Tom Wilson
August 1, 2005

Regular readers know we've been putting our 347 dyno mule to good use on Westech's SuperFlo 901 engine polygraph lately. Our recent interests have been a series of intake manifold tests, and while we're taking a bit of a sidetrack this month, we've got more intake tests in the works-namely the street/strip variety-so stick around.

But this month, as we get tuned up for higher performance intake manifolds to come, we're doing our best to answer a lingering question about choosing between Air Flow Research's 165 and 185 cylinder heads. These two heads anchor the bottom of AFR's Ford head offerings and are designed for the super-popular street or street/strip performance realm-AFR's more aggressive 205 and 225 heads are race-only units and should not be considered at typical street power levels. As such, the question is when to switch from the bolt-on 165 to the higher-performance 185 heads?

As always with small-block Fords, the answer depends heavily on two factors: how much displacement your engine has, and how many rpm you are going to turn it. Both directly affect the amount of air the cylinder heads will be required to process, and thus how "large" the heads need to be. Because small-block Fords measure anywhere from 260 to well over 400 cubic inches in the case of stroker Windsors, the displacement parameter is a meaningful variable to say the least.

The other looming question mark, rpm, is just like adding cubic inches. The higher the rpm, the more air the engine uses. So, you could have a nitrous'd, 8,000 rpm 302 on one hand or a 427 Windsor bumbling around on the street and be able to use pretty similar cylinder heads.

To give us all an indication of how the 165 and 185 heads react, we ran a pair of each across our 347 test engine. It is based on a Coast High Performance 347 Street Fighter short-block with a stout cast-steel crankshaft, H-beam rods, and forged pistons giving a bit more than 9:1 compression. The camshaft is a Comp Cams 258 Extreme Energy hydraulic-roller measuring 208/216 degrees of duration at 0.050-inch of valve lift, 0.533/0.544 total valve lift via 1.6 ratio Comp stainless steel roller rockers and a 112-degree lobe separation angle. This cam is recommended for "1,400 to 5,300 rpm on stock H.O. or with mild modifications" by Comp, so it is not a big bruiser, but at the same time, it's definitely well ahead of stock.

The rest of the supporting pieces are our usual dyno fare-full-length Hooker Super Competition 131/44-inch headers, a couple feet of 3-inch exhaust tubing and equally giant Flowmaster mufflers, an electric water pump, an Accufab 70mm throttle body, and FAST engine management. We've dyno-proven that all of this gear easily supports more power than we're looking at here, so none of it is a choke.

The last important piece in the combination is the intake manifold, and for this test we reached for an Edelbrock Performer RPM II. This is Edelbrock's current hot-ticket EFI intake for hot street/strip engines, and previous testing on this same 347 has seen it reaching toward 460 hp (with considerably more camshaft than we have on hand for this test). We used it because we knew it too would not be a choke on the cylinder heads.

Speaking of which, what we tested were box-stock, standard-production 165 and 185 AFR heads. These are the current standard production heads, and not the Competition Package for the 165 head (For more on these, see the sidebar). These heads are similar to each other, and from a practical level, differ only in their intake ports and intake valve sizes. In fact, we figured the heads were machined from the same casting, and while AFR says it is possible to whittle a 185 head from a 165 casting, that's not the way the company does it. CNC time is too dear to waste on cutting excess metal you really shouldn't have poured in the first place, and because AFR is a small company with its own in-house foundry, it has separate castings for each head.

Swapping these heads is as easy as swapping any other pair. The AFR's are bolt-on parts when it comes to fitment. Even the exhaust ports are not raised, so the often-compromised exhaust headers go right on these heads.

When we finally got down to running the two heads, we found the 165 vs. 185 head contest dead-simple to analyze. That's because in our combination, the 185 heads ran neck and neck with the smaller and supposedly torquier 165 heads up to 3,900 rpm plus a little, but from 4,000 rpm up to 5,800 rpm, where our camshaft had given up, the 185s exhibited a distinct advantage. So, the decision, at least at this power level, is clear. The 185s make notably more power on the top end and cost no power at all on the bottom end.

In other words, there is no reason not to run the 185 heads-they cost no torque down low-and you gain a distinct power advantage from the midrange on up on a healthy 347.

Clearly, if your engine has more camshaft, displacement, or rpm than our dyno mule, the 185s are the way to go. The question does remain, however, when considering engines less aggressive than our test mule. When is an engine too large for AFR 165 heads? We'd say anytime you have a stock camshaft and stock displacement in a 302/5.0 engine, the 165 heads are the best choice. Move up to a 347, and especially one with a bit of camming such as our mule, and you're in 185 territory.

Making AFRSAFR is an industry leader with a premium reputation for power-building cylinder heads, so it may be a surprise to learn they practically custom-build each head. This is especially true of their cottage-like in-house foundry where the aluminum is hand-poured. So, if you have to wait a couple of weeks for a set of AFR heads, now you know why.

