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MG MGA - Twin-cam vs (MGB engined) Pushrod MGA

Many years ago when I first read about the MGAs racing and rallying exploits, it was always the Twin Cam that caught my imagination.
The twin cam though was always beyond my budget and since the mid 1970s I have owned 2 FHCs and finally my present 1600 Roadster which I have owned for about years.

My car has a tuned MGB 1900 engine in it which makes it a lot of fun but I must admit that I have always wanted to have a twin cam.

Also,I thought my car was relatively quick for a pushrod engined car, that is, until I was having a it of a dice with Dave Stewarts twin-cam in Scotland a couple of years ago when he overtook my car on a pretty steep hill and left my car for dead!

So it looks as if I have some choices to make.

Whilst I am still working I could probably justify swapping my car for a twin-cam and it would get me the performance I would really like. But on the other hand I take the car on long distance tours into Europe and I need a reliable car.

Should I go for it and get a twin-cam ( if one comes on the market) or am I better off keeping with my pushrod or maybe even fitting a supercharger to it?

I would be really interested in your opinions on this.

Cheers

Colyn

It will be more difficult for me to justify buying a twin-cam once I am retired :-)


c firth

Hello Colyn,

You pinpoint things clearly performance vs reliability.
A Twincam appears exotic but with 2111 units built, I imagine such puzzle of finding it or finding parts to fix engine in remote areas.


My two cents advice:

Improving B-engine with few modifications, like: hotter cam, better carburettors and why not a crossflow head, etc, will be not so expensive and will give you some thrill...

Cheers,

Jean G
Jean Guy Catford

Try and test drive a supercharged car, you will be amazed at the increase in torque for going up hills

Dominic Cancy

Colyn

I want to go down the supercharger route for my 1800 having been put off a crossflow head following the recent discussion. It is just that I have been baulking at the price - yes I am retired, should have done it earlier! May be we should ask Moss for a discount for a bulk purchase!

Just off to get my lotto ticket.

Steve
Steve Gyles

Depends which twin can engine you choose - the BMC unit is probably no better than a well tuned crossflow MGB unit. A M or T series Rover unit will give much more power and dropping a V8 in would be even more grin factor.
Chris at Octarine Services

I was seriously tempted 2 years ago when one of our club members put his twin-cam up for sale ( I have always hankered after one ever since I saw one in a car park in 1959 - as it had my name on the bonnet!). The main thing that put me off was the asking price of £28k as well as the fact that the general feeling was that a well tuned 1800 would better a twin-cam and be less fragile and easier to maintain and have better access to spares.So I decided to stick with my 1600 roadster and helped him sell it to a chap in Australia
Cam Cunningham

Thanks for the comments, its looking as if I may well be heading down the supercharger route sometime in the near future then.

The process will be slightly complicated on my car as it is fitted with a modified fast road head and a matching Piper cam. So I will probably have to get buy a lower compression head and a standard cam before I fit the s/c. Then there is the fact that it is a 3-bearing MGB engine and so should I swap it for a stronger 5-bearing?

(Is it going to be less expensive to buy a twin-cam after all?)

I suppose that driving along a motorway at 70mph in top gear wouldn't stress a supercharged engine any more than it would a standard carburettored engine, as they would both be delivering the same power at that speed.

I would imagine that the cars climbing ability up those mountain roads would be drastically improved too but I will probably have to give some thought on the subject of keeping the car cool.

So maybe reliability will not be as much of an issue as I thought, that's assuming that I can learn to control my heavy right boot! :-)

This looks like it is going to be my retirement present to myself, once I have persuaded swmbo of just how critically important this is to my future happiness!

She will probably throw a few words of discouragement my way, including- new kitchen, new conservatory, divorce etc.

Wish me luck!

Colyn







c firth

I have driven an MGB with a Moss-supplied supercharger, and can say that it absolutely transforms the performance of the MGB, having owned one without the sc at the same time. I don't think you'll be disappointed.

George
George G.

Colyn

Mine is a HWMBO. She actually said in one of those voices to go and get one......and I chickened out!

Steve
Steve Gyles

I think I can recognise the exact tone of voice Steve. :-)

I have also experienced that unfinished sentence which means the "ABSOLUTE" opposite to the actual words spoken and has a visceral sense of doom at the end of it!

I think it goes something like "Oh do as you like then-------!"

I'm still shuddering! :-)

Colyn

c firth

I would talk to Peter Burgess: there may be possibilities to use the existing head setup with an SC.

