I dont know about the 4v,.. They are an entirely different animal compared to 2v 4.6 motors. They are as different in their power band characteristics from a 2v as the 2v is to an HO 5.0 motor. But I know for a fact the 2v will gain good HP from porting.
I have before and after numbers and the ONLY mod done was my hand porting using nothing but a dremel and grinding bits on a buzz wheel with a center extension so I could reach down in the ports. I didnt gain much below 4500 RPM. So from my experience porting the heads on a DD car is a do at your own discression (<---Spelling?) kind of thing.
How ever I did pick up 23 RWHP peaking at 5300 RPM instead of the previous peak at 5000 RPM. The redline was raised to 6200 and with porting the HP band only lost 24 peak HP at 6000 compared to 50hp less then peak at 6000 unported. So porting does offer alot of potential.
This is how my car Progressed.
1996 GT bone stock except flowmasters with 28k miles
Base line 174 RWHP
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Stage 1
96 GT.
Bone stock long block.
Stock intake and upper plenum.
75mm BBK TB
BBK fenderwell CAI
Screamin Demon ignition modules
BBK 1 5/8 Long tubes with 2.5" collectors
2.5" BBK O/R H-pipe
Standard Flowmaster 40 series mufflers into dumps.
Tune consisted of a JET Stage2 performance chip plugged into the top of the computer.
By this stage the car had 65K miles
Made 208 RWHP and 272 trq SAE corrected on a DynoJet.
Next build,..
96 GT.
Stock SHORT BLOCK
1999 Windsor PI heads.
2002 PI lower intake with aluminum cross over and stock 1996 upper plenum.
The rest is a carry over from the first setup except now got a professional tune done by Brian of EFI-Unlimited when he was still with James at RaceRelated.
Motor had 140k when did the PI head swap.
Base line was 249 RWHP and 285 trq.
After tuning was 268 RWHP and 292 trq SAE corrected on a Dynojet.
Next touch ups.
The cams in the heads had a lot of bad scarring in surface area where they ride in the cam towers. Normally a professional engine builder would have thrown these heads in the garbage,.. I only paid $100 for the heads so I decided to use them anyway. The heads had some bad valve guides in them and needed a little bit of help. So I sent them out to the machine shop.
1999 Windsor heads -
Shaved .027
New stock valves, springs, seals, and 99 windsor PI cams replaced with 2002 Romeo PI cams. (Same cam profiles,.. just that these had a smoother surface area)
Heads were hand ported by me following my own template with a goal to match Patriot Stage 2 heads.
Stock 2004 upper intake plenum port matched to 75mm BBK TB and then honed out and polished to match the lower intake gasket. Also performed an EGR delete.
Next dyno session on the same tune as the previous dyno tune.
291 RWHP and 298 trq SAE corrected on Dynojet.
A total gain of 23 HP.
How ever,.. There was no HP gain below 4000 RPM,.. all the gain was from 4000 - 6200 RPM with HP peak at 5300 vs 5000 RPM peak for stock PI heads. No HP was lost below 4000,.. well not enough to write about.
If I would have fly cut the pistons and used something like Comp270 cams I could have easily broke 300 - 315 RHWP NA on a 2V.
These were the heads fresh from the machine shop.
The start of my template.
Still some more to go,..
I scanned this out of Sean Hyland's book on 4.6 engines.
Edited by me. It shows the swirl fin I am talking about.
This pis shows a casting from the intake port of a 2V PI heads. I shaded the area's that I removed for my template. PLEASE NOTE,.. the shading is NOT TO SCALE. But will give you an idea of how to port them should anyone want to try it themselves. The idea is to open them up to match the intake,.. then blend them in narrower like a funnel down toward the valve to maintain velocity and minimize low end torque loss.
I focused most of my attention to the intake ports.
All I did was polished inside of the exhaust ports taking out any flash and ridges from the castings and then polished them to a smooth surface.
I did not flowbench the heads. I have no way of doing it myself and because I had a total of $380 in these heads including purchase price and machine work I didnt really care.
Hurst