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Old 05-24-2012, 06:24 PM   #1
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Default GM 3800 series I vs II real world mpg

I was trolling the internet for more info on 3800 stuff and I came across this post from rjolly87

"From what I understand, the series 2 is a pretty different animal than the series 1. The intake manifold issues are no big deal once fixed, and should not be used to determine which you choose. Series 1 is a torque monster, a real stoplight warrior. True, the upgrade market is just not there, and it is not OBD 2, but the Series 1 does have one thing working for it strongly, fuel mileage. Especially when coupled with a 2.84 FDR, properly tuned up with a couple of mods, they will completely own just about any other similarly sized car (30'* reliably, some reports of 40'*) despite cruising speed (up to about 80-85mph). Series 2 is more mid to high range power, and do better when wound up at speed. They also have OBD2, and the aftermarket following. Not even counting that they can hold their own in the fuel mileage race too, but they are pretty speed sensitive."

I ask because I'm looking for a used 3800 and I've passed over several 1995 series 1'* (Including a beautiful 95 Red Regal Gran Sport Coupe with 24k) because I keep telling myself I need to have OBDII for ease of maintenance, and a Series II for the better power and mpg.

OEM numbers (as well as the wikipedia article) "claim" that the series II'* get better mpg and more horsepower due to a better intake and EGR design. rjolley87'* post seems to have more insight into this.

I would just like to hear some real world MPG numbers from people who own stock Series I/II and aren't whipping them stoplight to stoplight. My car is a 75, and I drive like a 90 year old grandpa to get 11.9 mpg around town (other people would probably get 6-8 lol). So I'd like to hear how I'd do with a 3800.

I was looking at 88-92 Toronados, and in a youtube video someone'* 88 Toro computer was reading 15mpg which I thought was pretty low. In another forum, someone claimed they got 38mpg in a series 1 using premium fuel, but stating that if you use normal octant you'll get around 12-15 in a Series 1. Let me know any thoughts any of you have on this!

There is also a Supercharged 95 Olds LSS on the other coast from me, which if probably one of the rarest Olds ever made, but since that is a Series 1 and there'* no aftermarket, I'm staying away. Or should I? I'd like to not have to use premium fuel. But I would if it yields mid 30s in a series 1. Has anyone tried this?

Thanks

Doug
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Old 05-24-2012, 07:17 PM   #2
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Suppose I should clarify that those numbers and such were loafing along on the highway. Around town, if running properly in their native application, I would expect low to mid 20'*. With that much weight, you would be working the engine that much harder, and the fuel economy would suffer.

An updated drivetrain would probably do you good, but I am not sure what. Something that is not working too hard to move the car around, with a fair amount of low end torque. I myself would not immediately consider any 3800, as it would be working too hard in this application.

I would want to do some research on this, and let the experts chime in with the insight that they have.
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Old 05-24-2012, 07:40 PM   #3
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Thanks for the info Rjolly. We both use Fuelly .

I'm considering the 3800 because here in FL they seem to come up with lower mileage for not much money from the retirement crowd. I'm trying to find one with leather and a sunroof, but I'll cave in if the price is right. And the junkyard is full of the 90s 3800s so I know they would be very inexpensive to maintain.

My brother and Dad both have Cougars with the 4.6. They are nice cars and more abundant and less expensive then GM 3800 cars here, but the 3800 will do better on gas. Plus I think it would be cool to pick up a 90s Olds.
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Old 05-24-2012, 07:40 PM   #4
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My average drive to work is about 2 miles of city(small city) and 20 miles on the interstate. Even with the occasional romp I'm topping off at the end of the week at about 380 miles per tank. This week, I had 3 gallons left at 380 miles. This also has the 3.29 FD.
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Old 05-24-2012, 07:54 PM   #5
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I think I may have misunderstood. Were you looking to motorswap, or simply getting another vehicle to save fuel?

In a real world application, I think it seems like the Series 2 does a little better, but for sheer highway economy, the series 1 does better.

In my car, the Series 1 with 2.84 FDR (like in mine) takes a bit to get going, so I suspect the in town fuel economy suffers for it, but there is serious ownage going on when the cruise control is set at 75 on flat level ground.

Well, maybe not in my case, I have some work to do, and it is starting to really complain.
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Old 05-24-2012, 08:07 PM   #6
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if you are looking for better overall mpg, get the II. if you look at my fuelly it really depends on how i drive that week. if i drive like a normal human, i can get 24mpg easily, and thats pulling on the cars behind me at lights. the low numbers you see are generally me driving like a chicagoan. as far as highway goes, the II is definitely the better choice. im running the original o2 sensors with no mods but a gutted airbox and on the drive from chicago to memphis i was in the 30'* every single time.( only started using fuelly recently) the last time (when i was moving back up north) i drive over a truck scale and i had 600lbs over the sticker on the door.