My "1500" A has a SC, 5 speed gearbox and a fast road cam, lighter flywheel and a 1622 over bored engine, and goes like the proverbial sh*t off a shovel with about 130 flywheel HP. The spare engine is even hotter with a full SC oriented spec from Peter Burgess and Chris Betson, and should be worth another 10 HP when it eventually makes it into the car. The Moss SC is apparently a transformation, but makes a lot of noise.
Dominic Cancy

Colyn The supercharger will be OK with the fast road cam.
SC have a calming effect on the feel of a hot cam but the compression is best under 9:1. The Piper 255 gives excellent results but people report good results up to a P280. I use a cam with 289* E and 280*IN and it pulls hard right through the range. My SC has been on the B for 10 years and I cant imagine the car without it. The power is quiet and seamless. Denis
D M HILL

I can see that You have never driven a proper Twin Cam MGA.Given a better cam,a c/r gearbox,Weber carbs it will outpull a lot of bigger cars and is a sheer Delight to drive...
Dirk/Antwerp
D. Van Ussel

Thanks Dominic and Denis, that's the exactly the kind of information that I was hoping for.

Im almost certain that my cam is a Piper 255 as it showed the characteristic flat power curve when it went onto Peter Burgess's rolling road a couple of years ago.

Also Im encouraged to hear that Dominics engine is a 1622 as I am fairly sure that my 3 bearing MGB engine
shares the same design crank and con rods and hopefully would survive being supercharged.

I had better give Peter a ring to see if we can use my existing head before I do anything else. (I have access to a 1622 head if the fast road head had too much compression)

Cheers

Colyn


c firth

Hi Colyn,

I have recently installed a Moss supercharger kit in my ZB Magnette. It has a 3 bearing 1800 +0.60 with a Piper 255 cam and one of Peter Burgess's heads along with a LCB exhaust manifold and a reasonable exhaust system. Peter does a head specially developed for use with the supercharger, it has bigger inlet and exhaust valves, he says that he opens out the exhaust ports quite a bit to help get those gasses out more quickly.

My compression ratio is about 8.5:1. I have still to sort out the ignition yet and get it all set up properly by Peter, however, I am really happy with what I have so far. The car goes really well.

Feel free to drop me an e-mail if you want to ask me more. I'm very happy to chat. I am also currently rebuilding my 1622 in my MGA at the moment.

David
David JM

Dirk, you are right,I have never driven a twin-cam which is maybe a good thing as I know that I will always want one.

Im trying to to be sensible here and probably will go the s/c route ( if you can ever call installing a supercharger sensible! )

Everyone who knows me will understand how hard it is for me to be sensible when it comes to cars and engines! :-)

Colyn
c firth

Colyn,
If you get the chance I would buy a Twin Cam as they are great investment due to their limited production volume - here in Oz they sell for around $55-60k compared to $30-40k for a push rod roadster in very good condition. While in standard tune they cannot match it with a modified 1800 engined MGA, they still go (and stop) okay!
If you want an A with potent engine, go for the modified 18V engine because if you blow the engine up you can easily find a replacement block/head. It would be such a shame to modify a twin cam engine and then damage it!
That said I would love a modified twin cam with all the goodies (twin 45 Webers, C/R gearbox, lsd diff, widened peg drive wheels, etc) to add to my stable - as you can see I prefer modified to concours!
Mike


Mike Ellsmore

Hi Chaps,
Just bought an 'A' with an Oselli stage 2 1950 5-bearing B engine with a Ford type 9 5-speed box. It has approx 130 bhp, and is a joy to drive, no lumpyness, smooth and quiet in traffic. I had a 5-speeder fitted to an 1600 mk2 I had a few years ago, but the latest car is much nicer to drive, faster, smoother and easier. Like a lot of you, I really quite fancied a twin cam, but they are so hard to find now, and so expensive, I gave up on the idea. However, why not fit a twin cam engine to an existing car? When I saw Peter Wood a few years ago he had several rebuilt units under his workbench, and he's by way of being an expert on the A ..... Cheers AB
A Bennett

Take a look at the dyno curves on the MGB engine and the Twin Cam some time.

The pushrod engine stubs its dick at around 5,000 rpm. The Twin Cam doesn't peak until 6.900, so it is rather like adding 20% more range to the pushrod. Ever driven a Honda VTEC engine? They putter around under 6,000 and scream off above that. The Twin Cam is similar, at a bit less rpm.

Your MGB has a 12.5% displacement advantage over the 1588 cc Twin Cam, so torque low down is better in the MGB, but the Twin Cam likes rpm, and with a close ratio gear set and a 4.55 diff and no other changes, it improves 0-100 mph times by 11 seconds!

The Twin Cam is a different kind of animal from the pushrod engines (of any size) and while I much prefer them, they are also very expensive compared to a pushrod, so I have to side with those suggesting that a nice 1800 with supercharger will get a very decent result for much less money.

