Rolling Road Session - Report

[jono]

I had my Plus 2 on a rolling road over the weekend to set up the ignition curve. (it runs wasted spark ignition and a MJ control unit).

The engine is freshly built with 2k miles now on the clock and has the following specification:

+40 over size on std L block
Sprint inlet valves and 33.7mm exhaust valves with some light porting work to the head
Large bore exhaust manifold.
Air box enlarged to address shrouding of the trumpets on 3+4 inlets
QED 360 cams timed in with verniers
40 DHLA carbs jetted and choked to QED recommendations for the 360 cams
full balance (for what it's worth)

I have attached the graph - pinch of salt perhaps but I was anticipating an honest 135bhp out of this engine which appears to be borne out by the RR session.

What did surprise me is the torque figure - much higher than I expected, could this be correct?

the main finding was that the mixture is variable and too rich in the lower rev range. The idle jets are 50 - does anyone think I should go down a size?

To his credit, the operator admits he is not good with carbs as he mainly work on FI engines. The car runs much better now it has been set up - much more willing to rev and the engine tone has 'hardened up' (if that makes sense). The basic map was too advanced in the upper range apparently.

My inclination is to do what I always intended to do an go to full FI but I would like to at least see if I can tweak the carbs to get them better before I spend a lot of money.

Comments always welcome

Jon

[rgh0]

The air fuel ratio curve is pretty typical of the twin-cam. It is deliberately rich at low rpm to ensure it responds OK when you plant you foot ( and why the choke is never needed!). It leans out once the transition to the main jets occurs and then gets slightly richer as you go from cruise rpm to full power rpm. Overall not a bad outcome and looks like QED did their homework on the jetting pretty well ( as I would have expected)

You can maybe do a little better but really need to do the playing on a rolling road with a range of jets to try. The new type idle jets and emulsion tubes the Keith Frank has designed ( see the yahoo group sidedraft_central) can achieve a better flatter curve.

The dyno is perhaps a little optimistic by a few hp in its conversion from rear wheel to engine estimated torque and hp but it is not far off for your specification.

cheers
Rohan