Rear return system questions

[jjump59]

i asked this over at Pro-touring but should have posted here where we've disussed this system before so i'll put it here also.

Took my 70 GTO to the tuner, FAST XFI, aeromotive A1000 inside Ricks tank, Aeromotive return style regulator mounted at tank and Aeromotive filters. Everything is plumbed with -10 for feed and -8 for the short return. Right away he told me it would not work the way I had it, he was concerned about the fuel going through the regulator, he thought the regulator would be a restriction that would cause the engine to starve for fuel. He recomended putting an additional -10 hose using t-fittings at the inlet and outlet, bypassing the regulator to help feed the engine. Have you guys had any problems that required this kind of fix?

Second question concerns no fuel at rails during restart, I have to let the pump run two or three times before the car will start. it seems that the fuel is returning to the tank and not staying at the rails. kind of stinks having to turn the key on and off three times before it will start. any easy fixes here? maybe a check valve of some type?

thanks for the help guys.

[GregWeld]

I'm running a 427 cubic inch SBC -- with Imagine Injection 8 stack efi... 400 lbs RWTQ

I'm running -8 feeds and -6 return - with an aeromotive regulator... and electric pump @45 lbs of pressure.

My regulator is mounted CLOSE to the fuel rail - I feed one side - loop to the other side - and out - to the regulator.... I'm running 39 lb injectors.

My car starts instantly = just like a new factory EFI car does.

I think the problem you're having is too much distance from the rails to the regulator... the pump is having to build pressure from the regulator - back to the rails and all the way back to the pump -- you have HUGE lines.... so it's taking the pump a bit to build this pressure up.

Your "tuner" questions the size of the lines -- it's a mathematical equation as is the required size of line to feed and the size of the injectors. If you're feeding with -10 -- and the motor uses some of the fuel -- then -8 return should be plenty. I would question the -10 feed line -- you must have a HUGE engine!! LOL EEEEEEEEHHHHHAAAAAAA

[camcojb]

I have run the rear regulator system on several cars, they all started instantly. It takes less than a second for full pressure to the system. Basically by the time the key is turned on and you start cranking the starter you have pressure. No, the pressure doesn't remain in the lines, but it didn't when the regulator was up front on the rails either. I think you could do a one-way valve or specific pump that would hold the pressure for a bit, but most all the aftermarket stuff doesn't. Then again, it's never been a problem with mine that way.

I will say, the cold and hot starts are two areas of tuning that can take a while to get right; it's a balance of cranking fuel, IAC position, temp modifier tables, etc., and with the cold start you only get one try per day to get it tuned.

Jody

[GregWeld]

Excellent response Jody -- and you're spot on. I've warned many friends that EFI is not for the faint of heart... and that dyno tuning is fun and gets the big stuff out of the way... it can take days of seat time and a couple more to get the hot start and cold start right.

With my 8 stack - there's no choke -- but it starts immediately and purrs like a kitten even in very cold weather!

[camcojb]

Originally Posted by GregWeld

Excellent response Jody -- and you're spot on. I've warned many friends that EFI is not for the faint of heart... and that dyno tuning is fun and gets the big stuff out of the way... it can take days of seat time and a couple more to get the hot start and cold start right.

With my 8 stack - there's no choke -- but it starts immediately and purrs like a kitten even in very cold weather!

thanks Greg. And that's why it's important in my opinion that the end-user knows at least the basics of tuning his system. The dyno guy/tuner can get the car up and running, do some dyno pulls as you say, but then it will take a fair amount of time to get the little things all dialed. Who's in the car more, you or the tuner guy? You drive it every day so it really behooves you to know how to tweak the starting, after start corrections, part throttle driveability, etc. as you're the one in the car all the time. He only got the car for a few hours at best.

Jody

[64duece]

Aeromotive offers a one way check valve that will screw directly into the pump to maintain system pressure. PN15107 is the 10AN version. As stated, slow starts can be combined with a combination of system prime, minimum iac or throttle plate position and cranking fuel/timing.

Most of my customers usually start with a full day of tuning and we try to minimize our dyno time and usually can get the WOT stuff sorted out in less than half a day on a NA application. We try to spend as much time with hot/cold idle, transient and cruise driving. Trying to teach the end user as much as we can. We generally refer to it as a "tuning/training session" for those that are more hands on.