BBC output overview.

General engine tech -- Drag Racing to Circle Track

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David Vizard
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Re: BBC output overview.

Post by David Vizard » Wed Oct 03, 2018 4:03 pm

Zmechanic wrote:
Wed Oct 03, 2018 3:43 pm
Been mulling this over more. In the context of port bias, that runner entry makes more sense now. And the lack of velocity gradients does too. It's almost like a way to trick the port into behaving as though it were biased and canted over like a DRCE port.
I guess that is sort of one way of looking at it.
DV
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Re: BBC output overview.

Post by Frankshaft » Wed Oct 03, 2018 4:07 pm

David Vizard wrote:
Wed Oct 03, 2018 2:52 pm
Orr89rocz wrote:
Wed Oct 03, 2018 2:31 pm
How did the power on dyno or track respond to the increased bias as you call it? Very interesting
Our engines were so often the ones too beat. On the drag strip my daughters 1380 mini was totally untouchable by any size NA mini. She shut down all pro built mini's and on one occasion this included the factory's 8 port aluminum headed, fuel injected, titanium rodded so call super mini by such a big margin in qualifying that the pro driver driving it refused to to race her in the afternoon.

I don't know if this exactly answers your question but whatever was being done was beating the other guys.
DV
So, I am assuming the mini Cooper had a BBC in it? Or am I confused?

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Re: BBC output overview.

Post by GARY C » Wed Oct 03, 2018 4:27 pm

Frankshaft wrote:
Wed Oct 03, 2018 4:07 pm
David Vizard wrote:
Wed Oct 03, 2018 2:52 pm
Orr89rocz wrote:
Wed Oct 03, 2018 2:31 pm
How did the power on dyno or track respond to the increased bias as you call it? Very interesting
Our engines were so often the ones too beat. On the drag strip my daughters 1380 mini was totally untouchable by any size NA mini. She shut down all pro built mini's and on one occasion this included the factory's 8 port aluminum headed, fuel injected, titanium rodded so call super mini by such a big margin in qualifying that the pro driver driving it refused to to race her in the afternoon.

I don't know if this exactly answers your question but whatever was being done was beating the other guys.
DV
So, I am assuming the mini Cooper had a BBC in it? Or am I confused?
The context of that post was 2 posts before it.
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Re: BBC output overview.

Post by Frankshaft » Wed Oct 03, 2018 4:36 pm

GARY C wrote:
Wed Oct 03, 2018 4:27 pm
Frankshaft wrote:
Wed Oct 03, 2018 4:07 pm
David Vizard wrote:
Wed Oct 03, 2018 2:52 pm


Our engines were so often the ones too beat. On the drag strip my daughters 1380 mini was totally untouchable by any size NA mini. She shut down all pro built mini's and on one occasion this included the factory's 8 port aluminum headed, fuel injected, titanium rodded so call super mini by such a big margin in qualifying that the pro driver driving it refused to to race her in the afternoon.

I don't know if this exactly answers your question but whatever was being done was beating the other guys.
DV
So, I am assuming the mini Cooper had a BBC in it? Or am I confused?
The context of that post was 2 posts before it.
No. The thread is about big block Chevies. Not mini coopers. I am sorry to be a smart ass, but what does it have to do with anything related to this thread? It tells me, he has no experience in the real world with it. Or, he would have given a story relating to the thread, no? Or am I the only one that sees it that way.

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Re: BBC output overview.

Post by Kevin Johnson » Wed Oct 03, 2018 7:17 pm

Frankshaft wrote:
Wed Oct 03, 2018 4:36 pm
...
No. The thread is about big block Chevies. Not mini coopers. I am sorry to be a smart ass, but what does it have to do with anything related to this thread? It tells me, he has no experience in the real world with it. Or, he would have given a story relating to the thread, no? Or am I the only one that sees it that way.
He is relating both a relevant story about engine development and tuning as well as a wonderful memory of his daughter.

Moving on...

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Re: BBC output overview.

Post by Kevin Johnson » Wed Oct 03, 2018 7:21 pm

David,

I am curious if you have had any opportunity to measure the stability of the main caps during dyno testing of the BBC? Another member mentioned that you had rigged an engine with extended studs (?) passing through the oil pan of a different (?) motor to measure this.

Thanks!

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Re: BBC output overview.

Post by GARY C » Wed Oct 03, 2018 7:39 pm

Frankshaft wrote:
Wed Oct 03, 2018 4:36 pm
GARY C wrote:
Wed Oct 03, 2018 4:27 pm
Frankshaft wrote:
Wed Oct 03, 2018 4:07 pm


So, I am assuming the mini Cooper had a BBC in it? Or am I confused?
The context of that post was 2 posts before it.
No. The thread is about big block Chevies. Not mini coopers. I am sorry to be a smart ass, but what does it have to do with anything related to this thread? It tells me, he has no experience in the real world with it. Or, he would have given a story relating to the thread, no? Or am I the only one that sees it that way.
It seems so.

The post that led to this. The context is in regard to port bias!
I believe I had got started on the subject of port bias and the inflection point in the CD at 0.250 valve lift. The point I was about to address is that understanding how port bias can factor in here can be instrumental toward achieving high lift flow efficiency. In fact bias can be he key ingredient for making even the worst ex. port flow efficiently.

