z-ya Posted July 6, 2009 Share Posted July 6, 2009 Just a point of reference. I may have to replace the springs as Paul noted. So far 4 years of track days and time trials and it still runs strong: - L28 N47 head - Comp cams 460 lift 280 dur. cam - Stock L28 N47 springs (180k miles, spring height measured within spec.) Note that Comp Cams advertises peak power at 6000RPM, and that is about where the power starts to drops off. As far as I can tell there is no valve float. How long will stock springs last? I have no idea. The next head I build will have performance springs. this is a budget motor and it doesn't want to break (likes to blow head gasket though). Pete Quote Link to comment Share on other sites More sharing options...
Xnke Posted July 7, 2009 Share Posted July 7, 2009 Robert, the 4500 rpm thing is when the AFM maxes out and the ecu goes to a pre-programed fuel curve, not really a fixed duty cycle. as RPM goes up, fuel goes up, as RPM rise slows down, the fuel curve changes a little flatter, ect. I don't know how the '87 L24e ECU works, but the '75-'83 units work like that, from what i am able to read and search out on this site and others. The Z31 ecu's from '84 and up are different, and use a different method. Here in the states they stopped using the L-series in 1984, as far as I know, and the last L24E here was in the '84 Maxima. Your Milage May Vary, as you well know. If it still is a Bosch L-Jetronic injection computer, and is NOT similar to the Z31's VG30E computer, then I would bet on it being just like the '75-'83 units and swapping over to preset curve as soon as the AFM maxes out. IF you have a different system, like the Z31's and newer systems, that use a mass air flow sensor or manifold absolute pressure sensor, then all bets are off and I have no clue how the computer will react. By the way, the Early Z31 ecu's often get swapped over to the S130 cars by some simple tricks, such as replacing the CAS with the S130's optical dizzy, and swapping the AFM for the equivilent Z31 part. Probably some major rewiring as well, for what that's worth. If you have an optical dizzy, and something other than the Z-car/Maxima/Cressida/L-Jetronic style AFM, the chances are that I am totally wrong and the car will run great. It's hard to say for certain. But if it's the same as a Z car, and on all the L-series in the USDM to '84, it is, then going too big on the cam will crush any kind of power or performance goals. Quote Link to comment Share on other sites More sharing options...
Robert Posted July 7, 2009 Author Share Posted July 7, 2009 Zya, Could it be float that cause your dip afte 5800? Nice numbers, but whats with all the ups and downs? Quote Link to comment Share on other sites More sharing options...
Robert Posted July 7, 2009 Author Share Posted July 7, 2009 Robert, the 4500 rpm thing is when the AFM maxes out and the ecu goes to a pre-programed fuel curve, not really a fixed duty cycle. as RPM goes up, fuel goes up, as RPM rise slows down, the fuel curve changes a little flatter, ect. I don't know how the '87 L24e ECU works, but the '75-'83 units work like that, from what i am able to read and search out on this site and others. The Z31 ecu's from '84 and up are different, and use a different method. Here in the states they stopped using the L-series in 1984, as far as I know, and the last L24E here was in the '84 Maxima. Your Milage May Vary, as you well know. If it still is a Bosch L-Jetronic injection computer, and is NOT similar to the Z31's VG30E computer, then I would bet on it being just like the '75-'83 units and swapping over to preset curve as soon as the AFM maxes out. IF you have a different system, like the Z31's and newer systems, that use a mass air flow sensor or manifold absolute pressure sensor, then all bets are off and I have no clue how the computer will react. By the way, the Early Z31 ecu's often get swapped over to the S130 cars by some simple tricks, such as replacing the CAS with the S130's optical dizzy, and swapping the AFM for the equivilent Z31 part. Probably some major rewiring as well, for what that's worth. If you have an optical dizzy, and something other than the Z-car/Maxima/Cressida/L-Jetronic style AFM, the chances are that I am totally wrong and the car will run great. It's hard to say for certain. But if it's the same as a Z car, and on all the L-series in the USDM to '84, it is, then going too big on the cam will crush any kind of power or performance goals. Interesting. If Nissan used Licenced Bosch injection systems, then I can believe its crap... Ive searched the web for hours now, but cant find anything except this post that tells me the AFM max out.. I searched Wikipedia, not the most reliable source of info, but they claim the L24E was produced from 1977 through 1986 in 810s, skyline, maxima and laurels -- http://en.wikipedia.org/wiki/Nissan_L_engine#L24E . If you are correct, I could be in trouble. Ill start a new thread on the subject, in an attempt to find some more info.. Quote Link to comment Share on other sites More sharing options...
z-ya Posted July 7, 2009 Share Posted July 7, 2009 Zya, Could it be float that cause your dip afte 5800? Nice numbers, but whats with all the ups and downs? I don't think it is valve float because it runs fine over 6000RPM, it just doesn't make as much power up there. The AFR is consistent in the 12.5-13.5 range cross all RPMs. The torque dip in the 3700RPM range is typical for NA L6s. Not sure what the dip at 5200RPM is. The dotted plot was with a stock port matched L6 EFI manifold with a 60mm TB. The solid plot is a dual TB SU manifold thing I put together. Pete Quote Link to comment Share on other sites More sharing options...
Xnke Posted July 7, 2009 Share Posted July 7, 2009 Pete, I truly envy that engine bay. Hopefully mine will look similar some day... Anyhow, in getting my cylinder head ready to go back together, I am going to be using a set of New L-6 springs, that came with my last motor buy, and a cam with a .454 measured lift. I know and understand that this is not ideal, but I will be changing the springs later, with a different cam. (That different cam is not in existence yet, or I'd go for it, and skip the two-stage thing) Assuming that the springs are close, but not bound, what would the minimum acceptable clearance be, between coils? This would tell us for dead certain what the max cam lift could theoretically be, before the cam would physically no longer fit in the head. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted July 7, 2009 Administrators Share Posted July 7, 2009 I don't think it is valve float because it runs fine over 6000RPM, it just doesn't make as much power up there. The AFR is consistent in the 12.5-13.5 range cross all RPMs. You'll know it. It makes an ugly sound... sorta like a drunken woodpecker AFR's scatter and adjustments do nothing. Quote Link to comment Share on other sites More sharing options...
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