does anyone know what stock 041 heads flow?

 

I got this off the net. This is a flow test of the 040 head
it is the same as the 041 head.

We recently flowtested a set of 041's with moderate porting a and 2.02's and 1.60 We got 225@.500"which agrees with JD2 below. This is typical for a moderately ported head in this class.
Its aso aproximatly the same as an out of the box vortec or Performer rpm head.


TESTS JD1 JD2 JD1a JD2a
LIFT CFM CFM CFM CFM
.050" 32.9 32.2 32.5 31.5
.100" 64.3 61.0 63.0 62.4
.150" 97.9 90.8 95.7 89.3
.200" 127.6 122.0 123.3 116.1
.250" 154.9 147.8 146.1 138.4
.300" 177.0 172.9 165.3 155.2
.350" 197.7 193.6 177.1 170.0
.400" 203.0 212.8 184.5 181.8
.450" 210.6 227.6 188.9 189.2
.500" 215.5 230.5 191.3 189.2

Tested using a 3/8" clay radius on the intake port and nothing on the exhaust port.
Used a 4.00" cylinder bore size.

This is a small block Chevrolet 040 casting cylinder head. This head is very simalar to the old 462 casting FI heads. It is rare and found on 1968 thru 1972 Chevy trucks.
I kept the small 1.94" intake valve size, using a manley "Pro-Flow" style valve.

TEST JD1 had been mildly ported and gasket matched to a FelPro 1205 Gasket size.

TEST JD2 is the result of making the bowl area under the valve bigger. I didnt make it much bigger, probably only removing about .020" of material. The port lost quite a bit of mid-lift flow and gained a flow from .400" to .500". After .500" lift the flow still drops off. (This is typical of any cast iron OEM chevy head.)

TEST JD1a was made using a 1970 Chevy Camaro Z28 aluminum hirise intake manifold and 750 CFM Holley Carb on the JD1 Port.

TEST JD2a used the same manifold and carb on JD2 port. As you can see the gains made in enlarging the bowl area did not improve flow once the intake manifold combination was installed.

I feel the flow lost in the low lift ranges will hurt performance. I need to test the JD2 port with an open plenum intake manifold such as the Holley Strip Dominator 300-25.

 

Keep in mind, with your 283 you have to take into consideration that port volume air speed (velocity) playes and important roll. Further porting and enlarging the port beyond this will get you more flow,(mostly at higher lifts) but the air speed will start to get lazy relative to rpm. Meaning you have to rev the bejesus out of the lil 283 to see a gain and bottom end torque will tend to get lazy.
This head ported like this is a good compromize for a hot street
283. 380/ 415 hp potential with the right combination.
Even then you'll need a stiff rear gear and high stall converter to keep the motor in its best range. Hope this helps.

 

do you think it would be best to just match the ports and polish it to keep the bottom end?

 

All depends on what your trying to achieve. If you're going to keep the cam you have now, then a maxed out huge port is not what you want. But there is some material that has to go.
Intake port:
Open up the bowl pocket directly below the valve seat.
On a mild 283 you don't nesssessairly want to hog it right out,
but create a funnel or venturi under the valve seat while smoothing the machined edge under the valve. This will retain the low and mid lift flow and volocity. The "funnel" diameter should be .85% the size if the valve seat.
The valve guide needs to be slimmed trimmed and streamlined.
You'll notice that the bowl pocket is offset under the valve seat
towards the common wall.
Don't try to straighten this out by over hogging out the side near the exhaust vale. this offset or "port bias" is there
for a reason. It creates a swirl effect as the flow enters the cylinder.
All the rough cast finish needs to be removed from the port.
But do not polish the intake port at all. Carbide cutters die grinder stones and 40/60 grit rolls are all that you need.
The roof needs to be raised all the way from the inlet to the bowl
About .125" or to match the gasket.
The common wall needs to be cleaned up and straightened.
This area in the bowl between the common wall and roof an guide boss is the high flow area. Concentrate your work there.

I like to finish with a rat tail file that has been cut off to fit the die grinder or electric drill. Really helps to straighten out your work. The floor of the port only needs to be cleaned up.
The short side radius needs to be smoothed and blended into a nice radius from the valve seat to the port floor. Again do not lower the floor. The port opening only needs to be squared up
to a stock gasket and cleaned up . Do not make it huge.
The pushrod wall only needs to be cleaned up.

