Guest dvlax28 Posted November 2, 2004 Share Posted November 2, 2004 Hey I just acquired a N42 block (75-80 280z) and the N47 head off an 80s Maxima. They were in storage, not abused, and the block and head were taken care of. But they have been sitting. Head is not on block. In my Auto Tech class I am planning on a rebuild project, so I'm making a list of steps to take, in the right order, so I don't mess something up. This is not going to be a stroker or turbo, it is my first rebuild so I want to learn a lot first. Help me out - add stuff and switch orders... 1. Clean 2. Pictures HEAD 3. Take, bag, label valve springs, seals 4. Remove cam 5. "Shave" - (is that the right word) to how many inches? 0.00xx 6. Cam need work? 7. Rods need work? 8. Buy, replace valve guide seals 9. Other seals? 10. ? 11. Reassemble BLOCK 12. Remove oil pan 13. Keep dished pistons, or buy flat tops? About $120 and I want to use pump gas 14. Rings? 15. Crank need work? 16. Bore? How much? (not siamesed) 17. Clean the corner metal filter thing 18. Machine head/block? 19. Gasket set - price? 20. What are all the seals I can replace? Lower crank seal, etc. 21. What do I port? what is port/polish? 22. ? 23. Attach head to block 24. Re-clean, prep, paint block 25. Polish head 26. ? Thanks Jason Quote Link to comment Share on other sites More sharing options...
Guest 83supaZ Posted November 3, 2004 Share Posted November 3, 2004 well if you're not building for PERFORMANCE as much as just to learn.. i dont know if i'd use the maxima head... because first, you at a minumum need a 2mm HKS head gasket to lower compression ratio. the maxima head has smaller valves so you'll you need to fit the larger valves from the stock head and unshroud the valves so they are not limited in the larger 2.8 motor. all this will have to be done by a machine shop unless you are skilled in these areas.. you def will need a new cam. if you get this head DO NOT shave it unless it is warped.. putting this head on is going to increase compression ration dramatically. shaving the head will only raise it more (this is def not a good idea) im going to be doing a maxima head switch myself... let me know how it goes for you and any tricks ya learn Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted November 3, 2004 Share Posted November 3, 2004 Tell ya waht.. since your not doing it for performance.. you send me the maxima head... I'll send ya a bone stock N42 head fair swap right? -Ed Quote Link to comment Share on other sites More sharing options...
Guest dvlax28 Posted November 3, 2004 Share Posted November 3, 2004 hah. I'm not doing it for performance like i wanted to at first, such as have huge compression and bored out to the max, with a monster cam, because i want the car to idle lower than 3000 and i want to use pump gas (im ok with premium) just not racing fuel or worse. so yes, i will be using this maxima head and i want to have 9-10 compression, nothing too high. so keep dished pistons? because first, you at a minumum need a 2mm HKS head gasket to lower compression ratio. the maxima head has smaller valves so you'll you need to fit the larger valves from the stock head and unshroud the valves so they are not limited in the larger 2.8 motor. all this will have to be done by a machine shop unless you are skilled in these areas.. you def will need a new cam. okay i'm not an expert, so can you write what this means about the "fitting" and "unshrouding" ? what's HKS? company? since no one has a nice list for me, where do i start? Jason Quote Link to comment Share on other sites More sharing options...
Guest 83supaZ Posted November 3, 2004 Share Posted November 3, 2004 from what i've learned in another post you do not need to use the 2mm head gasket... use a felpro .8mm head gasket... maxima valves are smaller (because the maxima is a 2.4L motor.. your 280z is a 2.8L motor which requires more flow. thats why larger diameter valves are used... you have to take the head to a shop.. get them to mill the valves so that the larger 280z valves will work. also.. you would want to get the head beadblasted (cleaned with a sandblaster type machine) resurfaced.. and the valves unshrouded.. here is the definition of unshrouding from flyinmiata.com "Due to limitations of the casting process used to manufacture heads, part of the circumference of the valve is blocked by the head. This metal is milled out to allow flow around the entire diameter of the valve. One of the best hp-per-dollar modifications. Highly recommended." basically the shop mills the valves to remove ridges inside that block airflow. for performance im going to use a .495/290 cam. using the max head you would want flat top pistons. your compression would be around 11.2:1 and you could run midgrade gas... im probably going to run premium though.. i'm also going to have SU carbs. hope this helps.. need any help let me know.. i plan on doing this same build in the next couple of months. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted November 4, 2004 Share Posted November 4, 2004 If you want to try something else, I have a complete 2.4 L6 in my garage, it's yours, just pick it up..... Quote Link to comment Share on other sites More sharing options...
