Since the stock injectors in the 350TBI I swapped in a few years ago have developed a leak, its time to replace them. But, of course, we never just do the quick and easy thing, right?
At this point, I think I'm going with the rebuilt/blueprinted 46mm TBI from Extreme-FI. If I'm reading the posts right, the BB TBI isn't as driveable as the SB (idle circuit differences?), and the Holley 670 seems to have its share of problems too. In either event, with the 1 11/16 bores on my manifold, I'd have to bore to 2" to fit either one. The 46mm unit shouldn't require much more than a slight chamfer to fit, and fits in well with my rebuild philosophy of bumping everything up "just a little bit more than stock", without going "too big" on anything. I'll add an AFPR when we do the swap. My question is, what injector size to go with? The 65#/hr ones from the 'cop car', or the 75#/hr BB ones? Appreciate any thoughts, comments, suggestions.

 

This is going to be your limiting factor, actually it probably is your limiting factor right now. Unless you are willing to spend the money or Ed is willing to burn you another chip for free then don't wast your money on changing the TBI. Anytime you change the size of your injectors, or how the engine ingests air the ECM is going to need reprogramed. The problem with the mail order crap is that there is no way to just guess out of thin air what any particular set of parts is going to need. This is why we harp on DIY chip tuning on this board so much.

With that said, don't waist your money on the 46mm, just wait till you can burn your own chips and buy a BB unit. You'll get the bigger injectors and the bigger throttle bores in one cheap shot. TBI doesn't have an idle circuit per say, at least not like a carb does. They do have an idle air control valve, which functionally are the same between SB and BB units. The reason people say that the SB units run/idle better is because they don't retune the ECM for the added air flow. The beuty of FI is that it doesn't rely on intake velocity to atomize the fuel, so in theory you could run a 100 mm TB and it would work fine on your motor with tuning, it would just reach full power at 1/4 throttle because you don't need the extra air flow. Also the holley TB's are fine as long as you don't get the older units with the black plastic caps on the injectors, they were a cheaper injector and holley has since switched to the stock style delphi injectors.

 

Thanks Monte...there's a lot of good info there. And I had to smile...cause I guess I knew it was all gonna get to the chip. That's like black magic to me...I think you guys do voodoo to make that work. But seriously..yeah, I know you're right. What I was looking to do was set up all my hardware first...the engine's built, I'm planning a full MSD ignition as soon as time/money permits, but TBI needs immediate work...and then turn to programming to bring it all together. Am I backwards? But either way, the leak needs to be fixed this week, and its gonna take a lot longer than that before I'm ready to burn my own chips. So looking just at the hardware now, and planning to replace the TBI (the one on there now was on the junker truck engine we rebuilt...it could have a million miles on it for all I know), any thoughts on that?

 

As long as the injectors don't leak, and the throttle still moves there isn't really anything that wears out on a TB. It's probably fine for now, there is a very real chance that you could make the car undrivable and I can garantee you will hurt performance if you go changing the TB and injectors without retuning.

I can help you get into chip tuning much faster, spend the money you had planned on the MSD ignition on the chip burning equipment. You'll gain 5-6 hp by just sticking with the stock stuff....yep the MSD is worth nadda, zilch, kaka. I've spoke with a few dyno facility operators, and they all say they have gained power or at least didn't loose any by going back to the stock GM module and throwing the MSD in the trash. I don't have any hard before and after dyno sheets so I'm sure some one is going to throw the BS flag. This is coming from people in the industry that know what they are talking about. You don't need ignition upgrades on your stock motor, heck I don't think you need them on an under 6000 rpm NA motor no matter how much power you are making.

 

The wear item on any TB/TBI is the bushing for the throttle shaft. Excess wear leads to vacuum leaks, just like on a carb.

 

Guess I should have said, "moved SMOOTHLY"

 

I did before and after dyno tests on my L03 when the MSD 6A and/or Blaster coil bit the big one, and I went back to a stock ignition. Check the sig for the results.

 

My front-pull TBI is actually leaking right now. With the A/C off in Park/Neutral and the Minimum air rate screw backed all the way out I have an 800 RPM idle with 0 IAC counts. Sprayed a little carb cleaner on the linkage side and it picked right up. The spacer is not leaking, I have done the intake gaskets several times lately as well. I swapped a 4.3 rear pull TBI unit on top with my pod and found that the idle dropped down where it should be.

I always use quality ignition parts be it GM or aftermarket. Steer away from anything Valucraft/Duralast/Bosch/Ultraspark and most other autoparts brands. I used cut to fit Accell 300+ race wires on my 350. It has a MSD coil (stock GM failed). This ignition is adequate for anything you can throw at it and should be for a long time to come. After about 5,000 miles the heat from the van engine compartment/headers cooked the Bosch wire boots, deteriorated them, causing the spark to jump to ground, and severe engine miss-fire.

 

"As long as the injectors don't leak"...well, actually, they do, which is what got me started on all this. So that's something I'll have to deal with. But I like your idea of holding off on any ignition work and getting started on chip burning (actually, I hate the idea...LOL...but that's only because I just don't understand it...can't get a handle on it...and get confused as hell when I try and teach myself the basics by reading the DIY-Prom posts). If your offer to help me get into chip tuning faster is sincere, I'll take ya up on it. I'm a pretty quick learner, just don't have the confidence to go off and start trying this stuff all on my own. And I'm not really in a position to start fabricating all sorts of connectors, harnesses, whatever else I need in the way of hardware (I do, however, have access to a laptop at least!). So what I think would get me started the quickest would be a list of what I need, and the sources to get it, and once that's all together, maybe a nice slow tutorial on how to go about this. If this has already been put together somewhere on a sticky here, I'd be glad to start there. Thanks again.

 

Boy it would be nice if some one put a nice slow tutorial that had a list of all the things you needed to get started along with an example of how to tune a basic bolt on's motor........Ohh wait there's one in the stickies on this board

Check out the "free tune" sticky and see if that helps you. I'm not the best communificator, but it has helped a few people get started.