Project '78 Seville STS !st Gen style ;)
April 13th, 2020, 05:12 PM
#1
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Join Date: Apr 2020
Location: Oxon Hill, MD (Metro Washington D.C.)
Posts: 8
Project '78 Seville STS !st Gen style ;)
First of all, as a Newb greetings to everyone here on the boards. While I'm not new to cars and/or enthusiast boards, I am new to Oldsmobile. My experience with these cars dates back to my early childhood when My father's mechanically broken '68 Olds Cutlass sat in our back alley for years, never seen running again. We left the car once we moved, as my father traded for a room divider (much to my then 10 1/2-year-old disappointment) Even today, I really would've like making that car my first to drive and learn to wrench on, even over our 76 Nova (which ran second to a distant and much hated/unreliable 86 Escort L, but I digress) We had always been a GM family, mainly Chevys after the Olds, but still I was bummed even more to learn about that Cutlass much later, finding out it was not only one of the most legendary iterations of the Cutlass platform, but also how much it appreciated as a collectors car. Our Olds for sure was in great physical shape, and sure as hell didn't deserve to be traded for a piece of furniture long tossed out.
Anyhow, decades later, I find myself in the strange position of purchasing a Cadillac with unusual "genetics" lol. I loved the Sevilles back when they debuted in the mid/late seventies... mainly because they looked like classier Novas. What I didn't know then, was that same trusty Olds 350 that was in our 68 Cutlass was in the Seville. (Only greatly detuned and structurally weakened in the mains) Now that I have this knowledge, and have got you up to speed, this is what I'm looking to do.
I want to restore this car back to prime condition. Mechanically speaking, I want to go beyond just "prime" condition. What I want to build is in my title. What GM should've done but didn't. I understand Caddy's back then were not meant to be "sports" machines. However, the Seville was meant by Cadillac to be the first Euro Luxury sedan fighter of the 70's, hence the Nova X body foundation. It was engineered well past that point enough to get it's own designation, the K body. Well cool, I can find X/F body parts from the Nova/Camaro suspension bin and tweak it in the aftermarket. What I need help with is the motive force of a certain 350 rocket engine (that has lost a little too much "thrust" over the smog 70's)
The current motor is pretty much stock, supposedly has 78K miles on it. Without any other paperwork to confirm this, I seriously doubt it's wrong as the odometer works, and Sevilles were rarely driven as much as other cars I've found. The stock EFI was having issues with cold start and high cold idle. It also misfired and stalled once warmed up and put under load. The restoration shop I have it at did find a problem with old fuel, rotten pick up assembly in the tank (rubber pieces breaking off) and a sketchy lift pump that couldn't hold pressure once warmed up. All of that was cleaned out and replaced. That solved the misfire and stalling under load warmed up issue. It partially helped the cold start, but the high idle condition remained. At that point fuel system-wise, I had the tech stop as I was now pondering my next avenue of attack.He had already seen that the ECU had been replaced once before recently (probably because of the lift pump issue as I've seen on the Caddy boards) I told him people either: 1) Restore the factory EFI for collector's value 2) Change to aftermarket TBI (for more reliability and flexability in tuning) or 3) Convert to carburetors for ease of manual tuning and reliability (nothing beats old school simplicity to get you home, whereas even aftermarket TBI can let you down)
The cost of a TBI system is tempting, but still a bit beyond where I want to go right now. I have no vehicle to drive, and this will be my daily for now. Once I get it on the road. I don't drive much per day in my commute... about 35 miles round trip Monday - Saturday, and am home (thanks Coronavirus craziness) on Sunday, I have other physical needs to get this car ready for MD inspection and Emission (just barely got within the coverage of 1976 model year and newer... dammit!) Sigh. Oh well. So, here's where I'm at. I want this Seville to be what GM/Cadillac took 12 years to finally build. (I know there was STSes in the 80's, but they weren't the real deal. Only in the 90's with Northstar did Cadillac start trying... Northstar issues aside lol. This car could be one hell of a first attempt with the right help, and having the engine of GM's Sport-Luxury division powering it seems like a match in heaven if played right.
