Thanks,

Gavin/Beandip, Got It!

Ed Palmer

Putting a P79 head on your 78' motor will lower the CR to about 7.6:1. Great if you are planning on turbocharging it, not so great for an NA setup. The best, but not the easiest way to increase CR is to change your pistons to flat tops. This will give you about 9.8:1 with the N47 head. No shaving or tower shimming needed.

If you increase the CR, you will also need to add some way to adjust the fuel enrichment. One way is to add an adustable fuel pressure regulator. The older L-Jetronic EFI cannot compenstate automatically for engine changes like modern EFI systems can.

Pete

thanx z-ya, i was hoping to get the car into the mid or low 14s N/A and suspension work, but if i can get the money of course i will be looking for some turbo ideas.

thanx for the info on the p79 head

Andrew

Pete,

I was looking at it from three directions. Cutting/shaving the N42 head appx .060 and using with the dished pistons; or shaving the P79 head .080 and using the existing ZX bottom end, as stated in the article; or putting the stock N42 head on the ZX bottom end (flat tops) with the 2MM head gasket, for appx. 9.6-9.8 CR.

The article relieved my mind on one point, and that is the benefits or feasibility of the P79 head with the exhaust inserts. Apparently they work well, if you blend them to the valve seat.

I may try it. Purely going to be a street engine, but I want at least 200 HP and it appears that this will provide it.

I have a clean good running N42 rebuild and a low mileage 83 ZX engine, with an extra head for each. Oh the possibilities! The flow rate for the P79 exhaust was my real question and apparently it works fine.

Ed Palmer