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DIY Head Porting

Posted by MGB_Norm 
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I have a 12H2923 MGB head, the one with the larger 1.625 inlet valves, and am considering doing some DIY porting work before getting the valve seat inserts/valve job/surfacing work done. Peter Burgess's book "How To Power Tune MGB 4-Cylinder Engines For Road & Track" describes how to do porting, with several different stages. I would like the "fast road" variety, which you can purchase from Peter here:

I will probably be using a 270 cam, modified & rebuilt HIF-4 carbs per Peter's book, and most likely a Peco exhaust system.

Wanting to save some cash, and feeling that I have the necessary skills and most of the tools to do the job myself, I would like to do it. I will need to buy a few carbide grinding bits. Problem is, after reading the instructions I still don't feel that I have 100% of the knowledge required to do the job. I would like to find some more detailed photos/instructions/measurements of how to do the work, as I do not want to end up cutting into a water passageway.

Any tips/information/photos would be greatly appreciated!

PS I am doing a restoration on my 1974 MGB, and most of the engine work. The bodywork will be done elsewhere. The tuning level needs to support some mountain road driving, along with interstate travel occasionally, and yes I did also purchased an OD trans. I am also planning on doing a full rebuild to the block with probably a .020 overbore, balance, higher compression pistons, possibly a vernier cam gear set too.

I had the head pressure checked (under water) and there were no leaks.


rcedward Avatar
Rob Edwards
Raleigh, North Carolina, USA   usa
1951 MG TD MkII "TDC6000"
1969 MG MGB "182608"
1969 MG MGC GT "8806"
1969 MG MGC GT "Rcedward"
1970 MG MGB GT "Donor"   → more
The best advice? Pay the money and send it to an expert. There's a definite art to it, and you won't pick it up out of a book (at least not without a bunch of cracked heads to practice on AND access to a flow bench.)


Rob Edwards
Raleigh, NC

If you're in NC, check out the North Carolina MG Car Club!

Sean Brown Avatar
Oregon, USA   usa
1976 MG MGB
First get all the guides out of the head before starting.

The exhaust guide boss needs to be cut down until it measures 1.3" from the spring seat. (see Burgess's book). Other than that, leave the exhuast alone for a DYI job. Do not be tempted to open the port out to the size of the gasket as that will only make matters worse. Polish the short turn only, do not alter it at all.

On the inlet side, the biggest gains come from narrowing the center port divider. I'd be sure to make it concave rather than convex. Do not sharpen the point, just leave a small radius on it. On the 2923 with the intended use in mind, do not over-work the area around the guide to "deepen" the bowl, it won't do much good for you. Do not alter the short turn much either. Peter's recomendations for race engines do NOT apply to what you're doing.

Lastly, working the pushrod junction area just in from the manifold face can be of benifit, but you must be sure you do not make the turn more abrupt. Blend on the top and bottom of the port wall (corners) so that the apex of the turn is cut away making a larger radius through this area and leaving the middle of the port wall basically untouched.

I wouldn't bother polishing anything for myself, but if you do, use 60 grit on the inlets and 80 on the exhausts and chambers. You're largely wasting your time though.

The chambers don't need any work for your level of use or modifications.

I'd have 1 7/16" OD X 1 3/16" ID seats installed on the exhaust side so they are flush with the original spot facing in the chamber. The exhaust valve job should be .020" 28* top cut, .058" 45* seat with the OD matching the valve, the bottom cut should be 60*. Back cut the valve 35* to narrow the seat to match the one in the head.

Inlet seats should have a .020" 35* top cut, .050" 45* seat with the OD matching the valve, and a 60* bottom cut. Back cut the valve 30* to narrow the seat to .058"

If you do it all right, you'll notice a sizable difference. Do plan on this taking a number of days and not just a few hours.


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rcedward Avatar
Rob Edwards
Raleigh, North Carolina, USA   usa
1951 MG TD MkII "TDC6000"
1969 MG MGB "182608"
1969 MG MGC GT "8806"
1969 MG MGC GT "Rcedward"
1970 MG MGB GT "Donor"   → more
Well, an expert just said you CAN do it. I stand corrected!!! ;-)

Rob Edwards
Raleigh, NC

If you're in NC, check out the North Carolina MG Car Club!

Thanks Sean for the detailed info. I have a couple of follow up questions:

Can I use a wooden dowel and a hammer to punch out the valve guides or do I need a press to get them out?

