About a week ago I had a 350 GM Goodwrench installed in my 86 IROC, I kept the same carb, intake, and fuel pump.
Mods include, Edelbrock TES Headers, flowmaster, Accel HEI Dist., underdrive pulley, KN airfilter, and all emissions crap has been removed.
The car has 2:73 gears, but OD doesn't work, with the 305 I had in it I would get 14-15mpg, but now I am getting 10 mpg, any ideas.

 

did the overdrive not work before? if it did, that's definitely the problem. Otherwise, I would check the timing and you may need to adjust the carb to adapt to the larger engine. Keep in mind, you are feeding 45 more cubic inches so you are going to use some more fuel. Just a fact.

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Kyle Osterholt
Okarche, Oklahoma
ASE Master Certified
86 T/A 383 TPI
89 TTA #1002 T-top/Leather
89 TTA #1358 Hardtop/Leather
80 T/A Pace Car
73 Opel GT
73 bronco

 

The OD has never worked since I got the car, and I do realize that I am feeding a bigger motor, but it is definately in better running condition than the 305, the guy who installed said he advanced the timing, but I am not sure how much though.

 

Have you still got your ecm? It control the locking of the TC. If you don't (and I suspect not or you'd be getting SES codes), you should wire in a TC switch to lock it. Also, if you have elecric fans, you should wire up those too. This is something people forget about when they dump their FI (and ecm) and go carb.

Also, besides a larger engine you also have a new engine which tends to be tighter. They tend to burn more gas when they are breaking in and will loosen up a bit as you drive more miles.

 

My ecm is no longer hooked up since I got the new distributor, the car was never FI. My egr is also blocked off and the service engine soon light is coming on, does this mean that the ecm is still engaged. Also I don't have an electric fan. I hope the engine breaks in soon because I can't afford 10 mpg.

 

Geez, even if the tranny won't shift out of Drive (into OD) with 2.73's, you should still be doing much better than 10mpg's, and should also have been doing better than 14/15mpg's with the 305.

This just the base Goodwrench engine?

I'd be thinking about a few things..one, is the tranny slipping? If it's not going into OD, it may also be slipping.

Next, look at the distributor, make sure you have the vacuum advance hooked up, and it's operating correctly...and that your timing is set properly.

The only thing left is the carb, form the motors point of view.

Also, thinking about it, you should check the exhaust for restrictions as well, crushed pipe, bad cat or crumbled muffler can restrict the exhaust, and kill MPG's and performance too.

 

The exhaust should be fine, the cat is off and I have a flowmaster, I know the tranny could be factor but not that big of a factor, I'll check the vacuum advance once it stops raining. I guess I will just wait and see if the motor loosens up and gives me better gas milage.

 

With headers, even a small difference in camshaft duration can hurt fuel economy significantly. Do you know the specs on each camshaft?

Another point I have to bring up being a carb-lover. The same size carb on a larger engine will almost always run richer than before. Unless you enlarge your air-bleeds in the carb, it will meter in more fuel with the increase in signal at the boosters. A larger engine would create a richer A/F ratio.
This is why many people actually run quicker with a larger carb.. not so much from more air to feed the engine, but because it leans them out at high RPM.
You may be able to lean out your primary circuit a bit to recover some mileage.

other than those things, there are many other possibilities.

Running to lean will also hurt fuel economy but to a lesser extent. You would normally feel a drivability problem if you had lean misfire.
You are more likely too rich than anything.

ODB

 

The cam in the motor now is 195/204 nothing that should hurt gas milage.

 

nope that shouldn't be hurting it. Did you check your valve lash?


[This message has been edited by The ODB (edited February 25, 2001).]

 

I'll second that

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--Steve S--
1984 Trans Am 305 LG4, 5 speed
Daily Driver, Flowmaster 80 Series
NOW FEATURING: Holley 600 cfm & vacuum advance

 

There shouldn't be anything wrong w/ that, it is a brand new GM Goodwrench 350. I've read that when you have a new motor it will be tight and get bad mpg, once it loosens up it will improve, ever heard of this, could this be the case.

