OVERKILL
$100 Site Donor 2021
Originally Posted By: Kuato
Originally Posted By: OVERKILL
Originally Posted By: Kuato
My brother ran a vehicle requiring 87 on 93 for several years. Deposits formed and eventually it started lightly knocking on 93. The vehicle was stepped down gradually from 93 to 87 after I bought it from him. Any heavy acceleration would cause.detonation until it had run on 87 for 5 or 6 tanks and had a spark plug change. YMMV but in your case I would stick with 87.
I also had a vehicle that began to knock lightly in the late fall. Turned out that there was water in the tank, either from a questionable station or condensation. 3 consecutive tanks with Drigas cleared it up.
Hope that helps.
I ran my Mustang (called for '87) on 91 (because I advanced the base timing to 14 degrees) for years. When I took the heads off it the pistons looked fantastic.
Mind you the engine had the living tar beat out of it regularly (it was like one constant ITU) but I don't think that higher octane gas causes deposits. It is more resistant to preignition and burns a bit slower, which allows you to run more ignition advance.
I can only report what I experienced, and surmise that without advancing the timing, you'd probably have had deposits too.
I highly doubt it. I've seen numerous engines run on 91 because the owner thought it was "better" and they were also clean.
Some engines are prone to carboning up due to chamber design, which, in conjunction with the top of the piston shape, dictates flame front propagation. Driven lightly (think lower load, which means slower inlet air flow, poorer air/fuel blending and lower cylinder pressures), certain engine designs will also carbon up. An "issue" that can be alleviated simply by running them hard periodically. Other engines, like the Ford 302, don't seem to care one way or the other, the same goes for the 2V Modular.
As I said, the higher octane rating means the fuel is less prone to pre-ignition and detonation/pinging and also burns slightly slower, allowing the flame front to fully propagate across the bore in situations that require it (the higher octane fuel). On an engine that does not require it what this means is that you have some still burning/expanding combustion gasses exiting the exhaust port. This does not create deposits. Remember, combustion is not an "explosion" but rather a controlled burn of the air fuel mixture that rapidly expands outward from the ignition point. Proper octane fuel for a given application means that the combustion is complete; the air/fuel mixture burns evenly across the top of the piston providing even downforce and producing no piston "rock" and that the air/fuel mixture is not ignited prematurely by deposits (pre-ignition) or during the combustion event at another point in the chamber (detonation) which can cause damage and results in an incomplete combustion event.
Higher octane fuel allows for the advancement of ignition timing, meaning that the air/fuel mixture can be ignited earlier (as the piston approaches TDC) so that you get more effective gas expansion before the exhaust valve opens; the mixture is "more useful" and this results in a gain in power. Of course this is only to a point and varies wildly with engine/chamber design and camshaft timing. Going much beyond 14BTDC on a 302 Ford for example does not yield any additional power. This is probably due to the short 3" stroke.
A higher static compression ratio also requires increased resistance to pre-ignition and with the mixture more compressed, this promotes a faster burn, requiring a fuel that burns a little longer in order to allow for complete flame front propagation.
Ultimately the fuel being more resistant be being ignited by a source other than the spark plug as either pre-ignition or detonation does not lend itself to producing deposits. But it does mean that you usually accomplish nothing by using it in an application that doesn't require it. That said, on some cars, with knock sensors, they constantly "learn" how much ignition timing they can get away with and will in fact make more power on higher octane fuel, even if they don't call for it. Others, due to the reasons I already mentioned, won't. My HEMI is an example of the former, requiring a minimum octane of 87 with 89 "recommended".
The usual sources for deposits are:
1. compromised injector spray pattern resulting in a less than optimal mixture entering the chamber (think fuel puddling and the fuel not blended perfectly with the air that it was sprayed into as the intake stroke ingested it) which will in turn screw up the readings that the oxygen sensors see, further exasperating the issue.
2. Worn plugs causing periodic misfires or partial/improper ignition (you stated you also changed your plugs.....) or plugs with carbon deposits built-up on them, which can cause detonation or pre-ignition (or both). This also results in mixed readings from the O2's and can result in improper mixture optimization by the ECM.
