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detonation vs compression, static or dynamic??

Posted By: Michael Ecks

detonation vs compression, static or dynamic?? - 07/21/13 05:44 AM

Playing with numbers on my night off. Using the compression ration calculator on the kb-silvolite website using the the parts I am considering for my build I come up with very different numbers. 10.929 static that's way too high for pump gas, but 9.420 dynamic which seems okay if I am understanding quench correctly.

So which one is the important one for avoiding detonation problems, as I am planning a pump gas motor build? Static or dynamic?

The combo I am looking at is a stock stroke 360, 4.040 KB107 pistons at zero deck, RHS X heads, Voodoo cam (Lift: .475/.494 Duration: 265/271 LSA: 112), and .039 Fel Pro head gaskets for .039 quench.

Trying to learn and figure all this out before I start ordering parts and
Posted By: MR_P_BODY

Re: detonation vs compression, static or dynamic?? - 07/21/13 06:09 AM

Static is just a cyl volume thing(bottom to top with
head and gasket).. it doesnt take into account when
the valve closes and really starts the compression stroke
Posted By: goldmember

Re: detonation vs compression, static or dynamic?? - 07/21/13 06:11 AM

Not even close to a workable combo of parts on pump gas.
Posted By: MR_P_BODY

Re: detonation vs compression, static or dynamic?? - 07/21/13 06:18 AM

Quote:

Playing with numbers on my night off. Using the compression ration calculator on the kb-silvolite website using the the parts I am considering for my build I come up with very different numbers. 10.929 static that's way too high for pump gas, but 9.420 dynamic which seems okay if I am understanding quench correctly.

So which one is the important one for avoiding detonation problems, as I am planning a pump gas motor build? Static or dynamic?

The combo I am looking at is a stock stroke 360, 4.040 KB107 pistons at zero deck, RHS X heads, Voodoo cam (Lift: .475/.494 Duration: 265/271 LSA: 112), and .039 Fel Pro head gaskets for .039 quench.

Trying to learn and figure all this out before I start ordering parts and


Is that duration at .050 or what.. thats alot of duration
for a small lift(I dont know the Voodoo stuff) other
than a fancy name
Posted By: Michael Ecks

Re: detonation vs compression, static or dynamic?? - 07/21/13 06:44 AM

Quote:


Is that duration at .050 or what.. thats alot of duration
for a small lift(I dont know the Voodoo stuff) other
than a fancy name




Copied from Jegs site. Come to think of it I'm not sure where they got those numbers. Here are the numbers from Lunati's site.

Advertised Duration (Int/Exh): 262/268
Duration @ .050 (Int/Exh): 220/226
Gross Valve Lift (Int/Exh): .475/.494
LSA/ICL: 112/108
RPM Range: 1400-5800
Part Number: 10200702
Posted By: Michael Ecks

Re: detonation vs compression, static or dynamic?? - 07/21/13 07:04 AM

Quote:

Not even close to a workable combo of parts on pump gas.



Didn't think so. I think I found the error in my math and it leaves me with a dynamic of 10.38.

I could switch to speed-pro's .015 in the hole and thick gaskets which would put me at static 10.14:1/dynamic 9.64:1. But then I've lost all quench!

Back to the drawing board I guess. Any recommendations? I was hoping to use hypereutetic pistons and have it run a little better than the mopar 380 crate engine.
Posted By: goldmember

Re: detonation vs compression, static or dynamic?? - 07/21/13 07:17 AM

Quote:

Quote:

Not even close to a workable combo of parts on pump gas.



Didn't think so. I think I found the error in my math and it leaves me with a dynamic of 10.38.

I could switch to speed-pro's .015 in the hole and thick gaskets which would put me at static 10.14:1/dynamic 9.64:1. But then I've lost all quench!

Back to the drawing board I guess. Any recommendations? I was hoping to use hypereutetic pistons and have it run a little better than the mopar 380 crate engine.

without more info it's very hard to make a recommendation other than to say do not push the comp if your limited to pump gas. how does the 380hp crate engine run? Ported heads,better camshaft and intake may be all you need.
Posted By: MR_P_BODY

Re: detonation vs compression, static or dynamic?? - 07/21/13 07:21 AM

If you went with more duration the pressure would be
down during low rpm (which is the problem area) and
still use the same piston BUT you have to take the revs
higher ... but that also needs the head flow... just
a thought... plus what are you talking for pump gas
EDIT
Plus a looser conv would help so you dont load the engine
at low rpm... along with the rear gear.... my 416
is a 10.5 static but with a 260/270 at .050 cam and
a 5000 stall conv and 4:10 gears in a some what lighter car
Posted By: Dodgem

Re: detonation vs compression, static or dynamic?? - 07/21/13 03:26 PM

You are going with aluminum heads that is huge in resisting detonation.
I do vote for the looser converter and bigger cam though.

