Lead Additive? Octane?

[CriticalMass]

Using search I see this topic has been beaten to death, but none of the threads quite answered my question, so:

My father passed away and I'm left trying to maintain his ERA 427SC (feel like I'm going to have to give this background every time I post since otherwise you would wonder my I can't take care of my own damn car )

There was a time (when pump gas was 89 cents/gal) when he ran his car on leaded racing fuel. I don't remember the octane rating but it was somewhere around 110. Other times he used pump gas with a lead additive/substitute. The problem is that I don't know exactly what he was running it on when he passed away.

There is a 99% chance that its pump gas...but I can't be sure if he was using a lead additive/subsitute and/or octane booster.

My question is without knowing the compression ratio of the engine can I just go to the pump and get premium (91/93 octane) and be relatively safe that it wont need retuning? Should I use a lead additive/substitute? Should I also use an octane booster or mix pump gas with racing fuel? Or is solving this problem going to require figuring out the compression ratio?

Essentially I won't use any octane below 93. So if I happen to put in fuel of higher octane than it's used to will it cause any problems? If so, what needs to be adjusted.

If you suggest any additives and you have recommendations of brand names I would appreciate it...I've never had to run a car on high octane fuel.

Thanks.

[Excaliber]

You'd be surprised at what you can get away with, even with a really high compression motor. There are a couple of "keys" to makeing the motor live on less octane. Here are some ideas.

1. NEVER run the motor under ANY kind of load if it's overly hot. For instance, your downtown, the temp keeps climbing, 220-230. Thats mostly OK for a "normal" motor. Then you need to go up this steep ramp to enter the parking garage. That means lugging the motor at low rpm and a big load while hot. A recipe for disaster with high comrpession.

2. Don't advance the timing to much, back it off. To much timing with to little octane is a killer! You might consider two things here. BASE timeing (6 to 8 degrees) and TOTAL timing (less than 30).

3. Keep the rpm's up. DO NOT "lug" the motor, EVER! If cruising rpm is to low at 55 or 60 mph (2000-2300 maybe) consider using 3rd gear to keep those rpms up. Or increase you cruise speed.

4. Avoid high rpm! Don't approach it's red line, probably 6000 rpm or so. High rpm is classic cause of pre-ignition (ping). Because of the rpm and load it can cause serious damage REALLY QUICK! Often the engine tends to run "lean" at the upper rpm range, a double whammy for pre-ignition conditions!

5. If it runs a little "rich" this is a GOOD thing! The last thing you want is to run lean!

I was using Dale Earhardt Jr. octane booster. It's NOT the size of the bottle of that counts, it's the amount of booster per "dose". Dale Jr. bottles are small and easy to carry and offer about the max dose allowed by law. No doubt there are some boosters out there that are little more than smoke and mirrors!

Lead? No worries there, focus on how to make the motor live with high compression. It's likely the engine valve train was up-dated long ago to deal with unleaded fuel. Actually even engines that HAVEN'T been are only subject to valve damage during LONG road trips at SUSTAINED rpm. Sure lead "helps" with pre-ignition, but the boosters are a much better way.

Finally, you could take some compression readings to get a base idea of what you've got. Tricky though, cam profile can really throw off cranking compression readings and lead to false conclusions. BUT, say it cranks in the 200 plus range, 230 or 240 even! Yup, count on it, you DO have BIG compression! Hopefully you'll come in around 160 or so, but they MAY be because of cam profile.

By the way, I have a Living Trust "clause" that stipulates my Cobra must be sold and not transfered to any family members under any conditions upon my passing. Do drive careful, these things are dangerously quick.

[Ron61]

That is a rather difficult question to give a definate answer to but here goes. If you can still get 93 octane gas where you live, you can try it and take the car out and drive it until it is good and warm then start putting a load on it such as a pull up a hill or accelerating slowly. Don't go to high in the RPMs. Listen for any valve clatter, I know, hard to hear in one of these things, but if you have iron heads on the engine, you can use that pump gas for normal driving. All we can get out here is 91 octane which is more like 88 actually. With my 11:1 compression and the iron heads, I can back my timing down just a little and drive the car fine as long as I don't get on it. Otherwise, lots of valve clatter. With my aluminum headed stroker and 11:1, I really don't have much problem with pump gas, but still use the 110 leaded racing gas in them if I am going to be running hard. Higher octane than you actually need won't hurt it, but you will be wasting money. I use an additive when I am out away from my barell of racing gas called Fast Forward that works with gas and alcohol. It has worked well for me. And from time to time, I add 5 gallons of the 110 racing gas to my 65 Comet with the stock 289. Makes the gas mileage a lot better as this crap we get for gas doesn't burn well at all. But it doesn't hurt it at all. If you have hardened valve seats, the pump gas is ok if the compressiojn isn't to high. Mainly the lead acts as a lubricant. Another thing that you could do is take a sample of the gas that is in the tank and have it analyzed to see if it is the racing gas. Here the 110 is bright red. Pump gas is not a bright color here, just a sort of dull reddish. Sorry to hear about your Father.

