LS Engine Swap in Seville

[hjlint]

Has anyone done a LS engine swap on a 1978-9 Seville? or installed a 4 speed auto trans? Fuel milage is very poor.

[TJ Hopland]

What mileage are you getting?

[hjlint]

About 12 city,14 highway. Tested sensors, they are good.

[INTMD8]

Should be relatively simple to swap an LS/4l60 into that car

[TJ Hopland]

That seems like its in the ballpark for that size car in that era.   

Are you expecting these possible mods to pay for themselves in fuel savings?   If so give up now, you would have to be very lucky and do a lot of the work yourself and then drive a ton of miles on top of that to even come close to breaking even.    If you just like tinkering with cars and think it would be fun to spend a fair amount of time and money on the project then it may be worth exploring. 

A similar sized car from the 80's with overdrive would maybe get you up to 20 mpg on the highway.   This was a car designed with that transmission and gearing and had a 'tune' in it to get the most out of the combo.   Just swapping in say a 700r4 you may not gain that much just because the engine may not 'like' running at the lower rpms.    You will need an adapter to mount the Chev transmission to the Olds motor.   Rear mount on the 400 was at 28 inches, the 700 is at 23 so you will need some cross member work.   The diesel optioned sevilles had the 200 trans which was 22" so maybe there are holes in the frame to allow the cross member to move forward.   You would also need a 'lockup' controller to operate the locking torque converter which is one of the things you would want to try and gain a few mpg's.   

Going to a complete LS engine drive train should help a lot.   Not as much as it being in a modern more aerodynamic car but should be a more fun and efficient combo than the earlier 'old school' engines.   The LS engines really seem to do best when they are with the 5 and 6 speed transmissions.   Putting one with a 4 (or 3) speed trans they just don't have the power.   Picking up a donor pickup truck seems to be a good start to get you most of the parts.  You can then buy aftermarket harnesses and mount kits to make the swap easier. 

[hjlint]

That seems like its in the ballpark for that size car in that era.   

Are you expecting these possible mods to pay for themselves in fuel savings?   If so give up now, you would have to be very lucky and do a lot of the work yourself and then drive a ton of miles on top of that to even come close to breaking even.    If you just like tinkering with cars and think it would be fun to spend a fair amount of time and money on the project then it may be worth exploring. 

A similar sized car from the 80's with overdrive would maybe get you up to 20 mpg on the highway.   This was a car designed with that transmission and gearing and had a 'tune' in it to get the most out of the combo.   Just swapping in say a 700r4 you may not gain that much just because the engine may not 'like' running at the lower rpms.    You will need an adapter to mount the Chev transmission to the Olds motor.   Rear mount on the 400 was at 28 inches, the 700 is at 23 so you will need some cross member work.   The diesel optioned sevilles had the 200 trans which was 22" so maybe there are holes in the frame to allow the cross member to move forward.   You would also need a 'lockup' controller to operate the locking torque converter which is one of the things you would want to try and gain a few mpg's.   

Going to a complete LS engine drive train should help a lot.   Not as much as it being in a modern more aerodynamic car but should be a more fun and efficient combo than the earlier 'old school' engines.   The LS engines really seem to do best when they are with the 5 and 6 speed transmissions.   Putting one with a 4 (or 3) speed trans they just don't have the power.   Picking up a donor pickup truck seems to be a good start to get you most of the parts.  You can then buy aftermarket harnesses and mount kits to make the swap easier.

I do most of my own work. If I do this I will use the complete LS Engine drive train. I appricate all the Info.

[Gene Beaird]

I'm thinking that's kind of low for a Seville, but I don't drive mine that much to really, tell, and the transmission needs a rebuild anyway.  That said, you should probably look at fitting a 200r4.  It's a lighter, metric transmission that was used behind the Buick Grand Nationals, so they're pretty strong, and will have the BOP bolt pattern. 

