Hey guys,

I've had this 350 block sitting in my garage for over a year now with plans to put it in but honestly, I've started to question why I wanted to do it. The main reason is my original motor is leaking like a siv right now, going through about 2 quarts of oil every 3k miles. If there is a seal on the motor...it leaks.

I have an 84 T/A with the L69 305, 700R4 and 3.73 gears that is my daily driver. I get 19 or so mpg in town and 22-23 on the highway. Since it is my daily driver, I'm forced to contemplate the amount of performance I want out of it balanced by the fact that I need to drive it every day.

Since Gas is running $2.99 around and I know it's only going to go up. Gone are the days of $1.20/gallon gas.

I could build the 350 into a 350hp+ machine like was my original idea but that's not going to make the pocket book happy with the way gas prices are looking.

The more I look at it, the more I think that if I do put the 350 in it, it's going to be a relatively pedestrian 250-300hp build and I'm I'll drop the gearing from 3.73 to something like 3.27 or so. Problem is, I don't know what sort of mileage I would get out of it.

The other option, would be to get a newer 305, mild cam, Vortec heads, headers and a 3" exhaustput some mods on it and expect that the most HP I would get would be around 250 or so in the hopes that I would keep the mileage I've got? I could also drop the gearing on this option. With the steep first gear of the 700R4 I'll still get fairly good acceleration.

So what do you guys think? Should I go with a 350 mild build and lower the gears from 3.73, or stick with the smaller 305? Keep in mind that I want to get 24-26mpg out of it if not more. If I can't squeeze more out of it, I'm going to wind up giving into the wife and getting a honda or Toyota...she hates my car.

 

With everything else basically the same, I'm getting about the same mileage out of the 350 as I did with the 305 on steroids, which is about what you're getting.

3.42 gears would help the economy without hurting performance drastically. 3.23's would be even better for economy but would feel a lot more sluggish than 3.73's - but, if you do both the 350 and 3.23's at the same time, you'll think you still have the gears.

 

like 57 said, if both engines are built similiar they will get pretty much the same gas mileage, the difference would be the 350 would make more power.

 

If it is EFI, you could expect even more. With proper tuning on a basically stock L98, I was getting US 30 mpg on the highway. On a heavily modified 383, my buddy is able to get US 25 mpgs with EFI. He's running a Miniram with some AFRs & a solid roller - so you can have your performance & fuel economy with EFI and proper tuning.

And, given the relatively cheap cost now with the Holley Stealth Ram setup, you can retro-fit EFI relatively cheaply too.

 

Just remember, bigger engines don't have to work as hard as smaller engines. Meaning less fuel. Thus, you should get the same gas mileage as long as you don't hot rod it.

 

dp

 

Well, I'm running a Q-Jet on it now and if/when I build the motor, that's what it'll have until/if I can afford an EFI setup. I do think I like going down in gears though...

Has anyone heard of somebody doing a comparative analysis of the MPG gained/lossed while changing their gearing?
.

 

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What gearing/transmission are you running to get 30? That would be flat out awsome
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I'm not looking for a monster motor, just something in the 300 range for a nice kick in the pants. I've got a 67 Camaro that I'm going to flat out rock with a BBC...one of these days.
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WTF is up with the automerged posts!!???? grrr...

 

wow, you guys are pretty aggresive drivers, I have a stock 305 with a 5 speed, and I get in the early 30's quite commonly, I dont know who screwed around with the gearing (my speedo reads very fast, about 30 over consistantly) but at about 120kph, the car runs at about 1,800 in 5th.
Thats kind of the ticket right there.

 

You're probably running 2.90 gears or somewhere in there. Also, manuals get better mileage than automatics. On the highway at 70mph, 700R4 with 3.73 gears I'm running at about 2600 rpm.

 

30 miles per gallon, or 30 kilometers per gallon?

 

Damn I envy ya'll...mine was getting about 10-12 mpg before it got all squirrelly on me. Now im hoping that the LS1 im gonna stick in will get the ~20 mpg im told it does...However with me in control and no more money being sucked into a pit it wont stay that way =)

 

That's a good point, never occured to me when he was saying "KM"..hehe