tec280zx Posted May 18, 2002 Share Posted May 18, 2002 After sorting through the temp sensor problems i was having the car is running now. She runs really good too. Not to metion I fixed the major exhaust leak. Previous owner broke 4 exhaust studs and just left them, go figure. So i can actually hear the engine now. The only problem i'm dealing with is my car is starting to ping at over 4,000 rpm. I knew this would happen. Other than racing gas or octane boost (too expensive) what are some ways to fight detonation? I've been told is caused by too much air and not enough fuel to the motor, is that basically right? I'm wondering if a fuel pressure regulator would help? Anyways, thanks for your guys previous help, my baby is back on the road!! Quote Link to comment Share on other sites More sharing options...
DAW Posted May 19, 2002 Share Posted May 19, 2002 I'm not sure which head swap you did, but if you've got an '81 280ZX n/a then I assume you put an N42 or N47 from a '75-'79 L28 and now have just over 10:1 compression. First, make sure your initial timing isn't set more than 10 or 12 degrees BTDC. Check your thermostat, you want 180 dgrees, not 195. Next, you're going to probably go out of emission specs so write down what you do in case you need to reverse it (you're probably out now anyway due to the increased compression). Splice in a Radio Shack resistor into one of the leads of the temperature sensor (either cylinder head or water temp, whichever you have), start with about 700 ohms. Remove the cover from the Airflow Meter and adjust the spring tension by two notches so that you are decreasing the spring tension on the flap/door of the AFM. Try these changes and see what you get. If not enough, then try substituting an 800 ohm resistor in the temp sensor circuit. DAW Quote Link to comment Share on other sites More sharing options...
Mike C Posted May 19, 2002 Share Posted May 19, 2002 YOu also need to check your total advance and at which RPM it comes in. Different distributors have different amounts of vac advance added in. You can get a dial back light at Sears for $69. Quote Link to comment Share on other sites More sharing options...
tec280zx Posted May 19, 2002 Author Share Posted May 19, 2002 Yea, i put on an n47 head... i'm not sure of the year though, but it has round exhuast ports. I haven't adjusted the timing yet and i did install a 180 thermostat. I'll look into the resistor on the temp switch. What exactly does that do? Will passing smog be a problem once i adjust it properly? Quote Link to comment Share on other sites More sharing options...
yo2001 Posted May 19, 2002 Share Posted May 19, 2002 Extra fuel, and back the timing alittle. Quote Link to comment Share on other sites More sharing options...
DAW Posted May 19, 2002 Share Posted May 19, 2002 The temp sensor tells the ECU how cold or warm the engine is; the cooler the engine, the richer the mixture it will need. The sensor is a variable resistor that starts out with a lot of resistance cold, and it drops in resistance as it warms up. If you add some resistance, you add some richenning across the full temperature range (which you need if you increase compression, to increase performance and decrease ping). DAW Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 19, 2002 Share Posted May 19, 2002 You know that the N42/N47 heads were designed for the dished pistons. I have seen them run higher compression, but they are not optimized for the flat top pistons. I would consider the N47 you have as a temp measure until you could find an E88 or modify a P90 for the compression (That is what I am doing on my track car) Mike Quote Link to comment Share on other sites More sharing options...
tec280zx Posted May 19, 2002 Author Share Posted May 19, 2002 Thanks for the info, i'm gonna give the resistor a try tomarrow. I'm hoping between that and more octane boost my car might not ping till i can afford the fuel upgrades. Shock96: Thats just what this is, temp solution. This motor has 220,000 miles on it! I know nissan motors are pretty tough so i'm gonna push this till the envelope pops and begin my turbo project. Quote Link to comment Share on other sites More sharing options...
DAW Posted May 19, 2002 Share Posted May 19, 2002 The head swap you did isn't a temporary solution as much as it's a budget solution. You would need to richen the mixture when you increase the compression no matter what head/block combination you run. You will have a little more ping to deal with when using the N42/47 L28 head because it isn't a high quench design as the "closed chamber" L series heads. I would just try to tune the ping out and see what you get. Your alternative is to take the P79 head you removed, shave it 0.080", shim the heck out of the cam towers, and install N42/47 valves (0.100" longer than P79/90). Or, you could use a Maxima P79 head (L24) which is a closed combustion chamber and higher c.r. than the N47 on a F54 block, install N42/47 intake valves and put it together, maybe using two head gaskets to drop compression a bit if needed. The combo you've got will work. I've been using that setup with triple side-drafts on my autocross car with good results. You become very aware of what gas stations have better quality fuel than others. DAW Quote Link to comment Share on other sites More sharing options...
tec280zx Posted May 19, 2002 Author Share Posted May 19, 2002 Well I just backed the timing a bit, well actually quite a bit. I must of had the timing advanced way too far. Engine no longer pings!!! Power increase is definatly more noticable now. Too bad its raining today, been spinning the tires through 4th without trying. Doh. Should I still try that resitor trick? Engine pulls very smooth now, how much will this help? THanks for your guys help. Quote Link to comment Share on other sites More sharing options...
tec280zx Posted May 19, 2002 Author Share Posted May 19, 2002 Well I just backed the timing a bit, well actually quite a bit. I must of had the timing advanced way too far. Engine no longer pings!!! Power increase is definatly more noticable now. Too bad its raining today, been spinning the tires through 4th without trying. Doh. Should I still try that resitor trick? Engine pulls very smooth now, how much will this help? THanks for your guys help. Quote Link to comment Share on other sites More sharing options...
