[bigdog7373]

I currently have a 350 sbc in my 78 firebird but i'm seriously thinking about an lsx swap. The 5.3 motor. The car is getting restored and converted to a trans am, and i would hate to finish it and not be happy with it. It currently has a 350 backed by a th350 trans. It makes an honest 290hp, probably more. The thing is that it's going to be my daily driver and the gas mileage is terrible. I was also planning on doing some upgrades to the small block but when i priced it out i can do the ls swap for about the same price. My other thinking is that even if i do leave the sbc as it is vs doing the ls swap, i'd end up spending more on the 350 because of the fuel mileage. So i guess the ls would pay for itself in only a few months.

One thing i'm wondering is that i just picked up a muncie 4 speed and i'm pretty set on using it. Can i use it with the 5.3 ls?

People who have done the swap: What are the pros and con s(if any) that you have come across after the swap? Is the fuel mileage a big difference? How much did it end up costing you?

I guess I've kind of convinced myself that it would be good to do, but i just don't know if i want to do all that work and money.

Any opinions or experience would be really awesome.

[vinniekq2]

There is a local shop here that wont even bother with the old engines unless you specify thats what you want.Their most popular swap is to install an LS-3 with hot cam(480 hp) and the 6 speed transmission. slight bump at idle very smooth power delivery,decent mileage,easy to service,excellent drive ability. you can build an old engine the same with roller cam,fuel injection etc,most people with old cars are using carbs and flat tappet cams and HEI,

[bigdog7373]

Originally Posted by vinniekq2

There is a local shop here that wont even bother with the old engines unless you specify thats what you want.Their most popular swap is to install an LS-3 with hot cam(480 hp) and the 6 speed transmission. slight bump at idle very smooth power delivery,decent mileage,easy to service,excellent drive ability. you can build an old engine the same with roller cam,fuel injection etc,most people with old cars are using carbs and flat tappet cams and HEI,

Yea i'm thinking it's not worth it to mess around with the old motor when the technology of the lsx is so much more advanced. I'm trying to keep it around $1000 if possible, which is why i was leaning towards the 5.3. I'm not looking for insane power either, I'm perfectly happy with a solid 350 horses. I mostly am looking at it because it's like once you get it installed and tuned you never have to worry about it again. No setting timing or adjusting the carb, it just seems nicer that way. And from what i have read on different forums, the fuel mileage is a lot better. I'm hoping someone who has done and lsx swap can give me some actual mpg numbers.

[vinniekq2]

blake@speedtech-performance.com
blake@speedtech-performance.com
contact him,ask him about his 70 ish nova that he raced against a porsche on a road race track.
Hes a typical business guy but they do great work and use the LS engines in a lot of cars,like his dads 53 studebaker

[PatM]

To clarify -- I do not have before and after experience with an LSx swap.

But, regarding the milage, I think you should uderstand that much of the difference you've heard about with LSx milage is a direct result of the fuel injection (which is for real) and the gears (which you could use with the old motor). In my wife's C5 Corvette, we get 27 to 30 MPG on the highway. But that's in Sixth gear, rolling along at about 70-75 MPH at only 1500-1600 RPM. The car is quite light, and certainly slippery. In the old (now gone) '69 Vette, we'd get 16 MPG, but were turning 3500 RPM at 70 MPH. Big difference. BTW -- The '69 also had more horsepower.

I'm not saying the engineering and engine management in the LSx motors doesn't have an impact, as I'm sure it does. But it's not the only reason for the extraordinary milage many of these cars produce.

Build a smooth running, mild street engine that produces torque all the way down to 1500 RPM, put a 0.50:1.00 ratio top gear in your transmission, and you can likely get north of 23 MPG too, on the highway with an old iron block 350 in your heavier Firebird.

JMHO

Pat

[ap72]

EFI and gears do contribute a lot to mileage, an LT1 swap with the 4 speed OD trans would pick u pa lot of mileage over what you currently have.

BUT the LS engines are way above and beyond the gen 1 stuff- especially in stock form.

Take the 5.3L, swap it in and you'll instantly pick up power, mileage and driveability. Then down the road swap the cam, throw on some headers, swap to an LS6 intake and port the stock heads and install LS1 intake valves- you know have 450+ flywheel hp and STILL have better mileage than when you started.

There is nothing better about the old stuff than the new stuff.

[bigdog7373]

I understand that the fuel injection is what makes the difference but from what research i've done it would take me almost twice as much money to get the same mileage and power out of my 350 as it would to just swap in the 5.3. It's either keep the 350 as it is or go ls.

