I am curious to know if any of you guys can tell me what is consider a very good flow on cylinder heads ( 3.2, 3.3) at 500 lift. any inf will be appreciated, stock, modify, anything.

 

I have waited to see if any of the experts replied to you on this. Seems it is not any great secret what these heads flow. Rather the opposite. If I knew what someone was offering in flow from ported heads I might buy from them. Most times the flow numbers are exaggerated along with the dyno numbers. Not many shops have flow benches or do their own porting in house. Then the numbers really get hokey. I do not have any tonite, but I will get some tomorrow and give them to you.

From my own experience, the exhaust ports need all the help. Any increase in the Intake side, needs to be added more to the exhaust side. Up to a point, porting help, but then the Valve sizes become the limiting factor. There is a mathmatical equation which calculates the amount of air required to produce 1 HP. If I can find this, I will supply with the flow numbers. As with all upgrades, the amount you need is all based upon the performance and use.

Tito, PM me with your email address and I will provide offline.

 

Calculating HP really depends on the efficiency of the engine and the Brake Specific Air Consumption (BSAC) can help you determine a theortical hp level for a given mass of air.

If for instance, you know your engine is consuming 1500cfm of air at standard conditions, you can find out its mass (1500cfm * .076) which is 114lbs of air, and if you know the BSAC of the engine, lets say 7.5, then you know the engine should be putting out 855hp (114lbs * 7.5BSAC).

If you know the engine capacity, fuel injector size, fuel pressure, air fuel ratio, and injector pulse width, you can calculate the actual air flow, air mass, %VE, BSFC, and BSAC for a given RPM.

I agree with M42Racer that the 930 head benefits from larger exhaust valves and the intakes benefit from the smaller diameter stems.

 

I have waited to see if any of the experts replied to you on this.

I have waited 5 years for all the experts and Thank God we have survive without them...................

Regarding the heads they are 3.2 heads with

Ferrera Stainless Steel Valves Undercut
Custom Bronze Valve Guides
Custom Seats
Ported
Racing valve springs and titanium retainers

and last one.... of the kind prototype exhaust insert to speed the velocity of the air out of the heads, the numbers are.....


LIFT in ex
.100 77 60
.200 163 116
.300 219 164.5
.400 255 204.5
.500 280 227.2

But I was curious if any of all of this 800hp guys can share some numbers.

 

Tito,

I'm not sure that there are that many 800hp guys out there, I applaud your lofty goals. It has been my experience with a 964 based engine, not the 3.2/3.3 stud spacing engine that longevity at the higher HP levels is an issue. We have a 3.8l that is putting out a true 700HP to the rear wheels at 1.1bar of boost. It has issues leaking at the cylinder to case connection, the heads warp over time (both factory Porsche 3.6 Turbo heads, and CMW Billet heads), and the Mahle pistons tend to crack around the wrist pin area. The engine does make a lot of power, has been reliable (no catrastrophic failures), but it truly is a 20-30 hour engine. At 1.3 bar of boost it might produce 750rwhp or so, but our dyno can't hold it to test it.

As on the other board, I shared with you my flow numbers from 3.2/3.3 heads tested over the winter, your numbers look good, but not as good as a 3.6 based head which are over 300cfm on the same flow bench.

 

Geoffrey,


I'm kinda curious, how do you know what bench machine they were flowed on???

 

I only know what bench and more importantly what setup was used on the heads I flowed. As I've mentioned before, flow numbers are like dynos, they vary from bench-to-bench, mfg-to-mfg, day-to-day, setup-to-setup. You cannot accurately, in detail compare flow numbers posted on the Internet. You can get a general idea of how it flows by the trend the port takes.

What I was referring to was the ratio of exhaust port flow to intake port flow. There is a significant difference in the ratio of the ones Tito posted compared to the testing I did. Overall, it looks like his exhaust valves flow more in number and percentage than the testing I did which leads me to believe that they may have larger valves in the exhaust side.

Same flow bench meaning I used the same flow bench for the 3.6 heads as the 3.2/3.3.

 

Thanks for the input................

I was trying to compare to others................but I see that theres no many people playing with this staff, but once more thanks......

 

Flow numbers can be compared if the testing is done accurately, and the flow bench is properely calibrated. It should be the head that is different, not the test equipment. The results should always be corrected back to 25 ins of H2O, the temps etc included, as this is the industry standard. Most modern shops have all the flow bench data collected and formatted by a computer program, which controls not only the Flow bench, the recorded data as well.

Yes you are correct in your opinon that numbers seem to change from one shop to another. In the end, its the shops who give out bogus numbers who are fooling every one including themselves.

I gave Tito some numbers which are typical 2V late model RSR numbers. The RSR heads with 51.50mm Intakes and 43.50mm Exhausts. No one I have ever spoken to who does porting and flow work on these 2V heads has ever seen + 300cfm, if the numbers recorded were corrected to 25 ins. Maybe heads with 54.00mm Intakes flow this. There were several cars running engines in IMSA with 54.00mm valves.

 

The factory 993RSR sprint heads have intake valves at 54mm which is the main reason these are 30 hour engines.

The industry standard and recommended flow by bench manufacturers is 25in as you mentioned, however, many people flow at 28 in and can be considered an "industry standard" if you will.

Also, the setup on the bench WILL affect the flow numbers, particularly on the intake port where you may put a smooth transition in place. Other factors are the length of the stand, typically you want at least as much height as the stroke of the engine. I still stand that the numbers can vary widely depending on setup and method used to collect the data. I know because I can produce different numbers on my bench with different setups.

