Octane additive

[steve cowan]

An increase in clearance will substantially reduce squish velocity. Squish may have a greater effect on performance than CR.

What if we have a 53cc aluminum head on a 350ci engine...What gasket thickness is called for for 93 octane for a street strip dual plane wit 280 degree seat to seat cam? What is safe compression ratio?

I know people running 12:1 with pump gas but all of them said the cam opening and closing points were the key to making that work.

Yes,see and hear about it a bit but the question I ask is what is the trade off with power if intake closing and exhaust open points are out to lunch?.
If you crutch compression with a big cam it must narrow up the power band window so to speak which has to include additional reversion issues especially when piston is heading the wrong direction.

[BobbyB]

What if we have a 53cc aluminum head on a 350ci engine...What gasket thickness is called for for 93 octane for a street strip dual plane wit 280 degree seat to seat cam? What is safe compression ratio?

I know people running 12:1 with pump gas but all of them said the cam opening and closing points were the key to making that work.

Yes,see and hear about it a bit but the question I ask is what is the trade off with power if intake closing and exhaust open points are out to lunch?.
If you crutch compression with a big cam it must narrow up the power band window so to speak which has to include additional reversion issues especially when piston is heading the wrong direction.

Lets say cam and heads are fixed...What gasket thickness to make what compression ratio for 93 octane?

[David Redszus]

You could do a interesting test on your 358 using your 49 cc heads and your 64 cc heads.
Add a extra stack of common head gaskets that equal the Combustion chamber CC difference.
Hint: its right about .066" extra using common sbc 4.166" bore head gaskets.
Pretty easy using 1 extra .040" gasket + 1 extra .026" head gasket..
This adds back in the 15 cc chamber difference.
The total (3) headgasket stack will be .106"...
The CR will be the same as if running your 64 cc heads.
Will it run on your pump gas?
Whats the perf difference? ET. MPH or dyno tested HP.

Does it want any different WOT spark advance?
The CR is Equal. But the total piston to head Quench clearance is now bigger.. Whats the effect?
Then take away one of the EXTRA gaskets.
Will it run on pump gas. Does the spark advance change?
Now take away the last EXTRA gasket.
Use what ever fuel you want.
Whats the engine perf now.. Does it need any different spark advance?

Reinstall you 64 CC heads again and run as a control test... (could test with both your pump gas and yiur race gas (brew) and compare that.. timing? perf?

Does the quench clearance change (with an EQUAL compression ratio) make any difference?
Or is it a bunch of hoooie?

An increase in clearance will substantially reduce squish velocity. Squish may have a greater effect on performance than CR.

A good test to see if that is true.
How much?

Clearance -
.066", squish velocity = 28.1 m/s
.106", squish velocity = 18.3 m/s

Based on holding bore, bowl dia and rpm constant.

Actual effect on combustion would require dyno or track testing.

[BobbyB]

An increase in clearance will substantially reduce squish velocity. Squish may have a greater effect on performance than CR.

A good test to see if that is true.
How much?

Clearance -
.066", squish velocity = 28.1 m/s
.106", squish velocity = 18.3 m/s

Based on holding bore, bowl dia and rpm constant.

Actual effect on combustion would require dyno or track testing.

So, do you think a .040 gasket & piston .010" in the hole, yielding 10.4 to 1 compression is optimum for street strip, or would you suggest another gasket for higher or lower compression ratio?

[steve cowan]

A good test to see if that is true.
How much?

Clearance -
.066", squish velocity = 28.1 m/s
.106", squish velocity = 18.3 m/s

Based on holding bore, bowl dia and rpm constant.

Actual effect on combustion would require dyno or track testing.

So, do you think a .040 gasket & piston .010" in the hole, yielding 10.4 to 1 compression is optimum for street strip, or would you suggest another gasket for higher or lower compression ratio?

I don't like going over 0.040" - 0.042" piston to head.
My cast iron headed 383 has 0.030" piston to head,11.45 : 1 static compression and a 240 deg @0.050" intake lobe.
With the small cam I run that engine on MS109 fuel,I doubt it would tolerate pump fuel without adding way more cam.
I am Mocking up another 383 at the moment and I want to run a 241 - 251 @ 0.050" 600"- 580".
108 LSA in at 106.
Static should come in at 10.83:1 and with that short cam I should be able to run pump fuel.
Engine will be on dyno in couple of months.
The bigger piston to head clearance on a NA engine is not preferred.

[HQM383]

An increase in clearance will substantially reduce squish velocity. Squish may have a greater effect on performance than CR.

A good test to see if that is true.
How much?

Clearance -
.066", squish velocity = 28.1 m/s
.106", squish velocity = 18.3 m/s

Based on holding bore, bowl dia and rpm constant.

Actual effect on combustion would require dyno or track testing.

Hemi aside, different head designs have different total of squish area. We have squish velocities but what could be the expected differences with different percentages of the air fuel under squish in the combustion event?

[David Redszus]

Hemi aside, different head designs have different total of squish area. We have squish velocities but what could be the expected differences with different percentages of the air fuel under squish in the combustion event?

