gjc5500 Posted October 1, 2006 Share Posted October 1, 2006 i read that to run a blow thru on a carb requires you to equalize the fuel bowl and the intake pressure. i have duel weber dgv carbs on a 73 240z. i noticed today that from the top of the carb i can see straight to the fuel bowl. if i were to run a box ontop of the 2 carbs(like the aircleaner box, but covers both carb tops), would it pressureize the fuel bowls enuff to keep the air from running back? Quote Link to comment Share on other sites More sharing options...
gjc5500 Posted October 2, 2006 Author Share Posted October 2, 2006 come on, someone has to know Quote Link to comment Share on other sites More sharing options...
TimZ Posted October 3, 2006 Share Posted October 3, 2006 come on, someone has to know I've not used those carbs, but it sounds like that would work. You will also have to regulate the fuel pressure relative to the pressure at the inlet to the carb. So, if you normally run 4psi to the carb, you'll have to get a regulator that regulates to 4psi over the pleum pressure. (4psi fuel pressure at 0 boost, 14psi fuel pressure at 10psi boost, etc) Quote Link to comment Share on other sites More sharing options...
gjc5500 Posted October 3, 2006 Author Share Posted October 3, 2006 so... if i run 8 psi, i would want like 12psi of fuel? wont that be bad at idle?? Quote Link to comment Share on other sites More sharing options...
TimZ Posted October 3, 2006 Share Posted October 3, 2006 so... if i run 8 psi, i would want like 12psi of fuel? wont that be bad at idle?? Sorry - I didn't explain this well enough. You will have to use a pressure referenced fuel pressure regulator, similar to those used with EFI, except the base pressure will be, say 4psi, instead of 38psi. Also, instead of referencing to manifold pressure like EFI does, you will want to reference to the pressure at the carb inlet. This way your fuel pressure will be 4psi until you start running boost, and then it will be 4psi plus whatever the carb inlet pressure is when you start running boost. You have to keep the fuel pressure 4psi (or whatever those carbs normally use for fuel pressure) higher than the pressure at the carb inlet at all times. If you let the pressure at the carb inlet (and thus the float bowls) go higher than the fuel pressure you will no longer be able to pump fuel in there. Quote Link to comment Share on other sites More sharing options...
gjc5500 Posted October 3, 2006 Author Share Posted October 3, 2006 so if i had a box that ran BOTH carbs, the best spot to pull a line to supply boost for the FP would be the box right? and thx ALOT for all your help. ive been trying to figure this out for aboutl 3 months now Quote Link to comment Share on other sites More sharing options...
gjc5500 Posted October 3, 2006 Author Share Posted October 3, 2006 i forgot to ask, do u know of a good regulator, or pump w/ build in reg. that will work for this? i searched on holley and found nothing like this. Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted October 3, 2006 Share Posted October 3, 2006 Mallory #4309 Bypass Fuel Regulator is what you need. Hook it into your intake box on the carbs. I am working on a simular set up with side drafts. I do not think the stock fuel pump will put out the required pressure so will use a electric fuel pump. Quote Link to comment Share on other sites More sharing options...
veritech-z Posted October 3, 2006 Share Posted October 3, 2006 I believe MSD makes a regulator that will do that also. I'm pretty sure they just modify the bosch regulators with a preload adjustment, but they are really affordable. I think that if you are able to close off the entire carb assembly in a box, it would work fine. I've seen it done on a v-8 with a multi carb setup that had 8 air horns, and the top of the box was glass or plexi, I don't know which, but it was pretty cool looking. Quote Link to comment Share on other sites More sharing options...
gjc5500 Posted October 4, 2006 Author Share Posted October 4, 2006 hmmm. thx for the info Quote Link to comment Share on other sites More sharing options...
gjc5500 Posted October 4, 2006 Author Share Posted October 4, 2006 how would u mod one of the bosch regs? Quote Link to comment Share on other sites More sharing options...
veritech-z Posted October 5, 2006 Share Posted October 5, 2006 There is a detailed explanation with part numbers on this website, but I haven't tried to do it myself. It looks an awful lot like the MSD regulator. http://www.dune-buggy.com/turbo/fuelsystem.htm Quote Link to comment Share on other sites More sharing options...
gjc5500 Posted October 5, 2006 Author Share Posted October 5, 2006 hmmm. good article. imma do that. cuz there is a reg from msd that is a control box for lke 250. 70 is alot cheaper. hope it works. thx Quote Link to comment Share on other sites More sharing options...
TimZ Posted October 5, 2006 Share Posted October 5, 2006 hmmm. good article. imma do that. cuz there is a reg from msd that is a control box for lke 250. 70 is alot cheaper. hope it works. thx What is the base fuel pressure for those regulators? It looks like those are meant for higher pressure, like those used with EFI. I don't think you'll be able to make one of those do a base pressure of 4psi. $70 is only cheaper if it doesn't blow anything up. Quote Link to comment Share on other sites More sharing options...
veritech-z Posted October 5, 2006 Share Posted October 5, 2006 yeah, the article is about EFI now that you mention it...my fault! Quote Link to comment Share on other sites More sharing options...
gjc5500 Posted October 5, 2006 Author Share Posted October 5, 2006 the basic idea is the same. idk y that woulnt work w/ ne good fuel reg. i have a few laying around for carbs. i think imma give it a shot Quote Link to comment Share on other sites More sharing options...
TimZ Posted October 5, 2006 Share Posted October 5, 2006 the basic idea is the same. idk y that woulnt work w/ ne good fuel reg. i have a few laying around for carbs. i think imma give it a shot I think you'll need to find a bypass-style regulator to mod for this. I don't think a non-bypass regulator could respond fast enough. Quote Link to comment Share on other sites More sharing options...
veritech-z Posted October 5, 2006 Share Posted October 5, 2006 Tim, a non-bypass regulator can never get lower than the base fuel system pressure, right or not right? I've been trying to figure this out for awhile now... Quote Link to comment Share on other sites More sharing options...
rztmartini Posted October 5, 2006 Share Posted October 5, 2006 thats the regulator in front of the fuel rail correct? if so then it seems to me that it cannot get higher than the base fuel pressure, bc pressure cannot build in the system btwn the reg and the pump...just speculating... Quote Link to comment Share on other sites More sharing options...
veritech-z Posted October 5, 2006 Share Posted October 5, 2006 no, creating a restriction is how they increase pressure. The basically pinch the line to bring the pressure up. This reduces the flow volume, but increases the fuel pressure. Think of putting your thumb over the end of a hose to make it shoot out further. That's due to the pressure increase. How you would reduce pressure with a device like that without a bleed off escapes me. Quote Link to comment Share on other sites More sharing options...
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