But an LS swap is possible.  A friend did one (that's how we got our 79, as he found a 76 that was in better shape, so let the 79 go to us).  He used a 4th Gen Camaro drivetrain.  It had the 4L60 transmission and LS1 engine.  For that drivetrain, it needs to have the front of the K-member notched on the right side for the A/C compressor.  There are a couple of companies out there that make swap parts, and I think he used those for the engine mounts and transmission crossmember.  The swap kit he used was to put a LS engine into a Nova.  The crossmember had to be sectioned and widened.  I think he used the exhaust manifolds out of his Pontiac G8.  Not sure why the Camaro manifolds didn't fit.  He said the radiator dropped right in, like it was made for the Seville.  He replaced the instruments with an aftermarket gauge set he set into a flat piece of plastic that sits behind the stock lens.  He opted for a GPS speedo so he didn't have to dork with converting the electronic speedo to mechanical on the Seville.  It really looks nice there.  He also installed the engine cover off his G8, replacing the Pontiac emblems with a CTS-V emblem.  It looks factory! 

His 76, of course, doesn't have the limited slip diff that the later models came with, and he says he can spin the tire at will at just about any speed under 60.  He loves it.  I thought about it on ours, but think if i replace what's under the hood, it'll be an Oldsmobile crate engine with Edelbrock heads and aftermarket FI.  I'd be looking for more of a hotrod that looks stock, though, than a nice cruiser. 

[bcroe]

Has anyone done a LS engine swap on a 1978-9 Seville? or installed a 4 speed auto trans? Fuel milage is very poor. 

I have a 77 Delta which at 4150 lb, small block Olds, TH400 trans is very comparably
for economy.  Even with the larger 403 engine, 19 mpg on the road is typical in good
conditions, never less than 16.  Axle ratio is 2.41:1; the car moves right along. 

I would suggest that first you make sure your car is running right.  I could check out that
ECU to see if its functioning properly.  If you haven't replaced the original timing chain
yet, its way, WAY overdue.  Cat converters plug up and ruin performance.  HEI advance
mechanisms can fail.  I think your axle is 2.56:1 which is reasonably economical.  My
TH400 has been converted to switch pitch, which might be worth 1/2 mpg, besides adding
a lot better response & smoothness. 
good luck,
Bruce Roe

[Eric DeVirgilis CLC# 8621]

About 12 city,14 highway. Tested sensors, they are good.

Your fuel mileage is absolutely normal for this generation Seville.

Furthermore, it would surprise many that a Seville weighs more than a 77/78/79 Sedan deVille with 425 - making your observed fuel mileage even more understandable.

Swapping the engine is a question that should be pondered closely as doing so will harm the value of the car. If that is something that you can live with, by all means, proceed.

However, if the reason for doing this fuel savings, don't even waste your time. You'd have to drive the car ~200,000 miles before you saved your first nickel.   

[INTMD8]

Swapping the engine is a question that should be pondered closely as doing so will harm the value of the car.   

Guess it depends on who's buying it.  I would personally pay a lot more for that year Seville with a clean LS swap.

[Rob Bruining CLC 12428]

I've owned a '77 Seville the past 31 years. I recently cleaned the throttle body  bore with spray cleaner and a toothbrush.   It made such a difference that I had to adjust the idle speed down. I also use Lucas FI cleaner in the gas occasionally.  They recommend injection cleaning every 30,000 miles with newer cars, why wouldn't it be needed on this injected car? It does! 
I'm getting 17mpg on the highway. The car is really running strong now. Try it, you don't have much to lose.

[hjlint]

I appricate all the Information I'm getting. Timing chain, Tight, injector's, clean. Rebuilt distributor with less that 6,000 miles. I sent the PCM to a specialest when I first got the car and thy said it was fine, New monollithc ? cat, Haven't cleaned the throttle bod (yet) will do. I tested the compression several weeks ago, 100 lb all cylinders, did a wet test on three and went to 150+. I did a top cleaner process with GM top cleaner, put about 2 ounces in each cylinder,let it soak for 1/2 hour or so, crank the fluid out ant then drove it awhile, compression now 130 to 140 each cylinder. I am going to lift the injector rail and watch for leaky injectors, after a hot run, car is rough running for a short perion then clears up. Buckroe asked about the PCM, how can I check this, and I also have a second PCM but it is not of a California car (mine is)

