Inlet manifold

Post by **alex_holden** » Sun Dec 10, 2006 10:46 am

Does anyone recognise what kind of inlet manifold this is? Will it take a standard carb and will it give better performance than the standard manifold?

Post by **Innovator** » Sun Dec 10, 2006 11:36 am

Not sure of the actual make but if you get it for under £10 its worth the gamble. It should flow better than a stock manifold.

You may have to play around with the adapter plate to get a 1 1/4" SU on as most aftermarkets are for 1 1/2" and bigger.

John

Post by **alex_holden** » Sun Dec 10, 2006 11:40 am

Thanks. I hacksawed my manifold in half this morning and just broke through into the inlet half, so I could do with a replacement anyway...

Post by **alex_holden** » Sun Dec 10, 2006 11:49 am

And then eBay stopped responding just as I was about to place my bid...

[Alex bangs head on desk]

Post by **Innovator** » Sun Dec 10, 2006 11:58 am

I often used to cut through one side when splitting the manifold. I used to braze on a plate to cover the hole.

Post by **alex_holden** » Sun Dec 10, 2006 12:01 pm

I have brazing equipment, so that's Plan B. Luckily Fenchurch is off the road at the moment so it doesn't matter if it takes a couple of weeks to get hold of a replacement.

Post by **Packedup** » Sun Dec 10, 2006 1:53 pm

Somewhere around here I've got a 1/2" inlet manifold - It's cast and has clearly been cut off a combined inlet/ exhaust (maybe Mini). Has some surface rust down the holes so needs a good cleaning out, but should be serviceable. No cable brackety bit though.

That one listed is for a 1/2" (HS4) carb, but looking at the pic it might also have the vertical mounting holes for an HS2 - Looks like there's screws in there but you never know, might be an unscrew and fit studs job? Worth asking the seller unless you're happy enough to go HS4 (which personally I would on a 1098 anyway given the option)

Post by **alex_holden** » Sun Dec 10, 2006 2:02 pm

I missed the one on eBay as the site stopped responding at the wrong moment. Is the one you have equivalent to a standard one performance-wise? I think if I'm going to have to buy one I might as well go for something better than what I have now.

Post by **wanderinstar** » Sun Dec 10, 2006 4:27 pm

Alex, I have a combined one from standard 1098 you can have if you want.

Post by **alex_holden** » Sun Dec 10, 2006 4:57 pm

Thanks for the offer Ian, but splitting another standard manifold is a last resort if finding a more efficient intake and patching the one I've got both fail.

Post by **wanderinstar** » Sun Dec 10, 2006 5:09 pm

Well it's there if you want it.
Actually if you have split one and gone into inlet, doing another should be easy. just go more into exhaust side. I did mine with angle grinder and cutting disc. Having two manifolds makes it a lot easier. You dont have to be so precise.

Post by **Packedup** » Sun Dec 10, 2006 7:30 pm

alex_holden wrote:I missed the one on eBay as the site stopped responding at the wrong moment. Is the one you have equivalent to a standard one performance-wise? I think if I'm going to have to buy one I might as well go for something better than what I have now.

Yeah, the one I've got is a standard Mini one (at least I reckon it's Mini - It's standard cast something or other A series!). Means you can go to an HS4 carb instead of the HS2 found as standard on the Minor, but obviously isn't anything fantastic in terms of uprated flow. But then, unless you're mesing with ported heads and longer camshafts you might not make use of any extra flow - Bear in mind too large on the bores only hurts low end and gives next to no increase in top end on a standard engine.

I'm surprised you even tried to seperate exhaust from inlet without sacrificing one or the other - I used to just get 2 and butcher the required bit off each!

I know someone who recently paid about 10 or 15 quid for a s/h aftermarket MG Metro-alike alloy inlet at a local Mini specialists. Might be worth a try if you're looking for go faster

Post by **alex_holden** » Sun Dec 10, 2006 8:12 pm

Packedup wrote:I'm surprised you even tried to seperate exhaust from inlet without sacrificing one or the other - I used to just get 2 and butcher the required bit off each!

