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 What Octane Grade Fuel for 3800 SC?

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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Tue Jul 15, 2008 4:21 pm

RivieraRyan wrote:
Gas is crazy nowadays, is there any mixture i can use instead of premium every time?


Assuming you drive a supercharged Riv?, you CAN run lower octane, if you want to risk long and possibly short term engine damage. Not worth the risk, IMO, for the 20-30 cents difference between reg and premium.

Today a gas station that had closed a couple years ago, reopened, and lists all octane levels at $3.79/gal, so I'll be filling the Riv after work. smile
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Tue Jul 15, 2008 5:31 pm

You need premium to push the throttle more than a little, or drive up a hill, or when it gets extremely hot... what I would consider normal driving conditions.

Using 89 "plus" grade will create knock in your engine. 87 "regular" will create more knock. This can be shown with a scan device to monitor KR. The engine will try to combat knock by retarding timing and reducing power, but the knock still occurs even if it is kept under control.

We know using anything less than premium causes knock. We don't know exactly how much knock is bad for the engine. We know knock can damage spark plugs and chip pistons. It can also lead to preignition, which can burn a hole through a piston in one or two revolutions.

My advice is to use premium to be on the safe side. If you do mix in some regular, drive very conservatively. Best way to know the answer for sure is to use a scanner to "see" how much KR is occuring in your engine.

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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Tue Jul 15, 2008 5:44 pm

RivieraRyan wrote:
Gas is crazy nowadays, is there any mixture i can use instead of premium every time?

just read the whole thread you posted to. It's all explained in here... wink
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PostSubject: 87 octane   Wed Aug 06, 2008 9:03 pm

I have been putting 89 octane in my Riv and noticed no problems. I just put 87 octane in because it was 17 cents cheaper at 3.60/gal here.

Just wondering if anyone else does this and if it will trigger a knock sensor code? I'm taking my Riv down to TN from IN next week and cheaper gas would be nice, just don't want it to start missing or anything.

My last car was a turbo eclipse and it called for premium and I ran the cheap stuff in it with no problems.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Wed Aug 06, 2008 9:15 pm

im running 93 with 2 bottles of octane booster
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Wed Aug 06, 2008 9:21 pm

palermocorey90 wrote:
im running 93 with 2 bottles of octane booster

I'm sorry bonk

I guess I'm gonna run this 87 and see how it performs without getting into boost much.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Wed Aug 06, 2008 9:40 pm

i run that because thats what its tuned for. its tuned for 93, but 3 or 4 more octane points wont hurt
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Wed Aug 06, 2008 10:00 pm

manofmany wrote:
I have been putting 89 octane in my Riv and noticed no problems. I just put 87 octane in because it was 17 cents cheaper at 3.60/gal here.

Just wondering if anyone else does this and if it will trigger a knock sensor code? I'm taking my Riv down to TN from IN next week and cheaper gas would be nice, just don't want it to start missing or anything.

My last car was a turbo eclipse and it called for premium and I ran the cheap stuff in it with no problems.
No, 87 is bad for supercharged Rivs. It causes more knock when you use it. It's really only $4-$5 extra per fill up from empty to use 93/94 octane. It might not cause a code but it's bad for the motor regardless.

lol, don't worry someone else is dealing with the problems of your old Eclipse now. Good thing you bought a Riv! Every Eclipse I've seen people mess with the boost or do some modding and then the motor blows. I know, my friends all tried it and a few of them blew their motors in the process. Mostly 2G Eclipses and 1Gs, no one had the 3Gs or newer.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Wed Aug 06, 2008 10:38 pm

If the knock is too bad I think it will set a code. I will find out.

I will probably just keep finding stations that have 89 for 10 cents more a gallon rather than the ones who are 17-20 cents higher.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Wed Aug 06, 2008 10:43 pm

Quote :
im running 93 with 2 bottles of octane booster...its tuned for 93, but 3 or 4 more octane points wont hurt

Octane boosters only give you .10 octane increase over the pump.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Wed Aug 06, 2008 11:06 pm

Use Torco accelerator for octane boost, it actually works.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Wed Aug 06, 2008 11:12 pm

Quote :
Use Torco accelerator for octane boost

If you need to increase octane, I agree with going Torco. I have heard a couple of good things about it. Better yet, if you do the proper mods, you can run 93 with no adverse affects!
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Wed Aug 06, 2008 11:30 pm

manofmany wrote:
If the knock is too bad I think it will set a code. I will find out.



I don't think a code is set, you just wind up with a LOT of Knock Retard. So your timing is pulled back, resulting in lower power and reduced gas mileage. Hmmm.... scratch
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 12:56 am

1998 Riv wrote:
manofmany wrote:
If the knock is too bad I think it will set a code. I will find out.



I don't think a code is set, you just wind up with a LOT of Knock Retard. So your timing is pulled back, resulting in lower power and reduced gas mileage. Hmmm.... scratch

You will blow head gaskets or worse, the computer can not pull timing fast enough to protect your engine. Run 91 octane or sell the car.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 8:25 am

Don't do it. Just run 91 (minimum) if you can find it, 93 if you can't. Or you'll be looking for head gaskets or pistons first.

If you really want to run 87, take off your supercharger belt.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 12:53 pm

manofmany wrote:
If the knock is too bad I think it will set a code. I will find out.

