removal of obstructions/hot spot Ruby manifold

[Zetomagneto]

I'm just a sheep... sorry. I was thinking it was about heat transfer, but it just seemed a good idea as saw it written down. Hopefully others will answer!
(If it doesn't work then I'm happy that I've removed a few grammes, which is sure to help acceleration)

A cool charge gives more power so reducing the hotspot is a good idea, also if you can duct air into the area of the intake this will help rather than letting the carb draw in warm air from the engine compartment.
Always makes me laugh when you see these boy racers who have put a cone air filter in the engine compartment whereas the OE filter always takes air from outside the engine compartment.

[Robert Leigh]

As far as matching ports goes, I feel that if the manifold inlet ports are not blanked at all by the block there is little to be gained by removing metal, and like wise in the exhaust ports try to be sure that the manifold does not blank the block exhaust ports. You will get smoother gas flow by having the ports exactly matched and polished, but it is a diminishing returns situation in relation to effort.

["Slack Alice" Simon]

I removed the manifold, ground out the "restriction", and replaced it.

No improvement at all.

But:   there may be other factors affecting the result, I'm afraid.   I subsequently found that the engine is fitted with particularly wicked oil control rings, such that there is quite a lot of resistance to up and down movement of the pistons.

Which may have masked any change made by opening out the manifold.   Which may also be the reason that my raised compression early head made not a lot of difference, either.

Simon

[Speedex750]

Hi JonE,

I've done a couple of these, one being a Reliant downdraught type. The only extra thing I did was to hacksaw down to the manifold stud holes either side of the inlet ports. I did hear a while back that on flow testing, the restriction in the cross over part of the side valve engine was such that the other parts, including the eye in the inlet flange, didn't cause any ill effect. Matching ports has little effect on oversized ports like the A7. If you want to do something just make sure the downstream side - the block port - is slightly tapered so that any square edge at the join is on the upstream side rather than facing into the airflow.

Hope of use, Dave

[JonE]

Dave - the first bit presumably to further reduce the percolation of warmth into the aircharge-stream walls?
I've ordered another pack of ebay Hong Kong grindstones...!

[Paul N-M]

Dave - the first bit presumably to further reduce the percolation of warmth into the aircharge-stream walls?
I've ordered another pack of ebay Hong Kong grindstones...!

Well if removing the hot spot from the standard cast iron set up your pics show you will not see much if any improvement. That is because even though it reduces the charge temp it will only do this for a very short time as the cast iron exhaust/inlet combination will heat up and take you back to square one very quickly. So the hot spot helps with initial cold running. A larger carb in theory can flow more air/fuel but as the shape of the inlet is soooooo bad it will be marginal and thats assuming you have optimised the jet/needle.

Paul N-M

[Colin Reed]

HI All,
Has any one done a proper test on the blended Fuel that is used in the UK, To ascertain if it is at all necessary to remove the hot spot , the seven is not the only engine with this feature .
and as Paul points out  it will only work till the Whole manifold heats up.

Colin
NZ

[Bob Culver]

Hi Slack Alice

It is an aside but when I was running my car as everyday transport eons ago the neighbours sons worked with Lester Reeder on specials iand on his Rubber Duck. They had all run Sevens and were adamant that the steel 4 piece type oil rings killed performance. They reckoned Sevens only went best when worn out!