Factory 396/427 chevy cylinder heads

[1972ho]

Has any of you guys ever had your 396/427 chevy stock unported cylinder head flow tested and if so can you share that info here.Im just curious to see if the ford 351 cleveland 4v heads flow equal to or better than the stock big block chevy heads.I have some flow data on a set of cleveland open chamber 4v heads with only a valve job and flowed with a 4.030 bore.Ill show the flow data after I see if someone will put up a chevy head flow.Just curious???

[Alaskaracer]

Pretty sure there is flow data out there on them. Just need to look around a bit

[Ericnova]

Oval port BBC or Rectangle port BBc head??

All the flow numbers you are looking for can be found here for most stuff unless it is a really new head offering.
Stan Weiss Cylinder Head flow at 28° water Database
http://www.users.interport.net/s/r/srweiss/tablehdc.htm

[mag2555]

The Ford heads are better on the Intake side then the Intake oval port BBC heads ( 2.06" 1.72" ) and about the equal on the Exh side, the rectangular BBC heads ( 2.19" 1.88" ) are a tad better on both ends then the Ford heads.

Just as a side note , you can port the 2 bbl Ford heads to flow as good on the Intake side as a stock 4 bbl head, and far better on the Exh side then the stock 4 bbl heads when fitted with bigger valves.

[vortecpro]

Has any of you guys ever had your 396/427 chevy stock unported cylinder head flow tested and if so can you share that info here.Im just curious to see if the ford 351 cleveland 4v heads flow equal to or better than the stock big block chevy heads.I have some flow data on a set of cleveland open chamber 4v heads with only a valve job and flowed with a 4.030 bore.Ill show the flow data after I see if someone will put up a chevy head flow.Just curious???

A typical stock 215 396/427 unmodified head flows in the high 240s @ 28 inches, @ .460 lift, 4.350 bore.

[1972ho]

Vortecpro do you race stock eliminator if so I was wondering how a bbc 396/427 chevy camaro can run in the high 9’s at 3400# plus with a head that is suppose to be stock with such low flow number compared to a 351 cleveland.The heads would have to be ported out to max and covered up to run over 135.00 mph right.

[vortecpro]

Vortecpro do you race stock eliminator if so I was wondering how a bbc 396/427 chevy camaro can run in the high 9’s at 3400# plus with a head that is suppose to be stock with such low flow number compared to a 351 cleveland.The heads would have to be ported out to max and covered up to run over 135.00 mph right.

Thats easily explained. A well done 375 HP 396 makes 625 corrected HP, It takes 602 HP to run 132 MPH @ 3400 pounds. 132/1320=10.00 and that formula is just a jumping off point for A/SA Camaro you can do much better. So when you take into account how far past peak HP the 375 combination will RPM it makes a great race engine. Stock 840 casting heads flow 280 CFM @ .520 lift @ 28 inches.

[tenxal]

The heads would have to be ported out to max and covered up to run over 135.00 mph right.

The heads can't be "...ported out to the max and covered up". NHRA lists a maximum volume for the intake and exhaust port on each cylinder head. For a '69 Camaro 396-375 with the 858, 391 or 840 heads, the intakes can be no larger than 326.0 cc and the exhausts no larger than 120 cc. The 291 heads can have a 327 cc intake port and a 122 cc exhaust port. The 401 aluminum head that's also legal for this combination has the 320 cc intake/120 cc exhaust.

These, and many other NHRA Stock Eliminator engines, are extremely fast because every facet of the engine is examined and optimized to work together. They are extremely efficient, given the limitations set forth by the rules.

When you extend that sort of thinking and effort to include the entire race car, good things happen.

[Jeff Lee]

Vortecpro do you race stock eliminator if so I was wondering how a bbc 396/427 chevy camaro can run in the high 9’s at 3400# plus with a head that is suppose to be stock with such low flow number compared to a 351 cleveland.The heads would have to be ported out to max and covered up to run over 135.00 mph right.

Thats easily explained. A well done 375 HP 396 makes 625 corrected HP, It takes 602 HP to run 132 MPH @ 3400 pounds. 132/1320=10.00 and that formula is just a jumping off point for A/SA Camaro you can do much better. So when you take into account how far past peak HP the 375 combination will RPM it makes a great race engine. Stock 840 casting heads flow 280 CFM @ .520 lift @ 28 inches.

It’s 1320/MPH = Optimum ET

[Jeff Lee]

It should also be mentioned that NHRA has allowed BBC several “superseded” part numbers for the 396/427 cylinder heads; including offerings from Edelbrock. There has been much development on not only the cylinder heads over the last few decades, but also in the short-block and drivetrain. Long gone are TRW pistons with 5/32” rings (even 1/16” rings are obsolete with allowable ring spacers which allow super thin metric rings), Aftermarket rods, cranks, blocks, oil pans, you name it, the parts are nothing like those in use 20+++ years ago.
Don’t jump on the “they are cheaters" bandwagon. Times have just changed. If you don’t think that’s right...that’s a different argument!

[bobmc]

discussion has left out the main difference in stock elim engine-cam with stock valve lift but unrestricted duration

[tenxal]

discussion has left out the main difference in stock elim engine-cam with stock valve lift but unrestricted duration

Yes. With the rules mandating stock valve lift for a particular engine (.520 int/ex in the case of the 396-375's being discussed), cam profile and low lift flow are major players in the power NHRA Stocker engines make.

On a well done combination, you can put a set of 'big' heads on and not pick up much. Ditto the camshafts...a 'bigger' cam won't show you much with the NHRA legal Stocker heads that have been optimized to work with the NHRA legal cams.

On engines with poor exhaust sides of the heads (most assuredly not the case with the BBC heads referenced above), you have to look at header design to help you out. Which leads you back to moving the cam lobes (intake and exhaust). Which leads you to...well, you get the idea.

[PRH]

Imo, the question of “which flows more in OE form” could really only be properly answered with a pretty unmolested example of the best of each, tested back to back on the same bench, using the appropriate bore size for the head being tested......4.00” for the Ford, 4.25” for the Chevy.

[Diodedog]

discussion has left out the main difference in stock elim engine-cam with stock valve lift but unrestricted duration

The duration rules were opened up back in the 80s and in some flat top engines like the 383 you're very restricted because of valve to piston clearance. Unlimited spring pressures and shaft mounted roller rockers on Chevies along with the aftermarket blocks was a huge gain for them.

[tenxal]

Unlimited spring pressures and shaft mounted roller rockers on Chevies along with the aftermarket blocks was a huge gain for them.

Rocker mounting must remain as produced in Stock Eliminator. In short, you can't run a shaft rocker system on any engine that originally came with stud mounted rockers. Like small/big block Chevies.

The unlimited spring pressure rule applies to all engines in Stock Eliminator, not just the Chevy stuff. And there are replacement blocks allowed for other makes, as well.