c3_dk

Strokemyaxe

Love this show

NewbVetteGuy

I'm still watching it, but I'm afraid where they go.

They started off pretty well describing that it is the cross-sectional area that actually matters, but then the discussion starts to focus on intake volume...

If they're comparing AFR heads only, designed with the minimum CSA possible and are then drawing broad conclusions, it can and will result in people making bad decisions.

I agree that if you're buying top-tier heads design with min and average CSA and velocity at the forefront that you can get away with bigger ports and a smaller cam, even on 23 degree heads. With old-school, 23 deg heads, you can still get into trouble and end up with a lazy port.


Adam

Neil B

I love the show too. The reason the 165 head worked was because of the wimpy 218@.050 cam. The combo was cam limited, not head limited. I'm not saying it was a bad cruiser combo, but put a bigger cam in it the the bigger heads would have walked away. The 5,400 rpm power peak simply did not need any additional port cross-section. Nobody in their right mind would run a 220 head with that cam but it was interesting that the added port volume/cross-section (and presumed drop in velocity) didn't give up any low end torque. That definitely dispells some myths.

NewbVetteGuy

So what happened with the 220cc head? My guess is that the 2.1" intake valve is too big for the bore.

I would've liked to see the 220cc head with the same 2.05" intake valve; I think it would've had best torque by a tiny bit and best hp by quite a bit.
The torque was killed by the valve size and valve shrouding and not the difference in the min / avg CSA -that's my guess.



Adam

v2racing

There is a lot wrong with this test. First is that the manifold port upstream of the head should match the port size of the head. The stock intake port opening at the head is obviously going to be too small for the 220 head and this can cause problems. Velocity drops as air exits the manifold and enters the port. This tends to make fuel drop out of suspension and lessons the airs inertia in the port.

Secondly they are not addressing the L/D (lift over diameter) for the larger valves in the bigger heads. The 1.94 intake valve lifted to the .500 they used gives a L/D of 0.257. This is in a decent street performance range.

The 2.05 valve has a L/D of 0.243, handicapping the 2.05 valve a little from the better 0.257 of the 1.94 valve.

The 2.100 valve has a L/D of 0.238 which is dropping well below the ideal L/D for the 2.100 valve. The correct lift to equal the L/D of the 1.94 valve would be .540.

In a performance engine an L/D will usually run at least .300. Race engines can go as high as .400 L/D. I run a .650 lift on my 2.100 intake valve giving me a L/D of 0.309.

One other issue that could be affecting results is the fact the 220 head has a smaller 1.57 exhaust valve whereas the other 2 heads have a 1.6 valve. With the increased flow of the 220 port head along with it's larger 2.100 intake valve, the exhaust to intake flow ratio could be and probably is down from the other 2 heads. This would tend to call for more duration of the exhaust lobe to optimize this head.

The short 218 duration also does not address the higher rpm potential of the 220 head.

It all boils down to building the right combination of parts that work together to make the best results. Had they addressed the needs of each head for combination, the 220 head probably would have blown the other heads away in torque and horsepower.

Mike

Neil B

I agree the valve was too big for the bore, but I think port cross-section played a role. For Max HP RPM of 5400 and Bore of 4.030 and Stroke of 4 is a Cross Sectional Area of 2.02 Square Inches. The 220 head was just a bit too big at 2.2 sq. in. Put a real cam in that motor where it peaks at 6k+ and watch the 220 heads shine. It's all in the combo. But I agree the 2.1 valve needs a bigger bore.

v2racing

The valve is not too big for the bore. The ideal valve to bore ratio for a wedge engine is about 52%, which comes out to about a 2.100 inch valve for a 4.03 bore.

It is pretty much impossible to get too large of an intake valve in a small block Ford, Chevy or Mopar.

Mike

PS: Four valve heads usually have much greater valve area to bore size than two valve heads. They do not suffer from torque loss. Larger valves do not kill torque.

