matchek

This may be a dumb question , but does this 442 require premium gas? Would 87 or 89 ruin the engine or would you just notice poor performance?

Thoughts from theory and experience?

oldcutlass

You need to run the highest octane available and tune to it. 87/89 will net you poor performance and detonation with stock tune.

MDchanic

Yes.

At 10.5:1 compression, the only way to avoid destruction of the engine at those octane numbers is to retard the timing so far that it would barely run.

Your engine is designed to use gasoline with about 98 octane on the AKI scale, which we currently use in the US and Canada, which is a good ten points higher than what you asked about.
By retarding it, you may be able to safely run it on 93 or 94, but you won't like it.

Your best bet is to either find a gas station that sells racing gas, and then mix that with 93 or 94 accordingly, or buy Octane Supreme and mix that with 93 or 94.
Neither option is cheap, but neither is a new motor.

- Eric

matchek

The Sunoco by me sells 91 without ethanol and 93 with ethanol

Is there some additive you recommend to add to a full tank at auto zone or eBay that would increase the octane to safe levels?

Thanks so much

MDchanic

Did you read my post?

- Eric

matchek

Thank you Eric , good to know. A 32 oz can of octane supreme is 40 on eBay. I assume cheaper at the store. Not sure what store.


I was wondering too if people also had luck with more inexpensive brands like Lucas. I can get a case for like $80. Lol

tru-blue 442

Best we can get around here is Sunoco 93 laced with ethanol.
The 66 400 runs fair with it, doesn't ping. But I still had to retard
the timing some so it wouldn't.

oldcutlass

You should be able to get by on the 93.

MDchanic

The guy selling it in the link I posted is selling it for $23 a quart / $130 a case of 6, plus shipping.

A bit more than a quart would raise a 20 gallon tank 5 points, from 93 to 98 octane.
Compare to the price per gallon of 108 or 110 octane at the pump, if you can find it.

Once you start using it, you can experiment with adding less, until you get some pinging, to find the amount that your engine actually needs.
In an unmodified 10.25:1 engine, I found that I needed about an ounce a gallon, which declined markedly after I removed the heads, cleaned the piston crowns, and polished the combustion chambers.

There are many other ways of increasing octane. The most common is toluene, which, if I recall, requires at least a gallon per tank, and which reduces lubricity, and may increase cylinder wear.

- Eric

35tac

I run 93 Octane/ 10% Ethanol and it runs fine.
Wayne

matchek

Thank you very much Eric. I did not go to the link at first. Very good to know. Yeah, I need to find the right mix for what works for me.

Glad to hear some other 93 works too.

matchek

Hey Eric, how is the Octane Supreme legal? It has lead in it. Did not know you can still burn lead.

MDchanic

Who says you can't?

- Eric

matchek

Glad you can as lead lubricates.

matchek

Thanks again for the link. Seems like the best bang for the buck.

MDchanic

It was the best deal I could find when I searched around, but I haven't re-checked since then.

I consider it sort of a gold standard - once you get the engine right on this, you can try other things if you want, and you'll have something to compare them to, so you can judge the effect (and if something doesn't work very well, a bit of this will get you through).

Good luck!

- Eric

88 Cutty Classic

anyone run mixtures of 110? im not a chemist but would a gallon of 93 and a gallon of 110 give you aprx 2 gallons of 101.5. or is that not how it works?

http://www.sunocoracefuels.com/fuel-finder

sadly i remember only 10 years ago i could get leaded or unleaded 110 for about $5.25 a gallon at a local sunoco.. i'm talking 10 minutes from downtown pittsburgh. now you gotta go deeping into the rural PA areas to dirt tracks to get it.

a drum looks to be about $500 or so for 110.

88 Cutty Classic

found this too

http://www.wallaceracing.com/octane-mix-calc.php

MDchanic

That calculator presupposes that a fuel's octane rating is like the concentration of a solute, which, as far as I know, it is not.
Different grades of gasoline may reach their rated octane by using different combinations of additives, so the result of mixing them may not simply be an average of the two.

That's why a bit of trial and error, after making a rough estimate, is almost definitely in order.

- Eric

natedrag

Never opened 400? Stock steel shim head gaskets and pistons? If the heads have been off and felpro head gaskets installed, then its down from 10.5 to maybe 9.9 now. Dont know your engine, just something to think about.

jeffsims

Very interesting read. I have a question how this relates back to ignition timing. Based on other posts, I have my 67' 442 timing set at 35deg @ 3500 RPM w/o advance connected. I am about 50deg with advance. I run with 90 octane ethanal free. There is a Marathon gas station near by that sells 110 octane racing fuel (I am pretty close to the Talladega Super Speedway). If I decide to mix 10gal of 90 with 5 gal of the 110, that will get me around 96 octane. Granted I am mix a little more 110 to get the average higher. Sooooo....do I need to adjust my timing closer to stock if I decide to go this route?

