M103 Custome Turbo (Some Questions)


New Member
Jan 7, 2003
Tiny Island
After much research, I reckon the easiest way to squeeze horsepower from the M103 engine is to install a Turbo. The Mosselman kit is out due to high costs so I'm going the custom way.

I am looking to improve low-end/off-the-line response and plan to boost no more than 6psi safely. Probably use a small turbo for quick spool up. Some questions for the gurus:

1. Would I need install an intercooler? Temp around here hovers between 90F to 110F year round.

2. Since I plan to run no more than 6psi, would the stock engine management system be able to cope? Perhaps some way to increase fueling on the CIS-E system?

Need some expertise here. Have a nice weekend. Thank you.


1962-2010. Gone, but not forgotten.
Jul 21, 2002
Guess this ones down to me then :)

The M103 engine designation covers loads of 6 cylinder engines - most of which have 2 independant exhaust manifolds (that I have seen anyway) - This means either a pair of Mosselman manifolds - or a custom 6 cylinder manifold!

This in turn brings on a further problem - a T25 turbo will be too small for a 3.0 engine - even on low boost as it has a ceiling of 240/250 hp even when being driven hard - and when driven this hard the inlet temperatures are too high for safety.
This leads us to either the Mosselman twin T25 turbo scenario - or a single large T3/T4 - which will be laggy but provide suitable throughput.

The ideal solution would be the twin T25's as these can flow enough air to make decent power at low temperatures, whilst still spinning up very quickly to give the required power delivery

90-100 degree temperatures will necessitate a decent intercooler - though with those temps I would seriously look at a water/air setup (called a chargecooler over here) for increased cooling capacity.

We have already proven with Koolvins setup that the std fuelling is insufficient for any serious amount of boost - and he is having an extra mappable fuel injector added to supply the necessary fuelling - and that was at 5Psi - not 6!
The extra injector is a Cosworth one which will supply enough fuel for about another 70/80 Hp

The Mosselman kit looks very expensive - but it is well engineered and fits very well indeed. If you could get the manifolds then it would be a different proposition, as a pair of T25 turbos could be had for under £1000 brand new!

Its your money - but without the fabrication facilities it could end up costing a lot more than a complete kit!




New Member
Aug 9, 2003
I want to get the twin turbo kit for my M104 (S320/300 SE) motor. I hear its a very good company, are their products very high quality? also what is the cheapest price i can find a kit for my W140 S320? thanks for help

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