Kaama: Looking forward to seeing your results. How's Dave doing? Did he get the Supercat together?

I went to lapouttres shop today (he is our local head pro -head porter). On the phone last week he said he had flowed a set of afr 305's a customer brought in that had chamber work and pocket porting done to them by afr(I'm going to assume that this mean't afr's cnc chamber option). He said they barely flowed better than a set of stock heads with a pocket port job,he also flows his heads without a "cheater pipe" on the exhaust for copmarison reasons at 28" water column press. He showed me the sheet for those afr's today and personally they still looked pretty good:
intake exhaust
.200-162---131
.300-233---184
.400-291---219
.500-317---239
.600-326---248
CANFIELD 310 w/full CNC? I don't know what size they actually were cnc'd to
.400-268---203
.600-356---268
Anyways,he showed me flow sheets for several cnc'd heads (darts,canfields etc) and NONE of them ouflowed the 305's under .500 lift,were close to equal at .500 and had about 40 cfm at .600 and increased steadily from there on up. Now,i explained to him again, i have a 540 that i run a .620 lift cam in, it has to idle and make good torque when not under boost (cruising rpm's-2500-4000) and not have ports that will create a LACK of velocity or reversion,He did admit the afr's actually did have some excellent low lift flow #'s in comparison to most the rest and also said the cnc ones would probably compare to the bigger cnc'd competing brands. I plan on buying the cnc 315 afr's,i will have them flow tested,they might flow 30-40 cfm less than what they claim but they should still have around 350/270 at .600 if they gain 10% compared to the ones he flowed,Smitty

Check out the cylinder head database that chevy hiperformance mag is putting together. The idea is same bench/operator/techniques. The numbers for a particular head might be different from what others have measured but should be comparable with the numbers for other heads in the same database.

They often test the exhaust both ways; with and without the pipe. It's not a cheater pipe. Since the head will be used with pipes in real life maybe you should port for the best flow with a pipe.
Unfortunately they have not tested the AFRs.

http://chevyhiperformance.com/techar...98/index9.html

Here's an example:

He showed me the sheet for those afr's today and personally they still looked pretty good:
intake exhaust
.200-162---131
.300-233---184
.400-291---219
.500-317---239
.600-326---248


Here are some numbers from a ported Dart head with and without a pipe @ 28"
......Exhaust.......W/pipe

.2.......149..........156
.3.......203..........216
.4.......288..........262
.5.......265..........295
.6.......281..........318
.5.......297..........327
.7.......308..........344


Somthing you guy's may be missing is that the venturi areas are very close to the same in the AFR and Dart heads. The Canfields may be bigger I don't remember. The valves are the same size. So at this point we are compairing apples to apples. Because of valve overlap and piston speed (or lack of) checking airflow is not that important at lifts below .200.
Im running out of time, more to come

Hi Jim:

Good point about venturi and valve size. I was trying to visualize this idea. When you have time could you comment on the following:

There are two ways to reduce resistance to airflow and they apply to cylinder heads like anything else.

1) Make the hole bigger. The hole can be venturi area or the area between the open valve and the seat. For lots of reasons we don't want a bigger hole than necessary, so the second method is usually the one we want.

2) Reduce losses through the hole. In my business we call this reducing the loss coefficient. In practical terms it means preventing flow from detaching from the wall and going turbulent.

Nowhere is this more important than between the valve and the seat, and in the area immediately before and immediately after the seat. Correct me if I'm wrong but isn't this where it's at for lower lift numbers and the main benefit of porting?

Once the valve to seat area is wide open at high lift, then maybe the "small" venturi becomes the restriction.

One thing I don't understand; do smaller venturis always give better low lift numbers than large venturis? Is this because the larger venturi creates a sharper radius into the valve seat on the floor of the port?

I like the idea of your wedges because raising the floor makes the short radius bigger. I never understood why Edelbrock/GM didn't raise the floor of the "square-oval" aluminum heads. If you're going to keep port volume small it makes sense to do it by raising the floor vs lowering the ceiling of the port.

Tom

Two years ago when I was shopping for heads I talked to AFR & told them about my motor. (bbc540, procharged with 10-12lbs boost 8:1 compression, crane 741 cam, & cmi elbow tops) Who ever I talked to said that they felt the 315's were too small, the 335 were what I wanted for a boat motor & that the 357's were too big. Don't know if they changed their mind but I do not feel like I am lacking any HP. On plane at 2200 rpm when I go WOT the motor instantly goes to 4400rpm & then starts pulling from there to max rpm. Could not ask for any more low end torque.

Turbojack,i talked to afr today and they also told me out of their lineup of heads the cnc 335's were the way to go on my 540 too,Smitty

Smitty,
I'll be more then happy to fax you a couple of dyno sheets on marine engines with small square port heads, a 540 and 572. Just for reference if you would like. Cylinder head mfgs are good guys, but most think power begins at 5000 and doesn't stop till 8500.

Chris

Hey Chris:

I'm looking for a good base engine to put my system on and sell as a package. I would be interested in hearing about your dyno tests.

Tom

(416) 709-8714

Chris,in your opinion what head would you reccomend for my application? Currently 540 ci,.600 lift hyd roller,lightning headers,8-1 compression,procharger w/intercooler 9-10 psi boost,502 merc efi plenum and intake,merlin vr heads that are supposed to flow around 300cfm in/200 cfm ex at .600. On dyno last year w/ 5-6 lbs boost and 4 degrees less ign timing it made 600+ft lbs torque from 2800-5400,peaked at695 at 4300,hp was flat 630- ish from 5300-5500. Since installing in boat w/dissapointing results i have lowered base fuel pressure 5 psi,increased total timing 4 degrees and raised boost 4-5 psi gaining 8-10 mph,i'm guessing it is now around 800 ft lbs/725-750? hp. I didn't look at the merlin flow #'s when building the motor,the intake to exhaust ratio is only 65 % or so,when i freshen it this winter i am thinking a set of better flowing heads (or at least ones w/a intake to exhaust ratio around 80%) would give me more topend horsepower. The boat will already accelerate thru the midrange like it has nitrous but i would(like everyone else on this board)like more top end with out giving up ANY midrange. I am also planning to ditch the fuel injection as i am at the limit of what it will do and go w/a carb,aluminum open plenum intake etc. The afr cnc 315's with 20 % more intake flow and 30 % more exaust flow are looking pretty good to me but afr says the 335's are the way to go.So when you say small square port heads, what yours mindset of size and flow you would use,what kind of flow #'s did you have and dyno results? I may even have this motor dynoed when it comes out this winter(its not hurt) so i have before and after results of what i build,Smitty