JCan Posted October 2, 2012 Share Posted October 2, 2012 Topic - This note discusses the advantages of heating SU carburetors and provides a source to purchase a new Manifold Heat control thermostat. __________________________________________________ I'm Jim and am restoring a 72 240z with my 15 yr old son. As this project is designed to teach my son how cars work we chose to use SU carburetors and had the great folks at ZTherapy restore our old carbs for us (they did a great job by the way). SU carbs are fantastic! The simple design delivers a nearly constant air/fuel mixture over a wide RPM range and are easy to adjust (once you know how). This design does have an issue, however. The air/fuel ratio delivered by this and other types of carbs is a function of temperature. To solve this problem, Datsun uses engine coolant to heat the SUs therefore greatly improving Air/Fuel mixture consistency over operating temperature and as a side benefit improves atomization of the gas (parafrased from Nissan Service Manual page EC13). In a '72 240z (referring to the attached schematic attached) Nissan Engineers take hot water just below the engine thermostat (when closed ie startup this is a high pressure ) the water is run into the left side of the intake manifold, touching the carburetors then out the right side of the manifold to a manifold thermostat then around the back of the motor to the input / low side of the engine water pump. The manifold thermostat is normally open and monitors the temperature. At ~140 degrees a valve inside starts to close and closes completely at ~150 degrees. Unfortunately, in the blogs and in person most people have the manifold heater disabled. Its no wonder, after 40 years the plumbing gets clogged and the thermostat stops working thus causing poor running conditions. Last night, after looking for a thermostatic control valve for this application, I found two! the first was too expensive, however the second from Therm-omega-tech in the midwest, sold me one for $100 (http://www.thermomegatech.com, P/N 213-000000-140 Data sheet TVHAT attached below)! TVHAT.pdf I know $100 is a lot to pay for this functionality so I have three alternative implementations that are less expensive and should provide the same results: Look for the original thermostat on craigs list and rebuild that (drawing below). Ebay sells 12V solenoid valves for $<20 and you can purchase a thermostat switch for <$10 which would most-likely work (however I worry about how long it will last). Purchase a simple hand valve for <$20 and you can turn it on in the winter when you need it! Brian and I have almost completed the assembly of the motor, however we have not started assembling parts onto the newly stripped and painted body. Once we get the car running, I will measure temperatures and post them here (most-likely in March 2013. I welcome comments, Thanks! Jim Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 2, 2012 Share Posted October 2, 2012 (edited) Sir, I want to be the first to THANK YOU for your diligence! Having that thermostat available makes some items much easier in regards to total cooling flow. The bypasses around the thermostat back to the front of the pump can both be closed once up to temperature and the Thermostat has cracked to allow pump output to flow and not cavitate. Now if only I can figure out a way to introduce this on the internal block bypass.... Maybe if I convert it to external... Being it's stainless, it's easy to clean as well! Clog resistant. Edited October 2, 2012 by Tony D Quote Link to comment Share on other sites More sharing options...
JCan Posted October 2, 2012 Author Share Posted October 2, 2012 Thanks! When I started restoring the Z, I was amazed at the knowledge base I found on this and other sites. As I find information not covered, I'll post it. Long live the HybridZ database! HAHA Jim Quote Link to comment Share on other sites More sharing options...
johnc Posted October 2, 2012 Share Posted October 2, 2012 Man! I just thought of 10 different uses for that little in-line thermostat and it can handle fuel and oil with Viton seals! Thanks Jim. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 3, 2012 Share Posted October 3, 2012 Yeah John, same here! That's a handy little gadget which I have seen at work a million times and never gave it a second thought that I could use it on the Z! It's a steam tracing control valve, keeps the condensate nice and controlled. "BIG DUH" on my part. "Brilliance is the act of seeing the obvious through eyes which don't see it as obvious!" Quote Link to comment Share on other sites More sharing options...
