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Old 01-22-2018, 09:09 PM   #1
dbgrigsby93
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Default SC2 top end mods for fuel economy

I have a 2001 Saturn SC2 that is in need of new valve stem seals. I drive 50 miles to work and then back 5 days a week and I'm going through about 2qts of oil a week. I have concluded that the problem is more in the valve stem seals than in the piston rings because my 1999 SL1 burns oil half as fast (b/c it has half as many valves). So this summer I am planning to pop the head off my SC2 and have new valve stem seals put in because I plan to drive this car to 1,000,000 miles and beyond. I'm getting about 36 MPG right now but know I can restore it closer to the 38 MPG expected and I don't see why I can't push above 40 MPG with some other simple mods while the head is off. So I want to get your opinion on the following mods I am proposing:

How much can I deck a DOHC head? The car should have a static compression ratio of 9.5:1 from the factory. If I can shave a little bit of material off the head, I can raise that static compression a bit to improve thermal efficiency.

Now let's talk about the dynamic compression ratio. I can raise the dynamic compression ratio by advancing the cam shaft. Does anybody know the cam specs of an SC2 motor? In particular, I need to know how many degrees ABDC the intake valve closes. Also, how many degrees advance do I get per link in the timing chain? I was thinking I could get away with advancing the cam about 4 degrees.

I still want to run 87 octane so don't let me get out of control raising my compression. But I figure I can offset increased heat of combustion with a colder thermostat. I found a 185 high flow but if anybody can point me to a colder one if needed, please do.

Lastly, I heard about people modifying their intake air temp sensor to have a higher resistance in the line making it think that the intake air temp is higher than it actually is. Therefore the computer delivers less fuel to the cylinders causing the car to run a little lean. I'm sure I could figure that out but I figure I could also build a custom mount to place the intake air temp sensor near the exhaust manifold.

That was a lot. I'm excited to hear your opinions. I'm hoping to be able to easily maintain highway MPG above 40.
Also, I know that I should rebuild the bottom end or at least re-ring the pistons but I'm being kinda cheap and writing that item off. I'm not too worried about it since my 1999 Saturn SL1 has 250K miles and runs great for cross country road trips.

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Old 01-23-2018, 12:14 AM   #2
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Default Re: SC2 top end mods for fuel economy

You might try looking at the specs listed on DifferentRacing.com, in "Tech Articles" and search on Sixthsphere.com I know I've seen them posted on DifferentRacing's site at least and 6s has enough modding info to keep just about anyone happy.

If MPG is what you want, then the best mod you can do to a DOHC is put a SOHC head on it and swap the 5spd to at least the SOHC 5th gear.

Last edited by fetchitfido; 01-23-2018 at 12:26 AM..

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Old 01-23-2018, 01:47 PM   #3
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Default Re: SC2 top end mods for fuel economy

Yeah, the 5th gear swap should put you in the 39~40 mpg range (depending on your speed, of course) on its own. You'll lose cruise control, don't know if that is important. The 5th gear thread shows what you have to do to get cruise back.

Some good MPG threads to read are by Cheapy Bob (cheapybob?) and DIYguy. They tended to document their changes pretty well.

A few people have built actual hot air intakes (redirecting warmed/hot air into the intake box) for mpg without "fooling" the IAT sensor (IAT is reading higher because intake air is actually warmer )

There's a few threads about running higher octane gas and getting better mpg, but whether it is worth it or not is going to depend a lot on how much more the gas is in your area. I've not tried this myself because I don't think I do enough hwy driving to make it worthwhile. there's a link somewhere that will show gas stations near you that don't have ethanol in their gas, which will help your mpg. think this is it
https://www.pure-gas.org/about

Another thing that I haven't tried yet (common theme ) is springs for the brake pads. They hold the pads away from the rotor when you are not braking. Someone posted it up and I bought a set, just need to do my brakes and I will install.

I've got about a year of commuting on my SC2, have been writing down my mpg, so should be a decent test.

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Old 01-24-2018, 11:48 AM   #4
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Default Re: SC2 top end mods for fuel economy

Every single person I know and have seen here who has done valves, valve guides, and/or seals to cure oil use has been disappointed.

That said, if you stop the oil burning the mpg's will improve.

As far as internal gains, I did a mild port job on my SOHC and seemed to pick up 1-2 mpg's as well as a bit of hp. Best guess on the hp would be 5ish.

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Old 01-24-2018, 09:24 PM   #5
dbgrigsby93
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Default Re: SC2 top end mods for fuel economy

Highmile,

Any thoughts as to why folks are disappointed replacing valve stem seals to cure oil burning? I don't want to fully rebuild the bottom end. At some point, the value of the car isn't worth it. But I did think about popping the oil pan off the bottom of the engine to push the pistons out and re-ring them. While in there I could also probably replace my rod bearings.

Your thoughts?

And in reponse to having to possibly run higher octane fuel after decking the head, I figure that the engine was designed with straight 87 octane in mind so now that colder burning 10% ethanol fuel is the norm, raising the compression should equal out to make the car run on 10% ethanol like it did on straight 87 octane.