In fact, AFR says it takes six weeks to build a set of heads, and like a better burger house, it doesn't build a head until it is ordered. So, without these heads sitting under heat lamps on the AFR counter, either coordinate with your dealer or get your order in early.

Bench & Dyno NumbersAir Flow Research supplied us with the following flow data for the pair of heads we dyno'd for this test. It shows how the street-oriented 165 head stalls at 0.500-inch of intake valve lift, while the 185 head keeps flowing, albeit with slow improvement, all the way to 0.600-inch intake valve lift. Exhaust flow is compromised at 0.550-inch lift as well, and both heads flow the same on the exhaust because both heads use the identical CNC-ported exhaust port and 1.600-inch valve.

165cc head
Valve Lift 0.200 0.300 0.400 0.500 0.550 0.600
Intake 123 186 225 250 250 250
Exhaust 118 153 178 185 190 191
185 cc head
Valve Lift 0.200 0.300 0.400 0.500 0.550 0.600
Intake 129 189 234 267 279 282
Exhaust 118 153 178 185 190 191

All flow in cfm; flow measured at 28 in. of water.

We made our own dyno numbers, of course. They were obtained at Westech, using a SuperFlow 901 engine dyno:

  AFR 165   AFR 185   Difference  
RPM POWER TORQUE POWER TORQUE POWER TORQUE
2,500 180 378 181 381 1 3
2,600 185 375 188 380 3 5
2,700 194 378 197 384 3 6
2,800 206 386 207 388 1 2
2,{{{900}}} 217 392 216 392 -1 0
3,000 225 393 225 393 0 0
3,{{{100}}} 233 396 233 395 0 -1
3,200 243 399 243 399 0 0
3,300 252 402 256 408 4 6
3,400 264 408 267 412 3 4
3,500 275 413 277 416 2 3
3,600 285 416 287 419 2 3
3,700 295 419 297 421 2 2
3,800 302 417 305 421 3 4
3,900 310 417 312 420 2 3
4,000 318 417 {{{323}}} 424 5 7
4,100 327 419 331 425 4 6
4,200 335 419 344 430 9 11
4,300 344 420 353 431 9 11
4,400 357 427 364 435 7 8
4,500 365 426 372 434 7 8
4,600 373 426 381 435 8 9
4,700 380 425 388 434 8 9
4,800 388 424 398 436 10 12
4,900 393 421 404 433 11 12
5,000 396 416 410 430 14 14
5,100 398 410 412 424 14 14
5,200 400 404 415 419 15 15
5,300 401 398 418 414 17 16
5,400 403 392 418 406 15 14
5,500 404 386 419 401 15 15
5,600 {{{405}}} 380 418 392 13 12
5,700 403 371 413 381 10 10
5,800 396 359 402 364 6 5
5,900 394 350 399 355 5 5
6,000 396 347 404 354 8 7

Details & PricingAs noted in the main text, the 165 and 185 AFR heads are practically identical, save for the intake ports. The 165 head uses a 1.900-inch intake valve; the 185 heads sport a larger intake port and matching 2.020-inch valve.

For about a year now, AFR has been offering a Competition Package on only the 165 head. The Competition Package is aimed at the exhaust side of the head, and is "a more detailed port," according to AFR. In other words, it's not a huge change from the standard 165 port, but rather adds a bit of attention to difficult areas. Probably the largest single difference is the addition of material in dead flow areas. The valve remains 1.600-inch.

Currently there is no Competition Package for the 185 head and there are no plans to offer one even remotely soon. Instead AFR seems to be working on larger, racier Ford heads, as the current 165/185/202 heads make all the power anyone could possibly use/want/think, they want at the hot street or toy race car end of the market, while the serious racers always need more power and often can't use forced induction.

AFR says the Competition Package is popular with the "insane power" street people running turbos and boasting power figures only racers dreamed about a decade ago. They say this head works well with a stock-type piston and 1.900-inch intake valve, which turbos respond to. If you examine the flow-bench data elsewhere in this article, you can see how the Competition Package would wake up the typical street bruiser that uses plenty of boost and a modest camshaft. Such engines are typically exhaust strangled, so the Comp Package is a good fit for them.

Pricing on the Competition Package reflects the extra CNC time needed to whittle it out as shown in this breakdown of assembled AFR heads (per pair):

Head Price
165 std $1,350
185 $1,375
165 Comp Pkg $1,699

There are a few options from AFR. One is upgraded valves and springs for $180. The stock springs, such as the ones we used in our dyno tests, are your typical 120-pound-on-the-seat stuff, so they are good with the stock cam or something just a little larger. Likewise, the standard valves are good-quality street parts. The upgrade springs deliver 145 pounds on the seat and will hang in there with 0.600-inch-lift hydraulic rollers. Upgrading the springs only is $60.

If you have your own valvetrain already, omitting the AFR valves and springs will save you $120. Clearly, buying these heads dressed from AFR is a good deal for street bolt-on folks. It's tough to get valves, springs, and associated parts installed for only $120.

Titanium retainers are a popular option. They are $109. We should also note your choice of pedestal or bolt-down valvetrain hardware is available, too.