[grandam1979]

Go to auto zone they carry a few brands not to hard to find.

[70GS455]

Mix in half and half E85 and 93. May need to richen the carb however

Sent from my SM-T817V using Tapatalk

[dmac]

Originally Posted by Jay S

The boosters to run from are the ones that are vague on the octane increase. Maybe will say they add point or 2 for octane, but the instructions mostly imply the additive has great cleaning properties.

In common language, when most of the auto parts store octane boosters say '2 point' increase, it really means .2 increase, as in going from 91 octane, to 91.2.

I don't know if saying 'two points' is really honest, when most of us would say 'point two' instead of 'two points.'

[Sirrotica]

I try to build the engine to accommodate the fuel, not rebuild the fuel to accommodate the engine. If you can't afford to buy the correct fuel, you need to find another hobby. After my $3000 learning experience, I find it to be the best way.

Agree on the .2 octane increase, over a 2.0 octane increase with octane booster. The fine print is what usually gets you, it got me. If you can get 2.0 points out of a pint, or even a quart can, why is it that when adding xylene, acetone, or tolulene, it takes nearly 2 gallons per tankful to bump the number one or two full points?

[Jay S]

Lol. That .2 sounds about right on some of them. Browsing the parts store octane booster selection I would avoid the “boosters” that come in 15 to 16 ounce bottles, and most will say treats a tank of fuel or 25 gallon per bottle.

When these older 389s get rebuilt most shops use cast pistons and have a very poor quench, pistons end up down in the deck .030” or better. Combined that with the huge quench pad of the small closed chambers heads, with a small cam, most pump gas plans are pretty much done.


FWIW, with regard to these normal octane boosters that the parts stores sell in the 15 to 16 ounce bottles…..We bought an aluminum headed race engine once and did a compression check and it was running about 210 psi. Thought it had a chance to run on pump gas instead of the race gas we were running. Drained the gas and put 5 gallon of 91 pump gas in, added 2 of the 15 ounce cans of boosters. Lol the engine pinged setting there idling when we first started it up. We went back to town twice, cleaned all the parts stores out of their “octane boosters”. We were stubborn and thought it would eventually make a difference. I think all said and done we had 8 of the 15 ounce cans mixed with 5 gallons of gas before we have up and drained it and put race gas again. Would ping and knock idling in neutral. Lol

[Goatracer1]

Assuming the engine was rebuilt to close to stock how big a chamber would I need on a factory later model head to lower the compress ratio to something usable?

[Jay S]

Originally Posted by Goatracer1

Assuming the engine was rebuilt to close to stock how big a chamber would I need on a factory later model head to lower the compress ratio to something usable?

Staring out it this 389 is likely 10:1 and has a 68-70 cc head. Probably a 17, 47 or an 11 from a 68-70 350s would work well, low to mid 80s cc’s. Compression should be 9 ish. 68-70 small valve 400 could be about the same too. The next step below that would be the 70 455 heads. The 71 and later 350 and 400 heads are 90-100 cc’s, getting on the soft side for compression.

My 2cents, very few street miles, leave it original, blend the gas with something (use the better examples.. not the crappy 15-16 ounce so called boosters) and run it as is. Unless the plan is to put the car on the road more, probably not putting enough miles on the justify a head change.

[Kenth]

Originally Posted by Goatracer1

Assuming the engine was rebuilt to close to stock how big a chamber would I need on a factory later model head to lower the compress ratio to something usable?

Who knows what camshaft that lurks in your rebuilt 389?
Since the PO couldn´t stand the ping and sold the car i would guess a "modern grind" that was modern 1971 and aimed for low compression smog engines.

All you may have to do is replace the camshaft for one that lowers the Dynamic Compression ratio to enjoy your engine.


Eric Douthitt on
OCTANE BOOSTERS:

I love this topic. Most octane boosters are hydrocarbon solvents already present in gas. Some claim to be real lead. Others are products banned by the EPA.

