View Full Version : "Lead" Fuel Additives?

04-07-2004, 05:48 AM
I'm interested in any information about fuel additives that *really* improve octane. For those of you who do not live in the USA, my best local "premium" gasoline is unleaded 92 octane(RON-method).
I've done a "Google-search" and have found lots of claims for products. I've looked through some of the older posts here. I've talked to race friends, a chemist (he owns a Cobra)and the guys at the local speed shop.
I hear lots of unproven claims by the companies selling the stuff, but I'm leary of this (snake oil?).
Some of the products talk about extending valve-seat life and cleaning the fuel system...I don't care about these features. I'm really only interested in preventing knocking under acceleration.
My car isn't an extreme example of "race tech" but it will be used for sprint and enduro races: this Winter I replaced the old 7.3:1 compression pistons with 9:1, milled the head and replaced the cam with a modest performance unit. I'd like to run 32 degrees of total ingition advance.
I don't think I really need to start buying Klotz or CAM2 in 50 gallons barrels yet. Many tracks sell high-octane race fuel, but not all of them, and anyway, I'm still going to drive this on the street once in a while.
Right now I'm looking at the Klotz fuel additive, mostly because their other products are decent. Any other advice?
While I'm at it, has anyone seen any real good information about the use of aviation fuel in cars? I hear all kinds of plus/minus stuff about this.

04-07-2004, 07:32 AM
Race gas prices have stayed pretty stable for years.
Pump gas prices are shooting through the roof.
By the end of summer, race gas will cost no more than pump gas.
Problem solved, with thanks to OPEC and the Bush energy team.

04-07-2004, 08:23 AM
Some of the "lead" additives that lean their advertising as simply reducing valve wear (due to lack of lead) are nothing more than Kerosene.

"Relead" - sometimes found in marine supply stores is supposedly one of the few really effective additives that actually have a replacement for lead.

As for 100LL - I'm running that in my VW engine right now, works absolutely fine, no lead-fouling so far. It isn't unusual to see a few of the area racers come out to fill up at the pumps too.

Dave Russell
04-07-2004, 01:26 PM
Take a look at this;

[ 04-07-2004: Message edited by: Dave Russell ]</p>

04-07-2004, 01:37 PM
I did a science project on 104+ when I was in high school. It did improve octane and anti-knock performance. Assuming it's as good as it was in 1988, it should work for what you want it for.

As I understand it, many fuel additives contain an octane improver and a lead substitute, but the two are not synonomous. Sounds like you need octane improver only for your purposes.

Matthew E. Herd
04-07-2004, 01:56 PM

What is your intended setup? I did my reading and talked with my engine builder (who has built engines for cars on the cover of NHRA magazine, so he definitely knows his stuff, even if it is about V8's). He recommended the conservative approach concerning compression ratio, but I run (at his recommendation) Sunoco Ultra 94 with my 10.5:1 CR. (that's 94 octane by the (R+M)/2 method). I think you meant 92 by that same method, as that is the standard in the US according to what I've read. In a nutshell, my internal engine setup is with a Kent Cams TH5 camshaft kit, high ratio (1.55:1) roller rockers, 10.5:1 compression and 34/35 degrees total advance. Overall, I'd say I can get away with another 1 or 1.5:1 on the rato, but I might be pushing my luck. I've had the advance up to 39 degrees with absolutely no ill effects. The only difference is that it idled with a slightly unusual sound that I deemed undesireable. The car (essentially the same as yours) pulls well at any rpm, even with this rather hot camshaft and my recently addressed misadjusted valve situation. If I didn't detect knocking at half of expected lift under all circumstances with a timing of 34/35, I'd say you'd be safe with standard rockers and pretty much any racier camshaft all the way up to 10.5:1 (of course that's only my opinion, I can't substantiate that with hard fact) even when using only 92/93 octane available at most stations.

As to boosters, there's an article which I believe to be trustworthy on the Scions of Lucas page from some time ago addressing the actual change with a 12-16oz bottle of octane booster. Basically, the conclusion was that to make more than a .5 point boost, you need a LOT more of it. However, to make the stuff (and mix in a 30:70 ratio w/ 92 octane) it only cost about 2-3 bucks a gallon supposedly and would provide an octane (claimed) of about 99 (if I remember correctly). Basically, if I detected a problem, I'd either get 100LL or mix the recipe myself. Otherwise I'd stick with pump gas (in my opinion, not a problem at the level of tune you're likely to achieve due with your 1500 engine).

