Good morning,

I have a question and I'm not sure how to use the site yet. It was removed from one forum and not sure where it went.
I have a 73 Mustang with a 302 engine which was rebuilt from the block up with Edlebrock components and carburetor
After having put gas in the car (87 Octane), we noticed the engine is starting to ping (knocking lightly) and after turning it off, it is hard to start with light white smoke coming out the rear.
I have always wondered what octane to use for a vintage car and its quite confusing. My local gas station has 87, 89, 91 & 93. I can probably find something else if there is such a mixture.
Last point, i also heard about some type of lead additive?
Can anyone help this old Mustang guy?

Use the lowest octane that it will run with, without "pinging". Make sure the timing and spark advance is working properly as well. Try moving up to 89. If it runs well then try alternating between 87 and 89 on fill-ups. If that doesn't work, stick with the 89, etc.

No, you don't need or want any kind of lead SUBSTITUTE. There are no such things as "lead additives". What most common "lead substitutes" are, is mostly kerosene with traces of naphtha, benzene and/or isobutane, etc.

 

What Woodchuck said.

 

If your 302 still had all the factory components, 87 octane would be fine. A 1973 302 was a "smog motor" with very low compression. However, if you have Edelbrock aluminum heads, the compression ratio likely changed.

As Woodchuck suggested, you might check your ignition timing to make sure it isn't excessively advanced. Aluminum heads are pretty resistant to pinging, so if you are running aluminum heads, something is going on.

 

Verify that the 89 octane is not E15 fuel. You want to stick with E10 for normal fuel. E0 is, of course, fine as well but avoid any alcohol higher than E10.

I posted this because I seem to remember seeing an 89 octane E15 somewhere on a trip. My memory could be faulty.

 

Verify that the 89 octane is not E15 fuel. You want to stick with E10 for normal fuel. E0 is, of course, best but avoid any alcohol higher than E10.

I posted this because I seem to remember seeing an 89 octane E15 somewhere on a trip. My memory could be faulty.

Fixed it. (Granted, for normally aspirated street engine)

For OP:

Aluminum heads allow more cylinder pressure before detonation.

I would start by backing timing off a couple degrees.

 

I found this photo on the web. I think my memory may be fine.

 

Must be from our last government administration...


the

 

Thank you all.
Yes, i have aluminum Eldelbrock E-street heads along with a Holley 570 Street Avenger too name just two of numerous replacements.
So I will slowly increase the octane (E10) until I find a comfortable fit.
Thank you......

 

It is good to know what the heat range of a spark plug means. The heat range describes how much heat the spark plug passes to the head for cooling the plug. A cooler plug will pass more heat to the head. This gives a tuner a selection of plugs when attempting to get optimum burn in an engine.

To verify your issue is not being caused by too hot of a plug, pull a plug and look up the specs for the plug number. If cooler plugs are available, you could change the plugs as an attempt to eliminate the ping. This would only work if the source of detonation heat is the plug itself and not something else like compression pressure.

 

NGK V-Power Nickel Plug Number BKR5E

Seat: Flat
Thread Size: M14
Heat Range: 5
Hex Size (in): 5/8 Inch
Preset Gap (in): 0.044 Inch
Thread Reach (in): 0.750 Inch
Number Of Ground Electrodes: 1
Center Electrode Core Material: Copper
Center Electrode Tip Material: Nickel
Approximate Resistor Value (Ohm): 5000 Ohm
Insulator Height (mm): 50.5mm
Center Electrode Design: Standard
🙃

 

I'm going to disagree with the advice to use the lowest octane E0 or E10 that will prevent pinging, and suggest instead that you use the highest grade E0 or E10 available.

Yes, you may be paying for an octane rating you don't need, but you're also getting the best additive package. For example:

https://www.bp.com/en_us/united-states/home/products-and-services/fuels.html#accordion_what-are-the-differences-between-bp-amoco-regular-bp-amoco-silver-and-amoco-ultimate%C2%AE

I've got my flame resistant suit on, so let 'er rip!

 

I'm going to disagree with the advice to use the lowest octane E0 or E10 that will prevent pinging, and suggest instead that you use the highest grade E0 or E10 available.

Yes, you may be paying for an octane rating you don't need, but you're also getting the best additive package. …

What @Woodchuck is suggesting is the octane and detonation resistance grade, not the fuel quality. Assuming all of any brand's fuel contains the same additives and refining quality (which is always a benefit), then only the AKI or octane is different, in that brand.

All bp and Amoco gasolines contain Invigorate®, our innovative dirt-busting formula …

So, all grades of BP have the same stuff, and the only difference is octane. Choose the lowest octane that works properly in your engine. Any more is a waste of money for the same quality fuel. That said, the octane is the first to leave in vented storage, so you may want higher octane than required if you have periods of vehicle storage. Likewise, don't tune your engine on old fuel.

 

Lots of assumptions required to get to the necessity of slower burning, more expensive, fuel.

Only a side note, that higher-octane fuel of the same type is not slower burning, only more resistant to spontaneous combustion (detonation) initiated by heat.

