Any one have Flow Numbers for LS6 BBC heads with rect port heads

 

290-310 at .600 lift. I have flowed several sets and the heads that I have flowed have had several valve jobs over the years, etc. and so the #'s are always a lil different but these #'s are what I see fromn them.

FWIW, I would only use these on a "#'s matching" car and use a set of oval ports with larger valves for a street car or building TQ and I would use some aftermarket heads for a serious build up.

These factory Sq ports have LARGE runners and do not flow like they should when compared to oval ports done correctly or aftermarket Sq ports.

Oval ports will give you about the same CFM with alot smaller port. Any aftermarket head will outflow them with smalle ports and if you need the runner volume and CFM, you can get ALOT more air from a slightly larger port.

NightTrain66

 

do u have the flow numbers so i can plug them in the dyno

 

I doubt if I have a complete flow chart of a stock one but I will check tomorrow and post tomorrow night if I find one.

Lloyd Elliott
NightTrain66

 

Lloyd: it's been a long time since I dealt with a BBC. Your comments about the rectangular port heads are interesting. So, do you mean to never bother with factory rect port heads?

Thanks.

rich Krause

 

That is surprising! Anyone who has seen the factory BBC LS6 heads knows what I'm talking about. The runners are massive! I guess it just proves that runner volume isn't the only ticket to making a head flow well...

 

I was always told that the LS6 heads flow real well. The cars made 450hp estimated but was close to 500hp. From what i understand Rect. port heads are for more uper Rpm performance use. THe guy that help with my big block told me to stay away from the oval port heads.

 

RK-
If you have the heads and are gonna "slap" and engine together, they work OK or if you on a budget and have to chose between stock, unported oval ports or stock SQ ports an wanna make 600 HP, than the Sq ports will definitely be better. I would not say "NOT" to use them but there are better choices in my opinion.

84-
Those cars had high duration solid lifter cams, LOTS of compression, etc. They made good power for the technology they had but properly done ovalswill make good TQ for most street stuff and after market heads will be a better choice for "SERIOUS" build ups. Sorry, I do not have any stock flow #'s.

The stock heads have LOTS of runner volume compared to the CFM they flow and crummy shortside radius (int and exhaust) as compared to aftermarket heads.

You can make good flow #'s with the Oval ports and 2.19/1.88 valves and end up with a small runner. The 781/049 casting open chamber ovals can flow about 300-310 and have awesome low and mid lift #'s. The 215/063 casting close chamber ovals will flow about 285/290 with awesome low and mid lift #'s and make AWESOME TQ. These heads will flow KILLER #'s by laying back the shortside more but you lose low lift flow doing it.

My personal engine is a .030 over 454 with 10.0 to 1 comp., semi closed 215 castings, 2.19/1.88 valves, mild hyd roller, Victor Jr, 850 DP and it made 545 HP (5900 RPM) and 573 TQ. (3900 RPM). The HP and TQ curves are FLAT. Over 500 ft lbs of TQ from 3000 RPM to 6000 RPM. Average TQ was 520. The engine is done by 6200 RPM and was built for TQ. More compression, larger cam and open chamber heads will make these #'s even higher but I wanted TQ for my mild 55 Chevy.

Enough gear, converter, light enough car, NOS, etc. will make factory Sq. ports work "OK" but in my opinion, there are better choices.

NightTrain66@msn.com

 

My engine only uses oval port heads. I wouldn't even consider using rectangular ports unless I had 500+ CID or was going to spin the engine well over 7000 rpm. I'd also consider using them if I decided on using a blower. For a NA engine with a shift point below 7000 rpm, oval port heads with big valves are the best bang for the buck.

I even still use a 4150 850 cfm carb when everyone thinks they need to use a huge Dominator.

 

The LS6 head is casting 291. Although GM produced many different castings for BBC heads, this isn't the most popular rectangular port. The 990 casting is a bit better and getting harder to find.

The most popular oval ports are 781 and 049 since they are both open chamber heads. Except for a wide variation on combustion chamber sizes, there are no real bad BBC heads.

There is one exception and it could be what the guy who's helping you is talking about. Late model truck heads are considered peanut port heads. They have a very small oval port and have no performance potential. They're designed for low rpm torque engines needed in a truck. I have a set of peanut port heads in my garage. I bought an engine and only wanted the block. One of the heads makes a good door stop.

With the amount of heads currently available in aftermarket, finding and using a set of 30 year old 990 or 291 heads isn't cost effective if the heads need a lot of work. Changing a set of street heads to race heads gets expensive.