RENE'S RAGE

iTrader: (96)

Anyone seen the head to head test in the May 2012 GM High-Tech Mag?
Mast 245 Cathedral Port vs Mast 256 Rectangular Port.
With supporting cams for each head, results were almost equal.
Even though the Rec. head flow 25 cfm more at .600 lift. 360 vs 335.
And the Cat. heads made better low-speed power and produced peak torque
lower than the Rec. heads.
The Rec heads did flow 372 cfm at .700 lift. But how many of us are running
.700 lift cams. Not me, I'm running .624 lift.
So flow numbers are just numbers. Just because one head out flows another head, doesn't mean it will make more hp.
It's really all in the combo.

JS01

iTrader: (10)

Ding ding ding, been preaching this for years in regard to the LS3 stuff. Theres alot more to it than flow numbers although they are relevant in comparing certain things. Discharge coefficient and wet flow are just two of the other major players that determine how well a head will perform and that is where the LS3 stuff lacks big time IMO. The LS3 stuff would have been a lot nicer if Gm would have moved the intake valve more toward the center of the bore ala mini-LS7. Though, on really big engines the LS3 stuff isnt that bad IMO and can be a decent performer.

Mez

iTrader: (1)

All heads are flow benched at a fixed valve lift. But on a running engine, the valves open and close causing the air flow to slow down and speed up. The bigger the port, the slower the air velocity. That is where port velocity is important. A smaller port results in a higher port velocity which translates to better cylinder filling....to a point, of course. At high RPM, the larger ports have an advantage but at lower RPM, the smaller ports generally produce better torque.

So the bottom line is large ports and CFM don't mean squat when it comes to predicting torque and horsepower. There was another test of 11 heads about a year ago. Guess what? As set of low cost CNC stock heads with the smaller ports and relatively low CFM rating made the most power.

B'klyn9C1

I know that MAST makes great stuff but I wish they would compare more of a stock vs stock comparision. Like CNC ported 243's versus CNC ported LS3/L92's I wonder how much the test may of been was thrown off by using 11 degree versions of those heads???

Of course MAST would optimised both the cathedral design and the rectangular design. Especially if they are going through the trouble of changing the valve angles of both and who knows what was changed in the process. With that I would of like to have seen how these two designs act againist each other in their stock factory casting form. After all that is where 90% of us who undertake a LSx build will be messing with.

Question: is this test saying that the cathedral design is better for overall performance even on 400+ ci LSx strokers???? I was going for ported L92's for my LSx stroker build now I have my doubts.

Any thoughts?!?!?!?!?

427LS7HCI

[QUOTE=Mez;16184250]All heads are flow benched at a fixed valve lift. But on a running engine, the valves open and close causing the air flow to slow down and speed up. The bigger the port, the slower the air velocity. That is where port velocity is important. A smaller port results in a higher port velocity which translates to better cylinder filling....to a point, of course. At high RPM, the larger ports have an advantage but at lower RPM, the smaller ports generally produce better torque.

So the bottom line is large ports and CFM don't mean squat when it comes to predicting torque and horsepower. [B]There was another test of 11 heads about a year ago. Guess what? As set of low cost CNC stock heads with the smaller ports and relatively low CFM rating made the most power.[QUOTE]

Is there a link?

dwill73

This all comes down to how much cfm and cross section you need for a given application. A head that flows 370cfm is capable of supporting over 880 fwhp in a max effort application compared to a head that only flows 335cfm which is capable of supporting 800 fwhp in a max effort application. If I'm trying to build a 650 fwhp street motor it's pretty obvious which head I would choose.

cwalsh

iTrader: (9)

[/URL][QUOTE=427LS7HCI;16184659][QUOTE=Mez;16184250]All heads are flow benched at a fixed valve lift. But on a running engine, the valves open and close causing the air flow to slow down and speed up. The bigger the port, the slower the air velocity. That is where port velocity is important. A smaller port results in a higher port velocity which translates to better cylinder filling....to a point, of course. At high RPM, the larger ports have an advantage but at lower RPM, the smaller ports generally produce better torque.

So the bottom line is large ports and CFM don't mean squat when it comes to predicting torque and horsepower. [B]There was another test of 11 heads about a year ago. Guess what? As set of low cost CNC stock heads with the smaller ports and relatively low CFM rating made the most power.

Compare Link

Here is a link
Chris

COPO9560

So the head with the smaller intake runner had a peak torque at a lower rpm - would anyone not expect this? Cams were also slightly different - again this sets up more confusion than providing true facts.

Bottom line is both are heads I wish I owned - either one in the right set-up will make a lot of power.

Mez

iTrader: (1)

I suggest you go back an read the article. They tested both heads with both cams, so I feel the test was showing true facts for these heads. Yes, smaller ports usually make more torque at lower RPM but the peak HP were almost identical.

You will never see every head tested with every cam combo, so all you can do it go by the tests. In this test, the impressive flow numbers of the big square port heads did not translate into more HP over the smaller cathedral port heads even with the 4" stroked LS2. The 11 head test last year showed the same results.

I already knew this when I had my LS2 built using CNC 243 heads and small Lingenfelter GT-11 cam. It now dyno at 473 rwhp that idles at 675 rpm with no lope or bad behavior. Except for the louder Corsa Sport mufflers, most think it is stock.

Get the right size head for your build. Not the heads with the biggest CFM rating.

ringram

What were the cam specs?
What about intakes? Both fast102's?

Jimbo1367

Yes. both FAST 102/102s. But remember that the catheral port FAST mani offers bigger gains than the rect. mani

LSX-coupe

iTrader: (1)

Mast stopped the med bore ls3 heads now.

LC

What do you mean?

MOZEZ

No, We didn't stop making them. We discontinued the small bore LS7 a year ago, your probabaly referring to the thread from a week or so ago. It was a mis-leading title. We make more Med bore ls3 and Big bore Ls3 heads than anything else. Just wanted to clarify.

Cary