Re: JMM dev 5 head specs
The JMM heads are all about upping the flow to give you a few more top end rwkw and hold the power to the cut out.
First stage was the DEV3HL big lift = bigger flow from stock head. Works well on the AU and EF XR6 stock heads which have the 47mm inlet and 41 mm exhaust valves like the DEV4/5 heads. Around 140-150rwkw pulls from 3000rpm and peaks at 5000rpm but holds on to 5600rpm
Next "DEV4" or mild porting and slight compression increase to 9.3:1 I think with steel gasket.
With the increased flow you can go for DEV4 cam with less lift and more duration to get around the 160rwkw. This should peak around 5300rpm and run to the limiter 5900rpm.
Latstly the "DEV5" extensive porting as they say and compression increase to 9.8:1 or there abouts. This gives max flow which will suit big durationa nd lift cams to rev hard to the cut out. This will now peak at 5600rpm and go to about 6300rpm the safe effective limit of the long stroke six.
AUII Auto wagon 4.0L InTech Pacemaker PH4480 extractors, 2.5" exhaust, JMM DEV3HL Cam Unichip 144rwkw. 1/4 mile email@example.com