Do you have all the specs on heads head gasket pistons and so forth to do compression numbers??
Posted By: Dodgem

Re: detonation vs compression, static or dynamic?? - 07/21/13 03:40 PM

If your going with a real mild cam like that maybe a piston like this
http://www.hughesengines.com/Index/produ...mp;partid=27848
Posted By: moparacer

Re: detonation vs compression, static or dynamic?? - 07/21/13 03:43 PM

You are way too small with the combustion chambers on the RHS heads right?

I ran into the same problem with 318 magnum heads and the flat top zero deck engine I put in my Barracuda.

The cheapest solution for me was to open the chambers up to 68 CC.

Attached picture 7784379-cuda103.jpg
Posted By: Swedcharger67

Re: detonation vs compression, static or dynamic?? - 07/21/13 08:03 PM

I think the dynamic one is the important one for considering the risk of detonation.
At higher revs the cylinder pressure may rise slightly, but the engine may at the same time be less prone to detonation.
Posted By: Kern Dog

Re: detonation vs compression, static or dynamic?? - 07/21/13 08:17 PM

Are you sure the math is right?
The dynamic equation relies heavily on the intake closing @ .050 PLUS 15 degrees. I'm making some changes to avoid this very thing. I chose a Lunati Solid. This one closes at 57 degrees. With the 15 additional degrees it comes in at 71. That takes my 10.7 ratio down to a dynamic of 8.138.
I can't imagine that your static and dynamic can be so close to each other.
Even with my old '509 cam, I still had a dynamic reading of 8.8, so I think you may have made an error in calculating.

*******************************************************************
The stories I hear, anything above 190 psi cranking compression or 8.5 dynamic are getting into race gas territory.
Currently in my Charger I get an average psi between 185 and 192. I cannot run more than 31 degrees of advance. Even at 31 I'll get detonation at full throttle.
Posted By: HotRodDave

Re: detonation vs compression, static or dynamic?? - 07/21/13 08:42 PM

It will be fine

I Run stock pistons with .035 quench in a 318 mag it a heavy high geared ram With a stock cam and have no detonation

Mag chambers and tight quench are awesome.
Posted By: 5spdcuda

Re: detonation vs compression, static or dynamic?? - 07/22/13 01:29 AM

That's a fairly small cam with a pretty wide LSA so I don't think it's going to bleed off very much cyl. pressure. If the RHS heads are the ones I think they are they are iron with closed magnum type chambers. I would either open up the chambers a bit and unshround the valves or use the KB 362 pistons which are designed for closed chambers. The 362's are a step-dish design with excellent quench and lighter than the 107's.I would also run the pistons at .004-.005 in the hole. You will still have good quench and if you ever have a head gasket problem you will still have enough deck left for a clean up cut.
Posted By: Michael Ecks

Re: detonation vs compression, static or dynamic?? - 07/22/13 03:24 AM

Thanks 5spd. That piston may be just what I need, I like lighter and it should get me the compression I was looking for.

My only question with them now is, can Eagle SIRs be safely narrowed to 1 inch on the small end? I have a set of SIR and factory magnums sitting here, and the small end looks similar thickness minus the factory ones balance pad and casting lines.

I know Eagle's don't have the best reputation anymore. Since this engine will never see nitros, and since I am going with light pistons instead of heavier forged I am hoping to get away with running them since I have them already.
Posted By: 5spdcuda

Re: detonation vs compression, static or dynamic?? - 07/22/13 05:14 AM

Eagle "H" beams are no doubt stronger than the SIR's, but if it's any consolation I friend of mine used them in his .030 360 mid 10 sec. Dart and they held up. He crossed the stripe in the quarter at just over 7,000 rpm and shifted at 6,600. Pretty good for a budget built 360. I should point out that this was a really light car on alky. Still mid 10's at 124 mph and 7,000 rpm+ with KB hyper pistons and SIR rods ain't bad. I would check with your machine shop about narrowing them to 1 inch. I run the 362's with narrowed LA rods in my'Cuda. Pistons are under 600 grams with pins. I shift at 6,200, rev limiter is at 6,600 and I have bounced off it a few times. My engine is internally balanced FWIW.
Posted By: Wedgeman

