4everDATSUN Posted March 28, 2005 Share Posted March 28, 2005 i plan on building a n/a high compression 280z engine, and had questions on rods. i have read that 240 rods can be used to increase compresion while gaining better stroke. is this true? and if it is can they be used with stock 280 crank. i plan on making other mods to the engine to increase compression. changing rods isnt all i have in mind. i would like to increase the rpms tho while im at it tho. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted March 28, 2005 Share Posted March 28, 2005 The the stroke, by itself, will not be affected by the rod length. The longer rod (5.3 mm) will require a custom piston if used on the 280 crank that allows the pin to be moved higher up the piston by half this amount. Not knowing much anymore about the L6 motors, I'd say you don't have 2.615 mm of room to push the piston up using stock pistons. Quote Link to comment Share on other sites More sharing options...
4everDATSUN Posted March 28, 2005 Author Share Posted March 28, 2005 your right, i didnt mention but i plan on using forged pistons with a shorter deck height. using the 240 rods is supposed to increase rod to stroke ratio. But i have no proof of this, i just want to know if the rods will fit the 280 crank, and if the rods will actually allow higher revs. and if anyone has done this, id like to know how it runs. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted March 28, 2005 Share Posted March 28, 2005 It will definitely increase the RL/S ratio (over the OEM 280Z), which should be of benefit at the higher RPMs, but my understanding is that (and again, someone more knowledgable needs to chime in) the crank is the weak link with high rpms, and not necessarily the piston speeds. Quote Link to comment Share on other sites More sharing options...
preith Posted March 28, 2005 Share Posted March 28, 2005 As far as I know, or what I've come across, most custom domed forged L28 pistons out there, are made for the L24 rod. I have JE's which use this configuration. It does help with higher rpms with less piston side load, however the compression ratio should not be affected. Theoretically, one could try to use the L28 pistons and have them extend above the deck, and therefore increase compression, but I've never heard of this done, and not sure what kind of clearance issues there would be, or machining required. The crank being the weak link is probably open for debate, but it does need special attention. Quote Link to comment Share on other sites More sharing options...
4everDATSUN Posted March 28, 2005 Author Share Posted March 28, 2005 well i dont know of any inexpensive aftermarket cranks. ive heard of using the ld28 crank (V07) but i dont want to change stock 2.8 crank specs. and im actually not looking for the 240 rods to increase compression, id rather them not, i have other things in mind. so im guessing the answer im getting is a no for the rods? Quote Link to comment Share on other sites More sharing options...
Tim240z Posted March 28, 2005 Share Posted March 28, 2005 If you need a set of rods, you can have a set for free. One snag....you will have to take the 2.4l engine that they are in Quote Link to comment Share on other sites More sharing options...
Guest billyzbear Posted March 29, 2005 Share Posted March 29, 2005 From what I have read. The 240 rod is better to use. If you want high rpm motor go with a big cam like 52 lift and 308 duration. I had one for awhile, pita for street. Pulled real hard from 3000rpm's to whenever you decided to shift. I set the rev limiter at 9000. Make sure everything is balanced. Are you planning to bore? Just how high compression are you wanting? Are you always going to want to pump race fuel in this? Quote Link to comment Share on other sites More sharing options...
4everDATSUN Posted March 29, 2005 Author Share Posted March 29, 2005 im really aiming for around 12:1 but im sure ill only end up with 11:1, so nothing real crazy. ill prob run premium. my plan is to have a .040 overbore, with forged flattops. im really not looking for a stroker by far. but i liked the idea of getting more revs, even an extra 500 would be nice. but ive heard mixed opinions on the 240 rods, ive kinda been talked down from them. but if you have anything good to say about them im willing to listen Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 29, 2005 Share Posted March 29, 2005 There should be no mixed opinions on 240 rods. They are just as strong as 280 rods, if not more so (with 9mm bolts). If you have them, use them. The difference in the rod ratio isn't going to be huge, but there will be a difference. There is no downside to it, and since you're buying custom pistons anyway it won't be any more expensive. I wouldn't pay a whole bunch of money to get the 240 rods, but if you've got them you should use them. The L6 crankshaft has a harmonic problem going over 7500. Keep it under 7500 and you won't have your damper and your flywheel bolts back out on you. Quote Link to comment Share on other sites More sharing options...
