DOHC - Creating a 2.3 8v hybrid

While the tuning options for the 2.0 DOHC engine are limited, one option that interested me was the creation of a 2.3 DOHC engine for the Sierra - using the bottom end from a 2.3 16v Ford Scorpio and a 2.0 DOHC 8v cylinder head.

 

History of the 2.3 8-valve hybrid project:

Having owned and driven a DOHC car since 2000, I believe that the 8-valve "I4" DOHC engine fitted into the Sierra from 1989 is a relatively capable engine. Yes, it's not as cheaply tunable as a Pinto it replaced or even as reliable as the venerable boat anchor that is the all-iron OHC, but it's smooth, got nice low down torque and in standard EFi trim will easily see off a similar capacity Mk.1 or Mk.2 16v Zetec-engined Mondeo from a standing start.

While the twin-cam is noted for its cylinder head problems surrounding the head casting, head gasket and timing chain, the bottom end is actually fairly robust and was used as a starting point for the 16v DOHC "I4" engine first used in the Mk. 5 Escort RS2000, and thereafter in the Galaxy MPV, and Scorpio. In the Galaxy and Scorpio, the engine was available in 2.0 (8v and 16v versiona) and 2.3 (16v only) capacities.

As highlighted in the DOHC Tuning guide published on this site, there is only so much that can be done to economically increase the power output of the 2.0 8v engine. Having done most of those myself, yet not being able to afford an aftermarket super- or turbo-charger configuration, the next stage would be to fit an engine of increased capacity - which to me is the 2.3 DOHC.

Used in conjunction with Escort RS2000 16v camshafts, throttle bodies and aftermaket injection, much larger power outputs are being seen from an engine that was originally lamented for it's smoothness and refinement, putting out 145PS in standard form. One quoted figure I've seen on a forum is circa 300bhp, though I have no idea how reliable this quote is or how much "pub room bullshit" was involved in coming up with it as I've not read the artical directly myself or even spoken to the guy owning the car in question.

It's certainly an eye-opening increase though, isn't it? Escort RS2000 owners are regularly seeing close to 200bhp from naturally-aspirated 2.3 engines with the use of the RS camshafts, engine management system and an uprated fuel pressure regulator.

I didn't have time to source and fit the complete 16v engine, with the associated plumbing and wiring changes that must be undertaken, to what is in effect my "daily driver" - let alone create a custom throttle body inlet manifold, or wire up and tune aftermarket injection systems necessary to get it to run afterwards so my options for the use of the 2.3 engine were essentially limited.

However, investigation showed that there are many similarities between the Sierra 2.0 8v and the Scorpio and Galaxy 2.0 / 2.3 16v engines - the head gasket interface in particular - and I started thinking that it would be relatively easy to build up a 2.3 block with a regular Sierra 8v cylinder head on the top.

Such a project would be very interesting for the following reasons:

  • The standard 8v EFi setup can be maintained, removing the need to rewire the engine bay or fit aftermarket injection / engine management systems from the outset.
  • Standard intake and exhaust systems can be retained - less need for custom fabrications.
  • The engine would essentially look completely standard - ideal from a street-sleeper point of view. :-)
  • The 2.3 8v engine would produce increased amounts of torque due to retaining the 8v setup while increasing capacity. BHP is great, but Torque is what accelerates you faster!
  • The 2.3 8v engine would essentially be a straight-swap for the 2.0 8v unit making installation a one-day affair.
  • To the best of my knowledge, it had not been done in a Sierra before.

So I did - I went out and built one - and the results were very impressive!

 

Building the 2.3 8-valve DOHC engine:

All links will open in a new window.

 

CLICK HERE to open up the complete "How to" document (approx 1.6Mb in size).

My 2.3 8-valve DOHC engine sprang into life on 11th November 2006 - HERE is the "running report" I wrote for the Winter 2007 edition of the Ford Sierra Owners Club magazine, Jellymould, that describes the early experiences with the engine.

As this was an ongoing project, CLICK HERE to open up the project thread in the Ford Sierra Owners Club online forum, where I discussed aspects of the build as it progressed, and where others had input / asked questions about what I did.

As always, treat the linked website and pdf documents as guides only. You may need to improve brakes, steering, suspension and tyres if fitting a larger, more powerful engine than your car was originally built with! Therefore if you are unsure as to any point in the linked thread or the documents, seek clarification or consult a qualified mechanic before you choose to "dive in" yourself - I will not be responsible for what you do (or break) on your car!

You will need the Adobe Acrobat reader to open these 'how to...' feature documents.

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