[Fot] Weber vs Mikuni

[Ted Schumacher]

SU sizing. All side draft SU's start with the premise of a 1" throat. 
Then the larger sizes are given in 1/8" increments above the 1" throat.  
So an original Bugeye Sprite for example, used 1 1/8" carbs or "H1", TR3 
used 1 3/4" or "H6". Ted


On 10/18/2018 5:48 PM, van.mulders.marcel--- via Fot wrote:
> 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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-- 
Ted Schumacher
tedtsimx at bright.net
http://www.tsimportedautomotive.com
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