Perfect240z Posted December 27, 2011 Share Posted December 27, 2011 Hey guys, I've been searching on here for a few hours now and can't seem to find a few answers to my questions. I just picked up a 83Xt block and it needs to be rebuilt. I don't have much to spend, but from I hear I can do a high compression motor fairly cheap. 1. Do I need to get flat tops since I'm running it n/a? 2. I heard you can use L24 rods for higher compression or is the stock rods that it has now will work? Any other help/insight will be appreciated. I have pics of the items I have on my build thread. Here http://forums.hybridz.org/index.php/topic/101191-1970-240z-project-very-slow-money-is-tight/page__pid__973113__st__40#entry973113 Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted December 28, 2011 Share Posted December 28, 2011 Are you running carbs or EFI? Stock or highly modded....Any basic rebuild will cost around $1000 for a full longblock( unless you assemble it all yourself) If you want high comp you need to use flattops and stick with the L28 rods. Quote Link to comment Share on other sites More sharing options...
Perfect240z Posted December 28, 2011 Author Share Posted December 28, 2011 I'm going triple carbs. Ok, flat tops and the stock rods. That's a good answer. I heard L24 rods, but then I heard that would be for a stroker set up? Quote Link to comment Share on other sites More sharing options...
rejracer Posted December 28, 2011 Share Posted December 28, 2011 1. If you are using an N42 (open chamber) use dished pistons to lower the compression to stock levels. N42's on flatops will detonate. 2. L24 rods will not work with stock L28 pistons. You can use L24 rods with stock or stroker cranks assuming you can find the right piston. Suggestion: If this is a mild street engine I suggest you get a P79 or P90 head and use stock flat tops on stock rods. If you just want a high compression engine on the street you need a closed chamber head, and with a 22 to 25 thousands piston to head clearance. An MN47 on a stock F54 block will get you in the neighborhood of 10:1. These heads are prone to detonation, so the necessary mods need to be made to support it properly. If your not willing to spend the hours upon hours to get yourself up to speed, I suggest you pick an engine from a particular year (block head combo) and build that. In my opinion the stock 81-83 P79/F54 combo is the best of the stock engines. On a limited budget, or limited knowledge scenario it's wise to start with a known engine and mod it with known and proven mods to avoid serious mistakes. An example of that would be buying flatops and running them under a stock N42. Hope that helps. Quote Link to comment Share on other sites More sharing options...
cockerstar Posted December 28, 2011 Share Posted December 28, 2011 (edited) I think that rejracer gave some pretty solid advice. Having a successful build all comes down to getting some goals and a realistic budget before anything starts. Flattops with a p79/p90, triple 40's, a cam, an electronic ignition, a lightened flywheel, and a header/exhaust will make for a fun street car without breaking the bank. The n42 can be used as well if you keep the compression down. Keep the compression reasonable and the redline under 7k rpms, and you'll have a fun little engine that will play nice on pump gas and be dead reliable! Read these threads if you haven't already: http://forums.hybridz.org/index.php/topic/62691-l6-heads-pics-and-descriptions/ http://forums.hybridz.org/index.php/topic/53209-f54-block-what-are-my-head-options/ http://forums.hybridz.org/index.php/topic/41597-l-series-dimensions-stroke-bore-chamber-ccs-etc/ Edited December 28, 2011 by cockerstar Quote Link to comment Share on other sites More sharing options...
Perfect240z Posted December 28, 2011 Author Share Posted December 28, 2011 Ok, yeah I've been getting a lot of opinions, and ofcourse everyone has their own opinions, but ofcourse I was told about the flat tops with a n42/n47 head on a f54 block. Well my block i just purchased has dished pistons in it since its from a zxt. I guess I should stay with those then when I do the rebuild? I'll go ahead and read those threads too. Since I'm trying to keep to a low budget since my wife and I bought a house and spent all my money's, it's be better this way and I can get away with at least getting my triples that I just love the look of. Quote Link to comment Share on other sites More sharing options...
240zip Posted December 28, 2011 Share Posted December 28, 2011 I personally think a turbo build would be cheaper than a good NA build that you're describing. I did an E31, F54, flat top, .5mm overbore with upgraded cam, DCOE 42's, header, MSD 6AL, MSD mechanical advance distributor, and all the 'correct' things needed to make it work and I suspect I could have done a junk yard turbo swap for less. I also added a 5 speed, lighten flywheel, and fabricated a complete exhaust system. Getting the Webers, rebuilding them, getting a compete jetting kit, dialing in the Webers on the dyno, etc. ... it's all going to add up. I personally love the set-up. Lots of low end torque, fun at the track, incredible sound ... more like a vintage Italian car than your typical Datsun. But in the end, it was worth it. The car also has a R180 LSD from a WRX STi and a completely new upgraded suspension. We didn't go all that extreme. linear rate springs, Illumina's, urethane bushings, front / rear sways, front / rear strut tower bars, 15" wheels. Quote Link to comment Share on other sites More sharing options...
