About what kinda gas mileage could i expect going to TPI vs a carb? I'm running a 350 mild cam stock heads that I'll probly port or replace with better ones and I might move up a little on the cam.
Thanks

 

My 5spd Z gets a pretty decent 16-17mpg it seems. Highway just a little over (the gears hurt). I used to have a tbi which resembles a carb and I got really bad gas mileage w/same headers/catback and basically same tune up. I think my RS got around 13-14mpg maybe even 12.

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1990 G92 5spd LB9 - 3.42 80,000 miles

Accel Ignition/Wires (8.8mm), Advanced Timing, TB Bypass, Ported and Gasket Matched Plenum, Synthetic Motor Oil, 160 Thermo, TPIS Airfoil, K&N Air Filters, Centerforce I Pressure Plate and Clutch, Edelbrock TES Headers, Dual Cats, Edelbrock RPM Series Catback, Homemade Ram Air, Bosch +4 Platinum Plugs

14.4 @ 94mph w/2.0622 60ft (w/o headers and catback)

14.426 @ 96.19mph w/2.167 60ft(w/headers and catback)

 

I went from about 17mpg to 23mpg by going TPI. Same engine, heads, The only thing I did was install headers the same time I went to TPI. I am running a 3.73 gear as well. If I went to my stock 2.73 gear I would go up to about 26mpg. Of course this all goes on a 311 SBC engine. (040 over 305)

See sig for all my mods.

John

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87 Formula Yellow/Black
Engine & Transmission
.040 over 5.0 converted to TPI, 9.5:1 Compression, SLP Cam Dur 206/212, Lift 480/487, Cent Line 112, SLP headers, SLP cat-back exhaust, K&N Airfilter, Modified Stock cold air intake, Ported & polished Stock TPI intake, Holley Adjustable Fuel Press regulator, AC Rapidfire Spark Plugs.
Gil Younger (no yo-yo) Shift Kit, Aluminum Driveshaft, 3.73 Posi gear
Suspension & Brakes:
Baer 12" brakes 4 wheels, KYB AGX Adjustable Shocks & struts, Hotchkis strut tower brace, South side machine frame connectors, Custom reinforced control arms and pan hard bar.
Interior:
Custom Leather interior, CUSTOM Yellow Gauge Faces, Kenwood Receiver, Pioneer Speakers, Kicker Substations, Kenwood 10 Disk Changer, Pioneer Amp.

87 Formula TPI (5 Speed) Yellow/Gray STOCK

1967 Buick Riviera 430hp Turns high 14's (Not bad for 4300 lbs)

83 Camaro (Parts)
83 T/A (parts)

http://www.3rdgenformula.com

 

I take it you're both running overdrive? I'm running a TH350 without OD and 2:73 gears and get about 12 tops with a carb. So is it probly worth it to put on TPI or no IYO?

 

It's not worth it just for the gas milage. Although it will be better, you will see a bigger gain by going with an overdrive tranny. If you are looking for overall better drivability and cold starts, etc., then go for it.

Depending on how modified your existing engine is, the carb will probably make more power than the TPI, unless you do some porting and use aftermarket runners and maybe an aftermarket base.

That's why I say it might be wiser to use an overdrive tranny.

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89 Transam GTA, 350TPI, auto, 3.27 rear, dual cats, gray.
Magnaflow cat-back,
K&N open element,
Best E.T. 14.63@95mph

 

my car gets less then 12 and all i have is a stock 350 truck engine in a 87 camaro with a
edelbrock rpm intake and carb with headers

 

I get about 150 miles to a full tank

The car is in good tune, and runs very good otherwise. I estimate around 13-15 MPG. I think its due to the stall converter...I don't drive in OD until speeds over 55mph.

Anyways...am I missing something



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Mike L.
It ain't pretty.......

1987 IROC Z TPI 350 A4 3.27 Borg-Warner.

Mods: 2300-2500 Stall Converter, Shift Kit(GM parts), TPI Specialties Stage 3 PROM, Modified Airbox w/ K&N's, homemade cold air, Relocated MAT sensor, Gutted MAF, 160* thermostat, Accel 8mm Wires, bypassed TB coolant, Flowmaster 3 chamber single 3" in/out muffler, 3" MAC mandrel intermediate, custom dual !cat Y-pipe. airfoil, ported plenum. !smog

http://www.MichaelLasiuta.home.att.net

**BOYCOTT LAPEER DRAGWAY**

 

Definitely an overdrive will help with gas mileage, but tweaking the eprom can also help.

Before getting into eprom burning, I was getting 23-24 US MPGs with my basically stock L98 with 3.23s. By invoking "Highway Mode" in the eprom and playing with it (adjusting the speed where I prevent unlocking the TCC and the spark tables), I now get 28-30 US MPGs.

BTW, waiting until 55 mph to switch into OD is burning gas needlessly. Just leave it in OD and let the transmission shift into OD when it wants (just above 40 MPH IIRC).