aem fuel rail/guage issues

**Doug** · 01-31-2011, 10:26 PM

just curious if any of you have ever installed a aem fuel rail on a b series. if so, did you use a bolt on fpr and guage that bolted onto the fuel rail and did the guage read the rite fuel pressure?

haynes calls for 38 vacuum and 45ish no vacuum. when i set the fp so the guage reads this, the car runs extremely rich.... so rich it pours fuel out the exaust and smokes like a mofo

**godzhand** · 02-01-2011, 12:15 AM

did you expect to change the rail to an aem high flow and it not to flow dif?

**Ric** · 02-01-2011, 12:26 AM

Originally Posted by godzhand

did you expect to change the rail to an aem high flow and it not to flow dif?

this.

**TLMike** · 02-01-2011, 08:06 AM

put the stock rail back on, you dont need an AEM rail.

**Ric** · 02-01-2011, 08:24 AM

Originally Posted by TLMike

put the stock rail back on, you dont need an AEM rail.

I'm not sure about a honda, but on a lexus SC/toyota Supra the stock rail/fuel lines are good for around 7-800whp.

**Doug** · 02-01-2011, 01:27 PM

well, i understand it's a high flow fuel rail, but does that call for less fuel pressure?

btw, i do need the fuel rail, gotta lean it out to get through emissions. that's the main reason i put it on there.

**Sohcvtec1995** · 02-01-2011, 02:54 PM

lower the psi.try 35/40

**Ric** · 02-01-2011, 03:54 PM

bigger pipe (fuel rail) equals more flow at a given pressure. A bigger fuel rail at 40psi will flow more then a stock rail at 40psi. Then there's going to be another issue because if you go too low on the fuel pressure, the injectors won't spray correctly and you'll get worse emissions then stock.

The easiest way to pass emissions is to run e85.

**Doug** · 02-01-2011, 04:24 PM

dunno what e85 is. as far as the fuel rail goes, it's around 20-30 i think rite now. i had to lower it about 15psi from the book to get it to stop pouring out tons and tons and tons of smoke/raw fuel. it looked like i was going down the road with shot piston rings. ran like shit too.

**Ric** · 02-01-2011, 04:27 PM

take a lighter to the exhaust, it's fun

**dropcivic** · 02-01-2011, 06:00 PM

get it tuned. problem solved

**godzhand** · 02-01-2011, 10:41 PM

Even if you add an intake to a car it changes how a motor runs any mod period needs a tune to show any sort of real diff otherwise itspointless and it does more harm then good.

**dropcivic** · 02-02-2011, 05:56 AM

come to think about it, the rail should not matter that much. Think of the rail as a plenum. If pressure is still the same and the injector pulse is the same, a bigger volume of fuel in the fuel rail shouldnt matter. Your stock rail never empties with a "factory" style injectors.

But as i said, get the car tuned if you are running that rich

**TLMike** · 02-02-2011, 06:35 AM

Originally Posted by dropcivic

If pressure is still the same and the injector pulse is the same, a bigger volume of fuel in the fuel rail shouldnt matter

bingo

**dropcivic** · 02-02-2011, 07:31 AM

what size injectors are you running?

**Ric** · 02-02-2011, 09:26 AM

Not true. Fluid Dynamics 101.

A 1in pipe at 40psi will flow a tremendous amount more fluid then a .5in pipe at 40psi. The flow rate (speed of the liquid) will also be faster in the smaller pipe compared to the bigger pipe.

That's why on a correctly built turbo car intercooler system, you calculate your turbo's flow and pressure to size the intercooler piping correctly. Pretty simple college level math with the help from Google. Getting the pipe size wrong (example: using 10ft of 2.5in pipe on a car with a 65mm turbo) can SEVERELY affect your horsepower in the numbers of over 100whp. Same goes for exhaust pipe. It's not uncommon to see car's get 30-50whp more with big turbo's going form 3" exhaust to 4"

When honda designs the fuel system, they designed it with the flow that the fuel rail delivers. Change the size of it, you change the flow, changing your A/F ratio. Ever meet someone who puts a 255lph HP fuel pump on their stock WRX? bahahhahaha

Doing your math correctly, sizing the parts used correctly (not with what you think is pretty, but with math), is the difference between a car like Darin's Daily Driven Supra running 8's, and a kid that built his supra in his garage with the help from forums running 12s using the same turbo.

**dropcivic** · 02-02-2011, 09:51 AM

the flow is being restricted by the fuel nozzles opening and closing. If pressure remains the same as does the injector timing and size, you are still flowing the same. You just have more fuel on demand is one way of putting it.

**Ric** · 02-02-2011, 10:18 AM

Originally Posted by dropcivic

the flow is being restricted by the fuel nozzles opening and closing. If pressure remains the same as does the injector timing and size, you are still flowing the same. You just have more fuel on demand is one way of putting it.

By making the pipe bigger, you're putting more fuel into the system if you leave it the same pressure as the smaller pipe. Fuel injection systems are highly complex, especially on a honda where they are designed for fuel economy. The exact size of that fuel rail was designed into the fuel delivery of that engine matched to those injectors, fuel lines, fuel line dia, fuel pump, etc. We're not talking redneck engineering where you just look at Jegs, order something, and throw it on and expect power out of a carbbed 305. Fuel injectors also need a minimum fuel pressure to spray correctly. 20psi ain't going to cut it. It's going to drip and cause you to get far worse economy compared to stock.

The only purpose of a bigger fuel rail would be if you had LARGER then stock injectors that can outflow the capabilities of the stock fuel rail. You know when you're outflowing the stock rail/lines when you have to RAISE the base fuel pressure to keep up with the injectors (or on a turbo car where you're doing like 80psi @ wot). You add bigger rail/lines to lower the pressure to keep up with the flow.

I really don't feel like covering this anymore, this is why we use math. There's plenty of online sites that offer java/flash based equations and explanations on how to use them to figure out what you need to know to correctly plan/build/modify a car.

**Doug** · 02-02-2011, 10:23 AM

the car is not running rich, it's running like it's supposed to now. but my fuel pressure guage is only reading about 20 psi. at 38 psi it looks like a smoke machine.

stock obd2a injectors. it ran fine with the stock fuel rail+fpr. but i have no idea what fuel pressure was.

i should also add it's got a walboro in tank 255hp. however, it didn't make it smoke and shit with the stock fuel rail.

**dropcivic** · 02-02-2011, 10:23 AM

there is no more fuel in the system then when you started. Tell me how more fuel is gonna get into the engine when the limiting factor itself is the injectors. Take your hose idea. Take a 1" and a 1/2" hose and use the same nozzle and same pressure. Is the 1" hose gonna flow anymore then the 1/2"? No its not due to the fact the fluid can leave the hose as fast as the nozzle will let it.