Mini manifold

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_dwat_, Mar 11, 8:37pm
Im looking at putting a new inlet manifold on my 1275 engine, with the original cast iron manifold can you cut the inlet manifold from the exhaust as they are joined for a reason! cheers
incar., Mar 11, 8:53pm
yes you can, what type of manifold/carb are you running, i still have a early copper s i've had since 1991
clark20, Mar 11, 8:57pm
Yes, you can however you should get a better exhaust if you are doing the intake.
budgel, Mar 11, 8:57pm
Extractors and a separate inlet manifold were common on those engines.

Incar probably has a Cooper S ;-)
Copper ones are very hard to come by.
incar., Mar 11, 8:57pm
what you need to do is cut the inlet side off, but leave the bit in the centre just where in joins the exhaust, after that depending on type of inlet manifold grind the exhaust part down, it thinks its about 3mm thick (where they meet)
incar., Mar 11, 9:00pm
lol i have a cooper s mini i've had stored for over 20 years, those were they days
_dwat_, Mar 11, 9:01pm
its the cast iron mani with single hs4, ive got a set of twin hs2 and mani to go on it
incar., Mar 11, 9:07pm
yep just do that, the twin su manifold will be aluminium, one thing is when you sit it on make sure the bottom of the inlet ports are sealing, i used to sit it on then mark the bottom part of the manifold and gasket, that way you can see how much sealing you have with manifold and gasket, if not enough take abit more off the exhaust,
snoopy221, Mar 12, 12:39am
Shyte those were the days

Sandblast the body until it,s a GENUINE Reg Cook 50 lb body shell
Fit some Timken taper bearings on the primary gears and add some side drafts.

And voila zee ming al la LIVES.
smac, Mar 12, 5:47am
Yeah you can do it, but have a think about why. People think twins must be better cause, well, there's two of them. It really isn't that case. In some parts of the rev range you will actually be reducing the breathing.

Also, the exhaust on the mini is a bigger restriction than the carb set-up - so any improvements with filter or carb or inlet will not really be utilized without upgrading at least the headers, if not the whole exhaust.

So really comes down to what you want to achieve. If you want better performance, or power, then I wouldn't do it. I'd sell the twins to pay for what should be done first (filter, modify the filter box, inlet manifold, exhaust, different needle). However if you just want twins for the hell of it, go for it! But be REALLY careful cutting that manifold, REALLY easy to go through, or to go too thin and create a hot spot.
bwg11, Mar 12, 9:37am
Look for a used metro cast iron exhaust manifold. They have two outlets which connect to downpipes which join under the gearbox like "ordinary" long branch extractors. Just as efficient for a road motor as tubular extractors and seem quieter (less resonances) in the car than tubular extractors.

Probably quite a few of these lying around as many Metro motors have gone into minis, and most people use tubular extractors and don't recognise the merits of the cast two outlet manifold.
smac, Mar 12, 10:20am
Two potential problems though: if there's plenty laying around I'm damned if I know where. Seem to be more like rocking horse poo. Also, I think the stud spacing may be wrong for the OP's 1.5" carb.not 100% sure, been ages since I looked at the differences.
bjmh, Mar 12, 11:02am
go to coby and see if you can still buy a set of extractors,don't muck around using old manifold .minge will go good with twin carbs.Have fun tuning them ,you'll learn heaps.Ran an old Z car with triple S.U'S .Wade cam etc etc.sounded like the carbs would suck a golf ball thru a garden hose.
bwg11, Mar 12, 11:16am
The cast Metro exhaust manifold is a separate unit - it is not integral with the inlet manifold. I presumed the OP had a twin carb manifold.
elect70, Mar 12, 1:46pm
Hope its not aoldB/Callly maniufold,i had 1more porous than a sponge& flanges werenttrue,this was their early days of "performance" parts
socram, Mar 12, 2:22pm
I found that going to a LCB made life so much easier in terms of overall access - and a nice exhaust note.
Much as people like to malign the old SU's, once set up properly they never really need touching.
A twin carb manifold surely distributes the fuel better (two cylinders per carb) than a single (four cylinders per carb) unless you are hacking out the bulkead and put on a longer gas flowed inlet.Having said that, one decent carb will supply enough fuel.

I think #2 was a typo. Meant Cooper not copper.
budgel, Mar 12, 3:18pm
I know, I was just having a good natured laugh with him.
incar., Mar 12, 4:32pm
Yep it was lol
smac, Mar 12, 5:13pm
OK, have to take your word for it, the only ones I've seen were cast with inlet. Fact remains, they're not common.

Anywho, as above, comes down to what you're trying to achieve.
clark20, Mar 12, 8:18pm
And don't forget the heat shield.

My 1275 gets 65hp at the wheels, on 2 x 1 1/2s and a cam/porting. STD hp was 67 at the motor.
cowlover, Mar 12, 10:41pm
Get Vizard's book before you do anything.Twin carbs useless without all the other improvements/parts.
supernova2, Mar 13, 8:58am
The 1275GT Mini went pretty well.I'd rather a standard 1275GT manifold & carb & exhaust than a twin carb set up with a butchered manifold.Also how old and knackerd are the twin carbs!If they are old and worn they will need shaft bushings and new shafts at the very least.Have they got the correct needles and springs!Unless the carbs are in perfect nick you will have continuous problems getting it to run properly.
flockton55, Mar 13, 7:51pm
Can I add weight to the twin carb support. My mini was bought as an unfinished project, has a 1275 Allegro motor, with apparently a modified cam, tubular extractors and a single 1.5 carb. Sorted out the wrong needle etc for the carb, it went quite well. Came across a set of twin 1 and a quarters, fitted correct needles, adjusted and found a whole new upper rev range full of extra power. Still plenty of torque at lower revs but really gave the car some extra performance.
smac, Mar 14, 6:14am
If there really was such a dramatic increase, all that means was there was an issue with the 1 1/2". Smaller twins potentially give better throttle response low in the rev range, but that's about it.

Think about this: how much carb is any one cylinder seeing at any point in time!

Anywho, OP hasn't come back, so who really knows what they want to do .
electromic, Mar 14, 6:59am
I used an 1 3/4 carb correctly jetted for my engine with a custom inlet and coby exhaust. Good on a standard 1275 and great with a 1275 with cam and head work. The needle is the key for all su carbs.
I used a 45 webber for racing on a big bore, race cam, race head. That motor on GT gearbox with 3.44 diff and 12" rims had the best performance of any mini i have driven.