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  #16 (permalink)  
Old 12-17-2010, 09:46 AM
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Quote:
Originally Posted by 68NovaSS
In your other post earlier today, you talk about dome pistons, here you're trying to get your c.r. down?

I just moved from Anchorage, but Coker's did all my machine work on my blown 383 a couple years ago, they're gone now I think, but you should talk to the guys down at Alaska Drag Bike, super machine shop and knowledgeable people.
Oops, nevermind Alaska Drag Bike in Anchorage, I see your on the Seattle end of Alaska.

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  #17 (permalink)  
Old 12-17-2010, 05:36 PM
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flat tops put my CR at around 8.5:1... Not interested.


What I was trying to do is get my CR as close to 9:1 as possible. Actually I just wanna run 90 octane and not worry (so 9.5:1 with my cam). The smallest dome is 13.80cc and that puts me at 9.5:1.

Anyways Im gonna run the 820s
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Old 12-17-2010, 07:55 PM
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820 design and quench

Here's a post that says the 820s biggest drawback is lack of quench area

http://www.chevelles.com/forums/show...&highlight=820


What's he lookin at to say that? I thought quench was the distance between the flat part of the piston to the bottom of the cyl head...


So... How do I help this head? What do I do to get a good quench? Right now I think the pist is .025 in hole (stock), I planned on going to a 0 or .005" deck with a .040 gasket to get a .045 quench. Now I'm not sure what to do. I just want it less prone to det (with the 9 to 9.5:1cr and XR288HR cam, 90 octane gas).
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  #19 (permalink)  
Old 12-17-2010, 08:04 PM
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An optimal quench pad should be between .035" and .050" maximum. Using a closed chamber head like the vortec/fast burn style chamber the piston has an area to ram the charge into and create turbulence; if you have an open chambered head, not so much turbulence.

I zero-decked my 360 magnum and will run a .039 gasket under a stock magnum head, same 64cc chamber and profile as the vortec head, with flat top pistons - only thing that could be better would be domed pistons that match the contour of the chamber for a super violent squish.

Others will know your specific setup better than I.
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Old 12-17-2010, 08:26 PM
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So do they mean... The shape of the chambers being round hurts quench vs like a closed chamber design? That simple?
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Old 12-20-2010, 01:00 AM
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454, 90 octane

Hello,
I'm building a iron head (820s) 454. The fuel available is 90 octane (highest we have). Okay here's the deal, with flat tops and my 113cc chambers plus a .005 deck that gives me around 8.5:1 CR. That's too low for my taste. With a .005" deck and speedpro 13.80cc puts me at 9.59:1 and that seems a tad high. The speed pros are the smallest dome forged piston I can find. I'm trying not to order custom pistons or mod a set due to cost.

So I got ahold of comp cams and I was originaly looking at a XR282HR. They said if I bump it up to an XR288HR that should fix my problem.

My numbers say the DCR would be 7.4:1 with the XR288HR (70 degree closing point). So... That really should be okay right?

The reason I plan a .005" deck is I'm trying to get my quench around .040. With the .005" deck height and a .040 head gasket gives me a nice .045 quench/squish.

I'm having the 820s slightly ported and large valves put in and hope to get around 500hp so I figure hyper would be pushing it.

Greg




I'm wondering if this is really worth all the trouble and am once again half tempted to use 13.80cc domed pistons and keep the deck height where it is (.025). Tha't'd give me a 9.23:1 CR but screw with "quench". Supposedly these heads lack quench anyways (so I read) so would having a larger quench be at all a benifit?
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Old 12-20-2010, 01:12 AM
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I just needed to ask again because once the block is decked its decked there's no turning back. I've heard one guy say its no problem and one guy said it SHOULDNT. need more opinions
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  #23 (permalink)  
Old 12-20-2010, 02:08 AM
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I always deck for tight quench, tight quench has benefit of reducing octane sensitivity.

Often a slightly higher compression ratio with tight quench will tolerate lower octane better than a lower compression ratio with large quench, the tight quench improves turbulence and mixture homoginization.

Large quench clearance is never a benefit. Large quench either makes no difference, or it is detrimental - it has no up side.

The other benefit to decking is that it gives you a nice flat gasket surface for better sealing.

I'd be decking yours if it was mine.
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Old 12-20-2010, 05:26 AM
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Makes sense.. I wondered if that would be the case. So should I just do a zero deck or .005 for a slightly lower CR. I suppose maybe the zero then so I get a .040 quench?
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  #25 (permalink)  
Old 12-20-2010, 07:05 AM
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Zero or .005" down is your choice, it won't make a big difference either way, one is as good as the other. It is quench distances above .060" that are to be avoided.
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  #26 (permalink)  
Old 12-20-2010, 08:34 AM
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Quote:
Originally Posted by ekacpuc
The fuel available is 90 octane (highest we have).
Greg, remember that (unless you've already factored it in when you say "90 octane") YOUR octane is very likely calculated using the Research Octane Number (RON) method.

In the US and Canada, the octane is calculated by using the "Anti-Knock Index"- derived by averaging the RON and MON (Motor Octane Number).

Quench is important to octane requirement, and the small amount of compression ratio that you're talking about will not increase the output of your engine to any noticeable degree- while it CAN run you into detonation if you're not careful.

I'd build it w/plenty of leeway for fuel octane and intake air temperature, as far as the CR goes.

Bottom line is the actual octane of your fuel (comparable to stateside) is more like 87 octane at best.
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  #27 (permalink)  
Old 12-20-2010, 09:10 AM
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You had three posts, all about these heads, I've merged them here.
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  #28 (permalink)  
Old 12-20-2010, 05:21 PM
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Makes sense about the thread.


I must be missing what he's sayin about the octane... I AM in the US.. The fuel gets barged up from the lower 48... Alaska IS a state... Is that what you're saying? That alaska uses different standards for fuel rating? Thats silly...
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  #29 (permalink)  
Old 12-20-2010, 07:42 PM
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I mistook your locale.
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  #30 (permalink)  
Old 12-20-2010, 08:03 PM
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Quote:
Originally Posted by ekacpuc
Here's a post that says the 820s biggest drawback is lack of quench area.
What's he lookin at to say that? I thought quench was the distance between the flat part of the piston to the bottom of the cyl head...
You're correct, piston crown to underside flat part of the head at the chamber. Problem appears to be that these heads don't have a flat part to squish against....personally, I wouldn't use 'em....
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