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Lsx swap worth it?

20K views 48 replies 11 participants last post by  bigdog7373 
#1 ·
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.
 
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#2 ·
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,
 
#3 ·
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.
 
#5 ·
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
 
#6 ·
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.
 
#7 ·
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.
 
#9 ·
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
 
#10 ·
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?
 
#11 ·
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..
 
#12 ·
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.
 
#25 ·
Car Craft is a magazine dedicated to selling parts, keep that in mind any time they write an article.



Here's how to bolt a muncie onto a 5.3L using only stock parts.

For the TH 350 you'll need a spacer for the flex plate, it's like $40.

That's it.

No extra 5 bajillion dollar conversion cost.


Most "hotrodders" today can't build anything unless its been approved by a magazine editor and delivered by the UPS guy- that's not building, that's buying.
 
#27 · (Edited)
Car Craft is a magazine dedicated to selling parts, keep that in mind any time they write an article.

How To Connect a LSx Series V8 to older GM 4 Speed Manual Transmission - YouTube

Here's how to bolt a muncie onto a 5.3L using only stock parts.

For the TH 350 you'll need a spacer for the flex plate, it's like $40.

That's it.

No extra 5 bajillion dollar conversion cost.


Most "hotrodders" today can't build anything unless its been approved by a magazine editor and delivered by the UPS guy- that's not building, that's buying.
Haha i was kinda getting that feeling while reading the article:spank:

I actually saw that video while i was searching! :cool: Thats what i was talking about with the 4.8 5speed truck flywheel before, but then the article said that it would cause problems. Well i guess they lied. So
So what im seeing i need is the flywheel, the pilot bearing, the bracket for the z bar, and the correct clutch and i should be good.

Only thing is that in the video he mentions not to install the pilot bearing all the way, but then in the article they mentioned a bearing made specifically for the application. So if it's no overly expensive i think it would be better to go with that one
 
#28 ·
check out pirate 4x4, chevy thunder drive by wire, ls1tech, lt1swap.com, nook and tranny lsx info, gmefi.com for a bunch of info on the ls series engines. good stuff for a read-thru before spending money. don't worry about the car end of things, if you have the engine and trans etc it will fit into lots of different vehicles if you decide the old iron is too heavy or for whatever reason. a guy i work with put a 5.3 truck engine in his mustang and then threw a turbo on it and it worked out fine. you will have no problems if you have a few fab skills. I would recomend an overdrive with whatever engine you use. there is a reason most newer vehicles come with 5 gears or more, less rpm spread between gears, so you're not wringing the engine out like a wet rag before shifting, plus a good overdrive for mileage. also, there is always somebody looking for ls engine swap stuff if you get into it and then change your mind.
good luck
there is a guy on the ls1tech that has pics in the forums. it's a corvette engine in a '76 I think.
 
#29 ·
Cool thanks man. I'll check out some of the ls specific forums tomorrow. I'm pretty set on the 4 speed though. I've always wanted one for the car and it will go perfect with trying not to show what's under the hood. I recently sold my 5 speed car and i honestly found it annoying to drive around town since 1st and 2nd gear were wound out by 30 mph.
 
#30 ·
Everything you can do to make a short block and valvetrain easier to roll over is going to pay dividends in fuel economy. It's a huge part of the magic used to get those amazing power/economy numbers from modern engines like the LS series.

Quick crude example...
Take two mostly identical engines, except one shortblock requires 40ft/lbs to roll over using regular oldschool piston rings, the other uses a modern low-tension ring pack and requires only 13ft/lbs to roll over. That's a constant savings of almost 8hp at 1500rpm. If your car cruises at 2500, that equals a constant savings of roughly 13hp while you are driving down the hiway.
As a bonus, WOT at 7000rpm, the low-tension shortblock would have about 36 more hp on tap.

If you decide to go old school, do yourself a favor and build it with modern hyper pistons, skinny low tension rings, and a compatible cyl wall finish using torque plates. Not only will the engine will last a lot longer, but even more important, less friction in the cylinders will pay fuel economy dividends for the entire life of the engine. Less friction in the cylinders also means less heat being put into the cooling system. Oil temps come down as well. Proper clearances and thin synthetic oil will help too.
 
#34 ·
I don't know where you're from but around here they commonly sell for $400 from a junk yard- of course that doesn't include the harness or ECU, that's usually another $100.

I just pull all the pig tail connectors I need and make my own harness, IMO its a lot easier and it gives a cleaner install.
 
