boardkid280z Posted January 25, 2008 Share Posted January 25, 2008 I will have a GM TBI on my Supercharged 78 280Z and am trying to figure out any fuel system issues I might have. Here is a thread with pics of my setup: http://forums.hybridz.org/showthread.php?t=129378 The TBI only runs at 15psi or so stock. If I just hook up the feed and return lines with no other pressure regulator, will this cause any problems with the stock fuel system, especially the pump? Basically can I lower the fuel pressure on a stock system without hurting the fuel pump? Will the fuel pump actually have more flow because it is not having to work as hard to create pressure? Anyone have any experience with this?? Quote Link to comment Share on other sites More sharing options...
Guest TeamNissan Posted January 25, 2008 Share Posted January 25, 2008 Yes you can lower it without hurting the pump. The fuel pump is still creating the same pressure only up to the regulator. I'm not sure if you can run with no regulator, think it depends on what the pump puts out stock. I would bet you need one though. Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted January 25, 2008 Share Posted January 25, 2008 Get a fuel pump regulator with equiped with a return line hook up. This will keep the fuel pump happy. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 25, 2008 Administrators Share Posted January 25, 2008 Basically can I lower the fuel pressure on a stock system without hurting the fuel pump? Yes. Will the fuel pump actually have more flow because it is not having to work as hard to create pressure? Yes. A few items... 1) There is a '15 psi' regulator built-in (red circle)... Supply on the left, return on the right. 2) The only potential issue that I see is the size of the return side. It needs to be large enough to flow all unused fuel at low demand (such as idle). The internal orifice's are pretty small, so it may take a little massaging to make that happen. 3) The regulator is nominal at 15psi, but this specific regulator is 'all over the place'. It will probably require some attention simply becuase I think your potential HP out ways the flow capacity of your injectors. 4) Which brings us to... which injectors do you have? The most common ones I see are #5235206. See red circle... Those are rated for 55lbs/hr at 13 PSI The 9C1 police cars came with 65lb/hr at 13PSI There are several others if you dig. 5) I understand all these Rochester injectors are perfectly happy at 30-32 PSI. And some of them are good to around 70 PSI. I see no reason you couldn't take the stock Datsun regulator and piggyback it on to the GM regulator (essentially overriding it). 36-38 PSI *might* work just fine with those injectors, and you're probably going to need it. Quote Link to comment Share on other sites More sharing options...
strotter Posted January 25, 2008 Share Posted January 25, 2008 I would recommend an external, return-type, adjustable regulator; then consider a "dead-head" to the TBI inlet, w/ the outlet blocked off. Adjusting fuel pressure is critical to any serious tuning, and RonTyler is right - the regulators built into the TBIs need "attention": they are notoriously inconsistent and poorly calibrated. As a nice benefit, most external regulators have extra fittings onto which a nice-quality fp sensor can be fitted. Quote Link to comment Share on other sites More sharing options...
boardkid280z Posted January 26, 2008 Author Share Posted January 26, 2008 Thanks for all the responses guys. It looks like my injectors are # GM5235048*RPD - GM 4095. I don't know what app they came off of... but almost 100% certain it was a 4.3L V6. Anyone have an idea what these flow? Google's not giving me anything. If they are too small, I will just have to find some bigger ones to swap into the TBI (not a problem from what I have read). OK, so what if I just plan to install the stock regulator in the return line of the GM TBI regulator, with no vacuum source (atmospheric pressure at the signal input)(I can attach a boost signal if nececessary to up the psi with boost). Will the stock Z regulator produce a constant pressure or will the TBI regulator mess it up, since it is "iffy'? If I have problems with any of this I will probably pick up one of these adjustable regulators from work and make it fit: http://www.lindseyracing.com/mm5/merchant.mvc?Screen=PROD&Store_Code=LR&Product_Code=LR-FL-51501&Category_Code=944FUELREGULATORSDDAMPERS Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 26, 2008 Administrators Share Posted January 26, 2008 It looks like my injectors are # GM5235048*RPD - GM 4095. I don't know what app they came off of... but almost 100% certain it was a 4.3L V6. Anyone have an idea what these flow? I wasn't able to cross-reference those. Maybe call a GM dealer and ask if those supersede or have been. OK, so what if I just plan to install the stock regulator in the return line of the GM TBI regulator, with no vacuum source (atmospheric pressure at the signal input)(I can attach a boost signal if nececessary to up the psi with boost). You can do that. However, Strotter mentioned dead-heading the GM regulator. The most obvious advantage is reducing the possibilty of an undersized return. He may have other thoughts as well... maybe he'll chime. Will the stock Z regulator produce a constant pressure or will the TBI regulator mess it up, since it is "iffy'? Either way you do it, I don't see any conflict. Quote Link to comment Share on other sites More sharing options...
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