VE - what would it need to be for a small port stockish SC to make 225 RWHP?

Walt Fricke · 06-29-2022, 03:49 PM

PCA Club Racing is trying to group the 1979-1994 models into one class - 911 Cup. With some not awfully expensive adjustments (mainly weight) this seems feasible. The problem child is the US SC from 1980-1983, with the small 34mm intake port. Just how much air can you flow through that port absent forced induction?

The basis for balancing power here is use of stock engine internals - cranks, pistons, CR, heads, cams, rods, and so on all need to be stock, or where necessary permitted stock equivalents. So all engine performance modifications have to be bolt-ons, though for every model other than the small port engines very little in the way of bolt on go fasts is necessary, or in some cases has been allowed with offsetting compensation.

Boring small port heads to become large port heads doesn't meet the criteria, just as "better" cams, larger pistons, more CR don't. There are various suppositions as to what adding carbs to the small port engines will do, and what additional weight allowances will do (and will cost).

I've thought of approaching feasibility in another way: assume the internals are stock. What Volumetric Efficiency would be needed for a stock small port 3.0 to produce the hp that the late Euro 3.0 or the 3.2s, with their stock intakes and CIS/DME computer fuel injection and good race exhausts make.

Use 225 RWHP as the "standard" Dyno-Jet wheel HP for the cars currently running in this class.

Does anyone have an engine program which could do this? Enter the displacement, valve size, CR, cam, and 34mm port parameters and 225 HP, and solve for VE? The result could help in determining if allowing the best imaginable intake system (independent barrel valves, EFI, tuned, ignition, whatnot) might get these models into the ball park. Where some other parameters are needed (flow bench information?), maybe use a range if no specific data available?

There are a lot of figures out there in 911 land, but most are from guys who have modified their engines with no need to deal with rules. Debates go on about best cams, use of Max Moritz pistons, questions about how much CR you can run, the most cost efficient way to increase displacement, and so on. All that isn't directly relevant to the question here. The only real go fast on the big port 3.0s and the 3.2s is the exhaust (several out there seem to approach what is possible there, and sound levels are irrelevant), and 3.2 chips are free, which are part of the 225 WHP figure.

I have one or two somewhat simple programs which might work, but I've lost the passwords for them some while ago, and I'm not very good at this approach. I couldn't get my engine's measured RWHP to match calculations.

Neil Harvey · 06-30-2022, 05:13 AM

My advice is to go slow here. Once you give PCA the number, that may what you have to race with.

Calculating the VE is an easy equation to use, but requires some known parameters. The actual airflow is what you will need. Not a guessed number.

I suggest you start with a properly rebuilt cylinder head with the seats as high as possible, (not cut low the flow is hurt), the permitted valve sizes and new ones, the Intake system that PCA will allow then flow the whole system on a calibrated bench. Whatever cam profile is allowed, you will lift the valves the gross valve lift that cam profile will allow.

Then you have a real number to use as the measured airflow. Racers then have a number that they should aim for when building an engine to run. The other number is what you calculate from the engine size allowed.

Another suggestion is to ask for a minimum weight of each internal, not "stock". This way, reliability is not an issue. This stuff is getting old. Set a max CR number so the performance and balance of power will be set. This gives some wiggle room to use aftermarket parts and achieve some room for differences in vendor supplied alternative parts.

Trackrash · Trackrash's Garage

Why doesn't PCA use HP to weight. Seems to me to be a fair way to equalize performance.

Walt Fricke · 06-30-2022, 07:42 PM

Guys - the question is this: is it possible to get 225 RWHP from a small port SC engine, otherwise unmodified from stock except for the best race exhaust (no cats, no mufflers), but with the best intake/engine management system on top of that 35mm port?

There are dyno sheets out there which support the ability of the big port 3.0s (39mm port), with CIS, to achieve those RWHP figures. Same with the 3.2s with the DME chipped.

Could the best intake and management system above the small port reach that figure?

If the VE needed to do that is pretty clearly unattainable, best to look elsewhere. I have no flow bench numbers on those heads, but the port is going to limit the flow, is it not? Yes, some guesswork, but I am pretty sure there is enough expertise out there to support this kind of exercise. It may well be that only forced induction could get enough air through that small a port to the to that kind of HP.