Well I'd been told it was possible and I'm fairly nifty with a hacksaw so thought I'd give it a go. I almost managed it too - the blade only broke through at the middle of the thinnest part by a fraction of a mm

And when I'd separated the two parts it was obvious why - the blade had been bending in such a way that the exhaust half of the cut was convex and the inlet half concave - the outer edges of the cut were in the right place but the centre was nearer to the inlet.

Post by **bmcecosse** » Sun Dec 10, 2006 9:57 pm

The best inlet is the Mg Metro alloy one. But even a combined inlet/exhaust manifold fom a later Mini will flow 10% more air than the ghastly old Minor manifold. If you then fit the later 1 1/2" SU carb it will flow even more. And increased flow = increased power.

Post by **Packedup** » Sun Dec 10, 2006 11:58 pm

bmcecosse wrote:And increased flow = increased power.

But increased flow from huge bore sizes = less low end power through the range, with the extra power only kicking in at valve floating revs.

You need to keep the charge/ gas speeds up for better cylinder filling at lower revs, while still having a free enough flowing pipe/ tube/ bore to keep the volume (flow) up. If you're only interested in peak power figures then the performance through the range isn't a concern, but when tweaking a road car there really is more to it than going for a big number in the hp column. I'd rather have a 40hp engine that gave 30 or more from 2k rpm than a 60hp engine that gave less than 20 till 5000 rpm (figures hypothetical for effect).

The MG inlet is a little on the large side for a 1098, but probably the best easy to find option and certainly good at higher revs. Agreed on the Mini cast one though (and not just cause I've got one to sell ;) ), the rest of the engine isn't fire breathing so going for a better flowing but still not stupidly oversized inlet and carb would surely be a decent option. I know my 1098 Minis used to go quite nicely on the standard HS4 they came with. Fitting a HIF38 made a noticeable difference though, so might be worth looking for to go on whatever inlet ends up fitted

Post by **alex_holden** » Sat Dec 30, 2006 4:04 pm

I've now got a Minisport alloy inlet manifold. On the carb side it has a 1 3/4" dia. hole in a square flange with four 5/16" BSW mounting holes at 2 1/8" between centres. I could make an adapter plate to fit the standard carb, but I'm thinking of upgrading to a bigger carb instead. Will a HIF38 fit it without an adapter? Am I likely to need to change the needle to get it to run properly?

Also, what is the water jacket on the inlet manifold for? Is there any point at all in hooking it up to the heater return?

Post by **Packedup** » Sat Dec 30, 2006 4:29 pm

All sounds very technical with those measurements - I'd say it's almost certain to be an SU manifold given they nearly all are!

The HIF38 will fit on the same stud pattern as the 44 (which is 1.75", the same as the bore on your inlet so I'm guessing it simply has to be an SU one!), and also the HS4 will fit but only using 2 of the studs, at least one of the other two needs to be removed or it fouls on something IIRC.

You won't be running the optimum needle if you just slap a 38 on, but you won't be if you stuck a 44 on or just worked the old HS2 on either (different inlet so different flow, equals different fuelling). It depends what the carb you fit came off, but you'll probably get away with the needle that comes with it, though there might be flat spots through over or under fuelling at certain points. HS2 and HS4 carbs share the same jet size and therefor needle range, I can't remember if the HIF38 also uses the same needle range or not though - You might be able to simply fit your exisiting works OK needle, but it'll not run quite right all the same because of the change of manifold flow... Might not run not quite right enough to make any actuall difference of course

The heated jacket is an economy thing mainly, and can be ignored totally unless you want quicker warm up times and/ or have carb icing issues.

Post by **bmcecosse** » Sat Dec 30, 2006 5:26 pm

For a standard engine - the ports on the MG inlet will be just fine - the supposed loss at low revs will be very very slight (if at all) and more than compensated by all the other gains. There is very little 'ram' effect on the A series engine - remember it fires 3421 - ie it pulls twice on the 3-4 port and then twice on the 1-2 port, the gas between times in the 'unused' port coming to a shuddering halt !! It's the reason a 7 port (or 8 port) head makes so much difference to the engine. Sadly - they are not cheap. And yes - the HIF carb (38 or 44) will bolt straight on.