FPR - vacuum connected or not?

confUsed · Post by **confUsed** » Thu Mar 12, 2009 5:01 pm

Hi! Sorry if this sounds a bit stupid, I'm just wondering what the experienced people do with the fpr before tuning. I've read so many different things, so I'm a bit confused, and looking for pro's and con's... I have both a stock fpr and a bw unit, and I just wanted to know whats the best thing to start off with. Its a vitara d16z6 with 550cc presicion injectors, looking for ~250whp, if that matters. 1. Just leaving the stock fpr with vacuum connected 2. Stock fpr with disconnected vacuum 3. bw unit with vacuum connected or 4. bw without vacuum connected If I go with the bw unit, what kind of base fuel pressure would be a good starting point, and what to look for to choose the best presure? thanks

JaredKaragen · Post by **JaredKaragen** » Thu Mar 12, 2009 5:09 pm

leave it alone unless your fuel pressure causes issues with your tune. OEM FPR is good for a LONG time as long as it continues to do it's job.

confUsed · Post by **confUsed** » Mon Mar 23, 2009 11:40 am

OK, thanks Got the afr's dialed in just like I want now. Helped a ton to look at the graphs, and not just the tables like I did before

Post by **Bugermass** » Mon Mar 23, 2009 9:39 pm

If your boosting, you always need to run the vac line.. The reason its there is to equalise the pressure created by the boost in the intake. example.. Say your Fuel pressure is at 40PSI, then you add 10PSI of boost, well that boost pressure is pushing back on the fuel trying to come out of the injector, so your effective fuel pressure is now 30PSI.. BY having the vac line on the regulator it raises the pressure to the injectors in relation to boost pressure to maintain the same pressures at the injector firing end.. I think that makes sence how i explained it lol.. Honda regulators arn't exactly 1:1, and they arn't very linear so you may find your running out of injector earlier than you should be when using the stock regulator.. For lower power setups this isn't a big deal, but if you decide to go bigger, you'll get more outta your injector with a quality regulator.

xenocron · Post by **xenocron** » Wed Mar 25, 2009 3:07 pm

Bugermass wrote:If your boosting, you always need to run the vac line..

You need the vac line if you are running NA as well...

thething96 · Post by **thething96** » Wed Mar 25, 2009 3:56 pm

What horsepower numbers do you consider low and high? I'm asking because I'm going turbo, 14-16psi hopefully 350-380hp. I have an AEM FPR, but I've heard bad things about them.

Post by **Bugermass** » Wed Mar 25, 2009 5:01 pm

Xenos right, you need the vac line period.. Well really its not about high or low HP its more about are your 1000CC injectors only giving you enough fuel to support 400HP?? Its your fuel pressure not raising with boost in a linear fasion? Then mabey its time to get a good quality regulator.. I know for a fact the AEM regulator was junk back in the day, but I don't know if they ever fixed the issue or not.. But I can say that Aeromotive and Welden regulators are top notch.. If your regulator is doing its job and your not prematuraly running out of injector then don't worry about it. Otherwise its time to upgrade.. PS.. Unless you can verify AEM fixed their regulator issues, I'd go back to stock over the AEM unit.. There was a problem with them that would cause a sudden loss of FP under boost.

thething96 · Post by **thething96** » Wed Mar 25, 2009 6:43 pm

Yeah, that's what I heard, thanks.

confUsed · Post by **confUsed** » Sun Mar 29, 2009 5:04 am

Bugermass wrote:If your boosting, you always need to run the vac line.. The reason its there is to equalise the pressure created by the boost in the intake. example.. Say your Fuel pressure is at 40PSI, then you add 10PSI of boost, well that boost pressure is pushing back on the fuel trying to come out of the injector, so your effective fuel pressure is now 30PSI.. BY having the vac line on the regulator it raises the pressure to the injectors in relation to boost pressure to maintain the same pressures at the injector firing end.. I think that makes sence how i explained it lol.. Honda regulators arn't exactly 1:1, and they arn't very linear so you may find your running out of injector earlier than you should be when using the stock regulator.. For lower power setups this isn't a big deal, but if you decide to go bigger, you'll get more outta your injector with a quality regulator.

Thanks for the explaination. I dont know where I read it, but someone was talking about just disabling the vacuum line, and bump the pressure to like 60 psi. Of course if you are running high boost I can see that would be a problem, and I guess the spray pattern would suck too, when in high boost... But anyway, I was just looking for the easiest approach, and I got the fuel dialed in pretty good with the stock fpr now, so no problem