Most of us have a pretty big gas tank in our Pontiacs. It would take a lot of little 8 oz. bottles to actually provide any measurable increase. Claims that, "adding a 8 oz. bottle of our octane booster will raise octane 4 points". Actually, they mean .4 points. Sunoco did a test a couple of years ago and tested the major products on the market. None of them raised octane when used be the manufactures recommendation. In fact a couple actually lowered it. Only when dosing 4X the recommended volume, one product raised it a few points. The problem was they were only now up to 96-97 octane and had surpassed the cost of a tank of race gas.

Some of the products claim they will minimize valve seat recession. They do this by adding a heavy weight oil that gets introduced to the chamber via the gas and lubes the valves. Valve seat recession is primarily a problem in sustained high speed operation (racing, autobahn, etc.) Test data shows a 1970 engine operated at 70 MPH averaged 1.5 mm of seat recession in 7,500 miles per year. However, this is 7,500 miles at 70 MPH. I know my Pontiac only gets driven approximately 2,000 miles/yr, mostly cruising and a few drag strip runs.

Gas line antifreeze products are typically used by us northern and mid western people. These products are typically, Ethyl, Methyl or Isopropyl Alcohol. If you are using Ethanol blended gas, using these products would be a total waste of money, as there is more alcohol already in your tank than you are adding from an 8 oz. bottle.

I am not stating that none of the products work. The better products under the right conditions might provide some advantage to a car owner that has problems with knocking. What I am saying is, the additional octane provided is less than you think, meaning your car does not require as much octane as you think. Additionally, there are thousands of people out there that are adding fuel additive's that do not need to.

Jim Hand on
Cams And CR:

Most cam companies recommend increased CR to be used with their "higher performance" cams. Why is this necessary or recommended?

Let’s review CR and what it really means. "Static" or "rated" CR is a ratio of the fixed volume of space above the piston top in the cylinder at Top Dead Center (TDC), to the volume of space displaced by the piston when moving from bottom dead center (BDC) to top dead center. When we look at actual cam timing specs, we find that the intake valve does not close until sometime after BDC. There can be no compression until the intake valve closes, so actual CR will be less then the static. How much less will be determined by the closing point of the intake valve. This actual CR will be referred to as the "dynamic" CR. These two different CR values are predictable and calculable. There is a third type of CR which represents the total cylinder pressure, and is the result of many more variables, but this value is unpredictable and for all practical purposes, unmeasurable. We will discuss it in later sessions.

Here are some examples of static CR and dynamic CR of a given engine using different cams. The dynamic values are as calculated by a Performance Trends Engine Analyzer program, and they may vary slightly from the absolute values. However, they will suffice for comparison purposes. There are equivalent math formula for calculating these values, but are quite involved. Assuming a 462 engine with different static CR values as noted, the real (dynamic) CR will be listed by cam type.

Comp Cams 268H (Intake 218 duration, 106 LC, Exhaust 218 duration, 114 LC). Intake valve closes at 35 degrees ABDC.

8 Static CR, Dynamic CR = 6.14

9 Static CR, Dynamic CR = 6.87

10 Static CR, Dynamic CR = 7.6

Comp Cams P-306R (Intake 275 duration, 102 LC installed,, Exhaust 278, 106 LC
installed). Intake valve closes at 59.5 degrees ABDC.

10 Static CR, Dynamic CR = 5.09

11 Static CR, Dynamic CR = 5.55

12 Static CR, Dynamic CR = 6.00

13 Static CR, Dynamic CR = 6.46

What do these numbers mean in regards to practical CR? What they show is that a shorter duration/ advanced intake lobe cam, will have much higher real compression then a long duration high performance cam in the same engine. Note that the 268 provides higher real CR with 8-1 rated CR then does the 275/278 at 12 - 1 rated (static) CR. How can we use this information? First, if we have a factory high-CR engine, we sure as heck don’t want to install a cam like the 268. We want to look for a cam that will provide the desired power range while keeping the dynamic CR as low as
possible/practical. Note the intake closing points of the two cams above - the 268 closes at 35, and the race cam closes at 59.5. If we can find a cam that has the intake closing later then 35 but before 59, we should have a better chance to live with the resulting CR. How abut the Pontiac cam grinds?