Perfect240z Posted December 28, 2011 Author Share Posted December 28, 2011 Alright, well it looks like I'll just have the block rebuilt with the dished pistons it currently has. The rings need to be replaced anyways. And then I'll just use my n42 head for now since I want to drive my car after I'm done painting her. I'll book mark those links to keep in mind when I want to finally do a high compression build. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted December 29, 2011 Share Posted December 29, 2011 I wouldn't bother with dished pistons... FWIW, I ran my 3.1 with a stock N42 at 10.25:1 CR for years with a stock cam, at 35deg advance. Currently at ~11.5:1 with the N42, with a 310deg/.550" cam and some headwork (minor bowl reshaping), running pump gas with no problems. Last dyno runs it made the same power from 34deg to 38deg total advance. That said, I am aware of at least one stock N42/flat-top build where ignition timing had to be backed down to 26deg, so ymmv... Me? I'd go with the N42/flat-tops, particularly if future mods are planned (cam, porting, etc). Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 29, 2011 Share Posted December 29, 2011 I wouldn't bother with dished pistons... FWIW, I ran my 3.1 with a stock N42 at 10.25:1 CR for years with a stock cam, at 35deg advance. OP is in CA. Maybe with ethanol blends it would work OK, but before ethanol on CA 91 octane super, this was not a good idea. Quote Link to comment Share on other sites More sharing options...
z-ya Posted December 29, 2011 Share Posted December 29, 2011 Oh no, not again.... Dan, nice to see you back on HybridZ. Still got the Z? Pete Quote Link to comment Share on other sites More sharing options...
Perfect240z Posted December 30, 2011 Author Share Posted December 30, 2011 I wouldn't bother with dished pistons... FWIW, I ran my 3.1 with a stock N42 at 10.25:1 CR for years with a stock cam, at 35deg advance. Currently at ~11.5:1 with the N42, with a 310deg/.550" cam and some headwork (minor bowl reshaping), running pump gas with no problems. Last dyno runs it made the same power from 34deg to 38deg total advance. That said, I am aware of at least one stock N42/flat-top build where ignition timing had to be backed down to 26deg, so ymmv... Me? I'd go with the N42/flat-tops, particularly if future mods are planned (cam, porting, etc). I didn't know that I could use them is more what I was confused about since in a lot of videos I've been watching all the L series I've bee seeing had Flat tops, so I was concerned since this is a turbo block with dished pistons. I know the rings are bad on the pistons, so they have to come out and the block honed. So what i was going to do was get flat top pistons and, even though I haven't decided yet if I should do the honing or take it to a machine shop and have them do the honing and perhaps boring it out. But since I really just want to drive my car, I was going to use the dished pistons and just get new rings and hone the block myself if thats what needs to be done. I've never done any motor work before, so thats what my dilemma is on deciding if Im capable of doing it. I have every book available and the FSM, and Hybridz, but its still questionable since I don't want blow the thing when I finally run her. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted December 30, 2011 Share Posted December 30, 2011 Oh no, not again.... Dan, nice to see you back on HybridZ. Still got the Z? Pete Dropped in to see what's shaking and plopped myself right into the same P vs. N "discussion" that's been ongoing for eons now! I drove the Z down to Atlanta last week, to be shipped from there to its new owner, fellow HybridZ-er Bob_H. So, end of an era for me, but it's going to a very good home. The Z was partial trade for his (now my) '94 RX7 with 500+ LS2 V8 horsepowers. Wheee! Quote Link to comment Share on other sites More sharing options...
