[Jay S]

Maybe I have this wrong Murf, maybe you have more than one cam in mind. The cam I thought you might want the 2.19s in had a bigger E/I split. I thought it was something like 230@.050” on the intake and 244@.050” on the exhaust with a 112LSA, comp XFI xe lobes, not 236/242.

The valve shrouding does look like a concern, I was thinking the bigger 2.19 valve might scavenge better with that big split on the other cam. Was my original thinking though, I had a different cam in mind than the one you listed at the top of this thread.

[slowbird]

Personally i think 2.19 is a good size to go with on a 4.18+ bore

[Murf]

IDK Jay. I ask you so many questions, I probably got you confused. 😁

So it sounds as though the larger valve is a no go. I will never have enough motor to warrant it.

Thanks to all for info!

Murf

[steve25]

Murf, if you want to take maximum advantage of scavenging then number 1, you need to run headers with a merge collector ( expensive) and 2nd, run a open exh with straight pipe length of between 15 to 18” off of the collector.

Also adding to that said above is the fact that your cam is not big enough to take good advantage of Exh scavenging .

What you can to do to help maximized any
scavenging effect that might take place is to reduce reversion .
A good start to this is keeping your 2.11” valve and making sure that your exh port outlets are smaller then the header tubes they are feeding / dumping into.

This type of arrangement restrict’s back pressure from the closed exh system from delaying and contaminating new intake flow, but does allow any vacuum ( negative pulse) that might be made to get into the chamber a kick off a early start to intake flow during the overlap period.

[slowbird]

Originally Posted by steve25

Murf, if you want to take maximum advantage of scavenging then number 1, you need to run headers with a merge collector ( expensive) and 2nd, run a open exh with straight pipe length of between 15 to 18” off of the collector.

Also adding to that said above is the fact that your cam is not big enough to take good advantage of Exh scavenging .

What you can to do to help maximized any
scavenging effect that might take place is to reduce reversion .
A good start to this is keeping your 2.11” valve and making sure that your exh port outlets are smaller then the header tubes they are feeding / dumping into.

This type of arrangement restrict’s back pressure from the closed exh system from delaying and contaminating new intake flow, but does allow any vacuum ( negative pulse) that might be made to get into the chamber a kick off a early start to intake flow during the overlap period.

Cam timing is absolutely the best way to control how scavenging. The rest is just band-aids

[steve25]

You mean like I posted in my second paragraph I would assume!

[Steve C.]

From the paperwork supplied with Edelbrock PERFORMER RPM ALUMINUM CYLINDER HEADS........

"Any header or manifold designed for Ram Air IV
heads will fit the Edelbrock Pontiac Cylinder Heads. Exhaust ports are
CNC-profiled to a high-flow “D” shape. However, Edelbrock #7281 or
Fel-Pro #1436 round exhaust gaskets are recommended for this
application. Do not change size or shape of exhaust ports in heads!"

I would presume this applies to the Speedmaster heads regarding changing the shape of the exhaust ports.

This said, while not changing their port exit shape I was told the fellow that has done my sets of Edelbrock cylinder heads did do some minor internal massaging of the exhaust ports, thus increasing their cfm flow slightly on the bench.
However please note I'm just passing this tid bit on and not here to recommend any changes to the exhaust ports.

.

[PAUL K]

We're currently working on a factory block, pump gas engine using standard pushrod location Edelbrock Performer RPM heads with a 2.11 valve. These are the flow numbers:

.100 79
.200 152
.300 217
.400 264
.500 304
.550 333
.600 338
.650 342
.700 344

It's a relatively small but efficient port.

[Steve C.]

As typical, great job Paul ! What I like about those heads are the numbers at .600" lift.

Most of the time numbers are touted at .700" lift, yet as pointed out often the cams used do not provide that type of lift.
Example even many of the hydraulic roller cam lobes, even with a 1.65 rocker ratio.
The bigger hyd roller lobe lift examples being the Comp QXI lobes with .3990" lobe lift and their Xtreme Marine has .3800" lobe lift.

Vizard is a big proponent of valve lift and points out a typical 2-valve ported cylinder head responds to valve lift without a sacrifice of idle and low speed qualities.
So is Tilden Technologies:

"Once the four timing parameters are established, the cam should be designed for maximum lift."



.

[steve25]

Nice work Paul!

[pastry_chef]

Originally Posted by Steve C.

So is Tilden Technologies:

"Once the four timing parameters are established, the cam should be designed for maximum lift."

I disagree with that blanket statement.

The problem with that is.. if you increase the valve lift and the engine responds with a positive increase in mass flow, the pressure differential at the intake closing will be different. There can be cases where the resulting higher cylinder pressure will require earlier intake closing.