#35 ·
Its not hard to put a Muncie behind an LS motor; and a Luk Repset clutch is absolutely fine for what you're doing. Best thing you can do is figure out which Muncie you have; Ive posted it all before, or just PM me. If its an M21 or M22; You'll want a 3.73 rear to get your tank moving. At that point you may be better off selling it and saving your pennies. If you're mechanically inclined and have a shop press, you may want to disassemble the trans. If its a stuck pig, planning your build around it will take on another $5-700 easily. I'd say the best bet for you is an M20 (2.52 1st gear), but you're still going to want something like a 3.23 or more rear gear. There is a 2.98:1 1st gear M22 gearset (aftermarket only), you could run 3.08s happily but between that and an overhaul kit, you'll be in it almost a grand in short order (you'll probably need forks, mainshaft reverse, the splined reverse idler and I'd definitely pop for an iron midplate). This is assuming the countershaft bore hasn't had a cobb-job to keep it from leaking.

I love 4 speeds; but Ive seen a lot of junkers and I want you to be realistic. Nothing worse than planning around something, muscling it into place and finding out it in sad shape. Then you gotta tear it out, find the money, fix it and shotgun it back in there.

BTW the Z-bar is the way to go. A lot of hydraulic setups in the aftermarket just don't seem to last long, or work as expected.
 
#36 ·
Thanks for all the responses guys you're all a lot of help. I'm not buying anything until i get the tranny checked out to make sure it's in good shape. I got it for cheap out of a driving car so i'm not too worried. I believe its an m20 but i'll find out for sure. Around here it's not unheard of to get the motor for $350. They are all over the junk yards in wrecked trucks. I'm going to grab the computer and harness with it and modify the harness for what i need. Doesnt seem like too bad of a job, plus i'll save a lot of money over an aftermarket piece. I dont want the 6.0 cause they are expensive and it would kind of defeat the purpose of the swap since i'm really wanting more mpg's so i can drive it more.
If the 4 speed isn't in as good shape as it seems then i might get the trans with the motor. But i'm hoping that's not the case and i can have the 4 speed i want.
I'm not doing anything with it til the summer but i like to plan ahead so i can get an accurate parts list and get the swap done trouble free instead of having to gather parts with the engine half way in the car. I hate working like that.
I'm not too worried about how fast the car will be, i just want something that i can take on the highway comfortably without it revving sky high or anything. So i guess i'll have to do some more thinking about what i want to use for the transmission. I can always sell the muncie for what i bought it for and come out even. Plus i still have the running small block and the th350. If i were to sell the current engine/tranny i could easily pay for at least half the cost of the swap.
I really want to modernize the car without losing the classic look. I got some bmw e46 seats planned for the interior, all new gauges, vintage air a/c, keyless entry system, the works. Only thing holding me back is school:drunk:

Any more advice about the swap i'd really appreciate. Thanks!:thumbup:
 
#37 ·
If you're just wanting to get good mileage and decent power a TPI 305 with a T5 will get you suprisingly good mileage, and with a few little parts can get over 300hp. I picked up a chevy WC T5 for $200 about a month ago, freshly rebuilt too.

A well build gen1 sbc can get good mileage, but it will never be the Gen III/IV stuff.

If you're really after mileage you either need an OD trans or need to swap the rear gears. Drop your highway cruise speed to right under 2,000 will make a huge difference.

LS swaps have a lot of potential, but they do cost more than swapping in a different gen 1 sbc- if cost is a major factor (which it sounds like) then you may want to explore other options.

an LT1 is a great in between compromise, as is a Vortec enigne with a intake swap (thought going MPFI is more expensive going this route).
 
#38 ·
I definitely want as ls engine. I had the 5.3 in my tahoe and they are really awesome motors. Smooth as hell, good power, good mileage. I want to get the car up to the 21st century, get away from the usual small block chevy that everyone and their mother has. I want to keep costs as low as possible but i don't have a problem with spending money. To me it's not worth upgrading to anything else because i know i would regret it in the future.

The 5.3 is a go. I'm really just down to deciding on a transmission. Is the 4 speed going to hold me back? I want good mpg and highway drivability but i don't want it to be a slow pig. With the 4l60e that comes on the 5.3's i know i will have the benefit of overdrive but i dont want it to be boring to drive. I really enjoy shifting actually and i dont want to get bored of the auto.
 
#41 ·
Lets do the math.

