Octane Increase - Which Alternative??

[Joel T.]

Hi Guys;

My rebuilt 396 is running roughly 10.7CR and I have been running Exxon premium.. there is about 150 miles on the rebuild. The car knocks once it gets well warmed up (which does not take long). Timing is at factory spec.

I've been through the archives looking at threads which talk to octane boosting and have basically come to the conclusion that I have roughly three alternatives..

1 - Buy some Av Gas (100 LL) from my local airport (just down the road) and mix with what is in the tank already.

2 - Buy some of Jack Podell's MaxiLead

2 - Buy some Supreme 130 from Kemco

Before I do anything, I thought I would check in and see if I could find a consensus as to which option to pick....

Thanks, Joel

[Joel F.]

Re: Octane Increase - Which Alternative??

Hi Guys;

My rebuilt 396 is running roughly 10.7CR and I have been running Exxon premium.. there is about 150 miles on the rebuild. The car knocks once it gets well warmed up (which does not take long). Timing is at factory spec.

I've been through the archives looking at threads which talk to octane boosting and have basically come to the conclusion that I have roughly three alternatives..

1 - Buy some Av Gas (100 LL) from my local airport (just down the road) and mix with what is in the tank already.

2 - Buy some of Jack Podell's MaxiLead

2 - Buy some Supreme 130 from Kemco

Before I do anything, I thought I would check in and see if I could find a consensus as to which option to pick....

Thanks, Joel

Hi Joel,

When does your engine knock? I am surprised you would need it with a 10.7:1 CR, so you may want to ensure your timing map is optimized for your car (timing may be coming in too fast? )

To be honest, the 100LL is probably going to be the most sure-fire way of getting that octane up. In this scenario, the lead content and octane are guaranteed to be what they are advertised. This may or may not be the case with the others.

If you feel the need to have something you can carry in your car for emergencies, from what I have read the Octane Supreme 130 looks promising. According to Kemco's literature, it contains 15 grams of TEL per quart. I believe I read elsewhere that in the Kemco product the TEL is suspended in a toluene carrier. Toluene is an octane enhancer used quite extensively in refining, so you can feel safe using this product in your car (assuming this is the actual carrier). 100LL contains about 2 grams of TEL per gallon. According to the literature I saw on this product, 2.5 oz of this product is needed to bring a gallon of 93 up to 100 octane, which would be a little over 2 grams of TEL in that gallon of 93.

I have heard the Jack Podell product is small quantity of TEL suspended in kerosine.

Good luck. I will be very interested to see how this turns out for you. Please do post a follow up.

Joel

[Stuart F.]

Re: Octane Increase - Which Alternative??

Joel;

I have used Jack Podell's additive for at least 10 - 12 years with complete satisfaction. I've been with him long enough to see the price go up near double. I buy it by the 12 qt. case now, but used to get the gallon jugs. Mine is a 63 340 hp w/ advertised 11.25 to 1 CR. I use an enhanced ignition curve and 10 or 12 initial w/ a B28 VAC. I have no spark knock to speak of, and it acts just like the old days, i.e. runs cooler, very responsive, etc., etc.. My carb likes it, my fuel filter likes it, and so I like it. There are a number of ways you can go, and you've mentioned three good ones. Perhaps a cost analysis is in order.

First! Like Joel said, check your ignition map and any other trouble shooting recommended for your engine to make sure there isn't something amiss.

Stu Fox

[Jim T.]

Re: Octane Increase - Which Alternative??

My 68 327/350 original engine has 11:1 and I can make it ping if I labor/lug the engine, however I don't do this. I keep the rpms up, don't shift early, never in a big hurry to get it shifted to 4th. Only use premium available from the pump. Have the M21 Muncie with 3:70 gears and like my 68's owners manual says in stop and go traffic below 30 mph I use second gear, no need to go to third. On the 396/425 you should have full time vacuum advance. When lugging/laboring engines vacuum for the vacuum advance is very low and can be low enough that there is no advance contributed by the vacuum advance unit.

