polished exhaust ports?

[Simon m]

Hi

Is there a way to sensibly modify an unleaded Cylinder head, and or cam shaft, to squeeze a bit more HP out of a 1098 engine? There are some pretty wild claims about how polishing the head or just the exhaust ports etc can increase the power etc but I am a bit cynical tbh.

Would anyone, please, be able to give me a view on how much it would likely cost to have the head polished or cam 'reprofiled' (is that right?) and, as a guesstimate, what is a likely realistic increase in HP, if any at all ?

Apologies if this has already been answered elsewhere.

Cheers Si

[philthehill]

Unless you get the head and the camshaft modified by a reputable company you will be throwing good money after bad.

I would suggest that you purchase a head already modified and a new sports billet camshaft from known tuning companies.

You are talking about spending several hundred pounds plus of your hard earned cash if you want it done properly.

You will increase the power output bhp but you do need to make sure that the engine is in good health before modifying anything.

Here are two examples:-

https://www.minisport.com/stage-3-1098c ... -head.html

https://www.minisport.com/ken246m-bl-ke ... drive.html

Just polishing the ports and changing the camshaft is only the beginning!

[Simon m]

Cheers, much appreciated.

Confess having seen the costs I will probably just leave as it is

[philthehill]

You can do the job cheaper by using a standard 12G295 head which bolts straight onto a 1098cc engine and a standard MG Metro camshaft. Both will increase the power output but again a S/H 12G295 head will cost around £250 and a MG Metro camshaft around £70. Add the cost of a larger carb and manifold (approx. £75) to make the most of the larger valve, better port head and better camshaft.
Which ever way you go the costs soon add up and you still have to make sure that the engine is in good health before doing any modifications.

[Sleeper]

I think there are two trains of thought re. polishing the inlet ports , one ( polished ) is that it helps gas flow , the other ( rough ) is that it helps swirl the mixture... ?

John ;-)

[philthehill]

The ports do not have to be mirror finish polished just smooth and well shaped.
These are the ports of a Manx Racing modified 940 head similar to that fitted to my Minor. As can be seen they are not mirror finished.

Manx head 8.jpg (302.77 KiB) Viewed 980 times

Manx head 7.jpg (482.48 KiB) Viewed 980 times

[don58van]

My understanding is that the idea that highly polished ports increased power by increasing flow has been debunked by tests on flow-benches by the likes of Vizard.
Think about our Olympic-standard swimmers. On the basis of extensive research, they have been wearing full-body suits with shark-skin-like (a type of fine roughness or texture) surfaces to reduce their drag through water. They have been banned because of the huge advantage they give. This is analogous to air and port walls in cylinder heads.
So, unless I am very much mistaken (I miss Murray) high polish increases drag.
This is all from the dark recesses of my mind, so if anyone wants to challenge it--by all means go for it.

Don

[Myrtles Man]

I believe it's the same branch of physics that leads to golf-ball manufacturers using dimpled surfaces rather than smooth ones; something about laminar airflow I seem to recall. They know rather a lot about it in the aircraft world too from studies of airflow over wing surfaces etc.