David, "Muscle Mustangs and Fast Fords" did a HUGE cylinder head shoot-out a while back. Dollar for dollar, AFR was the best available. However, they're damn near a race head. That stated, I wouldn't go over a 185 for your 331. I have a friend running 165s on his 1991 Mustang and he's LAYING DOWN over 500hp at the wheels (supercharged).
The difference between the 165s and the 185s is the valve size. The 165s have 1.9 intake and 1.45ish (not positive) exhaust, while the 185s have 2.02 intake and 1.6 exhaust.
If you want a heavy-breather, go with the 185s, but I'd recommend the 165s if you want more driveability than power. It's your call.
I like the TFS high ports , but they bringing out CNC machined heads like AFR have been doing the last few years...The difference with 165 and 185 is the inlet volume in CC plus the valve size.. Keep in mind with 185's you need to notch any std piston for valve clearance..The TFS/ twisted wedge heads are deeper and generally don't requre piston notching..A lot depends on total package.. There's NO point in fitting any heads that breath much better than GT P's if std manifold is fitted..Even Explorer type unless ported..If forced induction is used then heads like the TFS R series can be used as velocity is not an issue with forced induction...I'd tent to use total package like the Holley systemax or TFS. Edelbrock package.. They have put some work into these combinations, there's no point in being a pioneer when these guys have it a million times....A cam over 220 / 530 lift is getting serious so top end street heads inlet etc can be used..But keep in mind power under 2800 rpm will be wanting..A 3:7 final drive and 9.5 comp help keep torque up to reasonable pulling power under cam ...
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The TF CNC 205 head is the one I specified. It is all over the place in the US. You don't have it down under? With the TF R, I don't see how their high port fits in. Anyway, the R is just too big with 235cc ports when CNC'd.
This will be a solid roller, so we are looking at something between 234/242 and 247/251 with a Comp XE Street Roller or TK. That is close to or around .700" lift in any case. If you are using Comps newest hydraulics you will be near or over .6" lift with Cleveland rocker ratios.
In all my simulations, the Trick Flow 205 CNC wins with the CHI 185 3V second. I may have runner lengths and area wrong though, since they are not published. If there was a 195-200cc CNC version of the CHI 185 3V with a relocated spark plug, it would probably be the winner. However, if such a head exists I can't find it.
Hoping for driving charateristics like an S2000. Tractable (not necessarily fast) from 2000-5000, coming on like gang busters at 4000-4200 with a practical redline around 7000. For drag racing, that redline would be extended to 7800 or so.
That is possible with a solid roller. A hydraulic roller would need more cubes and fewer revs. A solid flat tappet would be challenged with the revs and would have to have so much duration that it would not be tractable.
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