Anyone have any ideas or opinions on how well the 03 cobra heads perform in comparison to the navi heads? I'm attempting to gather some info on the best cylinder head designed for the 4v motors.

 

03 cobra heads flow more it was in a recent stang magazine they even out flow the fr-500 heads i would use them with one of the more radical cams from the other motors ( or the fr500 ) and make a crap-ton of power

 

It seems that all the 4V head designs have a certain amount of compromises, they all have something good about them and they all have some things not so good.

I chose the FR500 heads for my project based on port shape and flow potential alone. I know they have the smallest ports of all the 4V heads but they are the best shaped, besides thats what they made grinders for . I have a set of Navi heads and I wouldnt even consider them because of the two reasons already listed.

With that said, I wanted to run the Navi lower intake and the intake is so big that it wouldn't seal on the FR500 intake flange so the heads had to spend some quality time in the weld shop. Then be machined and ported so now the base fits.

As far as the '03/'04 Cobra heads, they have an intake that is similar to the FR500 in shape and it is actually quite a bit larger in volume but is not as large as the Navi head. The Navi head has a bad intake port shape, the port aims straight at the back side of the valve with no short turn what so ever and is said to be all done at 8000 rpm or less, no matter what the flow bench says there is something wrong with the heads.....IMHO its because it belongs on a truck/SUV/station wagon and as a true tumble port design was meant to be efficient at lower speed.

The Cobra exhaust ports are also alot larger than all but the GT head. Some guys are all gah-gah over the Cobra exhaust port flow out of the box....Well, it is a lot larger so that would probably have somthing to do with its stock flow numbers....as for me, IMO having the biggest exhaust port is not the best way to go for a turbo setup, however having an extremely good flowing port is important.
Both the Navi and Cobra have water passages between the siamesed exhaust ports and the FR500 is dry...Since my heads are not going to be used on the street much or a long distance race this also wasn't a concern. The FR500 heads don't have the best cooling passages at least not as good as the new Cobra heads but there are fixes. My FR heads are going on a 5.4 block with a much more rubust water pump and coolant flow and that right there should take care of any (if any ) problems.

If you were to find out what all the top 4V mod racers think of cylinder heads, I think they would only consider the FR500 or the old Cobra R / new GT cylinder heads, Most seem to be rushing to the new GT head which by the way has ports that are very similar in shape to the FR500 but they are a lot larger, valves are bigger too.

To answer your question about the two cylinder heads you have chosen to gather info on, with out a doubt it would be the '03/'04 Cobra head, I don't think the Navi head is even in the race.

Didn't mean ramble and jump around so much but I also have spent a good deal of time gathering info on 4V heads the last several months. The info gathering is over with and they are in the port shop now.
Dale

 

Will the new 3 valve GT heads bolt to a cobra block? I've been out of the car for about a year now focusing on playing with turbo bikes

I'm not even aware of any info on the GT heads, other than they are of 3v design.

 

I think your confusing the 3V Mustang GT heads with the 4v Ford GT supercar heads.......night and day difference. The FORD GT 4V heads are identical to the '00 Cobra R heads. They are THE head of choice for making power right now.

 

Ahh gotcha. I was not aware of despariging differences. I was under the impression that the new 3v heads would offer a lighter reciprocating mass and a single exhaust valve. Making them favorable for forced inductions and specifically turbos.

As far as the GT heads go. Where do you get them and what do they run on the average?