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MG MGB GT V8 Factory Originals Technical - Fuel injection height reduction

QUESTION - Has anyone machined the upper face of the inlet manifold (ie the face that mates to the ram stack housing) as part of their height reduction steps? Is this viable? There are 4 places where the casting is thin and hence would "break through" the upper face. However, I don't think this would interfere with any of the ports. Any thoughts?

BACKGROUND - I am about to fit a twin plenum fuel injection system from a late Rover Vitesse. External inspection suggested that the tried and tested "Roger Parker" height reduction method would be suitable (although wider, the plenum chamber and ram stack housing are the same height as the regular single plenum system). However, unlike the standard system, the 8 inlet rams are angled 5 degrees off the vertical. Machining 15mm off the ram stack base will therefore create a mismatch of about 1.5mm between the ram stack exit ports and those at the top of the inlet manifold. I guess I could live with this as the rams/ports are 20% bigger capacity than standard anyway, but it isn't ideal. I notice that the top 10mm of the inlet manifold input port is reasonably vertical. Machining 10mm off the inlet manifold top face would mean having to machine only 5mm off the bottom of the ram stack housing and therefore restrict the port mismatch to 0.5mm
Thanks, Pete
Pete Green

Pete,
I've never seen a twin plenum arrangment but it sounds interesting, here are a couple of random thoughts. Be warned though, I'm just in the early stages of engine installation myself and am no expert.
You've got three parts; the plenum top, the trumpet tray and the manifold on the bottom.
You should be able to get at least 12 mm off the manifold under the trumpet tray, I recently saw an example of this.
Also, if your trumpet tray has a top edge like the single plenums, then you can get about 12mm off it if you are prepared to weld up the vaccum take offs ("Phil from Arizona"'s idea). That 12mm plus the manifold 12mm might do the Job for you. Glenn Towery (hope I've got it right Glenn), who seems to know what he's about, maintains that 0.7 inches (17.5mm, with his lower engine positioning brackets) is enough.
The general concensus seems to be that the plenum top itself is difficult to fixture, hence expensive to machine (or weld?). I had orionally thought of getting stuck into the upper plenum cover and taking all the room I needed out of it until other more experienced heads convinced me that its cheaper and easier to take all the hight out of the middle trumpet section, not an option for you I gather.
Peter
Peter

Peter
Thanks for the info...it would seem from your observations that it is safe to take 10mm off the upper face of the inlet manifold (any more than 10mm and the port is no longer vertical...port alignment with the trumpet tray would be lost). I also plan to take 3-4mm off the top edge of the trumpet tray (I'd rather not mess with the plumbing) and 9-10mm off the base of the plenum chamber top. That will give me about 23mm, so I may be able to get away without machining anything off the bottom face of the trumpet tray. I'm using a rubber bumper Xmember, so I should be able to mount the engine low enough?
Pete
Pete Green

I've got a single plenium system, I took as much as possible off the BOTTOM of the trumpet tray, as this does not disturb the trumpet clearance. Using the old Pre-SD1 rocker covers (Rover P6/MGV8 style)gives a little more clearance for removing metal from underneath,whilst still leaving room for air inlet to clear rocker covers. I also removed all the finning on top of the plenium chamber, and flattened it off with an angle grinder to as low as I dared.

Mine now comfortably clears an RV8 bonnet, with soundproofing attached.

Mike
Michael barnfather

Thanks Michael...that's the approach I had planned to take! However, because I found the trumpets of my twin plenum system are angled 5 degrees off vertical (away from the centre line), I need to avoid machining the bottom face of the trumpet tray, or the port alignment to the inlet manifold upper face will be compromised. I now see that Nick Smallwood's alternative method involves machining the inlet manifold upper face....which is good news. Has anyone else had first-hand experience of this?
Pete
Pete Green

Pete,

". I'm using a rubber bumper Xmember, so I should be able to mount the engine low enough?"

Based on Glens remarks, this is what I'm hopeing. The steering rack seems to be the main problem. I'm hoping to locate it in between the back of the pully and the front of the engine, that is if the exhaust extractor manifold doesn't foul the steering shaft. Too difficult to tell at this stage, I'll know in about two weeks!.
I'm going to try for 12 off the top of the tray and 6 off the bottom to begin with. The fuel pressure regulator sits right under the tray on my motor and if 6mm is enough I won't have to weld in an addittional distanceing bit of fuel pipe.
By the way does any-one know an alternative (ie.easy/cheap)way around this problem? Is it easy to swap the pressure regulator to the other end of the rail? Does it absolutly have to be scewed on, or can an older federal (flapper style) regulator (which has hoses and hose clamps) be used, are they the same?.Was location of the fuel pressure regulator a problem for you Michael, others?

Regards
Peter
Peter

Peter,
I actually switched the regulator for a high performance adjustable one from Rimmers, this is mounted on a longer bracket that comes with it, so no problems.

Lowering the plennium chamber by removing metal at the bottom did mean I had to reduce the length of the rubber cinnecting hoses to the injectors slightly, bit from memory this was the only mod I did,

Mike
Michael barnfather

This thread was discussed between 26/08/2002 and 28/08/2002

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