BBC output overview - chapter 2

General engine tech -- Drag Racing to Circle Track

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woodaca3680
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Re: BBC output overview - chapter 2

Post by woodaca3680 » Fri Oct 26, 2018 4:13 pm

i guess,i misread sorry

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Re: BBC output overview - chapter 2

Post by David Vizard » Fri Oct 26, 2018 8:22 pm

woodaca3680 wrote:
Fri Oct 26, 2018 4:13 pm
i guess,i misread sorry
Yeh well I've done that too.
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Re: BBC output overview - chapter 2

Post by WPH » Sun Oct 28, 2018 1:14 pm

OK now lets take a look at what we have here.

If you refer to the text books that we had back when I was a student you will find that it was commonly quoted by such folk as Taylor,Ricardo, Hayward,Etc (in other words some of the greats in engine science), that peak power occurred at 300 ft/sec and peak torque 240 ft/sec. Well for their day (1940's to maybe 1960's) these were good numbers to go with for a typical 2 valve engine of the day.

AS it happens they are not too far off what we see for the mean velocity in a typical modern 2 valve engine. As you can imagine many factors conspire to inch this 'magic number up somewhat. Cutting the engines internal friction and parasitic losses are one such factor. The amount of internal losses on a 1960 race engine and what we see now even for a serious street motor are night and day. However there is one factor that has brought up the peak power port velocity of the modern 2 valve engine dramatically and that is the flow bench.

When Stan and I wrote the IOP flow bench program we needed to categorize the velocity so that it applied to what happened in the real world. That proved a whole lot simpler that might be expected. What you see in the graph is a curve that can be used to establish if the port is too big, too small or just right.

For the best combination of flow and velocity our test head needs to have between 300 and about 330 ft.sec to get the best balance between flow and velocity. As you can see the small port head has almost 300 ft/sec at full lift. Pretty good but still not quite good enough.

Let's assume that we have enlarged port area at the smallest cross section and the resulting velocity drop is 6% from 332fps to 313fps. Would you see a similar drop, smaller drop or no change in flow bench reading if the port was on the "sweet spot" regarding area vs. flow ?

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Re: BBC output overview - chapter 2

Post by SchmidtMotorWorks » Sun Oct 28, 2018 8:43 pm

The images below show velocity distribution on the following cases:
1. An open port
2. The same port with a left turning manifold and a right turning manifold (view trimmed to the head opening)
3. The left turning manifold
The distribution of velocity at the opening of an intake port is determined by the manifold.
port_velocity.jpg
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Re: BBC output overview - chapter 2

Post by digger » Sun Oct 28, 2018 9:48 pm

So each cylinders port should be ported/shaped differently based on the manifold runner upstream and how it biases the flow to the left, right, top or bottom ? In effect each should be different

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Re: BBC output overview - chapter 2

Post by SchmidtMotorWorks » Sun Oct 28, 2018 10:05 pm

digger wrote:
Sun Oct 28, 2018 9:48 pm
So each cylinders port should be ported/shaped differently based on the manifold runner upstream and how it biases the flow to the left, right, top or bottom ? In effect each should be different
Given the limitations of existing castings and the small opportunities for change/improvement in that area, there are better things to do with our time.

If you have the opportunity to develop and head and manifold together, you might find some small improvements, but the market for an exclusive head+manifold combination has a very long break-even point.
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Re: BBC output overview - chapter 2

Post by GARY C » Sun Oct 28, 2018 10:12 pm

SchmidtMotorWorks wrote:
Sun Oct 28, 2018 10:05 pm
digger wrote:
Sun Oct 28, 2018 9:48 pm
So each cylinders port should be ported/shaped differently based on the manifold runner upstream and how it biases the flow to the left, right, top or bottom ? In effect each should be different
Given the limitations of existing castings and the small opportunities for change/improvement in that area, there are better things to do with our time.