[bigdog7373]

Originally Posted by ap72

EFI and gears do contribute a lot to mileage, an LT1 swap with the 4 speed OD trans would pick u pa lot of mileage over what you currently have.

BUT the LS engines are way above and beyond the gen 1 stuff- especially in stock form.

Take the 5.3L, swap it in and you'll instantly pick up power, mileage and driveability. Then down the road swap the cam, throw on some headers, swap to an LS6 intake and port the stock heads and install LS1 intake valves- you know have 450+ flywheel hp and STILL have better mileage than when you started.

There is nothing better about the old stuff than the new stuff.

You posted right as i did lol.
So basically if i have the time and money there is no reason not to swap to the lsx engine. I guess i should add it to my plans then

[vinniekq2]

you keep posting LS-X ther is an X in the series.Go with the 5.3 for economy.the LS-3 has enough everything in one package at 430 hp,a hot cam and minor tweeks is 480 hp

like I posted above,its the roller cam/fuel injection and ignition that makes it a nicer package. spending 12 k to save $100,oo worth of fuel is not good math.If you want it all in an old car the the LS line has a lot to offer.

Old engines can accept fuel injection,roller cams and better ignition. The cathedral heads do offer more potential. O/drive transmissions come in many varieties,but at a cost

[bigdog7373]

Originally Posted by vinniekq2

you keep posting LS-X ther is an X in the series.Go with the 5.3 for economy.the LS-3 has enough everything in one package at 430 hp,a hot cam and minor tweeks is 480 hp

like I posted above,its the roller cam/fuel injection and ignition that makes it a nicer package. spending 12 k to save $100,oo worth of fuel is not good math.If you want it all in an old car the the LS line has a lot to offer.

Old engines can accept fuel injection,roller cams and better ignition. The cathedral heads do offer more potential. O/drive transmissions come in many varieties,but at a cost

Lsx is just a way of just saying ls series without specifying which one. If i do the swap it will definitely be a 5.3 since they are so abundant.

One thing that worries me is the transmission. I've heard you can use the flywheel from a 4.8L 5 speed truck and then just bolt up the rest. Can anyone confirm this is correct? What about the clutch linkage, will it clear everything?

[E.Furgal]

A few things..
1) your 78 firechicken is a tank.. over two tons is not unheard of..
2) your milage will be no better with that 4spd and the 78's rear gears..(my bet 2.73 or 2.43)
3) add up all the little things after the engine cost.. the clutch to work with the m-20/21/22, the flywheel, the motor mounts, the headers, the oil pan if the one on your 5.3 doesn't clear, the front dress, that may not clear the engine crossmember with out fab work.., ele fans if not already in use.. rewiring the car to limit electrical noise, (add many ground straps everywhere)


the lsx is a great engine, but you'd be better served spending the cash in other places,, like with 343 or 373 rear gears and a tremic 5 spd kit..
those years f body had tallish tires.. and the smog rear gears.. jive great highway milage, but around town.. not so much..
most times the lsx swap the a/c compressor and engine crossmember want the same realstate..

I looked into it for my 86SS, the 5.3's are cheap.. but it's all the little crap that adds up fast..

[bigdog7373]

Originally Posted by E.Furgal

A few things..
1) your 78 firechicken is a tank.. over two tons is not unheard of..
2) your milage will be no better with that 4spd and the 78's rear gears..(my bet 2.73 or 2.43)
3) add up all the little things after the engine cost.. the clutch to work with the m-20/21/22, the flywheel, the motor mounts, the headers, the oil pan if the one on your 5.3 doesn't clear, the front dress, that may not clear the engine crossmember with out fab work.., ele fans if not already in use.. rewiring the car to limit electrical noise, (add many ground straps everywhere)


the lsx is a great engine, but you'd be better served spending the cash in other places,, like with 343 or 373 rear gears and a tremic 5 spd kit..
those years f body had tallish tires.. and the smog rear gears.. jive great highway milage, but around town.. not so much..
most times the lsx swap the a/c compressor and engine crossmember want the same realstate..

I looked into it for my 86SS, the 5.3's are cheap.. but it's all the little crap that adds up fast..

The gears are getting changed either way to whatever works with the 4 speed. I bought the trans because that's the one i want. I understand the car is heavy but like i said i'm not looking to get 30 mpg and win races all the time, just something better than i have really. As for the a/c i will be using a vintage air kit so i can purchase a compressor bracket when it comes time for that but for now it's not a major worry for me. If i can pull it off for $1k i'd be very happy, i i dont see why i couldnt really. I can get the engine, computer, and harness for like $500. All that leaves in the accessories, fuel system, and connecting the trans, the rest is just labor.

