hi,
i'm no stranger to chevys, but i've never owned a FI vehicle before.
naturally i've got a lot of questions, but i'll try not to get out of control.
my TBI 350 has 240,000 mi. on it and i'm anticipating an engine swap.
i've got a 350 longblock from a 72 monte carlo, i think the comp. is 9.5:1.
i've done some research and it seems like the only reasons it might not work would be,
smog or too high C.R.
i am aware that this engine was not exactly
"made for" my rig, but unless there's someone out there who's tried it with bad results, i'm thinking i'll go forward with this project.
it's got a performer manifold, a 206@.050
comp. cam and headers.
this mill ran great with a q-jet on it in my last pickup.
i'm interested in hearing any feedback, especially from anyone who's attempted this.

 

Stock 305 TBIs are 9.5:1..

 

IIRC the stock 350 TBI CR is somewhere right around there, so it should work fine. If you keep the early model heads it might have a bit more top end but a bit less bottom, since it will be missing the "swirl" ramps.... aaaaawwwww.... actually, I'd expect ALOT more top end, which is where those truck motors nose over.

------------------
"So many Mustangs, so little time..."
ICON Motorsports

 

thanks for your help guys.
i haven't been near a computer for a few days so i couldn't reply.
ends up that there's a goodwrench engine out there known as the H/O T.P.I. that has specs similar to mine, so i can go off that.

the thing i'm wondering is,what did the designers do to my 350 to make it such a dog?
is there a governor on it,or what?
it feels like there is.
i have had this thing run through a diagnostic and supposedly everything is as good or better than it ought to be.
but the performance is not nearly as good as my carbed engine was.
how to fix?
any feedback appreciated.

 

The reason it's a dog is that it's TBI.

The heads are arguably the worst 350 head ever. They are of the "swirl port" design, in which there is a huge lump of material cast into the intake ports to create "swirl" to re-atomize the fuel after it settles out of the air in the intake tract like it will always do in a wet system (like carbs). They did this primarily for emissions reasons.

A 72 350 motor is no example of performance excellence, but it should run a whole lot better than the garbage that's in there now.

------------------
"So many Mustangs, so little time..."
ICON Motorsports

 

thanks again RB,
it sounds like you know more about this stuff than i do.
i' ve been doing some browsing and theres definitely some interesting stuff out there.
any chance i could shoot you an e-mail or two?
i've got some decisions to make before investing in parts (or labor) and my local parts guy isn't all that knowledgeable.
i've never owned a chevy that wasn't smog exempt, and i know what i'm looking for but i dont know how to get there from where i am.
it's also helpful yhat you're from cal. ,
maybe you can point me in the right direction, or know someone who can.

a lot of the messages i've read point to the fact that guys are into using smaller cams than they used to and turning good times
and getting good economy to boot.
that's pretty interesting i've always been into the small cam / tall gears approach.

so is it the fuel metering , the spark curve, or what? that needs to be corrected
to make this thing work?
or is the TBI a lost cause?
is there a regulator that is connected to my speed sensor?

well thanks, and i'll let you know how things are shaping up if you're interested.

solong

 

TBI itself isn't all that bad, but the factory's implementation of it is. It's supposed to be a sort of intermediate step between carbs and port FI, at a far lower cost to build. Look at the parts count of TPI compared to TBI and you'll see what a difference it is.

As built, it is incapable (without the "tweaks" that impair performance) of delivering the kind of emissions numbers possible with port FI. It suffers from all of the same fuel distribution and atomization problems as carbs, with the slight improvement from the fuel being forcibly sprayed instead of sucked. If you could undo all the little goofy things the factory did to it trying to satisfy the smog *****, it wouldn't be near as bad as it is. You could put the TB and injectors on top of a much freer-flowing intake, re-program the computer to make it aware of the flow changes, and in theory get a pretty powerful motor. In practice though I've never really seen it work very well beyond just a slightly modified motor, which yours would qulaify as. If you build the motor as you describe, you should have a far better-running piece than what came in the truck.

For an example of a fairly cheap-to-build port system that actually runs pretty good, look at a Cadillac V8 like a 4.9.

Feel free to e-mail me, I'm not going to promise that I can help out much, but I'll try. There are also a number of people on the TBI board on this site that might have a few tricks that would help you out. One thing that I can tell you about that will improve your build, is getting a good 4-barrel intake, and mounting the TBI on an adapter.

------------------
"So many Mustangs, so little time..."
ICON Motorsports

[This message has been edited by RB83L69 (edited September 05, 2001).]

 

that's some good information, rb, thanks.
i was looking for a sign as to which approach i should use in building my new motor;
the totally illegal yet user-friendly and paid for (carb).
the legal yet gutless (tbi)
or expensive and exotic (tpi)
the computer erased my reply to your message while i went to double check my password last nite. i'm going with the carb.

it's good to know that my tbi can be bolted atop a performer manifold using an adapter, thataway if i should find myself in the mood, i can tinker with it, cause that's what it sounds like it takes to really get it dialed in.
and i'll be saving my $ for a tuned port if i decide there's a need to get more serious.

meanwhile, if anyone has any useful info on how to improve the part throttle response of a tbi, feel free to contribute.

i am in the middle of performing the ultimate tbi mods.
gotta get back to the shop, i'm makin' a spacer.
by the way, those gasket kits are expensive for a tbi. i suggest pricing some before disassembly.

later