[hjlint]

I've owned a '77 Seville the past 31 years. I recently cleaned the throttle body  bore with spray cleaner and a toothbrush.   It made such a difference that I had to adjust the idle speed down. I also use Lucas FI cleaner in the gas occasionally.  They recommend injection cleaning every 30,000 miles with newer cars, why wouldn't it be needed on this injected car? It does! 
I'm getting 17mpg on the highway. The car is really running strong now. Try it, you don't have much to lose.

I'll give this a try. I have been using guout in the fuel. Haven't clean the throttle body.

[hjlint]

Your fuel mileage is absolutely normal for this generation Seville.

Furthermore, it would surprise many that a Seville weighs more than a 77/78/79 Sedan deVille with 425 - making your observed fuel mileage even more understandable.

Swapping the engine is a question that should be pondered closely as doing so will harm the value of the car. If that is something that you can live with, by all means, proceed.

However, if the reason for doing this fuel savings, don't even waste your time. You'd have to drive the car ~200,000 miles before you saved your first nickel.   

I don't put many miles a year on this. I'm still going to try to find something to improve millage. Like to keep injectors, not sure if a Carb would be much of an improvement.

[Eric DeVirgilis CLC# 8621]

I don't put many miles a year on this. I'm still going to try to find something to improve millage. Like to keep injectors, not sure if a Carb would be much of an improvement.

By all means, try a few tweaks but don't expect miracles. As I have said, the mileage you observe it normal for one of these cars.

Also keep in mind, degree of transmission wear, fuel grade & blend (ie ethanol), driving habits all have bearing on fuel consumption - to name a few.

A carb will not give you any improvement worth talking about - if at all.

For whatever it may be worth, Car & Driver magazine reported 11 MPG observed fuel consumption on a 1981 Sedan deVille with 6.0 liter V-8-6-4 when tested new ( driven by CD's self-admitted collective lead foot team) with ~ 13 MPG expected under more typical driving.

From personal experience - whenever we took in RWD 1981 V-8-6-4 for the car lot back in the day, the mileage showing on the dash MPG computer always read 12.9 - with uncanny consistency.

[bcroe]

I appricate all the Information I'm getting. Timing chain, Tight, injector's, clean. Rebuilt distributor with less that 6,000 miles. I sent the PCM to a specialest when I first got the car and thy said it was fine, New monollithc ? cat, Haven't cleaned the throttle bod (yet) will do. I tested the compression several weeks ago, 100 lb all cylinders, did a wet test on three and went to 150+. I did a top cleaner process with GM top cleaner, put about 2 ounces in each cylinder,let it soak for 1/2 hour or so, crank the fluid out ant then drove it awhile, compression now 130 to 140 each cylinder. I am going to lift the injector rail and watch for leaky injectors, after a hot run, car is rough running for a short perion then clears up. Buckroe asked about the PCM, how can I check this, and I also have a second PCM but it is not of a California car (mine is) 

You can check for leaky injectors with a fuel pressure gauge.  Connect to the rail, turn on the key,
the pumps will run briefly and shut off.  Pressure should go to 39 psi and hold for some seconds if
nothing is leaking. 

There is no doubt, driving style hugely influences mileage.  If the engine never gets
warmed up on short runs, it will be terrible.  Stepping on the brake is throwing away
gasoline; learn to minimize use of the brake.  Hills will cost more fuel.  I drive cars as
heavy and more powerful than yours, I drive fast and far, and mileage is always in
the upper teens (rarely reaching 20). 

The main difference between a 49 state ECU and a 79 CA is the OX sensor.  A 49 state
78-79 ECU will run your car just fine.  Of those I have tested, the OX sensor circuit usually
didn't work.  No parts available to fix the 8748 micro.  However, I can fix the rest. 