The engine has been rebuilt to stock specs.

MDchanic

Those timing numbers are about right, though, in the end, you have to customize to your exact engine.

90 octane seems extremely low for a 10.5:1 Olds engine with iron heads to have no detonation, especially with timing as described.

It's hard to know the exact octane when you mix two fuels, but essentially, you want to find a mixture where you can use optimal timing settings and get no pinging.

Mechanical advance maxed out at 35° at 3,500 sounds like it is in the neighborhood of factory, so I'm not sure what you mean by setting your timing closer to stock. You may find that changing the advance springs to get the advance all-in by 2,500 or 3,000 gives you better results.

You didn't answer Nate's question above: Was your engine rebuilt with original 0.016" steel shim head gaskets, or with Fel-Pro 0.045" gaskets, or something else?

Sounds like you're making progress.

- Eric

jeffsims

MDchanic -- The service manual says I should set my initial timing at 7.5deg BTC w/ vacuum advance disconnected. If I do this my car runs like crap. After I set my timing to 35deg max at 3500RPM, my initial timing became ~16deg w/ vacuum advance disconnected. Car runs awesome. 7.5deg BTC is what I mean by timing closer to stock.

I know I has steel shim head gaskets, but not sure about thickness. I will have to dig that info out.

I went ahead and purchased 5gal of the Sunoco 110 octane leaded racing fuel. $9.99 per gallon! I haven't put it in the tank yet, but will soon. Of course I can get super unleaded 92/93 octane cheaper, but I refuse to put ethanal in my car.

oldcutlass

Are you running an HEI or points? Ethanol will not hurt your engine, a lot of us have been running it for many years with no issues. Its your money.

jeffsims

Orignal distributor with Pertronix Ignitor ignition. I might have to change my mind on the ethanol mix. Just thought it caused problems in older cars.

MDchanic

At this point, we have established with reasonable certainty that you really do have an original-spec. motor (sorry, but people have a bad habit of saying that their engine is original when the only thing it has in common with the original is that they both burn gasoline).
So, since your displacement, compression ratio, cam, intake, exhaust, and carburetion are all within the specification range of the originals, we can ASSume that the original timing specifications should suit the combination well, especially since 1967 was a "pre-emission-control year," when GM tried to come close to optimizing timing settings (though it is possible it could be improved upon).

Take a look at the outer edge of your distributor. It should have stamped number 1111042.
Just for the heck of it, take a look at the flat part of your vacuum advance (both top and bottom surfaces, sorry) and see if there's a stamped number there. In the highly unlikely event that the vacuum advance is original, its number would be 1116232, and it would probably be stamped "232." Since rubber deteriorates, it would probably have failed and been replaced decades ago.
If it's got a different stamped number, we can look it up and see what its characteristics are supposed to be.

Next, disconnect and plug the vacuum advance hose, and, using your tachometer and timing light, check the advance through the RPM range.
(Note that the CSM gives distributor specifications in distributor degrees, but I have indicated crank degrees here, which are double the distributor degree specification, because you will be taking readings at the crank, rather than using a distributor machine)
At 400 RPM, it should be 0°-4° advanced at the crank.
At 900 RPM, it should be 12°-16° advanced at the crank.
At 2,000 RPM, it should be 20°-24° advanced at the crank.

Then, connect the vacuum advance to a vacuum gauge, and either a vacuum pump, or just a length of hose that you can suck on to produce vacuum, and start the engine and run it up to a steady RPM (you want the speed to remain fairly constant, so that the amount of mechanical advance doesn't affect your readings). Apply vacuum to the vacuum advance and track its effect on the amount of advance with the timing light.
It should begin to pull in (move from 0° advance to 1°) at about 6"-8"hg.
It should produce 18° advanced at the crank between 16½"-19½"hg.

If your advance numbers are significantly different from these, then you have a good reason why your car doesn't run well when set to the factory specified timing at idle.

Once we know more, we can provide more specific advice.



They should all be the same thickness, more or less, so that means you likely have a nominal 10.5:1, and an actual 10 or 10.25:1 compression ratio.



You should be able to mix that to get the octane you want (need).

