Thursday, December 02, 2004


Ford GT 5.4L Head Flow Numbers


Impressive mid-lift numbers, but the max flow ain't that great when we consider how exotic this engine is. I'd like to know what the cam specs are - I'm guessing they don't use a huge amount of lift, but that's to be expected with the small valves inherent in a 4-valve head design (especially one going on a 3.55" bore). Most heads will stop producing significant amounts of flow once valve lift exceeds 1/4 of the valve diameter (that's when the area of the valve curtain equals the area of the valve surface, and therefore the maximum throat diameter available directly behind the valve seat), so "mid-lift" on a two-valve head might be "max lift" on a four-valve design.

The reason I say that the maximum flow isn't great is because GM LS6/LS2/LQ4 heads and Chrysler Hemi heads put up not-dissimilar flow numbers. I think the point to all of this is to demonstrate what GM or Chrysler could do with a forced-induction system on a GenIV or Hemi engine. The Ford GT produces 550 SAE HP (actually more like 600+, given the fact that it makes maybe 525 at the rear wheels), and there's no reason to expect anything less from the pushrod V8s of the other two guys in town. Ya know, if they wanted to.

Gotta love the LT1-vs-Mod discussion that the thread eventually devolves into. It's been 12 years since the debut of the LT1 in the F-body, and Ford's still hard-pressed to equal it. I hope someone in Dearborn is really regretting this whole SOHC mess. I think that Ford will have lost about 15 years' worth of progress by the time the Mod motor runs its course.

I'm not sure what head flow numbers you're referencing but your evaluation is frankly off in left field. Box stock Ford GT heads flow roughly 310/255 at peak on a 3.552" bore at 28" H2O.

LS2/LS6 heads stuggle to hit 260 cfm INT side on their stock bore diameter @ 28".

That's what I would call fairly dissimilar.

While rectangle port LS3 heads do actually deliver similar peak numbers as the FGT heads, but again they are absolutely slaughtered by the GT heads everywhere short of peak. If you treat a flow chart like a dyno graph, the GT heads simply embarrass the LS3's on "average flow". This is just as relevant as the average power argument when comparing dyno graphs, peak numbers are just a snapshot of the big picture and not a very important one at that. This mid and low-lift advantage produces superior cylinder filling characteristics and thus even though we have two 310 cfm heads, the 4V head can ultimately deliver more power in spite of nearly identical peak flow numbers.

The Modulars aren't going anywhere, especially with the latest 5.8 iteration taking the title of "world's most powerful mass production V8" with NO gas guzzler tax penalty. The 5.8 is making more power than the ZR1's LS9, which employs the exotic parts like Pankl Ti rods that are allowed by offering that engine in the $100,000+ ZR!. The 5.8; on the other hand, makes due with far more mundane innards.

Did you bother to check the date on the original post? It's from 2004. A lot has happened in the past nine years.
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