Squish Velocity (SqV) will change with rpm, area ratio and clearaance.
Same bore, stroke and rod as previous.

rpm.......Area ......Clear......SqV
8000......0.385%.....0.5mm....69.5m/s
6000......0.385.......0.5........52.1
4000......0.385.......0.5........34.7

8000......0.385.......1.0........42.7
6000......0.385.......1.0........32.0
4000......0.385.......1.0........21.3

8000......0.385.......1.5........30.9
6000......0.385.......1.5........23.2
4000......0.385.......1.5........15.4

8000......0.530........1.5.......44.3
6000......0.530........1.5.......33.2
4000......0.530........1.5.......22.2

While area ratio and clearance remain fixed, SqV will change substantially with rpm.

[BobbyB]

Hemi aside, different head designs have different total of squish area. We have squish velocities but what could be the expected differences with different percentages of the air fuel under squish in the combustion event?

Squish Velocity (SqV) will change with rpm, area ratio and clearaance.
Same bore, stroke and rod as previous.

rpm.......Area ......Clear......SqV
8000......0.385%.....0.5mm....69.5m/s
6000......0.385.......0.5........52.1
4000......0.385.......0.5........34.7

8000......0.385.......1.0........42.7
6000......0.385.......1.0........32.0
4000......0.385.......1.0........21.3

8000......0.385.......1.5........30.9
6000......0.385.......1.5........23.2
4000......0.385.......1.5........15.4

8000......0.530........1.5.......44.3
6000......0.530........1.5.......33.2
4000......0.530........1.5.......22.2

While area ratio and clearance remain fixed, SqV will change substantially with rpm.

What is the area ratio a ratio of?

What is the relationship between knock tolerance, SqV & compression ratio for a given octane fuel?

[NewbVetteGuy]

What is the area ratio a ratio of?

The squish area to the total bore area.

What is the relationship between knock tolerance, SqV & compression ratio for a given octane fuel?

As the squish velocity increases to a squish velocity "speed limit" (15-20 meters / second or 28-30 meters / second in some engines according to some sources -At Peak HP RPM), the engine's tolerance to knock at a given cylinder pressure and octane INCREASES (it's propensity to knock decreases). -Exceeding the squish velocity speed limit / rate of pressure rise can start to INCREASE the likelihood of knock.

The turbulent flame speed increases as squish velocity increases, too which requires less ignition advance and also gives less time for detonation to occur.

Tight squish: push that air and fuel mixture out of the cylinder extremities and into the cylinder, even out chamber temps and hotspots, increase turbulent flame speed / reduce ignition advance speed (because of the "reverse squish" action of the now burning flame front being then "pulled" into the outer extremities of the rapidly increasing chamber volume).

1st Squish Event: Push mixture from the outer extremities into the chamber -BTDC
2nd (Reverse) Squish Event: Pull now burning mixture back out to the outer extremities of the chamber -ATDC


Free "mechanical octane booster +(turbulent) flame speed booster" with every fill-up!



Adam

[frnkeore]

Back to the additive question...........

Toluene seems to be the cheapest, safest most commonly available additive. It is a common paint thinner, found in all paint and hardware stores. Are there any formulas for the amount that it takes to increase the octane number?

[F-BIRD'88]

Paint thinner . (Lacquer thinner Has some tolene in it but its mostly methel hydrate and methel ethel keytone..
A gallon of pure tolene is not cheap.
House paint thinner is mostly mineral spirits.
Not a good octane booster.
Too much tolene added makes engine starting and "drivability". much worse.
The main reason it tends to improve gasoline octane is its hard to ignite vs other components.

You want to avoid getting tolene on your skin or breathing the fumes.
None of these chemicals are "safe". You want to avoid exposure when handling all this stuff.

[6.50camaro]

I Think I remember seeing Toluene has a R+M/2 octane rating off 114. 1 gallon of toluene to 4 gallons of 93 R+M/2 would be around 97.2 according to my math.( 93x4) +114 divide that by 5 = 97.2

[Chris_Hamilton]

Toluene is about $10-$11 per gallon. Ive sourced it locally for around $55/5 gallon barrel.

Here is a source online. have no idea what the shipping would be.
https://cqconcepts.com/product/toluene-99-5-gallons/

I remember reading somewhere that F1 cars of the 80's used 86% toluene. Thought that was interesting.

[Truckedup]

Toluene here in rural NY is 25 bucks a gallon at retail stores or about $100-200 per 5 gallon from mail order when shipping is included. Locally I can buy VP leaded C12 for $120 for a 5 gallon can.. My vintage racebikes do like the TEL .....Mixing toluene at 35 percent into a gallon of 90 octane non ethanol gives about 98 MOT octane? The engines may get by on 100 octane MOT, but 90 degree valve angle air cooled hemis that go into detonation at WOT can sieze a 150 buck forged piston in seconds...Not worth the risk for a few gallons....And what about reed valve pressure and 90 degree C evaporation rates? with a the home done toleune mix?
My engine builds are less radial and go just as fast as the other guys who need constant fussy tuning so maybe fuel is much more than octane....

[65-fastford]

An old (circa 1974) Basic Engine Hotrodding book mentioned adding 5% Tolulene to regular fuel... not sure what octane that produces . Never had a detonation problem with any engine Ive run for Demo derbies, Bomber stocks, or old school 12:1 cast popups on the street... they all experiened overheating that should have had them pinging bad... never did
Just sharing memories of some fun low buck playtime