Re: detonation vs compression, static or dynamic?? - 07/23/13 03:25 AM

Quote:

Are you sure the math is right?
The dynamic equation relies heavily on the intake closing @ .050 PLUS 15 degrees. I'm making some changes to avoid this very thing. I chose a Lunati Solid. This one closes at 57 degrees. With the 15 additional degrees it comes in at 71. That takes my 10.7 ratio down to a dynamic of 8.138.
I can't imagine that your static and dynamic can be so close to each other.
Even with my old '509 cam, I still had a dynamic reading of 8.8, so I think you may have made an error in calculating.

*******************************************************************
The stories I hear, anything above 190 psi cranking compression or 8.5 dynamic are getting into race gas territory.
Currently in my Charger I get an average psi between 185 and 192. I cannot run more than 31 degrees of advance. Even at 31 I'll get detonation at full throttle.



Precisely,
do not forget to add 15 degrees to the closing point of the intake valve.
Pretty accurate from my experience.
I used the RHS before in my 408 and worked great !

Do not pass 9:1 dynamic c.r.

Dan
Posted By: 451Mopar

Re: detonation vs compression, static or dynamic?? - 07/23/13 07:31 AM

Need a bigger cam, and maybe more cylinder head chamber volume to get dynamic CR closer to 8:1.
Posted By: Pale_Roader

Re: detonation vs compression, static or dynamic?? - 07/23/13 12:26 PM

Quote:

It will be fine

I Run stock pistons with .035 quench in a 318 mag it a heavy high geared ram With a stock cam and have no detonation

Mag chambers and tight quench are awesome.



Sounds like something i've been thinking a lot about recently.

I'd be interested to know more about the combo...
Posted By: HotRodDave

Re: detonation vs compression, static or dynamic?? - 07/23/13 04:06 PM

I towed 5000 lbs up some big passes last night with the AC on and 87 octane (up to 10% ethanol) in the tank and did not hear one ping out of it I would hate to figure out what my dynamic compression is, true 10 to 1 static and a stock cam
Posted By: goldmember

Re: detonation vs compression, static or dynamic?? - 07/23/13 09:29 PM

Be interested in seeing the ignition timing program. The factory timing is way conservative and if it's been death flashed its even worse. When I've knocked 10 degrees out of a good tune I always lost performance but would run on crappy gas.
Posted By: dogdays

Re: detonation vs compression, static or dynamic?? - 07/23/13 11:30 PM

Dave, what was the elevation of the passes? That can make a HUGE difference in octane requirements.

Remember one Smokey Yunick built Pikes Peak racer that had the warning, IIRC, do not start under 7600 ft elevation?

R.
Posted By: moparniac

Re: detonation vs compression, static or dynamic?? - 07/24/13 12:19 AM

Altitude will affect dynamic cranking compression and dynamic compression ratio. The cooler weather racing will cause the numbers to go up. So "figure" up your pump gas build at zero altitude type racing weather. The cam specs your posted do not show timing events either the higher the Intake Valve closing ABDC greatly helps.
Posted By: polyspheric

Re: detonation vs compression, static or dynamic?? - 07/24/13 12:38 AM

"Altitude will affect... dynamic compression ratio."

How?
Posted By: Kern Dog

Re: detonation vs compression, static or dynamic?? - 07/24/13 01:23 AM

The air is thinner and shows less pressure for any given compression ratio.
Posted By: 451Mopar

Re: detonation vs compression, static or dynamic?? - 07/24/13 02:23 AM

The Dynamic compression "ratio" stays the same, but the cylinder pressure is reduced with altitude.
A dynamic compression ratio of 8:1 should create cranking cylinder pressures of about 163.5 psi at sea-level (14.7 psi air pressure), but around Denver, the air pressure is around 12.0 psi, so the same engine (dynamic compression of 8:1) would only have a cranking cylinder pressure of about 133.5 psi. FWIW, 7:1 dynamic at sea-level (137.2 psi) is about the same cylinder pressure as 8:1 dynamic in Denver.
Posted By: HotRodDave

Re: detonation vs compression, static or dynamic?? - 07/24/13 02:46 AM

2000 ft to 4000 foot and 95 degrees, factory timing on my mac mentor shows around 30* at and near WOT. Never heard of a 318 getting a death flash only 5.9s. I actually had more pinging before milling the block and going to thinner head gaskets.
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