trowa47 Posted January 4, 2007 Share Posted January 4, 2007 are the l20a rods and crank as strong as the l24-l28 rods and crank ? there is not much talk about this I don't think to many people are looking to destroke there engine as I am. and one more thing can some one tell me why is 1.60 the ideal rod to stroke ratio ? is it so the rod is not to long or... ? Quote Link to comment Share on other sites More sharing options...
NZeder Posted January 4, 2007 Share Posted January 4, 2007 The L20a rods (or L20aE but must be from a pre 80's engine as the later L20aE use a longer rod 135mm center to center with the smaller big and little ends much like the later Maxima L24E vs the 240z L24) Back to the first part - L20a rods are a great choice as they will have the 9mm rod bolts have the same center to center length as the L24 rods ie 133mm and look to be the same rod infact so strenght is not a problem I thougth the ideal rod/stock ratio was 1.75 in a short stroke motor which all the L series are. The 240z has 1.80 (and I believe this is one of the reasons it like to rev). The L26/L28 have a 1.65 and the L20a a 69.7 stroke so with the 133mm rods that = 1.90 I would take to Tony D on this site about the L20a as he is now running one in the land speed car I believe and it is making good HP too. Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted January 5, 2007 Share Posted January 5, 2007 L20A rods are 128mm http://www.ozdat.com/ozdatonline/enginedesign/ Quote Link to comment Share on other sites More sharing options...
djz Posted January 5, 2007 Share Posted January 5, 2007 No, he is right, they are 133mm. That calculator and the L engine calculator are both wrong. Quote Link to comment Share on other sites More sharing options...
trowa47 Posted January 5, 2007 Author Share Posted January 5, 2007 Dang it well i dont know if that will do me any good I want to us the 69mm stroke of the l20a but with 133mm conrods that just kills it lol Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 6, 2007 Share Posted January 6, 2007 PM Sent. We use the L20B rod in the LSR car if memory serves. 145.5 mm I believe. Overbored .020" to clean up rusty bores, and then destroked accordingly to keep us within the 1998cc original stock capacity. Quote Link to comment Share on other sites More sharing options...
trowa47 Posted January 6, 2007 Author Share Posted January 6, 2007 Thanks tony d i got your pm Quote Link to comment Share on other sites More sharing options...
NZeder Posted January 7, 2007 Share Posted January 7, 2007 Here in NZ we can find L20aE engines quite easy (from Fairlady Z imported from Japan both S30 and S130, also a number of other sedan Nissan cars ie Skylines, Leopards, Laurels etc however most are the later type with the longer 135mm rods (usually the L20aET engines) with the smaller journal ends (ie big ends) and pin ends (little ends)) For years we just pass them over thinking they were no good and just replaced them with L26 or L28 that we could find. But once a few of use did some research and remove a few rods we can confirm 100% that the pre 79 engine (this will garrentee they are the correct ones) are 9mm rod bolts 133mm center to center rods. Now given that the ozdat calculator and the L Series Calculator programs were made in Australia were they did not get the L20a in larger numbers I can only assume these figures they have in them are what some believe them to be or were wrong ones ie the 135mm c to c rods with the smaller ends. As we all know most L6 have a 38.10mm pin/compression height with the stock rod/crank setup - however this is not the case with the L20a they used a 40.10mm pin/compression height. All L6 (petrol) blocks are the same height = 208mm (well 207.9mm to be correct) so using the figures from ozdat (notice the L20a has -1 for the block height = might not know what it is). 69.7 stroke 128 rod and 38.1 pin height = 69.7/2 + 128 + 38.1 = should be the block height which is 207.9 but this combo is 7mm short = way wrong. Now using the figures that I know to be ture. 69.7 stroke, 133mm rod and 40.10mm pin height = 69.7/2 + 133 + 40.10 = 207.95mm bang on the money....... The reason I believe Nissan went to the longer 135mm rods in the later and turbo engines was so they could go back to the 38.10mm pin height but remember these longer rods only have the 51mm big end (not 53mm like most of the L4 and L6 range) and 19mm little end (not the normal 21mm) Hope this clears some of the misinfomation out there about the L20a blocks/rods/crank setup out there. Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 7, 2007 Share Posted January 7, 2007 With the 145mm L20B rods and a tight ring stack (27 or 30mm pin height can't remember) and that slight offset grind compensating for the bore increase, the R/s is over 2.1 in our LSR car... But as stated earlier, the early L20A rods are the same rods as in the other L-engines, there is no '128' length rod made specially for the L20A. It's the same as comparable L24 rods. The L28 went short at 130mm. It's academic really, you will be getting custom pistons, put whatever pin height you require after measuring the components yourself! Nothing is fixed, crank can be offset ground a mm or so to play one way or the other...you can use the later rods with the smaller crank end journal size for even more movement of the stroke, and then finally pin height is adjustable within reason. Our tight ring stack probably isn't the best for a street engine (thin rings). Quote Link to comment Share on other sites More sharing options...