Also, Peter's book, page 30, calls for cutting the exhaust boss guide down to 25mm from the spring seat, which is just under 1.0 inches for a 'fast road' application. Your recommendation of 1.3" is about 33mm. Is 1.3" all I need here? I know Peter's book is 10+ years old at this point, and perhaps outdated?

Finally, the angles he recommends for the valve job are slightly different also... On the exhaust, he calls for a .020" 30* top cut, .070" 45* seat, and 60* bottom cut into throat. He back cuts the exhaust valve 30*. On the inlet side, he recommends a .010" 30* top cut, .050" 45* seat, and a 60* bottom cut into throat. The back cutting of the inlet valve is actually .060" at 30* and then back cutting at 20* into the valve. Again, perhaps this is outdated. Have you had better luck with your angles?

In response to Bob - I am one of those perfectionists who will measure 10 times if I can avoid messing up the head, so I think I can do it. I plan on posting before/after pics so if I mess it up, you'll know about it!

1974 MGB being restored
Charlotte, NC

Edited 1 time(s). Last edit at 2006-01-08 03:49 PM by MGB_Norm.

USA   usa
1963 MG MGB MkI "Patience"
I would like to offer a small bit of advise:
buy a cheap head at a swapmeet or eBay and practice on it first. In my experience: if you've never ported and polished a particular model of head before you will make mistakes that you won't make the second go around.I suggest that you take the time to do it twice. You will notice that the second head will invariably be much better than the first.

moreso74 Avatar
David Maples
Augusta, Georgia, USA   usa
A pro will get more airflow out of that head than you will {just so you know}.

If you are intent on doing it yourself then.....
I suggest that you grind away with the exhaust guide still in there. It's not going to be reusable and will serve as a steady for your grinder and as a "guide". Plus it protects the hole untill you are ready to drive it out.
gypsyfox has a good suggestion - practice first.


To intsall and remove valve guides out you need a guide punch. Goodson sell them. They are steel punch that a OD slightly smaller than the guide and the small end fit in the ID of the guide and pilot off that, then you just hammer them in and out. The thing that make a guide punch or drift different from one you may already have in your tool is that when they reduce for the guide ID they are cut at 90 degrees. the ones you have in your tool box are than likely tapered at the reduction and will just wedge into the ID of guide and damage it. As simple a toll as this you can make one in the lathe and I have, but they don't last as long as the hardened one that Goodson sell. There are cheap and you should buy one for this project so you do it right, go to and find the one that will work with the MGB, measure the OD and ID of the guide to determine size. Oh when you get those old crappy steel guides out of your head it would be a perfect time to get some new bronze guides to put back in.

Lee Avatar
Lee Miller
Mburg, PA, USA   usa
1966 MG MGB
1967 MG MGB
1971 MG MGB
1971 MG Midget
Valve Guide Driver what size?

PHL-2250-G 5.0mm ID, 9.0mm Driver OD, 4.75mm Pilot Price: $ 19.99
PHL-2255-G 5.5mm ID, 10.5mm Driver OD, 5.21mm Pilot Price: $ 19.99
PHL-2260-G 6.0mm ID, 10.5mm Driver OD, 5.72mm Pilot Price: $ 19.99
PHL-2258-G 6.0mm ID, 9.1mm Driver OD, 5.72mm Pilot Price: $ 19.99
PHL-2234-G 6.6mm ID, 11.8mm Driver OD, 6.29mm Pilot Price: $ 19.99
PHL-2235-G 7.0mm ID, 11.0mm Driver OD, 6.6mm Pilot Price: $ 19.99
PHL-2228-G 7.95mm ID, 11.0mm Driver OD, 7.76mm Pilot Price: $ 19.99
PHL-2236-G 8.0mm ID, 11.7mm Driver OD, 7.8mm Pilot Price: $ 19.99
PHL-2229-G 8.7mm ID, 12.3mm Driver OD, 8.56mm Pilot Price: $ 19.99
PHL-2231-G 9.5mm ID, 12.3m Driver OD, 9.32mm Pilot Price: $ 19.99

Lee Miller

Experience - hobbyist, rotisserie restoration 1967 MGB, welding, bodywork, painting, wiring, interior, suspension, clutch, engine, SU HS4 carburetors, windshield, and installing convertible top.


