TBI with Multiport?

[genesis]

Hey all, I have a 99 Tahoe, Old Body Style, and am wondering if anyone has ever done a TBI setup in the Vortec 350 with what I believe is multiport. I know for sure that dont have TBI so I am merely assuming its multiport, not direct port. But am wondering if anyone ever has added TBI to this setup, or is it even possible. Clearly I am a semi-newbie, but have been reading the forums and am just looking to boost the hp and torque a bit for towing purposes. Am hoping to do CAI and Exhaust soon, along with BB for the power, but was wondering about the TBI for extra fuel delivery. Speaking of Towing, anyone recommendations tranny upgrades? Vette servos, shift kits, torque convertors, trans swap, retune?

[95TwinTT]

How heavy is the trailer and how often will you be pulling it?

Long hauls or short?

[TIM Z]

No, you cant add TBI ( throttle body injection) to your multiport setup.

You either have one or the other.

The Throttle body injection ( TBI) is used on chevy/gmc full size trucks from 1987-1995.

A TBI setup is basically a carburetor with 2 fuel injectors in it. It was a step in the right direction for driveability but not as powerful as a multiport injection system.

A Multiport system has one injector for each cylinder and it also has a " Throttlebody", which is mereley a valve or "flap" for letting air into the engine.

The air and fuel ae mixed together in each cylinder. VS the TBI where air and fuel are mixed together in the throttle body then having to travel thru the manifold then to each cylinder.

Multiport is the standard for fuel injection nowadays and way more effecient/powerful that TBI setups.

Hope this helps.

If you are staying with a stock motor dont waste time/money on larger throttle bodies/spacers /or Mass air flow sensors for multiport engines.

Get a CUSTOM tune and exhaust and cold air intake and you'l have a great running enine assuming everything is tuned up under the hood.

[992dr]

I know of someone who had a GM TBI Vortec manifold modified to MPFI.
He's a member of a couple other forums.
Another option is a Marine manifold.
You gotta love the spider mess GM developed. Although someone has designed an upgraded spider assembly with high output injectors instead of the stock 19lbers.

95TwinTT,
Your truck is insane. That motor is bad ass.

[haks310]

It's been done.

Check out the last post, should point you in the right direction:
http://www.fullsizechevy.com/forums/general-discussion/performance/315077-gauging-interest-aftermarket-spider-mpfi-conversion-manifold.html


Simple CSFI to MPFI, also:
http://www.theautoshop.net/VortecMPFI.htm

[genesis]

Thanks I appreciate the input. The tahoe will remain mostly stock with the exception of the CAI, exhaust and tune. Am just looing at basic power upgrades for now as the engine has 220,000 on it. To answer the question on towing. I am usuallyp ullins aroung 2000lbs with it but just built an 8x7x24 foot long ice house that doubles as my hunting shac and that is right in at about 7000lbs. on long drives I get 6mpg. its usually about two hours pulling it. problem is, tranny likes to kick in and out of overdrive on every little hill. so I am hoping that these extra horsepower mods will help and any thing I can thinl of for a tranny. I asked about TBI cause I know that it can make tremendous amounts of torque when done right. so wat hoping there was a way to do both. Even if it was similar to a NO2 setup where the TBI only kicked in at a percentage of throttle.

[95TwinTT]

Sounds like for your situation, a performance tune and leave it in drive, while towing a trailer is your best option. The injector system you have is capable of adding more fuel. From the factory they would never exceed 80% saturation, for size and duration.

Third gear or 1 to 1 has been recommended for towing for years. Turning a few hundred more rpm’s is good for the drive train. For many years, 3,000 rpm’s was normal for 60 mph. It is the move towards higher mileage that drives the industry lower rpm’s. By nature, gas engines tend to make their power at higher rpm’s. If it were a diesel, it would be different. Then again, we would not be having this discussion.

The transmission is also less likely to have problems in third versus fourth, for towing down the highway.

Lots of people ignore the obvious and concentrate on CAI’s and Headers, while not doing anything about cam and heads. The actual flow of air in the heads is the key to power. :)

[992dr]

It's been done.

Check out the last post, should point you in the right direction:
http://www.fullsizechevy.com/forums/general-discussion/performance/315077-gauging-interest-aftermarket-spider-mpfi-conversion-manifold.html

Simple CSFI to MPFI, also:
http://www.theautoshop.net/VortecMPFI.htm


Both are what I was talking about. I have inquiered with the company that did that manifold in the FSC forum and the total was $900 not including the Vortec manifold. You will need to find a TB for the application to. A lot of people go the Marine manifold route over the custom MPFI manifold for the cost factor and ease of installation.


95TwinTT,
What heads would you recommend for our motors? What other mods would you recommend for max power gains?


Here's a question.
Does the aluminum spacer make any difference in power?
This one.
http://www.streetandperformanceelectronics.com/vmax.htm

[TIM Z]

I understand you now ,

You want to replace your Vortec manifold with an alum True multi port manifold right?

I thought you wanted to add a TBI throttle body to your Vortec manifold, my bad.

Heck for a grand you can get an edelbrock MPI system ready to go.

