Questions about my 2.7L build.

[wakdog]

I have recently built a 2.7L M20 for track use:

ETA bottom end with Euro 10.2:1 pistons
731 head ported to approx specs of an 885
reground cam (unsure of specs)
Hartge throttle body (63mm butterfly as far as i am aware - 3mm bigger than b25 tb)
Match ported b25 intake manifold
Custom extractors -> 2.5inch exhaust
1.5L surge tank with bosch 044 pump
22lb injectors
AFPR running 3.5bar
Megasquirt 2 ECU

Here is a shot of the dyno graph:



What im wondering is, is there much i can do to make it create more power at the top end... Its making almost 150whp@3900rpm but only makes 9whp more @5700rpm....(we cant figure out whats causing the dip in power @4000rpm, it reproduces it every run on the dyno, but it is very similar to what happens to the 2.8L m20 that the same workshop built that makes 202whp)

Would running a 288deg cam help me (only thing is i doubt my pistons would allow this...)

[MR 325]

It would definitely help if you knew what cam is currently in the head. I think you'd want something more in the 280 range.

[jlevie]

It could be that the engine is mass flow limited up high. A 731 head has slightly smaller valves as I recall.

[digger]

it looks more like a spike at 3900rpm rather than a dip to me because after 4100 the graph is smooth and consistent. If it is the same on another M20 maybe they aren't strapping it down hard enough and the wheel comes off one of the rollers under max torque and then settles back on as the torque falls.