What is worth modifying on the inlet manifold ?

[mtb_tuli]

Just working on my SD1 heads, which means enlarging resp. smoothing the ports, not too much, just "smooth".
Yesterday I have dismantled the HIF carbs, everything ok, but will use the SU service packs.
The adapters (at the carbs) for the ellbows have a terrible "design" inside and the gasket restricts the inlet further. Have modified them and will install them with Hylomar (no gasket).
Have looked on the (standard 3.5) manifold which came back from blasting and the ports also look very raw. Smoothing is no problem, but is there any advice with the manifold from the experienced guys here ?
It´s the first I do this, so I thought about matching the inlet manifold to heads, but the holes in the inlet manifold are so large, you can mount it "some millimeters" in all directions. The ports of the inlet manifold, for sure, are significantly smaller than the ports of the heads, which is ok with this variance in mounting, so I think, it can be even worse to enlarge the inlet ports or there is a trick to match them ?

 

[clive P62]

I cleaned up the inlet ports on my vitesse heads only to remove the Sharp area behind valve seats.
Port matching is a good idea if it can be done accurately.
On the old mini you would dowl inlet in place with gasket to get correct line up.
Engine tuners do not mirror polish inlet ports as this can make fuel pool and not atomize , just leave them a ground finish.
Exhaust ports can be polished.
Clive

 

[mtb_tuli]

With the gaskets it works also on the heads. Manifold to heads looks different. Suppose, you have to (pre)install the heads and put everything together with marking colours, but you have to do it without the valley gasket and with the gasket, position is again different.
Lot of work, must think about, if it´s worth....

 

[ratwing]

I bolted the manifold to the engine with a cardboard 'gasket', then I unbolted the manifold and could see where the manifold and head port edges were.
Because my heads have been skimmed, the manifold sits lower and the bolts only just go in and doesn't move backwards or forwards - on a standard engine I've noticed the manifold can move backwards and forwards slightly before the bolts are tightened so I don't know if the card board gasket would be an accurate way to match the ports here?
Maybe you could mark the the heads and manifold so the manifold always gets bolted back in the same place?
It would be good if the manifold could be dowelled but they'd have to be parallel or you won't get the manifold on.
I used this pattern to remove the minimum of metal from the inlet manifold although I should say that my heads have had a little work on the ports and are slightly larger than standard.
I used a composite valley gasket and found it stuck out past some of the port edges. It wasn't much, only about ½mm but every little helps so I filed metal off the gasket to match.
It is important not to just open the head and manifold ports up to the size of the gasket or they'll be a poor shape - they'll get bigger heading towards the gasket then smaller towards the valve which is all wrong for a good flow.
I ground out the lumps and bumps in the carb - to - elbow adapters to try and get an even curve, also tried to smooth out the elbows (but I couldn't reach all the way inside them) and match the diameters at the joins.
The black plastic heat insulators were smaller than the carbs so I opened them out to match the carbs.
The tower on top of the manifold was a little smaller than the carbs too so I opened it out to match and also removed as many of the casting marks as I could reach from both the top and bottom of the manifold.
It's worth reducing the height of the valve guides sticking into the ports and put a taper on them too, if they don't need replacing then you can make a cutter that fits in the valve guide so you don't need to remove them from the head.
I don't know if all this has made any difference because it was done on a new bigger engine build but it only cost me my time and I can't see it doing any harm.

 

[mtb_tuli]

Great ! That helps. The "master" gasket is a good idea. My heads will also be skimmed, so I will place the manifold on the lower direction and will mark it.
Heat insulators fit exactly to the carbs and tower already. It´s a manifold from a later Land Rover, maybe they tried to make it better...
The gaskets (carb to manifold) on this one have an inner ring with a "shark teeth" opening (they are really sharp...), maybe to improve mixing when goeing into the manifold. The gaskets on the original P6 manifold did not have them.