octane

[BobDeSoto]

I know I don't want the Ethynol blend but do I want the 87 Octane - 89 Octane or the 91 Octane?

All are available here.

 

 

[greg g]

87 is more than sufficient.

[BobDeSoto]

And then I also add some lead additive.

[DonaldSmith]

I still have my bottle of lead additive from 18 years ago.   Neophyte purchase.  I soon heard that the valve seats are hardened, and lead additive is not needed, for the Chrysler family of engines.  True for a 51 DeSoto? .

Edited September 2, 2019 by DonaldSmith
Clarification

[Adam H P15 D30]

True, lead additive is not needed

[martybose]

Providing that the block hasn't had a valve grind in the last 50 years or so, the valve seats will be hardened.  As far as octane goes, for a stock compression motor I agree with the 87 octane recommendation. But if the engine is modified (cut head, different cam, headers, dual carb or more) go with the 91 or 93 octane.  My motor had all of the above, and my machinist told me that flatheads are prone to knocking by design, and you should run a higher octane gas to accomodate it.

 

Marty

[kencombs]

13 hours ago, martybose said:

Providing that the block hasn't had a valve grind in the last 50 years or so, the valve seats will be hardened.  As far as octane goes, for a stock compression motor I agree with the 87 octane recommendation. But if the engine is modified (cut head, different cam, headers, dual carb or more) go with the 91 or 93 octane.  My motor had all of the above, and my machinist told me that flatheads are prone to knocking by design, and you should run a higher octane gas to accomodate it.

 

Marty

Actually, it should not make a difference if a valve job is/was done.  the seats are not integral hardened seats like some.  They are fully hardened, replaceable seats and can be reground without losing the temper.  Hard on stones if that's the type of grinding equipment used, but doable, DAMHIKT.  OK, you didn't ask, but I'll tell you.  I could get a full grind, maybe two on a Chevy 6 head without redressing stones.  On a Mopar flathead, I need to dress the stone before and at least once, sometimes twice during a full seat grind.  That will depend on the stone brand and type of course, but they are good steel!

[martybose]

Ken,

 

Neither of the two blocks I have worked on came stock with removable seats; in fact, they had to be machined to accept removable valve seats.  I thought the seats were induction-hardened from the factory, and thus would have the hardness removed if they were reground as part of a valve job.

 

Marty

[kencombs]

15 hours ago, martybose said:

Ken,

 

Neither of the two blocks I have worked on came stock with removable seats; in fact, they had to be machined to accept removable valve seats.  I thought the seats were induction-hardened from the factory, and thus would have the hardness removed if they were reground as part of a valve job.

 

Marty

That's odd.  I only have experience with 218/230 blocks and all have had removable seats from new.  And, all the manuals I've seen specify removable seats.  Were your blocks originally US made and/or long blocks?  Not that I know if that makes a difference.  Just curious.

[Plymouthy Adams]

On the flattie..do not confuse the need for the exhaust valves and hardened seat insert with the intakes...I do not see on my blocks that the intake has inserts...these normally stay cool due to the flow of fuel cooled on intake....and as there is no high lift or aggressive cam profiles that allow slamming shut but rather a gentle closing via profile of the cam ramp...the need for hardened on intake is moot....a closer inspection of your block should show a defined circle that is the parting line block/seat for the exhaust.

Edited September 3, 2019 by Plymouthy Adams

[kencombs]

Thanks PA!  I was focused on the exh because I'm replacing exh guides on one this week, and totally forgot that is only half the story.  So I was half right, again. 

Edited September 3, 2019 by kencombs

[BobDeSoto]

So do we all agree? -

87 Octane with no Ethynol is sufficient-

and lead additive is not necessary.

 

[DJ194950]

Almost,

 

87 octane with ethanol and no lead additive is fine by Me.  No  ethanol is a plus!  ?

Not available in good ol" calif.  ?

 

DJ

[chrysler1941]

I wish we had 87 available in this country. 92 is lowest. Occasionally I add 20% Kerosene to fuel to lower the octane. Lowering octane gives a fuller combustion flame burn for side valve engines, more torque and minimizes vapor lock.  Only minus, exhaust odor ?

Diesel can also be used. 

[kencombs]

8 hours ago, chrysler1941 said:

I wish we had 87 available in this country. 92 is lowest. Occasionally I add 20% Kerosene to fuel to lower the octane. Lowering octane gives a fuller combustion flame burn for side valve engines, more torque and minimizes vapor lock.  Only minus, exhaust odor ?

Diesel can also be used. 

Most folks would like higher.  Not that they need it, just sounds better to some.  Is your posted octane rating derived using the Motors or Research method?  In the US, at least my state and I think nationally, it is calculated using both.  Motors + Research/2.

 

That led to some confusion when it was standardized (70's maybe?), as some gasoline retailers were advertizing only the higher and thus suffered a bigger drop.   So, our real loss of octane when lead left was not really as bad as it seemed.

[Plymouthy Adams]

higher the octane the slower the fuel burns...that is why it is there...raw low octane fuel ignites easier and is actually combusting long before piston is near the top of the compression stroke in higher compression engine....that is why timing and octane go hand in hand and why higher compression engine with altered cam profile need the retardant.    Many people think yet today it is a much hotter fuel blend and waste fuel dollars for no reason.   Todays higher compression engines often SUGGEST higher octane fuels and in truth these suggest are with merit and reward you with performance.....the timing is such that it is advanced by computer to the point of that first ping and holds off further advance....in the case of lower octane in the computer driven engine...the knock sensor will retard your timing so quick you will never know or hear a ping...which is what the analog driven car owner has to tune for and accept an "operational balance" on both ends as a result.  

[chrysler1941]

45 minutes ago, kencombs said:

Most folks would like higher.  Not that they need it, just sounds better to some.  Is your posted octane rating derived using the Motors or Research method?  In the US, at least my state and I think nationally, it is calculated using both.  Motors + Research/2.

 

That led to some confusion when it was standardized (70's maybe?), as some gasoline retailers were advertizing only the higher and thus suffered a bigger drop.   So, our real loss of octane when lead left was not really as bad as it seemed.

Interesting question. I never knew they where to norms for octane so I had to look it up. Here and most Europe use Research Octane Number (RON). They are even planning to drop 92 and offer 95 as lowest so next is 98 and 100 for modern injected cars.

 

 

Lower octane is better for stock flat heads due filling out burning in deform combustion chamber. (I'm sure this is not correct English )?

No difference on highways, but driving around town with lowered octane, there' is more torque and engine sounds more relaxed. Difficult to explain. And yes timing is important.

Especially in my Cadillac V8 flathead, there is a significant difference.  

 

With a compression of 4.5-7:1, who needs lead ?

Edited September 4, 2019 by chrysler1941

[kencombs]

Not exact for sure, but your 92R is about the same as our averaged 87.  Most sources say that there is a 5-12 spread between the two measurements, depending on the specific test.