Roman Posted December 22, 2015 Share Posted December 22, 2015 Hmmmm okay interesting about the heat difference thing, makes sense I guess. Yeah one of the big reasons for a returnless system is for emissions, when you sent hot fuel back to the tank it creates a lot of vapour which then either comes out the gas cap when you open it, or needs to be dealt with by burning it through the engine which I think creates less than ideal emissions thingys as well. Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted December 24, 2015 Author Share Posted December 24, 2015 Wow. Topical. Today I drove the viva to blenheim. Actually hannah drove and I tuned and tinkered with some new maps. Everything went great and we were happy. Even Kevin was happy. Car running well and idling sweet at around 14. We got to blenheim and it's hot like only blenheim seems to get. Too hot for bare feet on driveway hot. Park up at Olds and chill. 15 min later I think I'll move the car round. But now it's all lean and wants to stall. I end up having to dial in a bit more fuel around the idle cells. Damn. I check for vac leaks but nothing. Then notice how noisy pump is.. like aeration. Surge tank fucking hot. Remember reading sheepers latest post about changing his return to go back to the main tank. Mine currently returns to the surge tank. I can change this easily when home anyway. So I go for a walk to get an ice cream and think about it. Later with car cooled down a bit I start it up and as I guessed it's now idling a bit rich. Could hot fuel change the ratio that much. Certainly can't help. Btw - the iat sensor is a plastic gm one mounted in the alloy tube insulated from the engine by the big silicone bend into the tb. so I don't really think it's heat soaked sensor problem. But also worth checking. 1 Quote Link to comment Share on other sites More sharing options...
Roman Posted December 24, 2015 Share Posted December 24, 2015 Interesting! Will love to hear how you get on. Quote Link to comment Share on other sites More sharing options...
Roman Posted December 24, 2015 Share Posted December 24, 2015 I've got these peaks and troughs in my fuel map. Figured it would relate to intake manifold runner length.I was given some other fuel maps from various beams engines, found one of them was interesting. (Has ITBs)These are the fuel maps at WOT for both motors, mine on the left: So the peaks and troughs have moved to the left on the ITB engine, which is strange because it would suggest the tuned length of the runners is longer than mine.I asked the guy I got the maps from, and he confirmed it had crazy long runners. It looks like the fuel tapers off towards redline because it's heading into the third resonant "trough". He said some time after this they shortened the runners back down and gained power everywhere. It would be interesting to see the fuel map of a motor with ITBs with short runners and see how the fuel map moves around. 1 Quote Link to comment Share on other sites More sharing options...
Spencer Posted December 24, 2015 Share Posted December 24, 2015 You only get a few weeks/months in NZ to test the car out on real hot days so it's good you found that out Alex. You should dump that hot fuel back to the tank for sure. I also think a cooler on the return is a excellent idea, something I will do on any EFI installs in the future as I have had hot fuel issues in the past. 2 Quote Link to comment Share on other sites More sharing options...
sheepers Posted December 24, 2015 Share Posted December 24, 2015 run a fuel cooler for sure. in the blue car without it the fuel tank got hot, like really hot after about 3 hours on the dyno. second dyno session with the fuel cooler installed and the tank didn't get anywhere near as hot. made a big difference. 1 Quote Link to comment Share on other sites More sharing options...
kpr Posted December 24, 2015 Share Posted December 24, 2015 stuff battling this with mine at the moment. latest trumpets are too long. hence why it went slower at drags. will post some maps up later 1 Quote Link to comment Share on other sites More sharing options...
Celica RA45 Posted December 24, 2015 Share Posted December 24, 2015 dave it also has a lot to do with vvti and what the cams are doing with the fuel maps Quote Link to comment Share on other sites More sharing options...
Celica RA45 Posted December 24, 2015 Share Posted December 24, 2015 also what pipes are used on both motors Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted December 25, 2015 Author Share Posted December 25, 2015 When I get home I will start with moving the return to the tank. I wish Id noticed ages ago as its always been an issue on hot days when I park up the car at say the supermarket. Returning 10 min later and the engine will run lean for the first minute or so and want to stall if not careful. I think it was so much worse yesterday because so bloody hot here plus my timing at Idle had been advanced by around 5 degrees to about 15. The inlet temp sensor and alloy tube its sat in is just above the radiator so because I never moved the car it just sat there in the hot blenheim sun getting hotter and hotter. Fan would keep engine around 90 but all that heat was just going up right into the path of the tube and sensor. So this morning I started looking up the MAT correction and it seems this is a problem many people have because the developers are basing the base curve around the gas temp laws but they don't take into account heat soak of both the air sensor or the fuel. The correction table is here...(Dave will love this...) You can see that as temps go up it wants to continue pulling fuel. Problem is it pulls too much. Some people are turning that line into a U so as temps soar it starts adding a bit of fuel. I need to learn more and experiment. 3 Quote Link to comment Share on other sites More sharing options...
