BBC output overview.

General engine tech -- Drag Racing to Circle Track

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ns158sl
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Re: BBC output overview.

Post by ns158sl » Fri Oct 05, 2018 9:58 pm

I did just notice the prostock heads are towards a 10 degree cant instead of the stock 4-5 degrees. I guess I am totally curious now of the results, and then to find out the method of getting there. I guess I want to see a bbc head "shrunk down" on a sbc, like along the lines of a sdp or a big chief design, also.

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Re: BBC output overview.

Post by Frankshaft » Sat Oct 06, 2018 12:09 am

ns158sl wrote:
Fri Oct 05, 2018 9:58 pm
I did just notice the prostock heads are towards a 10 degree cant instead of the stock 4-5 degrees. I guess I am totally curious now of the results, and then to find out the method of getting there. I guess I want to see a bbc head "shrunk down" on a sbc, like along the lines of a sdp or a big chief design, also.
Sbx from CfE, little chief from Dart, 12 degree air strike from Profiler, to name a few. There is not a single low port 23 degree head in existence that will make anywhere close to the power of the mentioned heads, or raised runner 23 degree heads, such as an all pro rr245. An 18, 15 degree or 13 degree head won't either. All inline wedge heads. An Sb2.2 will smash those also.

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Re: BBC output overview.

Post by David Vizard » Wed Oct 10, 2018 6:50 pm

OK guys,

Dead line done.

Will get back on to the subject of 24 degree BBC heads and port bias in the next few days.
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Re: BBC output overview.

Post by David Vizard » Thu Oct 11, 2018 7:18 pm

Attached is a good example of port bias for a SBF.
The bias on the exhaust really woke up what was otherwise a passably decent port.
Note the intake has less of a pronounced bias.

Next look at bias on ports will cover questions such as 'how do we know when to apply bias and where does it influence flow the most'.

This will be looked at in the context of a 24 Degree BBC but for those wanting a pro-stock analysis I do have extensive data on the 2016 Australian 400 inch ProStock heads the equipped to fastest competitor of 2016.

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fastblackracing
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Re: BBC output overview.

Post by fastblackracing » Fri Oct 12, 2018 1:11 am

Dave, Is the bias being applied to help direct the flow towards the center of the cylinder?

In other words to get better exit/discharge past the valve minimizing the effects of shrouding?
Or is it being applied more due to the architect of the port?

Thanks.

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Re: BBC output overview.

Post by gruntguru » Fri Oct 12, 2018 2:31 am

David Vizard wrote:
Wed Oct 03, 2018 2:14 pm
. . . . A little illustration that harks back to my days hopping up Mini Cooper engines (BL's not BMW) The ex. each end of the head is virtually a square port which takes a right angle turn at the valve and has only about 3/8th of an inch to the valve seat. A more badly conceived port would indeed be difficult to find. After years of flogging these ports on the flow bench I became resigned to the fact that, for what it was, a CD closely approaching 0.7 was pretty good all things considered. My good friend David Anton of APT in Riverside CA, who also specializes in A Series engines, got onto a big winter development spree and much to my amazement he produced a port with a huge bias (about 50% of the valve diameter) and this SOB ran to 82% efficiency at about .35 D lift. . .
DV
Reminds me of a turbocharged A Series I played with about 40 years ago. I built a head with equal size valves (1.3" inlet and exhaust) and cut a lot of bias into those pesky cylinder 1 and 4 exhaust ports. I remember that head on the turbo engine (28 psi boost) worked way better at all rpm than a "race" head with the little Mk1 Cooper S exhaust valve and oversize inlet valve. No access to a flow bench or engine dyno in those days but the car was way quicker on the track.

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Re: BBC output overview.

Post by David Vizard » Fri Oct 12, 2018 8:58 am

28 lbs of boost?? Well gruntguru I'll wager that traction was a problem!!!

Most powerful mini I have had experience with made 220 hp at the wheels. This I suspect was a lot less than the potential your build had.

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gowest
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Re: BBC output overview.

Post by gowest » Fri Oct 12, 2018 10:15 am

When to apply or how to test to see if it is needed would be appreciated as the side the bias is applied seems to be a somewhat slow area.

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Re: BBC output overview.

Post by Orr89rocz » Fri Oct 12, 2018 12:20 pm

Do you have pitot tube readings on these port bias designs? Curious what the air speed gradients are within the port on the bench.

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Re: BBC output overview.

Post by David Vizard » Fri Oct 12, 2018 1:12 pm

Orr89rocz wrote:
Fri Oct 12, 2018 12:20 pm
Do you have pitot tube readings on these port bias designs? Curious what the air speed gradients are within the port on the bench.
Yes - and smoke tests - we will get to that down the road a while.
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Re: BBC output overview.

Post by David Vizard » Fri Oct 12, 2018 2:44 pm

OK here is where I am on the 21-1/2 degree Edelbrock street heads. I like these heads because they start life with a chamber of about 90 cc and this allows for a more effective chamber as there is metal in places that it's needed as apposed to that of the 115 cc chamber of the regular 24 degree heads.

I almost always start work on a new port by doing an effective valve seat job. What you see in the first photo is the seat applied to the radius. The seat is 0.055 and sits on the radius base form with approx 10 Degrees angle between the radius and the seat. I prefer cutting the seats in two ops. First the radius is cut and the machining of that radius is polished with a simple seat polisher that I made up.

After the seat is cut I go in and polish the entire seat with my finishing tool which centers on the guide and uses 400 grit emery as shown in the lower photo. Doing the seat in two ops with the actual seat the final move results in a more accurate seat with any form tool seat machine as apposed to a single point machine.

It's hard to see but it is possible to get on idea of what about an 1/8 inch biases looks like in that second shot.

Some of you have made the point that the cylinder wall side is often the slow moving wall. Smoke traces have shown the this is due to'spill' off the roof of the port as it passes the guide and moves toward the cylinder wall side of the port. This fast flow tends to run into the flow coming from the cylinder wall side and as a result slows that side down. The more this is minimized the greater the high lift flow becomes without any real losses at lower lifts.
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Re: BBC output overview.

Post by PRH » Fri Oct 12, 2018 3:05 pm

Just to be clear, what is the part number of the Edelbrock head you’re working with here?
Somewhat handy with a die grinder.

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Re: BBC output overview.

Post by David Vizard » Fri Oct 12, 2018 5:11 pm

Just got on to Edelbrock's site to find the part# of that head.

What a deal - they have changed it for the worse when it's a question of finding out what you have got/need. All I can tell you is what is on the ends of the heads - Performer 100 cc.

That should identify it if you call Edelbrock. As for finding it in their catalog - best of luck.
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Re: BBC output overview.

Post by stokerboats » Fri Oct 12, 2018 5:32 pm

Original performer 100cc oval was their "high compression" head
Roger H ported a pair of these for me years ago if this is indeed the same head.
That p/n was 6048 and no longer exists.

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Re: BBC output overview.

Post by PRH » Fri Oct 12, 2018 5:38 pm

There are two bbc bare heads with 100cc chambers offered.
The Performer(60489) and Performer RPM(60429).
Both are of the small square-ish “oval port” variety.
I haven’t had any of those in my shop in quite a while, but I believe the difference is the std Performer has a drilled heat crossover passage, and the RPM doesn’t.
Somewhat handy with a die grinder.

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