Trux

Hi,

I was wondering what heads do you think are better?
Why?

What are teh differences?

Are the degrees set for special applications?

Thanks:hail: :hail: :hail:

Oh, and TTA850, could you tell me a good place to look for coil overs for 3rd gens?

Thanks:hail: :hail: :hail:

:lala: :lala: :lala:

Monty

I'm running a set of Dart CNC ported 18* heads and they are definitely worth it. They are the main reason my naturally aspirated SBC 427 made 650hp and 580 tq on pump gas. Alot of people will tell you they are high-rpm heads only, but on a bigger cubic inch small block they help make good torque, my motor made 500+ ft lbs from 3000 to 7000 rpm, it was making 425 ft lbs at 2000 rpm.

Thier main advantage over 23* heads is better intake and exhaust flow. Here are my flow bench numbers:

Actual Intake and Exhaust flows (cfm) at 28" water are:

Valve Lift...... Intake (cfm)...................... Exhaust (cfm)
.200".............. 136 .................................111
.300".............. 213................................. 188
.400"...............274................................. 224
.500".............. 323................................. 242
.600"...............359................................. 253
.700".............. 378................................. 260


In comparison, the famous Splayed-valve cylinder heads only yield a 5% improvement in intake flow over 18* cylinder heads, and exhaust flow is equivalent to the 18o cylinder heads.

Compared to conventional 23o cylinder heads, 18o heads have radically raised intake runners, revised valve angles, relocated valve centerlines, smaller combustion chambers, and more efficient exhaust ports. These cylinder heads are the best choice for a maximum performance engine with in-line valves. The distance between the intake runner floor and the deck surface on these high-port heads is 1.220", compared to .650" on the low-port 18o degree heads, and .250" for a conventional Bow Tie aluminum head.

The valve centerlines are 1.955" apart to accomodate larger bores and reduce valve shrouding. The valve's location is as important as their angle. The intake and exhaust valves in 18o degree heads are positioned on the cylinder bore centerline. This change produces a substantial improvement in the total airflow potential. The valves in a conventional 23o SBC head are positioned .275" from the cylinder bore centerline. This location limits the engine's breathing ability because the valve heads are shrouded by the combustion chamber and cylinder walls as they approach maximum lift. Shifting the valves to the bore centerline reduces this shrouding.

The valves are also moved laterally in the 18o heads to enhance intake flow. The exhaust valves are shifted toward the cylinder walls to provide for larger intake valves. The intake valves are moved toward the center of the cylinder bores to unshroud the valves at high lift. The problems of valve shrouding and cylinder wall interference effectively limit conventional 23o heads to a maxuimum intake diameter of 2.100". The 18o degree heads can take advantage of the additional airflow offered by intake valves up to 2.200", depending on bore size.

The high-port intake runner flows more air at high valve lifts than the low-port design. The difference between the two ports becomes significant at valve lifts above .600". The high-port runner has a more direct line of sight path, which enhances ligh-lift flow. Both designs have excellent flow at low lifts due to their tall short-side radiuses and deep valve bowls.

The angle of the intake manifold flange was revised to accomodate the relocated intake runners. Conventional small-block heads are machined at a 10o angle on the manifold face, the 18o degree heads are machined at a 5o angle. The angle of the rocker cover rails was also changed from 17o to 9o.

The 18o degree head's reshaped and redesigned exhaust port yields an improvement in flow over conventional heads. The exhaust ports are raised .550" and widened .240" at the manifold flange. The port's high-side radius provides a smooth, gradual transition from the valve bowl to the header pipe, minimizing turbulence in the runner.

The angle of the exhaust manifold flange was changed from 35o degrees to 40o degrees on 18o degree heads. This revision smoothes the flow of burned gases at the junction between the ports and the primary header pipes.

18o degree cylinder heads feature small, efficient combustion chambers. Chnaging the valve angle was essential in creating a shallow combustion chamber. Reducing the valve angle in a wedge-type cylinder head forces the incoming air/fuel mixture to make a sharper turn from the port entrance to the valve seat. GM Motorsports Technology Group engineers evaluated head designs with valve angles ranging from 23o to 10o. An 18o valve angle proved to be a good compromise between chamber design and intake port performance.

Recommended valves sizes for engines with less than 4.060" cylinder bores are 2.125" intake valves and 1.620" exhaust valves. Engines with 4.125" and larger cylinder bores can benefit from the increased flow of 2.150" intake valves. Larger intake valves can be used, up to 2.20", depending on bore size. The raised runners roofs in all 18o heads require valves with extra-long stems. An overall valve length of 5.450" (.500" longer than stock) is used in most high-port heads. 5.350" long valves are used in low-port heads. This stem length will produce a 2.00" valve spring installed height with most racing valvetrain components.

The 18o heads' .600" thick deck surface and generous combustion chamber walls provide plenty of material for enlarging or reducing the final combustion chamber volume. If it is necessary to mill the head to reduce the chamber volume, the head should be milled flat, not angle-milled. Angle-milling an 18o head can impair airflow by moving the valves away from the cylinder bore centerline, thereby increasing valve shrouding.