 

sometimes fresh engines will run a little rough, a little hotter, and get bad mileage until the rings are completely seated.

You could do a compression check to see how the rings are doing.

I would still check everything else to be sure.

 

every goodwrench motor I've installed had no problems with gas mileage or anything. I would definitely be inspecting the timing and carb adjustments. I'd also get that tranny fixed because maybe it is slipping and the old motor wasn't strong enough to force it where the new motor has sped up the deterioration with it's increased power and you're starting to see symptoms. Just a possibility. if the converter is not locking up, you can be sure you've burned up the clutches in the tranny because it is designed to be locked up and because it is slipping it has overheated.

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Kyle Osterholt
Okarche, Oklahoma
ASE Master Certified
86 T/A 383 TPI
89 TTA #1002 T-top/Leather
89 TTA #1358 Hardtop/Leather
80 T/A Pace Car
73 Opel GT
73 bronco

 

Wait... You have an 86 carb, and don't have the ECM hooked up to it? And you have a non-computer distributor??? No wonder! The distributor and the carb are linked by the ECM. The fuel to air ratio and the spark curve are controled by the ECM, and based on info from BOTH the carb and the distro. So... Basically, it sounds like your carb is running in "limp home" mode, which means it's just throwing all the gas in there that it can.

I learned this because I'm currently disconnecting my computer and going with a non-computer carb and distro. I had an arguement with my father because he was telling me the distro would work fine without the carb, so I had to prove him wrong. LOL He knows Ford, so... Maybe that's how they do it over there, but not in Chevy Country.

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1986 Firebird, LG4 305, bored .040 over, Crane cam, Edelbrock headers, Hooker Aerochamber muffler, loud and fast.

"Gimme fuel, gimme fire, gimme that which I desire!" - Metallica, "Fuel"

 

LMAO, Good call Gilmor. I totally Missed that.

If he is running the E4ME unplugged, So to speak, Your lucky to make 10 mpg )

Also Check your Vaccum advance. If its not Hooked up your Milage is gonna **** too.




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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

So, how do I go about completely eliminating the ECM, since the distributor is not hooked up how about the carb., the only wire I have hooked up to it right now is the choke.

 

You get a Differnt Carb.




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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

What would be a good carb to go with. I heard Edelbrock ones have to be adjusted a lot. I want something with little maintenance

 

Any Holley 650 would be a good size. Can't believe i missed that one too

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--Steve S--
1984 Trans Am 305 LG4, 5 speed
Daily Driver, Flowmaster 80 Series
NOW FEATURING: Holley 600 cfm & vacuum advance

 

I have run Edlebrock carbs since 1988. they do not have to be adjusted a lot.

they just need to be kept clean.

people let moisture and dirt get into the air-bleeds, and needle/seat area causing it to run differently. They then go and rejet or adjust something.

I have nothing but good things to say about Edlebrock carbs.
my opinion

 

I'd get the edelbrock before I'd get the Holley. My personal choice would be a non computer controlled Quadrajet. Not only will it bolt right in place of yours, it is a lot more mild mannered around town, less problems and will perform just as well as the other two no matter what anyone else tries to tell you. If anyone says a quadrajet is a bad carb, they just don't know what they're doing. I have several friends running in the 11's with a quadrajet and they don't have the leaks associated with a holley.

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Kyle Osterholt
Okarche, Oklahoma
ASE Master Certified
86 T/A 383 TPI
89 TTA #1002 T-top/Leather
89 TTA #1358 Hardtop/Leather
80 T/A Pace Car
73 Opel GT
73 bronco

 

Agreed Snake.

I also like the Eddie Carbs, and would Go with one Before a Holley, Just from personal experiance.




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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

Just wanted to say thanks to you guys.