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.

Just so you are able to appreciate the magnitude of this that is about as good as cup car heads were some 20 years ago and blows the typical well ported aftermarket performance head into the weeds.

About 15 years ago I had an aftermarket aluminum SBF head to port and the exhaust did not respond until I applied a hefty amount of bias to it. Will look for a shot of such as soon as I can spare a little more time.
DV

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Re: BBC output overview.

Post by Geoff2 » Thu Oct 04, 2018 5:22 am

Frankshaft,

Yes it was a BBC, a 1380cc mini BBC. Happy now?

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Re: BBC output overview.

Post by Frankshaft » Thu Oct 04, 2018 11:01 am

Geoff2 wrote:
Thu Oct 04, 2018 5:22 am
Frankshaft,

Yes it was a BBC, a 1380cc mini BBC. Happy now?
Ok, glad you cleared that up.

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Re: BBC output overview.

Post by David Vizard » Thu Oct 04, 2018 5:51 pm

Now that I have pointed out how effective port bias can be on one of the worlds worst exhaust ports ('A series Mini Cooper engine)lets see what it's worth with a some of the various patterns of BBC exhaust ports.

Take a look at the port molds below. All the ports have been reworked to one extent or another.
Starting right to left is the port from a World casting featuring an intake port of about 325 cc. The exhaust port had a cursory clean up and a good valve job done on it. As such the port expanded a little as it went around the guide boss but other than that had no discernible bias. At 700 lift it was good for some 274 cfm and 280 at 1.000 lift. The port form shown here is how it looked after having about 3/32 of bias added to the cylinder wall side of the port. The Cylinder wall side BTW is the RHS of all of these molds. Initially this port with its minimal bias and a the valve seat job the flow (and consequently the discharge co-efficient) was good up until the 0.25D inflection point lift of 0.470. After that the efficiency stayed almost flat IE almost no increase in flow. After adding the 3/32 of bias the flow at 0.700 crept up to 278 but the flow at 1.000 inch lift rose from 280 to 303 cfm. The price paid for that was an increase in port volume of about 3 cc (total as shown 136 cc).

The center port mold was from the big port Edelbrock that 'MT Engines' made the point that, assuming you have the porting skill, will produce some stellar results. This casting has a raised exhaust port (about 1/2 inch) so, theoretically at least, it has the potential for more flow than a stock location port. As shown in the photo this port with some added bias (again about 3/32) went from the low 290's at 1 inch lift to 309 cfm. I am sure there is more in this port (Comment please MT) but I had to drop tests on this for a paying job which is the next example here.

The port on the far left is the one I developed for the 'Weird port' Dart head shown in my first post. It has about 3/32 bias and is cut much deeper at the side of the guide as indicated by my finger. This caters much better for the bulk flow which exits the cylinder from a point about in the center of the cylinder.With the trick valve seat job the flow at 0.700 was 318 cfm and at 1.000 inch a whopping 341 cfm.

I will post the curves on this next time around.
DV
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Re: BBC output overview.

Post by David Vizard » Thu Oct 04, 2018 6:19 pm

Kevin Johnson wrote:
Wed Oct 03, 2018 7:21 pm
David,

I am curious if you have had any opportunity to measure the stability of the main caps during dyno testing of the BBC? Another member mentioned that you had rigged an engine with extended studs (?) passing through the oil pan of a different (?) motor to measure this.

Thanks!
Kevin,

You have been incorrectly informed here as what you were told was out of context.

Let know if you need more info on this.
DV
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Re: BBC output overview.

Post by GARY C » Thu Oct 04, 2018 6:32 pm

I started to ask last night if you made molds and then decided not to post because I figured you were to busy to do so and didn't want you to stay up all night and miss your beauty sleep. :)

Glad to see those.
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Re: BBC output overview.

Post by digger » Fri Oct 05, 2018 3:50 am

how do you deal with the exhaust pressure being much greater than what it is on the flow bench? the data ive seen suggests the exhaust discharge coefficient is quite dependent on the pressure ratio, the effect becomes more apparent as L/D increases

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Re: BBC output overview.

Post by novadude » Fri Oct 05, 2018 8:25 am

David Vizard wrote:
Sat Sep 29, 2018 10:49 am
It does but the effect is very small in the case of the BBC. The classic BBC 'porcupine' head is not an optimum design. GM would have done better by just scaling up a SBC head.
DV
Very interesting statement. So all of the canted valve, semi-hemi, porcupine claims of greatly increased breathing and less shrouding was all Chevrolet marketing fluff? Is this true of even the "good" intake ports on the Mark IV head?

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Re: BBC output overview.

Post by Erland Cox » Fri Oct 05, 2018 3:28 pm

David! This is a really interesting thread. Thank you!
I have made flow bench gains on the exhaust by not taking the chamber up so much on the SSR side,
by cutting more under the seat on the SSR side and by having the area decrease over the short turn on the exhaust side.
How does the area change through your port?
Jon Schmidt did a terrific work at running my Volvo exhaust port in CFD at different depressions.
Big difference between flow bench pressure and higher pressures.


viewtopic.php?f=15&t=30828&start=90

Erland

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