Hello

I was wondering what would be the maximum CR that could be run with 93 pump gas and NO DETONATION using:

-55cc closed chamber w2 cast iron heads
-proper 0.040" to 0.050" quench with a 4" crank and dished pistons
-245° @050 street solid roller with about 600 lift.

would 10.9:1 put me in PING territory???

What are the rest of the cam numbers? With the correct cam you shouldn't have issues. That head doesn't like much over a 109 LSA.

I dont have the exact cam specs, as I dont yet have the cam, but would be nice to hear what kind of cam would work best for making power and avoiding pinging at that compression and pump gas.

this is for a stout full weight 70 Challenger TA 4 speed street car on pump gas.

Gearing makes a difference as well. You want to run a 3.23 gear it will be more prone to detonation.

Can you post all the details?

Its going in a real TA Challenger. so its gonna be in full street trim = heavy.

4 speed trans.

3.55 gears.

Stockish sized wheel/tires. Most Likely 275 rear tires and 235 front radial tas on 7" rallyes

stock intake and six pack setup. Heads redrilled to accept stock intake bolt pattern, and intake modified to match w2 intake ports.

Stock exh manifolds, but might go with tti headers, undecided yet.

Bear in mind that I dont want to back up timing or setup distributor in a way it doesnt ping, because it would kinda defeat the purpose ofhaving the extra compression to make more power. I want to setup the engine right for max power and avoid pinging. Its just that with the heads I have and piston/stroke combo I have I am gonna end up with around 10,9:1 compression if I shoot for a zero deck and 0,040" quench with the closed chamber heads.... If it pings I will have to take heads off and install thicker cometics to lower compression. I would loose the quench effect and I guess I would just have to go with around 9,5:1 compression so it doesnt ping w no quench and iron heads.

I guess thats about it....

I have a 416" Closed Chamber W2 combo. It has dished pistons with no quench pad, it is right about 10:1 and has a big roller camshaft. It cranks 170psi and runs fine on 91, makes 580-600HP.

I run more compression and smaller cam in my 410 with magnum heads, I think youll be fine as long as your not sucking hot air right off the headers or boiling the fuel in the line running next to the exhaust or something.

Is your fuel straight gas or does it have ethanol added to it?
Is the octane rating their the same as here(RO+MON divided by2) in the U.S.?
All the stock 340/360 NHRA class motors I helped like 30 to 32 degrees total timing, same on the hot street motors with good gas
I wouldn't run that much compression up here on our pump gas with iron heads

We do have some ethanol in out gas....what about it? Does it make it more or less ping prone? I would think its less ping prone?

Our rating is 98, i dont remember the specifics, but in the end it would be an equivalent to 92 or 93 on your octane ratings.

i'm very skeptical that 93 octane will support 10.9:1; good or bad quench.

for the record.....

I run 9.4:1 on a 440.6 pack with open chamber cast iron heads.

it has a small comp hyd flat tappet cam
224° @ 050
LSA 110°
.470 lift

Engine runs great with our 98 octane but its right there on the edge of pinging. It will not tolerate 97 octane gas (which we also have at the pump) or it will start to ping.

I guess thats about as high as I want to go with no quench and a small cam on a cast iron headed motor. Its what I have tested with our gas.

Now, If I did have an engine WITH quench and with the bigger solid roller....how much higher do you guys think I could push the compression based on what I said above?

You can if the combo is right.

I think the OP needs to drop his CR. He's asking a lot. He has tall gears, and IIRC he wants to run exhaust manifolds or something.

Just asking too much from what he has.

OP drop the CR.

Tall gear + 2.65 1st gear + stock ignition curve = problem.
The same engine with 4.10 gears, a 700R4, + 9" converter will never ping.

why is it that extra load on an engine makes it ping?

Isnt pinging just because of pre-ignition and colliding flame fronts?

But I do know from experience that when there is extra load it will be more ping prone, but whats the science behind that????

That's what I meant. You just said it better. It's exactly correct.

volumetric efficiency increases and this increases cylinder pressure. it's all about cylinder pressure and keeping oil and water out of the chambers.

Not a sb/w2 but My 383 has quench style dome pistons with closed chamber heads.
Around 10.8:1 with 250@.050 solid cam and it doesn’t like pump gas. Loves 100 octane tho

And the cylinder pressure is easily managed by spark control - which you specifically decided not to use.
An engine retarded to 10 ATDC will not develop enough power to idle. The advance position is a rheostat... if you want it to be.
Vizard described using an unregulated turbo @ WOT for road racing using spark advance instead of throttle 30 years ago.

The higher gear means it wont accelerate as fast meaning more heat will build up in the chamber meaning more likely to have a hot spot and a place for the spark to start at the wrong spot and wrong time. Also the piston will accelerate away from TDC faster meaning a slightly faster than normal flame front could still be chasing the piston instead of coliding with it witch causes more pressure and a faster burn that causes more pressure and a faster burn... long story short it burns so fast it is more like an explosion and damages your engine and causes audible knock.

Exhaust manifolds probably help reduce detonation as they reduce cylinder filling efficency plus there is going to be a slightly higher amount of inert exhaust gas left in the chamber that will slow down the burn of the next air fuel charge.

Yes... I think that will put you in ping territory.

