what kind of gas mileage are you mildly modded 350 third gen's getting??? I have TPI right now, but I want a carb and a T56 tranny...I just want to make sure i'm not gonna get like 10 miles or less to the gallon if I switch to a carb...I would probably add a mild cam in there too, not anything too drastic, but enuf to tell a difference...adn will the T56 help gas mileage or hurt it??? I can control my foot too so that should help out a little bit...

 

my goodwrench 350 with a holley 4150, 600cfm msd, headers new bowtie 700rf and 308 rear i get 19 around town and backroads. when i had a t-5 i could only get 17. of course i can get it into single digits sometimes.

 

I have a 350 with Dart IE 200's, 10.5:1 comp., Edelbrock Performer, Edelbrock 1406, Comp XE 268, with a T5 and 3.73's. With no fine tuning, I get 20 mpg on the hwy and 18 mpg of city/hwy mix. Now if I lean on the loud pedal too much, it drops severely. I still need to tweak my timing curve and rejet the carb a couple steps leaner and I'm sure I can pull a consistant 20+mpg city/hwy mix. I drive 200+ miles per day, so fuel mileage is somewhat a concern, as long as I get close to 20, I'm happy.

 

A friend of mine has 84 z28 with an 11:1 406 with a comp cams hydraulic roller cam with a tremec t5 and 4.11's that can run 11.5 in the 1/4 mile and gets 20mpg on the hiway.

 

my vortech headed 284 xe cam th 350 camaro got 18 on the highway........and about 6-8 on the street! it aint too bad , it ran 7.99 1/8.

 

If your carb is working right, you'll get good mpg. Especially with a mild build and high gears.
I had a Chevelle with a 210*@.050 int dur cam and a stock converter with 3.08 gears and it got 20-23 mpg hwy.

 

Most you can really expect with a mild 350 carbed engine is 20 to 22 mpg as most people have mentioned. That's about what I get.

However, a TPI motor should be able to pull considerably more...as much as 6mpg, particularily in mountainous terrain. TPI shuts off all fuel flow on downhills, whereas carbed cars do not. This can really add up on a long haul.

Now I'm a carb guy...but I'm going to make a suggestion. If you're going to have a fairly mild engine and want to use the T56, then keep the TPI. While a TPI engine can run quite happily at 1,500 rpm ( or lower ) at cruise ( typical with a T56 in 6th ) a carbed engine will not. You simply will not have enough booster signal. Gets worse if you add a cam.

TPI's limitations are if you want to run some higher RPM. The TPI setup was originally designed for the 305. They run out of breath around 4,800. On a 350, the runners are so small that the engine will hit the wall around 4,200 to 4,300. Sounds like a good reason to ditch the TPI......not so fast. The REST of the system is excellant!! In fact the factory GM computer is far superior to most aftermarket systems. It has a lot of " Hidden " features that most people are not aware of. Including a " Highway Mode " that goes into open loop. Can enable you to run very, very lean under ideal conditions...18 to 1 A\F or leaner. GM never enabled it because it is " Open Loop" and it would not pass EPA's 50,000 miles stress test. To do that you need to be in closed loop......but the code is in there. You just have to have a very Smart " Chip Guru" to burn it and play with the values. Also factory Computer has some interesting " Data logging" that most people are not aware of. Depending on year, 5 to 8 minutes of Real Time Data logging...including engine RPM's, what gear car is in, amount of throttle applied and the usual stuff such as temps, O2 reading and spark curve.

But I digress..... IMHO you should keep your TPI if you're going to drive the car on the street and build a fairly mild engine. Then save up your money and buy a Holley Stealth Ram intake system. That one change will make an incredible difference and I believe that you will be happier in the long run. Gas ain't getting any cheaper!!. The Stealth Ram can support high RPM motors, big cam motors as well, so you've got room to play if you really want to build some HP.

