This is a long awaited topic I've wanted to start for some time but have been eagerly awaiting some cylinder head flow data in order to start it. As a starting point, I'll focus on what Nissan gave us from the factory.
There has been a LOT of myths floating around in the public domain regarding what is and what isn't possible from a CG engine.
Way back in the mid 90's, when Nissan Motorsport Europe was still a thing, there was a well known statement that, on a good day, the standard UKDM cylinder head was good for about 130bhp. So, unless you were looking to try and exceed that, there was little value in putting money into the head. Well, based on the time spent on the SuperFlow bench and dyno, I can confirm that Nissan Motorsport Europe were bang on the money.
Flow graph for a standard UKDM cylinder head below (all flow figures measured at 10" water).
Translating the intake flow into theoretical power we need to do a bit of calculation. The caveat here is, the head has the capability of making these numbers providing the rest of the system can keep up, i.e. there aren't any restrictions elsewhere.
CFM x 0.43 x no. of cylinders = Theoretical power (bhp)
76 x 0.43 x 4 = 130.7bhp
Based on what we've seen on the dyno from various engines in the past, and what others within the competition arena have shown, this supports what the flowbench shows reasonably well. Granted, the flowbench isn't the be all and end all but it certainly provides a good guideline on how an engine can perform.
On a standard compression CG13DE with a set of Jenvey ITBs (effectively a de-restricted intake) a set of 264deg 9.1mm lift cams and a decent exhaust system, I personally saw 123bhp on a Dyno Dynamics rolling road. Between dynos and minor differences the average output range for this spec is typically around 125bhp average. Power wise, that's putting the head flow out to be 71-73CFM from a maximum potential of 76CFM.
Compare this to a stock intake manifold, which only typically musters around 100-105bhp depending on engine health with the same setup, this shows how much of a restriction the standard intake poses. Some quick calculations shows that, in order to make 100-105bhp the head would need to flow 58-61CFM equivalent peak. This is a significant drop on what the head is capable of so, the standard intake is helping to easily rob the engine of at least 10CFM right off the bat.
Given how much power the majority of people are seeing from the CG heads, both the dyno and flowbench shows that the standard exhaust valves and standard exhaust ports (although less than ideal on paper) are perfectly capable of flowing enough to be able to keep up with the intake.
Not that I am going to go into details on ported heads yet but, from what I've seen on a competition level and, again on the flowbench, a well ported head on standard valves also shows that the exhaust side of the head is man enough to support the intake flow. In fact, the exhaust side responds significantly better to porting than the intake side (typically by a factor of 2), which strongly suggests that another myth I've also heard (that it's not possible to port the exhaust side of the head effectively) is also false.
I've got plenty more data but it's going to take some time to go through, run some numbers. What I can say in advance is, the data shows why Nissan Motorsport Europe had a hard time reaching the golden 150bhp target that I see thrown around a lot.
There has been a LOT of myths floating around in the public domain regarding what is and what isn't possible from a CG engine.
Way back in the mid 90's, when Nissan Motorsport Europe was still a thing, there was a well known statement that, on a good day, the standard UKDM cylinder head was good for about 130bhp. So, unless you were looking to try and exceed that, there was little value in putting money into the head. Well, based on the time spent on the SuperFlow bench and dyno, I can confirm that Nissan Motorsport Europe were bang on the money.
Flow graph for a standard UKDM cylinder head below (all flow figures measured at 10" water).
Translating the intake flow into theoretical power we need to do a bit of calculation. The caveat here is, the head has the capability of making these numbers providing the rest of the system can keep up, i.e. there aren't any restrictions elsewhere.
CFM x 0.43 x no. of cylinders = Theoretical power (bhp)
76 x 0.43 x 4 = 130.7bhp
Based on what we've seen on the dyno from various engines in the past, and what others within the competition arena have shown, this supports what the flowbench shows reasonably well. Granted, the flowbench isn't the be all and end all but it certainly provides a good guideline on how an engine can perform.
On a standard compression CG13DE with a set of Jenvey ITBs (effectively a de-restricted intake) a set of 264deg 9.1mm lift cams and a decent exhaust system, I personally saw 123bhp on a Dyno Dynamics rolling road. Between dynos and minor differences the average output range for this spec is typically around 125bhp average. Power wise, that's putting the head flow out to be 71-73CFM from a maximum potential of 76CFM.
Compare this to a stock intake manifold, which only typically musters around 100-105bhp depending on engine health with the same setup, this shows how much of a restriction the standard intake poses. Some quick calculations shows that, in order to make 100-105bhp the head would need to flow 58-61CFM equivalent peak. This is a significant drop on what the head is capable of so, the standard intake is helping to easily rob the engine of at least 10CFM right off the bat.
Given how much power the majority of people are seeing from the CG heads, both the dyno and flowbench shows that the standard exhaust valves and standard exhaust ports (although less than ideal on paper) are perfectly capable of flowing enough to be able to keep up with the intake.
Not that I am going to go into details on ported heads yet but, from what I've seen on a competition level and, again on the flowbench, a well ported head on standard valves also shows that the exhaust side of the head is man enough to support the intake flow. In fact, the exhaust side responds significantly better to porting than the intake side (typically by a factor of 2), which strongly suggests that another myth I've also heard (that it's not possible to port the exhaust side of the head effectively) is also false.
I've got plenty more data but it's going to take some time to go through, run some numbers. What I can say in advance is, the data shows why Nissan Motorsport Europe had a hard time reaching the golden 150bhp target that I see thrown around a lot.
