tec280zx Posted May 6, 2002 Share Posted May 6, 2002 Hey guys, I recently just finished my n47 swap on my 81 and i'm running into a few probs now that i got the motor to start. To my surprise the motor turned over very easy and idled quite nicely. Definatly better than before. Anyways, my problem is the thermostat housing, if you notice on the n47 there is no CHT sensor, its actually on the thermostat housing. no big deal i say. I just lengthened my wires from the CHT to the thermostat housing and plugged it in. Now i'm not sure thats gonna work just because the plug fits. Secondly, my temp gauge doesn't work either. I'm not sure if i hooked that up right either. From what i've read in the archives the gauge is controlled by the thermal transmitter which is the upper left port on the housing. Is there a way to test if thats working or not? And if its bad where can i get a new one? Sorry for all the questions, but i've gotten this far and now i can't drive my baby. I just need someone who's done this swap to kind of guide me through. All help is appreciated Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted May 6, 2002 Share Posted May 6, 2002 Do you have the old head? If so why not just swap the water neck from the old head to your new one and then everything should hook up fine. The head swap is all you did right? I know on a turbo model, there are two wires that connect to sensors on(in) the water neck. I believe one turns on the fan(s) and the other is the temp gauge. I would have to look at mine to be sure, but I don't think the plugs interchange. I would also check the sensor to make sure it is working right. You will need a shop manual for the correct specs. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted May 6, 2002 Share Posted May 6, 2002 I noticed the CHT thing. IS the car not running to rich since you don't have a CHT? It should be. What head did you take off to put on the N47? Believe it or not, a P79 head is a really good head, especially if you mill it some and shim up the cam towers and add thicker lash pads to compensate. Most people don't believe that, but it is true. If your car is running to rich, you could put a resistor on the leads to the CHT pigtail, but that is not a very professional fix. It would solve the richness problem when the car is warmed up fully, though, although you might have some starting issues in cold weather. I would suggest you put a thermometer in the radiator and warm the car up fully to determine if you have a richness problem or not. Before I got my JWT box for my 83 turbo, if my CHT connector came loose, my car would just about not run when warm. You should have a similar issue I would think. Quote Link to comment Share on other sites More sharing options...
DAW Posted May 6, 2002 Share Posted May 6, 2002 The water temp sensor on the N47 head should work as a substitute for the CHT sensor on the P79. Canadian spec '81s had the same setup as what you're doing. The N47 head you put on might have been from a car with a temp warning light instead of a gauge like your car has. Take the old sensor out of the P79 and exchange it into the N47, it should be a yellow single wire. You are going to have to deal with some mixture-enrichenning factors now that you increased c.r. from 8.8:1 to over 10:1. First off, make sure that the thermostat you're running is 180 and not 195. Second, you can adjust the baseline mixture throughout the rpm range by adding resistance to the engine temp sensing circuit (water or cyl head sensor types). One way is to add a fixed value resistor (650-700 ohms, Radio Shack) in line with one of the leads to your sensor. I did a little finer tuning on mine by adding a second temp sensor (CHT or WT) in line (series) with the first, but placing it externally, outside of the water jacket, tucked under the intake manifold and in contact with the top of the exhaust manifold heat shield. That has worked very well for over a year and I just fine tuned it even more (leaned it back) by placing a 980 ohm resistor in parallel, not series, across the leads of the secondary temp sensor. I get over 20mpg with no pings on this 10.0:1 engine, and it pulls strong through a wide powerband. Further tuning would include adjusting the spring tension (small adjustment) in the AFM, but do the temp sensor first. DAW Quote Link to comment Share on other sites More sharing options...
tec280zx Posted May 6, 2002 Author Share Posted May 6, 2002 Hey guys, thanks for the input so far. I was able to fit the CHT sensor from my p79 into the bottom left port on my p79 thermo housing. So i'm hoping to bolt that back on and everything should wire back up the right way. And as far as running rich, i'm not positive. I didn't let the car run very long since the temp guage didn't work. But i'll deal with that next. I'll post if it works. if not its back to the drawing board, or the p79. Quote Link to comment Share on other sites More sharing options...
tec280zx Posted May 7, 2002 Author Share Posted May 7, 2002 Well the car runs, pretty well too. I got all the thermo connections hooked up. I took her around the block last night and man, it felt good. First time i've heard my engine without a major exhaust leak. Too bad on the way back home one of water lines blew out and i sprayed anti freeze all over the block. The car started smoking everywhere as i drove back into the garage. Once thats fixed she should be ready to go. I still have to perfect the timing and whatnot, and i notice someone said to get a lower degree thermostat? Right now i'm using a 195, should i go lower? 170 maybe? Thanks so much for your guys help. Quote Link to comment Share on other sites More sharing options...
DAW Posted May 7, 2002 Share Posted May 7, 2002 Get rid of the 195 thermostat and change to 180 degree. 160 is too cool for aluminum head engine from what I've read. DAW Quote Link to comment Share on other sites More sharing options...
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