02 SepFuel Injection Manifold
This article kicks off a series on how to go about fuel injecting a Triumph Spitfire 1500. The plan is to first install a trigger wheel and Megajolt, taking care of the spark side of the ECU by making the small jump to electronic ignition. Once the Megajolt has been fully configured and all it’s possible benefits explored, the next leap will be fabricating an inlet manifold and replacing the Megajolt with a Megasquirt unit controlling not only spark but fuel too.
Anyhow, here’s the first draft of an idea for a modified 1500 twin HS4 inlet manifold. The carbs will be removed, and 4 holes will be drilled at the front of the manifold where it attaches to the head. Bosses for modern injectors will be welded in, at an angle that allows them to fire directly into the intake port.
The nice thing about this method will be that it retains a bit more originality than creating an entirely new inlet manifold and plenum from scratch. Here, the plenum merely replaces the carbs as a bolt-on part of the induction system. Runners are shown as part of the plenum to maximise the length of the inlet tract, but these don’t even have to be included. Perhaps they could be made as a separate item, making this a multi-piece affair?
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Why not twin throttle bodies?
Even on a modified engine the benefit is fairly limited (mine’s a standard UK 1500) versus a well designed plenum with single TB – and then you have the added complication of having to synchronise the air flow between them, fabricate linkages and basically introducing a load more things to go wrong. Even many Ferrari engines use single throttle / plenum setups, so I think while it would be nice to explore that option one day on a highly modified engine, for my purposes this should do fine.
Unfortunately you chose to use the ONE manifold from Triumph that is absolute crap.
This carb manifold is extremely difficult to modify and limits the peak power of the engine to about 100bhp and 6000rpm.
You NEED to use a Weber type 4 entry inlet manifold to get power out of that head, even if your head flows only as well as the majority of so called specialists are currently delivering (about 73cfm grand max)