fasteddy

Its a Z28 with a 5.7....gets around 15 city and 26 hwy...Auto trans...not tuned and not bad.....v6's get a little more, not much more either.

Its my son's car but it has a bad lifter @110K miles.....

I want to build an engine that optimizes gas mileage. (cuz I pay the bill)

Should I stay with the 5.7 or drop down to a 5.3. My tahoe with an iron 5.3gets 15/20 avg and it weighs 5200lbs.

I'd like to see it I can get to 20/30 which is about a 30%/10% improvement.
I know thats a stretch type goal, but any thoughts would help.


The strategy would be to increase compression, increase airflow, and decrease the fuel.

So I was thinking a 5.3 with 243 heads and what manifold? should I use the LS6 or the truck one?

Any thoughts would be helpful.....NO TURBOs....
Even tuning thoughts.....like set the limiter at 5K.
Any cam thoughts?
Use narrow tires...pulls less tread...less friction.
Use taller gears...it has 273s now....

lil john

Is the car a stock ls1 engine if so work with it 1st....take what is written and apply it.....if not.........5.3 with stock cam/Call to see if they can make a more efficient custom cam, free flowing exhaust= duals, 4speed trans look at the 4th gear ratios 4l80 has the worst as far as 4th but it is the *best 4 speed in terms of power handling. 3.23-3.08 rear gear 3.43 would be best ..not making power/ going up a hill and a 3.08 rear. Compression should be in the under 10.0 range or right at it. Maybe hand port the heads/chamber work for a little Extra Hp and it helps promote better fuel atomization.Intake, a good hand porting to get better air flow....but 26mpg is really good but this would help....Also a good tuner can help more than u think

fasteddy

26 mpg at 70mph on level freeway.
15.5 in city driving.
Measured with the ultra gauge.....trip/usage is approx the avg.


OK...I can live with that strategy.....
Leave bottom end alone for right now....

Port the heads....
Port the intake....
What about the throttle body? will porting it make a diff?
How much compression can I run and still use 87 octane?

Find an efficient "good gas mileage" cam ...... ? I've never even heard of that.

Then tune it.

lil john

Well on the cam U could talk to some 1 like Tick to see if it's possible to do a cam that is more EFF. than a stock 1.
now on Compression...I no whats recommended for ole SBC...but with computer and EFI.....Vengence,LME,TSP would be a good start to find out how much true comp can be run but I'm thinking around 10 if not the old 9.5 compression ratio...although EFI helps this a lot. You want the engine to flow as smooth as water running...going in & coming out... get rid of all dead weight except for dummy tire and jack

allan808

iTrader: (3)

Youl be spending more money on gas with all those parts!

lil john

True but he asked....better exhaust and a good tune with a 3.42 gear should get him there but he asked so.....I gave him the bucket list of things that could help Fuel economy, in Houston TX gas is 3.02-.10 a gallon reg. and some places as low as 2.95. And trust me, my cousin & I know MPG try driving from Houston to Key Port, NJ then to NY followed by Canton Ohio and return home to Houston in a GM 2500 trk. with a 5.7 TBI 4l80 trans and a 4.10 gear....I really like the trans and gear the truck uses.....Thinking my Malibu will love it also with 3.90 gear and less weight....Also more HP..got the trans in the garage and rear-end gear is in the car.

drillbabydrill

As long as you have that V8 in there you're not gonna get great gas mileage. You can build whatever you want but when he gets behind the wheel and in town and you aren't there....it's still a Z28 with a V8!!!

Exidous

iTrader: (11)

Close to stock cam with AFR 205 heads. Higher port velocity with a slightly taller gear should get you a couple MPG. Once you go over 210cc on the heads (stock size) and a bigger than stock cam you WILL lose MPG but gain HP.

Many report increased MPG at cruise and HP at fat foot with the AFR 205's. A couple MPG at best though. Probably not enough to justify even the used $1500+ price.

redtan

iTrader: (5)

Get a 4.8 with milled heads. Toss a set of tiny turbos on it.

Hello 35+ mpg.

drillbabydrill

^^^ agree. I had the base 4.8 in my 2006 silverado and was seeing 25 mpg. I don't see you getting much better than that!

SSCamaro99_3

iTrader: (1)

The nice part of me says:

How many miles does your son drive per week? We can run some numbers and see if this even makes financial sense.

The not so nce part says:

What is the point of downbuilding a Z28 to pick up a small amount of gas mileage? Go buy something else.


In all honesty:

Right now you are at 15/26. To make the math easy assume a 50/50 split = 20.5mpg average. 20/30 will get you a 25 mpg avg. If you sone drives 10,000 miles per year he will use:

10000/20.5 = 487.8 gallons @ 3.25 = $1585.35 in fuel
10000/25 = 400 gallns @ 3.25 = 1300.00 in fuel

If you are fortunate enough to hit your goal, which out doubt especially the 20 in the city, you are going to save $285.35 in fuel per year. Is it really worth it to sacrifice a ton of performance to meet this goal.

87silverbullet

iTrader: (11)

Smaller motors are not always the best idea. When you have a smaller motor trying to lug around the weight of what a bigger motor was doing, you will find the smaller motor burning just as much or more than the bigger motor.

redtan

iTrader: (5)

That's why you add turbos

87silverbullet

iTrader: (11)

Yes I agree, but my rate of return just went in the dumpster with that notion.

thunderstruck507

iTrader: (18)

put in new lifters (stock or mild cam too if its junked), maybe mill the heads while they're off, get a good tune and leave the rest alone...

drillbabydrill

By the time you do everything these guys are talking about you've spent a years worth of gas money.

lil john

.better exhaust and a good tune with a 3.42 gear should get him there

fasteddy

I agree.....payback on the money spent is probably 5+ years out which by then the car will most have moved on.....and he only drives to school and BBall games.....so he uses a tank about every 2-3 weeks.

It's just an engineering project.....instead of maximizing TQ/HP....thought it would be fun to max gas mileage. I don't live in TX where gas is $2.95/gallon....I live in Socal and its $4 if you're lucky.....2.95? sheesh.

.......and "nice" V6 4th gens are very hard to find....they are either destroyed or people won't give em up....trust me I've looked....came to the conclusion that the diff in gas mileage isn't worth looking forever and the diff in performance.

Thanks for the thought.....I'll post an update when the lifter gets fixed and tune for milegage goes in.

Busted Knuckles

Short stroke, big bore is the most efficient engine, partly because of lower parasitic drag losses. Smaller ports = higher velocity, better cylinder fill.

Best way to improve mileage is to bolt a 2x4 on the floor under the gas pedal.

drillbabydrill

$4 a gallon!? That's insane!!! Ill stay in Texas ha!