BadDog

PhD,
Got a recipe for the Toluene and Mystery Oil? I wanted to mix up a small batch to carry for my B&M 250 502 in case I cannot get 93.

jdnca1

I run 93 Octane in my 10.5:1 632". Aluminum heads and BIG solid roller to bleed down cylinder pressures though. 32 degrees timing. Never any Detonation signs

mcollinstn

Sure,

Toluene is 114 octane.
Following mixtures are with 92 octane unleaded:
1 gal toluene to 10 gallons 92 gas: 94.0 octane
2 gal toluene to 10 gallons 92 gas: 95.6 octane
3 gal toluene to 10 gallons 92 gas: 97.0 octane
4 gal toluene to 10 gallons 92 gas: 98.2 octane
5 gal toluene to 10 gallons 92 gas: 99.3 octane

Just a tblspoon per gallon of MMO for a touch of topend lube.

Mix with 87octane?
1 gal toluene to 10 gallons 87 gas: 89.5 octane
2 gal toluene to 10 gallons 87 gas: 91.5 octane
3 gal toluene to 10 gallons 87 gas: 93.2 octane
4 gal toluene to 10 gallons 87 gas: 94.7 octane
5 gal toluene to 10 gallons 87 gas: 96.0 octane

** It is not linear scale, but figure on 2 points of additional octane for each gallon per ten you use, as long as you aren't going for more than 94 octane. This way, whatever you find: 87,89,91, 92, 93, you can "ballpark" your additives...

As you can see, when you pass 94 octane, the benefits get smaller and smaller.

jpclear

Damn, mc; That is so on the #s I have, but I never had the guts to try to tank mix it, so I go with an engine that will run 92 oct. and add the booster if I get stuck having to fill up where I have to settle for less. But, 38 deg. and 11-1/4:1 C/R.? ----WOW!--- Guess I would run nothing under 100 oct. and still do some judicious plug reading. --- Jer

mcollinstn

Mmm.

As I sit here, I still find myself saying in my head "38 degrees is past the optimum for a SBC". It's sposed to be 36 for optimum. While 2more degrees isnt night and day, in my mind it should keep making more power unless the fuel burn is too slow.

The stuff after this sentence is just me thinking out loud............
If we figure big cam, 34 degrees, NA, 92 octane, 10.5:1 would be about the limit. If we raise CR with octane, the guess would be 10.75 @ 93, 11.0 @ 94, 11.25 @ 95, 11.50 @ 96.

Around here, 100 octane race gas is more than $7/gallon.

10 gallons of 92 is $13.99
5 gallons of toluene (in drums) is $15.00
15 gallons of homebrew 96 is $29 ($2.00/gallon)

Working backwards from 100octane,

1 gal of 100= $7
1 gal of 92= $1.39
2 gals of 50/50 mix(96 octane)= $8.39 ($4.20/gallon)

If you have a 60 gallon tank, you need 20 gal of toluene to get 60 gal of HB96.

Now, you gotta get a handle on exactly what your motor needs. I've got an old MSD knock sensor that you can "borrow" to get some electronic help.

throw in some 100 octane. Set the knock sensor on high sensitivity, and make some passes to get the sensitivity set properly (we know you aren't detonating at your current settings). back the sensitivity down a little at a time until it starts giving false positives. Go back up till it doesn't.

Drain her dry. Back the timing down to 30 and put in some HB96. Make a pull, note the WOT rpm at the same trim setting, look for the MSD light and listen for detonation. Keep advancing the timing 2degrees at a time. Each advancing should give you a little more revs. When you reach a setting that lights up the MSD OR doesn't give you any more revs, then you are at the limit for that fuel (actually, you are 2 degrees past it).

If it don't run as well (as fast) as it did with 100, then your engine combo definitely wants more octane. Keep in mind, though, that when you "over - octane" a combo, you slow down and spend more money.

Here is my disclaimer: if you blow up your motor by trying to follow my advice, I am not responsible because you must not have followed my instructions properly.

(plug heat range is also an issue - keep an eye on the heat band on the electrode).

WETTE VETTE

Hey guys here is some more motor info for you. I am sure the new owner of my dad's old boat is very appreciative. Oh by the way 110 octane leaded racing fuel goes for about $3.00 / gallon where I am from. The cam in this motor is an Erson solid roller 246 /254 @ .050" lift with .568" int. and .529" net lift on a 112+4 installation. How well will a knock detector work on a solid roller motor with the extra valvetrain noise? Heads are Pro Topline 200 CC non ported (2.02/1.60) with a Holley Strip Dominator intake. The carb is an 800 Holley DP. Plugs are NGK 5673A-8, which are colder than MR43T's and slightly hotter than MR41T's and are non projected tip. Ignition is full MSD with the timing locked in. Exhaust is CMI etop and JE pistons make for 11.25:1 compression. The motor water runs at 150* to 160* and 15 PSI. Colder water temps will also help to stay out of detonation with less octane, but too cold has negative effects as well. As the motor sits with 110 octane leaded racing fuel and 38* timing there are no signs of detonation after WOT operation. I have become very well versed with a spark plug viewer and this is the only way to really check on how a motor is doing. The heat range of the plugs are correct, however colder plugs could be used at the cost of some performance. I like the way mcollinstn suggested testing the different timing / octane ratings, just be careful to take accurate info.

