BOTTLEDZ28

iTrader: (9)

I have a 91z28 with tpi and need a new project and more HP so I am really thinking of tossing the tpi and ECm for a carb setup this winter. Here are my questions:
What did you all do with your stock wiring under the hood. what can be tossed and what has to stay?
How do I keep my electrical speedo working with my T56?
Do they sell a bracket to mount my throttle cable on the carb?
whats the best fuel pump route to go with ie inline or new pump in tank?
What are all the small set backs that I will incounter along the way?

Yes have read the tech article on this but I still have tons more questions I just want you guys advice on parts and stuff

Jester

A vast majority of the stock wiring harness can just be cut out. A carbed engine needs 2 wires for the dist, 3 for the alternator, and thats about it. count on a couple extra wires for optional stuff, temp sensor, choke, etc.

Your stock cable can probably be adapted, but it's easier just to get a new cable. They're $30, plus $5 for a bracket, and about 20min to change out.

I personally hate in-tank pumps. I say get either an inline electric or a mechanical.

Odyssey

I have a 92 Z28 that's carbed. KEEP your in-tank pump. A lot more reliable and easy to do than an in line or mechanical pump. Mine has over 100,000 miles on it and it still works just fine. Not many inlines can do that. lol

BOTTLEDZ28

iTrader: (9)

Odyssey, I have a Holley in tank that I just put in. I would rather keep it there in case I ever decided to go back to TPI. what do I do get a low PSI fuel pressure regualtor? I would like to get more info from you on your change over since you had speed density like me. also, do yo ulike your setup? I have no clue on what setup to run. I am dump when it comes to carbs. I want to switch over and get more knowledge of it tough

Jester

You can do it that way. The cheapest/easiest regulator you can use for that is made by Mallory. The one thats a 3 port w/ bypass, I think it's about $80.
The next one up is wayy more expensive.

fakezcar

I would personally recommend leaveing the harness the way it is and just disconnect what you don't need off the intake. That way when you're dissappointed with the fact that it doesn't start or run the way you want (if it's a daily driver) you can put it back to FI. I personally cut my TBI harness for the same idea, and unfortunately I don't have a speedo when the lights are on etc. (a lot of little bugs). You also won't have a coolant sensor if you cut wires because it is sent to the computer before it goes to the dash. If you want more details about my wiring issues you can pm me or e-mail me @ Cdflyer14@aol.com. That way I can give you a little more indepth idea of everything I've gone through with getting mine running...

Crazy2.8V6Man

Why would any one want to go from a TPI setup to a carb one. I have a carb setup and woud love to goto a TPI.

1991tealRSt-topGuy

TPI lack top end power
TPI is very restrictive above 4500 RPM
with a carb you have more freedom to run an extreme cam
no PROM programming

need more?

88IROC350TPI

I took the group of wires going to the computer, held my breath, and cut them. Then I took every wire out of their plastic tubing and traced every single wire I had cut. To my suprise everything worked. I even ended up cutting out most of the wires/relays on the driver's side firewall.

bhaas

Hey Jester, what regulator is that? Can it be boost referenced? I have a carb setup and have been trying to figure out a fuel system for it. I'm putting twin turbos on it and need it to be boost referenced. Thanks.

Brad...

jwfirebird

iTrader: (2)

i had a mpfi 2.8 in my car and i swapped in a carbed 305. i put in a holley duel port regulator (summit# HLY-12-803 $21.95) one out to the carb and one i put a gauge in.the fuel line into the input of the regulator and capped the return line. I put a switch and relay in the car to power up the fuel pump.its been running like that for 2 or 3 seasons. I also got a HEI from a 70's small block to get rid of the computer controlled ign.i dont know about the guages all of mine are aftermarket.

Berlinetta00

For the edelbrock conversion on my 84 berlinetta, I just did the same thing as these guys are talking about, except in reverse. Because I had the digital dash with all optional gauges, I wanted to make sure all of them worked. The oil pressure comes off the back of the cyl. head (sort of) on the drivers side firewall. It is the sealed single prong connector. The water temp is a coralation of three sensors, I belive, one on the block (drivers side, under the #1 and #3 plugs), 1 on the water neck or intake, then one on the radiator. The Tach is on the distributor, and most of these wires go into the dash via the harness on the passenger side under the fender (where the antenna would be). Trace all of these, as well as any sterio wires and accessory wires (DO NOT forget the heat control wires, espacially if you live somewhere cold). Whatever is not the wires you want, cut. If one you cut turns out to be one you need, splice it back together. If you only cut two at a time, then check all your systems, you will help yourself greatly.

