Engine Rebuild

Post by **webbnuts** » Sat Sep 01, 2007 11:40 am

My understanding is the better the airflow in and out of the engine, the better it will be.

I thought ideally you wanted a mirror finish on the exhuast thoats and match the size of the ports to your exhaust manifold, where as you want a slightly rougher surface on the inlet ports so the fuel hits the surface and vapourises?

I am sure Vizzard knows what he is on about by now! The way i see it, two heads on two standard engines, polish and port one and that engine will be more responsive than the other.

Post by **picky** » Sat Sep 01, 2007 1:29 pm

There is alot of debate as to the performance gained from polished ports - eve those who do believe it makes a difference will admit the advantage is very slight, and it takes many hours to get a mirror finish. Porting the exhaust ports will make a big difference but porting the inlets will add even more. Remember a much larger volume of gas goes through the exhaust than through the inlet.

Post by **Orkney** » Sat Sep 01, 2007 2:59 pm

Polished out yes
Polished in debatable.
look at a weber and if you were obsessed with performance youd say hey that venturi could be aerodynamically streamlined quite a bit to get it through more efficiently.
Point is that doing so may minimally improve through flow but not necessarily the actual mixture and ignition of.
Think water injection - idea that you get the finest of mist sprays going in - oil (well petrol in this instance) is drawn to the surface of these mini droplets - increases the ignitable surface area dramatically.
Vortices seem to be good - theyve proven that covering an aircraft wing with dimply sticky back plastic has a drastic effect - not because of the increase in physical surface area but because of the mini vortices they cause actually result in a smoother and overall more efficient airflow.
On that basis a rough casting finish on inlet should = better burn, think i'll have to dig out the Viz bible and see whats said about it now cause I need to know !

Post by **bmcecosse** » Sat Sep 01, 2007 4:13 pm

But the exhaust ports and valves on the 940 head are PLENTY big enough for your 1098 to breathe through - provided you open that corner where the valve guide boss and the corner of the port almost touch. Opening that gap up will suffice - do more if you wish but the returns will be minimal with the 1098 engine. In fact exhaust ports should be smaller than manifold at the join - this to cause vortexes which will inhibit the return flow - but will permit outward flow. So they say - i have my doubts if it makes all that much difference!! On the inlet side - opening up the throats to only leave a thin inlet valve seat is a great idea, and some work on that corner and removal of guide boss helps too - but otherwise there is plenty of flow for that 1098 engine - the head won't be the limiting factor!

Post by **webbnuts** » Mon Sep 03, 2007 10:41 pm

here's the next question then, i have been offered a metro 1300 a series. Is this any good for my morris, eg the head and carb etc or is it no good. Am i right in thinking that you cant use the fwd a series in a rwd car? Thanks for all your help. It is very much appreciated.

Post by **picky** » Mon Sep 03, 2007 10:51 pm

head and carb are all good, as is camshaft. the fwd engine block cannot be used, although it is apparently possible to convert it for rwd use, you are probably better off using a rwd block.

Post by **webbnuts** » Tue Sep 04, 2007 6:48 am

When i say 1300, would that be a 1275? The scrappy i spoke to said it was a 1300, but i thought they only went up to 1275? Its tempting to get and bolt all the bits in/on my 1098 during the rebuild - winsu reckons it would be 65 bhp at the flywheel! Yay!

Post by **picky** » Tue Sep 04, 2007 9:50 am

1275 is rounded up to 1300 in the same way that some people would call a 1098cc engine a 1100, so the engine he is talking about will be 1275cc. you can have the cylinders bored out slightly and go up to 1380cc - 1400 but you need wider pistons etc. I have heard of a 1600 A series

Picky

Post by **bmcecosse** » Tue Sep 04, 2007 10:53 am

The head + carb will be worth having - but don't pay much for it. The inlet manifold not ideal - you want one (alloy) from an MG Metro. Standard metro cam is same timing as 1098 cam - except they ran it forward by 4 degrees - not worth the hassle. MG Metro cam is well worth having if you can find one.
Very doubtful you will have 65 bhp - it's all the same parts as the 1275 engine - which only gave 55 bhp!! So no chance a 1098 will even match that unless the MG parts are fitted, and with a decent exhaust manifold and system too!