Could be the timing is a just a touch too advanced. It's a free 30 second tweak that only takes a test drive or two to see if it helps or hurts performance and/or cures detonation.

Good point, and why I stated and asked this right up front. If not, then your quickie test is simply part of doing that tuning now. If tuning finds det before indicators reach max performance, then you have no choices but to either increase octane, or remain in a de-tuned state.

A common diagnostic is to increase octane to find optimal timing and performance baseline, in order to assess if reducing octane compromises too much performance. You can't know until you do.

You can't do diagnostics unless a baseline or comparator is established, and you're right, we can't assume. If it's not done, then do it now, and then re-assess the situation. Between us , I assume it has not been fully tuned, else things like plug heat range and required octane would already have been determined. It is entirely possible there will be no knock at max performance, once it has been tuned properly. We can't know until it is, and that's not up to us.

 

I'll show my privilege here and say that I'm not going to sweat the extra $18 difference between 87 octane and 93 octane when i fill up.

 

Let's see some more photos of the car...the engine compartment looks great!

 

If it's additives rather than octane, fair enough, but I'll use the octane savings to buy the additives in a bottle and add as much or more than they do. There are many brands of fuel detergent additives (cleaners) like Ivigorate®. Pour your pick and be happy.

 

You have a low performance engine requiring low performance gas. Millions upon millions were made, back down the timing or run the next grade up of gas. You will find what it wants, Good Luck!

 

Our Ethanol Free in my area of Florida is 90 Octane and works well in my 77 Scout. If I remember the last time Regular Unleaded was sold it was 89 Octane as the lowest grade

 

wow....so much information to consider, it's like chemistry class.....
I'll print all of this and do a lot of research.
First, i feel that i have to empty the tank of the low octane that is in there and start fresh.
I want to thank all of you for all the imput. I thought maybe it would just be a number to use and i'd be on my way. Boy was I wrong....
Here are some more photos. If anyone wants a break down in photos of how a 71 to 73 component is disassembled, let me know.

Finport

 

I don't think he'll have to worry about it too much. And with all the state income tax he saved, he can buy a getaway house in the Appalachians!

 

If available where you're at buy the 89 octane straight gasoline, no ethanol, my 289 runs way better when there is no corn.

 

I second the lowest-octane advice. Not only does higher-than-necessary octaibe waste $, it does not burn properly in the wrong engine.. Your engine will run better with the right octane level. Some people mistakenly think more octane is always better but not true.

I also second the recommendation to run non-ethanol (non-oxygenated) gas. assuming you can get the right octane level. In my area it comes only in 91. This is what the older cars like best and it will save your carb seals and gas lines.

 

Good morning,

After having put gas in the car (87 Octane), we noticed the engine is starting to ping (knocking lightly) and after turning it off, it is hard to start with light white smoke coming out the rear.

Can anyone help this old Mustang guy?

I'm curious about the white smoke - that is usually a sign of a leaking head gasket. Keep an eye on radiator level (check when cool).

That plus the car suddenly being harder to start makes me think something else is going on that is causing the pinging.

 

Good morning,

I have a question and I'm not sure how to use the site yet. It was removed from one forum and not sure where it went.
I have a 73 Mustang with a 302 engine which was rebuilt from the block up with Edlebrock components and carburetor
After having put gas in the car (87 Octane), we noticed the engine is starting to ping (knocking lightly) and after turning it off, it is hard to start with light white smoke coming out the rear.
I have always wondered what octane to use for a vintage car and its quite confusing. My local gas station has 87, 89, 91 & 93. I can probably find something else if there is such a mixture.
Last point, i also heard about some type of lead additive?
Can anyone help this old Mustang guy?

First thing is stop using that crap gas! You need to be running non-ethanol 90 or 93! Hopefully your cylinder head valves have hardened seats so you would not need a lead additive!
Ethanol fuel is destructive to our mustangs! Now unless you have all of the fuel system installed that is designed to run the ethanol fuel!

 

So, what is your compression? That plus ignition (recurved or stock) will help you figure this out. If you haven’t already, get a Ford shop manual, not Chilton, Ford…

In the mean time, use premium until you can figure it out. Have you called the previous owner to query how this engine might have been built?

 

Good morning,

I have a question and I'm not sure how to use the site yet. It was removed from one forum and not sure where it went.
I have a 73 Mustang with a 302 engine which was rebuilt from the block up with Edlebrock components and carburetor
After having put gas in the car (87 Octane), we noticed the engine is starting to ping (knocking lightly) and after turning it off, it is hard to start with light white smoke coming out the rear.
I have always wondered what octane to use for a vintage car and its quite confusing. My local gas station has 87, 89, 91 & 93. I can probably find something else if there is such a mixture.
Last point, i also heard about some type of lead additive?
Can anyone help this old Mustang guy?

The engine was meant to use 93 octane. Just use the highest number at the pump. Mine is 89. She runs just fine. No knocking or pinging. I have a 65 Fastback 289 Autolite 2 brrl carb.

 

First thing is stop using that crap gas! You need to be running non-ethanol 90 or 93! Hopefully your cylinder head valves have hardened seats so you would not need a lead additive!
Ethanol fuel is destructive to our mustangs! Now unless you have all of the fuel system installed that is designed to run the ethanol fuel!

