Re: Maximum CR open chamber iron heads no quench- pump gas
[Re: domingo]
#2497280
05/17/18 05:53 PM
05/17/18 05:53 PM
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Joined: Aug 2011
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From my experience with PING monsters in hot Southeast Texas, I would go 9to1 I built my alum head 512 with quench at 9.7, just to be on the safe side.
1968 Charger COLD A/C Hilborn EFI 512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim 2020 T/A 392 Stock 11.79 @ 114.5
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Re: Maximum CR open chamber iron heads no quench- pump gas
[Re: domingo]
#2497291
05/17/18 06:08 PM
05/17/18 06:08 PM
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There is much more going on in the chamber that changes with quench, including valve shrouding, squish turbulence, etc. Even if your quench distance is beyond conventional limits (best before .060", gone at .125"), having the surfaces approach each other to a closer distance at some points (a hemi does not) always helps. 1/2 point isn't worth 2%.
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Re: Maximum CR open chamber iron heads no quench- pump gas
[Re: domingo]
#2497375
05/17/18 10:48 PM
05/17/18 10:48 PM
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crabman173
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Re: Maximum CR open chamber iron heads no quench- pump gas
[Re: domingo]
#2497479
05/18/18 10:55 AM
05/18/18 10:55 AM
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Overlap doesn't reduce CCP (later intake closing does), but reduces knock slightly because of residual exhaust gas - less power. This will vary with local exhaust port pressure, and system backpressure.
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Re: Maximum CR open chamber iron heads no quench- pump gas
[Re: domingo]
#2497591
05/18/18 04:38 PM
05/18/18 04:38 PM
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Overlap will reduce low speed ping because of dilution but will also hurt low speed TQ so it is not the solution anymore than retarding timing would be.
Retarding the whole cam could help if you really were pushing the envelope that much, you get a later intake closing point so less low speed cylinder pressure as well as a later ex opening giving you more time to push on the piston.
I think with a stock open chamber head on that big of an engine you are not going to efficently fill the chambers at higher speed anyhow so I would shoot for 9.5 - 10.0
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Maximum CR open chamber iron heads no quench- pump gas
[Re: domingo]
#2497592
05/18/18 04:43 PM
05/18/18 04:43 PM
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Opening the exhaust early subtracts from the duty cycle (less energy turned to crank rotation, more lost in the pipe) in favor of reduced pumping loss. Closing it later (during OL) leaves more exhaust gas in the chamber, which both dilutes and heats the new charge. Typically cylinder pressure is higher than we want (I want zero!), so the exhaust forces the new charge backward until RPM is higher (with high vacuum this is even worse). This is one reason why "split overlap" (equal duration IO BTDC and EX ATDC) is nothing like equal events in terms of pressure balance. Again, it's a compromise like everything else.
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Re: Maximum CR open chamber iron heads no quench- pump gas
[Re: jwb123]
#2497684
05/18/18 08:42 PM
05/18/18 08:42 PM
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Its hard to get a tight quench with open chambered mopar heads. If you measure them you may find the chambers are not as equal as you might think both volume and height. Octane needs of the engine have more to do with dynamic compression than static compression. I use an engine program to decide what kind of fuel the engine will need. Performance trends, it calculates cranking compression, advance curve, and lets you try different octane fuels. It also calculates a ton of other stuff. Results on a real dyno are close if you take the time to put good numbers in the program. And it costs about what a good 1/2 ratchet costs. It's not hard to get quench. Stick the piston out of the bore.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: Maximum CR open chamber iron heads no quench- pump gas
[Re: domingo]
#2497694
05/18/18 09:09 PM
05/18/18 09:09 PM
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Cast Iron Heads.
Sea Elevation.
I think Im gonna play it safe and stay around 9:1
On an engine like this which should be putting around 500 hp (small block stroker with w2 heads). Each point increase in compression would equate to how much HP gains? Lets say if the engine made 500hp at 9:1 if it was bumped to 10:1 and race gas was used so it doesnt ping....how much HP would be gained from the full point increase in compression? There was a test on a 440 stacking gaskets to controle cr and from 9 to 1 to 10 to 1 gained 20 hp so maybe you would get 15hp.
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Re: Maximum CR open chamber iron heads no quench- pump gas
[Re: domingo]
#2497712
05/18/18 10:25 PM
05/18/18 10:25 PM
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I think he's referring to the "as cast" 452 etc. chambers in which the exact depth and especially the contour of the quasi-quench surface is irregular. The KB instructions begin with "mill this down until all 8 match".
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