Big Block AFR Heads and Headers

[Rat72]

Do I need to worry about what heads I'm running when picking a header for my big block? I currently have stock oval port heads but I'm purchasing some AFR square port heads. Can I use the same header or are the exhaust ports going to throw me off.

Thanks,
Whit

[Robznob11]

just have them afrs shipped to me and ill worry about it, no as long as your exh holes in the heads are smaller than your primary tubes it should work fine but if there larger you might want to get step down tubes or just go with a bigger primary, what kinda horsepower you plan on laying down 550 and up should handle 2in primary easy

[mnunn454]

Assuming you'd be doing the head and header upgrade at the same time, Ideally, you'd want your headers' gasket/flange shape to match the new AFR heads.

Oval ported headers on the rectangle ported heads would probably be okay on the bottom end, but would restrict top end performance.

Rectangle ported headers on Oval port heads would most likely hurt low end torque a little but help the top end because they're a little less restrictive right at the head.

JMO.

[Rat72]

Originally Posted by Robznob11

just have them afrs shipped to me and ill worry about it, no as long as your exh holes in the heads are smaller than your primary tubes it should work fine but if there larger you might want to get step down tubes or just go with a bigger primary, what kinda horsepower you plan on laying down 550 and up should handle 2in primary easy

You've hit on my problem. This is my daily driver and I'm trying to keep the keep it low on the RPM range, with the occasional full throttle fun. I'd love to have the cam and everything kick in at 1500 rpm. Even the smallest AFR heads would have been too large but I think the supercharger will make good use of the large exhaust. I guess I'm off on a tangent but will 2" primary/3-1/2" collectors work OK with on the low end with the supercharger? It's definately not a good combo without a supercharger unless I go with a lot more displacement.

Thanks,
Whit

[Rat72]

Originally Posted by mnunn454

Assuming you'd be doing the head and header upgrade at the same time, Ideally, you'd want your headers' gasket/flange shape to match the new AFR heads.

Oval ported headers on the rectangle ported heads would probably be okay on the bottom end, but would restrict top end performance.

Rectangle ported headers on Oval port heads would most likely hurt low end torque a little but help the top end because they're a little less restrictive right at the head.

JMO.

I have not seen that the header manufactures specify between Oval and Rectangular? I had my LT1 headers port matched to the heads but that was a custom header. Do any of the off-the-shelf headers differentiate between square and rectangular?

Thanks,
Whit

[Robznob11]

school time boys, oval,square and rec refers to the intake ports stock exh ports are close to the same, some after market heads use d shape ports, we all know headders are round, unless your getting full blown race heads most all header will work fine, only the full blown ones have the exh ports hogged out and require larger headders, if thats what you bought you wasted your money cause there to big for the street, the artical in car craft used afr's smallest set of bbc as cast and made 700+ on a 496 i think it was dec or jan issue might have been feb one of the three. don't mess up and buy 2in or larger headders if you got a stock motor with afr heads you need a good cam to let those heads breath,have fun

[Rat72]

Originally Posted by Robznob11

school time boys, oval,square and rec refers to the intake ports stock exh ports are close to the same, some after market heads use d shape ports, we all know headders are round, unless your getting full blown race heads most all header will work fine, only the full blown ones have the exh ports hogged out and require larger headders, if thats what you bought you wasted your money cause there to big for the street, the artical in car craft used afr's smallest set of bbc as cast and made 700+ on a 496 i think it was dec or jan issue might have been feb one of the three. don't mess up and buy 2in or larger headders if you got a stock motor with afr heads you need a good cam to let those heads breath,have fun

The exhaust port on the AFR head is completely different than the stock ports but not a lot bigger, just a different shape. And I hear you about about the big AFRs, they are huge! The small one's are almost too big but I couldn't justify all that money to buy oval port heads. Not that there is anything wrong with oval ports, they are actually more efficient than rectangular ports and probably a better head for most street rides. But I'll gladly give up a little streetability for a little fun.

Whit

[Robznob11]

well 049 and 781 gm castings will support 650+ hp and be killers down low, in the rpm range most people drive in, 2500-5000 now if your gonna drag race and are going to rap 6500 yea you want rec ports or aftermarket, how ever with the coast of machiene work i would take small afr or dart pro 1s any day becuase you can spend just as much on iron as makeing oe castings race worthy, but its a toss up becuase bottom line afrs are going to have budget race springs and valves and steel retainers where as you can go severe duty on the oval ports for the same price, the afrs will let you shave weight and run alittle more comp and timeing, but the irons will never warp and will likley cause less gasket issues etc, but if you got the money let it all hang out just don't be dissiponted with a hi rev head on the street go small youll be better in the end. bbc have issues heads are becomeing just like rotating assembles unless you have a good crank and heads ready to go, theres no reason not to stroke it and get aftermarket heads, you will miss a few sonic cokes but not many.....lol

[metalmassfab]

The best choice on the planet for BBC heads going on a truck...
Act fast on these, I think they were discontinued due to a lack of interest. Truth is, AFR did a crappy job advertising these babys, nobody knew!!! I'll be getting a set soon...


