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Squish Volume and combustion efficiency
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journeyman
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PostPosted: Mon Feb 07, 2011 1:17 am    Post subject: Reply with quote

clay wrote:
Personally I have had a bad experience with a high dome engine in the past. My best guess is the high dome was interfering with flame travel by shrouding the plug and just basically being in the way. I look at a dome as a wedge that is trying to seperate the fuel / air charge into two areas. I don't know if you have ever heard about these heads but this article should be an interesting read. Clay
http://www.hotrod.com/techarticles/engine/hrdp_9902_mark_vi_chevrolet_502_engine_build/intake_and_exhaust_valves.html


WOW. That was a cool article... Not like I am used to seeing in HotRod. I felt like they were speaking my language, something I could understand and was really into. But they left me hanging: Where can one get those crossfire heads (a quick search turned up nothing)? And where is part two of the article?
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journeyman
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PostPosted: Mon Feb 07, 2011 6:02 am    Post subject: Reply with quote

Big Dave wrote:
Hemi engines were the result of aircraft engine reseach conducted during WWII to increase the piston powered planes overall speed and power.

Yes if you filled the cylinder with a spherical dome you get lots of power and the efficiency of the engine is maxed out (so a 402 BBC with a hemi head would indeed blow away the SBC 400). Will it run on pump gas? Not at 15.0:1 compression ratios it won't.

And yes the Dart's Big Chief 14 degree head has a fairly small 74 to 85cc heart shaped combustion chamber chamber (74 as cast 85 cc when fully CNC machined) for use with a flat top or mild dome piston designed to accept the angle of the splayed valves. Brodix's PB1200 Man Eater 12 heads have 68-72cc chambers. You can pick up a set of either for around $4,800 a head complete or $2,500 for a bare casting if you have your own CNC five axis mill (like a lot of the pro's do) and make your own heads with your own flow characteristics.

The big block head was designed in 1962 with a slide rule and was reengineered again in 1967 based upon information that William T. Jenkins provided the design team with, but the engineers where still using log books and a slide rule. Modern aftermarket heads from most manufactures are relying upon CAD CAM CNC to bring a design from the computer to the shop flor and out the door.

Big Dave


76 cc looks great... $9600 does NOT. Hmmm. there has to be an alternative. I do like the article's featured intake: a $1200 Accel injection unit with 14' runners:

[/img]
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Big Dave
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PostPosted: Mon Feb 07, 2011 1:13 pm    Post subject: Reply with quote

Those heads where created by Jim Fueling who died in Dec 2002. His company only sells stuff for Harley Bik's now so they are unavailable. They do not exist as a "for sale" item. With a five axis CNC mill (and about twice the price of the mill in the necessary tooling) combined with AutoCAD software running on your family PC you can make anything you want.

The Accel EFI unit was designed and built originally by the late John Lingenfelter based initially upon the bottom of an Edelbrock tunnel ram manifold that he "tweaked" a bit.

Big Dave
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journeyman
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PostPosted: Mon Feb 07, 2011 5:49 pm    Post subject: Reply with quote

So sad on those heads.
That HotRod build was something that seemed almost custom tailored to me.
Unfortunately, I am having a hard time finding part 2 of the article.

They claim that intake has the equivalent of 14" runners... Wow.

BSFC numbers are interesting to me, but I really would like to take it a step farther to partial throttle BSFC numbers. I know that may sound ridiculous, but since almost all driving is done at partial throttle, it makes sense.
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clay
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PostPosted: Mon Feb 07, 2011 10:59 pm    Post subject: Reply with quote

I tried searching around Lingenfelter's site for anything but it doesn't appear he has really done anything for the BBC. He is another good source for what you are looking for - torque and efficiency. Here is a link to a thread on Speedtalk I remembered about somebody having some of the Feuling heads. Maybe try to get in contact with him - sounds like they are available. Clay
http://speedtalk.com/forum/viewtopic.php?f=1&t=21472&p=235861&hilit=feuling+heads#p235861

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PostPosted: Tue Feb 08, 2011 12:23 am    Post subject: Reply with quote

Even with the 120ish CC heads there is still about 40% squish. I wouldn't hesitate to put that at .041" on the 4.380" bore with the low rpm you are running.
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journeyman
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PostPosted: Tue Feb 08, 2011 3:42 am    Post subject: Reply with quote

Quote:
AFAIK, there were only 6-8 sets ever made.



Somehow, I find this statement (from the link) hard to believe. Investing that much in R&D, and then mfg. he HAD to have made a run of several hundred pairs.

Why wouldn't there be copies of these heads around?

It seems like these would be the ultimate low RPM heads. Also, with the spark plug location moved AWAY FROM the exhaust, it actually looks civilized!

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journeyman
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PostPosted: Tue Feb 08, 2011 11:55 am    Post subject: Reply with quote

There are other small chamber heads for the BBC:


These (Brand New Aluminum GM BB Heads #10051128) have a great chamber (72cc), but intake ports the size of a small warehouse. Unfortunately, they are also symmetrical port heads and are 5/8" taller than stock, so nothing will fit right on them.

Pontiac made a 60 cc head appropriate for the BBC I heard...
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journeyman
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PostPosted: Fri Feb 11, 2011 1:22 am    Post subject: Reply with quote

This article (HotRod) really opened my eyes, and maybe even inspired me.

How to build a BBC for efficiency/low BSFC?
The numbers they were throwing around (.35 Lb/bhpHr) are in the diesel territory and quite exciting to think about for a gasoline engine, especially one as robust as the BBC.

It seems that much of their gains were to be had from the head.
Isn't there a small chamber, small runner head available anywhere? I am finding that combination is like looking for unobtanium.

There HAS to be others that have wanted to build the BBC for efficiency. What did they use? Where did they get their parts?
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Big Dave
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PostPosted: Sun Feb 13, 2011 1:24 am    Post subject: Reply with quote

Well there is the generation VII BBC made by Mercruiser (they have since stopped production). It is basically the LS-x head stuck on top of a tall deck 496 BBC. There are no parts of the Mark IV Gen V or Gen VI that will interchange with the gen VII.

Big Dave
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journeyman
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PostPosted: Sun Feb 13, 2011 1:34 pm    Post subject: Reply with quote

Yeah, but I have heard frequently of 8.1 woes. I have not done any research, just anecdotal references, and it makes me wonder about advantages of the 8.1 over the VVT 6.0

I just think there HAS to be some efficiency stuff (heads/intake/cam combo) out there for the BBC. It is such a truly great motor.
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journeyman
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PostPosted: Tue Feb 22, 2011 10:47 am    Post subject: Reply with quote

Big Dave wrote:
Well there is the generation VII BBC made by Mercruiser (they have since stopped production). It is basically the LS-x head stuck on top of a tall deck 496 BBC. There are no parts of the Mark IV Gen V or Gen VI that will interchange with the gen VII.

Big Dave


Is the 8.1 combustion chamber a lot (how much?) more efficient than the gen 4/5/6 BBC? If so, that could be a big determining factor. I like the longer stroke with the moderate bore...
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