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Thread: Performance Q's: How to get the most out of my L24

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    Registered User metalmonkey47's Avatar
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    Default Performance Q's: How to get the most out of my L24

    Hey guys, just want to clarify my intentions: My 70 240 is seemingly on the low side of the power spectrum, and I KNOW I have a lot to be found. It's not my first L motor, but it is my first L-6 and my first set of side drafts. I feel like at one point it made a scary amount of power, but now I'm starting to feel like I'm lacking.

    My L24 has a stock bottom end with flat-tops, and an N47 head to replace to shot E31 that's undergoing a rebuild for my L28 build. For the time being I'm making do with what I have but I feel like I'm not getting enough power. It's got stock manifolds, bone stock exhaust with the original glasspack, etc etc.

    I JUST rebuild my N47 from the ground up to restore some lost compression, lapped valves, fresh seals, etc etc...

    The L24 service manual on Xenons30.com shows the timing table on the crank pulley is in 5 degree increments... I'm assuming the table starts at 0 degrees, correct? If that is so, I'm running about 13 degrees static timing.


    I believe I may also be loosing something in the carbs somewhere. Despite my attempts to dial in my SU's with my Uni-syn and lots of reading some walk through's, I can't help but feel like I'm doing something wrong. When I start my car, I notice that it distinctly sounds as if one carb is dead until a few quick revs, and all is well. I've followed all the guides on here, and don't seem to get any difference out of it. I'm 2.5 turns down on the nozzles, disassembled the carbs down to every piece when i rebuilt them, carefully reset the needles, blah blah, etc etc.

    Is there any common mistake made by SU newbies that I might be overlooking? I'm sure there's something obvious only an SU noob would overlook...

  2. #2
    No more body roll! SteveJ's Avatar
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    Matt, if you're worried about your SUs, get this video from Welcome to ZTherapy.com.
    Then some time when you're off on a weekend, see if you can take your car over to Tim McGovern's house and learn. It will be time & money well spent.
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    So you lost power after going to the 47 head? Or it had 'scary' power with which head?
    Don't forget the basics, a good tune is everything. Done a valve adjustment since installing the rebuilt head? Installing a 47 head you will loose compression despite being rebuilt with respect to the e31 head, so it won't run quite the same.
    What ignition are you running? More info is always good for troubleshooting!
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Quote Originally Posted by madkaw View Post
    So you lost power after going to the 47 head? Or it had 'scary' power with which head?
    Don't forget the basics, a good tune is everything. Done a valve adjustment since installing the rebuilt head? Installing a 47 head you will loose compression despite being rebuilt with respect to the e31 head, so it won't run quite the same.
    What ignition are you running? More info is always good for troubleshooting!
    Sorry let me clarify. The car had a blown head gasket and fatally wounded E31 on it We swapped it for a Maxima N47 junkyard head for the time being to get it running. Compression tested 90psi across the board, 110 wet. Rebuilt a spare N47 on the side and swapped it in a few weeks ago. It was running awesome at one point with the shot mN47.

    It has a ZX matchbox at the moment, fresh cap/rotor/wires/BPR5EY NGK plugs, etc etc. Literally everything 'tune up' related is new. Electric fuel pump with regulator @3.5psi, insulated fuel rail and fuel lines.

    Tonight a buddy of mine stopped by with my E31 head from his shop, got to talking about it, and didn't even occur the oil I'm running in the dashpots may be WAY too thick. It's either 10-30 or 10-40, the pistons are TIGHT. I'm going to pull the pistons tomorrow, drain and clean all the oil out, and fill it with ATF. I've been meaning to do that but forgot. That's a huge performance killer, and would explain my crappy gas mileage too.

    Quote Originally Posted by SteveJ View Post
    Matt, if you're worried about your SUs, get this video from Welcome to ZTherapy.com.
    Then some time when you're off on a weekend, see if you can take your car over to Tim McGovern's house and learn. It will be time & money well spent.
    Steve, I'm lazy and keep forgetting to do that. I'm on it some day this week. I have a lot of learning to do! I need to sit down and pick Tims mind.

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    Registered User madkaw's Avatar
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    Kind of weird the mn47 head gave such low CR numbers .
    The pistons should take effort to push up, but try some trans fluid and see what it does.
    How do you just find a mn47 head in the junk yard. I've been trying to run into one of those myself
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Nova Scotia,Canada,Earth Blue's Avatar
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    I put the same set up on a friend's 240z L24 and it works great. Here are some things to consider:

    -T ry setting your timing to 18 degrees at idle and do not use the vacuum advance.