A question of my own: what method is 100LL rated in? RON, MON, or (R+M)/2?

Jim Weatherford
04-07-2004, 05:13 PM
I have successfully used Toluene for years(You can buy it at your local Builders Supply store or a well stocked hardware store about $4.50 a gallon)

I add 10 US oz. per 10 US gals of regular pump gas. No problems, better burning, higher octaine.

Please note you are not adding "lead", this is a performance (octaine) boost only.

You just can't trust them "OldPeckers".

[ 04-07-2004: Message edited by: Jim Weatherford ]</p>

Dave Russell
04-08-2004, 03:26 AM
The Av gas octane ratings are based on lean burn - rich burn. Different system.
Some reading on AV gas;

"A question of my own: what method is 100LL rated in? RON, MON, or (R+M)/2?"

100 LL has a MON of 98.8 for sure & likely a RON of 101.2.

04-09-2004, 07:42 AM
Thanks guys, for all your different comments and links. The best plan is surely to buy plenty of leaded race gas when I'm at a track and store it, but I know that won't always happen. I'm trying to figure some alterenates.

My concern has been due to the reaction we had with high test (unleaded) street gas we ran in the other (1275 cc) race-Sprite that I occasionally drive. *That* car is pretty much the same tune as mine but has 10:1 pistons. My friend (the owner of the car) rigged up a home-brew knock sensor on the car. We detected fuel-knock (pinging) until we dropped the total ignition advance back to 28 degrees. When I drove it on nearby roads (with no helmet and a muffler) I also detected some knocking (verifying the accuracy of the knock sesor). Even with 28 degrees of advance, I still got it to 6500 RPM in 4 th at Summit Point (108 MPH), but retarding the timing seems like it would be cancelling out any advantage of the 10:1 pistons.

I choose the 9:1 compression on my 1500 to be safer, especially since I'm still running the stock con-rods (but with ARP bolts). In deference to the rods and non-blueprinted state, I plan on keeping under a redline of 5700. Last year, my car never went above a super-conservative 5500 (but that probably contributed to me winning our small-bore enduro championship).

I'm still looking and researching: I may try some of the home brew ideas mentioned above. I'll let you guys know if I learn anything.

Dave Russell
04-09-2004, 09:47 AM
28 degrees advance might not be too far off of maximum power. You only need enough advance to get the mixture fully burning by the time the piston reaches around 20 degrees past TDC. Higher compression decreases the time required to get things burning at maximum. Anything that increases combustion efficiency will require less advance.

The "anythings" are - optimum squish/quench chamber design, intake tract velocities, compact combustion chambers, chamber temperatures, fuel mixture, spark efficiency, rod length to stroke ratio, & on & on.

A lot of really efficient engines only require around 30 degrees total advance for maximum power. The less advance required the better the engine.

If, as you say, it is working well, I wouldn't worry too much. The more top end rpm it will pull for a given gear ratio the more power it is making, it appears to be doing pretty well.

04-09-2004, 12:33 PM
Nial, I'm only running 30 degrees total on the 1500 production car engine, at 13.8:1.
But, I run 110 octane leaded fuel, as well.

04-10-2004, 06:34 AM

You guys are correct. My original comment about 32 degrees of ignition lead would just be a baseline that I probably wouldn't exceed: if the car ran well on available fuel with 28 degrees, that would be fine with me (and yes, easier on the engine).

....all the same, I'd like to get the best combination/recipe of fuel that might allow a comfortable "detonation cushion".

Matt/Scott: The link provided by Dave (above)reinforces something that I've heard. 100LL has other additives in it that require richer settings for automotive use. Probably not an issue with a stock-ish VW engine, but might be a concern with a hotted up 1500 Midget engine. It's still not clear to me how AV fuel is rated (RON or whatever?). BTW, I'm running the same TH5 cam...it's pretty close to the stock twin-carb cam used in Euro Spits and Midgets.

Dave: I recall that the original 100-4s didn't actually have a timing spec and the cars were supposed to be set up *just back* from "pinking". With their modest compression and old-time leaded gas, a lot of these cars were originally said to be running at more than 40 degrees of total ignition lead.....is that true?

[ 04-10-2004: Message edited by: aeronca65t ]</p>

04-10-2004, 08:02 AM
I read that article too... All I can say is I've had no ill-effects, but I've seen no benefits either. When I drain the airplane fuel I put it in the fuel tank in the Migi (VW), which makes little or no difference in the actual formulation of the fuel I shouldn't think. I was almost out of fuel in the car recently so when I was filling the 310 I topped off the Migi tank at the same time. I already have that engine set up to run the higher (premium) octane fuels by the way.