Craig

mcollinstn

I've seen knock sensors on mechanical motors.
Supposedly the "frequency" that the acoustical pickup is tuned to is different than the lifter tap.

Obviously, the degree of acoustical accuracy on the mechanical motor would not be as wide since all sounds form cascading-level harmonics on even splits of frequency and bleedover into adjacent frequency bands as well. Knock sensors are usually mounted on the side of the block, though, and that mounting gives some degree of insulation from tappet noise...

At $3/gallon, there not a strong economical reason to home brew, aside from the need to occasionally boat where 100+ is not available. Downmixing 100 and 92 evenly will provide 80c/gallon savings if 96 turns out to be an acceptable number for the little monster.

Build specs sound great on that motor. Bet its mean.

robyw1

What actual cu-in are we talking about here incase I missed it? A lot of people make the mistake of thinking that a knock sensor is tuned to a certain frequency so as to respond to a knock. This is supposed to be true but isn't. No 2 knock sensors will work the same. I have seen knock sensors too sensitive that it would go haywire in a gear drive engine and I have seen one react to screw driver tapping on a valve cover. A knock sensor should be tuned to the engine. You have to install it so tight or so loose. Sometimes you need to use a little Teflon tape for the really sensitive ones. I have pulled all of my hair out many times getting these stinking things to work reliably. (lucky my hair grew back) To do it properly it takes reading exhaust temperature, experienced plug reading and dyno time. Now in my opinion 38 degrees does seem a little early for this engine and compression. Is this what the compression actually is? Have the combustion chambers been cc'd? Also how about the condition of the balancer? Has it slipped its ring? maybe? As I’m sure you know the plugs should be read right immediately proceeding a prolonged WOT run with no cool down cruise or idle allowed. How do they look? Based on what I have read if you are getting more performance at WOT with a hotter plug, more timing and your cam is +4 than there is a sign pointing me to believe that you may be a little overcammed.

What:
RPM are you running?
Cubic inch is the engine
Are the combustion chamber size of the heads in cc’s?
Rocker ratio are you using?
Reason are you using leaded fuel?

Roby

WETTE VETTE

I can answer the questions since Plum is the new owner and may not know. The engine is 357", and the heads are 64cc. Not only have the heads been cc'd, but the compression was actually checked by filling the combustion volume on the assembled motor with fluid, which is the best way to check compression. The motor runs real nice at 6000 RPM, which is where it is propped. As far as leaded fuel the lead helps keep the valves cool kinda like the mystery oil. In my opinion unleaded racing fuel should only be used if a catalytic converter is used, like in modern street cars. Really, 38* isn't that awfully much. On stock flat top SBC motors 36* will still be safe and will provide some power benefits over Merc settings. With the dome of the high compression piston essentially getting in the way of the flame it shouldn't be surprising that a couple of degrees more timing are required. These aren't "fast burn heads" which do run better with a few less degrees of timing due to the combustion chamber design and the swirl effect that is created. The Fluid Dampener is like new and is in good condition. 11.25:1 compression with iron heads is pretty high and good fuel must be run!! Less than 110 may be OK, but careful experimentation for the right formula will be required. The other option is to run the motor at 100* water temp, fatten up the carb a couple of jet sizes, run the timing at 34*, and run colder -9 or -10 plugs and maybe get by on 93 octane. At this point the motor will probably loose 75 + HP!! It is a game of give and take!! I like mcollinstn's idea and test.

WETTE VETTE

Just one other note. My 13.2:1 compression 496 with polished combustion chambers also liked spark timing in the 36* to 40* range. I did a test like mcollinstn suggested and checked the speed on radar / RPM at timing settings from 30* to 42* in 2 degree increments. The boat got faster and quicker each time until I hit 40*. At 40* and 42* it was still quicker, but the top speed was unchanged. I almost put an RPM activated switch on and ran 42* for the acceleration and at 5500 had a few degrees of timing pulled out to keep it safe on top. I decided to just compromise and ran 38*. I ran this motor HARD and never saw a scent of detonation during rutine plug readings after long 6300 RPM WOT runs. Anyway higher compression motors are a little different in what they like than stockers.