BBC output overview.

[David Vizard]

doesn't the canted valves have some sort of play in this? Larger lift=less valve shroud?

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

[David Vizard]

OK you head porters out there. I have just been playing with an
Edelbrock big port head (started life at about 355-365 cc) I have ported one of each port looking only at the airflow gains with the intent to get the most that is practically possible. At this moment in time I have 452 cfm on the good port and 433 on the bad port at 1.150 valve lift. Good port vol is 384 cc and the bad 380 cc.
Valve is still 2.3.

Any comments on this before I throw in my $2 worth of thoughts?

DV

[swampbuggy]

David, looks pretty darn impressive to me ! Mark H.

[JoePorting]

doesn't the canted valves have some sort of play in this? Larger lift=less valve shroud?

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

I agree!!! I always wanted to say that but knew I'd be bitch out by all the BBC guys.

[JoePorting]

OK you head porters out there. I have just been playing with an
Edelbrock big port head (started life at about 355-365 cc) I have ported one of each port looking only at the airflow gains with the intent to get the most that is practically possible. At this moment in time I have 452 cfm on the good port and 433 on the bad port at 1.150 valve lift. Good port vol is 384 cc and the bad 380 cc.
Valve is still 2.3.

Any comments on this before I throw in my $2 worth of thoughts?

DV

I'd go to a 2.4 intake valve, maybe larger if it would fit. Even if it meant going with a smaller exhaust valve. I always thought the BBC exhaust port and valve was too big. Maybe 1.75 may have been more ideal.

[David Vizard]

Joe,

Been contemplating doing just that!

A 1.78 Ex with a 2.4 intake would give just the same space between valves.

Before Joe or I go plowing into this has anyone tried this combo?

DV

[canada1]

I was wondering when the next DV authored thread would be started and when the next DV seminars start.

[JoePorting]

Somewhat related, I took an AFR #1068 227 head with 2.10/1.60 valves and replaced the seats/valves with 2.22/1.5 valves and Picked up 30 hp even though the intake flow only went from 310 to 318. The exhaust flow must have really gone down but I forgot to test it. The intake port was increased to a Felpro 1209 (2.4 X 1.4) and the pushrod pinch was welded up.

The strange thing about those heads is that the low rpm torque between 2000 and 3000 rpm really picked up. Not sure if that's because of the larger intake or smaller exhaust valve. Probably the smaller exhaust valve.

[pdq67]

It’s been awhile since I last posted. Had some pretty major surgery in the last 3 months including a big time hip replacement for a truly destroyed hip joint. That’s what running can do for you. Between 1980 and 2000 I put on the best part of 40,000 miles of running. Did my last run just after my 70th birthday – only about 3 miles but my hip joint was sure giving me a bad time. Unfortunately I assumed it was arthritis so the fix was delayed by almost 5 years. There are a bunch of other, lesser things, but each put me further back on my work schedule. My Ford book is currently stalled as Is my Race Engine Challenge build. (got the crank & rods, heads are provisionally ported and looking really good but I don’t think it’s the end of the trail yet on heads.)

On top of that I have about 10 model heads to do for digitizing for clients that actually pay money. What with the almost certain arrival of big medical bills I am having to plow on with these model heads.
I also have a bunch of dyno tests (about 450) that are (or rather were) slated for Volume 3 of my BBC books. I will be 76 next birthday and with the stack of work on hand I think I will have to forgo the production of BBC performance Vol 3. That said I don’t like the thought of all the BBC knowledge from the tests done over the last 3 years going to waste so my plan is to start threads like this on both the generalities of hopping up a BBC as well as some of the particulars in detail Also plan to do some video’s on the subject.


So, withstanding the nath sayers, here we go.

Those who have taken the time to look at the power curves of some of the BBC I have posted will have noticed that the torque per cube figures are significantly higher than normal.
The keys to achieving this is in cam selection and head design.
Here is what needs to be taken care of as far as heads (and we are talking 24 degree one here).

• No matter which way you cut it the BBC’s cube capability far outweighs the breathing capability of even the best heads. To match a SBC’s 2.02/1.6 valve size for a 350 inch short block a 454 would need a valve combination of 2.62/2.06. The biggest valve that is usually seen in a 24 degree BBC head is 2.3 or (sometimes 2.35)
• The consequence of insufficient valve size is compounded by the fact that a 454 is readily starched to as much as 650 inches with 712 being on if you want to deal with the extra hassles involve.
• Because of the relatively shallow angle of the intake port to the valve axis we find the best output is achieved with heads that are bigger in bowl size in relation to the size of the main body of the port than is so often the case with SBC configurations.
• The result of point 3 is that we need to develop a seat and bowl combination that flows well from right off the seat to very high valve lifts, that is up to about 40 -45% of the intake valves diameter.
• Although the bowl needs to be a lager than normal volume the port feeding it needs to be the minimum size to get the job done so as to achieve the highest specific port energy. This means big ports are out and big bowls are in.

