depends on your cam, but i would do a mix of the 105 and 93.

my 302 has 12.5:1 compression and i mix high octane and 115.

 

It's doubtful unless you retard the timing and have aluminum heads. I run av gas in mine with 12:5.

 

I have edelbrock rpm performer aluminum angle plug heads 70cc cut to 68 cc with forged srp pistons, solid lift mechanical cam 540 lift and duration around 290. I haven't even ranked this motor yet I was just wondering in case you go on a cruise and need fuel. I have never ran tis high compression before.

 

Not gonna work . 12.5 to 1 needs at least 112 octain. You could install water injection kit, goes for about $500 and not have to worry about it.

 

James,

Is that 12:1 calculated after actually cc'ing everything? What's your quench? If so, then you should run your combo through a dynamic compression ratio calc. to see where you're at concerning your camshaft events. A few people I know have run octane supreme 130 which contains real lead to bump up pump gas octane in higher compression engines.

 

my builder did the calculation and told me it would 12:1 with my set up.and this was after he cc'd everything. I was just wondering if you go out for a cruise and need fuel what to do so i can prepare for it.

 

12:1 thats what ome aims at if building a methanol or a CNG fueled engine
Yes petrol will run on a CNG or methonal engine..If the timing is adjusted.
But like running LPG or CNG on a petrol engine the full potentual of the fuel will not be reached even if timing is adjusted....still run good thu.
Higher compression less advance (Faster burn...too much cpmpression and it will self ignite like a deseil engine does....detonation issues ...excessive compression..cyclinder prtessure can be relived at lower rpms by a cam with more overlap )
Higher the octane more advance (slower burn more time to hit max cyclinder pressure at the critical piont of efficiency somewhere between 12 amd 18 degs ATDC)

 

is E85 an option in your area?

 

Similar one here. I had an 11.5:1 combo several years ago. I ran 93 octane on the street and I ran 110 at the track. I drove it all over for two years and went 11.30's all day at the track.

 

E85 is available. I had someone tell me the same thing gearhead said. I was just wondering if that was correct and was possible.

 

Similar one here. I had an 11.5:1 combo several years ago. I ran 93 octane on the street and I ran 110 at the track. I drove it all over for two years and went 11.30's all day at the track.

Yep good reasoning for hi coms in a street car also used for track
The primary engine build is for track times with suitable fuel.....
Then also used on the street with pump gas.
The primary need is track....secondary and less need for full efficient use of that power on the street.
Ideally the difference in timing can be configured for both
The dizzy on the track simply gets the intial , and therefore the total (intial +cent) the estabished power advance..VA can be still connected as it doesnt kick in at heavy loads, but still makes fireing up easy...
Then racing over turn the intial back to known postion/advance, and top up with pump gas to return home.
Way to go...best of the primary use, good to very good , not excellent for seconday use.

 

Your static compression is 12:1 but what is your dynamic compression? Your cam plays a big part in the equation. I ran 12.5:1 on my LS1 engine on 93 octane with no issues but my dynamic compression was around 8.5:1. I set my new motor up for E85 and makes more power and torque yet runs cooler. You can run up to 14:1 cr on E85. E85 is a lot cheaper than race fuel. It is around $3.29 a gallon in our area.

 

Dynamic Compresion Ratio (DCR) & whether you run aluminum or iron heads will drive the fuel you can use. DCR is the static CR + the effects of the valve timing. You can read more about it here & download a DCR calculator:

http://cochise.uia.net/pkelley2/DynamicCR.html

In a nutshell, 12.5:1 with a long duration cam and/or aluminum heads can get away with lower octane much better than tighter cam specs and/or iron heads which will demand higher octane.

 

dont see it happening here-we run av gas with alittle oil in it in our 383s with that compression for street

 

93 octane works with 11:1
12:1 look for 96 octane or better.
Some 100 nolead and 93 premium 50/50 mix would work.
As would adding 110 octane race fuel as long as you don't have a catalytic converter.

 

93 octane works with 11:1
12:1 look for 96 octane or better.
Some 100 no lead and 93 premium 50/50 mix would work.
As would adding 110 octane race fuel as long as you don't have a catalytic converter.

What is the point? just use 96, and mixing 110 the difference is piontless....
And the chances are its not a daily driver and race fuel sours even faster than our modern unleaded causing even more issues.
The only time mixing fuels like that is with pre 1954 british vechiles that had a Cr around 5 to 6 to 1 and designed to run on 60 to 70 octane...which is lower than the US octane std....then one mixes about 10 to 12 % A1 Jetfuel with 91 petrol.
Keep it Simple...
So long as the DCR is not to high to cause detonation, run the octane for best performance at the track
For the road highest common pump fuel possble and drop the timing 3 or 4 degrees for the lower octane on the street.
Who the hell wants to be mixing up blends of fuel on hot days, knowing that u cant store much of the blended or unblended without it going sour.?
OR fill up at one pump then fill up at another, again not filling the whole tank because it will just sour before using it all?