Big Block Chevy - 290cc Oval Port Magnum CNC Ported

For the ultimate in "Oval Port" performance, the fully CNC ported AFR 290 has no competition. With flow figures most small to medium sized rectangular port castings would be envious of, these high flowing "Ovals": produce tremendous airspeed and really pack a punch for monster torque. Ideally suited for 296-509 CID street and strip performance, as well as circle track applications which require strong low and mid-range torque to help accelerate a car coming off a corner. Once again, AFR has included it's trademark 3/4” deck, reinforced rocker stud bosses, and thick rugged castings, so you can own the strongest and most efficient heads on the market today. Premium hardware such as Ferrea 2.25/1.880 one piece stainless valves, 1.550 double springs, 10 degree locks and retainers, and high quality studs and guideplates all come as standard equipment. Take not the higher flowing exhaust ports are raised .375 over stock location, and therefore these heads might not be a direct bolt-on in every application. These heads have no EGR and are not emissions legal.

290cc BBC Racing Head Part Numbers
CNC Ported Pairs of Cylinder Heads Complete With Parts and Ready to Install
FREE Shipping on these Heads!
Description Part # Price/
Pair
290cc CNC Ported w/o Parts 119cc 3630 $2279
290cc CNC Ported w/ Hydraulic or Solid Flat Tappet Springs 121cc 3640 Discontinued
290cc CNC Ported w/Solid Roller Springs 121cc 3650 $2669
Note: Optional stud girdle required for 2° rolled valve angles and 1” longer head bolts needed on four bottom exhaust bolt holes.
Not legal for sale or use on pollution controlled motor vehicles in the United States.

You can also get as cast units, 265 cc, starting under $2000...

http://www.flatlanderracing.com/headsafr-bbcoval.html

[mnunn454]

My crappy headers are round 1-5/8 OD (1-1/2" ID). My Edelbdock Performer heads' exh ports are oval (about 20% or more bigger than the header). My main point was not so much port shape, but was warning against necking down the exh port size too much, particularly if the poster is going with a supercharger. At a minimum, I'd want my primaries to have the same (square inch) cross section as my exh ports. Going with anything smaller would be okay for low RPM torque situations but would limit top end power potential (IMO) as is clearly the goal with a supercharger add-on.

[PanelDeland]

I think matal mass has a good set listed.They have all the good stuff from the new technology and have small ports to keep the velocity up.According to the magazine engine builders this is crucial to street performance.They wont run out on the top end as well but will keep it much more streetable.I would call the cam manufacturer and ask for a recomendation with the heads you decide on.Make sure you have the info on the heads,gearing,CR,and anything else you can imagine.It will help determine which cam is going to give you the power in the rpm range you want.

[Rat72]

Originally Posted by metalmassfab

The best choice on the planet for BBC heads going on a truck...
Act fast on these, I think they were discontinued due to a lack of interest. Truth is, AFR did a crappy job advertising these babys, nobody knew!!! I'll be getting a set soon...


Big Block Chevy - 290cc Oval Port Magnum CNC Ported

AFR is not selling them any more. Do you know of a secret stash somewhere?

Whit

[metalmassfab]

I knew this was going to bite me in the arse! ya'll are going to buy these last few puppies out before i can get my sticky mits on 'em! the place I was going to purchase them from is sold out too. the last link is a head flow database that covers near every head! Brodix makes an oval port head too, but to get near the AFR cnc heads flow #'s you'll need to do a little port shaping and smoothing...and if all else fails, go with the AFR rectangle port heads and add a longer stroke crank to get the low end grunt back sorry...

http://www.treperformance.com/Heads/AFR/AFRBBC265.html

http://www.flatlanderracing.com/afr-bbc02.html

http://www.mopar1.us/headflow.html

[Rat72]

I had a shocker today. I use a machine shop around here that primarily does race motors. In talking with the owner today about AFR heads, he spun things all backwards on me. His theory was to undersize the cam and oversize the head. He thought that the 325/335 head was a better size for my application (street) and noted that the stock rectangular port head is about that same size and that the low RPM issues with the stock head only came because of the large cam. He then looked at my cam and told me that I shouldn't use anything more than a 220 duration at .5 lift. That's about 2 sizes smaller than I have. I was totally shocked but this guy understands torque and he doesn't really care what I do, he's just speaking from customer satisfaction view point. I understand the cam thing, I've been pissed before with an oversized cam but I've only been dissapointed with an undersized cam and I'm always happy at idle. And I agree with his view on the heads as long as the velocity does not overcome the flow benifits. I'd love to see some dyno specs with a small cam and the various different heads. That would mean a lot more than the speculation we will come up with on this thread.

BTW, I bought into his cam theory enough to purchase a new one. So I have a new compcams kit available for sale, K11-242-3. It's all been deboxed but never used.

Whit