I'm planning to build a 350 from the ground up to basically drop in my car (losing the EGR and AIR stuff), but I wanna keep using TBI for mileage and other EFI-pro reasons. I havn't decided whether to add a blower into the mix or not yet. Would it be easier to plop a Holley Projection TBI on top and tune the stock chip, or to get something like the Commander 950 that's meant to be user-tuned?

no emissions (yay for MO), for use in a daily driver so I prefer something that'll be (relatively) quick to get running right

 

You can get better then stock performance and functionality by going to UTBI or a PCM. The U-TBI costs alot less then the projection, and the PCM costs practically nothing. Be aware taht with the holley TBI, its not a direct swap and the bracket is different, which can cause issues with the TV cable geometry and line pressure. The best would be a stock 2" TBI and GMPP manifold bored to 2". Not the best manifold out there, but its a direct swap and wont require extensive tuning like an unheated aftermarket carb manifold will.

 

I'm doing very much the same thing, so this is great info.
But it raises some more questions.
"UTBI" -- what is it, & where can I get more info?
"holley TBI, is not a direct swap" -- precisely what are you
referring to here? I've seen the Projection (usually 4 bbl
config?) units, and their TBI replacement units. If I recall
correctly, the Projection flow capacity wasn't that
impressive - like 650?
"stock 2" TBI" -- More detail please. I thought the biggest
available from GM was (1 15/16?) on the 454 truck engines.
One option I've considered is the XtremeFI modification
(2" bore, etc. etc.) that claims 750 cfm.

The RBob EBL is a definite in the plans, so any recommendations
can assume that control system.

I never cease to be impressed by the expertise on this board.

thanks,
kk

 

The UTBI is RBobs EBL.

Holley TBIs as well as the big block TBIs have 2" dia. bores. These flow around 650 CFM, which is enough for most street motors. I have one of the larger TBIs on my 350, and the most I see is around a 1 inHg pressure drop through the TBI. Unless your planning a high winding 383, the 2" TBI should be sufficient.

 

Dimented & Rbob

Great comment.

I do not want to steal this thread, but I am throwing couple of questions into the mix.
Background info:
I am in a process of retrofitting TBI system based on 1227747 ECM (’90 Suburban) and factory harness into my 75 C-20. All sensors and actuators are retained from Suburban donor. I am also using a four wire NBO due to headers.
Retrofit plan is to install Holley 300-49 manifold in place of factory Q-Jet cast iron manifold. Holley (300-49) manifold is machined to accept 2.0” TBI throttle bores. In reference to your previous post it is not the best intake to use, but it avoids non heated manifold issues present with Air gap style manifolds. In my particular application the engine will never see the back side of 5000 RPM. I need a low end grunt to move 4800 lbs from a dead stop!
My current engine is a near stock 350CID coupled to a reworked 700R4 with Holley Spread (4175) bore carburetor. It took couple of weeks and several calls to Bowtie overdrives to get right brackets. Original Q-jet would not allow for Bowtie overdrives adaptor CAM (for TV cable) to bolt on – the throttle plate has a different shape. Go figure!
I have been reading 3rd gen and DIY EFI boards with great interest for the last six month while planning this retrofit. Carburetor combo runs OK, but this carb was specifically calibrated as Q-Jet replacement for 74-76 350 SBC. In my opinion, spending $350 for 4175 (0-9895) is not worth it. It is time for this carb to go, since I want better overall drivability. Future plan include replacing tired 350CID with warmed over 383CID (building it right now)

Questions:

I have a GM Throttle/TV cable bracket which came of 1989 TBI 5.0 L Caprice – will it work with 300-49 Holley manifold and a factory SBC TBI unit (450 CFM with 5.7 L Injectors (Black-Orange))? Bracket uses two rear manifold to head bolts to stay put.

Starting point is a stock 7747 ECM with ASDU, ARJU, and several other calibrations are available. For near stock, circa 1975 350, it should be a good starting point, or should I get EBL to begin with?

Since this is a truck application 383 CID will be build with a focus on low end torque (1800 to 3500 RPM range). Building plans call for 185 cc after market heads with a matching cam. Not sure which one to select at this time. Comments, suggestions recommendations?

383 CID will require serious ECM reprogramming. Should I get BBC TBI (injector size?) unit along with a corresponding ECM equipped with EBL mod (WBO should make tuning task easier a bit easier)?

Conversion devil is in details…

Sorry about a long rant.
RFmaster

 

U-TBI? PCM? could I get a bit more info on those, I searched them and got a butt-load of dead ends. maybe examples? I figured it would be easiest to get the Projection intake manifold. and as for the bracket, are you talking about these?

Holley TH700R4 Kickdown Bracket



Now you can use virtually any Holley Pro-Jection system in a GM vehicle equipped with a TH-700R4 transmission.


510-20-96 2-bbl TBI w/OEM Manifold
$19.99

510-20-97 2-bbl TBI w/Aftermarket Manifold
$44.99

overall, I'm really just worried about the tuning part, is tuning the chip and system that's in the car more difficult than a system that's meant to be tuned? if the Commander system is really that much easier, I might just spring for it (saving money for a month or two extra doesn't bother me; gives me time to keep thinking) as long as it gets good results and gets me on the road faster. I'm still trying to decide whether or not to get a blower, don't know how much that complicates things...

 

I've been pondering the TBI question for quite awhile.
Demented's reply (whose experience & reputation on
this board is highly commendable) has convinced me
that it will adequately support a strong streetable 350.
The implementation specifics remain.
So consider my
The Holley 2 bbl TBI series may be 2" bores, but they
advertise flow ratings max 650. I've heard other
comments on the board, of minor linkage problems.
Check-out the XTremeFI products on e-bay. I'm
happy with one of his Vortec products, & he seems
like a reputable merchant. He claims possible 700 cfm,
and his info seems reasonable. Do your own cost
comparisons. Manifold choices: Edelbrock 3704's
(good comments available, ebay-able in the $150 range),
the Holley unit and GMPP (not familiar with either) will
all have to be bored to accomodate a 2'' tbi. ECM &
tuning: I think RBob's EBL package may be the best
money spent in the entire project. I've discussed
my plans with him, and he is willing to include a
"starting point" chip with the EBL. And his tech
support will be "priceless".

A blower? Probably not the best idea for a daily
driver. especially without significant experience
of the devices.

Good luck, keep us posted.

 

Travlr

I bought Holley 300-49 TBI intake (SBC for pre 85 heads) manifold for my retrofit project. Holley uses this manifold for its Projection system?? I have measured intake bores to be around 2.030 inches. So, a stock SBC (BBC as well) TBI throttle body is a direct bolt on. However, I have not put my TBI system together yet, but I can take pictures of mock-up assembly if anyone curious. The only reason I chose 300-49 because it is a heated manifold (there is an EGR cross over passage) since TBI is a ‘wet’ manifold system. A heated or perhaps I should say a temperature stabilized manifold allows for easier fuel mixture tables. There is a very interesting thread that outlines issues relating to this issue (Rbob, Dimented).
Does anyone have experience with a stock SBC TBI and 300-49 feeding a lively 350??? BTW, I am still in a plumbing mode – bringing feed and return lines from my tanks.

RF