SBC mileage build

[formula95]

I have a 355 1st genSBC and I want to build it towards fuel mileage. Since it's going into a light 80 Monza(2900pnds) 25-30 highway mpg and 13.9 1/4mile is the goal. The car is going to see travel on gravel and mud, so the car has big suspenion(IROC springs, look big in the Monza), big tires and small wheels(24560r14, 21560r14's). I'm not sure if my goal is obtainable with a carberator. Does anyone know what a good setup for decent mileage would be for carberated motor? It has 3.08 gears and will be getting a 5 spd from a f-body(anyone know the final gear ratio for that trans?), I'm thinking cheap alum heads, RPM air gap intake, not sure about carberator yet. Also I don't know anything about 3rd Gen F-body fuel injection, I hear the TPI has decent torque, so that would probably help mileage, I also heard good things about vortec heads. With that I would have to change the gas tank, add some sensors, and computers too. This car is going to see alot of hwy km's(3-5000km's a month 4 5months of the year), so maybe fuel injection is the way to go? Sorry about the lengthiness of this post, but Any help is appreciated.

[Upinsmoke]

This would be the perfect ride with an LT1/6 speed, they are easy to get, fairly inexpensive and with a 2900 lb car the performance you want and the mpg would be there with the stock setup. If you really want to go with the early SBC then I would go with the fuel injection setup for the mpg. Either way it is going to be a fun car.

[five7kid]

The Performer RPM is a high-powerband dual plane intake. If you want torque and economy, you want the "plain" Performer. And you don't want the Air Gap, that's for high-density air/fuel charge, again for power, not economy.

The only carb you should consider is a spreadbore - either a q-jet, or Holley 6210.

Wide tires and fuel economy don't go with each other, either.

TPI is probably the best capable of producing low-RPM economy. You wouldn't have to change the gas tank, just put in an in-line electric pump. You will have to add sensors, the most difficult would probably be the VSS (but it can be done).

You want to keep everything mild - small intake ports, small valves. Aluminum heads don't fill that bill. Vortecs are close, but still have relatively large ports and valves. 305 heads would be more like it, and TBI swirlports are probably the best choice.

As for T5 gear ratios, borrowed this from thirdgen.org:
Model Yr...Engine(s).Input....Speedo.......Ratio........ Model # (BWA)
1983........2.8 V6......14............7..............T5E.78......1 352-015
1983........2.5 L4......14............7..............T5H.73......1 352-027
1983........5.0 V8......26............7..............T5G.73......1 352-028
1984........2.5 L4......14............7..............T5K.72......1 352-054
1984........2.8 V6......14............7..............T5E.78......1 352-061
1984........5.0 V8......26............7..............T5G.73......1 352-062
1984 1/2..LG4/LG9...26............7..............T5G.73......135 2-070
1985........2.8 V6......14............7..............T5P.76......1 352-071
1985........5.0 V8......26............7..............T5U.63......1 352-072
1985........2.5 L4......14............7..............T5R.72......1 352-083
1985........2.8 V6......14............7..............T5S.73......1 352-084
1986........................26............7....... .......T5V.61......1352-150
1986........2.8 LB8.....14............7..............T5P.76......1 352-156(aft)
1986........LG4/L69....26............7..............T5U.63......13 52-157
1986........L4 LQ9......................7..............T5R.72.... ..1352-158
1987........LB9 308....26............9..............T5U.63......13 52-166
1987........LB9...........26............7......... .....T5U.73......1352-178
1987........V6............14............7......... ......T5P.76......1352-181
1987........LB9 308....26............9..............T5U.63......13 52-182
1987........LB9...........26............7......... .....T5U.73......1352-183
1987........V8.............26............7........ ......T5U.72......1352-185
1988........B9 5.0L.....26............7..............T5U.73...... 1352-175(wc)
1988........LO3 5.0L...26............9..............T5U.63......13 52-176(wc)
1988........LB8 V6......14............7..............T5P.76......1 352-177(wc)
1992 1/2..LB9 5.0L...26............7..............T5U.73......13 52-212(wc)
1992 1/2..LO3 5.0L...26............9..............T5U.63......13 52-213(wc)
1992 1/2..2.8 V6.......14............7..............T5P.76...... 1352-214(wc)
1992 1/2..2.8 V6.......14............7..............T5P.76...... 1352-228(wc)
1989-92...LB9 5.0L...26............7..............T5U.73......13 52-195(wc)
1989-92...LO3 5.0L...26............9..............T5U.63......13 52-196(wc)
1989-92...LB8 V6......14............7..............T5P.76......1 352-197(wc)
1993........3.4L V6.....26............7..............T5Z.72......13 52-210(wc)