744 (RA III) (Intake 224, LC 113, Exhaust 236, LC 118) same 462 engine. Intake valve closes at 45 degrees ABDC.

8 Static CR, Dynamic CR = 5.6

9 Static CR, Dynamic CR = 6.25

10 Static CR, Dynamic CR = 6.91

041 (R IV) Intake 230, LC 112, Exhaust 240, LC 115). Intake valve closes at 47 degrees ABDC.

8 Static CR, Dynamic CR = 5.42

9 Static CR, Dynamic CR = 6.05

10 Static CR, Dynamic CR = 6.69

How about the cam that I use - Wolverine 234/244? (Intake 234, LC 107,
Exhaust 244, LC 117). Intake valve closes at 44 degrees ABDC.

8 Static CR, Dynamic CR = 5.55

9 Static CR, Dynamic CR = 6.19

10 Static CR, Dynamic CR = 6.84

Again, a review of these numbers shows us that a RA III or RA IV cam will provide the actual CR of the CC 268 while running a full point higher rated CR. None of this is to recommend or discount the use of any cam, but is only to show the relationship of the intake closing points on true engine CR. Another way to use this relationship is to see what cam might work best if we have low static CR and want improved performance in the driving rpm range. The CC268 provides almost a point higher real CR then does the RA III or RA IV, so on an 8 to 1 engine, we would have much better throttle response and engine power within the operating range of the CC 268. Do be aware that this type of cam has a much shorter rpm range then either of the Pontiac cams.

While the Wolverine 234/244 increased the dynamic CR of my engine slightly over the previously used 041, the change was minimal, and the resulting increased mid range power increase of the Wolverine provided about .1 ET gain, and 1 MPH gain over the 041 on my setup with no adverse effects on the CR/detonation relationship.

In summary, the cam has a direct control over the engine operating CR, and the controlling factor is the intake valve closing point. By selecting a cam with a later closing point that will provide power in the rpm range needed/desired, the tendency of the engine to detonate will be minimized. As previously mentioned, other factors will affect the engine’s cylinder pressure, and some of those will be discussed in the next segment.

[Sirrotica]

I have a 455 with 5C heads on it, (9,25-9.5 to 1). The CC 268HE does increase the dynamic compression so that even on 93 octane gas it will ping. That's even with a lazy mechanical advance. The same cam in a 455 with 71 455 HO heads (8.0 to 1, and never has any auditable knock), and is a good street cam for those heads. Give it 1 1/2 more points of compression, and it becomes a liability.

No doubt that cam selection will make an engine less prone to auditable knock than a cam intended to raise dynamic compression in a low compression engine, or one that is a stock grind near factory specs.

The 068 cam may be better to relieve some of the dynamic compression at low RPMs than a 067 is, and there are many other choices besides, that have already been posted.

Eric D probably has the octane thing down pretty good, if the aromatics are at or near 30% adding even more has almost zero effect on further raising octane ratings. Without knowing what the oil company has added to the base petroleum, you just guessing on what octane you'll end up with. Buying a product of known octane, is the best way to get a consistent product in the car, X + Y = Z............

The health risks from inhaling the aromatics when blending them can cause a lot of cancers down the line also, one reason I quit hauling fuel for a living is constant exposure to benzines and other aromatics.

[Jay S]

Photos the instructions from a very common octane booster found at part stores, and one from Race gas concentrate.

Instructions with the Chart. …X + Y = Z

Instructions with no chart, X + Y = ???

[bob d]

I bought that booster. All it did was foul my plugs. It put on some red crap on my plugs. I called them and they told me that was normal. It may be okay for wide open running but not for my 389 1965 GTO. I just add a gallon of race fuel and 91 octane non ethanol in my driver. Thanks Bob.

[Sirrotica]

The thing that's good for the companies that sell octane booster is, it's involved, and expensive to have gasoline tested for octane number. There's no easy cheap test other than to pour it in and see if the spark knock is still there. If the customer bitches they on the tech line have a litany of excuses, and ways to blame the customer, so they keep up their advertising campaigns duping more people into buying what they're selling, win, win, for them.