    -Try triple side draft carbs with 30mm chokes for more torque.

    - Try long duration cam

    - Rev to 6000 rpm before gear changes
    Last edited by Blue; 10-09-2014 at 05:45 AM.
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    Quote Originally Posted by madkaw View Post
    Kind of weird the mn47 head gave such low CR numbers .
    The pistons should take effort to push up, but try some trans fluid and see what it does.
    How do you just find a mn47 head in the junk yard. I've been trying to run into one of those myself
    Matt seems to have good fortune. He got the car itself for a song.
    metalmonkey47 likes this.
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    Nova Scotia,Canada,Earth Blue's Avatar
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    btw dash pot oil is not significant to performance when compared to state of tune, timing, valve lash, fuel metering compression and cam design.

    the oil in the carb only stabilizes the piston on bumpy roads and controls the fuel when transitioning to/from WOT quickly. If you "squeeze" the gas pedal, it will not make a difference.... only when you "hammer" the pedal will oil type be noticable.... and barely by the butt dyno. A/F monitoring with a WB O2 will show some aspects of the transition and oil interaction.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    Crumudgeon
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    You are seeing 90 to 110 psi on a compression test? You should be in the 150 to 175 psi range.

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    Which cam are you using? The cam from the N47 (C cam) or the cam from the E31 (A cam)?

  11. #11
    Registered User metalmonkey47's Avatar
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    Quote Originally Posted by madkaw View Post
    Kind of weird the mn47 head gave such low CR numbers .
    The pistons should take effort to push up, but try some trans fluid and see what it does.
    How do you just find a mn47 head in the junk yard. I've been trying to run into one of those myself
    Well, it was a junkyard head. Took a lot of cleaning up to run on the L24, seemed to be leaking at every valve.

    We (I say we, but it's actually a buddy of mine) have storage units full of oddball stuff, including an original '64 fairlady roadster, short window, etc etc. The head just happened to be sitting my the 240z, and we decided the E31 was probably a bad idea to put back on.

    Quote Originally Posted by Blue View Post
    I put the same set up on a friend's 240z L24 and it works great. Here are some things to consider:

    -T ry setting your timing to 18 degrees at idle and do not use the vacuum advance.

    -Try triple side draft carbs with 30mm chokes for more torque.

    - Try long duration cam

    - Rev to 6000 rpm before gear changes
    HMM.. I'll see what I can do with the timing tomorrow. I'm starting to get backfiring out of the carbs upon cold starts. Gotta see what's up with that.

    The triples and big cam are waiting on some bills to be paid, and my L28 to be built first. No sense wasting all that money on a bone stock worn out motor.





    I changed the oil in the carbs out for some Marvel Mystery Oil (suggested by a local) and it's a LOT peppier. Revs a lot quicker to 6000. Still not very quick though.

    I've been playing with my fuel adjustments over the last few days and can't get the damn thing to stop running so rich. Even at 2 1/4 turns down, it's still obviously rich when cruising. Double checked needle height, and float levels, don't understand why she's running so rich. I need to invest money in a new innovate LC-1 and replace the clock. i had one in my truck, and it kicked ass.

    Also noticed that when in second under about half throttle to 5000rpm, it starts to surge a little. Not sure if that has to do with it running rich or not.

    Quote Originally Posted by John Coffey View Post
    You are seeing 90 to 110 psi on a compression test? You should be in the 150 to 175 psi range.
    That was with the mN47 head, I've since then rebuilt a spare L28 N47 and slapped it on to straighten that out.

    Quote Originally Posted by beermanpete View Post
    Which cam are you using? The cam from the N47 (C cam) or the cam from the E31 (A cam)?
    Stock N47 cam. Is there a difference between different L-6 cams other then internal/external oiling?
    Last edited by metalmonkey47; 10-13-2014 at 12:09 AM.

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    timing #'s?
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Quote Originally Posted by madkaw View Post
    timing #'s?
    Just set to 15 btdc right now.

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    Quote Originally Posted by metalmonkey47 View Post
    Stock N47 cam. Is there a difference between different L-6 cams other then internal/external oiling?
    Yes. The A cam tends to make power at a higher RPM range than the C cam. My experience is the A cam will pull to 6k or so, the C cam pulls to about 5k. I can't say one will make more total power than the other but the higher RPM range of the A cam could feel like more just due to the RPM range difference.

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