So far, I have decided to go with an Edelbrock Performer 3711 intake. One to lighten up the engine of course, and two, it's the only smog legal performance intake I can find. I know about the Olds A4's, lurking around, but haven't been able to score those I know EGR's generally do more harm than good, and that MD generally does NOT do visual inspections, so normally I'd risk it with maybe a Performer RPM (or find and earlier Olds stock non smog intake) However, there's a decent chance I may have to move to the "Left Coast" and everybody knows where I'm talking about. They DO visuals over there, and I'm sure they'll see the difference right away. So I have to do this as if it were a Cali car, and seek out as much Federal/C.A.R.B stuff possible. That also means my Carburetor options are also limited. Either I could go true GM for authenticity (Q-jet 4 BBL) or Holley's 4165/75 series Q-jet replicas. Right now, I'm leaning to the Holley, as this place I'm dealing with doesn't do many Q-jets and are not comfortable with them. (I know about places like Cliff High that do know their way around the Q-jet, but I can't wait months to get one right now. The Holley can be had in days. I was thinking of staying on the lower side... a 650CFM with a C.A.R.B. legal 1-inch spacer that utilizes Q-jet like orifices that are helixed tapered downward towards the Intake mount for flow/mix purposes. It also helps the top end a little I read by simulating a taller single plane manifold (with the drivability of the dual-plane still intact) The smaller carb will help maintain velocity, and should provide enough fuel for now with some level of economy.
The next thing I want to do is tricky because it's a toss-up in benefits. Money is a bit stretched, as I need to get some other things done at a minimum for a functioning car that's roadworthy. The exhaust seems a little big, even though it's single. The last owner paid $200 to have a ghetto job from the cat back, and while it functioned, it hung down underneath the rear axle instead of over it. That's getting corrected. What I may want to do is get some smog legal headers to open things up a bit, but it will have to be single exhaust as California will not allow a dual system on one that was single stock. Now, I can increase the diameter of the single system, and eventually I may do that when $$$ permit. Until then if I can do headers I would, but if not, the only other option to help the car make a bit more shove is a mild cam, combined with bumping the rear gear to maybe 2.73 to max 3.08. Don't want to go higher than that as mileage will take a hit. One day, I will look into making this a 4 speed, whereas I can possibly go down to 3.46/3.73 max. Right now, 3.08 is as high as I go (besides Sevilles in high altitudes in Cali got this optional rear gear anyway, so it would pass as a GM authentic quality offered for the car) If I do a cam, it has to be mild enough to deal with the stock 8.0 to 1 compression ratio, allow me to not have to redo the entire valvetrain (I found Olds rockers are siamesed together and can't be adjusted...aargh!) I don't know how far one can go before it's mandatory you have to do something. I have been used to overhead cam engines from Germany, so I'm a bit out of my element here. If I can't do a cam while keeping the valvetrain stock for now, if I can find a good enough deal I may spring for it. At least swapping the rockers out for adjustable units, and appropriate springs. I just don't want to wild as I have a stock converter, and will see at least of I can get the gears shortened up about 10 to 20%. That combo of boost in low/mid torque, combined with some modest gear help could give this car the punch it needs without stressing a 40+-year-old motor too much. Once we get to more certain times and funds allow, I'll look at a full rebuild of this motor to more "proper" levels worthy of an STS possibility, late 70's style. Car stock in top tune (which it will get.. plugs, wires,,,etc..) goes 0 - 60 in 12.6 seconds and 1/4 in 19+. Our Chevy Nova with 305 2BBLs did 0 to 60 in 7.9 (self-timed after slight advancing of the distributor back in the 80's) No doubt shorter rear and 500 lbs lighter. But 40 less hp, and 30 less lb-ft torque than the Olds 350. Gotta be some way to get the Olds to push a bit more than the weezy 305 Chevy motor (enough Chevy fans told me back then don't ever build a 305. Not worth it lol)
I yield the floor to all who wish to respond...
Thanks for your help in advance guys!
Anyhow, decades later, I find myself in the strange position of purchasing a Cadillac with unusual "genetics" lol. I loved the Sevilles back when they debuted in the mid/late seventies... mainly because they looked like classier Novas. What I didn't know then, was that same trusty Olds 350 that was in our 68 Cutlass was in the Seville. (Only greatly detuned and structurally weakened in the mains) Now that I have this knowledge, and have got you up to speed, this is what I'm looking to do.
