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MG Midget and Sprite Technical - Needles Needles...

Bit of an unusual one here.

myself and my brother are rebuilding an old frogeye sprite that used to do rallying as a sebring sprite.

The engine has gone through a complete rebuild and stats stand as:

948 +60" (Flat top hepolites)
12g295 cylinder head
compression ratio 10:1
Camshaft: unknown(by gum we've tried but it seems from our estimates to be around a 300'/300' camshaft so pretty racey to say the least...)
Carbs: Pair of HS2's with no needles currently..

The problem is thus....where to start with needles? Will be taken straight down the rolling road to tweak but as its so off standard I'm thinking wasting £20 on a pair of the standard needles for a 948 frog might not be the best place to start.....


any advice?

Also: as the mechanical fuel pump is totally dead and have an electric SU hanging around we are going to use that. For HS2s would people advise having a fuel regulator?

sebringsprite.blogspot.com
D Paul

Not too difficult to measure cam timing/lift, and a good idea. Keeps confusion away and lessens the quantity of spurious excuses!

I'd suggest any needle near a modded 1275 or Cooper S. The nasty cam and overbore should make it act like a bigger engine, albeit the rpm will be higher = HIGHER!!

Actual Hp output for any setup with the same carbs will be in the ballpark. If you expect 70 Hp, that's stock S. If you expect 100, that's any top level 1275.

Vizard showing E3 as pretty widespread across small bore hot modded engines. AH2 also looking sort of "universal go fast"

Don't actually buy any needles, you must have something around and they will not be in there for long.

Certainly wants red springs in the carb pistons, I think.

SU pump does not require a fuel regulator. NO correct pump requires a fuel regulator - it is built into the pump as normal construction.

FRM
FR Millmore

I'm desperately trying to remember what the cam measured two (im 250miles from my notes unfortunately)

I believe it was around 300' in 300/' out with lifts of about 0.3inch on both. Spider drive. No Markings. It didn't match up to anything on the charts I could find but firmly puts it up in the 649 realm. Given that the guys that built it where a BMC Garage owner and lead mechanic and that most of the other tuning gear on it has all been BMC items.....but a 649 should be marked (haven't got Vizard to hand I'm afraid)

Thanks for the help so far, thats good to know was in the right ball park with how to work things out. Will double read vizards chapter on small bore hot modded engines (forgot that was added in the newer editions, for a long time was using a very early copy)
D Paul

I was actually using Vizard's first "Modify your Mini"!
And my "Tuning A Series" is ed 1.

Common saying from many including Vizard is that BMC cams were frequently not up to spec, and UK aftermarket were worse, so US regrinds were often used. Isky did excellent "649" profiles. Elgin made his own very well developed versions.

All the 300 degree range BMC cams are .315 cam lift. Most lesser ones are c.250

FRM
FR Millmore

This thread was discussed between 06/07/2012 and 07/07/2012

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.