87 Octane in a 3800 SC?

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My Buick (Posted in sig) has the 3800 supercharged engine. It recommends using premium gasoline. Online recommends premium gasoline to prevent knock and knock retard.

So when I first got the car last year, I started running it on premium for a couple complete fills, then regular for a couple complete fills, and back. I got an OBDLink LX to read values.

On regular, I have not heard any sort of pinging (only misfires after I screwed up one of my plugs. Replaced them all.), the KR value stays at 0, and my knock counter has never budged. I haven't noticed much of a difference in power or efficiency either. This was also when testing my 0-60 times from a stopsign, so this isn't all just casual driving.

So premium is supposed to be this great benefit for premium-requiring cars, namely SC and Turbo cars. But I'm not seeing any of it.

Could something be wrong with my supercharger? Perhaps the sensor? Or would I simply be wasting money on more expensive fuel? Is the effect residual, where I would see increasing KR over time?
 
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I'd trust the GM engineers that recommend your car using premium rather than you monkeying around testing and wanting to use 87 octane.
 
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If you had any idea how damaging pre-detonation is to an engine, you wouldn't be taking any chances. When you start seeing blue smoke coming out the tail pipe, you'll know then that the piston rings are broken.
 
You definitely want a high octane fuel with a supercharger. I'm sure GM has some pretty conservative timing and boost calibrations in the engine management computer, but under boost, I would want all the anti-detonation insurance I could get.

With the ROOTs-type blower in your 3800, it's under boost at some pretty low RPMs. I personally wouldn't chance it on 87 even in a pinch. In fact I might carry a bottle of Touline in the trunk.

Note that I do run a supercharger in the Miata, and the aftermarket computer is tuned for minimum 91, which is available pretty much everywhere, including the middle of nowhere. If I wasn't worried about buying gas at 4AM in some hick town I could tune for 93 (some stations here sell 94, but not all).

If i could get 99 RON at the pump. I'd tune for 99, because there would be power gains there to exploit.

Get a Costco card and run their 93/94 or whatever they sell in your area.
 
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OK, thanks for the strong suggestion, guys!

I suppose the advantage is ultimately the potential for a smaller SC belt in the future.
 
Originally Posted By: OpenClose
OK, thanks for the strong suggestion, guys!

I suppose the advantage is ultimately the potential for a smaller SC belt in the future.


In stock form the SC GM cars knock a lot. There is 2 knock sensors that quickly pull timing to save the engine. The problem is GM didn't intercool the engine and ask for way too much timing than it can handle at WOT in stock form. If you do a WOT run and stay in it to redline you will see KR. Usually getting worse around top of second gear and into 3rd (assuming you started at 0)

Also there is a lot of what's called "burst knock" which is with sudden acceleration/forced downshifts from an already cruising speed.

Turning on the AC will exacerbate the burst knock. You can also see knock come in while in TCC (torque convertor lock) during low rpm lugging. Also worse with AC on.

My buddy bought a 02 GS with a chipped #4 piston because previous owner wouldn't buy anything but 87 octane. Cylinder 3 is most common but cylinder 4 is next common to lose a chunk of piston from knock because they are the middle cylinders that are sandwiched between two other cylinders.

The SC version of the 3800 have heavier and slightly thicker pistons to handle the boost. However they will chunk up after lots and lots of abuse from knock.

I wouldn't increase boost (change pulley size) without some serious mods. IT WILL BLOW UP.s

Hope this helps.
 
Well, my information center is dead. The resistors burned out, and I replaced them, but they burned out again.

So what I have been doing is using my OBDLink LX to read values, and I use a tablet as my instrument cluster. There I have information such as KR, Knock counter, misfire history, and intake manifold absolute pressure.

I have never seen the KR and Knock counter change. And the only time my misfires changed was when I had a bad plug.

I figure with the MAP sensor reading, anything above 14.7 PSI is boost, since it can only come from the supercharger. Generally I can get up to 18-20 PSI on the MAP sensor, so about 3-5 PSI boost.
 