- Eric

MDchanic

Ethanol provides less energy per unit of volume, so, since carburetors regulate the fuel mixture based on volume, a carbureted car will run slightly leaner on gasoline with ethanol than on straight gasoline. This can be fixed by installing slightly larger jets and/or smaller metering rods.

- Eric

oldcutlass

I think someone has recurved your distributor if the mechanical advance reaches 35 and has stopped advancing at 3500. I would not worry about changing anything if your not drag racing the car. I would not change your settings.

jeffsims

Mechanic - confirmed distributor is stamped with 1111042. I put on an adjustable vac advance canister not too long ago to keep total timing below 50deg >=3500 RPM. Initial timing = 16deg. With advance at idle = 30deg. During rebuild I used a Standard vac advance. There was no spec other than it listed for my car. I was getting ~55deg at 3500 RPM

oldcutlass - Unless it was recurved before I got a hold of it, it has the original weights and springs (just cleaned everything up). My mom is the original owner, so I doubt she or my dad ever did anything with it. You questioned this based on reaching 35deg and stopped advancing @3500RPM. What should I be seeing? She runs great. At the same time I want as much as I can get out of the engine.

MDchanic

I just did the math on the factory specs I posted, and I realized that I should have either translated them to crankshaft degrees or explained that they were in distributor degrees.

Dumb on my part, but my fingers were busy duplicating what my eyes saw, and my brain decided to take a nap.

The CSM gives the distributor test specs in distributor degrees, under the assumption that the mechanic will be testing the distributor on a distributor machine, but you will be doing any testing installed on the engine and measuring advance at the crankshaft.
Since the distributor (and the cam) turns at half the speed of the crank, you need to double distributor degrees to get crank degrees.

I have changed my post above to reflect this.

The factory specifications suggest that at cruise (assume 2,000 RPM, 18-19"hg of vacuum) your advance should be about 40-48°, so it sounds like you're in the right range.

In the end, getting it dialed in for your particular engine is the most important thing.

It's always good to confirm that your timing components are behaving as they should, though, so that if there are any oddities, you can correct them.

- Eric

oldcutlass

Jeff your numbers work out fine and are within the rule of thumb with the exception that total timing should be all in around the 2500 rpm mark. I've found that most stock points distributors usually have more mechanical advance than yours. Like I said not an issue and should work fine.

jeffsims

I double checked and apparently I did not record the curve between idle and 3500RPM properly. I do get full mechanical advance @2790 RPM. It maxes out at 35deg w/ vac advance disconnected. This still leaves the initial at 16deg.

Back to the original post topic before I hijacked it a little. I have 10gal of 90oct and 5 gal of 110oct. This mix should put me around 96-97oct. There is a noticeable difference in performance. Throttle response is crisper/sharper and the secondary sounds awesome opened up! Not that it didn't before, it just sounds much different. Hard to explain.

I never noticed any detonation before, not saying it wasn't there. I will begin using the 92/93 premium that at 10% ethanol to save a few $$. The Sunoco racing fuel is a bit pricey at $9.99/gal. Definitely worth the test though. If Octane Supreme does what others say it does, it will definitely save me $20+ per tank vs. the Sunoco racing fuel.

MDchanic

Sounds like the mechanical is set right where it should be.

Different models of distributor should have different amounts of mechanical advance built in, and yours seems to have 19° at the crank (9½° at the distributor), which I would think was a bit too little (for the factory spec of 7½° BTDC just above idle, I would expect a mechanical advance range of 27½° at the crank), but it's the correct unit, and while the rate of mechanical advance can change as the springs fatigue, the amount of advance will not change with time and wear, so I'd say it's good.

Yup. Now you're in the right neighborhood.

Inaudible detonation will destroy your engine as much as audible detonation will, and if you've got enough of it, you will notice a loss of power, because the fuel is detonating, and beginning to push the piston down the bore, before the piston has reached TDC.

Glad you've got this figured out!

Now all you need is a little fine tuning (messing with the adjustable advance to see if you can improve part-throttle behavior), and you should be there.

One thing I would recommend, just to satisfy the obsessive in me:
When you get the gas tank really low (like you think you've only got about 20 miles left in there), pour in another gallon, or maybe two, of the 110 -
If she runs even better, you know that the mix you're using is still a bit low on the octane.
If it runs the same, you know you've got enough octane, and can back off the mix slightly on the next tank (and then test again at the end of the tank, to see whether you were low or high), so you can zero in on the right mixture.

Remember that there is a certain amount of octane that you need, and adding more after that will have no effect, so you can use your knowledge of your own gas tank and gauge behavior to zero in on the number that is just right, over time.

- Eric