Lesnocker

Been a great summer. Now I got a leaky head gasket. Bubbles in the overflow with a gas smell in the rad. So the t top is offically down. Now the motor in the car is a 81 N54 with a P79 head .My spare also has a blown head. That motor is a 80 N42 block with N47 head. The N54 has 200k + miles and has been a strong engine. Is one better than the other. Found all most everything I need at black dragon.com. Is this a good part source? Thanks

Lesnocker

The N42 has 126 k but I drove it 80 miles with a blown head and head gasket in a bottle.

SHADY280

id do the p79 combo, way better head. plus way better block.

Lesnocker

Ok haven't dug into details on the block. My reading is the P79 is a better flowing head. Now if I swap the p79 head over to the n42 block I will increase compression? I understand my N or F 54 lol its cast N 54 has siameesed cylinders and has a better coolent flow. But is there a reason the 54 is a better block? Do belive it has the same crank and bearings as the 42.

Lesnocker

Last time I let the shop choose what happens on the build. This time I'm takeing direction. Should I expect to re-use valve seats rockers lash pads? Should I dive into line boreing the crank and changeing pistons ect. Black dragon has a "piston set". Shop so far wants 400.00 to tear it down and inspect. Like to stay away from the rapeing and the ransom on my engine. Id like just the bearings and head to be freshened up and new seals to be replaced than a tottal rebuild. Is that a reasonable thought.

NismoPick

Click:

Datsun P79 cylinder head mods

The L Series Engine Heads

and the most important one:

Engine Design Utility

SHADY280

all it sounds like you need to do is a simple head gasket job. no need to speend tons on anything else if you dont need it unless your going to really start modding. best upgrade while the head is off is to take .080" off the p79 and grab some .120" lash pads (best way is to measure your stock ones and add .080") and some.080" cam tower spacers. start with that and leave the rest alone unless you really want to rebuild the bottom end which is most likely not needed.

Lesnocker

Thanks! What I was thinking. Had the idea of just doing it all. But already spent way to much on the rat rod project. Now since I got a 300 lb paper weight laying in the garage. The n42 motor should just be scrapped out? After of course I see what the head needs in the other engine. Valves springs cam for example. The lower end does have over 200k but were talking 800.00 vs 2000.00 to have every nut and bolt replaced. And no I do not trust my self at all doing the head myself. Lol we did a old mitsu motor and had the timeing backwards of the notch position on number 1 and after the first crank well we needed a new motor lol.

Lesnocker

Decided just to pull the motor and have a basic valve job done. Replace the head gasket. Inspect and replace the head parts. Replace the timeing gears and chain and have them set time for me. Once home I'm going to install the "correct" intake. New exaust manifold and exhaust. I'm thinking about useing the light weight flywheel black dragon offers. Not sure if it will benifit launching or not. Pa we have mountians =) so also concerned of driveablity. May choose to make the car a automatic. I'm sure it would make it an utter dog though. Just where I'm at in the process.

NismoPick

You pulled the motor and aren't going to check the bottom end?

I did that with my Geo Metro a few years ago... replaced the head gasket at ~235k miles... even though it would only be another hour to get the entire engine out, and $100 more in parts, I decided not to touch the bottom end. Well... one year later I was pulling the motor for a full rebuild.

EDIT...

The lightened flywheel will help rev up the engine more quickly, but since compression engines need rotating mass to keep spinning, the lighter the flywheel (counter weight), the quicker it will rev down too.

Heat Rave R installed a light FW in his 280zx and said it then always shuttered when he drove up his driveway.

Lesnocker

I'm just going with the brass tax. So far it will take 500.00 to get it back to the street. Ill get firm prices first this time going to a new shop. I have a short day tomarrow. So ill run out and get them to print me a itemized esimate. Now ill be able to scan the estimate and post on here? Also what's the thoughts on the automatic N/A? Thought id be nice to the wife. If its a turd well guess I'm not buying one .

Lesnocker

Holy ****!! Got home today and got brave and went where no lesnocker went before!! Took the head off my spare block.Pretty damn easy! Anyway all of my exaust valves got chunks broke off. No damage to the pistons? I drove it buried at 85 whole way home. Since it was dieing under 3500 rpm. 82 miles one way. Question why are the inake valves shinny and black and the exhausts rusted and broke? Lol just wild! The gasket looks perfect except the black portion is flakeing off "felpro" guess it had a gasket replaced before. Hope my engine in the car is not as bad. How did this engine keep going??

NismoPick

Because:

Lesnocker

Nice job! Solved my answer. Hmm but in figure 4 there is half a f+$king valve! Lol you would figure there would be heavy piston damage. Nope not a scratch. Ill take some pics tomarrow. Priced out every peice for the head. Added up to be 521.00 , whoops I lied I have a total of 36 rockers sure 12 are good. Going to take my head down to get a quote on rebuilding it and ill start there.