I'm a big fan of ls engines, a couple years ago I traded my 5pd, 4cyl Cherokee for an 04 gto w/m6. The Cherokee managed about 19/23 mpg, the gto with careful driving can manage a decent 19/26 mpg. Not that it matters, because the way I drive it yields much less. But I drive less than 10k miles a year so I fund the difference as "entertainment".

The swap, if well planned and executed, could provide a great improvement for your Firebird project. But, is it worth it?

To do this right we need to know how much you drive, before and after estimates of mpg, average price of gas, and what the swap really costs. I don't propose to argue the fine details of each parameter, instead I propose an example you can use to do your own calculations.

In my example, I assume you drive 10k miles a year, the bird is nailing down 15 mpg now and after the swap (using your 4spd as is, and with optimum tune, gearing, etc) you manage 20mpg (a 30% increase). I'll use the good gas at $4/gal; and expect to complete the swap for $1500 (low end estimate IMHO).

Monthly savings equals milesdriven*mpgafter/mpgbefore*price/12=10000*20/15*4/12=$55/mo
or
So before the swap you spent 10000/15*4=$2667/yr or $222/mo on gas.
After the swap you'll spend 10000/20*4=$2000/yr or $167/mo on gas.
222-167=55 (Notice the 30% savings in cost)

With savings of $667/yr or $55/mo, it'll take more than 27 months ($1500/55) to break even. While $55/mo isn't a fortune, it is worthy of consideration.

Of course you can change the assumptions used and get a very different result. Keep in mind the calculation is only useful if your assumptions and estimates are correct.

Now let's look at how changing the assumptions affect the outcome:

miles per year - double the miles, double the savings and cut time to recover cost in half (keep in mind though that double the miles also means double the total cost of gas).

ratio of mpg before/after - increasing this parameter is the heart of the matter, resulting in more savngs to match the improvement realized in mpg (again, keep in mind to achieve more improvement, expect to spend more on the swap)

price of gas - as prices go up your savings increase (the inverse ain't happening, don't get me started)

cost of the swap - increasing cost of the swap increases the time to recover your investment (this parameter is the most difficult to get right and the impact can be huge)

So is it worth it?
Put your own numbers in the calculation and you'll know (as long as you are honest with yourself, and not dreaming of going from 15mpg to 30mpg after a $1000 swap).

A few other factors to consider:
seat of the pants thrill an ls can provide
satisfaction from being smarter than the average bear (thx Yogi)
satisfaction of a job well done
pain and anguish of an unfinished project because of time, money, etc
 
#42 ·
Wow thanks! In my case the swap will pay itself off rather quickly. I have to use 89 octane in my current setup because of compression, so that's 25 cents per gallon more than the ls engine which i could run 87 in. I'd estimate 10k miles per year, is about right. Also in the car's current form I average about 12 mpg. So:
Now:
10,000/12=833 gallons@ $3.90 per gallon = $3248 per year.

Ls:
10,000/20=500 gallons @ $3.65 per gallon = $1825 per year.

That's a $1400 savings per year. So it will just about pay for itself in a years time, but wait there's more
Lets say i get $600 for the engine and trans i have. Well now the swap only costs $900 out of pocket. So if i do this swap this summer then by next summer i would have actually SAVED $500 over not doing the swap. Well what the hell am i waiting for?! Wow I'm excited now:thumbup:
 
#45 ·
$600? You must have the midas touch. a worn 350/th350 is worth slightly more than the price of scrap around here, maybe $300-$400. BE REALISTIC. your mileage and gas prices seem accurate though. $1500 for an engine and trans swap seems low to me, but entirely possible. you may want to figure an even 2 grand- so you'll pay it off in about 2 years (still not bad!)
 
#47 ·
you going to run headers..
bye bye budget..
for s_it's and giggle, start a journal, and list the cost as you go..

to give an idea.
my c-10 is a small block. I'm changine to big block
headers 580.oo (coated)
brackets and mounts 159.
front assor dress(brackets and alt/ps pump/ac compressor/ a/c lines/ power stear lines/ belts 1200.00 (remember your ls will not have us threads it be metric and the ps hose ends are different and you'll be paying for these to be made.. same with a/c hoses,
if you can connect to the exhaust under the car now.. say 40 bucks if you do the fitting/welding yourself
the custom coolant hoses
the electric fans
the relays
the fuel system..

please start a journal.. I'd love to see you come even at double your 1000.00 swap budget..
I've seen enough of these stuffed into g bodys to know what the cost really is like..
good luck tho..
wait till you get the sticker shock on the 02 senders cost..
oh, and plan on the oil pan not clearing, most go with the gto pan, and pick up
 
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