So where, in terms of head ports, does this leave us?
In simple terms It means having to cut seats that will give as high a coefficient of discharge (CD)as possible. Somehow, we must make that 2.3-inch intake valve appear to the cylinder as being much bigger than it really is. Seat design is the dominant factor to a lift value of some 18 -20% of the intake valves diameter. That works out to be 414 – 460 thousandths lift. Before 0.46 lift its all about the seat design - after that it is all about bowl and port form.
With an effective seat form established we must now make the absolute most of any high lift potential the casting being reworked may have. As far as the bowl work is concerned putting enough port bias into it will greatly help the need for good high lift flow. As far as the main body of the port is now concerned we must shape it to a form that best fills the bowl in an efficient manner.


Just for the record the best 300-320 cc port heads tried on the 572 GM update test engine wed did a couple of years back at Terry Walters shop in Roanoke was the AFR 320’s. Though down a little from the Darts flow (# 2 in our tests) they did exhibit the highest specific port energy. The shots of the head I am showing here out flowed and out energied the AFR’s by a goodly margin.

Take a look at the head shots.
Note the entrance to the port. Its shape is dictated by the #1 rule I give to my seminar attendees. IE ‘Cut the port where the air wants to go not where you think it should’.
The other shot shows the bowl shape used. It does not show very clear here but the port wall on the cylinder wall side is biased about 4 degrees inwards toward the cylinder center line. This was a big part of pumping the flow to the 420 cfm on the bad port (332 cc) and 432 (323 cc)on the good port.
Most heads with this port volume don’t make it past about 385 CFM on the same bench as used here (mine)
Also note the valve seat inserts. At this moment in time they are a full radius. The seat will be just one cut on this radius to produce a 0.060 wide seat.

Next post I will go into more detail with the flow curve illustrations and some dyno numbers.

DV

Dave,

I am now about 71.5 years old.

About the hip! Old arthritis too!! About the same time... I got to where I couldn't pack my little Grandbaby Girl around our house What, she was all of 8 pounds!!

I now have a complete Ti and plastic left hip as of Aug. 30th of last year.

I find that I can push my lawn mower as well as a grocery cart better than I can walk because I tend to, "gimp", on my left side

I ride my cheap Walmart Road Master step through bicycle that I put a Leeds electric pedal assist on all over town all the time.

You might want to get one?

https://www.e-bikerig.com/

I bought the 30K/20 mile kit and it is great!! PEDAL ASSIST!

Good luck and you will like your new hip!!

pdq67

[pdq67]

doesn't the canted valves have some sort of play in this? Larger lift=less valve shroud?

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

Or maybe kept the "W", flat head design and just made better/lighter domed pistons for it and stood the ports up right more!! Imho, the old "W" engines had zero valve shrouding unless I am missing something!

Same with Ford's old MEL engines!

pdq67

[user-17438]

OK you head porters out there. I have just been playing with an
Edelbrock big port head (started life at about 355-365 cc) I have ported one of each port looking only at the airflow gains with the intent to get the most that is practically possible. At this moment in time I have 452 cfm on the good port and 433 on the bad port at 1.150 valve lift. Good port vol is 384 cc and the bad 380 cc.
Valve is still 2.3.

Any comments on this before I throw in my $2 worth of thoughts?


DV

What head?

[pdq67]

Dave,

Would you please do an old --206 BBC head as well as the old -215 head and the way laid back open chambered smog head.

I ask this because the old -206 head and the -215 head can be used to up the CR of the old P/U Truck 454 engines.

Up from like 7.8 or do to like 9.+ CR using the old .020" thick steel shim head gaskets.

pdq67

[David Vizard]

Dave,

Would you please do an old --206 BBC head as well as the old -215 head and the way laid back open chambered smog head.

I ask this because the old -206 head and the -215 head can be used to up the CR of the old P/U Truck 454 engines.

Up from like 7.8 or do to like 9.+ CR using the old .020" thick steel shim head gaskets.

pdq67

Sorry pdq67,
I'm on a seven day week now - just can't stretch it anymore.
DV

[David Vizard]

OK you head porters out there. I have just been playing with an
Edelbrock big port head (started life at about 355-365 cc) I have ported one of each port looking only at the airflow gains with the intent to get the most that is practically possible. At this moment in time I have 452 cfm on the good port and 433 on the bad port at 1.150 valve lift. Good port vol is 384 cc and the bad 380 cc.
Valve is still 2.3.

Any comments on this before I throw in my $2 worth of thoughts?


DV

What head?

Don't have a part # - Edelbrock is still trying to identify a match would you believe!
Anyway here are some shots that might help.
DV

[David Vizard]

Just to get back on track here are the flow curves for a good port cylinder. Following the heads requirements as I outlined in the first post paid off as did lots of port mapping with flow balls and velocity probes. By paying attention to port velocity this port ended up at only 322 cc!
And , for a BBC specific port energy was really stout!

Next we will look at the discharge co-efficient and I will show how it can be used to guide the next step for modifications to the port.
DV