anyone turbo a tbi.....if so what is really involved for map sensor to understand boost and since tb would be under boost would you raise fuel press with boost press??

Thanks

 

i believe that nothing is required for the map sensor to understand boost, youve just got to program the computer to have the timing retarded once the map reports certain psi to work with the boost. that and a variable fuel pressure regulator with new 90lb injectors of ebay and your ready to make some power. they say the limits are 400hp naturaully aspirated, i think i can hit 500 with 454 tbi and special intake manifold and turbo. good luck in whatever your doin man!

p.s. ime planning on putting a turbo on my 350 tbi, email me if u want any info, ime getting parts for good prices too!

 

Stock TBI unit is 1-bar and will not understand boost. To swap to a 2-bar will require a custom prom. Fuel puddling in the intake will be an issue IIRC. Fuel delivery with TBI will be almost impossible due to limited injector sizes vs. idle quality. TBI is best suited for suck-through forced induction (roots/screw blowers), not blow-through (cenrifugal supers/turbochargers). If you want to turbo it right, save extra cash for a TPI unit. Much more turbo-friendly IMHO.

 

yes indeed the tpi setup is allot more flexable and responds well with tuning and injectors. but its not impossible with tbi to get a decent result before i spend the extra money to upgrade the injection. like i said you use a boost referenced ajustable fuel pressure regulator (no puddling, 9psi at idle, 15psi at wot). yeah they prefer pull through, but with a turbo you get a mild form of pull through, centrifugal superchargers don't work that great ive heard. with a wieland stealth intake, carb to tbi adaptor plate, vafpr, 454 throttle body, new 90lb injectors (been proven to exceed 100lbs with vafpr) and a turbo you could easily run 450hp, according to my calculations the intake setup can run 400hp naturaully aspirated, but with the injectors and a turbo, you never know! my mistake you will need a 2 bar sensor, and yes reproggramming is neccesary, tbichips.com, thay can do it, very competitve pricing. good stuff!

 

i am wanting to put this on a 454 tbi....so i guess larger injectors for the stock 454 tbi would be needed??

 

For moderate boost levels it might just be easier to run an FMU, and maybe a little reprogramming. The TBI setup is almost like it was built for a rising rate fuel pressure regulator + boost, since the relatively low base pressure plus tolerance for higher pressures play well towards that end.

Why? There’s tons of TBI cars/trucks out there that don’t have any problems. Adding boost will just raise the air temp and make it less likely.

You can get them to idle with just about any injector that is available for them, and if you need more fuel then that you can run more pressure or add auxiliary injectors (check out some of the supercharger setups out there, there are some pretty cool solutions for this).

you don’t want to draw through a TBI, at least not a stock one since they have relatively small bores and for a draw through application you need to size the carb/tb for the apparent size of the engine (engine+turbo) below it. Blow through you only have to size the fuel delivery for both. The second problem will be that you’ll have to find a turbo with positive compressor seals (relatively rare, especially in bigger turbos or one built in the last 20 years) to prevent from sucking oil past the seals when you close the throttle.

As far as “turbo friendly” there is a big advantage with TBI in that it injects the fuel further up the intake path, so you get some additional “intercooling” from the fuel vaporizing. You probably won’t be able to get enough fuel delivery for an all out race setup, but for a mild (say sub 400hp with big block injectors, 500 with higher pressure and those injectors) street setup then cooling effect of the fuel could be a big plus. TPI’s (or any multiport injection) big advantage is just the common availability of larger injectors. Of course, you could always get creative and go with multiple TB’s or adapt some ford parts (ford TBI setups used injectors that are very similar and interchangeable with standard injectors)

 

thanks allot for the info 83 crossfire t/a, yeah i think that guy TechSmurf was refering to map sensor as if it has primary control over fuel, like you said not the case with tbi's, theres a thread with the vacume referenced fuel pressure regulator that has the gm part number, this will solve the fuel problem (allong with the biggest injectors) just hook it up to the throttle body vacume. also 83 crossfire t/a have you heard of the x ram manifold? i think they said you gain 50 rwhp just from the intake change! just wondering cause thats a very impressive gain.
i don't know your numbers louich (hp numbers) but you should be good if youve allready got the 454 setup, might want to change intake manifold if you haven't allready.

just keep in mind with forced induction you should be able to hit 500 with good boost.

good stuff!

