This post is only indended to provide independent evaluation of the stock EVO VIII head vs. the head available from Cosworth. Both heads were flowed on the same bench.

Intake flow at 28.0"

Lift_________Stock________Cosworth
.050________47.5__________47.4
.100________87.5__________93.6
.150________130.9________139.0
.200________168.7________178.9
.250________199.2________211.2
.300________219.3________238.8
.350________230.1________258.3
.400________220.9________268.9
.450________224.2________274.6
.500________226.5________277.6

Keep in mind the Cosworth has valves that are 1.0mm larger than stock.

Another thing to consider is that the highest lift cams I'm aware of net .425" at the valve.

At peak lift the bench was cranked up to achieve 335cfm (Cosworth's number) and the test pressure was 41.5" H20.

 

Interesting. 41.5"?! Jesus. How much CFM do the larger valves account for?

 

What was flowed? Intake or exhaust?

 

I wonder how the cosworth would fair against a BJ stage 5 head. great post by the way. I was looking into getting the cosworth head. i have people telling me there are cheaper alternatives that work just as good.

 

This is the million dollar question. I would like to see the comparison against someone elses race ported head as well.

Ditto. Would like to know this as well.


BTW, good post. Looks like the truth will eventually come out about this product good or bad.

 

Are you Evo guys not big on port/polishing the stock head? Or are these "aftermaket cosworth" head a ported stock unit?

 

We're big on it, but it's very costly. Cosworth heads are a CNC ported/polished head, vs. most of the well known ported/polished jobs that are done by hand.

Cosworth's head is priced competitively because it includes a brand new head, while others require your stock core.

 

above the data it says: intake flow at 28"

impressive numbers for the cosworth head- solid gains across the range with huge gains up top.

 

I'm sure he can port a head that wil out flow the cosworth (anyone can) but consistancy across the head and port velocity also matters

 

The flow numbers look pretty close through .350 (only 12% difference at .350, just 6% before that, even using 41 pressure). If you account for the 1mm larger valves (without any analysis of valve shrouding, etc.) that would provide alot of the static difference in flow right there, although it would be different in real world use.

What is strange is that the stock head figures after .350 diminish rather than increase, even though the valve is fixed open wider for the measurement. Are you sure those numbers were correctly recorded and typed in? If that were true in real life, upgraded cams on a stock head would result in a HP reduction, not an increase... We all know that's inaccurate...

 

With a head that backs up like that you don't necessarily lose power if you lift higher. Not at all. You just have an inefficient head that makes less power than it could, and even that's not always true if you flow with a radius vs with a manifold - and even then it's not necessarily so unless you truly draw in right magnitude and duration pulses through the runners and in the right order.. which you can't do unless you actually run the system. For the most part it is true though.

Also, lifting more aggressively, the valve spends more time at, or over the mid to upper lifts, even though peak lift may be past peak flow. In other words just more area under the curve.

 

Guys,

This is a very informational topic. Lets keep BJ out of this thread. That topic has been beaten to death already. If he owes you money contact him personally. If you post it in this thread about how much he owes you etc.. it will turn sour pretty quickly.

 

Typically a head is flow tested on top of a cylinder which is very close, hopefully identical, to the stock bore of the engine; this accounts for valve shrouding and is possibly what is going on with the stock head at higher lifts but that's just a guess. There are some heads where you can reach a lift, say, .450, have a certain flow rate, and if you remove the valve completely the port will not flow any more air.

+6% in lower lifts is a good flow gain IMO; on a NA engine 6% across the board flow increase can be a 10% power increase.

I don't understand your 41 pressure reference. I also don't understand why this was even included in the original post. Air flow rate increases as the sqrt of pressure drop; quadruple the pressure and flow will double.

flow at P2= sqrt(P2/P1) * flow at P1

If you plug in the numbers you'll get 338 vs the 335 reported at 41.5

 

I think what your missing is the fact that 41" had to be used on the bench in order to see the numbers that were being given by Cosworth for their head flow. Therefore, yes there is a good flow gain with the Cosworth head, but is it as much as being advertised? No, not in a realistic situation.

 

I am not very good at math, but let me take a stab at responding. If you take the square root of your question and divide it by the IQ of a gerble, you will see that 335cfm was not achieved using the industry standard 28.0". You may not be able to verify this as I am using a special decoder ring from a cracker jack box.

BTW, I am just kidding with you, but my point is clear.