Actually, there is no substitute for displacement when we talk about naturally aspirated engines. The Duratec from Monty is one of the last "classic" engines and depending on the horsepower output by a change of camshafts etc. it will lose torque at lower speeds. But on the other hand, the Morgan is a light car and the driving pleasure is certainly great if you want to be sporty.
The engine of the Plus 4 Supersport that Chris also gets in his MGB is the (without tuning) 160 hp 2.0 engine from the Mazda NC. It had a variable intake camshaft, a nice engine, I had it in my Plus 4 Supersport.
Now comes my point, the small Sigma 1.6 of the 4/4 has adjustable intake and also adjustable exhaust cams. It was the pinnacle of Ford naturally aspirated engines before the Ecoboost came along. This engine, with a sport manifold, metal cat and ECU tuning, acts like it got more displacement and not just "top end" more power. That is of course only possible until about 145 hp. If you want more power it also applies to the Sigma to install other camshafts and have less torque for the road. But the power of 145 hp with a torque of 180 NM is perfectly suitable for my car.
If I wanted to tune a little more then I wish a shorter gear ratio. I am convinced that my 4/4 with the 4.1 ratio would be just right. Why do I mean this:
My other toy is the Elise I have from new since 2007. It has a 4.3 final drive ratio that was tuned for originally 136 hp. Now since 2008 I have 230 hp and 260 Nm already at low rpm thanks to a Rotrex belt driven turbo. The original gear ratio is too short for that. Since a few weeks I have a replacement gearbox from a MR2 (with LSD). It has 3.9 final drive ratio. At 4000 rpm I drive 140 km/h in 5th gear. Before it was 125 km/h.
Everything feels perfect and right now....
Back to the 4/4, it reaches at 4000 rpm 160 km/h in 5th gear with 3.7 final drive ratio. Absolutely much too long. I can already use the third gear on the B country road not fully because it revs up at 6500 rpm to 160 km / h which is complete nonsense. If I had a 4.1 diff I would not get too short which I now definitely know, but like the Elise it would reach 140 km/h in 5th gear at 4000 rpm.
So much for "my" tuning wish. I called Vitesse, instead of a 4.1 final drive it „would“ be possible to swap for a Mazda Nc 6 speed gearbox with the result that gear 1 to 5 had the same final ratio than the 4.1 Diff with the unchanged 5 gear box. But…it is too much a hassle and the 6 speed box is slightly wider which means a new aluminium cover with new leather for the gearbox plus another prop shaft…
Therefore my last attempt will be to find a company which could make a one off Sprocket and bevel gear because Simon stated here that BTR does not have the offer for a 4.1 diff.
