L28+(maxima)47 build

[madkaw]

I bought a f54/P79 zx motor about a year ago. Paid 200$ for a motor that came from a running car that had 110K miles-DEAL! 

I was just wanting a L28 block with flat tops so I could put my e88 head on when I was done messing with my L24. The bores looked great and it all cleaned up well. Had the block tanked and a ball hone on the cylinders. They magnafluxed the block and measured out the bores for me to check specs, all was good. 120$

At this time, I wasn't planning on using the P79, so I sold it off for 150$

 

Since my L24 project is going so badly, I thought I might try and work the L28 at the same time and use whatever engine is done first. But was headless.

Always have been intrigued with the maxima head. It might be the best value out there for performance. They aren't as scarce as I thought and they are pretty cheap. It bolts on and has a more modern chamber like the P79, just a LOT smaller. I have read the archives and several builders swear by them. Maybe myth busting or adventure seeking, but a street gas 11:1 l28 would be a hoot. I have an advantage to the average guy that bolts it on and crosses his finge; I have MEGASQUIRT to fight detonation and lean spots and timing curves and....

 

I found an "A" rated head for 150$ shipped to my door. It was very clean and I bet I could have bolted it right on and it would have worked. But it is getting freshened up to get ready for a Rebello cam.

 

 

[rossiz]

so what are the main differences between the maxima and p79/p90? i see the quench design and you mention a smaller chamber, but are the valves the same size? is the plug angle any different? do they flow differently?

[madkaw]

MN47-39cc

p79-53cc

 42 intake but 35mm exhaust

Flow numbers are out there in the archives somewhere. Stuff I've read that it's plenty good to 8000rpm. The ports are Dshaped, but not sure how much smaller, but I don't think it's alot. I believe i measured 35mm across the inlet.

Don't think there is any angle difference.

[siteunseen]

So in your opinion an MN47 is a better choice than a P79?  I've got the P79 already and now I'm thinking I want the MN47.  It wouldn't need the cutting or the tower shims, right?

 

Thanks,

Cliff

[madkaw]

Cliff,

Better in the fact it's about a bolt on with no real modifications, Worst in the fact of the small chambers gives you less control of CR . The P79 allows you to choose your CR based on how much you shave. They both have a great modern combustion chamber. And as Jeff pointed out; there are other options than swapping out valves to make the p79 work, i.e. adjustable cam sprocket.

The slight advantage of the Mn47 , from what I've read, is that the head was designed with small chambers and the ports have a smoother transition into those chambers. Where as the P79 with it's tall chambers has a tighter turn to make it into the combustion chamber.

I'm going for broke with a high CR motor. I have 93 and 94 octane  around here in Indiana. 1fastZ swears that with good fuel control and ignition this combo works well running full ignition. I do have an advantage running MS. Not sure if this motor will see Mikunis mounted on it or FI right away. I have a stock FI intake coming USPS.    

[siteunseen]

Thank you Steve for explaining, I'm intrigued as well.  It has less CCs than the E31 I'm working with now.

 

I have an F54 with new .030" over dished pistons.  I think the MN47 would make a nice lid for it. 

[madkaw]

First set back-head is so warped that it's junk. Good news is the junk yard refunded my money and I get to keep everything! So now I have a head to experiment and cut up on!!

[madkaw]

Cliff,

I believe the bigger the jugs, the better( I leave that alone-)

A bigger bore would allow for more unshrouding of the chambers which would lower CR to compensate for bigger bores. The unshrouding of the head would allow for better breathing!

[siteunseen]

FI? Programmable I suppose. Works good on race bikes and boats.

[madkaw]

Megasquirt is already installed if that's what your referring to.

Have another head coming from Florida of all places. Keeping my fingers crossed on this one.  

Edited May 11, 2015 by madkaw

[madkaw]

Here's some more pics of the project, mostly of the L-28 that supposedly only had 100k. The cylinders looked great as I said, but a good amount of rust on the crank around the flywheel end. A very strong groove in the seal area that I think might be an issue. The issue being that the amount of surface rust across the whole surface doesn't allow for moving the seal much to avoid the groove. I think I will be installing a speedy sleeve on there.

Also interesting to me that the pistons all were labeled P79, I wasn't aware that Nissan did that. Am I assuming too much?

Also asking(which makes me wonder if this engine was not touched) is the markings on the main bearings a normal numbering system?

 

The machine shop said the block was straight across the top and I decided to reassemble the block with one piston to check deck height. Well it seems the rumors are true- about .019 above the deck. I guess I will be taking the block back to get shaved!!

 

 

[madkaw]

Another MN47 is coming as we speak