Guest dvlax28 Posted November 4, 2004 Share Posted November 4, 2004 first off, I am fairly sure as I have heard from many differing sources that 10:1 and 10.5:1 are the MAX you can go with pump gas. 11:1 compression, as possible as that is with flat tops, would require racing fuel or it would ping. anyone else have any experience with compression to gas ratings? tim - check your messages thanks for the info on unshrouding and the head gasket. if i use a micrometer and the pistons are in spec, reuse the dished ones? Jason Quote Link to comment Share on other sites More sharing options...
DAW Posted November 4, 2004 Share Posted November 4, 2004 Find an N42 or N47 head for parts. Get rid of the Maxima intake valve springs and valves, leave the exhausts as-is. Have new L28 intake seats put into the Maxima head and lap-in the intake valves from the N42/47 head and use the intake springs. Get rid of the Maxima cam. If you're not installing an aftermarket cam at this point, use the N42/47 cam (and matching rockers). Unshroud the valves. Find a set of L24 rods with 9mm bolts (late '72-'73 240Z or late L16s). Take the N42 pistons off their rods, have the rim of the piston dish turned down until it is just in the same plane as the floor of the dish. Install milled pistons onto L24 rods (in the process, match up the weights of piston/rod assys and match rotating masses onto common crank throws). You'll want a bigger than stock cam for this because this set-up will yield well over 10:1 c.r. You might have to run octane boosters or racing gas to run this way. If you want a more streetable/practical set-up then do the piston/rod hybrid as described but just use the N42/47 head as-is for about 10:1 c.r. The Maxima head is better suited to 2.4-2.6L displacement performance engines and is an excellent retrofit on a 240Z shortblock in a conversion to f.i. The piston/rod hybrid approach gives a better rod/stroke than the stock L28 and bumps up compression. DAW Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted November 4, 2004 Share Posted November 4, 2004 with the right fuel and spark control I think you can go higher than 10.5:1. I've recently read of quite a few newer cars in the high 10's, 11's, and even one production street car (I think it was a mercedes or it might have been a Ferrari???) running 12:1 CR... a street car meant to run pump gas. At any rate, 10's or 11's don't seem too uncommon on newer sports cars. Hell even the Toyota Matrix runs a high 10:1 CR, and the editors at SCC thru a turbo kit on one of those! They blew the motor... and there's a whole story behind that as well... but it did sound like, given the opportunity to give it another go, it could have been made to work. The L6 head design may also have a lot to do with how much CR you can run. Do us all a favor and find a P90 head to run, set it up for high compression and see if it pings.... answering an age old question and putting an end to an age old debate ( I can dream can't I?) But P90 or N42 can't compare with modern heads, so I dunno if you could exceed 10.5:1 even with, say, an SDS or Tec setup, on a L6. Cam choice will have a huge part in how high CR you can run as well... bigger cam = lower dynamic compression = less chance for ping. Quote Link to comment Share on other sites More sharing options...
Guest dvlax28 Posted November 5, 2004 Share Posted November 5, 2004 DAW... i'm sure you have good intents, but i already owe my dad over a thousand bucks and i dont have the money to get my entire rotating assembly turned or machined or pistons flattened. i cant afford another head. what is "lap in" what is wrong with the cam? why would i want to weaken the piston and make higher compression by turning it down and flattening it? would increase my compression, which i cant afford to run racing fuel or have to retard my timing so much that performace is even worse j Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.