Port Matching Intake

[FirstEliminator]

   Hey guys,

   I've been reading a bit about port matching. The more I read, the more undecided I am to spend the time doing it. The engine is the same 445 stroker I've been talking about for a while. As cast Edelbrock heads, Edelbrock Performer RPM intake, cam is a Comp of Survival's specs 234/240 @.050 with a 112 lobe sep.
      Looking at the RPM intake I was surprised to see the ports much smaller than the ports in the head. From what I've read, there isn't much to gain with port matching on an engine at this power level with the RPM intake. If there's nothing to gain or very little, I'm leaning towards putting the intake on as cast.  Any thoughts?

     thanks in advance,
       Mark

[Qikbbstang]

The Perf RPM is unlike any other production dual plane with its lower plane resembling a cut in half single plane. Single planes have always been said to suffer from anti-reversion. The Perf RPM is one honking manifold that can support some of the top power producing 1-4V FEs including strokers.  The runners on the Perf RPM are extremely uniform in H&W. Unless there is a 2" high dwarf to climb into the runners its certain folks are not enlarging the RPMs runners from head gasket surface to plenum. Obviously if it's runners are uniform in H&W then all modified/ported Perf RPMs are still breathing through those inaccessible H&W runner sestions at some points and obviously they are still making the power.
   I believe you will find that the port mismatches are not equal as far as at the bottom, top and each side. I'd like to think Ed in their infinite wisdom would have planned the resulting steps to each be specific to the location of the head so the typical "steps" best serve to help control low & mid-range reversion.  Each Perf RPM head features two left side flowing runners and two right side flowing runners. Going all the way back to the Street Master it was obvious the port mismatch were even greater and they to were not uniform, that intake's claim to fame was making near duel-plane low and mid range power from a single plane. Supposedly the small intake runners were instrumental.  They were sold for RV vehicles.   Did Edelbrock intend the mismatched ports?

[turbohunter]

Did Edelbrock intend the mismatched ports?

On the Performer.
I always thought (dunno why) the small runners were done in order to be able to handle different port configurations?
In other words, save money and confusion in mass production over not having to match each size.
Or was it done striving for a particular performance goal. Ex. torque.

[FirstEliminator]

   Some of the mismatches were offset up, other down, some left and others right.  I've decided I am not going to spend the time to port match. In Jay's book he had mentioned there were no gains with port matching on the T-bird 428 and the other mild performance dyno mule while the 390 stroker only got about 10 hp up on top with a comparable loss on the bottom. The engine I am putting together will probably be more like the mild dyno engines as it has a fair amount less cam than Jay's 390 stroker.

   thanks for the replies,

    Mark

  p.s.  This was a fun pic from back in the day.
 
 

[Joe-jdc]

What heads are you using?  If Edelbrocks, then port matching will take the manifold from about 305cfm average flow to close to 340cfm airflow.  That is definitely worth the time IMO.  Joe-JDC. 

[jayb]

You will definitely pick up top end power with a port match, but you may lose a little in the midrange.  The smaller unported manifold runners will result in higher velocity of the A/F charge at a given engine speed, as compared with the port matched version.  More velocity will give you better cylinder filling, until the smaller size of the manifold's port opening starts to inhibit flow. 

I saw this effect fairly clearly while doing the research for my book.  In my dyno tests I used both an as-cast Performer RPM, and a port matched version, so that I could see the difference.  For my 500 HP 390 stroker engine (445"), the port matched Performer RPM gave peaks of 505 lb-ft of torque and 504 HP.  The as-cast Performer RPM gave peaks of 514 lb-ft of torque and 493 horsepower.  So, the as-cast manifold had more torque in the midrange, and the port matched manifold made more torque at the top end.  Whether to port match or not all depends on what you are looking for in the engine. 

Being a horsepower guy, I always port match 

[KMcCullah]

I think your on the right track mark. I recently port matched a Performer RPM for a 390 and based on several posts by Mr. Craine, I left ports 2 and 3 alone. Just smoothed them up. But you are running a bunch more cubes so obviously more cfm is required.
Some food for thought...... The ports in the manifold can be a lot smaller than the head and out flow the head by a good percentage. The second link is the one that  Mr Craine said "bigger is NOT always better". He proved it and I listened!

http://www.network54.com/Forum/74182/thread/1172630243/First+cut+on+Perf-+RPM

http://www.network54.com/Forum/74182/thread/1173738372/Victor+rework+flow+numbers

[turbohunter]

The ports in the manifold can be a lot smaller than the head and out flow the head by a good percentage.

Is that because of venturi effect?
And what happens to the charge (for lack of a better word) as it passes into the larger port? Isn't there some swirling or breakup of some sort?

[BruceS]

Excellent links to some of Joe's past work.  I've got a question on the port matching itself; how far back (from the port opening to the head) do you go?  I would guess 1-2 inches or enough to get a smooth transition to the rest of the runner?  Thanks, Bruce

[KMcCullah]

Is that because of venturi effect?
And what happens to the charge (for lack of a better word) as it passes into the larger port? Isn't there some swirling or breakup of some sort?
[/quote]

My understanding (crude at best) is the port is not what determines flow, the size of the valve and the valve job do.  The size of the port is what determines velocity. And the two kinda have to know each other to work together.

[jayb]

Excellent links to some of Joe's past work.  I've got a question on the port matching itself; how far back (from the port opening to the head) do you go?  I would guess 1-2 inches or enough to get a smooth transition to the rest of the runner?  Thanks, Bruce

I usually go back 2-3 inches, grinding the opening dimension to where I want it and flaring back into the rest of the runner from there.