N47 (maxima variety) buildup on my L24

[Guest Anonymous]

Ok just looking for some input/advice here, I scored a maxima N47 last weekend for 25 bucks at a junkyyard. Looks to be in great shape, even the water passages aren't corroded which is honestly a first for me when pulling an L series head (particularly one that appears to probably be the original head gasket). After the initial inspection of it, it is as has been said the baby P79. I'm going to probably get a cheap burette on ebay so I can get an accurate combustion chamber size shortly. It does indeed have the formerly "evil" round exhaust ports with liners, but I happen to have a round port header anyway so in this case that should more than offset the difference vs a square port head with the cast exhaust manifold. Plus with it being an L24 it probably is more than sufficient. Ok so for the head I know swapping the cam is important, for an L24 will the 44mm intake valve from a 280 make enough difference to justify the cost of installing them? At this point I'm not thinking it should. On to the block, I'm looking at a .040 over bore to clear the ehaust valves since it's got the bigger ones. Has it been determined that this is sufficient for the valve to clear the block? Or will additional notching most likely be necessary?

 

The other choice I'm faced with is since I'm going to have to get new pistons to go .040 over and after some research seem to have rather limited choices with Clevite, Sealed power, or customs from one of the forged piston companies being about all that is out there. I'm looking at about 35/piston vs 70-80/piston from cast to forged, I realize on a street N/A forged is overkill but for the price difference I'm wondering if it might be worth considering anyway and going with floaters on the pins while I'm at it.

 

Anyway, I'm thinking of doing this somewhat low-buck stuff for now until I can properly build up something more powerful (L28 Turbo or RB26DETT) Any big obvious things I'm overlooking in this arrangmement?

[DAW]

This is an excellent head for what you're doing. Don't worry about the burrette, you can calculate the cc if you can get the specs for the cc of piston dish on the Maxima L24E. It isn't very much and your flat tops will raise your c.r. higher than the L24E c.r. of 8.6:1. I'll guess your c.r. with this head will be about 9.0:1 so you may want to have it shaved a modest amount (0.15-0.20") to raise it another 0.5 c.r. or so.

 

However, if you're going to overbore that will increase the c.r. also, so you might be able to skip the head shave.

 

With your displacement and budget, you could skip the intake valve swap and use the 42mm L24E valves. You do need to swap the cam for a Z cam ((L28E from an N47 or P79 head would be easiest since it is rifle-drilled for rocker oiling vs 240Z and N42 spraybar oiling). You need to swap in the Valve springs for the intake valves also (from the 280Z head). BTW, if you decide to have the head shaved you can back off the rocker arms so all valves are closed, and the machine shop can shave the head. If they tell you you must disassemble if they are trying to rob you or they don't know what they're doing. Just clean the head well after and use compressed air to get rid of any possible shavings.

 

As to exhaust valve/block clearance you need to notch the top of the cyl bore on an L24 (even with a 0.40" overbore. It's not hard to do and you can do it without tearing down the bottom end.

 

If you need to overbore for wear reasons then don't just do 0.40". Consider 0.80" (83 to 86mm), and use Sterling pistons that are made to use L24 rod length. Then you can skip bore notching and head shaving, and increase c.r. and displacement and preserve the favorable rod/stroke ratio of the L24. DAW

[DAW]

Oops, that's 0.120" over to go from 83 to 86mm.

 

BTW, if your budget is really tight, you might be able to get by without overboring and just replace you rings. Nissan blocks are extremely tough. DAW

[DAW]

Addendum...maybe I should clarify why you would swap the Maxima cam for a 240-280ZX cam..the Maxima L24E has economy-minded intake lobe profile with less lift and a weaker intake valve spring than the L24/26/28 Zcar does. DAW

[Guest Anonymous]

Thanks for the reply, I'm overboring it for compression not replacement Aactually I just rebuilt the L24 that's in the car about 10k miles ago, but then the head cracked which prompted the 2 year garage queen status it's presently enjoying. The overbore is fine I just didn't think an L24 was good for that much of an overbore(86mm) or were you suggesting just take an L28 block and stock L28 flattop pistons using the 240 crank/rods?

 

That is an option I could do right now as I've got an L28ET engine in the garage with the F54 block. I've thought about this anyway as the L24 crank/rods would make the engine rev a bit quicker and might be an interesting combination. I was toying with just using flattop forged pistons in when I build that as a turbo, 2 birds with one stone were I to just get forged pistons now and then swap the crank and rods later (or not, maybe even just keep it that way on the bottom end when I build the turbo) That option is just a bit more expensive so I might just use cast flattops now and throw the forged ones in down the road. Just as soon start using the F54 block anyway.

 

I'll grab a p79 cam and towers from a junkyard or even the whole head they're easy enough to find and only 45 bucks or so anyway at the self serve places. Might decide to prolong the whole operation and get an aftermarket cam anyway, but at 450 or so for the whole operation (assuming I used MSA anyway) it's a rather painful expense that may not make enough difference on a street engine to justify the cost. On the valve note, with the 86mm bore, this bumps it up to about a 2.6 liter engine, think putting the bigger intakes in is worth the expense at that point?

 

According to the Lengine program using the 86mm with a combustion chamber size of 40cc I'd be looking at about 10.38:1, (10.59:1 with 39cc chambers since it sounds like they could be anywhere from 39-41cc's based on some of your prior posts I searched through) I might just buy the burette anyway since anything much less than 40cc's is going to push the compression higher than I'd probably like for the sake of not needing octane booster over and above premium unleaded. This is just because of the nuisance of having to have it around rather than the expense. I'm just thinking for the 30 or 40 bucks for a burette and stand on ebay it's somewhat good to know the cc volume before going any further.

 

I've got a pretty good machine shop to use here, I doubt they'd try to nitpick that much, my friend's a Supra guy and this is the place he goes which is pretty popular with Supra guys in Phoenix. (Frontier Machine) The guy that owns it did alot of the machine work for Total Seal rings for a few applications anyway when they were developing them so while they're a smidge expensive they seem to do really good work (at least based on what I've seen that they've done on my friend's engine anyway) If not I've got the old school mom and pop shop that's cheap but does wierd stuff like paint aluminum cylinder heads with aluminum colored paint if they can't get em looking good after tanking em (they did on my other friends L20B head on his 510 anyway) Other than that they do good work they're just quirky.

 

No big deal pulling the lifters out if they prefer it that way, big screwdriver under the cam pushing on the valve spring retainer makes it about a 3 second job per rocker.