low octane vs high octane in your 1971& older vette

[Domenic T.]

If all you want is to drive your vette in a parade or not experiance the real power they had using the right octane then these clips/ articles are not for you.

I am talking about the early high compression vettes 1971 & older.

Forgive me but this is in laymans term that I think are easier to understand.

These are real tests, not paper formula's of how it might work.

A 365 hp 327 with compression in the 11's probably looses about 20% of it's HP using pump gas.

To one that bought one later in life it feels pretty good but I want it to feel ORIGINAL and scare the he?? out of myself and others.

I am old enough to, and was able to drive these monsters back then and some even in the 1/4 mile.

Using todays gas your lucky to turn in the 14 second range when the same car turned in the 12's on the right fuel.

I think I read that 93 octane = 98 using todays method of measuring octane.

Thats not enough to get tha max HP tout of your engine. The tests using a 200K gas engine that determine knock say that it is 104 octane that is needed.

It was said on this forum that low octane and high octane burn at the same rate, tests prove otherwise reguardless of a formula on paper that is hard to understand.

I have a hard time understanding big words combined with formulas and acronyms.

One that holds a patent tells of a champion spark plug test that prooves different (see attached).

There's actually a lot of tests that show different, fuel burn propagation rate is one but I know there are more.

I will post the compression vs octane tests done in a lab as soon as I can get attached to another post here.

Here is a post that I read in another forum by one that holds a patent on this related problem.

(I will follow up with the test done with the 200K test engine.)

Why am I being repeatedly asked to answer questions that are explained with relevant SAE references in my patent 4,961,406?

Obviously most of you are younger and far more educated than I am. That being said I am the first person who ever applied for a patent on the concept of using a detonation sensor to control intake valve events for the purpose of altering combustion rates. Have any of you read Toyotas patent 6,848,422? Pretty much says the same thing I patented
over a decade before their patent was issued.

Many years ago Champion Spark plug would host seminars and demonstrate the different burn rates of low octane and high octane fuel. They would use two clear tubes about 50 feet long and put low octane in one tube and high octane in the other. They would light them both at the same time and you could watch the low octane burn to the end of the tube faster than the high octane.

Maybe somebody could explain to me how this doesn't demonstrate the different burn rates of low octane and high octane fuel?

DOM

[Domenic T.]

Re: low octane vs high octane in your 1971& older vette

This is the test done using the 200K test engine.



Subject: 7. What parameters determine octane requirement? 7.1 What is the effect of Compression ratio?

Most people know that an increase in Compression Ratio will require an increase in fuel octane for the same engine design. Increasing the compression ratio increases the theoretical thermodynamic efficiency of an engine according to the standard equation
Efficiency = 1 - (1/compression ratio)^gamma-1where gamma = ratio of specific heats at constant pressure and constant volume of the working fluid ( for most purposes air is the working fluid, and is treated as an ideal gas ). There are indications that thermal efficiency reaches a maximum at a compression ratio of about 17:1 [15].
The efficiency gains are best when the engine is at incipient knock, that's why knock sensors ( actually vibration sensors ) are used. Low compression ratio engines are less efficient because they can not deliver as much of the ideal combustion power to the flywheel. For a typical carburetted engine, without engine management [17,24]:-
Compression Octane Number Brake Thermal Efficiency Ratio Requirement ( Full Throttle ) 5:1 72 - 6:1 81 25 % 7:1 87 28 % 8:1 92 30 % 9:1 96 32 % 10:1 100 33 % 11:1 104 34 % 12:1 108 35 %Modern engines have improved significantly on this, and the changing fuel specifications and engine design should see more improvements, but significant gains may have to await improved engine materials and fuels.

In my own notes back in 1972 while studying this, (I quote the instructor) " high octane burns slower, more evenly and cooler than regular"

I can dig the books out on this also.

Today our older cars are not a concideration fuel wise.

As much as we try to keep things original on our cars we forget that a vette was a monster back then.

In another post it was said that maybe 1% raced their cars and that sounds like it may be the case but it's nice to feel the beauty the engine offers.

In another test they talk about engine damage using a sub standard octane in one that requires more.

Thereis a lot on our OLD fuel out there.

Re- time your engine, get 5 gallons of high octane and try it, the cops tend to go easy on us.

DOM

[Kurt G.]

Re: low octane vs high octane in your 1971& older vette

If I read your post correctly, I think you are asking how to find higher octane fuel for your higher compression engine. Easy answer, good luck and let us all know where you find it.

Now for a couple of tips. Sunoco in some areas still make a 96 octane unleaded, but the problem I have with that is the owner of Sunoco. Something else you can try to boost your octane is mix about a gallon of 100 octane avgas with 5 gallons of auto fuel. DON'T run it straight as it is very dry fuel and will burn your engine up like a match in west Texas grass. The last option is to find a fuel dealer that carries racing fuel and blend it with street gas to boost your octane.

Hope this answers what I think you were asking.

[Scott S.]

Re: low octane vs high octane in your 1971& older vette

To one that bought one later in life it feels pretty good but I want it to feel ORIGINAL and scare the he?? out of myself and others.

As much as we try to keep things original on our cars we forget that a vette was a monster back then.

In another post it was said that maybe 1% raced their cars and that sounds like it may be the case but it's nice to feel the beauty the engine offers.

Dom,

Agreed. A Corvette ought to scare most people, even at idle. When you start the engine, if most people don’t take a step back and think twice about wanting to go for a ride, then something’s not right

[Ronald L.]

Re: low octane vs high octane in your 1971& older vette

If you can't find 110 racing gas you can probably squeeze something from the local air port.

Scott - scared??? That rumble is the most inviting sound to say let's go, man has made.

[Scott S.]