-Berlinetta00

x5finger

I hope "have read the tech article" means you are reffering to 5finger.8m.com/tpi2carb/tpi2carb.html


Be that as it may, here are answers with quotes from the page:

"Do they sell a bracket to mount my throttle cable on the carb?"

HLY-20-95 (15$)
Needed bracket for Holley + 700r4
(also see my page for 2/3 studs you need.)

"whats the best fuel pump route to go with ie inline or new pump in tank?"

The site details several of them problems I had with the mallory regulator. Mine was junk, but that may not be consistent with everyones experience. Anyone used it themselves w/o problems? Also, I hear you can just disconnect the in-tank one and suck fuel through it, but no personal experience.

"What are all the small set backs that I will incounter along the way?"

Also detailed on my site, plus you have the fun of the stuff that runs through the computer. It would be cool to take apart your guage cluster and put aftermarket units in the stock location. Thats what I'd do, anyway.

You will also want to read my site for all kinds of good info, such as why the old HEI in a roller cam block is probably a Bad Idea.

Unless you get a bigger cam and heads, the biggest restriction is more those other items. Scott 88 GTA says he's running 13.4 with edelbrock heads, slp headers, ported stock tpi, and the stock prom. That'll beat a lot of Ferraris.

The search button is your friend, and you won't believe the benefits of speanding a little time with your friend.

As always, the above is IMHO, and your mileage may vary.
-5finger

82-T/A [Work]

I would REALLY like to know....

WHY WOULD ANYONE... want to go from a TUNED PORT INJECTION set-up, to a Carbureted set-up?

People pay thousands of dollars to get a multiport fuel injection set-up like the TPI for their small block Chevys in aftermarket.

I honestly can't see the logical reason for it.

Sure... comparing a PERFECTLY tuned carburetor set-up with a nice Edelbrock or Holley, the carburetor might have a little bit more top-end. But there's nothing that says you can't simply go to a better TPI plenum and intake.

What kind of modifications have you done to your engine? They can't be THAT significant that you're bottlenecked by the TPI unit? This has to be the stupidest thread ever. No offense, but dude, REALLY consider NOT removing your TPI set-up. That ODB-1 TPI set-up is one of the most reliable computer set-ups to date.

They sell tons of aftermarket parts, larger throttle bodies, larger injectors.

Listen, have you considered porting and polishing your stock intake yet?

Todd,
1997 Pontiac GrandAm SE
1987 Pontiac Fiero SE / V6
1984 Pontiac Fiero 2m4 SE WS6
1981 Pontiac TransAm WS6 (350sbc)

Timmys88Z

Well since I just started thinking of doing the same.....I'll answer.

Yeah sure, we could upgrade the TPI stuff and there is a lot out there but it seems like going with a carb costs about 1/3 LESS and achieves the same goal.

Ha...yeah I ported and polished my stock intake, a whole lotta nothin' that did.

82-T/A [Work]

Hey Timmys88Z,

Not to undermine your experience, just curious (don't know if you've done this or not yet), but have you installed a higher lift camshaft yet? Because if not, what makes you think that it's the TPI unit that's restricting the flow of your engine???

Honestly, I would first blame your camshaft. Replace that first before you go hacking away your TPI wiring.

Listen, you guys scrapping your TPI set-up would be like if I decided to remove all the fuel injection stuff in my 1997 Pontiac GrandAm and replaced it with a 2-barrel carburetor.

PLEASE guys, think about this first. Unless you're putting out like 350+ horsepower, I seriously doubt that your TPI is what's restricting your engine.

bluegrassz

iTrader: (3)

Well, I am looking at 475-500 hp with a carbed 383. It wont be a daily driver, just on occasions. No I dont wont to get into prom burning. And yes the parts for FI is way to expensive.

So you see there is reasons to change to carb. It all depends on what you are looking for. If you are looking for mpg then yes stay with FI. If you want power and not a drained wallet then go carb.

I got a used Team-G intake for 75 bucks, a holley 750 dp for 125. I found a used Accel Dist for 75 bucks and can get the regulator for 80. So this is alot cheaper than a set of runners, intake base, set of injectors, bigger TB, or even a Stealth ram system.

Not trying to be a azz hole about it, but there is logical reasons to go carb. Its alot cheaper to pull 6000-6500 rpm with a carb than TPI.

Timmys88Z

No I haven't done it. And you're right in stock form I dont need it. But I am thinking that I can add cam and heads down the line and I will have the intake already there. And I am thinking that putting a good carb on it has a lot more potential than the stock TPI. And lets see.... if I can switch to carb for around $200, sell the TPI for $200..... I'm even. And not to mention all the cash it would take to upgrade the FI parts, new intake, chip, injectors..... all expensive.

iroczrockz

OK I have a stupid question. What if money was no object? Just pretend. Lets say money is no object and you want to drive the car daily and you want good power (350hp or so), which is better? Would you get a stealth system or a big carb set up? I am not trying to prove any point I am just curious which is better.