44 4/25/12 211.0 7.00 30.1 4.159 0% cairo illinois, moving
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Old 05-25-2012, 09:02 AM   #7
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I've had both S1 and S2 motors in Bonnevilles of the same era. The mention of the 2.84 gear ratio is interesting because the S2 had the potential 2.86 gear ratio. When you look at S1 vs S2, the gear ratio doesn't come into play as there are comparable ratios for all three. 2.84 became 2.86, 3.0? became 3.05 and 2.92 on the SC motor became 2.93. Really a miniscule difference.

On the stoplight racer part. Spinning is spinning and spinning isn't winning you anything but a trip to the tire store. Having owned both 95 and 97 SC cars, there'* no torque difference on the line. They both spin more than they should. There is one misconception that Randy may have been led to believe. The Series I didn't have as much Torque Management as the Series 2. Torque Management is as it'* name suggests, the pcm managing the potential torque of the motor. Therefore it cuts injectors, timing and fuel to hold the car back from spinning the tires excessively. Which is where the idea about S1 having more low end torque may have evolved. I personally raced WillWren in his 93 at the track. We hot lapped repeatedly during a test and tune night. My car had a pulley and his had a ton of stuff. The race went to whoever got the jump. There was no led from the line by one car each time, it was relatively even as the cars are nearly the same car with different motors. The S2 performs better and breathes better at higher rpm than the S1. That'* the biggest difference. I had a buddy drive my 95 and me driving the 97 on the highway, the S2 was clearly superior at those rpm/speeds.

Overall though, both S1 and S2 are very comparable on fuel mileage.

S2 is really a redesigned, updated S1. Same with the transmissions. The reason you'll find much more breakage on the S2 and the 4T65E is that more modifications became available when the Grand Prix (sports car of the line up) got the power plant.
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Old 05-28-2012, 01:07 AM   #8
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Haha rjolly, your post makes much more sense to me now. Sorry that I didn't explain it better. I'm swapping cylinder heads on my 75 cutlass 350 to get better mpg. But the Olds body has lots of rust on the rear deck and body and needs a break from duty to be restored. The engine'* mpg is also not good for a daily driver (I suspect from the bad MPG the carb needs to be redone), so I'm looking for a newer daily driver with a 3800. I'll still be working on the Olds 350 Rocket to optimize it for mpg and horsepower, as I've read some amazing things about a well-tuned 350 getting 25mpg highway. (This was in a 72 Cutlass, which is lighter, engine was a '68 with a 200-r4 with 3.73 rear gears and 2.5 Flowmaster exhaust)

I really have grown to have a liking for pretty much all cars that came with the 3800. In college my roommate had an 4 door '87 Olds 98 Regency. Those cars arguably have the least appealing styling of any 3800 cars and a lot of people would call them ugly, but once I went for a ride in it, I was a hooked. There was something about the wonderfully comfortable seats, the nice ride, and the amazing visibility that made me constantly ask if he was driving. And my roommate was complaining about getting mid-20s mpg, while I was getting 12. So I figure the same platform, only newer, must be even better.

Thanks for the info, Mike. Do you divide your mile/gal for a mpg figure? What is a typical fill-up for you in gallons?

Thanks for the numbers, Elta. It'* good to know a heavier car like the Park Avenue isn't affected much by mpg as I would have suspected. I know the Riviera, Park Avenue weigh more then most other 3800 powered cars. Strangely, the smaller Regal weighs more then the larger LSS. (making sure to compare models that are both Supercharged or both not Supercharged)

Thanks Bill for your insights. Are you saying most transmission issues come from mods and people running performance parts and more HP through their factory transmission? I'll not looking to do anything but keep my car pretty much factory other then a K&N and some custom tuning for MPG.

But eventually, years down the road when I get another daily driver, I'm sure I'll probably do a top-swap, add a supercharger, and blow some young kids away in an Olds LSS or other sleeper.

Speaking of superchargers, here in FL you-pull-it junkyards I come across series I superchargers pretty often, but I've never seen a series II. I'm guessing they get unbolted pretty fast after the car is placed.
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Old 05-28-2012, 05:51 AM   #9
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That last fill up of mine was around 15 gallons. Because I started this new job back in April, I haven't really been paying close attention to the MPG.
Yes, I divide the total gallons used by the total miles to get my MPG figure.
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Old 05-29-2012, 08:43 AM   #10
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my 98 sse 3.05 gets 28 0% highway (e3,k+n drop in) driven by my wife who is far from patient.

her old mans 96 se 2.86 50% hwy gets 32 driving mostly for mileage. stock

i think matching the ratio to what type of driving you do will help quite a bit for max mileage. dont think you mentioned what type of driving you want to do?
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