Josh280z Posted February 16, 2012 Share Posted February 16, 2012 I'm getting a block with P79 head with flat top pistons. I have an original block that is sitting in my '79 with an N47 head. According to THIS, putting my N47 on a block with flat tops will give me a high compression. "The N47 came on the '77-80 280Z(X). It has diamond-shaped exhaust ports with emission liners, which some feel reduce flow. Starting in 1977 Nissan heads came with steel valve seats for use with unleaded gas. Like the N42, putting it on a flattop L28 motor puts compression in the mid 10's. I believe this is when Nissan changed from external oil spray bar to internal (oil holes in cam lobes)" My question, will putting my N47 head on a block with flat tops give me "compression in the mid 10's?" Quote Link to comment Share on other sites More sharing options...
BrandenZ Posted February 16, 2012 Share Posted February 16, 2012 Here's one of the best resources I've managed to find on the subject: http://www.xenons130.com/Heads.html According to this, you'd be looking at 10.4:1. I'm just about to get an E88/F54 combo back on the road, which also should be roughly 10.4:1. Give me a week or so, and I'll report back with how much timing I'm able to dial in on the combo using 93-octane without getting pinging. From my research, the biggest criticism of this type of a combo is running it without detonation issues. Some report having to retard the timing so much that they lose most of the gains of the bumped compression. Quote Link to comment Share on other sites More sharing options...
Josh280z Posted February 16, 2012 Author Share Posted February 16, 2012 hmm sounds good, let me know how it goes. I have some other ideas on how to deal with the pinging. Would cooling be an issue for this type of set up??? Quote Link to comment Share on other sites More sharing options...
BrandenZ Posted February 16, 2012 Share Posted February 16, 2012 Feel free to follow my rebuild thread here: http://forums.hybridz.org/index.php/topic/104074-burning-oil-in-2-looking-for-suggestions-as-to-why/ Fair warning -- it's long! I basically slapped a fully rebuilt E88 head on the F54 mentioned in the thread. I don't recall reading anyone having issues with cooling with that type of a combo. Personally I'm running a JTR radiator with multiple fans hooked up to a temperature probe, so I'm not terribly concerned about it. Regarding the pinging, I'm hoping I'll get "lucky" with my combo. The head was rebuild with the larger 280z valves (you already have this with your N47), and had the quench area opened up a bit. Additionally, I'm running the more aggressive (longer duration and higher lift) 240z cam which should help a bit (something like a stage2+ would be more ideal). My ignition is also rock solid, converted to optical style, and I'm running dual webers which should give me plenty of adjustability for richening up the mixture if necessary. Out of curiosity, what are you considering implementing to address the potential issue? Quote Link to comment Share on other sites More sharing options...
Josh280z Posted February 16, 2012 Author Share Posted February 16, 2012 The pinging seems to be explosion of the gas at the wrong part of the stroke in the cylinder. So, to properly detonate it at the right time, I'm considering adding a hydrogen generator to it, see how it goes... The hydrogen is exploded along with the gas to mkae everything burn better, thus reducing or eliminating my ping. Also, I think I will stick with the stock fuel injection for now so no cam upgrades at the moment. Quote Link to comment Share on other sites More sharing options...
BrandenZ Posted February 16, 2012 Share Posted February 16, 2012 Never heard of that trick before! Do you have any links on the setup / how to get it working in your Z by chance? Quote Link to comment Share on other sites More sharing options...
Josh280z Posted February 16, 2012 Author Share Posted February 16, 2012 My great uncle installs hydrogen generators, for better gas mileage but I think it will work for higher performance too. I said something about gas mileage in my car (so much for that idea), and he actually built me one.I know how to install it and everything. Unfortunately, there is no documentation only word of mouth. I could do a write up of it when I am finished though... Quote Link to comment Share on other sites More sharing options...
josh817 Posted February 16, 2012 Share Posted February 16, 2012 (edited) http://atlanticz.ca/zclub/techtips/calcs/engine%20builder/index.html You know your rods, crank, and pistons are flat tops so no dish to account for. You can either enter in the default number for the N47 and select your head gasket. If your gasket doesn't follow any of the numbers like mine didn't (90mm X .6mmm) then you can enter it manually. Or, you can go the time consuming way and say "I don't trust these numbers for combustion chamber volume, I'll do it myeslf" and go get a plastic syring from CVS or Walgreens. Doesn't have to be a needle, then get some oil, fill syringe, start squiritng into the combustion chamber making sure that the head is sitting level while upside-down and that the valves are closed with the spring pressure so that they don't ooze around the seats. Also have a sparkplug installed obviously. Keep track of how many mL of oil you squirt in. 1mL = 1cc Avoid creating surface tension of the fluid in the chamber. You can get down and eyeball it or you can get a small square of 1/8" plexiglass or clear plastic, enough to cover one of the chambers completely. Drill a hole in it the size of your syringe squirter tip thing so you can place this plastic over the combustion chamber and insert the syringe tip into the hole to fill the chamber. Or I suppose you could avoide all that, get some clay/playdough, squeeze it into there. Run a straightedge across the surface of the head so you cut off any excess. Now take the clay that is in the chamber, pull it all out. It doesn't matter if you lose the shape of the combustion chamber or anything, for all intents and purposes you could just as well roll this clay in a ball and get the same results, or if you have a narrow container you could chop up the clay as long as you get all the little bits. Drop it into a container of water, obviously this container should have readings in mL increments of at least 5 so you aren't guessing between lines. See how much water it displaces, keep in mind that there is a meniscus so read the water level not the meniscus level, and thats your volume. mL you have after you put clay in water - mL of water you had before clay went in = mL of displacement of clay = mL of combustion chamber 1mL = 1cc Kdone get to work. Edited February 16, 2012 by josh817 Quote Link to comment Share on other sites More sharing options...
