ideal port size for a 2.2 with mod solex cams?

[RobFrost]

Hi, my current plan is to take my 2.2E engine up to 86mm barrels and mod solex (DC30) cams with the intention of getting a bit more high-revving top end pull, but without losing too much in the way of mid-range driveability. As I undertand it, these are somewhere between E and S, with some modern improvements.

It'll be a counterweighted crank so should be safe revving nice and high.

I've not totally decided whether to go 9.5 single spark or 10.5:1 twin and I totally understand that decision will affect the answer to this question.

The heads are currently E heads, so already have 32mm ports. I'm just pondering the wisdom of taking it out to 36mm ports (assuming all other factors - exhaust / fuelling etc. are optimised). Will that increase the top end power significantly, and does anybody have relevant experience of how severe will the compromise be at low flow rates, in each of the two compression scenarios?

[Lightweight_911]

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Are you planning on retaining the mfi or switching to carbs ?

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[RobFrost]

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Are you planning on retaining the mfi or switching to carbs ?

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It's going to depend on the cost of re-camming the MFI. I have a set of Webers already but I'd like the better atomisation of fuel injection, of course. And MFI is part of the legend of these old engines. But my pockets have finite depth. It had also occurred to me that the MFI injector port could be affected by port machining, and I know little about that.

[neilbardsley]

I think you should of asked Mike Champion this question the other Sunday:). I think he has some software that will simulate/calculate this for you. As for if it's cost effective for you to ask or for Mike to answer this question is another question entirely

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[911hillclimber]

Yes, that could be a bit of a Trade Secret for those earning a living from this stuff.
Rob, does the Dempsey book give some leaders on this?

[RobFrost]

I noticed this week that the head intake ports are 32mm but the mfi stacks are tapered from 35mm to 37.5mm. With the throttle bodies tapered the most steeply, from 32 to 35.

So it's designed with steadily accelerating air, which I presume is a deliberate part of the design to maintain momentum of the column of air.

The greatest opportunity for improvement appears to be at the throttles themselves. The throttle flap itself is quite thick, with sharp corners and no aero over the shaft.

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[RobFrost]

I noticed this week that the head intake ports are 32mm but the mfi stacks are tapered from 35mm to 37.5mm. With the throttle bodies tapered the most steeply, from 32 to 35.

So it's designed with steadily accelerating air, which I presume is a deliberate part of the design to maintain momentum of the column of air.

The greatest opportunity for improvement appears to be at the throttles themselves. The throttle flap itself is quite thick, with sharp corners and no aero over the shaft.

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In response to some data I saw online, I checked the measurements I recorded. I had only made a mental note of these, and typed them here later, so I thought I had probably remembered wrong.

That did indeed turn out to be the case. The true facts are... the throttle body tapers from 32 at the port to 35 at the stack end. Then there's a sudden step up where this meets the stack, as the bottom of the stack is 38mm and continues up to the top at that diameter.

I'm not sure how the sudden step from 35mm to 38mm helps with flow - unless it causes the pressure wave to bounce back towards the cylinder at some high rev range. My gut feel is it'd flow better smooth, so I should gently taper the throttle body up to 38nn. But flowing the intakes is probably more of an art than I can investigate.

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