BOTTLEDZ28

iTrader: (9)

Money is the object here. money is what makes the world go round. You guys that say why change over, put togheter a good flowing tpi setup and add the total price of it out and figure out how much more horsepower you will get. now put togheter a carb setup that will get you the same horsepower level you got from the tpi setup and add the parts up. Wow, somehow you now have a lot more money in your wallet. for the price of a 52 or 58MM TB and tpi intake, you can get a cam, intake and carb for less. unless someone here can garrentee me an honest 400hp with a tpi setup that turns at least 6000rpms before it dies then I am still switching to a carb.

82-T/A [Work]

I guess there's nothing that we can do to convince you guys otherwise..

How about this...

WHY Not first get the cam-shaft, get the 1.52:1 roller rockers, replace your heads, and THEN when you've done everything else, then change to a carburetor.

Until you've done all that, your TPI unit won't be what's restricting your engine.


Listen, it's ***-backwards thinking to replace the TPI. Why would you replace the TPI unless it was actually what was restricting your motors? Neither of you guys have a 400+ horsepower 6000rpm beast engine. So why on EARTH would you want to pull your TPI set-up NOW? That's crazy.

Honest opinion, I think you guys are dying to make your car go faster, and you're honestly expecting that this little mod will make your car go faster. What makes you think that if you guys don't have the guts to go ahead and change out your camshafts.. what makes you think you're going to ever do it?

I bet one or both of you guys are going to rip out the TPI set-up, go out and get an Edelbrock carb and a new intake.. you'll have problems starting, the engine compartment will look trashed, and the car will run like **** until you decide to junk it.

Inwo

Because that would be a waste of money... Get a "computer friendly" cam with the proper amount of overlap duration etc so the computer doesn't think think the car is in the process of exploding, try in vain to tune it, realize that the engine falls flat on its face regardless of what you port at around 4200-4500rpm, then say "gee I guess I shouldn't have listened to that guy who has never swapped in a carb before." I guess if you have a whole bunch of money laying around that's a pretty good option. However, if you aren't mister moneybags it's a heck of a lot better to just get a carbed setup and have FUN with the car. Engine compartment looks trashed?? WTF?? Do you even know what you're talking about? Have you ever actually SEEN a properly done carb swap? Do you not realize that there is basically nothing in the engine compartment after the swap? You don't have to chop any wires, you can take the harness out completely intact then sell it to some guy who wants to turn his performance car into a nice slow daily driver.

88IROC350TPI

I gained almost 3 tenths just converting to carb without ANY other modifications (stock heads/cam, 3.27 gears, full exhaust). TPI was designed for the 305 ...it'll be a restriction on ANY bigger motor.


Does my engine bay look like crap? I couldnt even see the valve covers with TPI now I can tear my entire motor down in an hour taking my time.

RB83L69

Yeah, the usual reason people do that, is so that they'll have a chance of going fast. A good case in point: the ZZ4. This is the same short block and heads that goes in a 350 Vette TPI (except that the crank is forged, which doesn't make any difference to the issue at hand). As a ZZ4, it makes around 355 HP. As a L98, it does about 240. Does anyone detect a pattern here?

This is not to say that a carb is superior to FI in general, only that for going fast, TPI sucks.

I gotta agree about the wires, it is totally unnecessary, and just generally not very bright, to sodomize the car by cutting any of them. The ECM harness is a complete, discrete thing all on its own, that isn't required to run anything else in the car, and can come out completely intact down to every single wire and connector without ever picking up a pair of dykes. I de-computerized my 83 so I could put a bigger motor in it, including completely removing the harness; then when I moved to California, I was able to set that harness right back in place without any hassle at all, everything hooked right back up like it always had, so the car sailed right through CA smog. Even if I had a TPI car and did a carb swap on it, I would make every possible effort to retain every piece of the OE thing intact, for just such a reason; I had no idea in 92 when I did the swap above that I would be taking a job that would land me in California in 2000.

88IROC350TPI

I tried my hardest to get the entire harness out intact but just couldnt do it ...I got completely lost in the mess of wires so I figured I could always go buy a new harness if I ever went back to fuel injection.

bluegrassz

iTrader: (3)

What kind of et's are you getting with your setup?

82-T/A [Work]

Listen, let's not get confused. I fully understand
what you're saying about getting a higher top-end with
a carburetor.

But lets be honest, how many of the people who do this
swap really remove the TPI harness and everything intact?