And yeah I blend for my old british vinage cars so they run as well as they did when they came out of the factory..bit better really.

 

It depends on the DCR, not so much on the static. I ran 91 octane pump gas in my 357 with 13:1.

Ross #91462 15.2cc pistons

http://www.summitracing.com/parts/ROS-91462/

AFR 210 64cc heads

.041" gasket

Zero deck

268/274 @ 0.050" .630" roller cam

 

James,

Post the information from your cam card, like the previous post above.

I would seriously consider E85.

 

Keep in mind with DCR..a more than stock cam works at higher rpms, at low rpms it becomes ineffieent because the valves are open to long giving low compression.
Therefore much will also depend on the final gear ratio and if the engine is to run on std fuels around town.
Once those rpms climb up, and power on, the time the valves are open becomes shorter, the engine hold compression more and thats where pump gas, detonation and timing becomes an issue.
Detonation doesnt need to be audable, if u want that engine to last tune in pump gas uder power with a knock sensor and data logger OR keep pump gas for low rpms around town and the exoitic stuff for the track

Those who are running pump gas, do u KNOW these is no detonation? and how do you know? as the only reliable way is a dyno with knock sensors or data logger and knocksensors.

 

Detonation doesnt need to be audable, if u want that engine to last tune in pump gas uder power with a knock sensor and data logger OR keep pump gas for low rpms around town and the exoitic stuff for the track

Those who are running pump gas, do u KNOW these is no detonation? and how do you know? as the only reliable way is a dyno with knock sensors or data logger and knocksensors.

With my motor there was no evidence of detonation on the pistons or heads when we took it apart. If there was detonation you would see it. I only ran pump gas around town. When I went to the track I ran 116. When this motor was built I did not intend on using pump gas but the cam reduced the cylinder pressure. When checked cold it only produced 195 - 205 PSI.

A previous version of this motor (11:1 with similar duration cam but 102 ICL) produced 215 - 230 PSI cold. I ran that motor on the street with 91 octane for years. It was my daily driver. If it didn't detonate with 215 - 230, I was pretty confident it wouldn't with 195 - 205. Everything else was the same. :thumbsup:

 

If there was detonation you would see it.

Yep sever becomes obvious, with auditable.. not so till too late

I only ran pump gas around town. When I went to the track I ran 116.......When this motor was built I did not intend on using pump gas but the cam reduced the cylinder pressure

Which is exactly what I said way back and above....
And applied here to

A previous version of this motor (11:1 with similar duration cam but 102 ICL) produced 215 - 230 PSI cold. I ran that motor on the street with 91 octane for years. It was my daily driver.

And that must have had a reasonbly mild to stock cam to???? to pull those pressures...I assume 215 - 230 PSI cold on the starter motor and std CR gauge?
With those presures (CR) that engine is built for LPG.

OH and I should have said above "Those who are running pump gas,.....at the track or high rpms......."

 

And that must have had a reasonbly mild to stock cam to???? to pull those pressures...I assume 215 - 230 PSI cold on the starter motor and std CR gauge?

No, it was a Crower solid roller 264/274 @ 0.050", .630" lift, 106 LSA with 102 ICL. It closed the intake valve earlier than the cam I used with 13:1 SCR. I used the same gauge with both setups.

 

hey guys I cant get the cam specs to down load but here is the part number is 12-679-5 it is a comp cam.

 

Here are the specs.

 

I have a 383,600lift cam 11.5:1, pump gas, it use to ping until I switched over to a msd set up, although it does run alot harder with 100 octane

 

Thanks for posting it for me.

 

[/LIST]Here is the Cam specs we used with a 12.5 static ratio 302, it would run detonation free on 93, however it wouldn't wail... to keep it from being a slug-o I had to back up the timing.
The piston tops were treated, after being massaged to remove any sharp edges etc that might create a HOT spot and lead to detonation... if you can keep the intake charge from becoming stagnate (keep the swirling motion) and eliminate hot spot creators ( piston domes with sharp edges or combustion chambers with sharp edges which become heat sinks and act as SECONDARY Ignition sources) you are less likely to run into colliding flame fronts (detonation).

SOLID ROLLER

ADV Dur
277 INTAKE
281 EXHAUST

.050 Dur
242 INTAKE
246 EXHAUST

Gross Lift w 1.5 RA
.636 INTAKE
.636 EXHAUST

LOBE LIFT
.424 INTAKE
.424 EXHAUST

INTAKE Clearance .016 HOT
EXHAUST Clearance .018 HOT

LSA 112 deg


For deg cam all figs at .050 tappet
Intake OPEN 13.0 BTDC
CLOSE 49.0 ABDC

Exhaust OPEN 59.0 BBDC
CLOSE 7.0 ATDC


Extremely easy to drive, makes 15 in of vac at 1000 rpm with a wicked lick.

 

Is this supposed to be a track car that you want to drive on the street?
12:1 is an oddball ratio - too much compression for the street, but not maxed out for racing.
Who spec'd the engine and what is it's intended usage?