1971 MG MGB
1971 MG Midget
1967 MG MGB
1966 MG MGB restoration project

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Jerry Avatar
Jerry Harrington
north east, USA   usa
get an alloy head. look at that thing of is all ready and ported to the max perfect for the 270 cam.

Edited 2 time(s). Last edit at 2006-01-08 07:59 PM by Jerry.

alloy head1.jpg    46.9 KB
alloy head1.jpg

Thanks all...

A guy at a local shop said he ported an alloy head and had to take off a ton of material... Plus I don't want to spend that much cash. Between guides, some carbide bits, and and the 3 angle valve job, I might spend $300.

1974 MGB being restored
Charlotte, NC

Sean Brown Avatar
Oregon, USA   usa
1976 MG MGB
The alloy heads need almost as much work as the iron ones do to flow the same, so don't think they are any kind of serious short cut to performance.

The guide driver you will need will be .343 on the ID and a 1/2" OD is fine. I use one that chucks into an air hammer because it's super fast and I do a ton of guides.

My seat details are for that head casting exclusively and will work better than those posted in the Burgess book (which I believe is generalized for a variety of head castings). I've got lot's of flowbench data to back them up for sure.

When I'm done with the exhaust guide bosses, the guides stick into the port about 3/8" from the end of the boss. I made my template many years ago, but I'm pretty sure it's exactly 1.3". You may get more airflow out of the smaller guide boss that Burgess suggests but I know I settled on what I use for a reason way back when. Actually I think he suggests that the back of the boss be 1.3 and the front be only 1.0... I cut the whole thing to 1.3 and then taper the front out like an extension of the bulleted guide.


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exhaust-port-small.jpg    29.7 KB

exhst port-comp-small.jpg    16.2 KB
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MGB_Norm Wrote:
> Thanks all...
> A guy at a local shop said he ported an alloy head
> and had to take off a ton of material... Plus I
> don't want to spend that much cash. Between
> guides, some carbide bits, and and the 3 angle
> valve job, I might spend $300.
> Norm
> 1974 MGB being restored
> Charlotte, NC

Just getting the right stuff to do heads yourself with can get expensive quick. I do porting as part of my livelyhood, it's not all I do but I do atleast a dozen plus heads a year, when racers baulks at the $1500 it cost to do a race head they don't take in account for all the tooling and talent it took to get me to that point. Between my two die grinders, a electric Makita ($150) a Fordom shaft drive die grinder($250) probably at any given time, several hundereds dollars worth of carbide bits, stones, and cartridge rolls, and most of hard to find long shank stuff, Soiux valve grinder (used $1500) Kwickway stone grinder ($500) Neway cutters ($500),
Rimac spring tester ($600) Superflow 110 flowbench ($3000) etc, etc, etc. I have a fair little investment in head equipment to prep a heads and it's nothing compared to big head shop. I invested in most of my equipment long before I started doing this for a living and when I was just building and mantaining my own personal stuff. The first thing I realized a long time ago was a average machine shop was not going to invest the time and effort I wanted to make sure I have a good multi angle valve job and everything was lapped in good and good seal I needed to make power. I charge $150 for a valve job and considering the amount of time I spend on it, it is the best bargain in the shop, you will not get this type of effort from the average machine shop, they are just going to bang it out the door.

Great info Sean/Hap - Thanks very much.

Hap - You have quite the set up there. I guess I may have underestimated the cost of bits etc. What do you charge to port a head like I want "fast road", do a valve job with hardened exhaust seat inserts and bronze guides? Private message if you prefer. I am in Charlotte so Greenville isn't too far to drive and shipping wouldn't be bad either.

twigworker Avatar
Jack Austin
Blowing Rock, NC, USA   usa
Well...I am now certified as ignorant!

Earlier today I downloaded and printed the article by "Steve S., Virginia USA" and read it all. I am just blown away at the thought and detail with which he approaches a B series engine. I think that I found only one or two small details that he came down to my level on, so everything else in his 40 page, 33000 word epic was news to me. Of course I retained only about a 20th of it so it is going to have to be read and considered many times over before I lay out a plan for the stuff up in the shop, but what an adventure it will be! I thought that I was some sort of hot shot having "overhauled" so many English lumps and analyzed and gone through my 2.0 Dino but the theory and execution behind the proper way to deal with what appears to be a simple little iron motor was really unexpected. Probably won't be able to sleep tonight!


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