Heads and carbs

Post by **youngun** » Sun May 13, 2007 5:19 pm

Being a "damn youth" i will be looking to make my moggy go that wee bit better. Having looked around i see that there are two heads that pop up here and there, the Mini cooper 12g295 and the other one is a 12g940 (i think, might be wrong on that one). Now im up to date on what putting one of these heads on does, indeed i spend a lot of my time porting, polishing, and fiddling with squish bands on racing 2-stroke motorcycles. But, which is the best for PRACTICAL road use. And what carbs should be used in conjunction with these heads? Also on the subject, im a novice when it comes to differentials and the like, what can i do around that area to improve the mog?
I have a Jowett Flat four lying around the shed at the mo, might see if that will fit in the engine bay!

cheers,
Youngun

Post by **bmcecosse** » Sun May 13, 2007 6:09 pm

The Minor was designed to take a boxer four!! But that was cancelled and the sidevalve Morris 8E engine was used at first. The head I have on mine is the 12G940 head - to make sure the exhaust valves don't smack the block you need to sink them into the head by 40 thou (5 min job with a 45degree countersink in a pillar drill) - and then relieve around the seat with a small grindstone. This head then bolts on with 1275 engine gasket - you need to watch the clearance at the water pump - may need to file some metal off the top flange of the water pump. This head needs NO skimming - you should check the rockers line up ok with valve tips. I had a modified 295 head on my engine - it's FAR better with the 940. They are also cheaper to buy!! Use with an MG metro alloy inlet manifold - and a single HIF 38 carb - or you could try an HIF 44 but I think the 38 is fine for a 1098 engine. My car goes very well indeed with this set-up. Obviously a free-flowing exhaust system would make it even better - the next step.

Post by **Matt** » Sun May 13, 2007 7:27 pm

Or use the alloy inlet with a HS4, I cant see that a HIF has any practical advantage over a HS on a road engine. The HS's are much cheaper too

Post by **youngun** » Sun May 13, 2007 8:45 pm

Hmm, not up on the technical lingo here.....HIF carbs? Im used to twin su's and amal monoblocs!

Sounds like the 940 is the way to go then, is it recommendable that a different cam be used as well? I was thinking of boring out and fitting flat top Hillman imp pistons, but one of the cylinders needs to eb slightly off-set when being bored and i cant find an engineering company to do it down these 'ere parts.

Post by **alex_holden** » Sun May 13, 2007 9:06 pm

youngun wrote:Hmm, not up on the technical lingo here.....HIF carbs? Im used to twin su's and amal monoblocs!

HIF refers to a range of SU carbs, and the number is the throat size in mm. The HIF range is a newer design than the HS range and is reputed to perform better.

Post by **youngun** » Sun May 13, 2007 9:29 pm

Thanks alex!

Post by **bmcecosse** » Sun May 13, 2007 9:35 pm

HIF = Horizontal Integral Float. They are better carbs that DO NOT flood or gasp going round corners. I doubt the actual performance is any better - they are exactly the same when looking down the bore. So if you have an HS4 or 6 - go for it! Target price for an HIF 38 would be £5!! The Imp conversion is very costly - and just not worth the money unless going racing in a special class. Yes - an MG Metro cam is very desireable - hard to find these days and you need a different matching oil pump. I wouldn't go any 'wilder' than that. You will be well pleased with a 940 head on your engine- and of course that head can be 'improved' too following Mr Vizards excellent directions - i'm guessing you have been reading his book!

Post by **Packedup** » Sun May 13, 2007 11:32 pm

The HIF carbs flow better for a given size (eg 38 has more cfm than an HS4), and most have a better throttle linkage with a cam for greater butterfly control at part throttle. Also, IIRC, they all have a bi metallic strip in the float chamber for leaning out the mixture when warm - Like a waxstat, but not created by drunk wildlife without any engineering background.

Post by **bmcecosse** » Mon May 14, 2007 7:31 am

Don't see why it would flow any better - looking down the bore the set-up is exactly the same. But the additional attributes are well worth having - especially the no-flooding/gasping.

Post by **Packedup** » Mon May 14, 2007 12:02 pm

I don't have a copy at the moment, but if you check Vizard I'm sure the tables show the HIF equiv sizes do indeed have greater flow figures.

Post by **youngun** » Mon May 14, 2007 8:07 pm

Mr Vizards excellent directions - i'm guessing you have been reading his book![/quote]

Nope, havent ever heard of the man or the book! From where would one acquire a copy.

I see a variety of cams and high lift rockers are available from minispares.com, would these fit onto the mog 948 engine?

Sounds as if we have some conflicting opinions here.
The idea of the bi-metallic strip to lean out the mixture sounds like a damn good idea, and a simple one too!
How much can i pick one of these carbs up for, and how do they compare to a pair of 1 1/2" SU's?

Post by **Onne** » Mon May 14, 2007 8:17 pm

Amazon do the Vizard book
http://www.amazon.co.uk/Tuning-Engine-D ... 208&sr=8-1

Post by **bmcecosse** » Mon May 14, 2007 8:44 pm

Search ebay for the Vizard book - or get it from the Library! If its' a 948 engine then cam choice is very limited because it doesn't have the bearings in the block - so fancy cams are out and 'high ratio' rockers are a menace at any time - forget them. About the most cam you could safely fit (in a 948) would be the standard 1098 cam - AEA 630 - and do not use fancy strong springs with it. All in all - you would be better getting hold of a 1098 engine as a starting point - or going for a full 1275 engine ex Spridget or Marina. Twin 1.5" SUs are fine - but single HIF 44 is easier to set up and works even better provided it's on a good alloy inlet manifold ie ex MG Metro.

Post by **picky** » Tue May 15, 2007 10:55 am

everyone seems to have answered all your questions, but thought I would add one point. the main thing that will effect the "driveability" of the car is the camshaft - if you choose one of the longer duration cams then they produce more power - but only at higher rpm. at lower rpm the engine runs rough and will stall easily. I agree that you might be better off getting a 1098 or 1275 unit instead, as the they are stronger units and you have a greater choice of camshafts. If you dont mind a bit of rough running at low speed as a sacrifice for greater power higher up then I can recommend the kent cams 276.

Picky

Post by **youngun** » Tue May 15, 2007 6:06 pm

Indeed, the 1098 is tempting etc, but i would like to work on a 948 first to get to know my way around and know how to do all the basics before i find a 1098 and go and do some serious work! Ive heard that the 1098 is a rougher engine?
Thanks for all the help everyone.

Post by **alex_holden** » Tue May 15, 2007 6:58 pm

If performance matters you're better off starting with a good condition 1098 or 1275 unless you have a very good reason to want a 948-engined car (eg. to enter racing events with a 1000cc limit or because it saves you a lot on the insurance).

Post by **bmcecosse** » Tue May 15, 2007 8:58 pm

The 1098 is longer stroke - longest of ALL the A series engines and yes it will break the crank if taken much above 6500 for any length of time. The 948 if fitted with a crankshaft damper will rev to 7000 ok (not continuously!!!!) which is plenty for a road engine. It's just the lack of camshaft bearings in the block that hampers it. You can of course use a 1098 block - bore it +65 thou and fit standard 998 Mini pistons and rods - with the 948 crank this gives 998 capacity and has the cam bearings, so can take a more hairy cam and stronger valve springs!

Post by **youngun** » Tue May 15, 2007 9:49 pm

MMM, sounds like a plan to me.......