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Old 01-25-2018, 02:41 PM   #6
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Default Re: SC2 top end mods for fuel economy

Quote:
Originally Posted by dbgrigsby93 View Post
Highmile,

Any thoughts as to why folks are disappointed replacing valve stem seals to cure oil burning? I don't want to fully rebuild the bottom end. At some point, the value of the car isn't worth it. But I did think about popping the oil pan off the bottom of the engine to push the pistons out and re-ring them. While in there I could also probably replace my rod bearings.

Your thoughts?

And in reponse to having to possibly run higher octane fuel after decking the head, I figure that the engine was designed with straight 87 octane in mind so now that colder burning 10% ethanol fuel is the norm, raising the compression should equal out to make the car run on 10% ethanol like it did on straight 87 octane.
Because the rings are the cause of the oil consumption. Anything short of installing new rings is just a waste of time.

You could do a quick and dirty rebuild, new rings & a quick cylinder hone without replacing anything else but the head gasket and that'll alleviate the oil burning.

You can easily achieve 45-48mpg with the SOHC head and a well maintained vehicle @60-65mph. Start from there before you start modifying junk.

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Old 01-25-2018, 08:25 PM   #7
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Default Re: SC2 top end mods for fuel economy

dbgrigsby93, there are many opinions about replacing valve stem seals and/or re-ringing pistons. One method may help or add more confusion but it should be done before valve seal replacement - a compression check, dry and wet (oil squirted into each cylinder). A compression test can separate worn/coked piston rings from worn valves. Try to determine the overall state of health of your engine. Replacing valve seals in the overall perspective of a well worn engine may or may not be an answer

There's an old service bulletin from GM, posted here awhile ago but if you can't find it or someone doesn't point to a link I'll try to find and reprint it - the first thing someone brings to Saturn, when they were still around, and mentions an oil consumption issue, GM referred to their service bulletin and if the car was in warranty, replaced valve seals. This was probably occurring at the same time when GM wasn't aware of the two wire coolant sensor failures that ran excessive fuel mixtures to dilute the thin oil film on cylinder walls, created overheated engines when the faulty coolant sensor never sent correct temperatures and prevented the PCM from turning on the cooling fan. Overheating engines with the temperature gauge never pointing to a hot engine can be assumed to cook the engine (slow process of coked oil interfering with oil rings slowly allowing oil into combustion chambers and the rest is history. Perhaps at the beginning of the S-series, GM decided to replace valve seals before Saturn became mired in engine problems that ultimately pointed to every original round nosed plastic coolant sensor failure from '91-'01.........

You have options and can proceed with some semblance of logic at low cost by performing a compression check (185 psi is the go/no go point) then decide if rings and/or valves and/or valve seals are needed.

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Old 01-26-2018, 09:34 AM   #8
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Default Re: SC2 top end mods for fuel economy

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Originally Posted by AlexofNazareth View Post
Because the rings are the cause of the oil consumption. Anything short of installing new rings is just a waste of time.

You could do a quick and dirty rebuild, new rings & a quick cylinder hone without replacing anything else but the head gasket and that'll alleviate the oil burning.
yeah what AlexofNazareth said...

lot of folks will contend that cylinders need to be bored to get a good seal on the rings and I agree but with the point you are at anything is an improvement. And since the pistons will be out it's a good time to drill oil return holes in them. It can be done by hand in a matter of minutes per piston.

It can be done in the car however if it were me I'd just pull it and do all the work on the engine stand. It's faster in the long run or at least in my shop.

This really gets into the question of where do you stop. Since I drive my cars literally forever then putting a few bucks into an engine is really a no brainer. This is obviously not the case for everyone. A lot of people told me I was nuts when I did a complete rebuild on mine at 417K which with all new hoses, radiator, etc etc I spent in the $1800 range. But that was over 230k ago.

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Old 01-26-2018, 11:36 AM   #9
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Default Re: SC2 top end mods for fuel economy

this is not a top end mod but i have same year saturn and all i did to my saturn was K&N air filter and i added some abs pipe at the end cause i removed my air box from my car and put filter there and did lots of fuel mileage tests and im getting 67mpg, also not sure if yours was a 5 speed or automatic mpg will differ between manual/auto

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Old 01-26-2018, 12:53 PM   #10
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Default Re: SC2 top end mods for fuel economy

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this is not a top end mod but i have same year saturn and all i did to my saturn was K&N air filter and i added some abs pipe at the end cause i removed my air box from my car and put filter there and did lots of fuel mileage tests and im getting 67mpg, also not sure if yours was a 5 speed or automatic mpg will differ between manual/auto
Stop everything. This guys got all the answers.

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Old 01-28-2018, 08:05 PM   #11
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Default Re: SC2 top end mods for fuel economy

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Originally Posted by AlexofNazareth View Post
Stop everything. This guys got all the answers.
If you're referring to 67 mpg, I wonder if that's possible. The best was close to or around 50 mpg but this is miles per gallon. In Canada, I think fuel is calculated in kilometers per liter. Sometimes the math comes out incorrect if conversions aren't used correctly.

