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Re: 548 CI BBC Advice

Posted: Mon Mar 27, 2017 8:31 pm
by MadBill
David Vizard wrote:Joe,
Take a look at this test from the 572 thread. The 107 cam had slightly less duration than the 112 but look at the torque difference at 3300 rpm - it was almost 60 lbs-ft up.
The curves are noticeably smoother with the DV cam... :-k

Re: 548 CI BBC Advice

Posted: Mon Mar 27, 2017 10:56 pm
by David Vizard
OK Let's get back to those Edelbrock heads on this 565 incher. Take a look at the intake flow of the heads I ported for the GM 572 project posted else where.

The Performer heads are the thick blue line and the DV ported AFR's the thin line. At first sight it looks like the AFR's flow curve just disappears of the top of the chart into space but the reality is I drew these charts on a .700 lift scale before I realized I needed at least 0.800 to show where the AFR topped out. At about 800 the curve leveled out here - the flow was 404 cfm. Max flow was 409 at 900 lift.

As you can seefrom the gragh the Edelbrock Performer, almost tracked the AFR's over much of the lift. But in many respects the true difference as seen by the engine can be much more than we are perceiving here. Sure those big high lift flow numbers are an obvious asset to the breathing capability of the cylinder but that, contrary to what may seem logic, has minimal to do with affecting the poptimal LCA. To see how the cylinder is far more affected by the low lift flow the valves have we need to look at a graph of the flow per sq inch of the CD.
That is what we will do tomorrow.
DV

Re: 548 CI BBC Advice

Posted: Mon Mar 27, 2017 11:03 pm
by TBART1970
David Vizard wrote:OK Let's get back to those Edelbrock heads on this 565 incher. Take a look at the intake flow of the heads I ported for the GM 572 project posted else where.

The Performer heads are the thick blue line and the DV ported AFR's the thin line. At first sight it looks like the AFR's flow curve just disappears of the top of the chart into space but the reality is I drew these charts on a .700 lift scale before I realized I needed at least 0.800 to show where the AFR topped out. At about 800 the curve leveled out here - the flow was 404 cfm. Max flow was 409 at 900 lift.

As you can seefrom the gragh the Edelbrock Performer, almost tracked the AFR's over much of the lift. But in many respects the true difference as seen by the engine can be much more than we are perceiving here. Sure those big high lift flow numbers are an obvious asset to the breathing capability of the cylinder but that, contrary to what may seem logic, has minimal to do with affecting the poptimal LCA. To see how the cylinder is far more affected by the low lift flow the valves have we need to look at a graph of the flow per sq inch of the CD.
That is what we will do tomorrow.
DV
548 cu inch
4.600 bore 4.125 stroke

Re: 548 CI BBC Advice

Posted: Mon Mar 27, 2017 11:23 pm
by David Vizard
TBART1970 wrote:
David Vizard wrote:OK Let's get back to those Edelbrock heads on this 565 incher. Take a look at the intake flow of the heads I ported for the GM 572 project posted else where.

The Performer heads are the thick blue line and the DV ported AFR's the thin line. At first sight it looks like the AFR's flow curve just disappears of the top of the chart into space but the reality is I drew these charts on a .700 lift scale before I realized I needed at least 0.800 to show where the AFR topped out. At about 800 the curve leveled out here - the flow was 404 cfm. Max flow was 409 at 900 lift.

As you can seefrom the gragh the Edelbrock Performer, almost tracked the AFR's over much of the lift. But in many respects the true difference as seen by the engine can be much more than we are perceiving here. Sure those big high lift flow numbers are an obvious asset to the breathing capability of the cylinder but that, contrary to what may seem logic, has minimal to do with affecting the poptimal LCA. To see how the cylinder is far more affected by the low lift flow the valves have we need to look at a graph of the flow per sq inch of the CD.
That is what we will do tomorrow.
DV
548 cu inch
4.600 bore 4.125 stroke
finally the right #'s!
DV

Re: 548 CI BBC Advice

Posted: Tue Mar 28, 2017 6:48 am
by TBART1970
All stated in first post and in line one.
.

Re: 548 CI BBC Advice

Posted: Tue Mar 28, 2017 9:22 am
by cstraub
This things does not need cams thrown at it ......it needs the issues that it has fixed. The oil contamination being the number 1. It seems that the distributor gear issue has been addressed.

Re: 548 CI BBC Advice

Posted: Tue Mar 28, 2017 1:59 pm
by Newold1
I agree, this engine had some mechanical issues that probably affected time for adjustments and fine tuning but it achieved a result that was maybe just a little short of the OP's original expectation. The OP came on here asking for a little advise on camming, not asking for a pick a part of the entire build. Obviously per Mr. Vizard's concise and proven methods somethings could have been improved with ideal parts and rework but this OP is not looking for that at this point and he is just trying to get back to the dyno with some cam change and optimize what he has. Let's not over critique or analyse this situation here. I think all of us should just convey the idea to all new members here on Speedtalk that they should use and listen to good knowlgeable peers here and that the time to collect information and discuss choices and expectations is before they start choosing and buying parts and building their engines!!

I'll say it again " plan your work and then work your plan!"

Re: 548 CI BBC Advice

Posted: Tue Mar 28, 2017 7:19 pm
by TBART1970
Thanks.

Re: 548 CI BBC Advice

Posted: Tue Mar 28, 2017 9:50 pm
by raynorshine
David Vizard wrote: BBC LCA formula:- LCA = 133.5 –((cylinder displacement in CI/intake valve diameter) x 0.91)

Cylinder displacement is of course for one cylinder.

Guys - notice I took the advice to put in the extra brackets into the formula to make clearer the order in which to do the calcs.
Should have done that first time around!!

DV
David, does this formula work for SBC's? or is there another formula?

Re: 548 CI BBC Advice

Posted: Tue Mar 28, 2017 10:19 pm
by wyrmrider
there is another formula and a couple of very long threads to go with it

Re: 548 CI BBC Advice

Posted: Tue Mar 28, 2017 10:35 pm
by statsystems
raynorshine wrote:
David Vizard wrote: BBC LCA formula:- LCA = 133.5 –((cylinder displacement in CI/intake valve diameter) x 0.91)

Cylinder displacement is of course for one cylinder.

Guys - notice I took the advice to put in the extra brackets into the formula to make clearer the order in which to do the calcs.
Should have done that first time around!!

DV
David, does this formula work for SBC's? or is there another formula?

The 133.5 is for canted valve heads. 128 is for inline valve heads. The equation stays the same other than that. IIRC there is also some corrections made for CR and maybe some other stuff but that doesn't change the formula.

I'm sure DV will correct this if I'm wrong.

Re: 548 CI BBC Advice

Posted: Tue Mar 28, 2017 11:10 pm
by digger
What about hemi ?

Re: 548 CI BBC Advice

Posted: Wed Mar 29, 2017 12:35 am
by statsystems
digger wrote:What about hemi ?
IDK...guess DV will need to chime in.

Re: 548 CI BBC Advice

Posted: Wed Mar 29, 2017 8:44 am
by MadBill
When I threw a dart at the board, it hit '135' as the magic number...

Re: 548 CI BBC Advice

Posted: Wed Mar 29, 2017 9:16 am
by cstraub
With the oiling issues this thing has the dyno sheet is a mute point. A unhealthy engine is not going to make power potential. The focus needs to be on diagnosing the issues the engine has so the OP can get them corrected and move forward. At that point he can decided on who's cam he wants, but for now we have an engine with oiling issues.