 

It does. the computer uses a VE tables for fueling, the are RPM vs MAP

I strongly doubt that the VAFPR will do anything, from the way that i understand it working, it again will only compensate until zero vacume. it isn't a boost referenced adjustment. to get that you will need an FMU.

500 may be pushing it. Kingsta1on got 500 from his roots blown 355, with the 900cfm unit (4 85pph injectors). i really don't know that the injectors will support the power, even with the pressure cranked way up.

 

so you think if i put it on it would at least run under some boost to get tuned??

 

I don’t believe that I said that. The map sensor is the primary way that the engine determines load and therefore fuel delivery. Adding a VR FPR just allows you to run bigger injectors/deliver more fuel at WOT and still have a decent idle by confusing the ECM. The ECM has no concept of fuel pressure, it just expects a specific amount of fuel to be delivered if the injector is held open a specific period of time. By making the fuel pressure change you’re giving the fuel delivery a greater dynamic range. This will allow you to run larger injectors, maybe save a little gas at part throttle, but it will not compensate for boost. Normally a manifold pressure referenced FPR changes the fuel pressure relative to the manifold pressure which is where the injectors spray into, to give constant fuel delivery, delta P across the injector, but in this case the injectors spray the fuel above the TB which does not see vacuum, so you’ll be changing the deta P across the injector and therefore flow rate. Unfortunately, once you go into boost this will not add any more fuel (the change in pressure across the injectors will stay the same) since the throttle will be open and the pressure will be the same around the injector nozzle as it is in the intake.

If you were to reprogram the ECM and convert the 1 bar map to a 2 bar you could use the VR FPR to prevent running high fuel pressures under normal conditions. Basally, you could do something like run 96pph injectors with a base pressure of 25psi. you’d end up with about 12psi fuel pressure at idle, and you’d burn a chip for the 96pph at idle, but once you cross into boost you’ll have 25psi pressure differential across the injector, making it flow 152pph, or enough fuel for 2 of them to feed roughly 600hp.

If for the time being you don’t want to get involved in burning chips (I think that long term this is the only way to get this setup working perfectly, but just to get it running), you could rig the fuel pressure to go up at someplace between 2 and 3:1 ratio to boost pressure (I’m to lazy and tired right now to do the math, but at one point I worked it out to be in the 2.1-2.2:1 range for 10psi boost on a stock engine), and your fuel delivery will go up roughly the same as the increase in airflow from the boost (won’t be perfect, you’ll probably be _a little_ lean in the 1-2psi boost range and a little rich around 9-10psi, but it will be close enough and quite drivable, I’m not sure you’d even notice a difference after you burnt a chip to do it right).

In either case, you’ll need a TPI style intank pump or an inline boost pump to run the higher fuel pressures necessary. One of the assorted walbro intank pumps would be fine, I believe the TBI truck blower kits use an Airtex E2315 inline.

yea, it’s been around for years. It’s basically just a machined adaptor to mount the crossfire setup to the top of a standard 4bbl single plane, low rise carb, that they sell as a package. I’m not sure I like the idea. While nice at WOT I can’t imagine it not loosing some drivability at part throttle.

If I was going to do something like that with a crossfire I’d probably just make a top plate to mount the crossfire setup to an original Z28 crossram/smokey ram/edelbrock/offy (they’re all the same intake). As it stands, my crossfire car got crushed last year by a 6’ in diameter oak during hurricane Isabel, but I saved all the crossfire goodies to use on my truck.