If sc2 saturn did get 67 mpg; 1 mile = 1.6 kilometers, 1 gallon = 3.785 liters, 67 miles = 107.2 kms per gallon or 28.32 kms per liter. If there are any Canadians reading this, perhaps some input about kms/liter might put this in perspective.....

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Old 01-29-2018, 11:35 AM   #12
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Default Re: SC2 top end mods for fuel economy

I didn't see that was from Canuckistan.

My PR was 53.5 going 50-55 through Iowa.
If he's doing imperial gallons then its a 20% increase [64ish mpg]

But the point is his figure isn't really feasible during normal driving.
Ideally you can easily see 45+mpg if you're sensible and aren't driving 80mph

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Old 01-30-2018, 10:43 PM   #13
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Default Re: SC2 top end mods for fuel economy

Quote:
Originally Posted by dbgrigsby93 View Post
I have a 2001 Saturn SC2 that is in need of new valve stem seals. I drive 50 miles to work and then back 5 days a week and I'm going through about 2qts of oil a week. I have concluded that the problem is more in the valve stem seals than in the piston rings because my 1999 SL1 burns oil half as fast (b/c it has half as many valves). So this summer I am planning to pop the head off my SC2 and have new valve stem seals put in because I plan to drive this car to 1,000,000 miles and beyond. I'm getting about 36 MPG right now but know I can restore it closer to the 38 MPG expected and I don't see why I can't push above 40 MPG with some other simple mods while the head is off. So I want to get your opinion on the following mods I am proposing
Search our forums, for threads about modifying the EGR valve. I have seen one thread, where a SOHC owner was almost at 50mpg with some type pf restrictor in the EGR system.

Quote:
How much can I deck a DOHC head? The car should have a static compression ratio of 9.5:1 from the factory. If I can shave a little bit of material off the head, I can raise that static compression a bit to improve thermal efficiency.
Decking the head will retard camshaft mechanical timing, and thus reduce not only performance, but your effective powerband rpm range and fuel economy.

Quote:
Now let's talk about the dynamic compression ratio. I can raise the dynamic compression ratio by advancing the cam shaft. Does anybody know the cam specs of an SC2 motor? In particular, I need to know how many degrees ABDC the intake valve closes. Also, how many degrees advance do I get per link in the timing chain? I was thinking I could get away with advancing the cam about 4 degrees.
Compression ratio is only increased IF air volume/mass is increased within the cylinder. These engines operate at about 89-92% VE in their stock build. Advancing the camshafts may raise compression, but unless the PCM is reflashed for proper ignition and air/fuel ratios, you will encounter drivability issues. Without a RAM AIR system, it is nearly impossible to achieve 100%, or above, VE on a naturally aspirated engine. This modification will sacrifice low-rpm torque, which translates to lower fuel economy amd poor atomization at low engine speeds. The DOHC already suffers from a lack of low-rpm torque, due to the intake manifold designs and the aggressive factory camshaft profiles, hence why peak torque doesn't occur until 4,800rpm and peak HP is at 6,000 on the 1991-1999 models, and only 5,600rpm on the 2000-2002 models(due to the head port redesign and plastic manifold).

Quote:
I still want to run 87 octane so don't let me get out of control raising my compression. But I figure I can offset increased heat of combustion with a colder thermostat. I found a 185 high flow but if anybody can point me to a colder one if needed, please do.
Ethanol burns hotter than gasoline does, and is less energy dense, hence why fuel economy drops. You will find that ethanol engines have to run very rich mixtures, to prevent spark knock. About 9.8:1 static compression ratio is the limit for 87 octane fuel. 10.0:1 or higher will REQUIRE 91 octane(93 octane recommended).

Quote:
Lastly, I heard about people modifying their intake air temp sensor to have a higher resistance in the line making it think that the intake air temp is higher than it actually is. Therefore the computer delivers less fuel to the cylinders causing the car to run a little lean. I'm sure I could figure that out but I figure I could also build a custom mount to place the intake air temp sensor near the exhaust manifold.

That was a lot. I'm excited to hear your opinions. I'm hoping to be able to easily maintain highway MPG above 40.
Also, I know that I should rebuild the bottom end or at least re-ring the pistons but I'm being kinda cheap and writing that item off. I'm not too worried about it since my 1999 Saturn SL1 has 250K miles and runs great for cross country road trips.
Modifying the AIT sensor is certainly feasible, and since you have OBD-II, you can see the modifications at work with live data.

Other things to improve economy: Porting the Exhaust side only(low-rpm torque) to match the ports on the manifold

K&N/Spectre/Other Brands of racing air filters

Granatelli Motorsports 0-ohm wires

E3 Diamond Fire spark plugs w/indexing washers OR Side-gapping the stock plugs w/indexing washers.

One final question: Does this SC2 have an automatic transmission or is it 5-speed?

...
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"He checks the gas, and fills the oil....."

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