A. G. Olphart Posted October 9, 2011 Share Posted October 9, 2011 I'm putting a 2002 Camaro plastic tank in my 72Z, and wonder if the in tank regulator can be modified to lower the output pressure. I'd like to drop the output pressure to around 20 pounds, then run an adjustable return style regulator up front to get a steady 5-6 pounds. CruxGNX had posted a picture (long gone) showing how to gut the stock regulator. Since he was able to get the stocker apart, I'm hoping that it may be possible to replace the relief spring with a lighter one. Has anyone done this, and is it feasible? It seems that lowering the pressure should lengthen pump life... and I'm not sure if my (relatively cheap) return style regulator would handle the stock 60 pounds. TIA. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted October 9, 2011 Share Posted October 9, 2011 Unless I don't understand how the camaro regulator works, you should be able to just put a return style regulator on it, set for your desired pressure, and the in tank regulator should act like it's not there at all. It should vent fuel back to the tank to maintain 60 psi, if it never gets near 60psi, then it should never vent. The pressure would end up being controlled completely by the return new return style regulator. Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted October 9, 2011 Author Share Posted October 9, 2011 Unless I don't understand how the camaro regulator works, you should be able to just put a return style regulator on it, set for your desired pressure, and the in tank regulator should act like it's not there at all. It should vent fuel back to the tank to maintain 60 psi, if it never gets near 60psi, then it should never vent. The pressure would end up being controlled completely by the return new return style regulator. Sounds right. I've been wondering if the tank's 60PSI setting would flow enough through the regulator up front at idle and cruise to make the 3/8 return line look like a restriction. I think that could throw off pressure at the carb. Also not sure if my return regulator will have enough flow capacity to handle 60 pounds through a 3/8" feed. First one I've had. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 10, 2011 Share Posted October 10, 2011 You should be able to do it. Many times in Japan they run a carb inlet like that with an EFI pump and FPR downstream of a 'fuel log' (think double-pumper with two lines from the log)... This way full pump pressure and flow is available to the carburettor at all times, and you regulate backpressure to hold what you need at the float seat. Your fuel filter is upstream of the log, so if it's plugging the FPR compensates (to the point when it either collapses or blows out!) The EFI pump will push a LOT of fuel at the lower pressures of a carbbed requirement. It makes it much more 'dirty fuel' tolerant in terms of full-load fuel filter plugging. The feed side can be compensated flow-wise by increased pressure provided by the EFI pump... As long as you can maintain your recommended fuel pressure at Peak Torque/Peak Load on the dyno you don't need a larger line. What usually is more critical is the RETURN side at idle! There is the REAL challenge. That's when it's handling the MOST flow it will see. If you are undersized there, you will run into high fuel pressures, sinking the carb floats, running rich or even possibly pumping the float bowls completely full of fuel and spouting out the balance tubes! Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted October 10, 2011 Author Share Posted October 10, 2011 You should be able to do it. Many times in Japan they run a carb inlet like that with an EFI pump and FPR downstream of a 'fuel log' (think double-pumper with two lines from the log)... This way full pump pressure and flow is available to the carburettor at all times, and you regulate backpressure to hold what you need at the float seat. Your fuel filter is upstream of the log, so if it's plugging the FPR compensates (to the point when it either collapses or blows out!) The EFI pump will push a LOT of fuel at the lower pressures of a carbbed requirement. It makes it much more 'dirty fuel' tolerant in terms of full-load fuel filter plugging. The feed side can be compensated flow-wise by increased pressure provided by the EFI pump... As long as you can maintain your recommended fuel pressure at Peak Torque/Peak Load on the dyno you don't need a larger line. What usually is more critical is the RETURN side at idle! There is the REAL challenge. That's when it's handling the MOST flow it will see. If you are undersized there, you will run into high fuel pressures, sinking the carb floats, running rich or even possibly pumping the float bowls completely full of fuel and spouting out the balance tubes! Thanks Tony. We've all been presuming that the GM regulator is on the supply side, but I got to wondering why CruxGNX felt he needed to disable the stock regulator. The answer is here: http://www.racetronix.com/RX-F99-FPKG-2.html. "The return line feeds the pressure regulator on the fuel module...". Oops. That means everything ahead of it (including the carburetor) would be held to 58PSI. Man, what a fountain that would make. So I, too, will disable the factory regulator and just hope my 3/8" return line can flow the pump's full output without significant pressure drop (which, as you point out, would cause a rise in carb inlet pressure). Quote Link to comment Share on other sites More sharing options...
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