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Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: ahy] #2512147
06/23/18 01:09 PM
06/23/18 01:09 PM
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Windsor, ON, Canada
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Diplomat360 Offline
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Originally Posted By ahy
...With iron heads (even with decent quench) suggest you shoot for 9.5 CR max....


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.

Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: domingo] #2512178
06/23/18 02:26 PM
06/23/18 02:26 PM
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Porter67 Offline
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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.


Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: domingo] #2512186
06/23/18 02:37 PM
06/23/18 02:37 PM
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Tulsa OK
Bad340fish Offline
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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.


68 Barracuda Formula S 340
87 "Chrysler" Conquest
Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: domingo] #2512842
06/25/18 12:52 AM
06/25/18 12:52 AM
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Lima, Peru
domingo Offline OP
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LETS KEEP THE REPLY TO MY QUESTION SIMPLE-

I SAID:

Quote:
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.


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?

Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: domingo] #2512894
06/25/18 08:00 AM
06/25/18 08:00 AM
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The Netherlands
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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.

Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: domingo] #2513721
06/26/18 11:46 PM
06/26/18 11:46 PM
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Posts: 9,670
Lima, Peru
domingo Offline OP
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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.

Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: domingo] #2513732
06/27/18 12:24 AM
06/27/18 12:24 AM
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central texas
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krautrock Offline
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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...

Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: domingo] #2514050
06/27/18 06:14 PM
06/27/18 06:14 PM
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The Netherlands
BigBlockMopar Offline
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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 smile

Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: domingo] #2514118
06/27/18 08:56 PM
06/27/18 08:56 PM
Joined: Jan 2003
Posts: 9,670
Lima, Peru
domingo Offline OP
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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.

Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: domingo] #2515846
07/01/18 01:52 PM
07/01/18 01:52 PM
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Earth
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Rob C Offline
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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.

Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: Rob C] #2516475
07/02/18 05:02 PM
07/02/18 05:02 PM
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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.

Re: Maximum CR closed chamber w2 heads 0.040 quench- pump gas [Re: domingo] #2516478
07/02/18 05:05 PM
07/02/18 05:05 PM
Joined: Jan 2003
Posts: 9,670
Lima, Peru
domingo Offline OP
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Pistons are step dished, they have a quench pad. Icon IC745 pistons.

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