anyone who is afraid of EFI-to-carb swap - Carburetors - Third Generation F-Body Message Boards

Token · 08-23-2005, 11:27 AM

I would just like to let you all know that I get 17 miles per gallon with my built 350 in average city/highway combo driving. Yeah, I have 2.73 gears, which makes a difference, but I am getting nearly the same mileage as my old 305 TBI got. I have a higher stall converter, also. You can see all of my mods in the signature. Just wanted to let you all know.

About 13-15mpg strictly city, and about 20-22 mostly highway (no lockup switch)

Also, I noticed an increase of 1mpg when I switched from standard 10w40 to Mobil 1 10w30.

EPAisGAY · 08-23-2005, 01:19 PM

I actually used to get 25+ mpg highway w/ my 305 TBI and 3.23s. Now I get ~21mpg w/a 350. You might have had something wrong w/your old setup if you only managed 21mpg.

BTW I got about 21mpg w/3.23s and now 20.5 mpg with 3.73s on the highway. If I were you I'd get 3.73s

Token · 08-23-2005, 05:30 PM

Quote:

Originally posted by EPAisGAY
I actually used to get 25+ mpg highway w/ my 305 TBI and 3.23s. Now I get ~21mpg w/a 350. You might have had something wrong w/your old setup if you only managed 21mpg.

BTW I got about 21mpg w/3.23s and now 20.5 mpg with 3.73s on the highway. If I were you I'd get 3.73s

When I can afford it.

<--- college kid living on his own, working for $7/hr

zoomzoom26 · 08-24-2005, 09:45 PM

I have a 305 TBI right now with 3.23, stock th700r4. high flow exhaust and cold air intake, and i get like 22 average driving, and like 25+ highway, looking to do 350 tbi swap now.

mw66nova · 08-25-2005, 11:40 AM

my 310/700r4 w/ lockup/4.10 rear with the old holley 600cfm vaccuum secondary netted me consistant 22mpg on the highway. about 15 in town. WAY better than todays big SUV's!

Fast355 · 08-25-2005, 05:20 PM

My TBI 305 (well really 312) with a 700r4 w/2,000 stall, and 3.08 gears gets 17-19 city and 22-24 on the highway. This is in a 5,000+ lbs G20.

Token · 08-25-2005, 08:14 PM

Quote:

Originally posted by zoomzoom26
I have a 305 TBI right now with 3.23, stock th700r4. high flow exhaust and cold air intake, and i get like 22 average driving, and like 25+ highway, looking to do 350 tbi swap now.

CaptPicardsZ28 · 09-04-2005, 01:51 AM

LOL, my setup nets me 9/10 mpg.......and I love it!!!

Supervisor42 · 09-04-2005, 05:40 PM

Token:
I really enjoyed your audio clips in your sig. "Exhaust clips: idling (130k) revving (100k) lopey! (160k)" Thought I'd share mine:
Idling and reving (4mb)... and yes, that is a quadrajet.
Specs for the engine are in my post on this page.
Haven't gotten around to checking the mileage yet (keep doing WOT blasts) but I think it isn't going to be too good...

specvgini · 09-10-2005, 05:02 PM

What did you do about your higher pressure stock fuel pump when you switched to carb on your L98? i really don't wanna pull mine out and i'm looking for alternatives. i tryed turning it off and using a 4psi pump further down the line but that didn't work cause the new pump couldn't pull fuel past the old one. so can i leave my stock pump in and maybe get a fuel pressure regulator to turn it down a whole bunch?

Token · 09-10-2005, 05:13 PM

Quote:

Originally posted by specvgini
What did you do about your higher pressure stock fuel pump when you switched to carb on your L98? i really don't wanna pull mine out and i'm looking for alternatives. i tryed turning it off and using a 4psi pump further down the line but that didn't work cause the new pump couldn't pull fuel past the old one. so can i leave my stock pump in and maybe get a fuel pressure regulator to turn it down a whole bunch?

specvgini · 09-10-2005, 05:49 PM

nice. you have a part number? is that just a standard fuel pressure regulator? how much did it cost you?

85z28guy · 09-11-2005, 03:58 PM

I'm guessing that is more expensive then this one from holley, it was $75 Cad http://www.holley.com/products.asp?product=12-803BP .They aren't a standard regulator, being that it has to have a return line. A lot of them out there are just one in, and two regulated outs. You need one in, one regulated out, and one just out.

specvgini · 09-11-2005, 04:13 PM

so i'll be using my return line in my car then? also how about the computer? will the stock pump work without it?