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And yes, if I was going to go with a smaller pulley, part of the deal would also be changes to the ECM/PCM and an intercooler. SO that would be if I really want to get my hands dirty. I just hear the Regal GS has a lot of overhead for power.

And I'm pretty sure I'll be sticking to premium here on. Costs less than a cup of coffee per fill, anyway. I was going to try some Shell V-Power Nitro+ on my road trip this weekend.
 
Originally Posted By: OpenClose
And yes, if I was going to go with a smaller pulley, part of the deal would also be changes to the ECM/PCM and an intercooler. SO that would be if I really want to get my hands dirty. I just hear the Regal GS has a lot of overhead for power.

And I'm pretty sure I'll be sticking to premium here on. Costs less than a cup of coffee per fill, anyway. I was going to try some Shell V-Power Nitro+ on my road trip this weekend.


That's the only thing I buy @ Shell Vpower.

Log the MAP kpa value, subtract 100 then multiply .145 and that gives you boost psi.

If you aren't getting more than 3.3-3.5 psi of boost from that formula then you probably have a bad boost bypass solenoid. It's common and easy to replace.
 
I ended up going with just Marathon premium. I got my tank as low as I could and stopped by shell. Normal gas around here is around $2.60-$2.70. The Shell V-Power was over $3.70 at the cheapest station. $4.00 at some of the others. That's just excessive.

Also, It seemed like I had checked the solenoid a while back. My dad and I went out and took a look, and it seemed to move just fine, anyway.

I'll have to log my values. But that is basically the same conversion. In your case, you start with kPa(abs) and subtract atmospheric (100kPa) to get kPa(gauge), then convert that to PSI.

In my case, the kPa value is converted to PSI, then atmospheric is subtracted (14.7PSI). What I have generally seen is, again, 18-20PSI, so I think I'm supercharging just fine based on that. I'll keep an eye on it while driving a few hundred miles this weekend.
 
Originally Posted By: OpenClose
I ended up going with just Marathon premium. I got my tank as low as I could and stopped by shell. Normal gas around here is around $2.60-$2.70. The Shell V-Power was over $3.70 at the cheapest station. $4.00 at some of the others. That's just excessive.

Also, It seemed like I had checked the solenoid a while back. My dad and I went out and took a look, and it seemed to move just fine, anyway.

I'll have to log my values. But that is basically the same conversion. In your case, you start with kPa(abs) and subtract atmospheric (100kPa) to get kPa(gauge), then convert that to PSI.

In my case, the kPa value is converted to PSI, then atmospheric is subtracted (14.7PSI). What I have generally seen is, again, 18-20PSI, so I think I'm supercharging just fine based on that. I'll keep an eye on it while driving a few hundred miles this weekend.


I've never seen a SC 3800 at that level of boost. Something in your math is wrong. Give my method a shot and see what boost you are getting.
 
Originally Posted By: OpenClose
What, about 3-5PSI? I thought that was normal.


No, nominal output according to Eaton is 7.5 psi. It varies with ambient temp and humidity.

Stock you should see 8-10 psi. Stock exhaust is very restrictive. If you aren't getting more than 3-3.5 psi (I know you posted 3-5 psi) then your boost bypass solenoid is likely failed.
 
Originally Posted By: OpenClose
Interesting.

Is there any way to verify this, or check the boost bypass solenoid?


take the vacuum hose off that goes into the solenoid. It will be the one that enters from your right if you are staring at the solenoid.

Punch it and log your KPa. You should have full boost.

view


PS. picture didn't show up on my post but I think the link works. LMk
 
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Might be worth looking into a warehouse club membership (Costco/Sams Club/BJ's) if one is convenient to you. They're often the cheapest around for premium, and it's generally pretty fresh since they have a lot of cars cycling through.
 
OK, so to be sure, I am unplugging the tube indicated in red from either end, and this will disable the boost bypass valve, correct?

Will this create a heat problem? I hear something like this can create problems in the low-end of the RPM range.
 
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