12 replies to this topic

[rock1day]

I have a standard 1986 998 Mini City and thinking of Stage 1 tuning it.

 

I have acquired a Maniflow "Extractor" manifold, a twin box RC40 exhaust and a KN filter element originally from a Mini spares Stage 1 kit.

 

However, I don't have the Mini spares alloy intake manifold - will I lose much in the way of performance if I separated the standard cast intake 

manifold from the exhaust and run it with the Minispares Stage 1 exhaust manifold and exhaust?   

[blacktulip]

The standard intake does flow well but the area that it becomes a problem is the heat it gets up to which affects the performance. You could run it for now until you can get another alloy one from minispares.

[Tomm]

Just the other day i was reading the big yellow book and there was a break down of the intake manifold. The opinion seemed to suggest that the cast intake manifold had one of the best flows availible and that many after market options had worse performance properties than the original cast system. I also seem to recall that there were some modifications which could be done to improve the cast intake even further. 

[Gilles1000]

Blacktulip and Tomm, I agree with you.

 

If I remember well -also from my read of the big yellow book- just separating the standard inlet manifold from the exhaust would improve the flow quite a lot.

The reason is there would be less heat convection from the exhaust.

 

If so, would an additional heat shield also help to improve the flow??

[Turbo Phil]

Separating the cast inlet/exhaust manifold doesn’t increase flow, but it does increase charge density due to the drop in temperature.
If I remember rightly it’s quoted as quite a substantial improvement by mr Vizard.

Phil.

[Bobbins]

I separated one years ago as per the Master's recommendation ..... I don't know whether it helped the charge density but it certainly made me feel like Popeye after an hour with a hacksaw!

[baop]

Did this on mine, used an angle grinder, don't feel any need to change it or any lack of performance 

[imack]

I remember cutting one off with a hacksaw, it's hard work!

[blacktulip]

Also you could use an injection manifold gasket as they have a metal face which could help the heat transfer from head to manifold.

[nicklouse]

Just a note about using the old cast inlet. You may have issues positioning it. As it has no location cut out on the lugs. It uses the ones on the exhaust to do this. If your engine used the locating rings and the head has not had, or has limited, work done on the ports you can and should use these. Also clearance to the center exhaust pipe is very tight.

 

so have a look and a think before spending the time cutting and making clearance.

[absx2]

I have located them with a couple of 3 mm roll pins in the past but obviously the head was on the bench.

It used to be a free mod back in the day when there were plenty of manifolds kicking around to remove the " hot spot " by hacking up two manifolds to make one and with a bit grinding to optimise what you had it gave good results.

I still have them on the 850 and the mk3 as under the bonnet looks unmolested and I don`t believe a performance exhaust manifold gives any discernible improvement over the standard cast manifold in such a low state of tune provided there is not a step in the down pipe diameter to the performance exhaust as it will slow the gas down. 

 rock1day in your instance unless you are removing the head for a clean up i would buy a small bore alloy inlet for around £40, don`t use an MG Metro manifold as the ports are too big.

As Nicklouse says the clearance on the center exhaust is very tight and not all lcb/free flow type manifold will clear a cast iron inlet. 

[rock1day]

I`ve separated the intake from the exhaust (destroyed the exhaust in process) and then cleaned up around the cut just enough to clear the Maniflow exhaust.

 

To locate the intake, I decided to hold the manifold up to the gasket, center it on the intake holes and then pencil a line round the manifold face?

 

With an AAU needle and 5 degrees of static timing it runs O.K. - quite a noticeable difference in the midrange and it seems to rev better at the top end.

 

I`m using a metal air filter box (off an Austin 1300) with a metal intake horn (feeding air from above the rocker cover).

 

Having read the Keith Calver Mini tuning article re drilling extra holes in the airbox. does anyone know if it would be worthwhile adding a second intake nozzle and horn on the opposite side of the filter case?   

[unburntfuelinthemorning]

Having read the Keith Calver Mini tuning article re drilling extra holes in the airbox. does anyone know if it would be worthwhile adding a second intake nozzle and horn on the opposite side of the filter case?   

The most restrictive part of the air filter case you're using is the intake nozzle so adding a second one would certainly help airflow.