Roman Posted December 25, 2015 Share Posted December 25, 2015 You're right. I frigging love it. Post all of the things! 2 Quote Link to comment Share on other sites More sharing options...
downtrail Posted December 25, 2015 Share Posted December 25, 2015 Add in some more after / post start enrichment at that coolant temp range. Shouldnt need to change that graph into a u shape itll just make things weird if inlet teml gets that high whilst caning along. When I get home I will start with moving the return to the tank. I wish Id noticed ages ago as its always been an issue on hot days when I park up the car at say the supermarket. Returning 10 min later and the engine will run lean for the first minute or so and want to stall if not careful. I think it was so much worse yesterday because so bloody hot here plus my timing at Idle had been advanced by around 5 degrees to about 15. The inlet temp sensor and alloy tube its sat in is just above the radiator so because I never moved the car it just sat there in the hot blenheim sun getting hotter and hotter. Fan would keep engine around 90 but all that heat was just going up right into the path of the tube and sensor. So this morning I started looking up the MAT correction and it seems this is a problem many people have because the developers are basing the base curve around the gas temp laws but they don't take into account heat soak of both the air sensor or the fuel. The correction table is here...(Dave will love this...) You can see that as temps go up it wants to continue pulling fuel. Problem is it pulls too much. Some people are turning that line into a U so as temps soar it starts adding a bit of fuel. I need to learn more and experiment. Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted December 25, 2015 Author Share Posted December 25, 2015 How would inlet temp get that high when caning along? It reads so much cooler when driving.. like low 20s due to the cold air feed. It certainly never sees anything as high as the temps when parked up idling on a hot day. I think the after/post start enrichment only works for a few seconds? Me still learning. Happy to note that after having re-advanced the ignition table back to where it was ages ago we filled up in blenheim and had managed 32 mpg It certainly pulls a lot nicer in the mid range and smoother too. Man its fun when kept past the 4000 rpm on hill climbs Quote Link to comment Share on other sites More sharing options...
Raizer Posted December 25, 2015 Share Posted December 25, 2015 Can be solved with CO2 1 Quote Link to comment Share on other sites More sharing options...
Yowzer Posted December 25, 2015 Share Posted December 25, 2015 Is there some kind of advantage to supercooling fuel? Aside from freezing your injectors open Quote Link to comment Share on other sites More sharing options...
japawagons Posted December 25, 2015 Share Posted December 25, 2015 For alternative fuels in drag racing I believe Nitro etc. Something to do with the different expansion rates of the fuel components that change with temperature which changes the air fuel ratio... But honestly I don't even know... Quote Link to comment Share on other sites More sharing options...
Roman Posted December 25, 2015 Share Posted December 25, 2015 I dont really understand the units or maths of what's written below, but came across it somewhere and thought I'd jot it down and come back to it if I manage to get my head around it. The limiting factor on street cars is getting enough oxidizer (air) into the cylinder, not getting enough fuel. The heat capcity of fuel is.54 btu/lb - F and the latent heat of vaporization is 125 BTU/lb. The heat capcity of air is .25 BTU/lb-f. 1 lb fuel vaporized gets 125 BTU cooling, with 15 lb of air this will cool the whole mixture about 30 F. At 30 F thats about 5.5% increase in the amount of air than with out the fuel cooling effectIf the fuel was cooled down by 50 F, that would give 27 more BTU/lb or 21% more cooling or 6 F or 1.0% more air than before. 1 Quote Link to comment Share on other sites More sharing options...
Raizer Posted December 25, 2015 Share Posted December 25, 2015 In other words you need the full CryO2 kit as it adds hectik cryogenic boosts to your engine? I'll see myself out now... 1 Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted December 26, 2015 Author Share Posted December 26, 2015 So I could have NOS and CO2!!!! Wow. But really .. for me with my fairly stock moderate bhp NA Mazda engine I dont really need to worry about fuel being super cool. More just avoid it getting super hot when parked up at the lights then contributing to leaning out my idle. Routing it back into the tank will be a good start. Quote Link to comment Share on other sites More sharing options...
brocky41 Posted December 26, 2015 Share Posted December 26, 2015 Wow. Topical. Today I drove the viva to blenheim. Actually hannah drove and I tuned and tinkered with some new maps. Everything went great and we were happy. Even Kevin was happy. Car running well and idling sweet at around 14. We got to blenheim and it's hot like only blenheim seems to get. Too hot for bare feet on driveway hot. Park up at Olds and chill. 15 min later I think I'll move the car round. But now it's all lean and wants to stall. I end up having to dial in a bit more fuel around the idle cells. Damn. I check for vac leaks but nothing. Then notice how noisy pump is.. like aeration. Surge tank fucking hot. Remember reading sheepers latest post about changing his return to go back to the main tank. Mine currently returns to the surge tank. I can change this easily when home anyway. So I go for a walk to get an ice cream and think about it. Later with car cooled down a bit I start it up and as I guessed it's now idling a bit rich. Could hot fuel change the ratio that much. Certainly can't help. Btw - the iat sensor is a plastic gm one mounted in the alloy tube insulated from the engine by the big silicone bend into the tb. so I don't really think it's heat soaked sensor problem. But also worth checking. JUst pulled this off the net - looks like theres heaps of Economy Foamers out there (ill be one soon, maximising economy on an old LD28). Anyway - could it have vapour locked? I know many Holdens, when they dont start, will shut off injectors when hot if you hold the throttle to the floor while cranking. I have found that heating gasoline to 180 deg. F yields about a 10% return improvement in fuel economy. Detonation threshold seems about the same for a given octane value. Greater tendency to vapor lock during hot restart. Most OBII ecu s have the ability to recognize this condition and will keep injectors closed until engine restarts. May take 2 or 3 tries but it will fire up. Heating intake air also improves fuel economy but I have found a greater tendency to go into detonation especially when ambient temps. go above 60 deg F. If you run a dedicated water or water/methanol system you can effectively supress detonation with even the lowest octane fuel. Reply With Quote Quote Link to comment Share on other sites More sharing options...
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