By the way, I'm not saying that decomputerizing a car is bad,
I'm stating specifically that de-TPI-ing a car is bad..
not BAD, but a bad choice when your engine probably
isn't even putting out anywhere near 300hp.

Obviously, if you swap a STOCK TPI set-up with a
performance 4-bbl carburetor set-up, you're going to
get a bit more performance. But you're losing all the
benefits of the computer controlled TPI set-up.

I personally have de-computerized a car, two in fact.
A 1982 Pontiac TransAm that had a computer controlled LG4
in it, and a 1981 TransAm that had the exact same motor,
a 305 LG4 with the ESC (Electronic Spark Control).

I converted both of them to carburetors. One, (the 82)
I dropped in a Holley intake and a Holley 600cfm 4-bbl.
The other, my 1981, I dropped in an Edelbrock Performer
Intake, and an Edelbrock 1405 (converted to 1407) 4-bbl
carburetor. And that engine is putting out over 350
horsepower.

However, I have a LOT of experience with Throttle Body
Injection, AND Multiport Fuel Injection (TPI) as well
as Sequential (port) Fuel Injection, and I know very well
benefits of a computer. TUNING a computer controlled car
is NOT hard AT-ALL. It's easy as crap.



Listen, all I'm saying is that for those of you here who
DON'T already have a 300+ horsepower engine, think twice
about what you plan on doing. Make sure you're doing it
for the right reasons.

And by the way, I've replaced stock cams with "computer friendly"
cams in many different fuel injected cars, and I've never
had a problem. Everything from the small block chevy,
to the V6/60, to the Iron Duke/Tech-4.

bluegrassz

iTrader: (3)

so 82-T/A [work] what you are trying to say is that if you are building a 350 or less hp motor than stay with the TPI. But if you are like me and going for 475-500 hp and not a daily driver then carb is the way to go. Money wise that is.

then yes I would agree with you. Dont get me wrong, I like my TPI system, and may use it in a older car someday. But to get a TPI system to support 475-500 hp would cost a fortune. If I did go FI it would be the holley stealth ram, But then you would have to figure in all the cost along with it to upgrade.

When it all boils down to it, If you like to tinker with carbs, and your car is not a daily driver, then carb is the way to go.

If you drive your car a long distance to school or work everyday, and are looking from mpg then FI is the way to go.

Just a reminder, Look at the Hotrod Power Tour. How many of these guys run carb and drive across the country in various conditions. Just a thought.

82-T/A [Work]

bluegrassz, yes, you summed up my opinion EXACTLY.

88IROC350TPI

Haven't ran it at the track yet. I'm hoping for 12.7-13.0. When the car was TPI powered with just headers/catback the best it ran was 14.5 @ 93mph. I converted to carb and it ran 14.2 @ 97mph.

Pony Killer

TPI is fine on a 350 that's slightly modded.

But once you start trying to make it doe things it's not intended to do, IE make horsepower, instead of midrange torque. The whole purpose of it being there is defeated, sell it , cover your losses, and buy something more suited to your desired powerlevel.

if you've got a hardon for fuel injetion, go that way, if you've got a hardon for a carb go that way, but there's no glory in the self abuse of trying to make a stock induction system do something that it can't.

evil t/a

ALOT! And some of you guys seem to think that long distance driving , idling in traffic and starting cars on cold days just came to exist with MPFI. You dont seem to realize that there were millions of cars with carbs that did the same driving , same idling and start up on the same cold days that Todays fuel injected cars have to do.

Anyone that thinks that you cant get a carb car to idle , start or in general right wonderfullly is a dunce and should not be allowed to touch any car.

82-T/A [Work]

EVIL T/A, there is an ENORMOUS difference between a FACTORY Rochester QuadraJET and a Holley Eliminator carburetor.

jwfirebird

iTrader: (2)

the holley is more easily tuned than an emmisions style rochester

fuel injection just became popular in the last two decades but has been around for long time they must not have had too had of a time making carbs easily drivable

88irocz350- tech inspectors dont give you a hard time about that hole from your heater fan? i only got away one week with out covering that up

evil t/a

Is that right? I run a Holley 750 on my TA , and I ran a Holley 650 dp on my 85 stang , and Holley 600 VC on my 67 stang and they were both daily drivers. And my T/A makes the 70 mile one way trip to work in LA traffic every single time I need it to. And you are right there is a difference between a factory quadrajet and a Holley , the Holley can be made to run better.

Lastly do you think that every carb car has had Qjets on it? You do know that alot of cars came stock with Holleys , Carters and other carbs right?

Inwo

Of course not otherwise he wouldn't have made such a broad generalization.