Solid327

Okay, from reading the other threads on J. Podell's TEL additive, I thought it might make for an interesting and informative thread to discuss the pros and cons of TEL additives vs off road fuels and whether or not they are necessary for iron headed SHP vintage engines running original spec compression ratios at 11.1 to 11.25 to 1.

My understanding, from discussions with Duke and JohnZ, is that today’s 93 octane pump premium (as determined by Research Octane + Motor Octane, divided by two) is about the same as yesteryear’s 97 octane. Original RON octane specs for SHP engines were 99-101. So the best results would have been achieved running the higher octane premiums available at the time from some retailers. Duke recalled that sometime in late 1962-63, Flint began assembling SHP/FI engines with two thin shim head gaskets, which reduced actual CR about one a point. Apparently, this was due to customer detonation complaints. Duke says that his car had two head gaskets from the factory.

Apparently TEL is not necessary to prevent valve seat recession under normal operating conditions but it does increase octane and octane helps to prevent detonation in the older engines when set to factory specs.

For those of you with the SHP engine options, what set up are you using to run your engines?

Some of the choices: lowered compression, timing changes, add a TEL fuel additive to pump premium; what brand/ratio per gallon, run blended fuels-off road with pump premium, or just running pump premium.

ghostrider20

Quote
(For those of you with the SHP engine options, what set up are you using to run your engines?)

I am running a 50/50 mix of 100LL avgas and premium (92) octane pump gas.

I am also running my initial timing up around 16* BTDC. With no audible detonation.

I think the shop manual calls for 10* or 12* as the initial setting. At 10* I get no audible detonation with pump gas.

I have tried all kinds of timing combos and 16* initial on my 327/365 seems to be the best with the 50/50 mix.

I experimented this summer and a 25/75 combo worked as well. So I may only need to ad 5 gallons of avgas.

I have also run 100% avgas and the throttle response seemed to deteriorate, and pulled a bit slower on the top end. So in this case, more is not better.

Mark

Vetterodder

Ghostrider, if your distributor is at stock specs, 16º initial will put you at 40º total at about 2350 rpm. I could see where that might require some help in the octane department.

My 300 hp 327 was rebuilt with TRW replacements for the SHP 11:1 pistons. I've run as much as 38º total with the stock iron heads and with a much milder cam than the 30/30 without any sign of pinging and with pump premimum.

62fuelie

My 327 fuelie runs just fine on 93 octane. Total advance about 36 deg.

ghostrider20

40 seems to be the winning combo. I have tried more and less.

As mentioned, if I wanted to run straight pump gas 8*-10* degrees would yield a detention free combo.

I kept stepping the timing up in 2* intervals and it kept getting snappier and snappier. Of course I ran into some pinging so I added the 100LL and I was back in business.

Getting the timing in order and peaked out was a real performance boost.

100LL has a distinctive smell so it draws allot of questions. The first thing people ask is if they can run it in their car to get more performance. The fuel does not add any performance, only allows you to bring your timing up to peak performance.

Mark

JohnZ

My (stock) 11:1 '69 Z/28 runs fine on pump premium; 36* total (26* in the distributor, in at 2800, and 10* initial), VC-1810 advance can (15* @ 8" Hg.), connected to manifold vacuum, 25* advance @ 900 rpm idle. No detonation - the stock "30-30" cam helps here due to its high overlap - bleeds off cylinder pressure at low rpm. :thumbs:

SWCDuke

The extra shim type gasket from Flint reduced the CR maybe half a point from the advertised 11.25:1. I think most guys with original or rebuilt to OE spec SHP engines are running pump premium without significant detonation, and any light detonation can usually be vanquished by retarding the timing 2-4 degrees or slowing the centrifugal curve.

Centrifugal curves yield 24-30 degrees depending on the year and engine option - see you shop manual or AMA specs in your GM restoration package.

You want total WOT timing in the range of 34-38, so you can set the initial to achieve somewhere in this range. Most L-76/84 had 24 centrifugal with 10-14 initial. Most L-79 have 30 centrifugal, so you don't need as much initial timing. The mechanical lifter engines can take more timing at low revs because they have lower dynamic compression due to the extra overlap over and above the L-79 cam.