Speedo info
7=Purple Speedo
9=Red Speedo

Ratio........1st.............2nd.........3rd...... ...4th............Rev.......5th
T5E..........3.50...........2.14.......1.39....... .1.1............3.39......See
T5G..........2.95...........1.94.......1.34....... .1.1............2.73......Ratio
T5H..........3.50...........2.14.......1.39....... .1.1............3.39......Column
T5K..........3.76...........2.18.......1.42....... .1.1............3.76......Above
T5P..........4.03...........2.37.......1.49....... .1.1............3.76
T5R..........3.76...........2.18.......1.42....... .1.1............3.76
T5S..........3.50...........2.14.......1.39....... .1.1............3.39
T5U..........2.95...........1.94.......1.34....... .1.1............2.76
T5V..........3.35...........1.93.......1.29....... .1.1............3.15
T5Z..........3.75...........2.19.......1.41....... .1.1............3.53

[formula95]

I have a Q-jet already, so i'll probably go that way to start. I have a dual plane wiend. And I'll save some cash till I find a tbi or a Lt1 6spd(still kinda expensive up here)

Any views on Gen1 tbi into my 95 Lt1 f-body. I read about a carb swap, and it sounds like it would be alot of hassle changing the gauges, again fuel tank issues, motor mounts, headers, drive shaft, rad, and distributor. If my LT1 6spd got pulled for a tpi auto/5spd, about the electronics. Would the gauges on the 95 work? if not I could swap the dash and computer.

Vehicle Speed Sensor, is that on the tranny like the old cable style speedo, but digital? If so it'll give an reason to replace the 90mph speedo!


thanks again

[five7kid]

I can't see changing an LT1 to TBI - serious downgrade. Change the whole engine, maybe, but the LT1 is the superior engine in every detail.

The VSS was used in two different places, depending upon year - the early versions had the VSS on the back of the cable-driven speedometer. Later, they went to a direct transmission-mounted VSS, and actually changed the speedometer & odometer to stepper motors driven by a VSS module under the dash. The speedometer type is dependent upon the drive type (cable or electronic), but the max indicated speed of the speedometer is not.

When converting a non-computerized vehicle to closed-loop EFI, there are aftermarket adapters out there that will give you the VSS signal while retaining the cable driven speedometer.

[formula95]

I can't see changing an LT1 to TBI

i love the lt1 in my firebird! the car is good too. But fast is my thing and, if it were pretty easy to swap it with a tbi, i could drop my lt1/6spd into my Monza:eek:. Then get a tbi for my 355(original motor for the monza),a big cam, and headers. Put that in the firebird, then it might still run with a stock lt1 fbody and, my monza might see 12's(with traction) and 25mpg.:devil:

[95Formula]

This would be the perfect ride with an LT1/6 speed, they are easy to get, fairly inexpensive and with a 2900 lb car the performance you want and the mpg would be there with the stock setup. If you really want to go with the early SBC then I would go with the fuel injection setup for the mpg. Either way it is going to be a fun car.
whats up there buddy?

[Upinsmoke]

I know you, your the one with the bad ass GTO and your crazy enough to be in Iraq also. Talk to you tomorrow!!!

[edd gordon]

Last Spring I sold My 68SS Camaro I had a 406 Small block with 441 Casting Heads with 2.02 intake valves-Comp Cams 268XE Cam and an Edelbrock Performer RPM intake and a Holley Avenger 660 Carb and Hedman Header -4 Speed Muncie M20 with a 3:42 posi rear. I got 17MPG combo City and Highway and ran Mid-High 12s with Street tires in 70 degree weather. Just some info for thought