Hi Folks

I might have made a real mess up.

Basically I bought 20 year old 760 turbo (B230 ET) for a few hundred dollars(pounds in UK).

So the manual states 98 Octane for motor and the Volvo club here recommends Leaded gas. It has a high compression 9.0 - 1 so what are the effects to the motor if I run it on 95 Octane unleaded??

Anyway most of the damage should have been done by now as high octane 'super' unleaded doesn't seem to be available any more here in the UK.

How do I convert??
Matt

I could be wrong, since I have just a basic knowledge of mechanics and more detailed info on problems that I was forced to gain experience in.

but as I understand from different manuals I've read (for my 87 760), the knock sensor will send a signal to retard the timing if 'knock' (or pre-detonation) occurs.

this would seem to fit with my actual experience. when my kid puts lower octane gas in the car I hear no knock even in heavy acceleration. I do notice much poorer gas mileage and less power. all of these seeming to support the idea that the car has retarded the timing on it's own.

as a side note to my fellow cheap-skates out there. the difference in gas mileage between premium and regular unleaded is much greater than the difference in price per gallon between the two. it's actually cheaper to buy the more expensive gas.

"as a side note to my fellow cheap-skates out there. the difference in gas mileage between premium and regular unleaded is much greater than the difference in price per gallon between the two. it's actually cheaper to buy the more expensive gas."

I don't know where you get your information or why you think that. A car that can safely use 87 octane(and it is what is specified for the car and it is setup to work correctly) will get just as good gas mileage as a higher octane gas. If the car is setup and tuned to run on higher octane gas, then yes, you will get better gas mileage, and have an engine that runs properly and isn't possibly damaging the engine. Look in the 120 and 140 forums, we just recently had a couple of discussions on octane ratings and have a link or two on gas information.
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Kyle - attending Ore. State, while my lil '68 142 (256k, 74 b20, m40, iPd bars, other misc... =D) waits for its next outing... (My Cardomain site)

I don't know where you get your information or why you think that. A car that can safely use 87 octane(and it is what is specified for the car and it is setup to work correctly) will get just as good gas mileage as a higher octane gas. If the car is setup and tuned to run on higher octane gas, then yes, you will get better gas mileage, and have an engine that runs properly and isn't possibly damaging the engine. Look in the 120 and 140 forums, we just recently had a couple of discussions on octane ratings and have a link or two on gas information.

With the older engine management systems what you say is true.

With the newer ones, it is not.

For instance the 960's Motronic setup (and possibly the Regina system as well) will add fuel when it detects knock. That will have a direct impact on the fuel economy. While the car will run fine and not cause any damage on the lower octane gas, it will use more gasoline.

That said, if the engine is for whatever reason deviating from stock in a way that results in higher compression ratio (shaved head, carbon deposits, etc) the higher octane gas will prevent detonation. This will prevent the spark timing from being retarded, which will in turn probably help mileage a bit.

Also keep in mind that the newer engine controls are adaptive and may be tuned fairly aggressively so that they take advantage of higher octane gas when available. Indeed I think that Volvo has phrased the octane requirements that way (premium preferred, regular okay).

In answer, I think that with any somewhat modern EFI setup, higher octane gas will indeed impact mileage and performance.

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alex

'89 765T, 175,4xx mi

"For instance the 960's Motronic setup (and possibly the Regina system as well) will add fuel when it detects knock. That will have a direct impact on the fuel economy. While the car will run fine and not cause any damage on the lower octane gas, it will use more gasoline."

Exactly, if the car is knocking, you are using the wrong fuel. It needs a higher octane rating, and in this case, yes, the car will use more fuel. But that is only because you are using the wrong fuel. The car may run fine, but it won't run as well as it should be because of the WRONG fuel. For example, what i'm saying is, lets say you have a 740T and you use 87 oct gas, and you experience a little bit of knocking. If you put in some 89 oct gas and the knocking goes away, your car will perform better and will use less gas because it doesn't need to run rich anymore to keep from knocking. And then, if you put anything higher than that in it, lets say 92 oct, you will NOT experience a gain in mileage unless the car was still knocking and increasing the fuel to the engine or retarding the timing. Note that these aren't actual test numbers here, i'm just saying so to give an example.

Yes, some modern EFI systems can take advantage of using higher octane gas(but do you really think a volvo 740 with whatever efi system, automatically will advance the timing and/or lean the air/fuel ratio to take advantage of using premium gas? If that were the case, why would there be all those aftermarket chips out there that are specifically made to make cars perform even better than stock by manipulating the stock timing maps and fuel maps to take advantage of the higher octane gas?

There was an article i read somewhere a while back about actual testing i think between using different octane ratings and showing what gains there were or weren't for a few different cars... Can't remember where that was though, although it would be nice to take a look at again.

Peace,
--
Kyle - attending Ore. State, while my lil '68 142 (256k, 74 b20, m40, iPd bars, other misc... =D) waits for its next outing... (My Cardomain site)

Exactly, if the car is knocking, you are using the wrong fuel. It needs a higher octane rating, and in this case, yes, the car will use more fuel. But that is only because you are using the wrong fuel.

Again, not necessarily. Volvo recommended a higher octane, but rated the engine as safe to run. With those guidelines, lower octane gas is the proper gas, but not the ideal. Here's what the owner's manual says for my 89 765:

"Volvo engines require unleaded gasoline with an (R+M)/2 octane rating (also called the Anti-Knock Index, or AKI) of 87 or higher. This is generally equivalent to a Research Octane Number (RON) of 91 or higher. For improved performance, we recommend the use of premium unleaded gasoline (AKI of 91 or higher, RON of 95 or higher)."

