Imo Apita
Well-known member
- Joined
- Feb 28, 2009
- Messages
- 244
I'm trying to avoid the bigger is better trap.
Given the same flow numbers would you use a 2.02 or a 2.055 valve in a 4.030 bore?
Street driven, rarely track, 6500-700 rpm max.
Having a hard time choosing between the Brodix Ik200 (2.02) and the Brodix RR200 (2.055)
IK200:
http://www.brodix.com/heads/ik.php
RR200:
http://www.brodix.com/heads/raceritesb.php
If we assume same flow, same cost, is a 2.055 still better in other area's then flow alone or is there too much valve shrouding in a 4.030 bore?
IK 200 :
123 @ 0.2 lift
181 @ 0.3
230 @ 0.4
RR 200 :
125 @ 0.2 lift
182 @ 0.3
227 @ 0.4
We're talking about +2/+1/-3 CFM difference between the heads here.
That is 1.62% difference at 0.2 lift.
Is there such a thing as a linear translation to HP?
Now this is Cubic Feet per Minute so a volume of air.
This is where I get confused; (oversimplified) speed x cross section= flow correct?
So are we talking higher speed x smaller cross section for the 2.02
and lower speed x larger cross section for the 2.05?
So for instance at 0.3 lift its higher speed x smaller cross section = slower speed x larger cross section = 181 CFM?
If the above is the case do you get better cylinder filling (volumetric efficiency) with the smaller valve?
How does an intake with relatively narrow (higher speed) runners tie into this?
Is the better combination a fast intake with a fast (smaller) valve?
Or a fast intake with a slower( larger) valve?
Or a slower intake (larger runners) with a faster(smaller) valve?
My instinct tells me a fast runner with a slow valve and a slow runner with a faster valve should work as they "crutch" each other.
I've been reading the Smokey Yunick book and this shows you again that a little knowledge is dangerous (besides confusing).
Any thoughts?
Given the same flow numbers would you use a 2.02 or a 2.055 valve in a 4.030 bore?
Street driven, rarely track, 6500-700 rpm max.
Having a hard time choosing between the Brodix Ik200 (2.02) and the Brodix RR200 (2.055)
IK200:
http://www.brodix.com/heads/ik.php
RR200:
http://www.brodix.com/heads/raceritesb.php
If we assume same flow, same cost, is a 2.055 still better in other area's then flow alone or is there too much valve shrouding in a 4.030 bore?
IK 200 :
123 @ 0.2 lift
181 @ 0.3
230 @ 0.4
RR 200 :
125 @ 0.2 lift
182 @ 0.3
227 @ 0.4
We're talking about +2/+1/-3 CFM difference between the heads here.
That is 1.62% difference at 0.2 lift.
Is there such a thing as a linear translation to HP?
Now this is Cubic Feet per Minute so a volume of air.
This is where I get confused; (oversimplified) speed x cross section= flow correct?
So are we talking higher speed x smaller cross section for the 2.02
and lower speed x larger cross section for the 2.05?
So for instance at 0.3 lift its higher speed x smaller cross section = slower speed x larger cross section = 181 CFM?
If the above is the case do you get better cylinder filling (volumetric efficiency) with the smaller valve?
How does an intake with relatively narrow (higher speed) runners tie into this?
Is the better combination a fast intake with a fast (smaller) valve?
Or a fast intake with a slower( larger) valve?
Or a slower intake (larger runners) with a faster(smaller) valve?
My instinct tells me a fast runner with a slow valve and a slow runner with a faster valve should work as they "crutch" each other.
I've been reading the Smokey Yunick book and this shows you again that a little knowledge is dangerous (besides confusing).
Any thoughts?