Turbo dakota, fuel question

[moparzrule]

Hey guys, I think I've decided to attempt to turbo the 2.5 tbi in my 90' dakota, but I'm gonna go a very different route. I want to attempt to turbo the stock TBI. Basically I want to build a custom header, and then a custom box like a carb hat for the throttle body. Just going with a stock T2 turbo or something similar.
I'm doing this so I don't have the change the wiring harness, and don't have to build a custom intake. The header isn't as much of a big deal, I can weld the header. But I have no provisions for welding aluminum.
Now, to add fuel I'm thinking a FMU is the simplest. But I don't know what rate of gain to get. Anybody have any ideas? I'm only looking to run 5-6 PSI, non intercooled. I only want a little more power, not looking to make it a power house because I'm keeping the stock TBI bottom end which means lightweight rods.
Anyway, I was trying to find a 4:1 gain FMU, but could only find a 6:1. With a 6:1 with 6 PSI boost that would raise my fuel pressure 36 PSI. Isn't the stock fuel pressure like 30-35ish? So that would equal about 70 PSI. Now that I think about it like that it sounds like it's way too much fuel. What about a 3:1 rate of gain? I found one of those.
The fuel pump is a brand new stock style Bosch, and since I'm only going with like maybe 130-140 HP here I think even at 70 PSI it can handle it.
Anyway, looking on opinions on which rate of gain regulator to use.

Also, does anybody know what voltage the stock 1 bar MAP sensor reads for the TBI? Is 0'' = 5 volts to a TBI? I'm guessing if it sees any boost it will flip out or cutout? And I'm thinking a 2 bar MAP wouldn't work well either since 0'' is probably only like 2.X volts.

[Birddog]

I had to run a check valve and bleed in my '01 to keep the PCM from seeing boost and freaking out.

Just a goofy thought but, couldn't you do a cal on the '90 computer to compensate for the addition of a 2 bar MAP?

[BadAssPerformance]

^^^ sounds like a plan... '90 2.5L SBEC can be hacked right? Worst case can be swapped to a '89 SMEC?

I'm wondering about hacking a '92 318 SBEC II?

[moparzrule]

Well I don't want to do wire harness swapping. What are the chances of finding an 89 dakota 4 cylinder 5 speed harness? Plus any harness from any other car would have to be WAY modified, the ECU is on the passenger side in the dakota's.
Not sure how to add the 2 bar to a TBI cal, but that would be cool. Remember, I'm not going to multiport injection so I can't use any turbo cal's.

[moparzrule]

Anybody have an idea of which rate of gain regulator I should get? 3:1? 4:1? 6:1? Guess I can't really go more than 6:1, even with 6 PSI boost thats over 70 PSI, and with a TBI fuel pump even though it's new I can't stretch it that far.

[BadAssPerformance]

I put an extra needle valve on the vacuum line on the old Cartech I used to use and ratio was fully adjustable

Fuel pressure is not the best way tho, higher pressure doesn't always mean more fuel.

[moparzrule]

Why wouldn't higher fuel pressure give me more fuel? Any other way I see would make me pig rich when not in boost, and I DON'T want to take away much fuel economy as I get 20/25 MPG now and love it.

[BadAssPerformance]

For one, it depends on how good your pump is. Pumps, injectors, etc. are flow rated at like 43psi or 50psi and not as efficient at higher psi. I looked around briefly for a #/hr vs. p.s.i. graph but could not find one...

[moparzrule]

Well I know already that the stock turbo pump is good for atleast 75 PSI because I've run 20 PSI boost on the stock pump and the 55 base PSI fuel pressure in my 88 shadow. And I think the bosch pump that I got from autozone is a replacement for a turbo or non-turbo doesn't matter.
There was a chart I found awhile ago with the 190 LPH pump listed, and the 255, not sure if the stocker was in there. It also depended on the voltage supplied also, the chart had 12 and 13.5v. A big problem with our cars is the crappy wiring, it's suppose to send 12v but we may only really see 10v by the time it gets to the pump anyway.

