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? :D

[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 :thumb:

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

http://www.ztechz.net/sitebuildercontent/sitebuilderpictures/2015-chart.gif

[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.

[moparzrule]

I figured it would not cutout, but is there an issue with the 1 bar MAP never seeing more than 4.7v? With a 2 bar, it's just reading less boost. But with the N/A, does the throttle position sensor correspond with the MAP because at WOT the 1 bar MAP should be reading max 5 volts I suppose. If it only sees 4.7V will it add less fuel, less timing, etc?
Thats another thought with timing. Stock turbo computer backs out timing per pound of boost, I won't have that feature. Now I'm only gonna be running 5 PSI, but will I be OK just setting it at 12? Right now I have it set to about 17*, and on 87 octane it will ping slighty on a really hot day etc. I also do need to change the thermostat gasket, so I could put in a 180 stat so that would help too. But if I set the timing to 10-12* and run 93, I think I'll be OK with 5 PSI boost.

[ShadowFromHell]

What about a mild 2:1 and a extra injector... or 2?

[zin]

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.

I'm not real familiar with MOPAR TBI, the units I've dealt with have vacuum control of the fuel pressure, though it may not be as obvious as a reg, with a vac line going to it, most just have a port exposed to manifold vacuum. It the TBI unit is sealed, it should be fine, so long as the main fuel line gets boost compensated, which the FMU would do, especially the Holley unit I linked to.

Hope it helps!

Mike

[zin]

I figured it would not cutout, but is there an issue with the 1 bar MAP never seeing more than 4.7v? With a 2 bar, it's just reading less boost. But with the N/A, does the throttle position sensor correspond with the MAP because at WOT the 1 bar MAP should be reading max 5 volts I suppose. If it only sees 4.7V will it add less fuel, less timing, etc?
Thats another thought with timing. Stock turbo computer backs out timing per pound of boost, I won't have that feature. Now I'm only gonna be running 5 PSI, but will I be OK just setting it at 12? Right now I have it set to about 17*, and on 87 octane it will ping slightly on a really hot day etc. I also do need to change the thermostat gasket, so I could put in a 180 stat so that would help too. But if I set the timing to 10-12* and run 93, I think I'll be OK with 5 PSI boost.

I'm not sure at what point (map volts) the computer will decide something must be busted on the map, but I would suggest using the highest volts you normally see running around town, you could also experiment with higher voltages to find the "freakout point", allowing you to max the fuel delivery. IIRC the air temp sensor will have a pretty big role to play in the timing, you might be able to trick the computer into thinking it's much hotter out and get it to pull timing. Otherwise retarding the timing manually should have the desired effect. You might be able to use a boost retard ignition, like MSD's.

Lots of ways to skin this cat!

Mike

[MiniMopar]

IIRC, the goofy TBI injector has the regulator built-in.

[moparzrule]

Yup the regulator is actually inside the TB, thats why I'm not sure if it has a vacuum line going to it LOL.

[zin]

Yup the regulator is actually inside the TB, thats why I'm not sure if it has a vacuum line going to it LOL.

That's how the GM TBIs are, and they do use vacuum, but not via a hose, just a passage in the casting. The instructions for NOS kit 05153nos has a pretty good picture of that TBI unit, might take a look just for reference. Still can't be sure on the Mopar units though I would expect it.

Mike

[moparzrule]

So, it should still add fuel on a 1:1 ratio if a vacuum line is hooked up to the FPR in any way. Interesting, not sure how much extra fuel I'll need? Perhaps a cold start injector would do the trick?

[zin]

So, it should still add fuel on a 1:1 ratio if a vacuum line is hooked up to the FPR in any way. Interesting, not sure how much extra fuel I'll need? Perhaps a cold start injector would do the trick?

Figure .55-.6lb/hr per HP you plan to make (extra). The cold start could work, but if it isn't varied with the boost, you'll be very(?) rich at low boost and about right when you are at max boost.

I'd look pretty hard at that Holley regulator, it's meant to work with the existing FPR and only act as a RRR when it sees boost, pretty much what you what.

Mike

[moparzrule]

The problem with an adjustable one is I won't know how much fuel is being added because I'm not running an in cab fuel pressure gauge. I mean I could just set it rich and bring it down to the proper A/F ratio, but I'd rather know what rate of gain I'm doing.

[Vigo]

the reason tbi regulators dont have a vacuum line is because they operate at a fixed pressure regardless of manifold pressure. since the injector is not behind the throttle plate it operates in a fairly stable pressure environment. the reason cars with injectors behind the throttle plate i.e. port injection have vacuum referenced fuel pressure regulators is that pressure inside the intake manifold varies a lot, and the fuel pressure varies along with it to maintain the same pressure differential across the injectors. i.e. if youve got an injector operating at 50 psi fuel pressure in a 0 pressure intake manifold like an na car at wot, you've got 50 psi of differential. if the manifold pressure goes up to 20 psi (boost) you've now only got 30 psi of differential and the injector is only going to flow 60% as much at the same pulse width. the computer is calibrated for a flow rate at a steady pressure differential instead of computing the different flow rates at varying ones. the injector in a tbi never sees those changes in differential so it doesnt need a vacuum reference signal.

honestly i think the easiest way to do this job would be to make it a drawthrough and relocate the tbi to the intake of the turbo.

also, i dont see the need to mount the turbo on the exhaust manifold if you dont want to. you could run a pipe from the exhaust manifold, whichever one you decide to use, and put the turbo wherever you want.


sounds pretty cool, cant wait to see what you'll do.

[moparzrule]

Vigo, thank you so much for your input, great ideas indeed! Never even thought of a draw through, but the problem with that is I think I'd have to go with multiport injection to do that, and that means I'd have to swap an entire wire harness to a turbo one. Not really interested in that because if I ever want to go back to plain TBI I want to make it an easy swap.
Yeah I'm thinking of using a stock turbo exhaust manifold and welding on a pipe to the flange to remote mount the turbo anywhere handy.
Still thinking of making the carb(TBI) hat/box, and just using the FMU to compensate. So, if I need atleast 1:1 to compensate for the pressure differential, how much more do I need? I'm thinking maybe a 4:1 FMU? My choices are a 3:1, 4:1, or 6:1. Don't think I'll need more than 6 and they don't make a 5 that I know of. And again, an adjustable one isn't really any solution for me as I don't have an in cabin fuel pressure gauge so when I'm in boost all I can go by is an A/F gauge and trust that whatever FMU I get is doing it's proper ratio.

[zin]

The problem with an adjustable one is I won't know how much fuel is being added because I'm not running an in cab fuel pressure gauge. I mean I could just set it rich and bring it down to the proper A/F ratio, but I'd rather know what rate of gain I'm doing.

Here are the instructions for the RRR Holley sells, it's adjustable and the ratio can be changed. The instructions aren't that great, a call to the tech dept would be helpful if you still have questions, but it seems like a perfect fit for what you are doing. It was created to make Holley's Supercharger kit for the F150s work and as such it is made to work with the stock regulator, so you wouldn't have to worry about it (the stock reg) at all. I'll assume no matter what way you decide to go, you'll have the means to tune it. I've actually got one waiting for a future project! :D

Mike