coltsneckbob

I have been putting Sunoco 110 octane leaded racing fuel in my 1970 442. It makes a noticable difference in terms of the engine running a little smoother.....at least that is my perception.

However, I am also getting the sense of a slight loss of power. Not much but some. I was wondering if this could be because the car was last tuned for unleaded Sunoco 94. More specifically I think for the 94 the timing was just slightly set back (perhaps 2 degrees) from the max recommendation in manual. Given that octane is resistance to ignition perhaps the higher octane actually performs worse with the timing as it is set for unleaded. Does this make sense?

The obvious cure is to advance the timing (which on virtually any car gives more power - until/unless you start to ping/knock alot). I am sure I can advance it that considering I have the octane level of 1970 gas and I probably will, but just was wondering if my theory on this sounds plausible to you all.

OLD SKL 69

I am not surprised that your car runs smoother with the 110 octane gas. I notice that with my Riv too. Not sure why it would feel like it was down on power though? I don't think it should make a difference.

I have rejetted carbs to run on today's gas and usually that means increasing the jet size and/or decreasing the main metering rod size. Running leaded 110 octane should actually richen up the mixture a little more, which could give you more power if you were running on the lean side to begin with.

Olds64

I am confused. Why would you run 110 octane gas in your car unless you have high compression pistons? Most Oldsmobiles will run just fine on pump gas.

ROCKET VAPOR

FWIW, I have been running this same mix for 15 years in my completely factory stock '70 442 with no problems, and clean plugs.

5 gallons of Sunoco leaded 110 (purple) and 15 gallons of Shell/ Texaco 91 unleaded.

BTW, the first year I had the car, I would run Sinclair 93 with STP lead substitute (gray bottle). The car ran good on this mixture, but the plugs would get a gray ash like build up.

coltsneckbob

The compression ratio per the manual is 10.5:1. That alone is high enough to support using a 100 octane plus fuel. I am also assuming some carbon build up over the years and so it might actually be somewhere between 10.5 and 11 to 1. Also, the timing on the car is recommended to be at least 10 up to 12 degrees before TDC. All of this says a high octane fuel is preferred. Another reason is because I cannot get a leaded fuel with less then the 110 octane rating....at least not around here yet. I do mix it up a bit though. I will put in some Sunoco 94 (at a bit over $3/gallon here) and when available I try to get Sunoco 105 unleaded (which is a bit over $4/gallon).

I don't like the lead substitutes for the fact that I too noticed it seems to foul up plugs (at least gives them a burnt - grayish - color). Then there is the fact that I don't like handling the stuff. If you read the labels it warns to avoid contact or fumes. I may be a bit paranoid, but I didn't like putting on rubber gloves every time I put the stuff in the tank.

jensenracing77

i have no doubt that it will make an engine with 10:1 compression or higher run better but don't know why it would loose power. i would not think you would have much of any power difference in the 10 to 10.5 compression range.

coltsneckbob

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Not sure if I understand the comment you made. Well, I am not certain that I really have experienced any power loss, I just get the sense of it. I'll probably check timing and other things in next day or two. I also do believe I need a carb rebuild......sometimes when accelerator pump starts to falter it seems like you're losing power.

My442

Higher octane gas burns slower, so it will resist detonation when under a high compression squeeze.

The 10.5 to 1 advertised compression may be less than that. It all depends on the tolerances and stack up in the engine.

I build a 9.7 to 1 455 that was dyno'ed and tuned to perfection. It runs super strong on 93 pump gas. The total timing is 34 degrees (14 at the balancer, and 20 in the mechanical advance). The vacuum can is limited to 10 degrees. This timing allows the engine to run great on 93.

BTW, 110 race leaded gas contains TEL, or Tetra Ethyl Lead.

This additive is hygroscopic, which means it will permeate soft tissue and mucus membranes and be absorbed into your body - not good.

compedgemarine

it feels like it is down on power because it probably is. a 10.5 comp motor would only need around 100 octane fuel. the higher the octane the slower the burn rate so if there is not enough compression it will not burn completely. on our marine engines a Mercury Racing HP525 (around 540 horsepower) the motor is 8.2 compression. it will lose power on any thing other than 87 octane. I would run the mix like Rocket Vapor does as that will get you around the 100 octane and it would match with the engine compression

RAMBOW

Get yourself some Kemco additive (has TEL in it) and run 1/4 - 1/2 a bottle with a full tank of gas.

Several friends have engines on the ragged edge of having too high of compression for pump gas, They all swear by it & buy it by the case.

coltsneckbob

OK, well I had the car in a Memorial Day parade and burned off half a tank. I will top off with Sunoco 94 which should get be to about 100 octane. Based on your comments that should be about right for my engine. I will see if I get more surge/power out if it. Frankly, I think I will cause I tend to agree with ur analysis.

And Yes MY442 I do know the dangers of leaded gas vapors.....but I gotta say I love the smell of leaded gasoline in the morning....it smells......of..........the 70's

jaunty75

Oh my god! Most parades are what, a few city blocks in length? How long was this parade? 200 miles?

coltsneckbob

Jaunty,

LOL. OK a bit of an exaggeration It was 2 miles and about 5 mph was about the speed we moved. No I didn't really burn half of a tank, but the gas gauge certainly appeared to have moved an appreciable amount !!!

jaunty75

I know what you mean. I was in a couple of parades back in the '90s with my '75 Delta 88 convertible, and there is a lot of idling and creeping along, and even in short parades you can notice that gas gauge dropping. In fact, I always made it a point to fill the tank just before getting into the parade line because the last thing I wanted was to run out of gas! After all, how embarrassing would THAT have been?

442much

When I re-did my 455 I also built it to accept todays diet-gas. (9.75 comp).

442much

Dang, I've told you guy a billion times, don't exaggerate.

Blk71SX

huh? how does octane influence the air / fuel ratio?

sure, going to larger jets richens the ratio and can have an effect on power but changing octanes won't richen or lean a mixture. the amount of fuel passing thru the jets is the same, be it 87 or 110.