I want to restore this car back to prime condition. Mechanically speaking, I want to go beyond just "prime" condition. What I want to build is in my title. What GM should've done but didn't. I understand Caddy's back then were not meant to be "sports" machines. However, the Seville was meant by Cadillac to be the first Euro Luxury sedan fighter of the 70's, hence the Nova X body foundation. It was engineered well past that point enough to get it's own designation, the K body. Well cool, I can find X/F body parts from the Nova/Camaro suspension bin and tweak it in the aftermarket. What I need help with is the motive force of a certain 350 rocket engine (that has lost a little too much "thrust" over the smog 70's)
The current motor is pretty much stock, supposedly has 78K miles on it. Without any other paperwork to confirm this, I seriously doubt it's wrong as the odometer works, and Sevilles were rarely driven as much as other cars I've found. The stock EFI was having issues with cold start and high cold idle. It also misfired and stalled once warmed up and put under load. The restoration shop I have it at did find a problem with old fuel, rotten pick up assembly in the tank (rubber pieces breaking off) and a sketchy lift pump that couldn't hold pressure once warmed up. All of that was cleaned out and replaced. That solved the misfire and stalling under load warmed up issue. It partially helped the cold start, but the high idle condition remained. At that point fuel system-wise, I had the tech stop as I was now pondering my next avenue of attack.He had already seen that the ECU had been replaced once before recently (probably because of the lift pump issue as I've seen on the Caddy boards) I told him people either: 1) Restore the factory EFI for collector's value 2) Change to aftermarket TBI (for more reliability and flexability in tuning) or 3) Convert to carburetors for ease of manual tuning and reliability (nothing beats old school simplicity to get you home, whereas even aftermarket TBI can let you down)
The cost of a TBI system is tempting, but still a bit beyond where I want to go right now. I have no vehicle to drive, and this will be my daily for now. Once I get it on the road. I don't drive much per day in my commute... about 35 miles round trip Monday - Saturday, and am home (thanks Coronavirus craziness) on Sunday, I have other physical needs to get this car ready for MD inspection and Emission (just barely got within the coverage of 1976 model year and newer... dammit!) Sigh. Oh well. So, here's where I'm at. I want this Seville to be what GM/Cadillac took 12 years to finally build. (I know there was STSes in the 80's, but they weren't the real deal. Only in the 90's with Northstar did Cadillac start trying... Northstar issues aside lol. This car could be one hell of a first attempt with the right help, and having the engine of GM's Sport-Luxury division powering it seems like a match in heaven if played right.
So far, I have decided to go with an Edelbrock Performer 3711 intake. One to lighten up the engine of course, and two, it's the only smog legal performance intake I can find. I know about the Olds A4's, lurking around, but haven't been able to score those I know EGR's generally do more harm than good, and that MD generally does NOT do visual inspections, so normally I'd risk it with maybe a Performer RPM (or find and earlier Olds stock non smog intake) However, there's a decent chance I may have to move to the "Left Coast" and everybody knows where I'm talking about. They DO visuals over there, and I'm sure they'll see the difference right away. So I have to do this as if it were a Cali car, and seek out as much Federal/C.A.R.B stuff possible. That also means my Carburetor options are also limited. Either I could go true GM for authenticity (Q-jet 4 BBL) or Holley's 4165/75 series Q-jet replicas. Right now, I'm leaning to the Holley, as this place I'm dealing with doesn't do many Q-jets and are not comfortable with them. (I know about places like Cliff High that do know their way around the Q-jet, but I can't wait months to get one right now. The Holley can be had in days. I was thinking of staying on the lower side... a 650CFM with a C.A.R.B. legal 1-inch spacer that utilizes Q-jet like orifices that are helixed tapered downward towards the Intake mount for flow/mix purposes. It also helps the top end a little I read by simulating a taller single plane manifold (with the drivability of the dual-plane still intact) The smaller carb will help maintain velocity, and should provide enough fuel for now with some level of economy.