[E.Furgal]

Originally Posted by bigdog7373

The gears are getting changed either way to whatever works with the 4 speed. I bought the trans because that's the one i want. I understand the car is heavy but like i said i'm not looking to get 30 mpg and win races all the time, just something better than i have really. As for the a/c i will be using a vintage air kit so i can purchase a compressor bracket when it comes time for that but for now it's not a major worry for me. If i can pull it off for $1k i'd be very happy, i i dont see why i couldnt really. I can get the engine, computer, and harness for like $500. All that leaves in the accessories, fuel system, and connecting the trans, the rest is just labor.

the vintage air will put the compresser in the same spot.. if it doesn't clear now, it won't then..
think you need to read up some..
the factory ecu will need a reflash, as the missing info from speed sensors/trans/gauges/ will send it into fits, = limp home mode..
fuel system.. unless you get a vette or newer lsIII with no return line.. you'll need that+ an intank pump, go price a efi tank..
cooling fans and wire'n
the clutch.. that might eat through your extra 5 bills alone..
the ls engine lack of a mount for the z bar, yes they make one.. thats an extra cost..
bellhousing to mount your m-20/21/22 to the lsx.. sit down when you price that...
good luck..
I'd stab a 96-02 g.m. truck/van vortec 350 in it 1999.oo(crate, less used) and get 350hp and 17c27hw mpg

the gains you think you will see, won't show up..
your 350 crapy mpg are from the 8 to 1 compression(guesing) and the drivetrain..
my 2002 truck got 28-30 hyway with a vortec 350
they run 9.4 to 1

[ap72]

Originally Posted by E.Furgal

the vintage air will put the compresser in the same spot.. if it doesn't clear now, it won't then..
think you need to read up some..
the factory ecu will need a reflash, as the missing info from speed sensors/trans/gauges/ will send it into fits, = limp home mode..
fuel system.. unless you get a vette or newer lsIII with no return line.. you'll need that+ an intank pump, go price a efi tank..
cooling fans and wire'n
the clutch.. that might eat through your extra 5 bills alone..
the ls engine lack of a mount for the z bar, yes they make one.. thats an extra cost..
bellhousing to mount your m-20/21/22 to the lsx.. sit down when you price that...
good luck..
I'd stab a 96-02 g.m. truck/van vortec 350 in it 1999.oo(crate, less used) and get 350hp and 17c27hw mpg

the gains you think you will see, won't show up..
your 350 crapy mpg are from the 8 to 1 compression(guesing) and the drivetrain..
my 2002 truck got 28-30 hyway with a vortec 350
they run 9.4 to 1

stock bellhousing will work fine
you'll have to make your own z-bar
you'll have to make a fuel system
any clutch with the right spline count will work
and you can either get a computer programer, or skip the stock route and run MS

Those are costs you need to factor in, but they're not as much as people think.

[bigdog7373]

Originally Posted by E.Furgal

the vintage air will put the compresser in the same spot.. if it doesn't clear now, it won't then..
think you need to read up some..
the factory ecu will need a reflash, as the missing info from speed sensors/trans/gauges/ will send it into fits, = limp home mode..
fuel system.. unless you get a vette or newer lsIII with no return line.. you'll need that+ an intank pump, go price a efi tank..
cooling fans and wire'n
the clutch.. that might eat through your extra 5 bills alone..
the ls engine lack of a mount for the z bar, yes they make one.. thats an extra cost..
bellhousing to mount your m-20/21/22 to the lsx.. sit down when you price that...
good luck..
I'd stab a 96-02 g.m. truck/van vortec 350 in it 1999.oo(crate, less used) and get 350hp and 17c27hw mpg

the gains you think you will see, won't show up..
your 350 crapy mpg are from the 8 to 1 compression(guesing) and the drivetrain..
my 2002 truck got 28-30 hyway with a vortec 350
they run 9.4 to 1

Well i have done a lot of research and i've found out that theres not as much involved as you're saying.
1. vintage air has numerous brackets to choose from, and if none fit i have no problem fabricating my own.
2.The fuel system only requires a high pressure pump, doesn't have to be in-tank. All ls motors after 2003 were non-return style.
3. The bellhousing is the same one for an sbc. $40 doesnt seem like a bad price lol
The thing that does worry me is the z bar

Also i will need the ls1 intake and injectors because of hood clearance issues. But luckily they make adapters to use the ls1 injectors on the truck harness.