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N47 Head on a Flat top L28


FlatBlack

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I am putting a new motor in my Z car, and heard of some people on here running N42s on Flat top blocks, giving a fairly good bump in CR. The motor I'm working on has a P79 on it currently. I have a couple of questions:

 

The N47 that was on my rebuilt L28 that I am replacing had the exhaust liners cut out of it, and I ported it and it is very smooth. I also had it 'decked' at a machine shop so it is level. A friend told me to use my other head, another N47 with exhaust liners. However, it came off of a motor with a blown head gasket and it looks nasty underneath and the cam has a pretty rough surface. Would anyone advise not using my decked N47?

 

I'm using ARP Head bolts and a Felpro gasket for an early L28, are there differences in cooling passages from the late L28 or can I use this gasket? I saw a different head gasket part number on a website for the L28 and ZX L28. And if anyone else running the N42 setup would like to chime in on random things you ran into I would greatly appreciate it.

 

Thanks

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Use the head gasket that matches the block. A F54 block/P79 head combo is from a 81 to 83 280zx. The heads passages are all about the same but the blocks are very different.

 

Yes, compression goes up with a N47 on a F54 block. Way up. To much for the stock cam. The cylinder pressure will be 220+ psi which is way past the safe limit for pump gas. If you plan on using a stock cam then use a P79 head. The P79 makes plenty of cr (8.8:1) for the tiny stock cam.

 

If you plan to run an aftermarket cam, then use the N47. I would not use less than a 270 degree cam with that much cr. 280 or 290 degrees would be even better.

 

A bigger cam (longer duration) requires more compression ratio because the intake valve closes much later than a stock cam, thus the motor captures less air to compress. On long duration cams, the intake valve is open for some period as the piston is rising up the bore to compress the charge, so the cylinder pressure is lower because it is "bled off". so a 10:1 engine with a 280 degree cam can have 180 psi of cranking pressure and a 8.8:1 cr engine can also have 180 psi if the cam is stock (248 degrees). But put the stock cam in the 10;1 engine and make 220psi. not good.

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I'd say some searching is in order, as the liner and HG issues have been covered here before.

http://forums.hybridz.org/showthread.php?t=134333

http://forums.hybridz.org/showthread.php?t=125186

 

The point of this thread was to talk to some members that had done this swap if they'd like to share information, not about the liners and gasket specifically. I search often, and i post infrequently, look at my join date.

 

Thanks to everyone else for the advice. I don't think I'll use the P79 though because I wanted to give this motor a little compression ratio boost, running on premium gas.

 

I had searched for this swap on here before I posted this thread, and was mainly wondering about which head to use.

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The point of this thread was to talk to some members that had done this swap if they'd like to share information, not about the liners and gasket specifically. I search often, and i post infrequently, look at my join date.

 

 

Ummm yea, Pyro gave you advice you did not want to hear, so you called in when you joined??? LAME. This site has crushed old and new alike.

 

Since you have interest in join time, mine beats yours, giving cred to some one was trying to help might help you.

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I'm not trying to be arrogant or condescending here, just trying to help. Believe it or not, I actually put some thought into most of my posts here. You specifically asked about the head gasket issue, and I gave you a link to my findings on it. I even took the time to wade through all of the postings by 1 fast Z one by one to find that post on the exhaust liners in case it was pertinent to you.

I don't think search should be seen as the S----! word here. I have personally seen many threads on this site that deal with the N47 head, its advantages and disadvantages in a multitude of configurations. Discussions on compression ratios and quench, articles and photos on shaving down, welding and reshaping the open chambers of the N47 to ideal dimensions. Discussions of static and dynamic compression ratios and cam grinds, etc... All of which contain useful information to be gleaned for personal use.

The information is here, by the bucketload. This is a great resource if used wisely. Good luck with your build.

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Alright, i want to apologize, I just get angry when every post I open is someone telling someone else to use the search thread, which is why I never ask questions on here, which is why I called in my join date. It was very lame of me. Sorry.

 

I searched to see if anyone was running this set up and got a couple of people saying they were running their car as a daily, and I read about zeiss150's car and a few others.

 

I got from reading posts that you could set your timing to compensate for the increased chance of detonation [along with using higher octane gas] and didnt realize the importance of the longer duration cam. Thank you all for the advice, this will be my last post, i promise to search only from now on :)

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I am running the N42/F54 combo on my track car. The head had been decked several times before I got it so the compression is really high. We could only get rid of detonation after going completely with race gas 105 octane.

 

We tried a mixture of premium/race and it was not enough to get rid of detonation no matter how much timing was adjusted.

 

After 5 years of track events( usually just 2 a year) the motor still checks at 200 to 210 across all 6 cylinders.

 

I am using MSA Stage III cam with triple OER carbs.

 

Tom

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I have run a 10:1 F54/N42 head (square exhaust port) combination with the stock cam but only because the SCCA Solo II BSP rules restricted the cam as stock. The combination is definitely prone to pinging but I used octane booster, conservative timing, rich mixture on the sidedrafts, etc., and got by.

The cranking pressure is around 210 last I checked. In spite of "detuning" for the combination to protect the engine, I still won BSP when I ran that combo.

 

I'd recommend using the best condition N47 of the two you have (regardless of liner status) and get a cam (it doesn't have to be huge, anything will be an improvement over stock). Unless you cam it, then stick with the P79 and maybe mill it (conservatively, like 0.015" and use Head-Saver shims under the cam towers). You have inherently better quench with the P79 chamber design and will be less prone to pinging with the stock cam and you'll only be at around 9:1, not 10:1, so you'll be less prone to pinging anyway and probably won't need octane booster (but at the expense of some responsiveness and power).

 

I have another 10:1 L6 engine with an N47 head which doesn't ping but it has longer rods (140mm) and longer stroke (83mm) than the L28 (figure that one out). Both of the high compression engines with N series (non-Maxima N42/47) heads I advanced the cam timing a couple of degrees.

DAW

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I guess Im getting ahead of myself here, Im just going to use the P79 until I can rework the liner'd sleeved N47 and save up for a cam. i can always change the head when the motor is in the car...

 

It seems like a worthwhile swap, thanks for all of the input!

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