Lotus Elan

Knife-edge Stromberg in Siamese ports

PostPost by: promotor » Tue Feb 20, 2018 5:54 pm

I have purchased a Stromberg cylinder head that I think is scrap and would be interested in peoples' thoughts and opinions.
Does any one have experience of porting/using a Stromberg head with knife-edged inlet ports? To clarify the knife-edge I'm referring to is at the join between the two siamesed ports.
It is my understanding that knife-edging the leading edge where the Siamese ports join causes disruption to the flow.
I think this cylinder head would have been OK had the porting work just been kept to the bowls and throats. I have a feeling that this head had been removed as it wasn't performing very well.
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PostPost by: jono » Tue Feb 20, 2018 6:01 pm

That's my understanding too based upon porting a few Mini heads and following Des Hammills instructions.

You want a radiused edge, not a knife edge.

That assumes that the flow principles are the same for a TC head of course.
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PostPost by: pauljones » Tue Feb 20, 2018 6:03 pm

Not that im expert in anyway, but strangely ive spent a lot of time recently researching mods to the twink. Every article ive come across says it should be blunted and shaped. i think David Vizard says the same.
In Miles book pg 35 to 37 it shows the blunted profile.

Hope it helps
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PostPost by: denicholls2 » Tue Feb 20, 2018 8:57 pm

As the person I'm aware of who has made the best use of Stromberg heads in his conversions, I'd defer to John McCoy. I know he strips a lot of the inlets off to do so, don't know whether your head would be a suitable core for that work or not. Worth an ask.
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PostPost by: rgh0 » Wed Feb 21, 2018 12:04 pm

With the siamesed intake ports the flow goes first to one side and then to the other. A sharp centre divide causes flow separation and turbulence as the flow goes across it to the port that is drawing at the time and thus restricting the flow. It is best to round it off to reduce this separation and turbulence.

Why a Stromberg head did not "work" when tuned is probably related more to the cam selection and carb tuning than to the flow divider itself. The Stromberg heads will tolerate a long duration cam much worse than a Weber head

.I agree the best use for a Stromberg head is a McCoy conversion

cheers
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PostPost by: RogerFrench » Wed Feb 21, 2018 2:01 pm

Can't you round off the knife edge?
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PostPost by: promotor » Sat Feb 24, 2018 9:37 am

Thanks for all the replies.

My plan was to get it running in a standard level of tune and see how it works out without deviating from a known starting point and then work backwards but didn't really want to start with it if I'd be chasing my tail forever. It looks like there's a slim chance I may not chase my tail forever with it so may give it a go.

Rounding the sharp parts off definitely needs to be part of the plan but I'm not looking forward to holding the tool to blunt off the edge - I might have to make some steadier/jig to stop the drill tool wandering down one of the ports, and to also not go too deep with it.

I can't believe someone even went to the trouble of porting this head!
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