Mark A Shields

Right now I get 16 mpg w/2:73 gears, if I go to 3:73 gears how badly will that hurt my mpg?

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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
FLOWMASTER
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
2:73 GEARS
Rebuilt 700R4, with manual valve body
B&M Megashifter
Soon to be installed
and Exhaust Cut-Out
"There is nothing more addicting than speed"

Grim Reaper

Something is not right, you should be getting way more than 16 mpgs with the mods you are showing.

I would work on getting your mileage more where it should be..in the mid 20s at least.

FYI, I get US 30 mpgs on the highway with my L98.

Rob P

iTrader: (1)

But Glenn, if this is the Glenn I think it is, don't you have "highway mode" invoked?
I agree, 16mpg is terrible with your mods and 2:73s. I used to pull 30mpg highway with my 305TBI 2:73 equipped convertible. What like 75mph at 2000rpm?
But yes, your mpg will decrease with the 3:73 rear end. How much I can't really say.

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Rob P
89RSconvtZZ4TPI
Edelbrock Hi-Flow Intake
SLP Dual Cold Air Intake
1 5/8" Headers
Semi-Siamesed Runners
MSD6AL/AdjFPR/IROC frnt@rear swaybar/wonderbar/steeringbox/alum drvshaft/ Alston SFC/3:23posi disc rear/MAC LCA/H.Adams Panhard Rod/KYB struts/ shocks/
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

Grim Reaper

You are right Pete, but even before invoking Highway Mode, I still got 25 US MPGs on the highway with my L98 and 3.23s.

Even with a carb, those 2.73s should get him darn close to 23-25 when its tuned right with a 600 CFM carb. And the Edelbrock can be "leaned" a little; which is what Highway Mode does.

Mark A Shields

How do I lean out the carb?

------------------
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
FLOWMASTER
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
2:73 GEARS
Rebuilt 700R4, with manual valve body
B&M Megashifter
Soon to be installed
Exhaust Cut-Out
"There is nothing more addicting than speed"

SUPER-SPORT-CHEVY

You can buy a calibration kit, part number "1487" and go leaner on the rods and jets.

How is your driving style? Your siq says you have a full manual valvebody your shfit points could be decreasing mpg.
you cold also get a carb that has vac secondaries like a holley 600cfm. Edlebrocks like to start dumping some fuel from the secondaires at 2500 rpm, even though you do not feel the 4bbl power.
SSC

Mark A Shields

I don't drive the car all that hard, it's not a full manual valve body, I can leave it in OD and it shifts. Could playing w/ the A/F ratio help, and if so which way do I turn the screws.
I recently went thru emissions and failed big time, one reading was 7x the limit and another 3x, could this be why I am getting horrible mpg, plus I don't have a converter.

------------------
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
FLOWMASTER
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
2:73 GEARS
Rebuilt 700R4, with manual valve body
B&M Megashifter
Soon to be installed
Exhaust Cut-Out
"There is nothing more addicting than speed"

Rob P

iTrader: (1)

If your numbers were 7X the limits, I'd guess and say your are running WAY rich. And yes, this will kill your gas mileage.

------------------
Rob P
89RSconvtZZ4TPI
Edelbrock Hi-Flow Intake
SLP Dual Cold Air Intake
1 5/8" Headers
Semi-Siamesed Runners
MSD6AL/AdjFPR/IROC frnt@rear swaybar/wonderbar/steeringbox/alum drvshaft/ Alston SFC/3:23posi disc rear/MAC LCA/H.Adams Panhard Rod/KYB struts/ shocks/
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!