JCan Posted October 10, 2012 Author Share Posted October 10, 2012 IT seems to be the trend to eliminate the manifold heater for SU applications on 240z. I contend that it is a mistake and will attempt to address it here. Before I start, I would like to introduce the opposing view as copied from an email I recently received. "However, if I'm not mistaken, this (manifold heater) regulates the intake manifold temperature, heating it to make sure that all fuel is vaporized (evaporated) by the heat generated by the conduction from the coolant bypass. That being said, this will deteriorate performance as the density of the fuel air mixture once heated is reduced. To maximize performance the mixture should be as cool as possible. This is the reason for turbo chargers, Intercoolers and fresh air intakes. I would delete this emission system component and completely block off the water flow to the intake manifold. You should enjoy a noticeable increase in performance on warm days and a slight increase in mileage. The only downside is a slightly longer warm up, but that is what a good manual choke is for!" While it is true, The inclusion of a manifold heater for your 240z with SU carburetors may work just fine in moderate climates >60 degrees, an engine designer must cover all corner cases. It is these corner cases I will address: Startup - When the engine is started in the morning, the engine thermostat is closed however the manifold thermostat is open allowing water to flow thus keeping the water pump from cavitating. Once the manifold has been heated, the manifold valve turns off and shortly afterwards the engine thermostat starts regulating engine temp. The addition of the manifold heater keeps the water pump from cavitating and improves warm up time. Driving in Cold temperatures - Lets go skiing! We start up our engine, it warms up then we drive to the mountains. Air temperature is 32deg F plus wind chill. What happens to your engine? well, the engine thermostat almost turns off and because of gasoline evaporation, the intake manifold gets very cold, Air/Fuel mixture deviates far from norm, more importantly the water pump cavitates (pumps but there is no place for the water to flow) and your car runs poorly. Feathering the choke wont hell. Conversely with the manifold heated , the water pump does not cavitate, and more importantly performance is maintained. Now lets rebuff the expected benefits of eliminating the manifold heater: Noticeable Increase in performance and better gas mileage can be had without a manifold heater - This comment makes no sense. During a moderate temperature day (70 deg ambient temperature), the intake manifold temperature is heated by the head (it is bolted to it) and stray heat from the exhaust manifold. I have not measured it, however I expect the manifold to heat above 150deg. Therefore there is no temperate difference and no improvement in HP. Now it has been several years (20) since I worked on my or my brother's z. Brian and I have just assembled our engine and I will pull out a thermostat and make some measurements. I welcome your comments Thanks Jim Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 10, 2012 Share Posted October 10, 2012 The Earlier 240Zs didn't have the thermostatic control,. and recirculated all the time. One important aspect to shutting off this flow is the shunting of hot water to the inlet of the water pump. You only want it open while the thermostat is closed for cavitation prevention and quicker warmup. After that point the thermostat closes, and you have exactly the same thing as if you didn't have water connected at all! The later 240's had that functionality, and a separate circuit for anti-icing. The people living where they never experienced icing will always pooh-pooh steps to insure it never happens. But the fist time you let go of the throttle and your engine doesn't slow down....you start realizing anti-icing measures may be a good thing! The key point to note is WITH this thermostat, the only time the circuit is active is when the car is warming up. Afterwards because it shuts off, it is transparent to engine operation. As for the 'choke' comments.... If the SU's had a choke, that may be applicable. The starter system uses far more fuel than necessary for a lot longer than one would think when the temperature is in even the MID 60's. Those that 'don't have any problem' are running with AFR's in the 10's just before puffing black smoke out the tailpipe. If your car is adjusted correctly for proper fuel mix at idle, you will have an issue till it's suitably warmed and have excessive lever action on the starter! Because you have it, the car warms up quicker, using less fuel if you drive it with the starter system partially engaged. Quote Link to comment Share on other sites More sharing options...
Leon Posted October 10, 2012 Share Posted October 10, 2012 I would hope that if you're going skiing in the Z, you have your heater hooked up! With the heater on, hot coolant gets shunted from the back of the head to the water pump inlet thus performing a similar function to the manifold loop. Now, assuming that the heater is connected and functional may be a big IF for Z-car owners (including myself ). I think icing is the big issue at play here, so if the car is only driven in warm climates, removing it doesn't cause much issue. There will be no water pump cavitation if the HVAC control is switched to HEAT while the car is warming up. Warm-up time will be affected, but not too badly if the temperature is already "warm". Quote Link to comment Share on other sites More sharing options...
