A Project Is Brewing...

[rossiz]

craigslist score #1

 

 

craigslist score #2 will be picked up soon...

 

 

let the fun begin!

[S30Driver]

Must mean there is no sign of that rebuilt head coming back....

 

But now, you might have a P90.  Just bolt it on, you'll be back on the road in a couple of hours. 

[rossiz]

actually, the N42 is coming back - dpllc is rebuilding a different one for me and sending it out, probably next week. he has been more than fair to work with so far, and i'm hopeful that the first head i got was an anomaly... will report back when i receive it.

 

i found a complete flat-top F54 motor w/a close-ratio 5 speed and plan to put the N42 on it for a high-comp setup. the motor comes with a P79, (wrong exhaust port shape) which i'm hoping someone else might be interested in. i've been wanting to do this for a while, and once the head comes back i should have a running car (fingers crossed) and the other motor on a stand in the garage, offering the time/patience to pick away at the build and do a nice job. 

[Jeff G 78]

The P79 is an awesome head.  I run a F54/shaved P79 combo in my race car with great results.  I shaved 0.050" and reworked the cam gear and chain guides so I didn't have to change valves or run tower spacers.  I love it!  With a Web #91 cam, it pulls to 7k and runs strong.  The benefit of the P79 over the N42 is that it's much more ping resistant so I can run more advance.  Here in the East, I have 93 octane fuel, but with only 91 out West, I'd be afraid of the N42/F54 combo.

[Diseazd]

Ditto what Jeff said......I have 4 Z's with P79 heads with 080 inches shaved off. I can't make 'em ping in any gear. The P79/ P90 is a more advanced combustion chamber......ping ain't fun!

[rossiz]

thanks for the input - i've been reading all sorts of opinions on both sides of the f54/n42 ping debate and some say it pings, some say it's great...

 

here's my issue: i've got a brand new msa 6-1 header that needs either the n42 or the p90, and i've got an n42 being rebuilt as we speak. so i would have to buy another head (p90) or another header (for the p79) as well as re-build the p79.

 

i'm trying to do this build affordably (did i just say that??) and don't have the $$ to re-purchase heads/headers.

am i setting myself up for disaster?

[Zed Head]

Aren't you still using the stock EFI engine management?  1978 computer, AFM, etc.?  The stock EFI system runs off of a "programmed" fuel enrichment map after the AFM opens a certain amount or the throttle is wide open.  The map doesn't work well with modified engines, apparently.  I haven't seen a specific reason why, but I would guess that it can't be balanced for both high air flow (RPM) performance, and clean running elsewhere.  It will be either gassy and rich most of the time, but fun when wide open, or run okay most of the time but down on expected power at WOT.  Jeff G and Diseazd would know more.

 

In short, most people say get your engine management right before modifying the engine too much.  If you put the N42 head back on the N42 dished-piston engine, you can drive it while you build the other one.

 

Some people say it's okay to use the square port header with a round port head.  I've matched gaskets and it seems tight but if the exhaust port liners exit inside the edges of the square header flange, there shouldn't be any dramatic flow hindrance.

[Jeff G 78]

To clarify and answer Zed Head's question, I run my F54/P79 on SU's.  My 280Z with F54/N47 is FI, but I tried and failed to get it to run right with the mild cam.  It runs fine with the stock cam, but the Web #91 cam didn't work at all.  Idle was rough and power was way down until high RPM where it was better, but still down from where it should have been.  The stock cam makes better power with that engine and fuel setup.  The same cam in my SU-equipped F54/P79 260Z is fantastic.

 

As for the ping debate, I'd be willing to bet that it's a regional issue.  The Western half of the US only gets 91 octane premium, while here in the East we have 93 at all stations and even 94 at some.  I run 93 octane premium in my F54/N47 street car with no issues.

 

EDIT:  I mistakently typed F54/N42.  I run a N47 head on my 280Z.  Same chamber, but different port shape.

Edited January 7, 2015 by Jeff G 78

[rossiz]

hmmm... more good info.

questions for those that have done this (jeff, guy + any others...)

• how feasible is it to run the n42 header on the p79 head (exhaust port question) - will i burn gaskets? hinder flow? notice a difference at all?
• can anyone confirm if the f54/n42 can run decently on 91 pump gas? 
• am i better off trying to find a p90 instead of replacing my header?
• is this worth trying???

[Diseazd]

I run stock(early) exhaust manifolds on all of mine. The stock manifolds don't match the P79 head either, but they work fine. The experts tell me the stock manifold is pretty efficient......no hollow sound either. I've also heard that a longer duration cam i.e. Stage III Isky is less likely to cause ping in higher compression engines. I also only use the SU carbs......they make plenty of street power with less hassle (IMO)......no idea what EFI does with a highly modified head.....sounds to me that it's a problem according to Jeff. I've never built an N42 head. Z Doctor in Roanoke built my first modified P79 head and I loved it so much, I did it 3 more times. Sounds like Jeff loves his set up too!

[Jeff G 78]

I've heard you can run the square header, but I've never tried it.  I also edited my last post.  I had a brain fart and incorrectly said that I use a N42 head on my FI 280Z.  I actually run a N47 head on that car.  They have the same chamber, but the N47 has the liners and round ports.  I run a 6-1 header on the N47 and a 3-2-1 header on the P79.  Sorry for the mistake.

[rossiz]

brought the lump home - a few "before" pics:

 

 

 

it looks like my square port 6-1 msa header should work fine on the round port p79 so i've decided to use it instead of the n42.

 

here's my dilemma:

i'd like to shave the p79 in order to get the comp ratio up to 10:1, (which i believe should be safe enough to avoid pinging with pump gas) but the po says it was warped and he had it shaved to fix the sealing surface, and i don't know how much they took off it... so how do i know what to take off at this point?? do i measure the chamber volume? and then what do i want the final chamber size to be for a 10:1 engine? and is 10:1 a good comp ratio?

 

lots of questions, i know... i just want to get the basics right before i dive too deeply into this.

thanks!