With iron heads (even with decent quench) suggest you shoot for 9.5 CR max. Better a little less.

A few 10'th's too much compression can be a PITA.

I have to disagree with this comment.

Not sure if you meant it to be specific to the OP's combination, but if meant as a general rule it is not the case, too much depends on cam timing events, etc.

Case in point, I have a 360 motor, heavily worked factory iron heads - open chamber (596 casting), thus terrible quench LOL as in -0.015 deck height and a good 0.090" of the open chamber on top of it. But my static CR is blueprinted at 10.6:1, yet the motor runs with NO ping using a very fast ignition advance curve on a pump 94 octane gas.

The cam in my case is: Hughes HE3844AL hydraulic flat tappet, 238/244 @ 0.050 on 108LSA.

Its always a bit iffy on what will ping and what wont with all things being equal but many things being different.

If ya want a fussy motor when it comes to fuel just build a 11:1, if ya want to be safe and not worry shoot for 9.5.

Weather a W2 motor or X or J motor if you use the proper parts a real 9.5 motor can run very well.

The silly banter of 10.0 vs 9.5 ect isnt going to affect the end result power wise much at all.

Ive had a few on the edge of the fuel needed and thats when you find who sells good fuel and who sells not so good fuel but would of rather had .5 less and never have the worry or keeping that can of octane boost in the car.

HOWEVER... The web tell me your near 5000ft above sea level, if thats the case you might be ok.

I ran a 340 with good quench at 10:1 with X heads, it had 212psi of cranking compression and ran great on 91 or 93 with 35* total timing. Its first few years of life it had a stock torque converter and It never showed signs of pinging. I was in high school when I had this motor so it never saw much time off wide open throttle lol.

LETS KEEP THE REPLY TO MY QUESTION SIMPLE-

I SAID:



THATS ON A E BODY IN FULL STREET TRIM, 4 SPEED AND 3.54 GEARS.

LIKE I SAY THE ABOVE ENGINE RUNS GREAT WITH NO PINGING, BUT WHEN I FILL IT WITH GAS JUST 1 POINT LOWER IN OCTANE,IT PINGS. SO THAT ENGINE IS RIGHT AT THE EDGE OF THE PING ZONE.

LETS SAY I SWAPPED HEADS ON THAT ENGINE FOR CLOSED CHAMBER IRON HEADS AND ALL ELSE REMAINED THE SAME. HOW MUCH MORE COMPRESSION WOULD PROPER QUENCH ALLOW ME TO RUN VS. THE 9,4:1 CR WITH NO QUENCH AND OPEN CHAMBER HEADS?

Personally I wouldn't act annoyed and start typing in ALL CAPS because the helpful info that is given is perhaps not what you expected/wanted to hear.

I say you need at least:
- Cold air intake.
- 160F thermostat.
- Efficient (digital?) ignition timing.
- Heatshielded headers to keep heat from enginebay.

For a streetonly car and no 'regular' 6k rpm blasts, I would close up quench distance to well below .040".

Most people think about cranking compression when dealing with fuels.

You could do a simple cranking compression on your current engine and see where you are at.
Use that as a rough baseline for your ping-limit.

Then use an online calculator to find out where you will be at with the other combo.


But to answer your original question; I dunno.

Sorry for the caps, Its not yelling, its just that I typed in caps to differentiate my new posted reply from the quoted text. My bad.

I guess Ill just experiment and see as I am uessing is no real definite answer to my question.

ill shoot for 9,8:1 compression w quench and see what happens. I can always add some toluene and raise the octane if it pings. I have access to toluene at my local paint supply store. Its a paint thinner thats like 95% toluene and does the trick.

I think with a good closed chamber and good quench...a cam that size, 9.8:1 is pretty conservative. I would be shooting for more like 10.2 or 10.4...

I'm daily driving a 360ci with 11.3:1 cr,
0.029-0.030" quench height and a CompCams XE256h with solid lifters.

Maybe try Propane as fuel

Propane would let you run high compression with no ping, but power would be way down due to lower BTUs of propane compared to gasoline.

All things considered Inwould not push the envelope on compression since it is not worth the headache on fuel octane requirements. If 1pt. of ratio is worth 3%, no matter what HP level you build it to the whole package is worthless if you can not properly feed it the octane it needs.

Your better off light by 1pt. of compression so you can run anytime anywhere without issues.
Your better off focusing on creating the best possible and least restrictive air flow paths in and out of the cylinder.

Induction wise, dependent on parts used and modified, there is an easy 50hp difference between good and awesome intake tracks. There’s even more with a well thought out exhaust system.

And it adds up to a hell of a lot more than making use of max compression.

The OP said the engine is using dished pistons. The squish only happens when the head and piston top come close together. The dish usually removes some piston material under a part of the cylinder head that could offer squish except the piston top isn't there.

When Mazda was developing SkyActiv technology, two of the things they did for gasoline engines to allow more compression for the same octane rating were:
1. Keep the intake charge cool.
2. Scavenge the exhaust gas out of the chamber. It adds heat to the incoming charge. The Mazda guys put an exhaust header on the engine.

And no, Dave, it wasn't all electronic control of fuel and spark.

R.

Pistons are step dished, they have a quench pad. Icon IC745 pistons.