Some solid info on changing GT-40X heads for AFR 205's. A friend of mine here in Houston was running a FMS 392 with advertised 430HP. This was the older engine that had the cast pistons. The motor dynoed @ 436HP out of the crate. The head change with no other modifications (left the original cam) made 497HP before any tuning took place. I don't know if he got more HP after fine tuning or not, but I'm sure he picked up a few more HP

Hope this helps

Mark

Rick, I don't think I said the AFR's are poor quality, I know in my car they sure made a lot of power. I just like the Jr's for out of the box, good not great performance and at almost $1000 a pair cheaper than AFR they are a good choice for a street engine.

RD

Good Comparison
 

Finding a good apples to apples comparison is hard for the GT-40x head. Some magazines have tested them against AFR185's. This is not a true apples to apples comparison in my opinion.

The GT-40x head should be compared to the AFR165. The Z304 FMS head is a better head to stand up against the AFR185.

I had to dig, but this is what I found from two different Muscle Mustang and Fast Ford articles:

Ford Racing GT-40x Cylinder Heads:
Peak HP: 390 hp @ 5,400 rpm
Peak Torque: 416 lb-ft @ 4,400 rpm
Average HP: 315 hp
Average TQ: 386.20 lb-ft
Peak Airflow Intake: 234 cfm @ .650 lift
Peak Airflow Exhaust: 157 cfm @ .450 lift
Average Airflow Combined: 275.38 cfm
Cost Per HP: $32.03
link: http://airflowresearch.com/articles/...Part4/A-P4.htm


AFR 165 Cylinder Heads:
Peak HP: 396 hp @ 5,400 rpm
Peak Torque: 378 lb-ft @ 4,400 rpm
Average HP: 288.89 hp
Average TQ: 353.86 lb-ft
Peak Airflow Intake: 240 cfm @ .550 lift
Peak Airflow Exhaust: 200 cfm @ .550 lift
Average Airflow Combined: 293.97 cfm

link: http://airflowresearch.com/articles/...art2/A-P11.htm

It's not just about HP. It's about torque and usable rpm's. If the car is 90% street use go with a head that provides higher port velocity thus higher torque numbers.

As you can see from these numbers, the GT-40x head trounced the AFR165 in the tourqe department. This is the important figure. The GT-40x head develops this torque advantage through exceptional port velocity. The guys at Ford Racing aren't completely in the dark:p .

People have been bashing the GT-40x head for years because of that one article where the AFR185 made something like 75 more hp over the 40's. Not a fair comparison but if you look closely the torque numbers for the 40's were not that far off. Torque is where it's at baby!:D It's the force we all love! You can have all the HP in the world but if the force is not with you...well you know the rest young Skywalker.

I agree, True American iron is about the torque. If you want rpm's buy a Ferrari.

This is exactly how misinformation starts. Hi-Tech, your comparison is not fair in that the GT40X test you cite (first reference) is based on a 331 stroker, not the same 306 ci engine the AFR 165's (second reference) were tested on. These are completely separate engines, dynos days etc. The second reference you cite is the 1st MM&FF Ultimate Guide to cylinder heads performed by the well known Richard Hoeldner (sp?). It is a great comparison because it tests the GT40Y and AFR165, among others, on the same exact motor and dyno. Per the test, the AFR165 had average 288 HP and 353 TQ vs 273 HP and 338 TQ for the GT40Y. I agree with you that the Z would be a better comparison for the 185 but that still does not mean the GT40X head belongs on a Supr427's 351W much less a 408W.

Edit Suck grammar

Oh I see, the first reference is from the second MM&FF Ultimate Cylinder Head Guide test using a 331. In this test, the GT40X showed average 315HP and 386TQ versus 343HP and 417TQ for the AFR 185 versus 339HP and 411TQ for the Z head. In addition to more cubic inches, this engine also sports a more aggressive cam - XE274HR versus the XE264HR for the 306 engine used in the first Ultimate guide test. Apples and Oranges.

Dude, I'm sitting here chillin' after a long day @ work drinking a nice cabernet. :MECOOL: Don't worry, don't get excited...I wasn't trying to misinform anyone. I simply took time out of a very busy day to research a fair comparison for the 40 head.

No problem at all. Just realize that your comparison is not fair.

Yes, TQ is great to get you off the line, but you need the HP to get you down the road.

Go with the 408 stroker kit, AFR205 heads for the HP, and if you want to improve low end TQ, take off the Vic Jr intake and go with a dual plane like the Performer.

Curt C.,
Even in the 306 test the regular GT-40 heads (not the GT-40X) made more torque than the AFR165's. Find a direct comparison with the GT-40X and the AFT165 and I'll bet $20 the 40's will make more torque.

Again, it's not about HP... TORQUE RULES!:LOL:

you said, "...but that still does not mean the GT40X head belongs on a Supr427's 351W much less a 408W."

Did I miss something? Where did I imply the GT-40X head belonged on a Supr427 351 or a 408? :confused:

For a large displacement 351, I would go with the Z304, AFR185's, or Ede Vic Jr.'s. The AFR205's would be a nice race head - high RPM motor. Just my opinion, but what do I know, I'm selling all my sbf stuff and going FE!

Hi-Tech,

Please read the article in full before you post again ok?

http://airflowresearch.com/articles/...art2/A-P11.htm

GT40Y on the 306 produced 338 average TQ and 363 max torque. The AFR165 made 353 average TQ and 378 maximum TQ. I will take your $20 dollars right now - thank you.

Edit. In fact, the AFR165 and AFR185 beat every other head in in all performance categories (Peak HP, Avg. HP, Peak TQ, Avg. TQ) in Guide 1 (306 engine) and Guide 2 (331 engine) respectively.

And lets not forget, it is torque at the tire patch that really matters, not necessarily torque at the crank. Why don't you put a John Deere tractor motor in your car and see how that goes :)

Now that you mention it, I think I will :LOL:

If had both AFR165 and 185 and both of these heads where excellant performer and I thought reasonably priced for the performance gains. They like spray to.

Here is a car math site. Use it to find what size heads you need for 408 cubic inche motor.

Dwight

http://www.wallaceracing.com/Calculators.htm