Valve reliefs in the pistons must be machined to match the 18o clinder head's revised valve location.

The 18o head's revised spark plug location also contributes to the efficiency of the new combustion chamber design. Compared to to conventional heads, the plugs are moved .350" closer to the center of the cylinder bore and shifted toward the top of the combustion chambers. Engines equipped with 18o cylinder heads typically require less spark advance (32 to 34o BTDC).

The revised plug location also improves spark plug access, and protects the spark plug boots and wires from heat damage caused by header pipes. The spark plugs holes in 18o cylinder heads are machined for .708" reach tapered seat spark plugs with 5/8" hex heads (Champion S series, formerly BL series, or equivalent) and 3/4" reach gasketed seat, 5/8" hex head plugs (C series). Spark plug heat range will depend on the particular engine characteristics. A 57 heat range is a good starting point for most naturally aspirated small-block racing engines.

The stock valve spring seats on 18o cylinder heads are 1.640" in diameter. Hardened spring seat cups or spring locators should be installed under the valve springs to protect the aluminum head. The spring seats for the two center exhaust valves must be modified to clear the center head bolt or stud. Check for adequate clearance between the head stud and nut and the valve spring and valve seat.

When using large-diameter valve springs on 18o heads, install the cylinder heads on the engine without the two center exhaust valve springs. This will provide wrench clearance for the center head bolts. Then install the remaining valve springs after the head bolts are torqued.

All 18o small-block heads require aftermarket shaft-mounted rocker arms.

Due to the heights of the head bolt columns in 18o cylinder heads, special stud or bolt kits must be used. Twelve-point nuts and small-diameter washers must be used with 18o heads to fit the .875" diameter head bolt counterbores. Special head studs must be used in the two bolt holes between the intake ports on high-port heads. The diameter of these holes are 15/32", the other bolt holes are 13/32". Special "step-down" head studs with 7/16" - 14 threads on the block end, 3/8" shanks, and 3/8" - 24 nut threads should be used in these holes. When torqued to 70 ft.-lbs., these high-strength 3/8" studs produce the same clamping load on the deck surface as conventional 7/16" studs. GM Motorsports recommends that steel sleeves not be installed and material not be removed from the common wall between the siamesed intake runners when porting these heads.

Trux

Thanks for the technical info Monty. It is really helpful
Thanks:hail: :hail: :hail:

B4Ctom1

there is another option for the street. the holley heads, they are only 185 cc intake runners and rarely known is that they are 20 degrees and rumored that they are cast by brodix or the casting design was from brodix.

Trux

Did not know that they wer 20 degree heads. I'll try to look up some info on them.

Thanks:hail: :hail: :hail:

89ProchargedROC

you know, i heard about these heads but cant find any info about them AT ALL

i know that Doug F had them on a 355 with a small cam that made 400hp n/a but i cant find any flow numbers, cc port size PONTENTIAL or anything else

seems like these would be a great head due to the valve angle

BACK TO 18* HEADS

yes they are great heads, but dont forget you need a special intake, special headers, and 18* pistons

If you dont want to go through all that added cost you can look into Raised Runner cylinder heads (23*). They are probaly the best kind of 23* head you can buy and is the absolute best you need unless you want to go 18*

Trux

Did not know you need a special intake to work with teh 18* heads. Would an After market efI system like Superram or Stealth ram be able to bolt up to an 18* head?

Thanks:hail: :hail: :hail:

Monty

Several companies make spacers that fit between the intake and the head to allow you to use a 23* manifold with 18* heads.

If you have Lingenfelters book, he mentions an 18* head, Superram 406 that made 600hp on pump gas.

Besides pistons, intake, and headers, you'll also need offset shaft mounted rockers, and offset lifters, with custom length pushrods. Most of this stuff is not that big of a deal if you need to buy it new anyway, but if you already have good parts you'd like to reuse, the switch to 18* heads can get costly. You can figure around $5000 for the heads, rockers, and valvetrain. I certainly wouldn't argue that they are a "good bang for the buck", but if you're after maximuym performance, they are a step up.

89ProchargedROC

possibly, but you'd need to fabricate intake spacers

i would doubt that the port on a superram base or the maybe the stealth ram could be enlarged enough to fit 18* heads, but i'm not 100% sure

Trux

So I can get spacers. There is a large diference in the port sizes on the 18* heads and the intake base?

Thanks for your help:hail: :hail: :hail:

Bobalos

I got this from Doug @ Holley this morning.

"They are Holley castings machined by AFR"

it looks like they are a good set of heads, but not fantastic. you can get a better set out of the box from AFR. They were not intended to be a killer head, just a good replacment for a stock head, kind of like the Edelbrocks.

BW

B4Ctom1

thats good to know, I was curious about the rumor.

Trux

Where did you get the roil overs on your car?

Do you like them?

thanks for the info:hail: :hail: :hail:

B4Ctom1

PA automotive