Exhaust port:
The exhaust port bowl needs to be opened up a little under the valve removing the ridge. Again radius the short side.
The exh. boss needs the same treatment as on the intake
slim it, trim it, and streamline it. The exhaust port opening does not need to be enlarged, really, just clean it up. You can polish the exhaust port and combustion chamber to your hearts content.
Port match the intake manifold to the head about 1.5 inches into the manifold. Do not polish your intake work.
Give it a good going over but use common sence here.
Don't make huge ports.
Follow this , and your lil 283 should boogie.
You may want to measure a calculate the true compression ratio of your 283. decking the block and or shaveing the head will correct it if it is too low. high perf 283's came with small chamber heads like 55 to 60cc and domed pistons.

 

what my plans for this engine are to get a 327 or 350 4 bolt block and put the 283 crank in that making a 302. i'm going to get the compression up to about 10.5:1(real 302s were 11:1 but i think thats a little high for pump gas). i'm going to get a higher stall converter and put in a cam with about 220-230 duration at .050 and about .450 lift(like the real 302s).

the 302s were rated at 290 hp but they say they were underrated so the could race. they are soposed to have like 350hp around 6000-7000.

 

Before GM built the 302, hot rodders of the era used to make their
own by boreing the 283 to 4.00 inches. Thus 4.00x3.00.
Most people called it a 301.
You would emulate a real 302 better by going this route.
The 283 block bores need to be sonic checked for core shift first thou. Once given a clean bill of health it is bored from 3.875" to 4.00" Then you use TRW forged domed 302 pistons. (Federal Mogul)
The real 302 had a solid cam.
specs were 254/254@.050 .485" lift 114LSA and .030" lash
Thus the name "30-30 Dontov cam"
The Trans AM racing 302's had 12.5 cr, fully ported heads and either of the off road Z28 racing cams of the era. These cams are listed on the GM performance Parts Catalog to this day.
Namely 1st design off road "140" cam and 2nd design off road cam. These were used in conjunction with a one off special
Dual holley carbed "Cross Ram" Manifold, and headers. When you bought a Z28, you could order this Race stuff, but it came in the trunk. You or the Dealer had to install it.
Power was right around 450HP in race trim. The power band didn't start till 4000+ rpm and would buzz well past 7000. There were no high stall racing converters at the time so all Z28's came with 4 speed manuals. Rear gearing was 3.73 stock but most ran 4.88 to 5.38 for drag racing, even on the street. You could buy the gears right from GM. This where the small block got the reputation of a high reving power beast.
" Nothing revs like a small block chev"
With the right Roller cam and valvetrain, a tunnel ram, and 6:1 gearing,
10,000/13,000 rpm is not unheard of in a fully prepared drag racing 302.

 

DEAR F-BIRD
can you tell me please where did you get the flow numbers? or where can i go?
i'm trying to get the same info, from a set of 416 heads.
thank you very much.
Fernando.

 

I don't remember exactly where I got those flow numbers.
There were other heads tested like Bowties and sportsmans,
but not the 416's. I've searched for a flow test on stock416's.
Not there. The 081's flow real close to the 416's in stock form.
The ports and valves are the same. Only the chamber is different. They flow 195cfm. The 416's will be within 5/10cfm.
Your going to port them and use bigger valves anyways right.
Don't get all wrapped up in the numbers. Get a set and do 'em up. They'll make power.

Here are few sites from professional head shops that
have some flow typical results on different ported heads.

These are not the last word on head flow but are typical.

http://www.kendrick-auto.com/head_flow_figures.htm

http://www.castheads.com

 

actually, i did port them myself and after did send them for overhaul with a 3 angle valve job, but no bigger valves.
i was thinking on selling them (i used to have a 5L. but replaced for a 350, now i'm repairing the 350 and i have those heads already overhauled and pay'd for, so i'm gonna use them as it is.
the old heads from my 350 were real crap, 76cc, 1:74/1:50 valves, with dished pistons.
as it was that 350 did rock a bit, but i think with these 416 heads as they are will be much better, tell me what you think please.
thank you very much for the sites, i'll sniff around.
Fernando