We have all heard too big head kills performance.
While agree with etreme amount to be true.

Wondering hiw many here have gone to bigger head and lost performance? If so how much bigger.

If like to compare yorr heads to formula/
Int require flow. ci x rpm/9140 exh ,75 to ,80(call it .75) x int, flow. Seems lots of factors would influence real world requirements of air needed

I have been told by cpl dyno guys most all engine work out to 2.1 to 2.2 x head flow, Take it for what it is worth. Real world comparison be nice here too.

While on subject of head flow. therory on alky motors needing bigger ports to accomidate extra fuel taking more available area for oxygen. Thoughts?

Just the formula. Hopefully Chad will chime in with real world flow information.

555 ci motor with Dart pro1 335CC heads ran 5.7s all day

582 with Brodix BBX3 380cc heads. 5.7s real good air 5.6s

Same car - same MPH.

I think we are well past the 2.1 standard. Most of my bracket style builds are in the 2.2-2.25 range. However a modern max effort Super Stock or Comp engine will be in the 2.4 range.

Example:
462 23º max effort made 915hp w/380cfm = 2.41
434 23º bracket makes 780hp w/340cfm = 2.29
434 23º max effort made 880hp w/355cfm = 2.49
380 23º bracket made 675hp w/310cfm = 2.18
355 23º Super Stock engine 665hp w/280cfm = 2.4
441 BBC Super Stock engine 840 w/385cfm = 2.18
437 13º max effort made 1035hp w/430cfm = 2.40
421 13º bracket makes 910hp w/400cfm = 2.28

What I like to do is take the efficiency of the head you are using and see how much flow/area you are using to make that power. Like the photo. However, low friction, vacuum pump, compression, etc play a HUGE part in all these numbers.

Yea heard 2.2 but always like to error on short side when giving out info, Ever have someone gripe because they got more than they where told? Well except on this site.LOL

This argue ment comes up a lot on Hemi vs bbc. Whie both have ton updates since factory stuff. Different reasons. One mostly NA and other domonates blower world. BBC has beeter valvetrain and Hemi had strongetr bottom end.

Hemi heads valve angle just make for good flow, When tell someone I nhave 30 yo heads that flow 500 plus. Well time for crap proof suit when fan come on. Good thing not tell them I get that with a 3% estimated loss just due to wear not that wore out.

So if take swag at 540ci hemi witrh BAE heads that flow 530 plus in perfect shape deduct for wear and estimate 1000 ho _+/- 50. Which is under desk top dyno numbers I am not over estimating. Of coarse that is with good tune and everything else working together.

One reply to over heading engine .I guess? would like to hear form any who put bigger head in and car slowed or saus crew it this is as fast as I am going.

An engine will perform it's best when the port is sized correctly for the application. Intended use, rpm and cubic inch will determine what the port should be. Port volume will be what it is when it's done. That's what I've learned from my former head guy and my current head guy. Both are some of the best in the industry, along with Chad. Chad knows them too...heheheheh

we have a 406 with AFR CNC 227 heads 20yrs old and a 1050 carb on K13 that will run 9.5X at 2700 lbs, every thing is just happy. And yea we have one of Chad's tweaked intakes 2925, with a 4500 adapter on it.

This message has been edited. Last edited by: HR3377,