It makes perfect sense to me.. I also see it in Rick Jones program and in Dynomation.

Same with the exhaust side also.

https://forums.maxperformanceinc.com...95&postcount=4

from Mike Jones - jonescams.com

The exhaust valve lift curve has two main jobs. To evacuate the cylinder, and to cause a pressure below the intake valve that is less then the pressure above the intake valve during overlap. Too much valve lift area before BDC will hurt power. Too much area between BDC and beginning of overlap will reduce the pull on the intake during overlap. Not enough area between BDC and the beginning of overlap will cause the pressure under the intake valve to be higher than the pressure above the intake valve.

The opening and closing points may be the same, but one application may need less exhaust lift area during overlap, to keep the velocity up over the valve seat.

Jones on intake closing.

Pressure differential is everything. No pressure differential, no flow.
It's like filling up a water balloon, do you want to use a 5 gal bucket, or a high pressure garden hose ? Both
will fully fill the balloon.
After BDC, the piston is increasing the pressure in the cylinder, so you need to keep lowering the valve lift to
keep the pressure on the port side of the valve seat higher then the cylinder pressure. The longer you can do
that, the more mass you will force into the cylinder.

Years ago I looked at sites like Tilden Technologies,, thought they had the answers. today I know they don't. Mike Jones is hands down the BEST online web resource for valve timing knowledge.

[Steve C.]

Thanks Mike, however way above my pay grade

I've just have the general understanding to put the valve lift up into the realm of the cylinder heads in use as best as I could. My 'simple' understanding the engine wants all the lift it can provided it's mechanically achievable or not prohibitive because of costs limitations, example like maybe going to a roller cam set up over a flat tappet cam. Some sacrifice maybe necessary.

Or like changing lobes with a flat tappet cam. Example the infamous Crower 60619 cam with .470 lift. Bullet has a lobe with the same 231 degrees at .050 but with .493 lift.


.

[PAUL K]

Originally Posted by pastry_chef

Years ago I looked at sites like Tilden Technologies,, thought they had the answers. today I know they don't. Mike Jones is hands down the BEST online web resource for valve timing knowledge.

Would DV be the best "literature" resource we have for valve timing?

[Steve C.]

And another from Tilden Technologies:

"A quick opening and closing cam will provide better low end performance than one that is slower opening."

I know Harold Brookshire has good information related.


“The problem is, if you are something of a novice at this engine business, just about everything to do with cams and valvetrains looks complex, and the truth is, it's that and more.
If cam and valvetrain design at the top level is in your future, you had better think in terms of a Ph.D. in mechanical engineering.”
David Vizard

https://www.svtperformance.com/threa...beyond.664268/

Years ago I had lunch with David Vizard after visiting his shop ( he flow tested one of my cylinder heads), Jerry Goodale was at the table as well. I listened to David intensively, kept my mouth shut and paid the bill

[pastry_chef]

Originally Posted by PAUL K

Would DV be the best "literature" resource we have for valve timing?

Probably true, not many others out there, slim picking.

This Vizard book is a great one. May have SBC in the title but much info is applicable to other brands.

How to Build and Modify Chevrolet Small-Block V-8 Camshafts and Valves – November 13, 1992
ISBN-10 ‏ : ‎ 0879385952
------
It likely could use a revision with new tech over the last 19 plus years.

Four-Stroke Performance Tuning by A. Graham Bell is decent but I never found good correlation to some of the equations in there. If I ever get inspired to do so I might be able to modify stuff there to work better today.

[Steve C.]

From that sight I linked above with camshaft information....

"Vizard writes the best camshaft articles available."


.

[pastry_chef]

https://www.svtperformance.com/threa...beyond.664268/

Tons of information in that article you shared there Steve. Long read but very worth it.

Interesting about "proper" amount of overlap..

The power producing potential of overlap is considered second only to duration. Under the right conditions a cam utilizing the proper amount of overlap can easily pull 20 additional horsepower over an almost identical cam on wider lobe centers.

[pastry_chef]

Originally Posted by Steve C.

From the paperwork supplied with Edelbrock PERFORMER RPM ALUMINUM CYLINDER HEADS........

Do not change size or shape of exhaust ports in heads!"

I need to find that podcast with Darin Morgan... he said if you gasket match, toss the heads in the trash you just destroyed them!

[Steve C.]

David Vizzard's comprehensive computer program for cam selection was not duration-driven but over-lap driven. The event timing of the cam, directed by the duration of the intake and exhaust, together with the LCA and the advance/retard position in the engine. One the overlap to suit a given application is decided, everything else falls into place. After my meeting with David I used it on a combo years ago.


.

[Jack P.]

So did we answer the OP's question?