Neil B

I might have said that wrong. I don't know my Fords, but a 4 inch bore is gonna run into shrouding issues with bigger valves. Kinda like going bigger than a 2.19 valve on a 4.250 bore BBC.

ajrothm

And who runs a gay *** 218* cam in anything besides a stock rebuild anyway??

I agree, the 220 heads would have ripped if it had a real cam.

v2racing

Having done an enormous amount of head development on a flow bench over 4 decades, I can tell you the larger valve will still flow more air than a smaller valve, even if it is getting closer to the cylinder walls.

Mike

Neil B

Ok. I don't have real world experience with this so I'll retract. But I do know that most guys don't recommend going bigger than 2.19 valve in a 4.250 bore BBC. I'm not sure what applies to small block Fords with even smaller bores.

NewbVetteGuy

Man, I love your posts! Some great stuff in this thread.


I've definitely heard that moving beyond a 2.05" intake valve for a 4" bore SBC can reduce velocity into the cylinder because of shrouding around the cylinder wall and that 2.08 and 2.1" intake valves are for 4.1" bore motors; you seem to disagree with that.

(I'm not saying you're wrong; this is just the first time I've heard this statement that you can't get a big enough intake valve in a typical small block chevy, ford, or mopar before, so I'm clarifying that I'm hearing you right and this statement isn't caveated somehow.)


Adam

NewbVetteGuy

It will flow more air on a bench, but will it make more power in a running engine where velocity is king? (real question)


Adam

v2racing

Very large valves in a stock BBC require notching the top of the cylinder bore to unshroud the valve and help with airflow on that side of the valve.

So if you are unwilling to do the notching, then yes, you probably don't want to run larger than 2.19 valve.

Mike

NewbVetteGuy

Lift over diameter, what a cool concept! Now to go and calculate mine!


I love these rules-of-thumb!


Adam

NewbVetteGuy

Mike,

I've got the 195cc Profiler heads with a 2.02" intake valve and an aggressive hydraulic roller cam and 1.6 ratio RRs so the intake valve lift is 0.600"; if I did this correctly, my L/D ratio is 0.297.


Now what exactly is this ratio supposed to roughly indicate/approximate? Avg Velocity of the air past the valve? (I don't see how that can be without taking into account RPM)...

-What's the purpose or reasoning behind the recommendation for the ratio?
[Edit] Decent intro: https://www.cartechbooks.com/techtip...e-performance/



Adam

v2racing

The big valve will definitely have more shrouding than a smaller valve, but it will still flow more than a 1.94 valve if you maintain the same L/D at max lift for each head/cam combo. You will end up with more valve curtain area with the larger valve resulting in more airflow at a given L/D lift percentage.

If you go to a larger bore, it will unshroud the valves more and the heads will flow more at a given L/D lift that is the same between the smaller and larger bores.

The thing about all the small blocks is there just isn't enough room to get a valve large enough to negatively affect the torque.

Mike

Strokemyaxe

Maybe I don't understand what this episode was about because you are all arguing a different question than the one that I thought was being addressed. The question I thought being asked was if the common internet myth of "Larger heads on a small cam decreases low end torque" was true or not across the board. That's all. What's being said is "No. Especially not in this setup".

-Stroke

v2racing

You are almost at .300 L/D which very good for a hot street engine.

It's basically a scale of size. A larger valve with a good port will flow to a higher lift than a similar smaller valve with equal quality port but smaller in volume at close to the same percentage of valve size drop. At some point you will reach a point of no return and sometimes even lose flow at too high of L/D. The port shape and size, valve shape/angles, seat throat area and shape will all play into what the maximum effective L/D will be.

To use as a good rule of thumb, .250 is a decent mild performance goal. For a HOT street/strip engine .300 is a good target. For all out racing, go up in L/D until there are no more gains in increasing airflow. But even going beyond point of no more gains in flow with high L/D numbers, as long as flow is not dropping off as lift increases, a higher L/D can still gain some power by increasing the degrees of intake duration that the valve is at maximum flow.

Mike