The next thing I want to do is tricky because it's a toss-up in benefits. Money is a bit stretched, as I need to get some other things done at a minimum for a functioning car that's roadworthy. The exhaust seems a little big, even though it's single. The last owner paid $200 to have a ghetto job from the cat back, and while it functioned, it hung down underneath the rear axle instead of over it. That's getting corrected. What I may want to do is get some smog legal headers to open things up a bit, but it will have to be single exhaust as California will not allow a dual system on one that was single stock. Now, I can increase the diameter of the single system, and eventually I may do that when $$$ permit. Until then if I can do headers I would, but if not, the only other option to help the car make a bit more shove is a mild cam, combined with bumping the rear gear to maybe 2.73 to max 3.08. Don't want to go higher than that as mileage will take a hit. One day, I will look into making this a 4 speed, whereas I can possibly go down to 3.46/3.73 max. Right now, 3.08 is as high as I go (besides Sevilles in high altitudes in Cali got this optional rear gear anyway, so it would pass as a GM authentic quality offered for the car) If I do a cam, it has to be mild enough to deal with the stock 8.0 to 1 compression ratio, allow me to not have to redo the entire valvetrain (I found Olds rockers are siamesed together and can't be adjusted...aargh!) I don't know how far one can go before it's mandatory you have to do something. I have been used to overhead cam engines from Germany, so I'm a bit out of my element here. If I can't do a cam while keeping the valvetrain stock for now, if I can find a good enough deal I may spring for it. At least swapping the rockers out for adjustable units, and appropriate springs. I just don't want to wild as I have a stock converter, and will see at least of I can get the gears shortened up about 10 to 20%. That combo of boost in low/mid torque, combined with some modest gear help could give this car the punch it needs without stressing a 40+-year-old motor too much. Once we get to more certain times and funds allow, I'll look at a full rebuild of this motor to more "proper" levels worthy of an STS possibility, late 70's style. Car stock in top tune (which it will get.. plugs, wires,,,etc..) goes 0 - 60 in 12.6 seconds and 1/4 in 19+. Our Chevy Nova with 305 2BBLs did 0 to 60 in 7.9 (self-timed after slight advancing of the distributor back in the 80's) No doubt shorter rear and 500 lbs lighter. But 40 less hp, and 30 less lb-ft torque than the Olds 350. Gotta be some way to get the Olds to push a bit more than the weezy 305 Chevy motor (enough Chevy fans told me back then don't ever build a 305. Not worth it lol)
I yield the floor to all who wish to respond...
Thanks for your help in advance guys!
April 14th, 2020, 05:15 AM
#3
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Look forward to seeing pics. Make sure you know your local smog rules as well as the smog rules for the "left coast." As far as I know aftermarket carburetors, cams, headers, etc. are strictly forbidden. You might be better off having your mechanic rebuild the stock Cadillac TBI.
April 14th, 2020, 07:53 AM
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Location: Oxon Hill, MD (Metro Washington D.C.)
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April 14th, 2020, 08:12 AM
#5
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Join Date: Apr 2020
Location: Oxon Hill, MD (Metro Washington D.C.)
Posts: 8
Look forward to seeing pics. Make sure you know your local smog rules as well as the smog rules for the "left coast." As far as I know aftermarket carburetors, cams, headers, etc. are strictly forbidden. You might be better off having your mechanic rebuild the stock Cadillac TBI.
About cams... that is a grey-black area I know, as most cams aren't tested and approved for sure. However, here you might be able to wiggle a bit... so long as one doesn't go to far. Visual inspections on cams I doubt happen (but then,I could be wrong lol) However, if I keep the cam conservative in grind (meaning somewhere closer to the OEM side of duration/lift, but better grinds for power and efficiency, jet the carbs correctly, let the EGR do it's thing, and a proper high flow cat (working), I could get the car to pass sniff test portion. The idle would still be smooth, not giving away the bit more aggressive lump inside. At least that's what I aiming for. And there are some conservative headers out there with C.A.R.B approval (I was shocked to find them, and it's not that much like the carbs/intakes for selection) but I take what works at this point.
If I can get this Olds 350 up into the low mid 200 hp range, with torque north of 300, that will be good enough for me. Smog legal, clean, and with gearing help, nasty fast enough to show Old School STS was possible if Cadillac and Olds really tried. (At least fast enough to hang with a late 70's early 80's Benz.)
Any Cam ideas guys? Been checking the normal sources, but Old's cam grinds are not as plentiful as the others (much like other performance parts I'm finding) So far, most seem probably too aggressive from what I remember how these are designed, but it's been a long while since I've been involved with American muscle. So, I'll go to those who've been here longer. Suggestions for the goals I've stated? Cost effectively?
Last edited by 78 Cadsmobile; April 14th, 2020 at 08:15 AM.
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