I wonder if they REALLY properly tested it; I haven't found anyone who could do that
except me these days.  I have started a list of COs that have said a bad ECU is good. 

Bruce Roe  CLC # 14630

[hjlint]

I have a 77 Delta which at 4150 lb, small block Olds, TH400 trans is very comparably
for economy.  Even with the larger 403 engine, 19 mpg on the road is typical in good
conditions, never less than 16.  Axle ratio is 2.41:1; the car moves right along. 

I would suggest that first you make sure your car is running right.  I could check out that
ECU to see if its functioning properly.  If you haven't replaced the original timing chain
yet, its way, WAY overdue.  Cat converters plug up and ruin performance.  HEI advance
mechanisms can fail.  I think your axle is 2.56:1 which is reasonably economical.  My
TH400 has been converted to switch pitch which might be worth 1/2 mpg, besides adding
a lot better response & smoothness. 
good luck,
Bruce Roe

WHat is involved with the Converter switch pitch?

[hjlint]

I'm thinking that's kind of low for a Seville, but I don't drive mine that much to really, tell, and the transmission needs a rebuild anyway.  That said, you should probably look at fitting a 200r4.  It's a lighter, metric transmission that was used behind the Buick Grand Nationals, so they're pretty strong, and will have the BOP bolt pattern. 

But an LS swap is possible.  A friend did one (that's how we got our 79, as he found a 76 that was in better shape, so let the 79 go to us).  He used a 4th Gen Camaro drivetrain.  It had the 4L60 transmission and LS1 engine.  For that drivetrain, it needs to have the front of the K-member notched on the right side for the A/C compressor.  There are a couple of companies out there that make swap parts, and I think he used those for the engine mounts and transmission crossmember.  The swap kit he used was to put a LS engine into a Nova.  The crossmember had to be sectioned and widened.  I think he used the exhaust manifolds out of his Pontiac G8.  Not sure why the Camaro manifolds didn't fit.  He said the radiator dropped right in, like it was made for the Seville.  He replaced the instruments with an aftermarket gauge set he set into a flat piece of plastic that sits behind the stock lens.  He opted for a GPS speedo so he didn't have to dork with converting the electronic speedo to mechanical on the Seville.  It really looks nice there.  He also installed the engine cover off his G8, replacing the Pontiac emblems with a CTS-V emblem.  It looks factory! 

His 76, of course, doesn't have the limited slip diff that the later models came with, and he says he can spin the tire at will at just about any speed under 60.  He loves it.  I thought about it on ours, but think if i replace what's under the hood, it'll be an Oldsmobile crate engine with Edelbrock heads and aftermarket FI.  I'd be looking for more of a hotrod that looks stock, though, than a nice cruiser.

ANy chance of talking to this 76 owner that did this swap?

[hjlint]

I have a 77 Delta which at 4150 lb, small block Olds, TH400 trans is very comparably
for economy.  Even with the larger 403 engine, 19 mpg on the road is typical in good
conditions, never less than 16.  Axle ratio is 2.41:1; the car moves right along. 

I would suggest that first you make sure your car is running right.  I could check out that
ECU to see if its functioning properly.  If you haven't replaced the original timing chain
yet, its way, WAY overdue.  Cat converters plug up and ruin performance.  HEI advance
mechanisms can fail.  I think your axle is 2.56:1 which is reasonably economical.  My
TH400 has been converted to switch pitch, which might be worth 1/2 mpg, besides adding
a lot better response & smoothness. 
good luck,
Bruce Roe

Hi: does this Olds have a Carburetor?

[hjlint]

I've owned a '77 Seville the past 31 years. I recently cleaned the throttle body  bore with spray cleaner and a toothbrush.   It made such a difference that I had to adjust the idle speed down. I also use Lucas FI cleaner in the gas occasionally.  They recommend injection cleaning every 30,000 miles with newer cars, why wouldn't it be needed on this injected car? It does! 
I'm getting 17mpg on the highway. The car is really running strong now. Try it, you don't have much to lose.

gained over 100 RPM at Idle after cleaning throttle body.