Duke

0X-AutoProducts

i don't remember the timing spec's on my '63 FI coupe, but i do know it's not stock. i think my base advance is much higher than stock, and that my cent+vac advance is limited to a less-than-stock amount. i do know that my base advance is set just below the point that the starter has trouble turning the engine over if i advance the distributor any more.

i think my total advance is around 36-38* by 2500 rpm. either way, my car runs great and has strong low end pull, which my car is not known for having.

i use TEL and i believe i can feel the difference, even with flat top pistons in place of the stock 11.25:1 domed. i've run straight 93 without noticeable knock. but i prefer having little extra octane because i know that engine damage can occur from knock/ping without me hearing it or noticing any driveability issues. i figure i need it because i have a non-stock distributor with a lot of base advance. it can't hurt, and it's a lot less expensive that aviation gas.

i do keep in mind the health effects of TEL.

Solid327

http://www.ducatimeccanica.com/gas.html

The article is from January '98 issue of Popular Hotrodding magazine. According to Sunoco research the popular octane boosters do little if anything to actually boost octane levels. Here is a couple of interesting quotes from the article:

"Octane boosters offer little help in the quest for higher octane. Most popular street-legal octane boosters claim increases in octane ratings up to five points, and those boosters intended for off-road use only claim up to seven points. That’s a lot of octane to hope for simply by pouring an additive in a tank. Sunoco told us that before they launched their GT-100 Unleaded retail pilot program, they wanted to be sure that a 100 (R+M)/2 octane street-legal fuel would be of value, and that enthusiasts would not be able to get the same (or better) results using an octane booster. Nine of the most popular retail octane boosters were put through a series of tests to determine where the consumer could get the most bang for the buck. The test results were verified by an independent testing facility, using several brands of regular unleaded and premium gasolines, just to make sure everything was legit.

According to Mark Borosky, Vehicle Test Engineer for Sunoco, "Of the nine octane boosters tested, none showed a significant increase, and one actually lowered the octane number of the test gasolines." Testing repeatedly showed a maximum increase in octane of 3.5 points by only two of the six street-legal octane boosters when the recommended treatment rate was blended with lower base 87-octane gasoline. The best the remaining four products could muster was less than a one point increase. "While clearly no one would actually use an octane booster in a low base octane fuel, we wanted to give the manufacturers the benefit of the doubt relative to their claims of five-to-seven point increases" explained Borosky.

When tests were performed using 98 and 94-octane fuel, even the two best products from the previous tests produced a disappointing 1.5 to 2 point maximum increase. The remaining four street-legal octane boosters showed less than a .5 point increase. Those products designated for off-road use only didn’t fare any better than the street-legal products. Subsequent tests where the dosage of octane booster was doubled, tripled, and even quadrupled produced only minimal improvements in octane, regardless of the base octane hum-ber of the test gas. In fact, quadrupling the treatment rate of the most powerful additive produced only a 3.5 point increase in octane when added to 98 premium, resulting in a cost of $3.25 a gallon."

on blending fuels:

"Blending a leaded fuel with unleaded, however, pushes the octane up a bit more than the math would suggest, due to the effect of the lead. Just a gram or two of lead blended into the unleaded fuel will raise the octane number significantly. Commercial leaded racing fuels contain anywhere from a trace to six grams of lead per gallon. If you were to mix 50 percent 110 octane leaded fuel with 100 octane unleaded, you would actually end up with an octane number around 106 to 107. Keep in mind that even the smallest amount of lead or leaded gasoline with unleaded, could spell the end of your catalytic converter or oxygen sensor. The same holds true for using octane boosters intended for off-road use only. A word to the wise, check for any lead content in all the additives you might mix with your unleaded gasoline. And check with your state emissions regulations for street use.

We asked Sunoco’s Wurth about using aviation fuel in an automobile engine. He was emphatic when he said, "Don’t do it. Even though Sunoco is a major producer of aviation fuel, this fuel is specifically blended for aircraft engines. Aircraft operate under very different conditions than automobiles, and the fuel requirements are quite different as well. Aircraft engines generally use very small pistons and run within a very narrow rpm range. There’s no need for transient throttle response in an airplane because after the pilot does the initial engine run-up, the throttle is set in one position and the rpm doesn’t normally change until landing. Also, airplanes fly where the air is cold and thin, and the atmospheric pressure is low. These are not even close to the conditions your street machine will see on the ground. Also, since most piston-driven aircraft cruise at 3,000rpm or so, the burn rate of aviation gas is much too slow for any high-performance automotive applications."