onephatz Posted November 6, 2003 Share Posted November 6, 2003 I've been thinking about this combo for some time and wanted to get your thoughts on the matter. I have an L28 out of an 81 non turbo (f54 block) and a L24 out of a '73 I also have a E-31 head. with a L28 block with 1mm overbore, L24 crankshaft, flattop pistons, a mildly ported E31 head and a mild cam, what kind of ceiling would we be talking about RPM wise. this would yield a 2.6L and about 10.2:1 compression and could run on 93 octane pump gas. any ideas what kind of HP would result? I like the idea of being able to run 7-9k rpm when I want to, it makes me feel all warm and fuzzy inside . thanks jesse Quote Link to comment Share on other sites More sharing options...
jonzer12 Posted November 6, 2003 Share Posted November 6, 2003 Will your valvetrain support 9k, also you will need the CAM to make use of the added rev range, I would guess a serious 250-275 hp. Never heard of that setup before. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 6, 2003 Share Posted November 6, 2003 I just researched this a bit. Seems like the stroker is a better idea. If you do the destroked engine, you won't see the benefits of the better rod ratio until you get to the point at which a standard lubrication system and ignition system won't cut it. A stroker can rev to 7K with no problems, and that's about the limit of factory ignition and oiling system. If you want to dry sump it and to crankfire ignition, then go for it and you should see some good results above 7K. Jonzer makes a good point about the valvetrain as well. Jon Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted November 6, 2003 Share Posted November 6, 2003 I have turned an NA engine way over 7k, had a friend who routinely revved his to 8k. To rev where you want though, you should consider forged pistons, I would also go to an added capacity oil pan, and try to lighten and balance as much as I could. Use ARP rod bolts, polish and shot peen the rods. Why not go out to 89mm, and give yourself roughly a 2.8? I have considered doing that with a turbo engine. Also, get the BHJ balancer. I would be interested to see what you get, if you go this route. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 6, 2003 Share Posted November 6, 2003 Factory spark starts to scatter at about 7k, according to all the books I've read that's because the gear drive isn't exact enough. Lots of people with Z's are floating valves way before 8K. BTW, I have a friend who tried to blow up his L24 by standing on the gas down a long straight in his town. He ended up blowing the head gasket out of the side of the head at something over 8k. That was with a points distributor. I wasn't trying to say that you CAN'T rev past 7k, I'm saying that 7k is when spark timing gets irratic, and irratic timing at that rpm is dangerous. Also valves start to float at some point, the stock cranks supposedly aren't that great for too much over 7k. Basically if you wanted to do that kind of rpm consistently (like if you were going to build the motor to work at that rpm) then you would spend a lot of $$$ to make it reliable at those speeds. What I found when I was looking into this is that you get more hp/torque from the increased displacement of a 3.1. That extra 500cc gives you a lot more than the destroked engine will unless you spend that $$$. If they're both revved to reasonable redlines the stroker is a better choice. Jon Quote Link to comment Share on other sites More sharing options...
240Z Turbo Posted November 6, 2003 Share Posted November 6, 2003 240Z crank stroke 73.7mm 280Z bore 86mm Exactly the specs of the RB26 How ironic, especially the exactness of the 73.7mm stroke. I have thought about it and this has been discussed several years back. My stroke is 84 mm and I rev to 7200 all day long. Quote Link to comment Share on other sites More sharing options...