[Joel T.]

Re: Octane Increase - Which Alternative??

Joel/Stu;

Thanks for the replies... I'll check the advance curve certainly but at this point I would assume that it is correct given that I just had the TI distributor rebuilt by Dave Fiedler...

The car does not knock when it is cool but once it gets hot(er) it will ping under acceleration.. you can actually hear it fairly clearly from inside the car with the top down... It's kind of a vicious cycle thing.. the knock makes it run hotter which in turn produces more knock...

I think I will swing by the local airport today and see if I can pick up some 100LL to start with, and I will probably visit with brother Podell or Kemco and pick up a case of booster as well.

Stu, I also have a '63 SWC 327/340 which protests a bit under heavy acceleration. I am running the same 10 degree basic timing as you with a B 28 can.. not as bad as the BB but I can hear it. Rebuilding the distributor helped a good deal but I still hear a bit of noise.

I'll follow up with some results....

Thanks again.

Joel

[Stuart F.]

Re: Octane Increase - Which Alternative??

I should probably mention that my 63 has the 3.36 posi rear with a close ratio (M20) four speed. With gearing this tall, it's easy to see why lugging can be a problem. I even on occasion find myself in traffic starting out in second gear by mistake. As such, any possibility for spark knock is unacceptable. I can't always drive in a manner to avoid it, I just won't allow it to happen under any conditions.

Stu Fox

[Duke W.]

Re: Octane Increase - Which Alternative??

10.7:1 is a bit high, assuming this number was computed using a CR calculator and accurate dimensions for piston volume, head chamber volume, deck clearance, and head gasket compressed thickness.

Is this how the CR was determined?

According to the data I have from Corvette News (Vol. 8 No. 3) the VAC maximum is 15@15.5", which does not meet the "Two-Inch Rule". It should have a 12" VAC represented by the NAPA VC1765 stamped "B20". The OE VAC was probably the 201. What's the number stamped on the installed VAC?

Also, it's not clear to me if L-78 has ported or full time advance. Can you check?

The same Corvette News (Vol 8 No. 3) lists initial timing as 10 deg. BTDC and a centrifugal curve as follows:

0 @ 1000
15 @ 1600
28 @ 4600

Can you verify that it meets OE spec?

You can probably mitigate the detonation by backing the initial off to about 6 degrees.

Mixing in a little 100LL avgas is probably the least expensive way to enhance octane, but race gas is another way.

The relatively few number of L-78s out there has made it difficult for me to verify various parameters as above, and you can really help me out (and others) if you can provide the requested data.

Duke

[John M.]

Re: Octane Increase - Which Alternative??

I've use the 100 octane Avgas mixed 50-50 with good success. The only problem is buying it, you can't drive up to the pump. The 110 race gas is great too, mixed 5 to 1. They're both a pain though and I plan to lower the CR to solve the problem. My experience with additives is that they don't work. Never used the Jack Podell lead stuff but lead is bad for everything, in engine and out.
JB McRae 30025 69 L71

[Jim T.]

Re: Octane Increase - Which Alternative??

John some airports have self serve pumps that just take a credit card, may not be one close enough to you to use though.

[Joel F.]

Re: Octane Increase - Which Alternative??

John some airports have self serve pumps that just take a credit card, may not be one close enough to you to use though.

My local airport is this way. What I have done in the past is go up to the pump with 2 5-gallon jerry cans and filled them. No one has ever said a word to me about this. I always thought that if they did ask what i was doing, I'd fib and say the fuel was for an experimental craft I am building in my shop. IMHO the fuel seller is more interested in moving the gallons than being a pain in your behind though.

[John M.]

Re: Octane Increase - Which Alternative??

Hi Jim,
Thanks. At our little airport out here in the boonies, Lebanon NH, you go to the service terminal, they call the guy who drives the fuel truck, he drives over, fills your can, gives you a slip, you go into the terminal and pay. All very friendly but it takes a while.
John

[Joel T.]

