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MG Midget and Sprite Technical - Engine build results

After literally years of faffing about, I've finally got my engine/gearbox upgrade to a point where I can drive it. Woo hoo!

I've just got back from a session on Peter Burgess' rolling road and I'm really chuffed, so I wanted to share.

I think the fashionable phrase is mission creep, and I've definitely crept. My Sprite now has a 1360 motor with an RE13 cam and matching Keith Calver head. The ignition at the moment uses an Ignitor and the exhaust and inlet are by Maniflow. HIF44 on the inlet. Ceramic heat insulation inside and out for the LCB.

I was dissapointed when I first drove it. I couldn't get it to run well low down or whilst cruising, although once it got going it pulled quite well. I thought I'd been too ambitious with my cam choice, and had visions of having to pull the motor again and put in something milder.

Still, I took it to Alfreton, and Peter and Keith have worked magic, so now I'm very happy. They found an extra 10% just about everywhere, and filled a big hole in the torque curve at the bottom end. Its now making as much at 2000rpm as the old tired engine did as its max output.

Future plans include a tryout of an Aldon Amethyst progammable ignition. (I struggled to get mine to work in time for my booked rolling road session.) The latest version discounts vacuum advance at very low revs, so that would compensate for the large signal from the manifold-side HIF44 vac pick up.
I'm also collecting parts to convert to fuel injection, inspired by Bob with his 1500. I future proofed the ex manifold by asking Maniflow to weld in two lambda bungs. I also used a 36-1 front pulley ready for a crank sensor. First I need to cure a slight diff oil leak, but I fear for my halfshafts being of the Dukes of Hazzard school of driving, so I can see more mission creep. Whilst I'm rebuilding a spare diff, I might just upgrade a little.

As I'm sure you'll agree, a bloke's got to have a hobby.


M Crossley

Looks a good result! Good torque curve.

Is 1360 achieved with a + .060 rebore?


C.J. Harris

Hi Chris,

I think that a +.060 gives 1330. There are also 72.5mm pistons giving about 1342cc. Mine are 73mm for the 1360, giving another oversize, the classic 73.5mm for 1380cc. You have to plan ahead though, with offset bores.

It does go quite well, thanks.

M Crossley


It sounds awsome...whats your opinion of the ex manifold ceramic coated inside and out... I wish I had done mine inside

Prop and the Blackhole Midget

I didn't use the exhaust before I got it treated, so I can't do a before and after comparison. I'll measure the temps of the area when I get a minute. Infra red camera from work should show any hot spots.
I thought it might be a good idea though, because I'm running a steel inlet manifold without any water heating/cooling, and it might be a bit vulnerable. I've got a carb heat shield.
The exterior looks tidy and is wipe-downable, and hopefully won't go so rusty as the painted mild steel ones do. I've never had great success with VHT paint. You can choose fancy colours, but I went with a boring grey.

Regards, Mk
M Crossley


Looks good. The one thing I particularly enjoy post fitting HIF44 and further enhanced by fitting the Metro head is the low down torque and the ability to drive the car in a less frantic manner. My inlet is also not water cooled - and only a very small heat shield fitted - no problems, but I have to say I removed my heat insulation on the exhaust on the thermodynamically inspired grounds of wishing to extract as much heat from the engine as possible rather than conserving it.

For the HIF, I also changed the needle from BDL to - if memory serves a BDK - a slimmer profile needle in any event, and refined the mix a little. Noticeable improvement here.....

Personally I have ceased all mechanical fiddling - for the moment - primarily as the costs now involved to modify further are somewhat high compared with the increase in performance on my wish list are possible Panhard rod and black minilite type wheels...for now anyways



Mark O


I understand what you mean about the low down torque and the less frenetic driving. Until it had been on the rolling road, it needed to be wound up to 2k5 to go. I thought that I'd made a mistake on the cam choice. Now its not too bad, and I definitely like the top end. I shall drive for the summer and see how it goes. I'm thinking clever ignition or possibly efi might allow a little more finesse around town or when stuck in a motorway queue. The light flywheel probably doesn't help the tickover. I do like the traffic light grand prix though.

I can highly recommend the Frontline front suspension and their RTL. Of course the diminishing performance returns on the spending is a bit of a dilema. I don't smoke and I don't have a season ticket to the football. Stronger half shafts and teach-yourself diff rebuilding next for me I think.

M Crossley

"I don't smoke and I don't have a season ticket"

Ah so that's why I have a pretty bog standard 1275 and failing lever arm suspension then! Who'd have thought it?

" I don't drink Scotch either" ... so I bet my 1275's bogger than yours, Matt!
David Cox

Do you have the torque or power version of the Re13?

Was in doubt about that cam but in the end went for the classic 286.
Running in now an it pulls like a train above 2500rpm.

Have an aldon amethyst programable ignition ready to fit.
Then a RR sesion though I'm not sure yet If I make it to PB since we have now found a good affordable RR in Holland
Onno K

Sorry, lazy typing. It's the RE130T, advanced by a degree, as recommended by KC. 1.5:1 rockers.
I struggled with the Amethyst initially, but I've discovered a machining error in the drive dog of the spare, new, distributor that I bought for the job.
Hopefully once I've sorted that out, I'll be able to upgrade from the Ignitor equipped 25D that PB tweaked for me.

As an aside, my Sprite was originally Primrose according to the Heritage certificate. If I ever get the courage, I'd love to repaint it that colour. Lovely.

M Crossley

Well mine was white according to the Heritage certificate and when I bought it I said the colour is the first thing to change.
Almost a decade later the primrose has grown on me ;)
Onno K


Indeed. I have mused long and hard about the Frontline conversion but opted instead for the cost effective refurbishment of (all) the existing lever arms filled with slightly thicker oil. A good improvement resulted, and whilst I am sure the Frontline set up would offer further improvement, I feel you would have to push the car pretty hard to see it. This is something I do not do that often (truly officer), so the value to me anyways is somewhat limited.

I also have 123 electronic ignition, which largely by trial and error, I feel I have optimised to suit the car and its modifications, though I am sure Mr Burgess could doubtless find another few horses.

Mark O

"I don't drink Scotch either"

David, No I'm guilty on that count as well and as age progresses my tatstes strangely become more expensive. Let's call it a draw for bad/good habits causing us not to have too many Carlos Fandango bits on our cars!

This thread was discussed between 17/06/2015 and 22/06/2015

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