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MG MGA - Cross Flow Head and Tuned Header

I am thinking about upgrading the performance of my MGA. How much of a difference should I expect by installing a cross flow head and a tuned header?
gerard hutchinson

When Derrington released their crossflow head for MGAs they didn't advertise a horsepower rating for it
All there paperwork was based on performance, but they also had higher compression pistons in their test car so there wasn't an actual direct comparison
I had one on an 1800 with twin webers and it went like a jet
I've got a roadtest sheet here somwhere from Derrington for the MGA--I'll dig it out and post it here sometime today
cheers
William Revit

Gerard
Found the writeup, but note-this is for the old original Derrington which was made specially for 1500cc BMC engines
Don't know what size your MGA engine is but if you're going for one of these later Xflow heads there are traps so be aware
You need to have the right sized combustion chamber for your engine, if say you got an MGB head and put it on your 1500-? it will have very low compression and won't perform at all well
I 'think' the later heads take MGB sized valves so depending on how much has to come off the head to get the compression correct for a smaller engine and also what camshaft you have, you will need to check that the valves don't hit the top of the block-
Anyway, here's the blurb on the Derrington, hope it will blow up enough to read- and the performance data I did a closer pic just in case

willy





William Revit

I have to admit that I think the crossflow head does look great, but there are some pitfalls.

It will not be easy to find an original HRG head that is not either cracked,distorted or both.

And the modern version, the MSX heads need a lot of work on the ports to get them to flow correctly. Apparently, there is a problem with the casting that makes it really easy to do irreparable damage to them whilst trying to gas flow the ports.
Not many engine tuners will work on the MSX nowadays, for that reason.
There is lots of info about the crossflow head on mgaguru and online.

FYI, you can get up to 140 bhp from a 1950 cc engine with a conventional cast iron 5-port head.

http://mgaguru.com/mgtech/power/pp201e.htm

Cheers
Colyn
Colyn Firth

I have a copy of the Derrington 1968 catalogue with 1973 updates including a sticker on cover saying VAT will be introduced on 1 April 1973.

This catalogue has 10 pages of info on these heads up to the Mk V, and it covers Magnette ZA though to 1800s in both MGB and transverse implementaions. It includes the attached graph comparing BHP for standard and HRG heads on MGB.

Catalogue also covers Weber’s.


Hope this is useful but like Colyn I have heard their very bad reputation with ageing.

Paul



Paul Dean

Ok, so I have what I assume to be a normal 1500 MGA head. It appears the new Moss Motors cross flow head (451-690) will require a new Weber carburetor (378-680) and a tuned header (454-855).

Are these parts "plug & play"? Or will I need to modify my engine block to accommodate? If so, it does not seem worth the trouble.
gerard hutchinson

I have the original Derrington brochure on my site here - https://www.rhodo.citymax.com/f/HRG_Information.pdf

You can print it out for your files.It gives power figures for 1588, 1622 and 1798 engines with the heads.

I second the suggestion that you not waste time with the MSX version unless the appearance is all you are after.

Bill
Bill Spohn

I have built B series engines with the MSX heads, but I always send them to Peter Burgess first!

If you want to understand how to make power out of a B series you should get and read Peter's book first.

You can't just bolt together random bits and expect to hit the jackpot.
Chris at Octarine Services

Both Chris and Bill have had a LOT of experience with building and porting the crossflow heads over the years, I would be strongly inclined to listen to their advice. :^)

Colyn
Colyn Firth

I support Chris’ suggestion, talk to Peter Burgess and buy his book.

I ran a ported big valve HRG Derrington head for some years until regular head gasket failures beat me (head was soft also 83.5 mm bore). Then changed to MSX head that required extensive reworking to match the Derrington flow rates (eventual getting MSX flow rate superior, MSX out of the box is pretty rough - I don’t have any flow figures for std MSX head)

Another issue is inlet manifold stud patterns are different on Derrington v MSX so you need different inlet manifolds!

Mike
Mike Ellsmore

You cannot go better than listening to Chris Betson and Peter Burgess. The two together made some very nice engines.
Dominic Clancy

Hi,
I have an MSX head fitted to my 1950cc engine .I had it polished and ported and gas flowed, but it cost me an additional £ 600.00 .The engine is fitted with 1.75" SU carburettors on a shortened MGB manifold.
Regards

David Speak
D M SPEAK

This thread was discussed between 02/06/2020 and 05/06/2020

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