cygnusx1 Posted June 25, 2011 Share Posted June 25, 2011 (edited) Just curious as to what kind of IAT you are seeing under WOT boost. I am seeing spikes to about 118F at 12psi in the datalogs. This was with about an 80F ambient and no cold air intake. Edited June 28, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
Oddmanout84 Posted June 25, 2011 Share Posted June 25, 2011 Crap, wish I had an actual data log to show you, but Haltech usually displayed around 100-110F when my engine was running last year. No cold air intake either, just a short pipe that put the filter just forward of the AC compressor bracket location and offset diagonally slightly to the wheel well. This is kind of irrelevant now, since I routed a cold air intake during my rebuild. I'll try to remember to post my new results when it's running again. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted June 26, 2011 Share Posted June 26, 2011 I'm getting about 220-240°F at 9 psi, no cai or intercooler. I need to order some IC piping. Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 27, 2011 Share Posted June 27, 2011 Uh, yeah, "letitsnow" has it correct: without an I/C you are going to have WAY more heat. "CAI" on a turbo car will have VERY little effect on discharge temperature, the I/C is far more important. Running 25psi on the dyno, never got above 45C on pulls. On the engine dyno, making runs in the 18 psi range for 5 minutes at a stretch the approach as given by the RTD's on the bench was less than 10C (meaning air temps out of the I/C were within 10C of Ambient.) What you should be concerned with is 'approach temperature' as this tells you about your cooler efficiency. A raw number discarding pressure and ambient is useless. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 28, 2011 Author Share Posted June 28, 2011 (edited) Yes I know delta is more informative, but I am just filling in MS data, and messing with the IAT based fuel corrections. I am not studying efficiencies of components in my system because I have no intentions of changing anything major regardless of how good or bad. The car feels really fast as is. I took note of IAT while trying to bandaid a vapor lock issue with the IAT/ fuel map. Just a tuning experiment that worked, but didn't. Next step is to un-deadhead my fuel rail to keep it from getting hot and leaning out. I suspected I was getting some heat related fuel delivery issues so I data-logged it. After a drive on a hot day, you can let my car idle with the hood shut and watch the idle go from 13:1 to 15:1 to 17:1 and then barely be able to idle anymore. Funny thing is that the pulsewidths never changed, and the fuel pressure didn't either. What is happening, is that either the injectors are getting too hot and sticking, OR the fuel is changing states in the injectors or rail. It effects the mixtures not only at idle either. What I did with the IAT fuel correction was add add fuel when the IAT got over say 110F and then ramp it up gradually. It worked, but it took power away from the top end as the air got hot from boost. Then I tried to ramp the temp up around 100F and then back down once past around 115F. That led to a strange power curve in the motor. SO I am going to attack what i think is the root cause; heat at the fuel rail and injectors. I was able to get EGO Correction to bandaid it as well, and it does a pretty good job, once you get the proper transport delays in place. My subject line led you to believe this was going down a turbo/intercooler efficiency route. My bad. I should have been more specific as to why I was asking. Thanks anyhow. Edited June 28, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 28, 2011 Share Posted June 28, 2011 Your fuel is changing states in the rail, you need to run a return line, and make SURE you aren't going under load on the roadway with less than 1/4 tank of fuel. JeffP was warned about this on the dyno by yours truly. It's in the archives here as well. The density change of the FUEL is what is killing you. Air correction density is not that bad, but the fuel BTU content that changes in fuel that is 58F and that is 140+F is PHENOMENAL! Jeff was experiencing the EXACT same thing because Mr. Cheap-Arse would only put 5 gallons of C16 in the car at any one time. Started out nice and cool on the first run. Second run the car was leaning. THIRD run the car was all over the place! EXACTLY like what you are seeing 17:1 at idle where on first run it was more like 13.8!!! Fuel in the tank went from 60F to 140 in about 20 minutes of idling and two or three passes on the dyno. If you want a more permanent solution, find one of those small power steering coolers, flush it well, and put it in the airstream of the fender well (well protected from rocks) then run your return line through it. You will be AMAZED how much more consistent your idle AFR's will be after cooling the fuel on the way BACK to the tank! It picks up a LOT of heat in the engine bay, and if you are running a return-less fuel system without a way to monitor fuel temperature and pressure (Like the BOSS EFI Systems do...) you're asking for these kinds of problems. Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 28, 2011 Share Posted June 28, 2011 Actually depending on the size of your injectors, and if you are batch fired or alternating bank, what indeed may be happening is that due to the RAPID drop of fuel pressure in the header when all your injectors fire, you get 'flash vaporization'... then getting that gasseous fuel out of the rail can be a total beyotch! Jeff didn't have that issue, but he found an accumulator that REALLY kept his fuel pressure steady at idle while those big 720's were banging away at idle. I think the fuel pressure on my precision gauge was dropping from 36 to like 20 when they fired! That's one atmosphere drop...that's enough to precipitate formation of gas pockets in your fuel. This may also be a consideration. You can try to go to 'alternating' to keep the pressure drop less by firing half the injectors each time, or consider putting a pulsation dampner/accumulator onto the fuel rail. I think JeffP put the information on the one he found on his Anglefire website. I think you're on the right track, but it's not IAT that is your problem, it's either solely your fuel temperature rising, or that combining with a pressure drop during injector firing events. