fhptom Posted December 14, 2005 Share Posted December 14, 2005 What's your opinion on whether or not to use a fuel return on Dual SUs. Car is mainly road track car slightly modified internals. Quote Link to comment Share on other sites More sharing options...
Z24O Posted December 30, 2005 Share Posted December 30, 2005 gee traffics slow on this one i would return the unused fuel to the tank for 2 reasons......to ensure a flow of COOL fuel to the carbies and prevent possible vaporisation problems(hot starts etc) however i would qualify this statement by adding that your fuel delivery system must be able to supply enough fuel PRESSURE at wide open throttle..........this may entail running a restricion in the return line to achieve this..........if your system is none standard you may want to plumb in an adjustable gate valve in the return line and turn it until you maintain adequate fuel pressure at WOT(this way you can adjust for later variables eg different fuel filter,bigger lines,different carbies etc) oh and i would insulate the fuel lines in the engine bay anyway only my opinion,seek others and then make up your mind paul western australia Quote Link to comment Share on other sites More sharing options...
Silent Posted January 9, 2006 Share Posted January 9, 2006 i dead head my su's ie not runnin a return, i have not had a problem with this in 2 years. i never saw the purpopse of runnin a return with such low pressure Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 15, 2006 Share Posted February 15, 2006 Low fuel pressure with heat is exactly what causes the vapor lock problem in the first place.... A little chemistry and/or physics will explain fully... If you dead head the fuel system.. you are asking for trouble... It may not show up in a wimpy street driven Z car... but high heat with track use will reveal a host of fuel system issues that show-shiners cannot hope to understand... The stock fuel rails work well but must be insulated where they are closest to the head and manifolds... A helper pump set to run all the time in the back... working with the stock mechanical pump in the front... is a great system capable of supplying fuel to SUs or triple DCOEs... up to about 225HP. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 15, 2006 Share Posted February 15, 2006 I ran the stock pump for years on my L28 with SU's, but finally I had issues with vapor lock at the track once when it was 105 degrees. At the end of a long straight it would just start sputtering, ended up having to short shift. Pulled in at the end of the session and popped the hood, and it would run for a minute then slow down and finally die. Wait an hour or so till the next session and it would fire right up again and run bitchin until about 2/3 of the way through the session. At the time I figured the heat was getting into the fuel through the fuel pump and the fuel rail. Touch either when the car's hot and you'll see what I mean. I took them both out, ran an electric Carter pump in the rear and a rubber fuel line across the rad support and then dead headed the SU's straight off the rubber line. Never had a problem again. Switched to triples, again no problem. Built the higher compression more hp motor, again no problem. I don't like the stock pump not because it won't flow enough fuel, but because of the heat it puts into the fuel. But that's just my take on it. Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 15, 2006 Share Posted February 15, 2006 that heat in the mechanical fuel pump is a good thought... I placed a temp probe on it after a hard session in 90 degree weather... that sucker was HOT!!!.. but it did not exceed 150 degrees... But the heat transfered to it was always a concern in the back of my mind... I have had good luck with the car's fuel system soo far as it is.... I would say that any well insulated system that is properly designed from the start will work well in a variety of conditions... A few thoughts though... I use the mechanical fuel pump as a regulator as well... just cheap, available, and already on the car....I have a holly red pump and matching regulator on a shelf... I was waiting for a reason to use them... I have no reason to change at this point. You want to place the regulator as close to the carbys as possible... you also want to minimize the effects of hose swelling/expansion... The stock fuel rail is hardline... and the pump is right next to it... Soo stock pump and rail is a great system.. as long as it is properly insulated... I used the original fiberglass/asbestos insulating wrap where the rail passes over the manifolds... I used a 260Z rail with plastic insulators between the tubes and mounting ears... you could further insulate it by modifying the mount ears to keep them from conducting heat from the bolts/head. Quote Link to comment Share on other sites More sharing options...
Silent Posted February 17, 2006 Share Posted February 17, 2006 hmmm, i have run mine very hard numerous times and never had one problem. highway races from 45-140. over and over again during the summer, for a good 4 miles at least. no vapor issues on my end. then again. this system was thrown together to get it moving, and seems to do pretty good. the pump has a built in return. maybe thats it. next fuel system will have a return Quote Link to comment Share on other sites More sharing options...
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