Re: low octane vs high octane in your 1971& older vette

Scott - scared??? That rumble is the most inviting sound to say let's go, man has made.

As often happens, I failed to communicate what I was trying to say. Par for the course

[Domenic T.]

Re: low octane vs high octane in your 1971& older vette

If I read your post correctly, I think you are asking how to find higher octane fuel for your higher compression engine. Easy answer, good luck and let us all know where you find it.

Now for a couple of tips. Sunoco in some areas still make a 96 octane unleaded, but the problem I have with that is the owner of Sunoco. Something else you can try to boost your octane is mix about a gallon of 100 octane avgas with 5 gallons of auto fuel. DON'T run it straight as it is very dry fuel and will burn your engine up like a match in west Texas grass. The last option is to find a fuel dealer that carries racing fuel and blend it with street gas to boost your octane.

Hope this answers what I think you were asking.

Kurt,
Thanks, actually I have a good source of av-gas and the purpose of the post is to let some of the high compression guys knpw that they are not getting the HP out of their engines with pump gas, 93 octane.

Their engines were designed around 104 or better if they have 11:1 or more compression.

Other than the beauty of the vette is the performance they were born with.

I did a post a while back about these old cars romping the socks off the rice rockets and the responce was that they didn't have what it takes to beat the new cars from light to light.

Well they DON'T using pump gas. I used the octane that the chevrolet built the engine for and have a field day out there.

I loose about 20% power when I use pump gas and I have to use the clutch to burn rubber.

With the correct octane I just depress the pedal and all he?? breaks loose.

There are those that are telling us that they run fine on pump gas, but FINE is - 20% of what the engines can do.

All I am trying to say is treat yourself to a batch of octane and see what you bought, then re-time and get practical and use what's available.

What is available is not to good for these engines according to tests.

DOM

[David P.]

Re: low octane vs high octane in your 1971& older vette

Here in Tucson, 100 octane unleaded racing gasoline is readily available in at least two gas stations. Not cheap though ($6.99/gal)!
These gas stations are located not too far from the local drag strip.

It might be possible that a similar situation exisits in other cities.

Regards,

DAP

[Don W.]

Re: low octane vs high octane in your 1971& older vette

I've posted requests for recommendations on my 69 base 427 rebuild. The advise I've received is to target 10.00:1 as the max...Don

[Pat M.]

Re: low octane vs high octane in your 1971& older vette

I loose about 20% power when I use pump gas and I have to use the clutch to burn rubber.

There are those that are telling us that they run fine on pump gas, but FINE is - 20% of what the engines can do.

Wouldn't that be 80% of what engines can do?

[Domenic T.]

Re: low octane vs high octane in your 1971& older vette

I've posted requests for recommendations on my 69 base 427 rebuild. The advise I've received is to target 10.00:1 as the max...Don

Don,
If you have over 11:1 compression you need 104 or more octane to get your engine to run at factory specs.

Some have said that General Motors compression ratings were not accurate but GM spent millions testing them and I tend to go with their recomendations and tuning specs for their engines.

I don't challenge what worked and much more what GM spent millions to test.

When you here that 10:1 would work as a target for 11:1 you are getting info thats not worth more than you pay for it.

We are having to run these engines using damaging octane rated fuels.
Its OK if you don't use all you have for carburation, but to get the full power you need to use what GM recomended for the year of your car.

I tend to think that some here are retired oil company workers and are protecting their retirement.

We don't have the fuel our engines werte desigened to use and we won't get it back.

All I am trying to say is you will have to tune to the gas you have available ane DO NOT EXPECT the HP that the engine was to put out unless you try the octane it was desigened for at factory tuning specs.

I am hooked on the 1/4 mile times these vettes turned right off the show room floor. They are hard pressed to get within 2 secs with the new fuel recomendations given.

DOM

DOM

[Peter M.]

Re: low octane vs high octane in your 1971& older vette

Dom - 2 seconds is huge in qtr mile. What was your experience at the time on what various corvettes (I assume you are talking the BB and SB HP motors) as to what they did right off the showroom floor. I do not have the benefit of what they did off the showroom floor as you did so definitely curious as to what your experiences were. also to whether your experiences differered from published road tests back in the day and, if different, your rationale on why different. Like you said, you were there so quite curious.

Thanks

Pete

[Joe C.]

Re: low octane vs high octane in your 1971& older vette

A change in octane level in motor fuel will make no difference, whatsoever in an engine's drivability and power output if the engine is not detonating with lower octane fuel.

If changing from 93 PON to 87 PON fuel causes detonation, and thereby forces less spark advance, then you can expect a sizable loss in throttle response off-idle, as well as significant drop on peak power output.

If changing from 93 PON to 87 PON fuel causes detonation, and the detonation is allowed to continue, then the power loss will be somewhat less than if the owner had backed off of the spark advance, but long term damage to the engine may result.

[Don W.]

Re: low octane vs high octane in your 1971& older vette

For my base 69 427, the listed compression was 10.25:1; so targeting 10.0:1 with some head work should be a good target.

Another question: If I'm currently running on regular pump premium and want to see how a tank full of 100 octane feels; will I need to adjust timing and advance; or just fill the tank and drive it?

thanks,

Don

[Michael W.]

Re: low octane vs high octane in your 1971& older vette

Don,

Joe C. has done an excellent job of explaining 'how it is'. Assuming your car is not presently suffering detonation, simply substituting higher octane gas will do nothing. As stated in another recent post, the octane rating of gasoline is simply a measure of it's resistance to detonation and nothing else. There is no connection to any other characteristics, real or imaginary. The common myth that an octane rating is a measurement of power or energy gas is false.

If the timing on your car is already optimised and there is no sign of detonation, a higher rated octane gas will do nothing but drain your wallet.