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MG MGB Technical - DIY head porting

A few years ago I ported out the head of my MGB. The only major modification I did was to trake out that step made in the intake ports when there were counter sunk to match up to the intake manifold. I say counter sunk bit from the looks of it a ball cutter was used to do this. I ground out this step and enough material to make a nice smoothe transition from the head face to were it branches out to each valve port. I was running a Kent mild road cam at the time. I would run the car down the road at a constant RPM and at a half mile or so all the power would go out of the engine and it seemed it would shut down. Letting totaly off the gas, it would recover. This happened consistantly. The only thing that solved this problem, after investigating fuel supply solutions with up-rated fuel pumps and richer carb needles was to raplace my DIY ported head with a stock one. I'm not positive I had the cam timed in correctly but I think I did. I have since replaced it with a Crane cam, that I am very satified with by the way, and I am positive it is timed spot on. I was thinking of trying my DIY head again with this Crane cam as it is an earlier head with the larger intake valves and bronze valve guides. Does anyone have any experience as to weather I have messed up the air flow in my DIY head by the the modification previosly described?
Dave Bush

Dave, I don't have experience with DIY porting but if you didn't do some work on the exhaust ports you will probably not see any improvement. I do have two heads that were reworked by Mike and Sean Brown, they made some rather extensive alterations in the exhaust ports. The heads work very well with the modifacations they do and they give a very noticable performance improvement. A note to Mike and Sean can give you a better answer. I lost their email from my bookmarks but someone will come up with it. FWIW, Clifton
Clifton Gordon

I did open up the exhaust ports to match the exhaust manifold gasket. And smoothed and flowed the exhaust ports under the exhaust valves. I have a feeling that I somehow changed the air flow through the two intake ports by grinding and smoothing out those champhers. But I have been totally unsucessful in finding anyone with any hands-on experience on this. May be the only way to find out if I've botched this is to try the head again with this Crane cam. For anyone who's interested, I puchased the Crane from a local American mustle shop for a good 40 bucks cheeper than getting it from Moss. Also some yahoo at moss assured me that this cam would'nt do a thing for me unless I was setting it up useing an earlier 60,s head. Not so. The cam improves perfomance real well, even using a late model head with the smaller intake valves. I would really like some imfo about my porting on this big valve head before I go to the expence of at least one , perhaps two head gaskets to try and run this head again. I had a valve job and bronze valve guides installed on this one too, and would like to use it if posible.
Dave Bush

I very much doubt that the porting is the cause of your problem.

It is just possible that the valve guides are too tight and are partly seizing on the valves.

The symptoms point to fuel starvation or carb icing. I think that the ported head is causing the mixture to run weak at part throttle opening and you need to go for a richer needle - preferably chosen with the aid of a rolling road.

I would have the guides reamed to the correct dimension and try the head again.
Chris Betson

Mike Brown's email; sevenshop@terragon.com

I got a head from him too. Very good work, yet I haven't installed it yet to report performance. He suggests mods to the carbs as well (and other components) matching mods to the head. Good luck. -Brian.
Brian Johnson

Dave;

I also have ahead ported by the Browns, excellent work. From my experience with their work, and porting I have done for myself over the years, I would agree that you did not do any damage to the performance of your cylinderhead with the port/manifold matching you have done. What you did falls under the category of "blueprinting", not "porting".

The intake ports on the standard "B" head are not really all that bad; the real gains come from some serious modification to the exhaust ports which are really pathetic. The problem for the home tuner is that it takes a lot of experience to know exactly how much and from where to remove the material. People like Sean and Mike have learned this stuff over years of trial and error and intuition, not to mention carefully honed manual skills.

I think you will find your"old" head porting job was not the source of your problem. Put it back on there and progressively eliminate other possibilities, like tight valve/guide clearances, lean spot on the needle, etc.


And then for some "real" power gains, consider letting a pro at your head with the die grinder!

Best of luck,

Dave
Dave

hello,
found a site withe some info about porting heads, it could be of some help. I found my information there and it works verry well.
greetings
http://www.sa-motorsports.com/diyport.htm
mg-mike

This thread was discussed between 03/03/2003 and 06/03/2003

MG MGB Technical index

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