Ok, looking for information for now and later on which bbc size and combo these heads are good for and why. The different mfg co. do not really give a close idea but rather a broad application. Why a company will say maybe a 325 is good for 396-502 and there 345 is good for 454-572? So if you have a 454 will you pick 325 or 345? The company says they both apply. When is it overkill for size? Do people pick the size of head like a cam (bigger is better) in the old days. Or do you pick the smallest one recomended for your size engine for better flow rate? Let the input begin...

It is a Very complicated question with too many variables but this is my thinking.

I went with 310 CC because of the low 6000 +/- RPM combination I am running. As a weak rule of thumb....The smaller you can get by with the better..BUT port velocity becomes very important. I am quite confident I could use oval port heads that have been bowl blended and massaged and still run in the 10's or maybe better in the RPM range I use.

They can also be opened up some more if bigger cubes are on order but 310 is within the range of performance I was looking for with my 540. My heads are still box stock.

But to decide on Heads.....

You also have to look at your pocketbook and time availability...I know I don't have the cash or more importantly the time to swap and test many different heads and modifications to heads, that is why I bracket race because shoe polish is much cheaper.

Pick an ET and/or mph you are shooting for, pick an RPM range you are willing to drive around with or can afford to pay for the bottom end of your motor to spin. know what the weight of the car will be, type of gas you are willing to pay for, blower? Nitrous?, etc. Then go from there to match your other components including your heads.

I believe these are the root decisions that need to be made before you can pick your heads...

Originally posted by 69bigblock:
Ok, looking for information for now and later on which bbc size and combo these heads are good for and why. The different mfg co. do not really give a close idea but rather a broad application. Why a company will say maybe a 325 is good for 396-502 and there 345 is good for 454-572? So if you have a 454 will you pick 325 or 345? The company says they both apply. When is it overkill for size? Do people pick the size of head like a cam (bigger is better) in the old days. Or do you pick the smallest one recomended for your size engine for better flow rate? Let the input begin... =
I guess it really depends on what you are building but here's my thoughts,,,,,,
A smaller good flowing port with higher velocity will almost always be a better street head but,,,,,,,,,
There is more to a port than just airflow numbers
The minimum cross section area is also very important.
For your engine to make power to XXXX rpm you need a minimum of XXX sq inches in area for a flat tappet cam, less for a street type roller & even less for a real good roller.
Otherwise at about 690FPS the air tends to get very unhappy. :D

The volume of the port in cc's is not as important as the cross sectional area of the of the port but volume in cc's is a pretty good indicator of heads of the same type though & a lot easier to measure.

Generally speaking, a smaller port (in cc's) that flows more air is going to be a better port.
BUT ONLY IF THE PORT IS BIG ENOUGH TO SUPPORT THE RPM YOU WANT TO RUN THE ENGINE TO!!

If the port has a minimum restriction that is too small the port will stall.
Unfortunately, most head suppliers don't publish this spec.
Wish they a would along with cc's as it is a pretty important number ;)

These are some of the reasons you cannot just say a 325cc head is going to be a better head on a certain size engine,, it is very dependant on what your plans are for the whole deal.

A 500" engine will probably be very happy with a 270cc port with say 2.2 sq inches until you start leaning on it then somewhere along about 5000 or so rpm you are going to be done.
This is an example,, I don't feel like doing the math :(

Put a bigger head on & you now have the capability of going further.
Works just like overcaming an engine with small heads,, all you do is shorten your good torque curve.
A small too head with a cam that wants to run from 4000 to say 8000 just defeated the purpose of having a small head. The cam doesn't work at low speed & the head can't work at hi speed.

Done the other way, Small cam, large ports,, the heads are lazy at low speeds & the cam cannot support the rpm the heads want to be efficient at :confused:

Just a few of my rambling thoughts to get your post rollin :D

Great info guys. SO lets take the 500 engine and we want to run say 3k-6200 rpm. You run a solid roller (or a flat tappet), on the street with bimonthly track runs. You want the best track time you can get and still run strong on the street. I think many people like this setup and the info would be helpful. Now let's throw a couple of more items in: sometimes your run the bottle so would that change the head choice? Is the greatly increased cost of cnc heads worth the $$? Would a stroker motor change the choice? Much to think about but I am sure many are thinking the same questions. Keep it going.... Some more info. Heavy car (4k lb) mid 10 or a high 11 sec car (different answers here probably).