[moparzrule]

Yeah found it, about 1/3 down the page there's 2 charts, one for 12v and one for 13.5v and this chart shows the 190 255 and 255HP pumps along with how much amperage they draw.
http://www.ztechz.net/id5.html

[BadAssPerformance]

Good find, this is what I was refering to

[moparzrule]

The stock TBI base fuel pressure is only like 30 PSI, so I got a good bit to work with.

[Birddog]

Anybody have an idea of which rate of gain regulator I should get? 3:1? 4:1? 6:1? Guess I can't really go more than 6:1, even with 6 PSI boost thats over 70 PSI, and with a TBI fuel pump even though it's new I can't stretch it that far.

Sorry a bit late but..

If you find one cheap just get it and then get the spring kit later. Provided you go that route... I have an 8:1 sitting next to the monitor right now that I found out I didn't need for 8-11 lbs boost on Mopars( R/T computer overruns the injectors big time)...
I'm also comparing apples to oranges as I'm trying to fool OBDII.

[zin]

Now, to add fuel I'm thinking a FMU is the simplest. But I don't know what rate of gain to get. Anybody have any ideas?

You might be able to use this: http://www.holley.com/512-505.asp

Also, does anybody know what voltage the stock 1 bar MAP sensor reads for the TBI? Is 0'' = 5 volts to a TBI? I'm guessing if it sees any boost it will flip out or cutout? And I'm thinking a 2 bar MAP wouldn't work well either since 0'' is probably only like 2.X volts.

You are correct in that a TBI MAP will read 0-5volts, just like a 2bar map, it just takes less pressure to max it out, you know, like 1psi...

I think the best way to go, would be to recal the stock computer, but I can imagine that you would likely be blazing a trail there, I don't know if anyone has done any dissassemblies of the TBI code. OH well, sometimes the "best way" to do something just isn't practical, though I would still suggest checking on D-Cal, or Chem to see is someone has done it. Would suck to go through all the other work to find out your could have gone this direction.

Mike

[moparzrule]

I actually do have a 90' TBI cal that shel-game gave me, but it's incomplete. All the tables say signed/unsigned etc. so I don't know whats what. Not sure if it even run the truck. Plus I do not have the SBEC socketed and I don't have any chips for SBEC's.
Trying to figure if I can put a 4.7V zener diode on the MAP like we do to eliminate boost cutout, I wonder if that would work or is it bad that the MAP will never see 5V?

[moparzrule]

You know, I was just doing a little research and I think a 90' TBI will only have 15 PSI base fuel pressure. Is this correct? If so, I got plenty of room to work with for fuel pressure.
I have no port or anything on a TBI to check the fuel pressure. I might have to put something inline I guess.

[MiniMopar]

35.5 psi for 1984-1985
14.5 psi for 1986 and up

[moparzrule]

I read something that 91-up went back to the 35 PSI?

Anyway, I have a 90 so I should have 15 PSI. Thats great.
I'm actually thinking a 3:1 RRR still might be too much because even at 5 PSI boost thats 15 PSI fuel pressure increase so I just doubled the fuel flow and total is 30 PSI. Fuel pump shouldn't even blink at that, but I'm thinking I shouldn't need to double the fuel flow for the boost should I? Will a 2:1 be better? Anybody have any thoughts on this?

[moparzrule]

I also have another question. Does the TBI FPR have a vacuum tube connected to it at all from inside the throttle body so it doesn't put as much fuel in when in vacuum? Or does the ECU do it all on a TBI?
If it does have a line to it, it should still add 1:1 when in boost.

[zin]

Trying to figure if I can put a 4.7V zener diode on the MAP like we do to eliminate boost cutout, I wonder if that would work or is it bad that the MAP will never see 5V?

Yup, no reason it won't work, as it does the same thing as a bleed, just electronically (a better way IMO).

Looks like Russ got the info on the fuel pressure.