I thought TBI ran on 12 to 14 psi pump? TPI is 40 to 50 psi. Are you going to regulate this?

 

I'll give the link a read.

In the quotes, that was all very much over my head. I'll have some more patience on this, and I'll let the thread ferment for a few days and see if I can pick up any more opinions on the matter.

if all else fails, I'll just chuck a blower on a crate SBC and call it a day lol.

 

I assume I would have to.

 

If you use a tpi pump, the cfi regulator will still keep it down at the 9-13 psi range. Excess fuel will be sent back to the tank through the return line. I can adjust mine from 4-18 psi or so, at some point above that the regulator is over adjusted & the pressure spikes to 50psi.

 

^Exactly. Someone w/real experience, speaks. OP, listen to this guy.


Right. Problem is *****, it's been done too many times and worked too well, (by folks who've done it) to be "poo-poo"'ed by the ECM tuning snobs, who haven't done it. Know who I mean?

I know how engine controls work. I agree that "it is always wise to tune the system" -that is stating the obvious. It's a red herring argument.

Is it Necessary to meet the criteria? No it is not. It may be the "best" way, but I and others have proven that it certainly isn' the only way. "Hill billy" or not, my way worked and cost less too.

 

Clarify that, please. "Very sensitive to change"...what does that mean, precisely, w/regard to the OP and his mild mod plans? Please speak from you CFI modding experience, using real world examples, would you? Thanks!

 

These thread alwasy go to ****, when non CFI people start posting...acting as if they're some kind of authority on the thing...then say things like:
"my head starts swimming about 2 TB vs 1"

Yikes. That should be a red flag to the OP. 2 TB's mounted separately on the plenum is functionally no different than 1 TB assy, that has two "holes" in it (two throttle plates), be it a MPFI like TPI, or a CFI compared to a standard 2 bbl TBI truck motor. A TB is an air valve and that is all it is. Doesn't matter if they're next to each other on the same shaft or mounted on opposite sides of the plenum. The stock CFI throttling system functions exactly the same as any other GM TBI: it has two injectors, one TPS, it has two IAC's that are controlled by one driver...as far as the ECM is concerned, it doesn't "know" or "care" that the TB's are in separate castings.

Changing the ECM and making it tunable is certainly desirable....everyone would surely love to do it that way, w/unlimited time/ resources. I sure would have like to. But, the realities of real life, time/money frequently limit the scope of our projects and so we have to get creative as to how we manage them, in order to meet our criteria.

Guys, CFI/EFI did a massively ported stock intake, cat back exhaust, "free tuning" (the very same tuning that Mr. *****'s lambasts), and a converter. His car would run in the 13's at sea level. His money invested was nearly nothing. Car idled like stock, driveability was like stock (only more so), RPM range was extended 1000 RPM, fuel mileage remained "like stock " ~24 hwy. What criteria was he missing out on? Something, I'm sure....but something insignificant.

Then there is me; I started w/an '83 Trans am, 305 CFI/auto. I changed it to a stick, did the "free mods"/tuning to the stock engine, added Edelbrock "tubular manifolds" and went 14.5/95. The CFI TA was originally a mid/high 15 second car. I went 14.5//95 doing the changes MR. *****'s call's "hill billy".

I put in a 350, made appropriate changes and enjoyed that engine for a few years, then put in a SBC 400, ported the intake, bored the TB's installed a 224/234 cam, headers, exhaust, roller rockers...among other things. Running on the stock ECM/chip/tune, that car would go low 13's/105ish. Car idled like stock, driveability was like stock (only much more so), RPM range was extended 1000 RPM, fuel mileage remained "like stock " ~24 hwy. What criteria was I missing out on? Something, I'm sure....but something insignificant.

Tuning is the best way, but not a necessity when keeping things (especially the cam) mild. This is from a guy who has done it.


.

 

When the wife was in her C3 mood, I did some asking around. Naturally I went towards CFI because it was not a carb. Talked to a few performance shops to discuss options. Basically, "With money, all things are possible". They did say that dollar for dollar, they thought I'd be better off in a TPI car based on the work required and the time spent.

 

I certainly miss "CFI-EFI" and the ole "RACE ON" ..............

There's over 10 pages of threads where "CFI-EFI" was a participant. Many very good reads - all interesting - some locked LOL

A search from "SEARCH THIS FORUM" button above "THREADS/POSTS" using the "ADVANCED SEARCH" and user "CFI-EFI" will surface them. Good reads and many smiles!!!

Use this link to search from, it will collect all C4 sub-forums

https://www.corvetteforum.com/forums...-1984-1996-19/

That is the best place to originate any search if it's C4 related .. covers all sub-forums.

 

Okay. So what i get from that is, i should update the regulator too?

And if i update the fuel system with a higher pressure regulator and the higher pressure pump, what would be the next step from there?

 

I know you werent exactly responding to me, but ive gotta ask. So youre saying getting a tuneable ECU is advisable, but not necessary for a mild mod setup like I'm going for?

I apologize for my ignorance, this is my first build and my biggest learning experience so far and its a tad overwhelming for the moment.

 

I will wear tuning snob as a badge of honor. Yes, I make things run to the best of its ability instead of best guess.

 

lsx swap.

the low revving intake is an issue.