Holley also makes a stealth ram that is similar to the LT1 style intake.

Or get a GMPP ram Jet intake.

Curious to see how ya make out.:)

[992dr]

Scroll down to post 118, thats what I'm talkin about. It doesnt get any cleaner than that.
http://www.fullsizechevy.com/forums/general-discussion/performance/315077-gauging-interest-aftermarket-spider-mpfi-conversion-manifold-6.html
The benefit of this manifold is everything stays in the stock location, so, you can keep your K&Nfipk or any other CAI and any SCer made for a Vortec 5.7 would bolt right up to it wih no mods. Another bonus, you keep all emissions provisions.
Here's the picture from FSC.
http://i804.photobucket.com/albums/yy321/992dr/MPFIVortec57.jpg

[TIM Z]

Havent seen that, very nice!

Thanks for the pic.

[95TwinTT]

Scroll down to post 118, thats what I'm talkin about. It doesnt get any cleaner than that.
http://www.fullsizechevy.com/forums/general-discussion/performance/315077-gauging-interest-aftermarket-spider-mpfi-conversion-manifold-6.html
The benefit of this manifold is everything stays in the stock location, so, you can keep your K&Nfipk or any other CAI and any SCer made for a Vortec 5.7 would bolt right up to it wih no mods. Another bonus, you keep all emissions provisions.
Here's the picture from FSC.
http://i804.photobucket.com/albums/yy321/992dr/MPFIVortec57.jpg

That looks great, but to make it really work well, you also need new heads. I always use AFR. The heads will cost $1500 to $2000. I would not want to invest in all of this without rebuilding the engine.

I am assuming there is some wiring to do for hooking up the new injectors?

[Cartwright]

I would do the basic performance mods and some gears.

[95TwinTT]

As I understand it, Genesis, was not looking to sink a lot of money into this project. He inquired about some gain in power to help with towing. Also the truck has 220k on the clock, so that should be kept in mind when making mod’s.

For those that are considering multi-port injection, you need to establish how much money you want to spend ahead of the project.

If you are Normally Aspirated, you must stay focused on the entire package. Any restriction in the air path will hinder the power. That means from air filter to the exhaust pipe. IT ALSO INCLUDES EVERYTHING IN BETWEEN. Like throttle body size, intake path, valve size, cam lift, exhaust valve size, head design, exhaust manifold, catalytic converter, muffler, tail pipe.

It is a combination of all of the elements that make engines efficient. It is also expensive to do it right.

The Vortech heads are pretty good heads to start with. They are mostly responsible for the jump in HP from 1995 to 1996. If you have money to spend, I like AFR heads. ( Air Flow Research). But, they are not going to make much difference without changing the intake, air doors, injectors, etc. You also get to the edge of what the OBD-2 can deal with.

It all comes down to how much money you want to “sink” into your truck. If you are depending on your truck for a daily driver, you might consider just keeping it stock and spending any extra money on making it more dependable.

I have pissed away over $60K just on the drive train of my 95. But, it is my hobby. I will never sell it and it will last me forever. Just 49 ,000 on the odometer so far.

From what I have heard, the performance tune’s can add about 25 to 35 hp, compared to the stock program. That’s about $10 per hp, but keep in mind, that is just going from a conservative factory tune to a “on the edge” tune. Everything was already there to make that power.

From there it will probably cost a lot more per hp. I have paid about $85 per hp so far. Just something to think about. So if you have a good job and income and you are not afraid of the economy being in the tank, grab your checkbook and have at it.

For those that want big power, might I suggest starting with forced, induction. It could save a lot of money in the long run.

[genesis]

Hey all, I appreciate the input. Alot if this is things I know as I am a diesel mechanic by profession, but when it comes that the actual tuning, I am still a newbie.
I was refering to doing a TBI onto a stock vortec intake, but switching to multiport isnt a bad idea either. I do like what theyve done with the engien in the pics, but as I had pointed out earlier, this engine does have 220k on it. I havent done much to it yet due to the fact that it is old and I dont need a high out put motor. on the contrary though my tuck is in perfect condition. a little above the windshiel rust but thats it. So depending on when this engine, or the tranny for that matter decides to take a dump. I will probably rebuild into something with a lilttle more power. for now it is just the conservative hp gain like CAI, exhaust, tune, port and polished heads would be nice as well. I was just wondering if anyone had tried adding the TBI on the stock manifold for the added mean of fuel delivery, especially the guys who have done forced induction.
I asked this especially cause in the next week or so I need to take the heads of to replace the valve guides to due burning oil and I also have the notorious lower intake manifold leak as my coolant is making its way into the oil. And I figured while I was at it, maybe something could be don with the fuel delivery system.
As you all have pointed out, it will not be as easy as I was hoping.
One question I do have is I average about 11-12 mpg combined which to me seems rather low. while I have this all torn apart, I was considering replacing the injectors as Im sure with 220K on them they could be dribbling or sticking and thus be a big portion of the reason as to why my milage is down. are stock injectors good enough for future power gains or would you recommend something a little bigger. remember, the purpose of the injectors is to try and get back to the 15-16mpg I feel I should be seeing.