You've got the rest of the system already in place. IMHO it would be a backwards step to go to a carb. Just my .02c

Edit: Spelling

 

yea i thought my car was realy outta whack, because when i first got it, the guy said he just replaced the plugs the same day we came to pick it up...so i figured the plugs were good...so i spent 450 bucks on a MAF and a new computer, because it actually had a 5.0 computer in it and no sensor for inlet air...so it still wasn't running the best, so i got a new cap, rotor, and plug wires...it ran a little bit better, but not the way it should....so i was bored 1 day in auto class and desided to take my plugs out.....well i got half of them out no problem, the other half were so brittle they broke, and i looked at all the plugs when i got them out, there was 3 differnet kinds, 3 different sizes!!! some were long, some were short...so i got new ones, and she's runnign pretty good now, and i took it to a mechanic/buddy and he said thats abotu the way a TPI should run, he sadi they run a little bit rough, and i guess i was expecting it to run like a newer engine....so i'm satisfied with the TPI now, so I think i'll just stick to the FI and get a 6 speed..less work for me, and it sounds like its the better thing to do...thanks for all the input...

 

Go and get a GOOD fuel injection cleaning. BG Chemicals has one of the best systems on the market. Only one approved by BMW and Mercedes. They have a direct feed system that plumbs into the fuel rail. Some professional shops have these as do most dealerships. Well worth the money. Amazing difference. Removes ALL deposits from Injector tips. BG also has a "Pour in Tank " cleaner ( BK44 ) that is one of the best on the market. Not as good as the Direct feed method, but a can of that every 10,000 miles or so will really help to keep deposits off the injectors.

http://www.bgprod.com/home.html

 

those 20mpg are highway miles right?
cause i have a mild 305 600cfm carb and i think i get 10 or so street i dont do much highway driving.

 

i know we have all the plumbing and stuff to do that direct feed cleaning at school...I know my teacher has some bottles, but I don't know which brand it is..where can i get this BG chemical stuff from?? I'll have to do this before I put it away for the winter...or should i do it in the spring instead??

 

Do it in the spring when you can get out and drive the car after cleaning. The BG website has distributor locations listed:

http://www.bgprod.com/bgdistloc/distloc.php

 

Yeah that is highway. You should be able to get a lot more out of that 305 even in stop and go than 10. Much of it comes down to how rough you are with the go pedal. Now that I have disconnected my faulty MSD, I am seeing almost 12 mpg city with my Q-Jet'd 383 and 3.27 gears. I am pretty conservative when I drive though. I also hit 18 mpg on a highway trip with no OD! Woohoo! We'll see if things change when I put on the Holley shortly.

 

well i have 3.73's in the rear so even od doesnt do much and i dont do much heavy traffic driving. but im usually on that peddle too.

 

I have a 1986 trans am with a 1969 chevy 350 with around 420hp and a 700r4 trans with 3.73 gears while running on 215/65 r 15s on front and 275/50 r15s on rear, if I baby the car I can get 12 mpg on highway but thats also if I stay right at or below speed limits. I have never checked the city mpg , and I cant guess. I put it this way on mondays when my butt is dragging to work the car gets better milage, but the closer I get to the weekend the milage starts to drop.

 

My old 85 Z28 with a 355, 700R4 4.10s, Edelbrock 600cfm carb + all the standard bolt ons got 450km (about 285 miles) per tank on the highway. When I installed the 4.10s and took out the stock 3.08's my in town milage got better. I could get another 30 or so miles on a tank with the 4.10s than I could with the 3.08's

My 91 GTA with a 355 using stock items, is hard pressed to get 350km on the highway. I'm sure prom tuning could get that up a fair bit though.

 

My current setup - 24.6 Highway and around 12 city (thats just a guess, the highway is exact) - and that is with a 750 Holley...and its running RICH!

When i had my carter AFB I would get 19mpg at my very best...

 

id like to know wat ur guess would be on my gas milage iam planning on gettin the gm goodwrench 350 for my 91 firebird switchin from a 305 im putting on the 305 heads goin 3 inch hooker exhaust and headers, edolbrock 600cfm carb, performer rpm intake manifold, K&n open element ( i have a functional cowl hood) under drive pullies i plan on puttin higher gears right now its stock and puttin the trans-go shift kit on my 700r4 wat do u think will be my mpg??

 

What kind of carbs are being run on the cars getting 20 mpg...Lots of different variables being talked about and it doesnt add up...Also those that are giving horsepower #'s, how did u come up with them..are they a guess or can you back it up..Just has me wondering about the setups that are being run..its been my experience that a carb set for horsepower wont get the best fuel mileage...and vise versa...

 

My quadrajet carbed, performer rpm inducted, ported 305 headed 355 G20 Van was getting 17-18 MPG on the highway and about 15 MPG average. That was with a 700r4, 2,000 stall, and 3.08 gears.