Ron

[CriticalMass]

So running 110 octane racing gas (theoretically, I won't be doing that at this time) wouldn't require a timing adjustment on an engine that was tuned to run on 91/93?

If thats the case maybe I'll bite the bullet and run it on an octane that I know to be higher than what he would have been running it on until I become familiar with the engine (mix 91/93 with racing fuel). Then I could back the octane down to where it isn't wasted. Any issues with this plan?

Thanks for the quick replies, I appreciate the help.

[ItBites]

Ron,
1) Thats not valve clatter you hear, its piston skirt slapping the cylinder walls.
2) Using a fuel with more octane than you need will reduce power output (in addition to waste money), unless timing is advanced to accomodate the slower burn.

CriticalMass,
1) Do a compression test. Make sure to hold the throttle plates open. Divide the number in psi by 14.7. This won't give you the compression ratio, due to cam dynamic effects, but will get you in the ballpark if you're lucky. If the number is over 160 and you have iron heads, you will want some additional octane or back the timing to maybe 30 or 32 full in. If the number is way over 160, use high octane fuel.
2) I've never liked octane boosters. Most are just toluene, which has a high vapor pressure and will evaporate faster than the gas they are mixed with, resulting in a reduced concentration as time goes on. Some also color the plugs (Moroso) so that reading for mixture is impossible...
3) You'll hear a lot of naysayers chime in after I say this: I mix avgas in my gasoline to raise the octane. It cools the intake charge. It cools the intake valve and combustion chamber. It is infinitely more stable than pump gas. It will not outgas through a plastic jug in the way race gas will (if you store your race gas for more than a couple weeks in a plastic jug - guess what? - it aint race gas anymore...). Avgas is also cheap and you can use it without significant jetting changes.
4) Using VP110 or other race gas will require jet changes in order to avoid losing power. With 12.5:1 CR, I had to go up 10% in (effective) jet size in order to bring the power back in line with what I get from avgas/pumpgas mix. The reason for this primarily lies in the density (or specific gravity if you prefer) of the various fuels as well as the slight change in stoicheometry (even though we run far from stoichometric) and also the burn rate (which is related to but not totally controlled by octane).
5) Don't listen to the inevitable naysayers about avgas. When they post a link (and they will) to a site discussing pros and cons of avgas, read the site carefully. The sites I was referred to by the usual naysayers around here all came to the same conclusion that avgas is not as great as racegas (in terms of possible power production), but, given the cost provide a generally acceptable fuel for your hurting high compression motor.
6) Avgas smells good when burned
7) Mix 50/50 avgas/premium and drive the sucker. you'll be fine.



I will now await the potshots...

[Excaliber]

I don't think the higher octane fuel burns at a slower rate. I'd say it's a more stable controlled burn from the point of ignition across the combustion chamber. The higher octane makes it more difficult for "hot spots" in the combustion chamber to pre-maturely ignite the fuel. I doubt you could in any real world testing accurately measure any power loss from low octane to high octane. Assuming of course neither one was pre-igniting.

Yeah, using 110 octane when 91 octane will do the job is wasting money. The term "Valve Rattle" as it relates to pre-ignition has been around a long time, like myself and Ron, it's "old school". Still a useful saying to convey the basic message.

[John Martin]

I was wondering If the car was a turn key , there may be a record of your car on file at ERA , and if you engine came from Danbury comp , there may be a record of your compression (blue print )on file with Joe Lupine .
Sorry for your loss , enjoy your car

[CriticalMass]

No, not a turnkey. ERA #164. He documented just about everything related to the car (all his cars really) so I have a complete history of changes he made, even down to what dates he rotated the driver and passenger side seats to avoid uneven wear....of course though, the information I need is in another log book that I can't find.