Lesnocker

Hmm thinking today. Got the N47 off and ready to rebuild. Now that motor had dished pistons. Its a cam "d" grind. Now if I mate that to the 81 block with flat top pistons. That should bump up my compression. Now if the cam valve clearances are the same it should be a straight bolt on job? Higher compression I should get a lil more low end right?

Lesnocker

Or will going to the flat top make my engine into a six shot valve shooter?

SHADY280

the head will bolt on and yes it will raise compression. the cam is stock, but upgrading with no ecu is useless. be cautious about detonation with the n47 and set timing accordingly. it will work fine but dont be like me at 20 deg advance (36 deg total) i run that with the p79 shaved and pistons stick out of my block .020 at tdc. had to run a 2mm gasket to lower it down to 10.8:1. i was running it on the street at 11.8:1 but couldnt put any timing into it. my block is a n47 as well thats why the pistons stick out unlike the good f54 block

Lesnocker

Thanks finally getting some where. Now with the timeing I was just going to set it at factory and adjust till she smooths out if needed. This should raise me a good point or two on the compression I'm thinking at least into the 9 range 10 would be sweet. Eventully Id like to swap to the webbers. Takeing out the ecu / intake/ mass air sensor bottle necks. Just will need the intake carbs and a fuel pressure regulator. That's another chat. Since I'm planning that later Id like to have the exhaust sleeve removed and a good port and polish. Or do you think ill be wasteing money.

FricFrac

Taking the exhaust sleave out is pointless. It seems like a good idea but in practice it's not worth it.

Lesnocker

Saved me some money thanks. See I thought with the fuel injection that yea pointless. Like takeing a half inch pipe and adding a 1"1/4 drain pipe to the end. Meaning ok you got all the flow in the world out of the exhaust but you still have the funky choked up intake holding back the volume. Remove that and run tripple carb then it would be worth removeing? But at the same time doing that would make the exhaust gas "choppy" and not haveing the smoothness would rob some power. The p79 I get with the shaveing and shimming ok best deal. That's very advanced and I just don't want to get that nasty feeling going down the road knowing I got my cam "shimmed" that's the rat rod 79 is for. Did not get the chance to stop at the shop so that will have to wait till Monday.Do I just order every part for the head? Or do I let them tell me what I need? The bottom end I'm leaveing alone for now "contract expires december" and were nervious on spending thousands like I did last winter lol. Thanks for the help My hermit has thrown his arms up on doing another turbo swap. NO THANKS!

Lesnocker

What I'm aiming at is boosting the compression at least two points. I upgraded the igniton when I swapped this motor in. I don't mind running Premium to reduce the pinging. This should add a bit to the lower end which I will need if I do choose to make it a automatic. Lol we put around 15000 miles on it this summer. From hauling groceries to a 500 mile trip. We love the t top but the wife can't drive it lol.

FricFrac

You gotta spend money to make significant power out of the L without boosting it. The P90 is the turbo equivalent of the P79. If you get to the point where you need more flow than the P79 with inserts have you're better to go over to the P90 shave the head and shim the cam towers.

For the price of triples you can get an entire turbo swap and have money left over...

Lesnocker

Yea the 79 swap I had the shop perform l still regret. I know nothing about turbos and how to get past the electrical problems I still have. And honestly its fun it flys. But day to day driveing is a pain! Going to the inlaws with no A/C, open headers in your brain. And a high performance clutch in stop n go city driveing just sucks. Now a bad week or the wifes outa town yeah its heaven pop in some "Motley Crew Home sweet home" and hit the entrance ramps for some 8 grand shifts with the turbo screaming lol. I'm makeing the t top a honest daily cruiser. Automatic tranny working a/c since we found t tops actully suck at times when the sun is bakeing you to death lol. Pearls of wisdom. Thanks rebuild the head and throw on a fresh intake all new injectors and sensors. That will be perfect bumps me up a few horses that the automatic will eat and not to much $$

Lesnocker

Update sending my N47 head into the shop today. 110.00 to clean and inspect. Granted 3 of the exhaust valves need replaced is it proper to buy only the things you need? Or go and spend the 600.00 in parts to have the head fully rebuilt.? I'm also going to get a price on porting the head. Now onto cams would the p90 cam be any better than the "d" grind that I have now? Lastly the timeing freaks me out should I send my lower end in for them to set time replace front and rear seals. Also new pan gasket and finnally the flywheel cut?

FricFrac

No the P90 cam is going to be worse. The upgrade for the turbo cars is to swap the "A" grind NA cam in

Replace the valves and a valve job if it needs - you're wasting money on everything else. Porting isn't going to do anything without a cam and a cam isn't going to do anything without going aftermarket on the ECU.

Cutting the flywheel isn't worth it either unless you are building the car.