 

Geoffery,

I am interested in your opinon here. What do you mean by " sTand"? What do you mean by height and stroke on a Flow Bench? I have never heard of this.

I never knew the factory RSR's ran 54.00mm Valves. I will call Porsche and ask for the Part # as I now want these in my Heads.

In my opinon, the only reason some flow heads at 28 ins and don't correct to 25 ins, is to inflate the numbers, giving the appearance of better porting. I cannot think of any other reason. You can flow at 40 ins if the manometer goes that high, but you have to correct back to the bench manufacturers base number to even convert the raw flow numbers into the real flow numbers using the calibration values each bench is rated at. Its like using the observed Torque numbers off an Engine Dyno and factoring in some larger correction factor for the day to obtain a larger corrected Torque value.

I am very interested in what you mean by "stand"? Do you mean the fixturing to the bench and the Inlet used in place of the Intake. Most I know, use some sort of Trumpet and then re do the flow with the Intake attached to see the difference. The later becomes very hard when the Intake is some huge Plenum assembly, but when it can be done, it is.

 

By stand, I mean the fixture that you bolt the head to. The purpose is to approximate the volume of the cylinder and the "stand" the head off of the flow bench. In order to ge a proper measurement you need to make sure it is as long as the stroke of the engine. For example, on the testing I did with the 3.2/3.3 heads, I bought a steel sleeve 98mm by 78mm. This allowed me to do testing for the 3.4l cylinders and either the 76.4 or 74.4 crank. Remember that 100% air flow in an engine for a given RPM is RPM/2 * (engine capacity in CI/1728) * number of cylinders.

25in is the industry standard, however, for some reason 28in is also commonly used. I believe this began with the V8 head manufacturers as you pointed out to "inflate" their numbers and has become standard. Just a guess, I don't really know. There are also very good reasons to flow at different numbers such as to check for turbulance and other flow oddities. At a Superflow seminar a GM head engineer described a situation where during the LS6 development they flowed and designed a head but in practice it ran very poorly in light throttle, low velocitiy situations. Reflowing the head at various in of H2O showed some low air speed veloicity issues.

The issue of inflating numbers is exactly my point as to why its difficult to compare direct numbers you see posted on the Internet. This is why I was looking at the ratio of intake to exhaust and questioning the exhaust valve size because in my experience, I've not seen ratios like that using stock valves regardless of how they were ported.

I don't think you really want the 54mm valve heads. They will crack pretty much right at 30 hours of use and are about $2000 ea from PMNA. I wouldn't even think about putting them in a turbo car due to the heat. Even the 993 GT2 Evo uses 49mm intake valves.

 

OK, what has the displacement of the engine or cylinder got to do with the ports ability to flow. Yes I understand the theory of Piston displacement in an actual engine, but on the Flow Bench there is a constant Flow or suck. This pressure would be the same surely regardless of fixturing. I suppose if you stood the Head way off the bench, but who would do this. Is this not why these benches have adjustable motors/ pressures so that the correct pressure is measured by the machine right at the machine. Check where the manometer gets its signal from. Its not way up at the end of whatever fixture you are using. Its right at the flow bench. The flow bench then adjusts the motor speed to get the required test pressure. Or am I wrong.

As for the LS6 situation. Very different reasons here. Not the reason for flowing at 28 ins to obtain the overal flow potential of the head. Superflow benches are calibrated at 25 ins, so the correction numbers you use to multily the raw numbers by are all done at 25 ins. To flow at 28 ins and use these numbers and not correct to 25 ins is inflating the numbers in my opinon. Doing low flow tests etc is another matter, but these numbers should still be corrected back to 25 ins and then compared to further porting or whatever. In these tests, I'm sure its the difference that was compared, not an overall. Flowing at different pressures will always show different speeds, not sure what you mean here. Flowing at 1 pressure surely makes more sense to see differences.

I like this as I am understanding a different point of veiw and seeing how other do flow work. What makes this really good, is that we are given flow numbers as a result only, but here we can umderstand exactly how the tests were done. This way we can choose the most accurate way, and then choose the flow numbers we think best represent the true head flow capabilities.

Good work. I learnt something!

 

To be exactly specific, 25in is the industry standard for calibration for flow benches. 28in is the industry standard for most of the American manufacturers (GM FORD, etc.). Here in the USA, most aftermarket MFGs have followed GM and FORD's approach and flow at 28". In general, flowing at higher numbers allows a larger separation or scale from one reading to another. Also, the total amount your bench is rated at will dictate your maximum pressure for a given valve size. Check out your Superflow instruction manual, it has an in depth section on flowing. In short, I flow all of my heads at 28 in because it is the most common industry standard for measurement here in USA and the SF-600 can handle it. There is no absolute here, only an industry standard for calibration. Bottom line, test pressure must be included with the flow numbers to be relevant. This is why I can't tell if Tito's numbers are good or not.

You need to have the fixture equal to the bore of the engine the head is going on. The fixture straightenes out the air flow into the bench and creates a flow pattern equal to what the actual engine has. The height of the fixture also needs to be at least what the stroke of the engine but is not as critical as the bore diameter.

I always use a radiused inlet guide on the intake port to help guide the air into the port properly. Without it, the bare edge of the port will cause the air to flow in toward the center of the port rather than following the port walls, reducing the airflow. The difference can be as much as 30%

Which flowbench do you have?

 

I don't have one, but all of the work done on my heads in done on a Superflow 600 with computer control and Data acquirsion by Audie Technology, including electronic Valve control. It also has this dye machine where dye is injected into the Flow to watch the patterns etc. I also know they use a smoke machine as well. I am fancinated by this stuff. That is why I am so interested in our discussion.