KiD-ViD Posted November 6, 2003 Share Posted November 6, 2003 240z turbo: what length rods do you run? also out of personal curosity while I am asking stuff what are your cam specs? I would think its not really the stroke that matters but the length of the rods. The setup I had in mind was a 280 crank, l20a rods, ka24 pistons. this gives you 2.95l displacement and a 1.71 rod/stroke. It seems like a hot ticket to me. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted November 6, 2003 Share Posted November 6, 2003 What makes you think we used a points style dizzy? James I did also notice the similarity to the Rb engine years ago, and that is what sparked my interest. As for timing, if you are really worried about it, run a tec3 or an HPV1 or something like that. I have a 280 crank with 240 rods and spin mine to 7k, and so far, nothing has come out of the engine, although it did blow the headgasket the other day. But hey, 6 years at 15+psi of boost with a stock headgasket, why should I complain. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 6, 2003 Share Posted November 6, 2003 I assume the points style dizzy question was to me. Nothing makes me think you ran points. I never said anything about points, other than to mention my buddy who stretched his head bolts and blew his head gasket with a points dizzy. My 280ZX EI distributor is still driven by gears off the crank. That geared setup is apparently what makes the timing irratic at high rpms. I am not sure what you have in your car, but the NA distributors are all this way IIRC. Search for Dan Baldwin's dyno sheet. You can see his ignition get a little wacky at about 7K, and he has EI. That's the only point I was trying to make. One more time, I don't think that 7K will hurt an L series engine. I do think that the original build talked about in this thread being able to run 7-9k rpm when I want to, it makes me feel all warm and fuzzy inside is going to take more than just a simple slap together this crank, these rods, and these pistons, and it will run 7-9K all day long with no problems. I was mentioning the 7K thing since that's where stock ignition gets weird, and IIRC there are vibration issues with the cranks at 7.5K. To do 9K as originally discussed, I think you need to run a dry sump setup, all the expensive internals, and you'd need a valvetrain and camshaft that would both be able to get you there, and not float the valves once you got there. And you'd need some sort of better ignition system. If you don't want to do all of the above, you'll get more torque and hp from the larger displacement of the stroker vs the destroker. Jon Quote Link to comment Share on other sites More sharing options...
240Z Turbo Posted November 6, 2003 Share Posted November 6, 2003 240z turbo: what length rods do you run? also out of personal curosity while I am asking stuff what are your cam specs? 9mm 240Z rods Grind #155 Web Cam http://www.webcamshafts.com/datsun-auto.html#2 Quote Link to comment Share on other sites More sharing options...
yo2001 Posted November 7, 2003 Share Posted November 7, 2003 I was shifting my stock L28 bottom at 7200rpm via factory tach, Now I found out my factory tach is off by 300-400rpm under so who knows, it could have been 7500-7600rpm. I finally did span a rod bearing though. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted November 7, 2003 Share Posted November 7, 2003 Well mine used to rev right off the factory tach at 8k. granted stock pistons and rings don't like to do that, but it sure was fun to have a light flywheel, sidedraft webbers and do a 7k rpm clutch drop and freak people out. A cam helps too. Quote Link to comment Share on other sites More sharing options...
DAW Posted November 7, 2003 Share Posted November 7, 2003 I think it would be worth it only as a budget build up and that means no overbore or replacement pistons, just a L28 block and pistons with L24 crank and rods. The small displacement is the main issue. Look at the specs for the current generation 350Z engine. It is large bore and short stroke, but it has the displacement to make significant power. The L28 stroke (79mm) is certainly not excessive and the F54 block can be overbored to 88 or 89mm which still gives you an oversquare engine with a substantially increased displacement. The issue is the rod/stroke ratio which goes away when you increase the stroke in the L24/26/28 block. You could run LD28 or FJ20 rods (140mm) and have custom pistons made (I think the c.ht. needs to be about 28-29mm). The LD28 crank is not an excessive stroke at 83mm but it is not best-suited to high rpm use when combined with an abismal rod/stroke ratio. I think the answer is in a taller block ht, just as Nissan did when they evolved the L16/L18 block (=L24/26/28 ht) into the L20B block as they increased the stroke from 78mm to 86mm, in order to restore a favorable rod/stroke (130.4/78 vs 145.9/86). Nissan did the same thing when they increased the stroke in the L6 from 79mm to 83mm, i.e., they improved the rod/stroke (130.4 vs 140/83). So what's the point? Use the LD28 block when using the LD28 crank, that's why Nissan paired them up. Lots of documentation of fast 3.1 strokers using the L28 block...how much faster would they be with longer rods? Lots of rationalization re short rods. "When the only tool you have is a hammer, you tend to treat everything as if it were a nail". DAW Quote Link to comment Share on other sites More sharing options...
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