Josh280z Posted February 17, 2012 Author Share Posted February 17, 2012 I'm not following why that ^ was posted.... Please enlighten me. Quote Link to comment Share on other sites More sharing options...
(goldfish) Posted February 17, 2012 Share Posted February 17, 2012 It's how to figure out your compression ratio. I think you will really want a stand-a-lone so you can dial in your advance. Sounds like stock isn't so good under those compression ratios. Quote Link to comment Share on other sites More sharing options...
Josh280z Posted February 17, 2012 Author Share Posted February 17, 2012 (edited) Ah, good to know. I've thinking about going carbureted. Edited February 17, 2012 by Josh280z Quote Link to comment Share on other sites More sharing options...
cockerstar Posted February 18, 2012 Share Posted February 18, 2012 Just as a reference to the above method regarding the meniscus level. You want to read the low point of the meniscus for an accurate reading, not the high point seen due to the surface tension of the water. Also, make sure you're using a high density clay that will easily sink, but I think that part is a given. Quote Link to comment Share on other sites More sharing options...
Pyro Posted February 18, 2012 Share Posted February 18, 2012 I would add a little more cam. Get the stock cam reground to around 260 degrees duration with 0.420" lift (212 degrees at 0.050) at delta cams ($100) and get some 0.160" lashpad from courtesy to make up for the regrind. Should work with the stock springs and efi and would be a ton easier to tune with 10:1 cr as compared to the stock cam. Quote Link to comment Share on other sites More sharing options...
josh817 Posted February 18, 2012 Share Posted February 18, 2012 (edited) I'm not following why that ^ was posted.... Please enlighten me. "My question, will putting my N47 head on a block with flat tops give me "compression in the mid 10's?"" If you do change cams or get a regrind like Pyro says, resurface your rockers. If you have hydraulic rocker pivots, and you switch to a grind or earlier cam that was running on solid pivots, then be sure to change them out. Not doing either of these things will yield missing lobes and glitter in your oil. Changing pivots from hydraulic to solids is relatively simple. You would need a breaker bar or large wrench, I think it's 21mm. Be careful not round them off since they're oily. The solid pivots are a different thread size so you will need to order Timeserts. I haven't done this in years but... the part number is somewhere around here and they usually run like $30-$40 for a set of 12. These Timeserts have threads on the outside and on the inside. This allows you to thread it into the head, and then screw the solid pivot into that. Add Locktite and torque down; again I forgot the specs but I suspect something like 35ft-lb. If you get a hydraulic cam reground to something else, I'm not sure if one should change out the pivots.... Just don't run a hydraulic cam on solid pivots and vise versa. This however is probably all pointless because you said N42 head and I don't think that has hydraulic pivots... Just in case though! Refer to this if you decide to go to a stock cam with perhaps better specs. Also, at the bottom of that page is a blurb about which cams are the "good" ones so if you run hot springs, you don't fry your cam. http://atlanticz.ca/zclub/techtips/cam/index.htm Edited February 18, 2012 by josh817 Quote Link to comment Share on other sites More sharing options...
brianZortiz Posted February 18, 2012 Share Posted February 18, 2012 The maxima mn47 is the compression upper and the regular non maxima n47 is not. Quote Link to comment Share on other sites More sharing options...
(goldfish) Posted February 18, 2012 Share Posted February 18, 2012 The maxima mn47 is the compression upper and the regular non maxima n47 is not. Both N47 heads have smaller chambers than the P79! Quote Link to comment Share on other sites More sharing options...
Mack Posted February 19, 2012 Share Posted February 19, 2012 The Maxima N47 head will put your compression ratio OVER 11.5:1 on an F54 flat top block. ask me how I know! I was running this combo in a 280ZX 2+2 with a 260Z C stamp cam and megasquirt for quite a while. there would be some ping on some days, but it was only under full throttle and it really depended on the brand of gas I filled up with that week. I will probably be pulling the head off of the block in the next few months and see what kind of damage (if any) was actually done to the combustion chamber/piston tops. Plus, the maxima head with its smaller intake valves (higher port velocity) and super high compression makes for some nifty low end torque gains! Quote Link to comment Share on other sites More sharing options...
Josh280z Posted February 19, 2012 Author Share Posted February 19, 2012 Well I'll probably end up modifying a P79 head as mentioned on the Datsun z garage website. Switching to MS and installing 36lb/hr grand prix GTP injectors my friend is giving me. BTW, how do you know it is over 11.5:1 compression, what did you do?? Quote Link to comment Share on other sites More sharing options...
Mack Posted February 20, 2012 Share Posted February 20, 2012 the maxima n47 head has a 39cc chamber. flat top pistons have no dish (obviously) and actually have a positive deck clearance of .016" which is actually a 2.3cc DOME, and when you account for the head gasket space, you get an extra 6ccs of chamber volume, then take 459cc, which is the swept volume of each cylinder, add 39 and 6, but subtract 2.3 for the piston dome, to it to get a total of 501.7cc, then divide that by 42.7cc (the 39cc chamber plus the 6cc for the head gasket, minus the 2.3cc for the piston dome.) and voila! 11.75:1 compression ratio! Quote Link to comment Share on other sites More sharing options...
Josh280z Posted February 20, 2012 Author Share Posted February 20, 2012 So your saying a maxima N47 head will get you that compression ratio?? Quote Link to comment Share on other sites More sharing options...
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