4everDATSUN Posted March 30, 2005 Author Share Posted March 30, 2005 o see i didnt know that about the crank, 7500. What if i bring it to get balanced some place? im pretty sure they can balance the crank above 7500. And if im wrong whats the difference between the dielsel crank and the L6 crank? (stroke wise) cuz like i said before i DONT want a stroker Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 30, 2005 Share Posted March 30, 2005 If you don't want a stroker don't use the diesel crank. The stroke difference is 79mm vs 83mm. Balancing the crank apparently doesn't fix the harmonic problem. The 240 had a rod ratio of 1.8. The 280 had a rod ratio of 1.65. A 280 crank with 240 rods will have a rod ratio of 1.68. You can search here and on the internet and find tons of info on rod ratio and you can determine it's importance for yourself. The bottom line is that going from 1.65 to 1.68 isn't going to make a huge difference, but like I said, if you have both rods, it would be dumb IMO not to use the L24 rods. That makes me dumb, BTW... Quote Link to comment Share on other sites More sharing options...
Guest billyzbear Posted March 30, 2005 Share Posted March 30, 2005 When I had the full race cam in I didn't have a problem at 7500+. I used a ZX crankshaft pulley and a 10 pound flywheel. I found with the 10 pounder wasn't for me, 15 or so is where I like it. I think 11 to 1 could be a problem on pumped gas. Atleast here is SoCali we have crap for gas. This L6 progam mite help. http://forums.hybridz.org/showthread.php?t=97787 So, what's the hole plan for the car? All the work you have done and planning to do. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted March 30, 2005 Share Posted March 30, 2005 i've had a 280 n/a build up in mind for a while now.. I was told back when i was converting to carbs... that 240 rods were basically drop in compression increase. Run the stock 280 crank and pistons, put in some 240 rods and keep the same head and you should be lookn' aroun 9.5:1 compression increase right? Or did i severally miss something here? 7500rpm eh? so.. balancing the engine and takn' care of the valve train will allow this rpm? -Ed Quote Link to comment Share on other sites More sharing options...
4everDATSUN Posted March 30, 2005 Author Share Posted March 30, 2005 thanks mort for the info. Well i plan on boring out a 280z block and boring it .040 over using 240 rods and forged pistons. I want to use the mn47 with larger zx valves. not sure what size cam yet, prob just a mild. i am also going to port match and polish my new tripple webber manifold. im quite possitive premium pump gas will be fine. otherwise im in trouble, this cars goin to be a gas guzzler. tell me what ya think Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 30, 2005 Share Posted March 30, 2005 thanks mort for the info. Well i plan on boring out a 280z block and boring it .040 over using 240 rods and forged pistons. I want to use the mn47 with larger zx valves. not sure what size cam yet' date=' prob just a mild. i am also going to port match and polish my new tripple webber manifold. im quite possitive premium pump gas will be fine. otherwise im in trouble, this cars goin to be a gas guzzler. tell me what ya think[/quote'] 9000 rpm should ruin a 280ZX crank pulley in very short order. I got about 5 years out of a ZX crank pulley with a 6500 rev limiter. Switched it to 7200 and the pulley came apart in less than a year. Very common for the ZX crank pulley to come apart. Billyzbear you're either very lucky or your tach was wrong. Ed, if you stuck 280 pistons on 240 rods they would stick so far out of the cylinders that you couldn't bolt the head on. The rods are 3mm longer than the 280 rods. 4ever, the N47 already has the same size valves as the ZX. The ZX valve stems are just shorter in the P79 and P90 heads. You ought to get the How to Modify Your Nissan/Datsun OHC Engine. No offense, but it sounds like you're taking every rumor you hear on the internet and trying to use them to build your engine. That book has most of what you need to know, and after you read it you'll have a much better idea of what is going on. Quote Link to comment Share on other sites More sharing options...
Afshin Posted March 30, 2005 Share Posted March 30, 2005 Definitely buy the book, it’s the best investment you could make!! It's filled with great useful info. Quote Link to comment Share on other sites More sharing options...
preith Posted March 30, 2005 Share Posted March 30, 2005 jmortensen, thanks for your patience. About the crank. My source tells me that the harmonics come into play at 7500 and end at 7800. If you can run through this range quickly you can probably get away with it, but as far as I know not with a stock damper. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 30, 2005 Share Posted March 30, 2005 Yeah, you're right, but you wouldn't want to do it on an engine that needs to last any length of time, you DEFINITELY wouldn't want to do it on a ZX damper, and you'd need an induction system and a cam and an exhaust system that would still make power at those rpms to make it worthwhile in the first place. And you'd probably want everything safety wired at that point. At least that's the impression I've gotten from those who know better than I do. Quote Link to comment Share on other sites More sharing options...
4everDATSUN Posted March 30, 2005 Author Share Posted March 30, 2005 the n47 head im talking about came of a maxima actually and does have smaller valves than a zx and they are the same length. thats why i said mn47, m for maxima. its got the heart sheaped combustion chamber, and i believe 40cc. i dunno tell me if im wrong. and i will get that book and read up anyways, doesnt do any harm to learn more. Quote Link to comment Share on other sites More sharing options...
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