Knowing him its documented somewhere, but I've looked extensively and haven't found what I need.

I would just hate to have to tear the engine apart to check compression ratios when I know the car is tuned perfectly...for an unknown fuel mixture. Especially since I've never done it before. I have general engine maintenance skills and am technically inclined. I have the ability to tear it down and get the compression ratio, but nothing ever goes as planned. I don't trust that I have enough experience with this engine to troubleshoot problems that might arise during the tear down and rebuild.

I'll probably just put 1/16th of a tank of something around 100 octane in it and run it. Then I'll start cutting the 100 octane with 93. If I don't experience problems along the way I'll just settle on running it with 93 octane w/additives (whether that be racing fuel or octane booster). If I do encounter problems I'll at least know the ballpark I'm in.

But just to be sure, nobody thinks I need to add lead substitute?

Thanks for the replies.

[John Martin]

I forgot which year they started with the unleaded , but if your engine was built after that , they may have used bronse valve guides ( that is a big part of what the lead lubricated ).

[Don]

E.Wood:

Not having any experience with aviation gas, attempted to find a website with the specifications etc

http://purvisbros.com/afi/moderncivavgas.htm

Is there a " correct " aviation fuel to purchase when mixing with a high octane automotive gas ? Or, any other considerations ?

........thanks for the assistance

Don

[SCOBRAC]

I run almost 12:1 on 91 pump gas ( thats all we get here in Calif)... That said you must keep a high compression engine cool to avoid detonation regardless of gas you run. Never exceed the total timing safe for the temp you are running. Err on the conservative side with ignition curve. Don't run platinum plugs.

If you really want to run an additive use Tolulene or Xylene at no greater than 30%. Tolulene is 114 octane and can be gotten at most paint stores. It is commonly used as a paint remover.

[ItBites]

Don:

The only avgas to use is called 110LL ("110 Low Lead"). This stuff is usually blue, but can be greenish at times. Do not use red!! As I recall, the 110 is supposed to be 110 octane, but that isn't quite true (for car octane) and as I recall this has something to do with a difference from the octane rating used for pump gas being an average of the research + motor octane [(r+m)/2]. If you mix 50/50 with premium, it'll work great for even 12.5 CR, provided you're reasonable with the timing. Do not use with catalytic converters as it has lead in it. You're also warned about using it in conjunction with O2 sensors, but, while it will degrade the sensors, you'll experience lifetimes of the sensor of >10000mi even so. For most Cobras, changing a $75 O2 sensor every 10000mi would be a few years down the road.

I'm surprised the naysayers haven't chimed in. They usually post a few websites that I did find to be very informative. If you read the websites carefully, you realize that the gripes about avgas usually result in a conclusion that avgas is an acceptable, cheap way to keep from killing your high compression motor if you're just driving it around. In fact, I have seen no info that concludes any damage can be done by avgas. Most of the comparison info is related to racing and does conclude that when racing, racing gas should be used. Fine, but I'll tell ya avgas is a cheap way to drive around if you're not racing. It also smells good and will allow storage for longer without problems and will cool the intake valve and chamber. A pretty good compromise way to run around!!!

I can also add that if you change to race gas, expect to re-tune. Avgas seems to ruun pretty well with a pump gas tune

[Ron61]

ItBites,

I have a question about the avgas. Can you still get leaded avgas there? Here everything is NO lead period. I used to buy from a local airport and they went away from the lead quite a while ago. Also had several problems with their plane engines until they got them sorted out. One crash was traced directly to the NEW clean no lead avgas and it was still rated at 110 octane. That is why I started buying NASCAR 110 leaded to mix when I was going to be running hard. It costs $4.55 a gallon here.
I hear people by the dozens who have gone to other states on vacation talk about how much better their cars runb on gas in those states and they get much better gas mileage also. Then as soon as they get back to Calif. they say it seems as if they lose around 50 horsepower and the mileage dips accordingly. I have made several unscientific tests using my little 1965 Comet with the stock 289. Add 5 gallons of my racing gas to a tank and performance and mileage does go up noticeably. Then go back to the straight pump gas which I use and it drops right back down.No adjustments of timing or carb will help this as we just have shi$$$ gas. I heard of a place here that is supposed to sell 110LL gas, but so far when I have called, they told me it had no lead.

Ron