If you want to see what one CAN do with the Twin Cam, you can take a look at my 1950 cc version here

http://www.rhodo.citymax.com/f/Twin_Cam_conversion.pdf

If you have to ask how much, you can't afford it! ;-)


Bill Spohn

Thank you for posting that, Bill. While I can't afford to play with such things, I am glad to know that they exist.
Del Rawlins

Thanks for that Bill,
I have drooled over your write up of your MGB Twin-Cam Development quite a few times and I think that it has to be the ultimate in Twin-Cam development.

I think I will re print it out again but this time I will laminate it to try to make it drool proof!

Your description of the difference in the power curves explains why Dave Stewart's twin-cam just flew past me up the hill a couple of years ago in Scottish Highlands when I was pressing on foot hard down in 3rd gear.

I have only ever seen one other twin-cam engine built from a 5 bearing MGB engine and it was made by a certain James Horners father just a few years ago for road use.
He also said that it was a real challenge to make the twin-cam head fit onto the 1800 block as the studs don't quite match up.
I seem to recall he said they got well over 130 bhp from it and that it revved incredibly.

On the subject of my own car, I think I would be best advised to keep with a push-rod engine. I am more of an amateur mechanic than an engineer and so I think that setting up a twin-cam engine may push my mechanical abilities to the limit.

I have yet to speak to Peter Burgess about whether I can get away with using my 3-bearing 1900 engine with a supercharger or if I should really start with an (18V type) 5 bearing motor.
Thanks again Bill

David, I will send you an email to pick your brains some more about your s/c conversion.

Colyn

c firth

Colyn there are a few three bearing supercharged cars around that have had no problems. That being said you do get other advantages with a 5 bearing apart from the stronger crank. The rear main seal for one and in the case of the 18v the straight cut con-rods, lighter and stronger. My 5 bearing is a GD that had the angle rods which never gave a problem in nearly ten years of the SC , but I replaced them last year with a set of Pauter rods and the works. The beauty of the SC is that even though it gives you more power as soon as you touch the throttle, the biggest lead foot amongst us only uses boost about 2% of the time. I also use one of Peters supercharger heads. Denis
D M HILL

Colyn, would you please let us know Peter Burgess' thoughts on supercharging a three bearing MGB engine for MGA use once you've discussed it with him? Thanks.
T Aczel

The three bearing B engine is pretty much the same as the 1622 (same crank and rods), and it supercharges just fine.
Dominic Cancy

The 3 main MGB engine is a good one - stronger than the 1622 as it has larger diameter mains. How much it will stand up to is a good question - I've raced them for years (they seem to run a tad more freely than the 5 main, which makes sense) and I've even seen them win 7 hour endure races. Ask Peter what he thinks of the large bore supercharged capability as it is a bit outside my personal experience.

And yes, the Twin Cams do rev pretty quick, which resulted in a bunch of warranty claims back in the day because BMC didn't have the foresight to fit Lucas rev limiting distributor rotors like Lotus did on their Twin Cam Ford engine. A stock Twin Cam would run to 7,000 very quickly and all you had to do was go a couple of hundred rpm over and you'd have bent valves. My race engine doesn't bounce until about 7800 and I try to keep it under that but with a light flywheel it can be hard especially if you are 'busy' so I utilize an electronic rev limiter just in case.
I usually shift at 7200 - 7400 as the CR gearbox drops you to about 5800 rpm, right on the torque plateau for the engine.
Bill Spohn

I have had a brief email conversation with Peter, he is hard to get hold of on the phone.

Apparently the supercharger needs a larger combustion chamber than my fast road head has now.
So I will have to let him have a look at it to see if it can either be re-worked or to see if I can get away with fitting a spacer plate between head and block to help reduce the compression ratio.

I am going to sort out the supercharger kit over the next few months and then take the head off to look at it over next winter.

On the subject of the twin-cam, I have always been amazed at just how much more it revs as compared to the pushrod engine. Is the extra rev range possible because of the different valve gear and the better breathing of a crossflow head?

Colyn

c firth

"On the subject of the twin-cam, I have always been amazed at just how much more it revs as compared to the pushrod engine. Is the extra rev range possible because of the different valve gear and the better breathing of a crossflow head? "

Yes, in short.

I've seen pushrod engines that would rev to 10,000 rpm (Cosworth MAE) because they had the breathing and the valve gear to take it.
Bill Spohn

One thing to consider is with a supercharger, you never have to rev the engine hard to find power. I have a 5-main supercharged B with 150HP and 150 lb/ft, and the low end torque is fantastic. I find myself shifting literally half as much on a twisty road than I used to. So much useable power across the range.

I used to be a high rev driver, but over the years I've learned to appreciate torque in most public road situations. That said, the mostly stock 3-main 1800 in my MGA feels perfect for the car, mated to a 3.9 rear end. I never want for more power. It will comfortably cruise 80MPH all day on the highway with plenty of power still on tap.
Steve Simmons

This thread was discussed between 22/01/2014 and 09/08/2015

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