Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Monty Takes A Deep Breath

It's odd that Ford chose 65mm TB Rog, but it's definitely unnecessarily large, my theory is they went to 65mm because it works with the swirl flaps that are a big restriction, especially at idle where this is actually by design.

The swirl flaps are there to create a significant increase in air velocity at idle, this helps to keep the fuel from falling out of separation with the air and in-turn improves emissions at idle especially during cold start where internal combustion engives produce the most pollution. That's all well and good, but it's not like they disapear when they're not needed. The swirl flaps, which are really just a second set of vacuum operated butterflys, are indeed fully open above 1,500rpm, however, even in this fully open state the spidle remains a significant and undesirable restriction to airflow above 2,000rpm so for me they had to go, and fitting the FF inlet atomatically saw to this.

The idea of going with a smaller 60mm TB is to reduce the area exposed by the butterfly at small openings, going with a smaller butterfly exposes less area for the same throttle pedal movement which in turn tames any 'touchy throttle' syndrome on initial tip-in, I also feel a smaller TB it's a better way of increasing air velocity at idle and during low speed driving than those dreadful swirl flaps.

Admitedly, my idea of choking the inlet just in front of the butterfly is a bit of a bodge, in the perfect world Monty needs a good 60mm TB, I like this one from Jenvey:



https://www.jenvey.co.uk/single-body-60mm-sfg600

A 60mm TB is not only better sized for a standard Duratec Plus 4, but also easily capable of supporting Monty's tuned engine. Jenvey's SFG60/0 also comes with a snail cam type cable track/throttle wheel, this is an old idea but a good one. Back in the day you'd frequently see this setup on Jap four-cylinder motorcycles running multiple carbs; with no flywheel, aggressive cams and a butterfly per cylinder such bikes would have been virtually unrideable without a snail cam.

Running the cable over a large radius at small throttle openings and decreasing that radius as the throttle demand (pedal travel) increases, gives a nice progressive throttle action. This is especially useful when pulling away from junctions or when you simply need to make smooth progress through town as the whole setup becomes far less sensitive to rider throttle inputs at lower road speeds. The issue with Jenvey’s SFG60/0 is at £400 it's rather expensive, and while I suspect the stud pattern is the same as the Ford TB making it a direct fit, the other issue is there's no idle valve (IACV) throttle butterfly bypass port.

The best solution would be to fit a snail cam type cable wheel to the metal Pokess TB, and while not strictly as ideal as having a smaller 60mm butterfly, choking down the 65mm TB should work in a similar way. Using a velocity stack as the choke also delivers the additional well understood benefits of a bell-mouth, which works by using a smooth funnel-shaped flare to draw air from multiple directions, this prevents the turbulence and airflow restriction caused by the hard-edged opening of the standard Ford TB.

A bell-mouth velocity stack allows the engine to ingest a higher volume of air efficiently and relocating all this to the cooler side of the engine bay while at the same time deleting Monty's bendy intake pipe will create a 'best value' power increase, and tame any snatchy tip in too. Actually, Monty already has four bell-mouth velocity stacks buried inside the plenum chamber of his Fision Fabrications long runner inlet:



But he really needs one on the primary air entry point at the throttle body too.



Saying all this, by retarding Monty's ignition timing in the tip-in zone within his ignition table, I've already largely been able to eliminate the 'Touchy Throttle' syndrome.

This works by reducing torque in that critical tip-in area, dulling engine response and smoothing the throttle response as Monty first pulls away from junctions. I've highlighted this area below in my latest updated ignition table; by adjusting the load scaling on the X axis the new table also has better resolution in this critical area which helps dial in more accurate fuelling and ignition timing to deliver enhanced drivability..



As you can see below, the new table now also reaches out to 8,500rpm giving a logical ceiling above my 8,250rpm soft rev limiter, and 8,400rpm hard fuel cut strategies.



I'm now also idling Monty at 18 degrees BTDC with a revised closed loop idle target of 1,050rpm, this is achieved at a super stable manifold vacuum of 55 kPa; I'd challenge anyone in the ITB club to achieve anything close that level of vacuum stability on a set of their darling individual throttle bodies