Re: Octane Increase - Which Alternative??

10.7:1 is a bit high, assuming this number was computed using a CR calculator and accurate dimensions for piston volume, head chamber volume, deck clearance, and head gasket compressed thickness.

Is this how the CR was determined?

According to the data I have from Corvette News (Vol. 8 No. 3) the VAC maximum is 15@15.5", which does not meet the "Two-Inch Rule". It should have a 12" VAC represented by the NAPA VC1765 stamped "B20". The OE VAC was probably the 201. What's the number stamped on the installed VAC?

Also, it's not clear to me if L-78 has ported or full time advance. Can you check?

The same Corvette News (Vol 8 No. 3) lists initial timing as 10 deg. BTDC and a centrifugal curve as follows:

0 @ 1000
15 @ 1600
28 @ 4600

Can you verify that it meets OE spec?

You can probably mitigate the detonation by backing the initial off to about 6 degrees.

Mixing in a little 100LL avgas is probably the least expensive way to enhance octane, but race gas is another way.

The relatively few number of L-78s out there has made it difficult for me to verify various parameters as above, and you can really help me out (and others) if you can provide the requested data.

Duke

Hi Duke,

I will roundup the information requested later on this afternoon. The CR is a calculated number as you suggested. I will try and dig up the build sheets... the rest I can pick up from the car.

Joel

[Edward S.]

Re: Octane Increase - Which Alternative??

Joe,
I have a 396 for 7 yrs. now and never have had a knock. I use the Sunoco Super Hi-Test and have never had a problem - I did try a lead additive a few times which added nothing to the way the car performed
PS - I have a 3.70 rear.

[Donald B.]

Re: Octane Increase - Which Alternative??

I purchased a case (12 quarts) of Supreme 130 about 3 years ago and have used maybe 4 quarts. I now use AV fuel in the Z28. If I knew of anyone that wanted the Supreme 130 they could have it - but I don't want to deal with shipping "dangerous" items.

My '62 250 HP and the 289 HIPO seem to run just fine on 87 Regular.

[Wayne M.]

Re: Octane Increase - Which Alternative??

.... According to the data I have from Corvette News (Vol. 8 No. 3) the VAC maximum is 15@15.5", which does not meet the "Two-Inch Rule". It should have a 12" VAC represented by the NAPA VC1765 stamped "B20". The OE VAC was probably the 201. What's the number stamped on the installed VAC?

Also, it's not clear to me if L-78 has ported or full time advance. Can you check?

The same Corvette News (Vol 8 No. 3) lists initial timing as 10 deg. BTDC and a centrifugal curve as follows:

0 @ 1000, 15 @ 1600, 28 @ 4600

... The relatively few number of L-78s out there has made it difficult for me to verify various parameters as above, and you can really help me out (and others) if you can provide the requested data.

Duke

Duke -- a lot of conflicting L78 spec's out there. The '65 AIM, section K66 lists initial timing at 8 deg BTDC @ 800 rpm. The '65 TIM&JG lists the 201 vac can for the 1111093 distrib, but the Delco Remy Test Specifications supplement DR324S-2 (1964-66) says it should be the 355 can.

Same Delco supplement says centrifugal curve for the 1111093 distr. is 0-2 deg @ 550 rpm; 6.5-8.5 @ 900; 13-15 @ 2300; 12-15 (max) @ 3000 rpm. [data in DISTRIBUTOR rpm and DISTRIBUTOR degrees of advance].

Comparing 201 versus 355 vac advance (in distr. degrees) shows (from same Delco sources):
inches Hg to begin adv; 7-9 (201) vs. 5-7 (355).
Hg for max. adv. 15-15.75 (201) vs. 11.2-12.7 (355)
Max vac adv: 8 distr degrees (201) vs. same for (355).

A 201 can I have is stamped: MS_201 15; don't have a 355 to quote.

The 3124 Holley with the 4456 primary meter block is full time vac advance.