3. Faulty EGR
4. Faulty PCV plumbing resulting in oil burning, which reduces the effective octane of the fuel and will also create pinging
Using high octane fuel in a car that doesn't require it is a bit like using synthetic oil at 3,000 mile OCI's. It doesn't hurt anything but it isn't helping really either
Originally Posted By: OVERKILL
Originally Posted By: Kuato
My brother ran a vehicle requiring 87 on 93 for several years. Deposits formed and eventually it started lightly knocking on 93. The vehicle was stepped down gradually from 93 to 87 after I bought it from him. Any heavy acceleration would cause.detonation until it had run on 87 for 5 or 6 tanks and had a spark plug change. YMMV but in your case I would stick with 87.
I also had a vehicle that began to knock lightly in the late fall. Turned out that there was water in the tank, either from a questionable station or condensation. 3 consecutive tanks with Drigas cleared it up.
Hope that helps.
I ran my Mustang (called for '87) on 91 (because I advanced the base timing to 14 degrees) for years. When I took the heads off it the pistons looked fantastic.
Mind you the engine had the living tar beat out of it regularly (it was like one constant ITU) but I don't think that higher octane gas causes deposits. It is more resistant to preignition and burns a bit slower, which allows you to run more ignition advance.
I can only report what I experienced, and surmise that without advancing the timing, you'd probably have had deposits too.
I highly doubt it. I've seen numerous engines run on 91 because the owner thought it was "better" and they were also clean.
Some engines are prone to carboning up due to chamber design, which, in conjunction with the top of the piston shape, dictates flame front propagation. Driven lightly (think lower load, which means slower inlet air flow, poorer air/fuel blending and lower cylinder pressures), certain engine designs will also carbon up. An "issue" that can be alleviated simply by running them hard periodically. Other engines, like the Ford 302, don't seem to care one way or the other, the same goes for the 2V Modular.
As I said, the higher octane rating means the fuel is less prone to pre-ignition and detonation/pinging and also burns slightly slower, allowing the flame front to fully propagate across the bore in situations that require it (the higher octane fuel). On an engine that does not require it what this means is that you have some still burning/expanding combustion gasses exiting the exhaust port. This does not create deposits. Remember, combustion is not an "explosion" but rather a controlled burn of the air fuel mixture that rapidly expands outward from the ignition point. Proper octane fuel for a given application means that the combustion is complete; the air/fuel mixture burns evenly across the top of the piston providing even downforce and producing no piston "rock" and that the air/fuel mixture is not ignited prematurely by deposits (pre-ignition) or during the combustion event at another point in the chamber (detonation) which can cause damage and results in an incomplete combustion event.
Higher octane fuel allows for the advancement of ignition timing, meaning that the air/fuel mixture can be ignited earlier (as the piston approaches TDC) so that you get more effective gas expansion before the exhaust valve opens; the mixture is "more useful" and this results in a gain in power. Of course this is only to a point and varies wildly with engine/chamber design and camshaft timing. Going much beyond 14BTDC on a 302 Ford for example does not yield any additional power. This is probably due to the short 3" stroke.
A higher static compression ratio also requires increased resistance to pre-ignition and with the mixture more compressed, this promotes a faster burn, requiring a fuel that burns a little longer in order to allow for complete flame front propagation.
Ultimately the fuel being more resistant be being ignited by a source other than the spark plug as either pre-ignition or detonation does not lend itself to producing deposits. But it does mean that you usually accomplish nothing by using it in an application that doesn't require it. That said, on some cars, with knock sensors, they constantly "learn" how much ignition timing they can get away with and will in fact make more power on higher octane fuel, even if they don't call for it. Others, due to the reasons I already mentioned, won't. My HEMI is an example of the former, requiring a minimum octane of 87 with 89 "recommended".
The usual sources for deposits are:
1. compromised injector spray pattern resulting in a less than optimal mixture entering the chamber (think fuel puddling and the fuel not blended perfectly with the air that it was sprayed into as the intake stroke ingested it) which will in turn screw up the readings that the oxygen sensors see, further exasperating the issue.
2. Worn plugs causing periodic misfires or partial/improper ignition (you stated you also changed your plugs.....) or plugs with carbon deposits built-up on them, which can cause detonation or pre-ignition (or both). This also results in mixed readings from the O2's and can result in improper mixture optimization by the ECM.
3. Faulty EGR
4. Faulty PCV plumbing resulting in oil burning, which reduces the effective octane of the fuel and will also create pinging
Using high octane fuel in a car that doesn't require it is a bit like using synthetic oil at 3,000 mile OCI's. It doesn't hurt anything but it isn't helping really either