 

Yeah, you need to mod the regulator. On the rear throttle body there is a plug that needs to be removed/drilled out, this give you access to the screw that puts tension on the regulator spring. Threading in increases pressure, threading out lowers it. The problem is that when the regulator is installed the adjusting screw is facing down requiring a special J adjusting tool or remove the pod, adjust & retest.
When I first got my 84 years ago I was trying simple things to improve the performance, this was before the internet forums & the vette mags were useless, I made up an open air filter set up for each tbi. Even on a warm summer day that thing would sneeze every time I accelerated hard, telling me it was running lean. I did not know about the fuel pressure mod. The car was stock at the time and ran fine with the stock lid on it.
I think your first step is to get a die grinder & get to work. That's the most bang for the buck mod on a cfi engine.

 

I understand the desire to keep it stock looking but you really are tying one hand behind your back keeping the TBI injectors. These were GM first attempt at electronic fuel injectors and they are pretty bad. Be careful adding fuel pressure, they will become erratic or stop working completely with fairly modest pressure increases. That can be overcome with a higher current driver. They are also not very consistent injector to injector either so make sure you buy your high flow injectors from a good injector shop that can send you test data for the actual injectors you buy. I second the idea of using a Megasquirt but unless you can find someone else with a good map starting point you are looking at doing a LOT of tuning.

 

All I know is NOT to try and swap he front and rear TBI units, they need to remain where they are. The fuel pressure on an 84 is the same as for a carb set up, the TPI uses much greater pressure.BTW, My wife is from NSW

 

EX-X-fire has put up another very good post. Pay attention to what he has written.


I sure miss him too. He was a good man.


That is exactly what I'm saying. I'm not saying you should do it MY way. That's the only way to do it. -Like other posters are; I'm saying that you CAN do it that way, you CAN meet your criteria that way....it's YOUR CHOICE, which way you decide to go. You could:
*Do it the...ahem, "hill billy" way and enjoy it for years, as CFI-EFI and I (and others) did, successfully
*Do it the...ahem, "hill billy" way in the short term, then later find a tunable $olution as funds/time present themselves
*Go all the way at one, build an engine, decide on a tuning/engine control system, then buy that and tune.

Some posters are saying "it can only be done one way" "Any other way is wrong". I'm telling you, from 1st hand experience, that isn't true, and I'm telling you, not to convince you to do it the way that *I* did, but rather so that you're enlightened and you can make a proper, informed decision for YOU.

Low 13's, 24 mpg, stock like idle and drivability. IDK what others' criteria is, but at the time, that was mine and I met it with a stock 305 ECM/chip/tune.


Criteria *****. Meet the criteria.



That seems a bit absurd in this thread. OP wants to spend, what, ~$1000? and put in maybe 10 hours of work to get some low hanging fruit from his car? And you're suggesting a fairly radical engine swap (one you haven't made yourself, I might add) to achieve some preconceived RPM? What RPM? A well ported CFI intake will make useable power to ~6000 RPM on a 350. What RPM is "the right one"?


Absolute and complete HOGWASH. Cite your source. Clarify, precisely how those injectors are "pretty bad".


More total horse ****. The injectors are way better than good enough, to make for a great street driven car. Are you aware that those very same injectors -the ones you say are "pretty bad, stop working at modest pressures, not very consistent"...those same injectors have been used in marine application Chevy V8's, at pressures up to 30 PSI (not that one needs to run those pressures in a car to meet the criteria) while making over 300hp? And they have been used as OEM marine equipment right up into the late 2000's? That's over 25 years of OEM automotive and marine use. They may have some shortcomings, but none that matter to guys looking to add a cam, exhaust and ported intake to their car! In fact, based on my own experience, I'd say that they're far more reliable than other GM OEM injectors (cough! multec cough).


Actually carbs typically run 5-7 PSI or so....TBI spec in automotive form is 9-13 PSI -about twice that of a carb.


.

 

I've been designing gasoline fuel injectors for 32 years and I've also tested and torn down nearly every design ever manufactured. I've got multiple fuel injector design patents and my designs have been used in millions of automobiles and motorcycles. So I have a lot of good hard evidence when I say the GM "Maxi Injector" is one of the worse ever made. It has a huge amount of moving mass and a very slow magnetic circuit. The dynamic range of these injectors is pitiful, about 4:1. I've seen some of these completely stop working at 15 psi. I can tell you for a fact that a dozen new old stock injectors will have a lot of variation in flow. They might have been better 32 years ago, IDK.

We supply some of the marine engine builders and I'm very unimpressed by the quality of their engineering. Way below the standards of automotive OEM's. The fact that they kept using such a lame system for so long does not surprise me. This system has one positive attribute, it's cheap because you only need one or two injectors and a relatively low pressure pump. Yes it's good enough for it's day. That does not mean it's very good.

I will agree with your snide comment about Multecs I's, not to mention the CPI and SCPI abortions Delphi foisted on millions of unsuspecting SUV and truck owners. So maybe I shouldn't say the Maxi TBI are the worst injectors, Delphi did make some crap!

I'm not telling the OP not to follow his pursuit of higher performance with the cross fire TBI, just point out some potential pitfalls.

 

Doc,
Tom is abrasive at best and doesn't play with others.

 

The product you're calling "trash/next to worthless" is the TBI-400 SO.. maybe expound upon your design "at the same point in time" - what were your designs on at the time in a "multiple configuration? The TBI-300, TBI-500 and TBI-700 were 1-injector TBI also in about the same '82 - '90 time period. You were doing what specifically? If GM was so bad in the era and you were GREAT treat us to the "on what". I don't know that anyone was spectacular at the time BUT I don't know you or the what your product was on.

Toss out some Patent#'s - tell us about yourself - if you're GREAT introduce yourself.

Model #'s of your '80+ adventures?