I will probably just keep finding stations that have 89 for 10 cents more a gallon rather than the ones who are 17-20 cents higher.

Ok i'm sure 90% of cars will run fine on 87 octane even with premium , however i don't think the extra 5 or 6 bucks a week is worth having a 10% chance that your engine will grenade on you. It might not happen for 4 years , it might happen next week , it might never happen , but i just don't see how its worth the risk.

A lot of it depends on how you drive too. If you don't go past 1/3 throttle ever , you'll be mostly out of boost , so you might not have an issue. If you drive like me , you .want no less than premium.

If you're really really set on 87 , buy an Aeroforce gauge and monitor knock, but then again with the money you'd spend on that , you have probably two years worth of the cost of premium , and after seeing the knock you'd probably go back to premium anyway.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 1:00 pm

i run 94 all day everyday, i actually went to the gas station and payed first not knowing they onyl had 87 that day

my car has never ran so shitty, the car hesitated when i gave it gas....if anyone knows about if your going to slow for a gear, the steering wheel vibrates.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 4:13 pm

I'm just gonna stick with 89.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 4:17 pm

it says run only premium for a reason...
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 4:17 pm

Do a Google image search for "Detonation Piston" or "Preignition"


Last edited by Chicken on Thu Aug 07, 2008 4:20 pm; edited 1 time in total
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 4:19 pm

no shit
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 8:43 pm

So do the late 90 Cadillacs. I put 120k miles on a Northstar with 87 octane and never had an issue. 90+ octane is overrated unless you really need it. I didn't really get my car for the boost.

Besides, if it got that back the knock sensor WOULD set a code.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 10:04 pm

Seriously, I have to agree with everyone else - if you're going to drive a Riv and not put premium in it buy the N/A 3800 Series II or don't drive it. You're lucky the Northstar didn't run like shit, they hate not having premium (My grandma has one and it doesn't like anything but premium). Stop being a cheapass and put what the car calls for. As I recall it even says Premium only on the gas cap. You really do need it, the S/C makes it a necessity.
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Thu Aug 07, 2008 11:26 pm

i kinda actually thought i was being a dick not running octane boosters
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PostSubject: Re: What Octane Grade Fuel for 3800 SC?   Fri Aug 08, 2008 4:42 am

Quote :
Just wondering if anyone else does this and if it will trigger a knock sensor code? I'm taking my Riv down to TN from IN next week and cheaper gas would be nice, just don't want it to start missing or anything.

I did it once. I drove from OH to GA and decided to run 89 octane because it was cheaper. I figured since it would be set in cruise most of the way, I would be ok.. Around TN, climbing a mild mountain, I heard audible knock. My engine was detonating so badly, the PCM couldn't control it with KR. I immediately found some premium to mix in - problem solved, but I still took a risk, and that horrid noise!

No, the PCM won't normally throw a code. The PCM does a lot of things to deal with problems that do not result in codes. Similarly, the PCM throws codes that do not result in SES light illumination. What the PCM will do is retard timing in an attempt to fix the problem if knock/detonation. This can result in power loss. But if this doesn't work, and KR persists, the PCM can opt to switch over to a "bad' timing table. These are a separate set of timing values, used when the PCM thinks you are abusing the engine by using the wrong fuel.

Other cars can use similar methods to protect against self destruction, including your turbo Eclipse. When you put 87 in a turbo car, it can adjust timing and boost levels to compensate. The result is less power. With a supercharged car like the Riviera, the PCM cannot adjust the boost, so if timing doesn't do the trick, you will hear it ping. Your pistons will also hear it - loud and clear.

Quote :
If the knock is too bad I think it will set a code. I will find out.

Again, this will most likely not happen. The car may revert to the bad timing tables, but this is a band aid solution at best. At worst, you could chip pistons over time if you continue to run low octane fuel. You will not find out unless you hear the knock, or the engine becomes damaged from the abuse

Quote :
So do the late 90 Cadillacs. I put 120k miles on a Northstar with 87 octane and never had an issue. 90+ octane is overrated unless you really need it. I didn't really get my car for the boost.

Whether you want it too or not, your engine does make boost, and it will use it whenever you push the pedal hard enough. Your Northstar was a different animal, as it recommended premium rather than requiring it. 90+ octane is not overrated for a car with a supercharged engine like the Riviera. It is required if you want the car to function as it was intended. If you don't use the correct fuel, there will be a lack of performance, and possibly engine damage in the long term. I say possibly because there is a chance that if you baby the throttle at all times, you can run lower octane with very little knock. I do this sometimes for long trips, but I always have the scanner hooked up to monitor KR levels. If things get ugly, I know when to back out of the throttle.

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'98 SC Riviera 268k miles 298 HP/370 TQ 0-60: 5.79s ET: 13.97 @ 99.28 4087 lb 20.1 avg MPG Nelson Ledges Lap: 1:30
3.4" pulley AL104 plugs 180 t-stat FWI w/K&N 1.9:1 rockers OR pushrods LS6 valve springs SLP headers ZZP fuel rails
KYB GR2 struts MaxAir shocks Addco sway bars UMI bushings GM STB Enkei 18" EV5s w/ Dunlop DZ101s F-body calipers
EBC bluestuff/Hawk HP plus SS lines Brembo slotted discs DHP tuned Aeroforce Hidden Hitch


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