Octane Increase - Which Alternative??

[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 have a shot of the vacuum advance, if I could only figure out how to upload it! I believe it is full time advance. The vacuum can is a 355 as someone else has mentioned. I will pick up the engine build sheets in the morning with the CR calcs on them.

[Joel T.]

Re: Octane Increase - Which Alternative??

[IMG]file:///Users/joeltalka/Desktop/SANY0389.JPG[/IMG]Here is the picture, I hope...

[Jim T.]

Re: Octane Increase - Which Alternative??

Joel just looked at the picture of my Holley carb and it shows the location of your vacuum advance connection as a "timed spark port" with a note: there might not be any vacuum here at curb idle.

[Timothy B.]

Re: Octane Increase - Which Alternative??

Joel,
I don't know about the 1965 carburetor metering block but usually that is ported vacuum, full time vacuum advance will help engine temperatures.

You may want to experiment with power enrichment valve (power valve) to open at a higher vacuum, that may help engine knock on accelleration. I think the rule is 1/2 engine idle vacuum or approx. 2" below the lowest cruise vacuum, say 25- 35- 45 MPH so if your lowest cruise vacuum is 11" you would pick a 8.5 or 9.5 power valve etc.

[John H.]

Re: Octane Increase - Which Alternative??

My '69 Z/28 (stock 11:1) runs fine on 93-octane pump premium, without a hint of detonation; I run 10* initial, 24* centrifugal, in by 2800, with a B28 can connected to full manifold vacuum ("ported" was stock on the 4053 carb, but I teed it into the choke pull-off diaphragm line).

[Bill C.]

Re: Octane Increase - Which Alternative??

Just a bit of trivia for you all ---

MAX LEAD 2000 and LEAD SUPREME 130 are the same product.

Kemco bottles the product and sells it as LEAD SUPREME 130, they also bottle the same solution for MAX LEAD distributor.

I got to talking to an owner of Kemco and he gave me the skinny on the TEL product.


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To get the same level of lead content as in 100LL av-gas, you would need to blend around 2.5-3.0 ounces per gallon. But this will only get you around 98 octane; starting with 93 as a base.

[Duke W.]

Re: Octane Increase - Which Alternative??

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.

I think the centrifugal specs you quoted from the Delco source are pretty close to what I quoted from Corvette News if you look at the midpoints.

A 12" VAC is correct for the idle vacuum characteristics of the OE cam, so the 355 VAC is the best functional choice.

Many detonation problems can be solved with some slight changes to the spark advance map. In the case of L-78 it's fairly slow, and may not take kindly to quickening with today's pump premium.

Assuming the map in Joe's car is to spec I think the detonation may be solved or significantly mitigated by reducing initial timing to the 4-6 degrees range. The spec for '67 L-71 is 4 initial and the max centrifugal is 30 @ 3800, which is more aggressive, but the total is only 34! Joe would have 34 with 6 initial.

So Joe I suggest you verify your centrifugal curve with a dial back light and verify that you have full manifold vacuum to the VAC. Then back the initial down to six and see how it runs. You just never know how things were diddled with over the last 40 years.

Duke

[Anthony S.]

Re: Octane Increase - Which Alternative??

Safety FYI....................regarding Kemco's Lead Supreme 130............

Leave it in it's original bottle.

I decided to fill up some empty (clean) STP Gas Treatment bottles so I would have a good measure when I got gas, and I found the bottles semi-melted the next day and ready to give way.

Anthony

[Stuart F.]

Re: Octane Increase - Which Alternative??

Anthony;

Interesting that you should mention this. My first few gallons of the TOL material sold by Jack Podell demonstrated perhaps a shelf life problem with the gallon jug container. As I got down near the bottom of each, the bottle started to shrival up or have a melt down and I had to dispose of the rest. I have not had any trouble with the Quart bottles, and I've been using them for probably close to 10 years now. Perhaps one of our chemically literate members can explain.

Stu Fox

[Bill C.]

Re: Octane Increase - Which Alternative??

I was told by Kemco that the bottles are treated, flourinated ??? , so that the TEL and stabilizing agent do not leak.


I bought a case one time, and one of their EX employees did not process the bottles. The stuff leaked while in transit and never stopped leaking. Kemco ended up sending me 24 treated botttles and I had to transfer the mixture.

PIA ------------------------

The additive is VERY NASTY - and does not do well with most plastics at all!

The last case I bought was just fine!

[Stuart F.]

Re: Octane Increase - Which Alternative??

Bill;

I think we were parked close to you at the winter meet judging with my son's 78 P.C.. I remember your Vette - nice!

Stu Fox

[Bill C.]

Re: Octane Increase - Which Alternative??

Stu,

There was so mch going on that weekend - I barely remember who was parked next to me --

What color is your 78?

Are you from FL, Tallahassee here.

[Stuart F.]

Re: Octane Increase - Which Alternative??

Bill;

My son and I were there with his 78 Pace car (black and silver). I believe we were across the isle from you towards the middle on the west side. You, I believe, were facing west and near the end of the isle. We live here in Orlando just east of the airport. We trailered the car there, not just because it is a low mileage car, but because my son didn't have the registration straightened out (the car had not been titled as yet). It was a good show, specially as the weather cooperated so well at least for the NCRS portion of the event.

Stu Fox

[Randy S.]

Re: Octane Increase - Which Alternative??

[quote=Duke Williams (22045);358969]
Mixing in a little 100LL avgas is probably the least expensive way to enhance octane, but race gas is another way.


Duke
Does 100LL have any advantage other than quelling detonation? My 66 300HP runs fine on premium pump gas but I was wondering if 100 LL(Low Lead ) avgas has any other benefits? Would the increased octane "clean the carbon out" so to speak. Would the lead have any lubrication benefit ( I'm using CJ 4 oil now). I was thinking of a mild mix of 1or 2 gal of avgas per tank of premium.

Randy

[Joel F.]

Re: Octane Increase - Which Alternative??

Randy,

I can't speak for Duke, but unless you are experiencing detonation, I think avgas would be a waste of your money, and you'd be forgoing the additive packages the major oil companies engineered to keep your engine clean (Shell V Power, BP Invigorate, etc.). Street driven cars do not really need the lead for anything despite what you may have heard.

Joel