BBC output overview.

General engine tech -- Drag Racing to Circle Track

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gruntguru
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Re: BBC output overview.

Post by gruntguru » Fri Oct 12, 2018 5:47 pm

David Vizard wrote:
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.
DV
Ha - dirt track speedway car so traction was always an issue. Could only ever guess at the power - I always thought about 250 at the crank - enormous midrange. Engine was std stroke, 73mm bore (1370?), 10:1 CR, 30-70-75-25 cam, no intercooler, 67% methanol, 33% race gas, draw-thru one throat of a 45 DCOE. Turbo was Garrett TO4, M-2 compressor, O trim turbine, 0.3 housing.

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Re: BBC output overview.

Post by David Vizard » Fri Oct 12, 2018 7:56 pm

That's a shame if indeed Edelbrock have stopped making them - those 100 cc heads have a lot of potential.
DV
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stokerboats
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Re: BBC output overview.

Post by stokerboats » Fri Oct 12, 2018 9:18 pm

Back when Roger did mine he installed 2.250 int and 1.900 exh, as you know he was a proponent of a good exhaust port.
That particular head was rolled 1.5* prior to machining. By the time he finished, the chambers ended up at 108cc's. We had to have pistons made for them as they were non existent at that time. A company named "Golden Eagle Manufacturing" digitized the chamber and JE made a set SRP pistons for me. The heads ultimately flowed 349 Int and 298 exh@ .650 lift

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Re: BBC output overview.

Post by David Vizard » Sat Oct 13, 2018 1:06 pm

PRH wrote:
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.
PRH,

Thanks for that update.

should have some high bias ex port pics to post later today or tomorrow.
DV
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Re: BBC output overview.

Post by David Vizard » Sat Oct 13, 2018 1:50 pm

fastblackracing wrote:
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.
Sorry for the late response to a good question.about half the time the form of the original casting limits thing. The rest of the time it is a question of encouraging the air to flow in a path preferred by it and not the head porter.
DV
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Re: BBC output overview.

Post by David Vizard » Sat Oct 13, 2018 2:02 pm

Here is my current stock position BBC exhaust port.

The first pic shows the calipers set to the width at the manifold face.

The second shot shows the width at the guide boss. It does not show as well as I had hoped but the port bias here added almost a 1/4 inch to the port width.

When I have a little spare time I will mold this port but if you can't wait the
Ford ex. port I showed a few pages back is very similar.

DV
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Re: BBC output overview.

Post by cjperformance » Sat Oct 13, 2018 7:13 pm

If you flow the biased port with enough pipe attached to mimic the typical bend off of the head you will see in a vehicle, what difference do you see on the same port but with a pipe/bend mimicing LH and RH side fittment of that port.?
ie, putting the biased side of the port on the long side of the pipes radius on one side then the short side of the pipes radius on the other.
Craig.

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Re: BBC output overview.

Post by David Vizard » Sun Oct 14, 2018 10:03 am

cjperformance wrote:
Sat Oct 13, 2018 7:13 pm
If you flow the biased port with enough pipe attached to mimic the typical bend off of the head you will see in a vehicle, what difference do you see on the same port but with a pipe/bend mimicing LH and RH side fittment of that port.?
ie, putting the biased side of the port on the long side of the pipes radius on one side then the short side of the pipes radius on the other.
CJ,

Actually no I have not tested what you are proposing.

I did a very extensive amount of research on ex. port to pipe configurations when I was doing my 2 litre Pinto book so learned a lot from that. If the same trends carry through there are effects but not of any huge significance.

On the Pinto tests we did find that the form and direction of flow of the first 6 inches of header pipe did make a difference and I am thinking that the BBC falls into the same category.

I'd be interested in anyone else's comments on this.

DV
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Re: BBC output overview.

Post by swampbuggy » Sun Oct 14, 2018 10:31 am

David I believe I remember seeing NHRA Pro Stock headers coming off the port and going uphill for a few inches and then making the radius turn, doesn't that sound right. Mark H

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Re: BBC output overview.

Post by David Vizard » Sun Oct 14, 2018 11:06 am

First shot is the exhaust seat just cut. It is right on 0.060 wide.

The next op is to polish the seat and very finely blend it to the radius before and after the actual seat.

On both ports (second photo) the chamber side rad is slightly smaller than the under seat radius.

The under seat rad, especially on the intake, also changes as we go around the seat. This has to be done with a steady hand. the rad on the short side turn is smaller. This has no measurable effect on low and mid range intake flow but does add a few cfm at lifts from about 0.700 or so up.

You will have to look very carefully to see the actual seats here as they are at the limit of discern-ability.


Here is where I want to pose the next question:- how do we now when he port bias flow increases all done without having to go too far with the metal removal?
That is the question that is in the back of the mind of just about every porter.

Fortunaly there is a way to reach optimum without scrapping the head.

If we look at a graph of the discharge co-efficients from the inflection point on up and the port energy we will get a pretty clear indication of when enough is enough. Next post - the hard core port tech stuff.

DV
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Re: BBC output overview.

Post by RevTheory » Sun Oct 14, 2018 12:07 pm

Well, those are the prettiest damn seats I've seen. I'm guessing you've got the "fuel shear" argument addressed- perhaps forthcoming?

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Re: BBC output overview.

Post by Carnut1 » Sun Oct 14, 2018 12:11 pm

I was waiting for that Rev.
Servedio Cylinder Head Development
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Re: BBC output overview.

Post by David Vizard » Sun Oct 14, 2018 12:17 pm

Result time.

Here are some results with a BBC port. As for the head used I cannot remember. All I can say is the the casting was selected because any pot bias was absent so the tests started at no bias and went to about 0.200 bias.

Most BBC ports have, whether by intent or otherwise, a small amount of bias and the flow, when the port is given a simple 'skinny the guide boss and clean up the rest of the port' treatment tends to flow, on average, about 285 cfm max.

As can be seen the bias is a high lift flow enhancement tool.

It's effect on the engine is to cut the pumping losses seen as the piston comes up the bore on the exhaust stroke.

A port like this is especially good for N2O applications.

Next we will look at the discharge coefficient of this exhaust port to see how the bias plays into determining what to do next.

DV
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Re: BBC output overview.

Post by midnightbluS10 » Sun Oct 14, 2018 1:02 pm

Those aren't 7740 heads from Edelbrock? You can see 70% of the first 7 and 740 in one of the pics at the bottom of page 2. :?:

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Re: BBC output overview.

Post by Erland Cox » Sun Oct 14, 2018 4:10 pm

David, I asked before if the bias made the area larger before the SSR.
Bowl area larger than are over the SSR?

Erland

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