JCan Posted October 10, 2012 Author Share Posted October 10, 2012 It seems like we are all in violent agreement. Heating the intake manifold is a good thing as it improves engine performance during the corner operating conditions of startup and cold driving conditions. Perfect! Jim Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 10, 2012 Share Posted October 10, 2012 (edited) This 'icing' thing IS an issue even when 'warm'... At 90 degrees and high humidity you run a BIG RISK of icing! My VW would ice like a GDMF with the single Solex 32 NDIX Carb on it--that plenum manifold beneath it would get a 5-10mm thick ICE BALL stuck on it (and this was inside the engine compartment of a VW!!!) The later Carbed cars had the thermostat that shut off the flow to the manifold, but maintained a smaller passage through the carburettors to the base of them where the fuel passes under the throttle plate. This will get very cold especially at high vacuum (low opening angle) operations. Remember, this is a COOLANT flow, and those carbs COOL that on the way back to the inlet (same as a heater does when running with the fan on!) The recirculation volume is insignificant as long as the matter reintroduced is COOL and doesn't up the inlet temperature to the water pump. Loop it directly and you lead to overheating issues. Start your car, open your heater to HOT all the way, and keep the fan OFF. Go blast down the road and watch how hot your car gets. In fact it can contribute to a thermostat sticking or sluggishly opening as so much water is shunted off the back of the engine back to the inlet the stagnant flow in the thermostat housing area (if your small external bypass is blocked off) that it stays cool and the thermostat doesn't open! Which gives ANOTHER reason to leave that incremental flow through the 8mm pipe: without it, before the car opens up the thermostat, there is no way for the hot water to GET TO the thermostat housing and the element to warm it and cause it to crack other than the 2mm bleed hole present in the stock thermostat. If you run a Chevy thermostat, without punching that hole? You may see symptoms that LOOK like a thermostat sticking, but in reality with no carb heat circuit, and no 2mm weep hole, you have set up a system with no flow other than convection to the thermostat sensing bulb! To prevent cavitation, the internal single bypass can handle the engine idling till warm. You just don't want to rev it very high. You will also note that on the later ZX's there is a shunt AROUND the heater core---that supplementary poppet valve? That will open if you start the car, and rush off to highway speed before attaining thermostat cracking temperature. Seems Nissan Engineers realized the two internal bypasses were NOT sufficient volume to allow for anti-cavitation action, and added that valve on the ZX series. I retrofit it to mine since I tend to start and blast off without waiting myself. I'm such an impatient American... "Ahh, screw it, just run without a thermostat, you don't need it!" Edited October 10, 2012 by Tony D Quote Link to comment Share on other sites More sharing options...
Leon Posted October 10, 2012 Share Posted October 10, 2012 This 'icing' thing IS an issue even when 'warm'... At 90 degrees and high humidity you run a BIG RISK of icing! My VW would ice like a GDMF with the single Solex 32 NDIX Carb on it--that plenum manifold beneath it would get a 5-10mm thick ICE BALL stuck on it (and this was inside the engine compartment of a VW!!!) The later Carbed cars had the thermostat that shut off the flow to the manifold, but maintained a smaller passage through the carburettors to the base of them where the fuel passes under the throttle plate. This will get very cold especially at high vacuum (low opening angle) operations. Remember, this is a COOLANT flow, and those carbs COOL that on the way back to the inlet (same as a heater does when running with the fan on!) The recirculation volume is insignificant as long as the matter reintroduced is COOL and doesn't up the inlet temperature to the water pump. Loop it directly and you lead to overheating issues. Start your car, open your heater to HOT all the way, and keep the fan OFF. Go blast down the road and watch how hot your car gets. In fact it can contribute to a thermostat sticking or sluggishly opening as so much water is shunted off the back of the engine back to the inlet the stagnant flow in the thermostat housing area (if your small external bypass is blocked off) that it stays cool and the thermostat doesn't open! Which gives ANOTHER reason to leave that incremental flow through the 8mm pipe: without it, before the car opens up the thermostat, there is no way for the hot water to GET TO the thermostat housing and the element to warm it and cause it to crack other than the 2mm bleed hole present in the stock thermostat. If you run a Chevy thermostat, without punching that hole? You may see symptoms that LOOK like a thermostat sticking, but in reality with no carb heat circuit, and no 2mm weep hole, you have set up a system with no flow other than convection to the thermostat sensing bulb! To prevent cavitation, the internal single bypass can handle the engine idling till warm. You just don't want to rev it very high. You will also note that on the later ZX's there is a shunt AROUND the heater core---that supplementary poppet valve? That will open if you start the car, and rush off to highway speed before attaining thermostat cracking temperature. Seems Nissan Engineers realized the two internal bypasses were NOT sufficient volume to allow for anti-cavitation action, and added that valve on the ZX series. I retrofit it to mine since I tend to start and blast off without waiting myself. I'm such an impatient American... "Ahh, screw it, just run without a thermostat, you don't need it!" An air-cooled, long-runner VW engine is not analogous to a water-cooled L-series. If you're worried about stagnation in the thermostat housing, then don't turn the HVAC to full hot. Quote Link to comment Share on other sites More sharing options...