DAW Posted May 19, 2002 Share Posted May 19, 2002 I would do the resistor, then try advancing your timing until it pings; then back it off a bit. Both the mixture richenning and the advanced timing will improve throttle response. What's the point of increasing compression if you can only run it by detuning? DAW Quote Link to comment Share on other sites More sharing options...
tec280zx Posted May 19, 2002 Author Share Posted May 19, 2002 Yea, I lost a little throttle response from backing off the timing, that sucks. Can you go into detail about the resistor some more? I'm a bit lost. I just got back from radio shack empty handed cause i wasn't even sure of what i was looking for. What type of resistor would i need? Thanks for the help. Quote Link to comment Share on other sites More sharing options...
DAW Posted May 20, 2002 Share Posted May 20, 2002 They are really cheap and sold stapled to a card, usually there are 5 or 6 to a card, all of the same value. You're looking for little tan plastic barrels with multicolored rings painted on them and a thin solid bare metal wire out of each end. There will be a selection of these cards of different resistance values, probably on pegboard type hooks. You may not find exactly 700 ohms, the closest may be 680 or 720 or 740, etc., just cut the wire, strip the ends and join the wire ends to the resistor wires, solder if possible, and tape it to insulate. Nice attention to detail on the engine, BTW. DAW Quote Link to comment Share on other sites More sharing options...
tec280zx Posted May 20, 2002 Author Share Posted May 20, 2002 Hopefully when I get this motor dialed in it won't be too much of a temp solution. I really like the upped compression. Definatly more "punchy" in the lower rpm's. Today i'm gonna try retarding the timing a bit and use that resistor thing you mentioned. Here's a couple engine pics: I know, I need better camera. Quote Link to comment Share on other sites More sharing options...
tec280zx Posted May 20, 2002 Author Share Posted May 20, 2002 Alright, I just wired in the resistor. Quick question though, since the temp sensor has two wires, should i put one on each wire? Or will just one work? So far i have just one on. Also, the highest ohm resistance i could find was 560. Will this be enough? Still raining outside so i can't do any road tests yet. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted May 20, 2002 Share Posted May 20, 2002 1 wire is enough. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted May 20, 2002 Share Posted May 20, 2002 While you are changing stuff, I would swap out that intake manifold for one one that looks like a turbo intake manifold. I had a manifold just like your on my turbo engine, and when I got rid of it and put on a turbo one, I picked up boost. Something about that taper in the back. I think the older style 280 valves are 2 mm longer, which is .080 longer. Could be wrong. The P79 head is the way to go if you don't have the P90. I do not recommend running two head gaskets, buy the HKS one or the one from Nissan motorsports that is 2 mm thick. You can always mill the P79, change the retainers and run a thicker lash pad. All you have to do is get a lash pad with the additional thickness you shimmed the cam towers added to it. In other words, if you have stock lash pads and you shim the cam towers up 80 thousandths, then you need a .210 lash pad, approx. ( .133 stock plus .080 ) See? Double check me on the stock lash pad thickness. That is a cheaper way to go than getting 12 new valves and having a valve job done. Besides, you should be getting a 3 angle job done, it is worth HP over a regular valve job on a Datsun L series engine. You could also just swap out the head gasket for a thicker one. I think the HKS one is reusable. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted May 20, 2002 Share Posted May 20, 2002 If you are really worried about passing emissions, buy a potentiometer and that will allow you to adjust your resistence. Then you can set it back to no resistence when you have to do emmissions. If you wanted to, you could run the leads and the potentiometer into the car. Also, I would set the timing to factory spec's, and make sure my cam timing was correct since you did swap the head. I know I have done that many times only to find my cam timing to be off a little. Run your tank as close to empty as you can, and then fill it up with super unleaded and see if you have a problem. No sense doing a bunch of work if you don't need to do it. Also, make sure you have adequate fuel pressure, and your fuel filters are not plugged up. You could also look into getting an adjustable feul pressure regulator. JWT has a bosch one that works like the factory one, only it is adjustable. Raise you fuel pressure a couple points and see what happens. I get nervous about cutting a factory harness since you run the chance of losing the integrity of it at every splice point. Not saying people don't do it and don't have problems. I had to do it to mine with the JWT setup I am running. Doesn't mean I liked it. but everytime I have a little hiccup or bump, or the car misbehaves, i wonder if it was that splice job I did. Know what I mean? Quote Link to comment Share on other sites More sharing options...
DAW Posted May 21, 2002 Share Posted May 21, 2002 The reason N42/47 valves are exchanged into a P79/90 head that has had a big shave done is that they are .100" longer, thereby eliminating the need to buy thicker lash ($$) pads. One resistor is fine, it can go in either wire since it is just in series in the circuit. If you put two or more in it will just be additive which is OK to do. You can also bridge the two wires and create a parallel resistor circuit but calculating it is more involved, so I'd recommend sticking with in-line, series resistor(s). DAW Quote Link to comment Share on other sites More sharing options...
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