What Head To Use?

[69396Chevy]

Ok I have a 68 verty with a 350 with reall crappy heads. Looking to put some aluminum heads on it but not really sure what I should get in the means of specs. Its a 4spd with a Holley 650 carb and here are the cam specs. lemme know what you all think! cnpgalea@yahoo.com

Basic Operating RPM Range:
2,000-5,700 RPM
Intake Duration at 050 inch Lift:
218
Exhaust Duration at 050 inch Lift:
226
Duration at 050 inch Lift:
218 int./226 exh.
Advertised Intake Duration:
278
Advertised Exhaust Duration:
284
Advertised Duration:
278 int./284 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:
0.462 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:
0.470 in.
Valve Lift with Factory Rocker Arm Ratio:
0.462 int./0.470 exh. lift
Lobe Separation (degrees):
112
Camshaft Gear Attachment:
3-bolts
Intake Valve Lash:
0.000 in.
Exhaust Valve Lash:
0.000 in.

 

[Crimson Thunder]

AFR180's or Edelbrock perfomer RPM heads. Just be sure to stay below 200cc on the intake port and you will be happy.

 

[Vette79]

x2 I am purchasing the 180cc Eliminator Street Heads for my spring project.

 

[glen242]

I would purchase heads that match your cam numbers, if you are not going to upgrade soon.

Your cam has a max. intake lift of 0.462. What good will it do you to have heads that flow the max. @ 0.500-0.600 if you cannot get there with your cam?

I would welcome a discussion on this. I always see posts about going with heads that flow a lot, much more than valve lift, and wonder why?

Maybe I'm just stupid, but I run a cam with the max. valve lift of 0.500 and the TF heads flow as much @ 0.500 as the AFR heads do, but are cheaper.

I always thought components should be balanced.

Comments please.

BTW, engine is a 383, 10.3 CR, CC XE274 hydraulic flat tappet.

 

[Curtis]

Glen, I also would like to see this discussed... you know what it is though.. lots of people have this thing about buying high dollar aluminum heads just so they can say they got em.. I just laugh cause my iron stuff will put most of em in my rear view mirror, but for those where money is no object they will look real pretty.

 

[Vette79]

:eyerole

 

[milo30]

I would purchase heads that match your cam numbers, if you are not going to upgrade soon.

Your cam has a max. intake lift of 0.462. What good will it do you to have heads that flow the max. @ 0.500-0.600 if you cannot get there with your cam?

I would welcome a discussion on this. I always see posts about going with heads that flow a lot, much more than valve lift, and wonder why?

Maybe I'm just stupid, but I run a cam with the max. valve lift of 0.500 and the TF heads flow as much @ 0.500 as the AFR heads do, but are cheaper.

I always thought components should be balanced.

Comments please.

BTW, engine is a 383, 10.3 CR, CC XE274 hydraulic flat tappet.

I picked up a chevy high performance mag today because they had an article on camshafts duration and lift explained. In there this same question was asked if I am reading it right. Here is a shortened answer that was given for this.

Testing cylinder heads on a flow bench, you are flowing tn one direction at a constant depression against the restriction of the port. That gives you an avg airflow in CFM. When the engine is running, the intake sys has chaotic flow. It takes 720 degrees of crankshaft rotation to complete the 4 stroke cycle. Also, the piston is moving dn the bore on the intake stroke at different speeds and doesn't have constant suction on the inlet. This being said, the port is at peak flow for a very limited time in this 720 degrees. This is why we are constantly looking for more airflow out of cylinder heads. You don't want to make the ports larger. you want the smallest ports to keep the velocity high. The proper sized port will always run best and excellerate the engine the fastest.

On a street performance engine it is rare to see 100 % volumetric efficiency on the engine dyno.


Like I said I shortened the response but I think you get the gist of it. Does this answer the question? This is in the March 2008 issue FYI.

 

[Glensgages]

..... I always thought components should be balanced.....

http://www.maxchevy.com/features/2008/iii_1-snoke-1.html

Dale’s sedate little red runner has carded a best of 12.12 at 114 mph without any of those things you must have to go fast. And it does it with 3.08 gears on a measly 235/60 tire.

So what does it take to run those numbers without all the “must have” go-fast goodies? A humongous, thumping high-rpm roller cam? Nope. How about an old Lunati Bracket Master hydraulic flat tappet cam with 230 degrees of duration at 0.050-inch and 0.480-inch lift that sees less than 6,000 rpm?

Big compression and race gas? Nope. How about a nice pump-gas friendly 9.7:1 compression from the SRP forged pistons? They swing on Cat connecting rods on a stock Chevy cast crank balanced by Bill Mizia at B&T Performance Engine Balancing in LaVerne.

Big port aluminum cylinder heads with lots of massaging? Nope. How about out-of-the-box GM Bowtie Vortec Bow Tie castings (PN 25534431) that have 206cc intake ports, 77cc exhaust ports, and 65cc combustion chambers.

Big single-plane race intake and carburetor? Nope. A GM Performance Parts dual-plane manifold with a 770cfm Holley Street Avenger are all there is.

The latest, double throw-down trick of the week torque converter? Nope. A TCI 2,400 stall speed item in front of a Nick Magana-built Turbo 350 is connected to the 3.08:1-geared 10-bolt/Posi by the stock driveshaft.

Granted, this is a 400/406 CID SBC, that can probably better-use the 206 cc intake port (the GMPP catalog lists these heads as having a 215 cc port? ), but I'd think a 350/355/383 CID SBC, using a matching canshaft profile, intake and carb, could use the smaller port (185cc, P/N 25534421 ) Bow Tie vortec head, or even the non Bow Tie vortec head (P/N 12558060 ) to make gobs of power on a budget.

Curtis supplied me with a link to Scoggin-Dickey, who sell upgraded (springs allowing valve-lift to .525" ) vortec-head/intake kits for less-than $1,100, that includes head-gaskets and head-bolts, intake-gaskets and intake-bolts, and rocker-arms that'd be tough to beat, dollar-for-dollar, for most streetable C3s, that'll rarely see 6,000 RPM.

 

[Tom Bryant]

Keep in mind that if you have 2 identical heads, one cast in iron and the other in alloy, that you will need 1 point higher static compression ratio with the alloy head to make the same horsepower. This is due to the better heat transfer of aluminum heads. If you replaced your iron heads with alloy with the same size chamber you will more than likely slow your car down. Shoot for a cr of around 10.25 to no more than 10.50 with an aluminum head to be able to live with it on pump gas. If you use one of the performance iron heads like the Vortec or Dart a 9.3cr is ideal. There are tool box calculators on this site that will help you determine what chamber size and gasket thickness you will need to get these results without taking down the short block for different pistons and decking.

The above suggestions for small port cross sections to keep velocity up are right on the money for your cam and carb. My personal choice for your combo would be GM iron Vortecs. My engine I just finished for my stepside is similar to yours in cam timing and carb with flat tops and 9.3:1 cr with ported GM 1.94 iron heads. My first choice for a head upgrade would be Vortecs.

Tom

 

[corvette66]

I fully agree with Tom, go with the vortec heads. I have a large set of vortecs on my 69 (202 valves, bee hive springs, 1.6 rockers etc) The big flow vortecs can be had for less than $1000 complete and make tons of power!! Not bad when considering the Edelbrock RPM are a grand a piece! I wish i had a video to show you. THey really do keep up with the aluminum heads. Better than you would think.

If you consider using the vortecs send me a PM I can give you my .02 on them, My engine makes between 500-600 HP easy. yup with vortecs and a holley 500