Noddle Posted October 10, 2012 Share Posted October 10, 2012 An air-cooled, long-runner VW engine is not analogous to a water-cooled L-series. If you're worried about stagnation in the thermostat housing, then don't turn the HVAC to full hot. I had icing issue on my Ford 250 X-Flow engine running an after market intake manifold (aluminium) and a Holley carbie, start the car, drive 3-5 minutes, and it would run like a pig, stop , leave it a couple of minutes and it was fine, If you put your hand on the underside of the manifold, where the carbie sat, it had ice, leaving a few minute let the heat from the head transfer into the manifold , and warmed it up. note though, this manifold had no water passages in it. Nigel Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 11, 2012 Share Posted October 11, 2012 i had a nice long detailed response written, and the forum bug ate it. Not going through that again... My examples were just that, examples so you could see the dynamics at play. They are the same things happening in the L-Manifolds. Remove the heat, you run with the starter engaged for quite a bit longer than if it's working properly. Consequences of that are known to be negative. Don't take things too literally, but rather understand the forces at work. If it wasn't necessary for a majority of the vehicles, it wouldn't be there, it would be a field fit as-needed basis. Quote Link to comment Share on other sites More sharing options...
Leon Posted October 11, 2012 Share Posted October 11, 2012 I had icing issue on my Ford 250 X-Flow engine running an after market intake manifold (aluminium) and a Holley carbie, start the car, drive 3-5 minutes, and it would run like a pig, stop , leave it a couple of minutes and it was fine, If you put your hand on the underside of the manifold, where the carbie sat, it had ice, leaving a few minute let the heat from the head transfer into the manifold , and warmed it up. note though, this manifold had no water passages in it. Nigel A V8, cross-flow engine is also not analogous to the L-series. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 11, 2012 Share Posted October 11, 2012 (edited) But the Icing Phenomenon IS.... Triples don't do it because the THIN CASTING of the carbs lets exhaust heat them almost instantly. SU's have an issue because of all the crap in the way that prevent it. That is a consolidation of my previous bug-fodder post. *Edit* actually, even in the EFI engine, Icing is a concern, as well as gumming of the throttle plate from PCV Residues---it's why the stock TB's have heat to them as well---keeps the JT-Effect at bay when at low-angle openings. (also from the prior bug-fodder post.) Edited October 11, 2012 by Tony D Quote Link to comment Share on other sites More sharing options...
JCan Posted October 23, 2012 Author Share Posted October 23, 2012 Checking in with progress.... I received the low pass thermostat from thermomegatech. This device is designed for 3/8 in tubing in and out. Unfortunately it is a little long to connect up this way so I purchased a special tap 9/16 - 20 and drilled and tapped the intake manifold to accept this thermostat directly. I plan to use 3/8 inch aluminum tubing and route it behind the motor to the return side of the water. Attached are pictures of the intsallation. FYI Jim\\ Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 23, 2012 Share Posted October 23, 2012 Don't they come with Swagelock Ends? Some nice 0.375" X 0.035" Wall 304 Stainless is cheap and won't corrode like the Aluminum Tubing will. When my heat tubing went out, that's the route I went at least. It is a pain to roll the bead on the stainless compared to Aluminum! Quote Link to comment Share on other sites More sharing options...
JCan Posted October 23, 2012 Author Share Posted October 23, 2012 Tony will be aluminum tubing corode? Isnt the block aluminum, i know the heads are. How long will it take to corrode? I can easily swap to stainless tubing Thanks for the feedback. Quote Link to comment Share on other sites More sharing options...
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