trowa47 Posted January 9, 2007 Author Share Posted January 9, 2007 ok so i can get 8.0 to 1 or 8.5 to 1 with the 69mm crank. i was a bit whored about the 145mm rods giving me like 14 to 1 compression 135mm is giving me 8to1 Quote Link to comment Share on other sites More sharing options...
steveosupremeo Posted January 10, 2007 Share Posted January 10, 2007 someone else interested in a short stroke motor huh? Tony D and a few others have all but talked me out of it. Quote Link to comment Share on other sites More sharing options...
trowa47 Posted January 10, 2007 Author Share Posted January 10, 2007 Steve what setup where you thinking of doing i dont know but just to make it easy im thinking of just using a l24 crank and l24 9mm rods i dont know what i need to do to get the l20 crank to the 8to 1 i need for my turbo Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 10, 2007 Share Posted January 10, 2007 Rods do not determine your compression ratio, the PISTONS determine your compression ratio (along with your combustion chamber volume). In either case, you will have to fabricate the pistons---it will be absolutely NO USE making this engine without forged slugs---what is the point of building an engine who's powerband is 5000 to 9000 rpms, if you can only rev it to 7000 because of cast pistons. The rods will determine what pin height you will have to use to get a zero-deck or negative deck height (and my how much)---the piston configuration will determine your compression ratio. To get 8:1 on your L20A crank, you need to have the right PISTONS made for it. Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 10, 2007 Share Posted January 10, 2007 someone else interested in a short stroke motor huh? Tony D and a few others have all but talked me out of it. You were talking about non-turbo. Meaning absolutely no torque whatsoever below 4000rpms, and an absolute miserable car to drive in stop and go traffic. A short stroke turbo motor, making 3psi before boost threshold will act like a much larger engine upon throttle application, and the rush to redline will be even more interesting since thie redline is so high comparatively. You also wanted to use stock pistons, and for the same reason I gave trowa above, "what's the point"? The questions were totally different. Don't generalize my statements to his situation in comparison to yours without telling all the facts related to your original question. Which, as I recall, was predicated on the premise that "L28's don't rev fast"... Quote Link to comment Share on other sites More sharing options...
trowa47 Posted January 10, 2007 Author Share Posted January 10, 2007 thanks tony d i really want to do this now so whuld you us the t3/t4 turbo or some other turbo. and what can you tell me about the z harmonics problem at 7500rpms or is that only with the l24 l28s Quote Link to comment Share on other sites More sharing options...
steveosupremeo Posted January 14, 2007 Share Posted January 14, 2007 whoa there Mr. D, didn't mean to ruffle any feathers or generalize anything, but don't do the same to me. it was not predicated on how fast the L28 can rev but rather the attainable RPM between it and the L24. lots of engines tach up quick but don't rev high. it was also on the premise of being a toy and not a daily driver car that sees lots of traffic. thats what i recall, anyway... Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 15, 2007 Share Posted January 15, 2007 And the discussion went (with Dan Baldwin Chiming in) that in either case (l24 or L28) the 'attainable difference' of rpms was nil, therefore the engine with more displacement will be the more driveable. The discussion also was diverted onto forged versus cast pistons, wherevy the limit was 7000 due to piston limits---then redirected again to a rod and piston speed discussion about how cast pistons would survive to 8K on a long rod short stroke motor because of piston speed... And even at 8K, the bigger displacement engine will have the advantage because of more torque down low. Now Turbo is something altogether different from N/A, as you can alter the torque characteristics radically using forced induction. I'm not feather ruffled, I just didn't see where the comment had any place in the guys post since the engine build was totally different. Harmonics? Some people discuss critical speeds, and in industrial applications the cure to critical speeds is accelerating the engine THROUGH the critical zone as fast as possible, and not hanging at the critical speed. We cammed our Bonneville Engine to come "On Cam" hard at 7K. Meaning we pull hard through the critical of 7500 fairly fast (as we did on the L28 engine as well). We had the engines sitting at 8200+rpms for most of the run. The only time we had anything at 7500 was on our first few runs where we were only going in the 140's. After that we regeared and went faster, at higher rpms. Quote Link to comment Share on other sites More sharing options...
steveosupremeo Posted January 16, 2007 Share Posted January 16, 2007 Tony, i had a question about your bonneville racer, i read that you offset ground the crank, is this true? and what for, never heard of it before. also, whats wrong with 7500 RPMs? Quote Link to comment Share on other sites More sharing options...
NZeder Posted January 16, 2007 Share Posted January 16, 2007 i read that you offset ground the crank, is this true? and what for, never heard of it before.You do this to change the stroke more ie take a LD28 stroke of 83mm offset grind to give 84mm = more stroke = more displacement Quote Link to comment Share on other sites More sharing options...
steveosupremeo Posted January 17, 2007 Share Posted January 17, 2007 awesome possum! 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.