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104+ uses MMT to better allow your gasoline’s ability to resist detonation and preignition through the use of manganese. A lot like lead, manganese releases vapors when subjected to the high heat and pressure during combustion that in turn stabilize the end gases in the combustion chamber (those in the quench area of the small block Chevy) and keeps them from being ignited by hot spots or spontaneously exploding due to intense heat created by the resultant pressure spikes in the combustion chamber at high engine loads. This is actually different than another members postulation that alcohol is the active ingredient, when in fact it is a relatively low quantity when compared to the other aromatics in 104+; but it is the manganese in the MMT that makes for controlled combustion.  It works, MMT is found in VP and Sunoco fuels, typically when the fuel is specified as containing metallic compounds other than lead.

That's why you're the man, Jerry  .  Mine went over 500, but we backed it off a bit.  Nice to know what it'll do, but no reason to run the original block and heads on the ragged edge without reason.

P.S.  I am still looking for a set of original standard black door and interior quarter panels for a '68, just in case you happen to stumble over some.

Cheers,

Michael Parker

Funny you should ask.  I use VP C-12.  This is advertised as 108, I believe.  I have a mechanical compression ratio close to 13:1, as well as a Lunati custom grind that necessitates the need for higher octane, and then some, just to err on the side of caution.  The engine saw extensive dyno time at Nickens Brothers while paying close attention to BSFC, BMEP, EGTs, and effective compression which required a fuel notably less than the octane rating currently in the car (98, I believe is where the car made maximum power).  The extra octane points I run just to keep it safe, and the fact that the local speed shop always has it and the fuel has a stabilizer is a bonus, since I only drive the car about twice a year.

My daily driver is a 600 Rear Wheel Horsepower 4.6 liter, which has a screw style supercharger running 19 pounds of boost and it gets 100 octane unleaded.

There seems to be a lot of people hanging onto "octane" in this thread like it is the "be all, end all" in the world of power production. This is certainly not the case, or the extremely high octane (approx 130 points) of LPG and CNG would certainly create more power, but in real world application, everyone viewing this thread should be able to see that they do not.

Let's start with Aviation Fuel:
The octane of aviation fuel is not measured in exactly the same way as it is in automobile fuel.

The motor method of ASTM (which once stood for the American Society for Testing and Materials, but now is an internationally recognized standardization body) testing is used to determine the motor rating of aviation fuel. This differs from the R+M/2 methods used for traditional automotive gasoline.

Because of the different ways in which automotive and aviation gasoline octane is measured one must be very careful when comparing absolute numbers. 100 octane aviation fuel is not equal to 100 octane automotive gasoline, however, the lean number rating of aviation fuel will be close.

Now let's discuss Race Fuel:
The most talked about and most easily misunderstood characteristic of gasoline is its octane rating, which is a measure of how resistant gasoline is to detonation and preignition (knocking). It is measured relative to a mixture of iso-octane and n-heptane. So an 87-octane gasoline has the same knock resistance as a mixture of 87% iso-octane and 13% n-heptane.

So how do we get gas over 100 octane??  Because iso-octane is not the most knock-resistant substance available, and when other additives or substances to enhance octane are used in the refining and manufacturing process, it skews the standard that was developed back when Jesus was still a teenager. Everyone familiar with high performance engines is aware that racing fuels and aviation fuels typically have octane ratings of 110 or higher.

It can be said that fuels with higher octane ratings burn less easily, yet they remain extremely popular because they are thought of as being a more powerful fuel.  Manufacturers recommend using a fuel with a higher octane so that an engine can be run at a higher compression ratio without having problems with knock. Compression is directly related to power, so engines that require higher octane usually deliver more power.  This is usually where the misnomer of higher octane = more power stems from.  It cannot be stressed enough that the power output of an engine not only depends on compression (naturally) but also depends on the energy content of its fuel.  Where the confusion sets in is that no simple correlation between octane rating and actual power derivation (energy content) of the fuel exists. Some people believe that adding a higher octane fuel to their engine will increase its performance, but this is not the case.  Engines perform best when using fuel with the octane rating that allows for maximum power production without detonation or preignition.  Given today's advanced refining processes and additive packages, this is typically easily obtained without the gargantuan octane numbers of yore.

Just my $0.02

I will wait for others to reply, but I'm not liking the looks of that stamping at all.

Could it be a mark to determine the shift??  Were the transmissions assembled in shifts??

Here is something else weird about my transmission.  It has "R-I" embossed in the case.  These letters are not engraved, they're raised.  It had to be drawn into the sand mold by somebody.  Does anyone else have this?? 

Here is mine...  P8D26, and then what looks like half of an "E"

Actually, my wife does.

Jerry, any luck finding me a set of '68 standard black door panels??  This is Mike in Arizona, the guy that sent you the AFLAC ducks.

HN could be either 327 full size or 69 350/300 hp 4 bolt full size.

The 3956618 was available as a two-bolt or 4 bolt 300 hp version of the 350 V-8.   There is no record of the HN suffix being used in a 327 3956618 block that I can find reference to.

I have HN as being as being a 300 HP (4bbl) 350 with a TH-350 out of a fullsize car.  No guesses on the car, other than it is a 1969 Chevrolet built in LA.  Maybe others will have more info???

You were trying to load them through the site.  These are hosted on imageshack.

Here is the engine stamp, lightened substantiially

Here they are, I did not touch them up, this is just the way I got them...