Ethanol is added to gasoline to increase the octane rating and as an oxidizer. Yes, ethanol, in itself, is pretty corrosive so bear that in mind.... I would avoid E15 or higher at all costs. If you use the vehicle enough that you are going through a tankful of fuel every couple weeks then E10 will be fine as long as your rubber components (hoses, fuel pump diaphragm, float needle tip, etc.) are ethanol-safe.... E10 tends to degrade over time rather quickly so if you DON'T go through a tankful of fuel every couple weeks I'd look for non-ethanol. Also, many times stations with "blending" pumps will mix proportions of non-ethanol "premium" with E10 "regular" to market their "mid-grade" so the resulting product may only be up to 5% EtOH.... something to consider.

Next point.... There is no such thing as a "Lead Additive". There are products marketed as "Lead Substitutes". These consist almost entirely of KEROSENE with bits of naphtha, isobutane and other "snake oil" in very low percentages...1 to 2%. You'd probably do just as well to buy paint thinner... Also, the OP states he has built it "from the block up with Edelbrock components" so if he has aftermarket cylinder heads valve seats are a non-issue. Even if he had the original '73 heads it's a non-issue as SBF cylinder heads have never had separate valve seats, the seats ground right into the head and induction hardened... right up to 2001. I have yet to see a head, other than a LPG conversion or marine/stationary engine with any significant seat recession, not due to lack of lead but of being operated at a constant load resulting in high combustion/EGT.

The engine was meant to use 93 octane. Just use the highest number at the pump. Mine is 89. She runs just fine. No knocking or pinging. I have a 65 Fastback 289 Autolite 2 brrl carb.

The engine, in its original configuration, was meant to use "regular fuel". In the US and Canada, pump "octane" ratings are listed as "AKI" (Anti-Knock Index) which is RON (Research Octane Number) plus MON (Motor Octane Number) divided by 2. The AKI is typically 4-6 points lower than MON, which was used prior to the early seventies. What the octane requirements are of the engine, in its current configuration is a matter of trial and error. It appears that the "bottom end" hasn't been rebuilt, so if the block is a '73 it has a taller deck height, at 8.229 inches to put the piston farther down the hole and reduce compression. In addition, we don't know the combustion chamber volume of the aftermarket cylinder heads.... The originals were 58.2cc and the typical Edelbrock Performer for a 302 is 60cc so unless the OP is using a steel shim head gasket the compression ratio is lower than stock and, depending on the camshaft used and how much cylinder pressure it helps create it may well run fine on even 86 octane.

 

Givin the question ...What octane do I run? OP does not know engines well... So go for a drive, listen,if it pings/rattles, back down the timing a few degrees. Next go for a drive again, listen, if it rattles put high test in it - It should stop pinging. You will probably end up using , mid grade, to supreme. Problem solved. Go get um, tigers...

 

Not only does higher-than-necessary octaibe waste $, it does not burn properly in the wrong engine.

The octane in pump gas does not change the burn rate. Without going into it; gasoline of sufficient octane or higher will function properly. Higher octane is therefore viable, but a waste if unnecessary.

Hopefully your cylinder head valves have hardened seats so you would not need a lead additive!

Unleaded is not a primary cause of rapid valve and seat wear. By research, the primary causes are #1) incorrect ignition timing and 2) consistently rich fueling. One of many proofs of this is that Ford did not change their seats or production methods when unleaded was mandated. BTW - standard "hardened seats" are no harder than stock, which are also hardened as already described by others here.

The reason modern versions (up to 2001 for SBF) last so long compared to ours, is primarily the much better control of ignition and fuel. The best safeguards for valve life are tuning your ignition and fuel (see reasons 1 & 2). Additional benefits are that your engine will run better and with more power and economy.

So go for a drive, listen,if it pings/rattles, back down the timing a few degrees.

Only if de-tuning is acceptable to paying higher fuel prices for the correct fuel. If the fuel and ignition are correct, the engine should run properly on the correct grade of fuel. If it knocks then, a higher grade of fuel is called-for, to suit the engine build. Knock (detonation) is only initiated by heat.

 

The reason modern versions (up to 2001 for SBF) last so long compared to ours, is primarily the much better control of ignition and fuel. The best safeguards for valve life are tuning your ignition and fuel (see reasons 1 & 2). Additional benefits are that your engine will run better and with more power and economy.

I would add that OD transmission started bumping up longevity earlier as well. While "a SMF will run all day at 4,000rpm", in relative terms it will run 2 days at 2,500rpm. With each revolution comes wear.

Only if de-tuning is acceptable to paying higher fuel prices for the correct fuel. If the fuel and ignition are correct, the engine should run properly on the correct grade of fuel. If it knocks then, a higher grade of fuel is called-for, to suit the engine build. Knock (detonation) is only initiated by heat.

Agreed if the engine is properly tuned. Often people try to "get a little more" and bump timing further than where it should be. In that case retarding it could be bringing it back into proper tune. We just do not know enough about the state of the OP's engine or it's tune to say what retarding the timing might do.

See inserts