You can do it all wrong and still get a mid-high 11 sec car with too-big heads.
IMHO the rave around the AFR's would point me in their direction. I run a set of dart rect port 320 castings (no longer made), edel RPM, holley 750dp/850 baseplate, roller rockers, solid roller cam, and did 11.8 at 116 with 1.825 60'.
And I am hoping (really hoping!) my old converter was junk.
10's are a different story. I think you would want high port velocity, the right size, the right cam, headers, exhaust, carb, etc. If I was going for a 10 sec engine, I would do alot of research or go to machine shop that deals with this stuff all the time. I did my engine bit by bit over time with different people, and I got a 10:1 rect ported mongrel that still turns decent times.
In a 454 that is not long-rodded and does not see well over 7000 rpm, I would never go above 325, and be more inclined at a 310 or 315.. whatever.
If you want a 454 race motor, with long rods, HUGE solid roller cam, that is gonna see 8k, then yes.. 345's, maybe..
This is where the guys who do it all the time come in.
IMHO my heads are too big.

Good luck.

Matt

Here is an example.
My 468, which is now gone....had the following components. Simple stuff, and mild by comparrison to some. It ran high tens in my 3500lb Nova. I drove it to the track, and home. Full exhaust. No bottle.

468CID
9.5:1 CR
Edelbrock Roval heads....box stock.
UD 255/263 .612/.638 110LSA cam (more than a few here use this cam)
Some would say it's too big for the CR......HA
Dart oval port intake and a 950 HP Holley.
10" B&M converter, 4.10 12 bolt 10x29 Hoosier(daddy) slicks.
This engine made only 561hp @ 6400 and 540 lbs/ft at 4600. Always ran on pump gas.

AFR told me that running their 305cc heads with CNC chambers...without changing a thing would add 100hp.......Really? They do seriously outflow the
Edelbrocks.

So how does one really know?
We can't afford to buy 5 sets of heads and compare them. And guess what....the car mags aren't going to run these tests either.

I think we have to educate ourselves, talk to the head mfgrs, and talk to other racers. See what they are running.

Then....just ask Mike at Wolfplace for a recomendation. We can't re-invent the wheel here, and there are combinations that are flat known to run.

Ron

If you mean a 500" engine with a 4.47"+ bore (502-509), Then i'd go 310-325 cc for what u want. I say up to 325 because if you ever want to step up to a 540, the heads would still work. For a 502, they might be a little overkill, with a 540 they might be a tad too small, but cam choice can fill the gap to the rpm range u want to run. Since you want to run juice, and your already talking about pretty big inch engines, you dont need to run a small head to build torque. Now if you dont want to go to a bigger block in the future, and your happy with a 496-509, I would probably go with a 290-310cc head for that rpm range.

Now you mentioned about nitrous affecting head choice. It does to a degree. Power-adders seem to need more exhaust extraction over an N/A engine, hense why most nitrous cams have much more lift/duration on the exhaust side. A head like the AFR's flow exceptionally well on the exhaust side, and the Canfields are great too. With the Exhaust/Intake % being so high, a single pattern cam is usually best for a street N/A combo. All this makes your head choice critical before deciding on a camshaft. With a head with good exhaust ports, u might decide on a cam with a little less radical exhaust lobe, compared to a head that flows poorly, u might want something with 10 degrees difference @.050. As far as intake port volume reflecting the performance on a nitrous engine, I dont think it would be anything significant, unless you were completely choking the air with a tiny port, or running a huge port that hurts efficiency, given the engine size and rpm you plan to run. Im sure there is someone better to give you more educated tips in that area.

534" pump gas, hyd roller, single plane 3.73 gears 69 camaro 3750 lbs w/driver.
Dart 325 heads.
Best to date 10.19 et @ 131 mph
Shifts are made at 5400-5600 (1-2) and 6000 (2-3)

Hoping to improve with a few changes, just thought I`d help with this info.

John L. once said that a good oval would support up to a decent 540 motor!!

I would dearly love to see a cast-iron, oval port Merlin brought out that had a 290 cc intake ports AND a 90 cc chamber THAT still used stock valvetrain parts!!!

And at the present cast-iron Merlin oval prices too....

I bet they would take the lower priced 454/468/496 head market completely over, imho....

Suckers would be dandy for stock 454 P/U motors too.....

pdq67