If you have the opportunity to develop and head and manifold together, you might find some small improvements, but the market for an exclusive head+manifold combination has a very long break-even point.
Yes, in DV's Intake book (out of print I believe) he wrote about this in regards to an SBC and the different approach to porting the inside runner vs the out side runner.
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Re: BBC output overview - chapter 2

Post by MadBill » Sun Oct 28, 2018 10:14 pm

I think I recall reading that some/all current NASCAR engines have port orientation optimized for their single 4 bbl. manifolds.
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Re: BBC output overview - chapter 2

Post by cjperformance » Sun Oct 28, 2018 10:18 pm

MadBill wrote:
Sun Oct 28, 2018 10:14 pm
I think I recall reading that some/all current NASCAR engines have port orientation optimized for their single 4 bbl. manifolds.
Was it the SB2 head that was 1st to do that? I coukd well be wrong..
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Re: BBC output overview - chapter 2

Post by Kevin Johnson » Mon Oct 29, 2018 7:28 am

MadBill wrote:
Sun Oct 28, 2018 10:14 pm
I think I recall reading that some/all current NASCAR engines have port orientation optimized for their single 4 bbl. manifolds.
https://www.hotrod.com/articles/small-b ... ar-engine/

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Re: BBC output overview - chapter 2

Post by Carnut1 » Tue Nov 06, 2018 8:55 am

1031181847.jpg
DV asked if I could give an update on this thread. Rough week last week and seminar. This week dyno testing at Terry's, small block ford cylinder head shootout. I am very excited to get some dyno experience from DV! Thanks, Charlie
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Re: BBC output overview - chapter 2

Post by RevTheory » Tue Nov 06, 2018 9:22 am

I'll just have to live vicariously through you until January. I'll show up with Sangria and the fixins for rum and cokes :D

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Re: BBC output overview - chapter 2

Post by David Vizard » Mon Nov 26, 2018 1:49 am

I will be showing my new 21.5 degree BBC head based on the small chamber Edelbrock casting at PRI. Here is a quick look at what you can see.

First why the use the angle milled 100 cc chamber street head? The intent here was to produce the ultimate street head for build in the 468 to 540 CID range. for an 87 octane burning street BBC there is always the problem of the chamber size being such as to require a large dome to get the CR into that sweet spot that BBC seem to like. by the time I had the chamber just about optimum for output even the starting point of 100 cc was still too big.
After carving it all out and minimally refacing it the chamber was still 115 cc. If I had used a conventional 24 degree head the chambers would have been in the 133 cc range. Not good unless there is 700 inches to feed.

Also the port design (intake and Exhaust) was done keeping a close check on the port energy. This tended too produce a port that has a bigger bowl being fed by a smaller CSA runner. Even on a 9.7/1 motor this concept of intake port managed to better 1.4 lbs-ft per cube.

The wet flow properties of the port were also studied. Take a look at the 'tail' emanating up from the side of the guide. this helped flow as well as breaking up more fuel prior to entry into the cylinder.

The chamber shape used is slightly different between the good and bad ports. The goal here was to minimize shrouding for the best airflow. since the air flow pattern was different on each of these ports it necessitated a design that complimented it. Also exhaust seats and the chamber closes to the wall along side of the exhaust was cut to favor super sonic flow close to and at the valve seat. This chamber shape also favored 'late phase hyper scavenge'

Because the BBC is so under-valved a lot of effort went into the design of the seats used on both intake and ex. Here the efficiency figures led to seats showing very high flow efficiencies to the point that the 2.3 intake valve was acting as if it was about 2.45 inches in diameter. The benefits of a very efficient valve is that the LCA required on the cam can be widened. this is very critical here as too many BBC require the LCA for optimum torque to be so tight (103-106 range that cam grinders simple don't have the blank in stock for such.

In short this head design ended up with the best chamber shape and had among the smallest port for the flow of any small port head out there. This is good as the typical BBC has a too slow a port to get the best of ramming the cylinders. As a result making big torque per cube numbers for a street motor is difficult. This head addresses that problem and produces good velocity and mass flow for a strong high energy port.

Here are some shots of the chambers and bowls below.
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Re: BBC output overview - chapter 2

Post by GARY C » Mon Nov 26, 2018 2:53 am

Lots of work in that one.
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Re: BBC output overview - chapter 2

Post by rebelrouser » Mon Nov 26, 2018 11:54 am

Just a dumb question, but since we are talking about different ways to port heads with right or left turns. Does the coriolis effect, have any affect on the flow, and is it different for the guys porting down under where it would make it spin the other way?

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