, 2018 2:12 pm 
Subject: Re: [Fot] Weber vs Mikuni 

-"...hitting a wall at that point..." : is it possible this is rather pointing to the camshaft than to the SU's? If it are the carburettors, maybe the power would decrease more gradually above 6500 rpm. 
-In general one choke per cylinder is better, and 2 Webers 40 DCOE isn't overkill I think 
- what about trying HS6 SU's on your actual manifold? 
At what maximum rpm is your engine still reliable? 
Marcel 


Van: "fot" <fot at autox.team.net> 
Aan: "fot" <fot at autox.team.net> 
Verzonden: Woensdag 17 oktober 2018 15:49:45 
Onderwerp: [Fot] Weber vs Mikuni 

I'm looking into switching out my twin HS4s on the 1296 race engine to either Weber or Mukinis. I know this has been done for years and I'd like to get close the best set up out of the gate. 

I don't think the SUs are up to the task of moving enough air with the new ported head and Stahl header. I've worked on the SUs and gotten them to finally deliver a good AFR , 12.6, at 6500 RPM under load but I seem to hit a wall (figuratively) at that point. I suspect that the openings just aren't big enough to deliver the mass of air required. (spreadsheet or other flow calculator link appreciated) 
Biggest gate I suspect is the intake valve, 1 3/8" head (~35mm) HS4 is ~38mm at best. 

Recommendations? I've seen all these setups at the track, each with pluses, minuses and overkill cause it looks cool. 

One weber DCOE 40 or 2? what jets, tubes etc for a starting point? Best manifold? 

2 or 4 Mikuni 40? jet size? 

thanks 
mike 

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