Note that they didn't say to avoid damage. Quite frankly I don't notice a huge difference between the mileage I get with 87 AKI and 91 AKI gas. 87 AKI gas is perfectly fine for a B230FT or a B280F.

BTW, if you believe your car isn't knocking at all on the “proper” gas, hook up an LED to your knock sensor (or google for knocksense). Chances are it will blink quite a bit more than you'd expect.

Yes, some modern EFI systems can take advantage of using higher octane gas(but do you really think a volvo 740 with whatever efi system, automatically will advance the timing and/or lean the air/fuel ratio to take advantage of using premium gas?

No, but I bet that the designers optimized the maps for the higher octane gas, but allowed the knock sensor enough control to overcome any detonation that slightly lower AKI gas may create. Keep in mind many companies (like Ford) didn't use knock sensors in many engines (the modular V8s come to mind) until a few years ago.

If that were the case, why would there be all those aftermarket chips out there that are specifically made to make cars perform even better than stock by manipulating the stock timing maps and fuel maps to take advantage of the higher octane gas?

There are no chips for the US spec red block engines. The only chips available for red block engines are for those equipped with the Motronic system (all US Spec gasoline powered cars got LH-Jetronic or the Rexx/Regina setup after 85).


There are other things to take into account as well..... such as carbon deposits and the general condition of the engine.

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alex

'89 765T, 175,4xx mi

"Yes, some modern EFI systems can take advantage of using higher octane gas(but do you really think a volvo 740 with whatever efi system, automatically will advance the timing and/or lean the air/fuel ratio to take advantage of using premium gas? If that were the case, why would there be all those aftermarket chips out there that are specifically made to make cars perform even better than stock by manipulating the stock timing maps and fuel maps to take advantage of the higher octane gas?"

in my case I was refering to a 760(I don't know if the 740 has the same fuel recomendations, I assume it is), but no I don't think it will advance the timing to take advantage of better gas, but they are designed for 92 octane, so what they will do is set the timing up to normal,

btw, the knock sensor is more sensitive than your ear, you won't hear the knocking before it is corected (at least I never had). I just notice after my son has driven the car, having lower milage, calling him on it and having him admit to putting the lower octane gas.

Don't worry too much. Us United Statesians have had unleaded gas for 30 years. The lead creates a coating on the valves which protects them from over heating. The lead also boosts the octane rating.
Because your car has run with leaded gas, the valves are already coated and protected. Using unleaded now will not hurt your engine. If you ever get new valves, just get the new upgraded ones that are sodium "filled". Your only problem is with predetonation, and that can be prevented by retarding the timeing by 1 degree, or not accellerating very hard.
We have octane boosters here in the US, but rather than waste my money I just drive slower - no more 7,000 rpms. Saves me gas, too.
If you happen to be a race car fanatic, or Jim Clark wanabee, go to an air port and see if you can get some 100 avgas. It has lead in it. I used to do that with my 74 BMW motorcycle, mixed with 93 octane unleaded, and that worked great.

Klaus
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95 854T, 88 780, 88 245

uhm...nooooo

the issue with the sodium loaded valves was to do with heat transfer..and lowereing the temperature on the valve faces to try and prevent fractures due to thermal gradients in the valve itself...the typical issue with cars unsuitable for unleaded is the valve seats wearing not the valves

as to unleaded gas in the states..well sort of, look at the aditive packages (quite a lot WORSE than lead btw) that were added to the fuel to try and make it work with iron not designed for it...

Knock sensors...hmmm again its a sort of...knock sensors work by detecting knock, then retarding the ignition..think about that again..they detect knock..so by the time they detect it its there..and that really not good...ok they do stop it getting too bad...but its still there, and if you care abotu your engine you really would rather it wasnt...

as for 7k rpm, i would hope you do as a b23/230 is NOT rated for that anyway as standard...your well above the red-line, which again is not a healthy place to be (and if you like living there go buy a turbo engine...6 k requires large spherical objects.....)

the issue with unleaded in heads not designed to deal with it is that all the deposited lead (not much actually - think about a valve seat for a second...) wears away very quickly and the valve seats then receed (the problem here being they are soft, unleaded heads have hardened valve seats fitted - this is the conversion often done to clasic cars) the first indication is needing to adjust the valves, the second is not beign able to adjust then far enough..the third is a good shop telling you your head is toast...go ask any morris minor owner who made the mistake...hmmmm (happens very quickly too!)

cant comment on what model volvo heads require what as i only own b230f's and up (though i look after a b230g and ab200e both of which are ok for unleaded...
) although i have just read a web page that catagorically says that ALL b230's had hardened valve seats so can run on unleaded - i suggest you ring up you local freindly volvo dealer to confirm that one though!


everyone also ought to bear in mind european/us octane ratings are different (just like our gallons & miles)

actually, volvo turbo motors come with sodium filled exhaust valves due to the additional heat. i wouldn't sweat the octane issue. 9:1 compression with no boost you mean, right? you can run 87 octane on that, unless its really hot outside (like 30 C). but like the other guys said, the volvo ignition system will retard the timing in the event engine knock is detected. however if you're running 1-1.5 bar of boost, be careful or you're first knock could be the last.