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Old 11-11-2004, 03:21   #1 (permalink)
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JMM dev 5 head specs

We all know JMM don't give out their cam specs but what about the specs of the dev 5 head. All their website really says is extensive porting, oversize exhaust valves and compression increase, is that shaving the head or just an au steel gasket, what "stage" would extensive porting be equivelant to, this information would be good to everyone for simple evaluation over other products and prices on the market.
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Old 11-12-2004, 01:29   #2 (permalink)
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Re: JMM dev 5 head specs

The Dev 5 head uses the same size valves as the XR6.
Yes its the head gasket and head shaveing.
And yes they do a fair bit of porting.
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Old 11-12-2004, 01:53   #3 (permalink)
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Re: JMM dev 5 head specs

yeah I spoke to them today looks like I'll be going dev 5 cam and street fighter head, jim said it's still good for about 160kw, so next week it should be done if I get this damn bolt off my cylinder head.
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Old 11-12-2004, 02:01   #4 (permalink)
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Re: JMM dev 5 head specs

What sort of car is it going onto?
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Old 11-12-2004, 02:08   #5 (permalink)
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Re: JMM dev 5 head specs

97 el gli auto, not an xf .
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Old 11-12-2004, 02:14   #6 (permalink)
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Re: JMM dev 5 head specs

Hahah, didnt think it was an XF, but was just checking.
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Old 11-12-2004, 03:04   #7 (permalink)
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Re: JMM dev 5 head specs

Quote:
Originally Posted by xfspacsix
what "stage" would extensive porting be equivelant to
I don't think you can put a "stage" figure on head porting unless its done with a CNC machine or flow bench and designed to run a certain CFM for a certain price.

I think the "stage" terminology is pretty stupid - but I guess it gives people like me and idea of being able to compare things - but only from the same manufacturer cos there is no ISO/ADR/SAE standard for "stage", that I am aware of.
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Old 11-12-2004, 03:38   #8 (permalink)
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Re: JMM dev 5 head specs

On top of that different engines flow better with different ports, I have done some research and was amazed that a mild port was sometimes a lot better flowing than a heavier port.
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Old 11-13-2004, 23:01   #9 (permalink)
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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.
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Old 11-14-2004, 00:10   #10 (permalink)
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Re: JMM dev 5 head specs

very good description there jonbays. Power with the 6cyl is all about torque. The engine doesnt rev and as such intake velocity is key. Big ports (as with big cabs on older cars) KILLS intake velocity and hence ram effect of TPI manafolds. This leads to a significant reduction in low end torque. As the 6 doesnt rev a loss of low end torque = one slow falcon!
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