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JMC L6 Head Project


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Hi all

Thought I would start a thread topic on the JMC head project as from what I can tell no one has done so already. 

would be interested to know if anyone in Australia is planning a build with one of these. 

for those living under a rock JMC designed and manufactured a brand new L28 head with various improvements over the oem N42 head.

- larger intake/exhaust ports with a uniform 2.5mm thickness between ports

- reshaped combustion chamber designed for higher compression 

- redesigned water jackets to improve cooling 

Overall aiming for a better flowing and more durable head for tuning the L28

Website supplying the US:


has spec sheets and pricing chart

video of the head in action

Video where they CT scan a worked genuine L series head and found a port wall thickness of 1.2mm 

The price for a head is around the $7-8k AUD mark. So a significant investment.

I haven’t seen any testing or performance/dyno figures with and without the head for example. 



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I think what they are doing is a great idea, given that OEM cylinder heads are getting harder to source and often in poor shape by this time. I also like the idea of a head you can bolt on that will straight away flow better than anything else. I am eager to see results also, given cost of porting a head and prepping it, the $7-8k is actually not a bad deal.

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  • 4 months later...
On 11/19/2022 at 5:50 PM, 240ZBUILTBYME said:

in terms of exchange rate to the yen there's probably no better time. Id love to get one but really want to see some solid numbers and testing come back from a western source. 

Are you intending on building an all out competition engine?

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On 11/22/2022 at 6:48 AM, hmd said:

My vote is to stay with an L6 with carbies. Just a rebuilt L24 but nicely tune.

Unless you want to do restomod with big flares etc.. then RB26 it.

L6 was always the plan, I never had an original L24, only a L20, so I have a L28 head and block for the build, Ive always planned to go with carbies but lately i have been toying with the idea of doing FI wit ITBs, combined with stroking it makes a pretty potent package. 

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