Porting Single Carb Manifold

[Clan]

Originally Posted by Burdekin

Not necessarily; if the casting has sharp turns, sharp edges, casting defects and things like that I would imagine they slow the flow of air so removing those would increase the velocity or maybe better put there will be fewer obstacles to slow it down. Of course volume is removed in these localised areas but at this stage I'm not thinking of increasing the port sizes unless they are undersized at the moment.

The same design of stub stack I added to the carb intake was flow tested by David Vizard and it increased flow by 5.8%. It did this by having a large radius and eliminating the sharp edge. So that's the sort of thing maybe could be done inside the intake, giving the air an easier path.

I'm looking at a supercharger for another project but this one is staying original, or looking original.

I think you are lucky in having a pretty well designed manifold , why not go for twin carbs ? but it you don't explore the range above 4000 rpm where the differences are noticed , its not worth doing anything really ..

[Burdekin]

Originally Posted by Clan

I think you are lucky in having a pretty well designed manifold , why not go for twin carbs ? but it you don't explore the range above 4000 rpm where the differences are noticed , its not worth doing anything really ..

Originality. I remember Dai (Classiswede) commenting previously that the manifold was poorly designed, restricted flow and he would like to get a better one made so am keeping an open mind. I was hoping someone may have previously done some modifying and could offer advice. Under 4000rpm is where I want to improve. I'm not chasing max HP, I'm just tinkering to see what works. I'm looking at improvements down in the low to mid torque range. It pulls considerably better than when I first got her and I was so happy on Saturday morning with the test runs with the new carb metering needle and the intake set-up mods. The O2 wideband was showing I hit the numbers I wanted.

I think I've nailed the suspension, geometry and tyres as she drives really nice and could handle plenty more power or feels like she could but I love the charm of the originality of the car but eeking out a bit of extra performance from areas that aren't seen is what I am exploring.

[Derek UK]

We're talking fractions but you might increase the torque but having a longer trumpet on the carb. Good if you can keep it inside the pancake filter.
Smoothing out the inlet tracts can reduce atomisation and that's a negative. Do not polish the surfaces.

[Burdekin]

Dug out a spare to have a gander. The casting is not too bad for what it is, the bend/corner into the outside runners isn’t as bad as I imagined but there are some sharp casting bits and the corner could be blended a little but you’d have to do it by hand. The outtakes have been machined a wee bit inside as you can see from some of the pics and this has created a ridge so this could be blended as well. Overall though there isn’t a lot that would be done I don’t think and the design is what it is.

[Burdekin]

Having a read through my David Vizzard and other SU modifying books last night and might have a play with a Stromberg and see if it can be made to flow a bit better. Anyone have a old Stromberg 175CD2SE they’d be willing to sell?

[Clan]

Originally Posted by Burdekin

Dug out a spare to have a gander. The casting is not too bad for what it is, the bend/corner into the outside runners isn’t as bad as I imagined but there are some sharp casting bits and the corner could be blended a little but you’d have to do it by hand. The outtakes have been machined a wee bit inside as you can see from some of the pics and this has created a ridge so this could be blended as well. Overall though there isn’t a lot that would be done I don’t think and the design is what it is.

Those stepped recesses are for rings to centre the inlet manifold ports to the head . PN 418408

[Burdekin]

Originally Posted by Clan

Those stepped recesses are for rings to centre the inlet manifold ports to the head . PN 418408

Inside the runners is machined, you can see it in the pics with the silver to dark area. There is a step at the dark area so could be blended there better.

[DWeed144]

I had been doing some cad work on a single carb manifold which would then work for a shorrock C142b supercharger as well. With all the air flow analysis available on solidworks it was quite easy to optimise it as far a possible with no particular expert knowledge. It is remarkable seeing what a few degrees of taper in the plenum chamber do, or as you say burdekin, a more generous radius on each of the cylinder feeds, for air velocity and equal delivery between cylinders.
I was designing for casting as I can do that myself but given how cheap it is now to send things out for cnc machining I wonder whether it would be worth redesigning. Interest levels peaked before I got to acutally making it....

[Burdekin]

Originally Posted by DWeed144

I had been doing some cad work on a single carb manifold which would then work for a shorrock C142b supercharger as well. With all the air flow analysis available on solidworks it was quite easy to optimise it as far a possible with no particular expert knowledge. It is remarkable seeing what a few degrees of taper in the plenum chamber do, or as you say burdekin, a more generous radius on each of the cylinder feeds, for air velocity and equal delivery between cylinders.
I was designing for casting as I can do that myself but given how cheap it is now to send things out for cnc machining I wonder whether it would be worth redesigning. Interest levels peaked before I got to acutally making it....

Nice work. I’ll take two. 👍😉

Now I’ve done the engine mods even though nothing serious I’m now just playing about with the intake side and seeing what the single Stromberg is capable of. I might also see if I can get it dyno’d as a baseline in the near future.

[Army]

Originally Posted by DWeed144

I had been doing some cad work on a single carb manifold which would then work for a shorrock C142b supercharger as well. With all the air flow analysis available on solidworks it was quite easy to optimise it as far a possible with no particular expert knowledge. It is remarkable seeing what a few degrees of taper in the plenum chamber do, or as you say burdekin, a more generous radius on each of the cylinder feeds, for air velocity and equal delivery between cylinders.
I was designing for casting as I can do that myself but given how cheap it is now to send things out for cnc machining I wonder whether it would be worth redesigning. Interest levels peaked before I got to acutally making it....

Having access to Solidworks is a luxury - how did you determine the air flow requirements?

Way way back in the day when I was learning about (now really old) FE software the main thing that was taught was to not always believe the number that gets produced. This kind of makes it interesting to learn how you set the flow requirements? Can you also fiddle around with wall roughness in the model or is it not that advanced?