85z28guy · 09-11-2005, 07:42 PM

Yea you will have two fuel lines buy the drivers side fender well. One will be 1/2". the other 3/8" I beleive. It was awhile ago, but I think the larger one was the return

The regulator is all marked, just don't overtighten the lines in. I just took the regulator and lines to Brafasco and Cummins hydraulics, and they made everything I needed with all the fittings for me for like $20. Things may be a little different for you, but I just took out ALL the wiring from the passenger side, including all the wires to the ecm. The fuel pump will not work, I just wired mine to a switch that I put in the ash tray (no one ever smokes in my car, ever). This is very easy since the wiring for the fuel pump is right behind the back seat if you lift the carpet. I beleive the pink wire was power, but use a test light to make sure . The best way would be to wire to a oil pressure switch, but this way if someone steals my car they won't get very far

Also, depending on year you may need to grab a vss box from a wrecker to get your speedo working correctly.

specvgini · 09-15-2005, 02:17 PM

ok i just got back from my local car shop. they are prett reputable, and the guy there said that going that rout wouldn't be good because the fuel pump will burn out.. i've been trying to figure this out for a long time now and all signs keep pointing tords pulling the damn pump out. so i'm gonna just do it and get it done. now my question is whats the process of bypassing the old pump? just a straight hose?

NastyL98_T/A · 09-15-2005, 07:57 PM

It will work, but the right way is to get an external electric pump. Not to mention the stock pump flows enough for 240 hp..

my3rdgen · 09-16-2005, 08:37 AM

Is the intank pump on the q-jet equipped 3rdgens the same as the tbi pump? I am asking because I replaced my mechanical pump with a Carter OEM replacement fuel pump, and I chucked the CC q-jet in favor of a q-jet from a 78 Z28.

It was running OK till I hooked the power to the fuel pump back up. Now its rich enough to melt your eyes out.

I have checked the return line to make sure it wasn't plugged. It was OK.

Purple82TA · 09-16-2005, 10:04 AM

i got like 8 mpg in the city and about 10-12 on the highway with my old roller 355...

redbird_400 · 09-16-2005, 11:26 AM

Quote:

Originally posted by Token
When I can afford it.

<--- college kid living on his own, working for $7/hr

yea.. and when gas is 7 dollars a gallon... lol Anyway, go work for a parts store if you have an interest in cars. They need younger people with a will to learn rather then old dogs that cant learn new tricks. Check the vendor review board for details. OR! if you know computers, get a tech job that starts at 11+hr with no experience.

For the topic, my 305 got 20mpg when I did a carb swap. But yea, the 650 is to much for it, even with smaller jets. Its all I got and I'm replacing the engine before I replace the carb!

specvgini · 09-21-2005, 04:48 PM

Ok i'm still freakin lost about this whole switch over. i'm reading what u guys post and what ppl tell me around town and everything contradicts eachother. this is what i've gathered:

By removing the intank pump and ecu i won't have gauges that work properly.

If i geet a pressure regulator and keep the stock pump i was told that would burn the pump out.

And i can't leave the in tank one in and run another down the line and simply turn off the intank...

i would like to do this the way its supposed to be done. and everyone says thats to remove the intank pump. well then how do i get the gauges to work correctly without using the ecm? cause the whole point is to get rid of all that. my main question is do i need a completely different sending unit or something from a carbed car? i donb't under stand how the intank pump is bypassed...

five7kid · 09-21-2005, 05:02 PM

You're taking what has been stated that was wrong and corrected by others as the facts, in most cases.

- The gages don't feed through the computer. No effect.

- If you keep the in-tank pump operating, you need a regulator that includes a built-in return, i.e., that regulates pressure by returning excess flow to the tank. That type of reg will maintain a constant flow through the in-tank pump, keeping it cool and keeping it from burning out.

- At least you got one out of 3 right, which is acceptable in baseball. Although some have reported leaving the in-tank in and unpowered without problems, the wise course is to remove it if you aren't going to use it (use it or lose it, you know).

- To by-pass the in-tank, remove the sending unit, remove the electric pump from the sending unit, add line to extend the pick-up tube down to where the in-tank pickup was, put a pick-up strainer on it, reinstall the sending unit.

85z28guy · 09-21-2005, 05:02 PM

Gas gauge is not ecm controlled, atleast my 85' wasn't. Fuel pressure is a sender, just keep the old one. Tach will work. Coolant will work if you keep the sender. Voltmeter will work. Only problem you may run into is needing the vss for your speedo, try it and find out. The thing about removing the pump or not is personal opinon. I have seen A LOT of people do it, and not seen one fail. In fact, a discussed it with a couple mechanics and they said it seemed like a good idea. Its up to you if you think its "right" or not. And no, I would never cut a hole in my trunk to get to the sender

specvgini · 09-21-2005, 05:05 PM

i'm in the process now of removing it its just a tremendous pain in the ***. now what your saying has been done a million times i would imagine so i'll take your word for it. thanks

Purple82TA · 09-21-2005, 10:54 PM

mine still has the in tank pump, i've been running a mechanical on the engine sucking through it for 5K miles without any problems...

i just don't have the time to drop the tank.. it looks miserable on these cars

specvgini · 09-23-2005, 05:23 PM

its terrible

Purple82TA · 09-23-2005, 06:41 PM

Quote:

Originally posted by specvgini
its terrible

well.. since it's not going anywhere untill next spring i might give it a try.. but i have a feeling that my dual exhaust is gonna get in the way