I'll never use it again, nor recommend for anyone else to try it after losing a fresh engine because I believed what they were saying was the truth. The OP can do whatever he wishes, but I have little to no faith octane booster will do anything, but lighten his wallet.

I did just check to see if Moroso still makes octane booster, seems they no longer sell it. That's what I used back in 1977 that ruined my high compression race car engine..

[Mike Davis]

I use any of them that contain MMT in my 66 NSS car. Most of the time it's Turbo 108. I mix 4oz to 5 gallons of 100LL Av Gas. Ran the car at the track, ran the same as VP C-12.
I mixed a batch and sent a sample of the 100LL mix and VP C-12. 100LL with the 4oz of MMT came back at 106.7 octane, VP C-12 was 107.7.
In my 67 street car with a 428 and 62 heads I mix 1 gallon of 100LL to 4 Gallons of Non ethanol 91 or 93. No issues with pinging.

[Redwolf]

If your engine has been rebuilt, it may not have a stock pontiac cam back in it. An aftermarket cam will usually build more cylinder pressure due to tighter lobe separations than the factory cams. That with the fact that your motor has close to an actual 10 to 1 or more in compression ratio, will cause your engine to ping on today's cheap quality fuel. I would check the timing to make sure it is fine and then check the plugs to see if they are around a 43 or 44 heat range to help with the compression. If everything there is good. I would recommend buying some VP 110 fuel and mixing about 3 gallons with a tank full of premium. That should take care of your pinging problem. I have had minimal success with any type of octane boosters. Your only other option is to tear into the motor to lower the compression ratio. In my opinion spending a few dollars extra on good uel is way easier than tearing into a engine on a limited use vehicle. Hope this helps.

[Jay S]

If the ignition system is stock the MMT additives will most of the time like a hotter plug to keep them from fowling. Fowling can be an issue, least of my issues since the cars I have that need high octane are high maintenance 13:1 roller cam’d race engines that really don’t belong in the street anyway… The hotter heat range using the MMT’s is opposite of what I would do with plug heat ranges trying to nurse a high compression pump gas combo. If you drop the heat range to the cold side of what the engine wants then add the concentrates to the fuel to bump the octane up with MMT it will likely fowl the plugs pretty quickly.

A cam swap in a 389 to something like a 068 cam from a basic smallish rebuild cam would likely allow it to run on 93. Make it more fun to drive too. Probably a win win if you were up to the effort.

I totally agree with the guys blending higher octane race and av gas with pump gas. It is my first choice, and then the MMT additives gets carried in the car for the day when I don’t plan ahead and I am pulling up to a gas pump with nothing else to blend.

These days you can even get race gas delivered to you, 55 gallon or 5’s. I don’t recall if they deliver to residential, I think they do, very easy if you have a place of business like me.

https://petroleumservicecompany.com/...4-gallon-drum/

[Jay S]

This octane/gas discussion came up a short time ago with my car friends. One of the friends was determined to run 87 octane to save money. We asked how many miles he put on the car since it was bought in the early 90s. He said something around 3500 miles. One of my other friends got his calculator out and figured what it would have cost per year to run $9/gallon straight race gas the entire time. It figured out to be about $150 a year more than pump gas. The car has a blend of higher octane in it now. Lol

[track73]

Back in the mid 70's I ran a hobby/sportsman stock car. I thought I was smart by mixing Moroso octane booster with premium gas. The kids that were helping me were increasing the amount needed with out my knowledge thinking it would help. I didn't realize by doing that it was fouling the spark plugs. I lost the championship because of that. And I really didn't need to increase the octane with only 10 to 1 compression.

[Goatracer1]

Please back to my question. How big a chamber would a later head need (in cc’s) to do me any good. Please don’t give me head numbers because I need cc’s. The heads I have to choose from are not stock.

[wakesupremo]

Does anybody over in US use powerpour I have been using it for several years . I don't know if it improves anything as I have been using it for so long I use it as a course of habit.

[68WarDog]

Originally Posted by Goatracer1

Please back to my question. How big a chamber would a later head need (in cc’s) to do me any good. Please don’t give me head numbers because I need cc’s. The heads I have to choose from are not stock.

This should answer your question. Wallaceracing.com