17 Aug320 Miles of Driving and 1 Fuel Injection Manifold

Here’s a few photos of what I’ve been up to today in my Spitfire. Left the house about 8am to drive down to see Tim (bestquality03), finally got there at 11am with no trouble at all, save for the wipers packing up on the motorway in torrential rain at 80mph 70mph (fusebox contacts…grr..), the cigarette lighter socket not charging my phone as I’d forgotten to connect the ground cable to it the day before, and a bit of congestion on the M6. So far so good though!

After having a good look at Tim’s awesome GT6, we went inside to the drawing board and started to look at the head and manifold I’d brought. After our phone conversation last week I decided to not use the original Triumph plenum, as there’d be so many compromises it’d kindof defeat the point of retaining it – so we planned on just using the flanges from it. However, Tim decided that the manifold was in too good condition to cut up, so instead we took the approach of tracing the flanges onto paper, making them up in CAD and then punching them out of 2mm aluminium and sandwiching them together to make a flange. Since it was just for mockup purposes it wouldn’t be a problem.

This is the machine that punched them out ^

…and the Spitfire manifold flanges that were then stacked and tacked together. Anyone fancy making some money? Just need a picture of the queen on them offcuts…  ;D

From the measurements that I took on Sunday, Tim worked out that we could get away with about 7″ of inlet runner length, so he then cut 4 equal sections from ally pipe with the same inner diameter as the Spitfire’s inlet ports.

The pipe was an absolute perfect match for the port when checking it. Why wouldn’t it be?  8)

My box of injection goodies lying on the table. PWM idle valve, dizzy to be used for cam position sensor. Mike, I was going to drill that fuel rail blank on the right for you like I did mine, but to be honest I’m not 100% happy with how I went about drilling mine and don’t really want to risk messing yours up – I think it was more luck that it fits than anything. So instead it’s probably best if I give you first refusal on the fuel rail in a blank state? I can give you the measurements to take it to someone to get machined.

By the way Tim, realised when I got home I forgot to leave the old inlet valve at yours – doh!  >:(

Tim’s expert welder attaching the runners to the flanges  8)

I removed the carburettors and manifold as a whole then just stuffed them out of the way so we could trial fit the prototype – first pair of runners fitted absolutely perfectly!

I was worried about the manifold fouling the exhaust, as I’ve got the Bell exhaust manifold with the lovely long straight exit out of the head, and I knew people struggle to get Weber manifolds to fit. Not our manifold! There’s actually loads of space, at least 5mm air gap from what I remember, which is great.

Surprisingly clean after 160 miles of driving, my Spit quietly waits while Tim tries out a new idea for the 3″ diameter plenum; a 45 degree extension, angled slightly downwards as well, that should give a bit more inlet tract length and facilitate hose routing after the throttle body.

That’s what torque looks like, or at least we think it is. We settled on the back of the plenum being 70mm from the centreline of port 4, which gives just over 10mm of space between the plenum and bulkhead. Apart from leaving it about 5mm longer at the front of the straight 3″ section of the plenum, this is what we’ve settled on. The throttle body is a 48mm unit from a Rover 25. Although it’s hard to see in this photo, with this location, you could quite easily choose to either run inlet hose under the radiator and to the front grille, or run it around the drivers side of the radiator (I’ll be doing the former).

We’re pretty sure the best place for putting the injectors will be about 1/2″ to 1″ away from the cylinder head, so we can aim the injector to spray right at the back of the valve head. Giving good fuel economy but also still reasonable amounts of power+torque. Just about all the other Spitfire injection manifolds I’ve seen have the injector placed right at the flange, and there’s no chance in hell that’d hit the back of the valve head – the port is at least an inch long before you reach the short side radius, so you’d just basically be hitting the wall of the port if you positioned them that close. What do you guys think on the matter?

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