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 28, 2011 Author Share Posted June 28, 2011 I always ran a Marren fuel damper right at the end of the dead headed fuel rail, to try to soak up some oscillations, but the root cause was still heat in the fuel. I ran the return line today, and left the fuel damper in the return line right after the fuel rail. HUGE difference, in not only idle, but the way the car drives on light throttle and cruise. My EGO is bottoming out to stay on the AFRs now. Fuel delivery just got much better. Idle 13:1 rock steady hot or not. Now I need to keep an eye on my tank temps. I'll use my IR thermometer to get some quick data. I think I'll go edit the subject line if I can. Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 29, 2011 Share Posted June 29, 2011 Heat is tolerable, it's just what amount of pressure you use to combat vapor formation. And as heat rises, vapor pressure falls. Check out those power steering coolers if you are an inveterate 1/4 tank-er! The heat-sink properties of a full fuel tank are amazing. Now....about that coil from the reefer system coiled in the bottom of the tank... (The Winter Rally Car 240's ran a loop of tubing through the fuel as a differential cooler! Now with triple carbs running you think icing might be a problem? Not if your fuel tank was running 120F fuel up front on a 20 degree day!) Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 29, 2011 Author Share Posted June 29, 2011 (edited) A full tank sure is the biggest heat sink in the car. Just don't get it too hot. Cooling it off takes a lot of energy too. I tend to keep the tank 1/2 and up. I kind of like the way it settles the back end of the car. Never thought about a fuel to air cooler before. I don't think I'll need one with my usage of the car, but I'll put it into my mental bag of tricks just in case. I will consider insulating the fuel lines now. Before, the dead headed rail got so hot that insulating it was pissing in the wind. Now, with the rail circulated, even after a long drive on the back roads, it's only warm to the touch. This is due to all the fuel flow stealing the energy. Insulating it NOW makes sense. Edited June 29, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted June 29, 2011 Share Posted June 29, 2011 (edited) I've actually used two fuel rails to get the returned fuel to cool the injectors themselves as opposed to only getting cool fuel through the rail and the return. I used dual feed injectors similar to ones found on 1987 and later 300zx but securing them to the manifold was a chore. Nissan put those scoops on the 280zx turbo and 300zx turbos for a reason and it was to get hot air out while sitting moreso than cold air in while moving and you will notice that nissan did away with the scoops the same year they got the dual feed injectors. Sure...it works but on later cars I just used the factory nissan blower for hot soak issues. As far as this happening when you are idling, the factory scheme will not help unless you do some fancy work and enable it to react to a temp sensor and run while the car is running. Edited June 29, 2011 by HowlerMonkey Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 29, 2011 Author Share Posted June 29, 2011 Side feed injectors are the ultimate solution. Maybe it's time for someone to mill out an L rail for side feeds? Hmm I need to investigate. Quote Link to comment Share on other sites More sharing options...
Arif Posted August 14, 2011 Share Posted August 14, 2011 I'm experiencing the same thing however my IATs shoot up from 100 degrees to 150-170 degrees if I shut the car off and then return in about 30 minutes to start the car. My fuel rail has a return line and I don't remember the car having this problem last summer. How do I prevent the IATs from spiking up so high once it's shut off? It happens whether I have a full tank or 1/4 tank. Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 15, 2011 Share Posted August 15, 2011 FYI, I just landed in Manila and on the plane was catching up on some new Japanese Magazines that I picked up at the airport. Latest offering from SARD: A FUEL COOLER! Nice to see someone else noticed what a tremendous effect fuel temperature can have on the way the car runs under load...to the point they now offer a neat cooler to combat the heat put into the fuel in it's little trip through the engine bay and back to the fuel tank. Understand IAT and Vapor Lock is not the same thing. The heat soak you get after a shutdown is something that you can't avoid unless you run a cooler thermostat (then you only limit it's starting point and terminal rise...)or remove your hood to let it radiate to the atmosphere instead of being all cooped up underhood. The fuel vaporization in the fuel rail is relative to pressure rise after shutdown, a leaking anti-return valve on the pump, or enough heat present to flash the fuel to vapor at the pressure it sits in the rail. That's not really vapor lock--though flash-cavitation at the fuel pump inlet can happen when the fuel in the tank gets hot. Quote Link to comment Share on other sites More sharing options...
280zex Posted August 15, 2011 Share Posted August 15, 2011 (edited) I'm experiencing the same thing however my IATs shoot up from 100 degrees to 150-170 degrees if I shut the car off and then return in about 30 minutes to start the car. My fuel rail has a return line and I don't remember the car having this problem last summer. How do I prevent the IATs from spiking up so high once it's shut off? It happens whether I have a full tank or 1/4 tank. I had the same issue. I got the factory fuel rail cooling fan (ebay 12$)and an aftermarket adjustable thermocouple (Hayden I think?) The thermocouple setup screwed right into the stock location in the heater core line (if you stil have this piece). Have a good battery too as the fan runs for a long time after shut-down. I have mine adjusted to run at coolant temps above 160F.. Edited August 15, 2011 by 280zex Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.