I purchased the Esslinger ARCA aluminum head. All I can say
is holy mother of all things that are good! It just looks like
it will flow lots of air, but I wanted to know for sure. To say
I was impressed is an understatement. I got the .585 in lift cam
with the head. I am estimated that my average flow will be in
the 230 CFM range. The head obviously needs lots of lift to flow,
but with roller cam, a lot of lift is ok.
I am now convinced that my goal of 400 hp is more then achievable,
and maybe slightly conservative. I am actually thinking that the
turbo I purchased from Martin M. may be too small.
As delivered ACRA head
>That is flow in CFM with a 28 inches of H20.
Standard Esslinger Aluminum
Your estimates are probably quite low. The power capability of your engine will now be limited only by the turbo size. Volume/pressure. The ARCA head is really the next generation of the SVO head that I have been running since 1994. Based on my recent experience with the midget head that is slightly different, your head will outflow what I have been running on my turbo engine, by a bunch, particularly on the exhaust side, which I feel is of paramount importance on a turbocharged engine. On a pure competition engine, the typical exhaust valve area and port size & shape is much too small and restricting. You will be capable of making well over 600 HP. Make sure that your bottom end, and fuel delivery system is up to the new demands. You have entered into an area that few have been and the learning curve is quite steep. Lots of luck with this new endeavour. If you have specific questions I might help with, feel free to contact me off list.
I respectfully disagree with Rick on one issue: I do not think the larger exhaust port is needed in any way. In fact I think it will hurt you a little. It will put more heat into your coolant due to the increase in exhaust port surface area and it will provide slower exhaust gas velocity to spool the the turbo with. That is just my opinion but I will back it up by saying that the boost threshold on my engine is lower than any "very high output" 2300 to my knowledge and at approx. 700 HP my exhaust / intake pressure ratio runs 1/1. This is through a header with an inside diameter of only1.37" and of course a "full" exhaust system all the way out the back of the car. Hardly a case of restricted exhaust ports.
I do however, look forward to watching Tim's progress and expect
he will make more power than his drive train will take. WITH EASE
Can you enlighten me a little to your terminology please? Specifically "boost threshold". Do you mean the limit you can run without detonation? What boost pressure is the 1/1 ratio at? You run high numbers(like 25+), correct?
Actually, Jon, I am addressing full competetion motors. I think
I mentioned that in my original note. If we look at most really
high output CART old F1 etc etc we find almost the same valve
area on intake and exhaust. Except in overlap conditions, the
exhaust flow is the same as naturally aspirated, and the .585
cam has only 19 degrees overlap. With the larger exh port, the
velocity will decrease as you indicate, but volume will increase.
The larger port will help the backpressure issue. Exhaust backpressure
should be equal or below that of inlet pressure. I measured 17psig
at the turbine inlet and 96" abs in the intake plenum.The
bar at Bonneville is 25" Hg so we are really talking about
35 psig, my exhaust backpressure was 34" Hg.Actual numbers
recorded on exh, observed data for the inlet pressure. The exhaust
backpressure is also largely a function of the turbine size. The
experimental blower I was using had a .96 A/R but actually provided
less backpressure than the 1.36 A/R I had on my previous T 04.
This is the measure of effency that I have been concerned with.
On the street I agree with you, but then I believe we can make 400 HP with an Iron head. Even though the flow bench says the iron head quits flowing at .500 valve lift, that is under vacuum conditions and with a pressurized intake system flow and turbulance will change somewhat. I have no specific knowledge as to how much, but I made enough power with the iron head to go 186 MPH average mile at Bonneville with 2.5L. Since we never dyno'd that package I have no idea exactly what power, but knowing that we went 208 with 600 at the rear wheels, the level for 186 has to be near 400. Thats as much as I want on the street.....ever....
I agree though the production type driveline will fail long before the power limit is reached in almost any SVO, Merkur, or Bird. BTW, the ARCA head exhaust port already has lots more area than the old round port. My turbo engineer really feels that flow thru my exhaust port is at or near sonic velocity. The square port will help that issue. We need to remember this head is designed for racing, not street use. The cooling issues are recognized, and actually, Dan Esslinger is working on some help now, but again it is for racing, and only a few willing to pay the price.
You, me, and now Tim. Actually there are some others. More than I originally thought. The new ARCA head and the slightly different midget head are a piece of art work. They are downright beautiful. 2.00" intake with 1.6" exhaust. As a N/A head they are quite nice. I am not trying to perputate a debate here, because none of us are brave enough to try what I have been advocating. Serious successful engine designers though have used almost equal valve areas for many many years on turbocharged engines. As I have written in the past, even the turbo'd P51 had exh valves of almost equal size to the intakes.
Esslinger TURBO 2.5 motor
The engine Keith made refrence to is a 2.5 with the ARCA head
and a .650" lift cam. They measured 600 HP at the rear wheels
at ONLY 22 pounds of boost. I do not know what blower was used,
but obviously quite large. What is impressive is that this new
head, made the same power as my motor, but I needed 33 to 36 pounds
of boost. 33 pounds at sea level. My math says they are now 25%
improved. I'd say that is something pretty good. As JD Blair emphasized
earlier though, the cooling is difficult, and on the street combustion
sealing may be tough. For those that are not familiar with the
Esslinger head, the history is interesting. 1984/85 The Esslingers,
a family business did the first alloy head with just racing in
mind. The intake ports were very high, and large. Intake valve
size is 1.890" with exhaust of 1.590". The head was
used in off road racing, SCCA - GTO (Roush Racing Merkur XR4Ti)
and anywhere else it could get in including Midget racing. The
Midget racing provided a great development ground, and in fact
the Esslingers went racing with their own deal and won the USAC
West Championship about 5 years ago. (boy is it that long).
They began improving the head around that time and developed the ARCA head along with the midget. The ARCA head is designed for gasoline and does not support valve lift much above .650" because of a weakness of only having 4 cam towers. It does however have beautiful square exhaust ports that are also now raised. The midget head has a slightly different chamber (for Methanol) and a 5th cam tower in the center so that valve lift can be increased to .735", and springs to support 10,000 RPM are not causing the cam to bend or the spring seat to collapse. I do not know what other changes between the two, but I know they both are seriously better than the original head with round exhaust ports that I have been running all along. Intake valve sizes are now up to 2.00 on the ARCA and 2.125" on the midget. Many on the 4 cyl lists do not like the Esslinger parts because of cost and a rather indifferent attitude to the turbo crowd, but the parts are among the best in the aftermarket. Period!