Dave Russell
04-10-2004, 12:21 PM
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by aeronca65t:
It's still not clear to me how AV fuel is rated (RON or whatever?).

Dave: I recall that the original 100-4s didn't actually have a timing spec and the cars were supposed to be set up *just back* from "pinking". With their modest compression and old-time leaded gas, a lot of these cars were originally said to be running at more than 40 degrees of total ignition lead.....is that true?
[ 04-10-2004: Message edited by: aeronca65t ]<hr></blockquote>
Nial, from what I can find,
100 LL has a MON of 98.8 for sure & likely a RON of 101.2.

Yes - It's true. My 100-4 is a great enigma to me. It has the "M" 8.5/1 pistons, but still relatively low compression. I have never been able to advance the timing enough to get audible "pink" on 87 R+M/2 pump gas. Even with total timing advance of 45 degrees. After studying engine design I come to the conclusion that with the very long stroke (4.375") & the even longer rods (8.185") the rod ratio is still 1.87. Long stroke long rod ratio engines just don't seem to be very timing detonation sensitive. I do have an aluminum head on it which probably changes conditions somewhat. The thing literally pulls like a tractor from 2000 to 5500 rpm but is limited to around 5000 due to crankshaft torsional vibration problems.

Being aware that destructive detonation can occur without making a sound, I limit total timing to 36 degrees. There is no measurable power increase by going to higher advance settings & I prefer a safety margin.

04-10-2004, 05:37 PM
Since the subject of avgas came up, it might be interesting to note some specs on a small, aircraft engine. This applies to a Lycoming O235 (235 cu-in/3851cc) flat-4 engine. These specs change with the different variations of the engine:

<ul type="square"> HP: 108-125@2600rpm Compression:6.5:1-9.7:1 Timing:20-25 (most models are set at 25)[/list]

04-10-2004, 05:45 PM
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Baxter:
with thanks to OPEC and the Bush energy team.<hr></blockquote>

Or more correctly..no, never mind, I won't go there...Please don't lets get into politics on this forum. You wouldn't want me to get political - trust me on that.


[ 04-10-2004: Message edited by: Basil ]</p>

04-13-2004, 09:59 AM
...back on topic.

I just saw this...and it looks like it has a lot of good info:


Matthew E. Herd
04-15-2004, 07:11 AM
Yeah, I don't know, Nial ... I mean, my '76 had 9:1 originally, on 87 octane and was run for some 76k before I got it (of course other things went bad) but there was no sign of detonation damage when it was rebuilt. Clearly, you can exceed 9:1 by some margin, but the margin is subject to debate. At any rate, you should be fine with pump gas at 9:1 regardless of setup because it was a factory standard and I'm confident they tested it.

Also, I'm so depressed ... if the euro versions had a similar cam, they must've been quite a sight. Of course, coupled with everything else, mine's quite a beast, but stock european cars must be something! And I did all that work ...

Dave Russell
04-15-2004, 05:46 PM
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by MGTF1250Dave:
I have a semi related question about gasoline. Has the method of posting octane rating at the pump changed since the 60's?

Yes - I believe the 60's pumps posted the research octane number. (R) With the present rating method of R+M/2, averaging the research octane number of 98 with the motor octane number (M) of 86 gives todays rating of 92 which is equivalent to the old 98.

04-15-2004, 06:51 PM
Mahalo plenty Dave. I thought that was the case but wasn't sure. It certainly makes sense.

Safety Fast,

04-16-2004, 03:59 AM
I have a semi related question about gasoline. Has the method of posting octane rating at the pump changed since the 60's? It seems that Sunoco, Amaco and others major oil companies all offered high octane gas in the high 90's to low 100's. Now using the (R + M)/2 octane calculation, 92 is high octane. When all gas became unleaded did removing the lead additives decrease octane ratings that much? Just wondering and though you guys might know.

Safety Fast,

04-16-2004, 11:58 PM
I can't add much in what ignition advance to run, but the last motor I had in my mini had pretty high compression (unknown number, but high nontheless) and pinged big time on 92 pump juice. I added some NOS brand Racing Octane Booster at double the recomended dose and it quelled the pre-ignition quite well.
*edit* Unless you have hardened valve seats, you might want to consider some "lead" additive for valve seat "cushioning". My machinist showed me some valves that had been run hard w/o "lead", and they were pitted horribly.

[ 04-16-2004: Message edited by: mongoose ]</p>