Perfect240z Posted December 31, 2011 Author Share Posted December 31, 2011 How bad is this detenation thing? Is it going to blow the motor? Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted December 31, 2011 Share Posted December 31, 2011 If you run it hard while it's detonating away, bad things... But you wouldn't do that I hope. If you get detonation/pinging, back the ignition timing off and you should be OK. If there's any chance at all you'll be tweaking this motor (cam, triples, headwork, etc.), I'd go with the flat-tops. If you just want a no-worries stock build, with less potential for building n/a power, go with the dished. That would probably let you run 87 octane, too. Quote Link to comment Share on other sites More sharing options...
z-ya Posted December 31, 2011 Share Posted December 31, 2011 How bad is this detenation thing? Is it going to blow the motor? Detonation. If you are running stock headgasket, you will be blowing them. If you use a metal gasket, you will be breaking pistons. To run flat tops and an N series head you mush have a good tune (~13:1 AFR), and you must also run premium fuel. Depending on the cam, you will also have to back off the timing. With a stock cam plan on running around 25-26 deg of advance. Head work and a stout cam will let you do what Dan has done. You sound a bit like a Newbie to all this, so I would just rebuild the motor with the dish pistons as a learning exercise. Dan: SPA here you come! Quote Link to comment Share on other sites More sharing options...
Perfect240z Posted December 31, 2011 Author Share Posted December 31, 2011 If you run it hard while it's detonating away, bad things... But you wouldn't do that I hope. If you get detonation/pinging, back the ignition timing off and you should be OK. If there's any chance at all you'll be tweaking this motor (cam, triples, headwork, etc.), I'd go with the flat-tops. If you just want a no-worries stock build, with less potential for building n/a power, go with the dished. That would probably let you run 87 octane, too. Didn't know exactly what I would do to make it work, sounds like I'll just stick with the dished pistons for now since they look in good condition. Thanks! Detonation. If you are running stock headgasket, you will be blowing them. If you use a metal gasket, you will be breaking pistons. To run flat tops and an N series head you mush have a good tune (~13:1 AFR), and you must also run premium fuel. Depending on the cam, you will also have to back off the timing. With a stock cam plan on running around 25-26 deg of advance. Head work and a stout cam will let you do what Dan has done. You sound a bit like a Newbie to all this, so I would just rebuild the motor with the dish pistons as a learning exercise. Dan: SPA here you come! AM I NEWB!?.... Well kinda lol, fixing up a car is new to me since I never had a car till now to fix up. But yea I have all these stock parts that I can use for now till I can understand more. My main concern was if I had to get the motor redone honed/bored, why wouldn't I put in better pistons, since its not that easy and convenient ya know? Im sure a lot of people can rebuild a motor on here during the weekend, but Ive never done it, so this would be my opportunity to maybe put those in without a hassle later and then add on things later that would put more performance on it. I guess thats what im looking for as far as an answer. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted December 31, 2011 Share Posted December 31, 2011 To run flat tops and an N series head you mush have a good tune (~13:1 AFR), and you must also run premium fuel. Depending on the cam, you will also have to back off the timing. With a stock cam plan on running around 25-26 deg of advance. Head work and a stout cam will let you do what Dan has done. FTR, I was running 35degrees (i.e., full) advance back when I was running the stock N42 head (with ~.010" shave) with stock cam, stock SU carbs, stock everything, at 10.25:1 CR, on pump gas, no problemo. Stock N42 with flat-tops should be 9.8:1. I dunno, maybe a 3.1 with N42 and KA24E pistons is somehow less detonation-prone than the same head with L28 flat-tops... Dan: SPA here you come! PA, actually, SP rules don't allow a different number of cylinders! Kinda arbitrary if you ask me... I went 0.8 seconds SLOWER in the monster RX-7 in October than my best time there in the Z Power steering issues. I.e., I didn't have any. VERY high effort and ZERO feel, I couldn't throw the car around with any confidence at all. Situation now rectified, as of today Quote Link to comment Share on other sites More sharing options...
z-ya Posted December 31, 2011 Share Posted December 31, 2011 FTR, I was running 35degrees (i.e., full) advance back when I was running the stock N42 head (with ~.010" shave) with stock cam, stock SU carbs, stock everything, at 10.25:1 CR, on pump gas, no problemo. Stock N42 with flat-tops should be 9.8:1. I dunno, maybe a 3.1 with N42 and KA24E pistons is somehow less detonation-prone than the same head with L28 flat-tops... PA, actually, SP rules don't allow a different number of cylinders! Kinda arbitrary if you ask me... I went 0.8 seconds SLOWER in the monster RX-7 in October than my best time there in the Z Power steering issues. I.e., I didn't have any. VERY high effort and ZERO feel, I couldn't throw the car around with any confidence at all. Situation now rectified, as of today Moving this conversation to a PM. Quote Link to comment Share on other sites More sharing options...
Perfect240z Posted December 31, 2011 Author Share Posted December 31, 2011 A lot of great info here! Quote Link to comment Share on other sites More sharing options...
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