Fiddling with somewhat rule of thumb VE calculators suggests that an air flow per cylinder of 33 grams of air per second might get you to that HP number at a VE of 100%. Alternatively, at 100% VE a cylinder could flow 25 liters per second at 6,000 RPM, which would be 32.3g at standard pressure (fairly close to the other estimate).

Are these figures ball park? Could the best intake system (least restriction, like barrel or slide valve, or any other) achieve that? Assumes you could buy one for a 34mm port (remember, no machining of heads). Would that small port head with just some sort of tube on the port flow that? Or some amount which, supplemented with some draw from the extractor exhaust, would achieve those numbers? Stock valves, stock lift, stock cam profile, etc?

HP/wt tends to be popular, but has its issues as well. Combining dynos with parts/engine specifications works best if you are serious about keeping the performance of the engine within a limit. CR and cams can be measured on site, and occasional checking with a dyno on site should keep the playing field level so we can all measure our skills against each other.

'78 SC · '78 SC's Garage

Walt,

Would an EFI/ITB engine with stock internals give you the data you're looking for? Most modern EFI software is tuned by adjusting a VE table.

I checked my notes for an example, but my research is for motors with high compression pistons and optimized cams. Al Kosmal (x-faktory) might have some relevant examples, but I would expect most of his builds have street exhausts. What about SPEC911? Don't they run EFI and race exhausts over stock internals?

dannobee · 07-01-2022, 05:29 AM

For reference, a bone stock 32mm 3.3L turbo head flows 219 cfm @ 0.500" lift. I would think that a 34mm head would flow about 225 cfm and would use that for input into one of the calcs.
Brand new 38mm head flows 240 cfm @ 0.500".

If you send me one, I can flow it for you and give you a *real* number, if needed.

Walt Fricke · 07-01-2022, 02:22 PM

'78: a small port 3.0 with the stock 9.3 CR and stock cam, but EFI/ITB would give pretty useful data. Especially if outfitted with a race, rather than street, exhaust. Even with a street exhaust it should be suggestive, as one can apply various exhaust factors. Because the question here is whether this kind of change can compensate (or how much it can compensate) for the restriction the small port represents. By my calculations, a 34mm port has about 3/4th the cross section of a 39mm port.

Dannobee - that 240 number is certainly useful - a 34mm head isn't going to flow that much. My understanding of the Euro SC head is that the port is 39mm. Anderson gives that figure. What sort of intake, if any, was on top of that head when flowed?

The only small port heads I have are the six on my engine, where they will stay until next they need to come off (which I hope isn't for a while).

Walt

dannobee · 07-01-2022, 02:30 PM

I don't flow with an intake, just a clay radius, which is very common in the industry. Exhaust is customarily flowed with nothing on the port, or a pipe. If flowed with a pipe, it is always disclosed, as it will nearly always improve the flow. You would need to know when comparing two different heads.

Walt Fricke · 07-01-2022, 03:06 PM

Got it - thanks.

Neil Harvey · 07-02-2022, 07:52 AM

So many ways to achieve a result. No way should be considered the only way. We all are after different level of result.

We typically flow the whole intake system which for us is the Cyl head, manifold and filter assy. This way we get a flow number that to us is representative to what we will see in the car. The only difference should be a positive one if we were to gain any increase in pressure from any ram effect. We do it this way when we design our camshafts, head work and valve train parts.

We use 25" as well as this is where our bench is calibrated. 28" is often used but I have seen where the conversion factor is never applied and the flow numbers come out larger than real life. Its like HP, big numbers sell head work.

Absolutely nothing wrong when flowing a head without the Intake, but the numbers are more representative when comparing one head against another.

If this endeavor is to give the PCA some info to rule by, make sure its correct and relevant. If an aftermarket Intake system and EFI system can be used in this category, can I assume the PCA are open to suggestion? Ask if the engine internals are judged by weight and not stock part numbers.

If the crankshaft, Rod or pistons are to weight, why should it matter what brand is used. It opens up the opportunity for business in the aftermarket. The race customer needs the aftermarket support and visa versa.

dannobee · 07-02-2022, 09:01 AM

Neil brings up a good point about flow benches. It seems that no two flow exactly the same, and like Neil said, big numbers sell. If anything, mine reads a tad low (or everyone else's reads high, you choose). I do calibrate mine every single time just before I test anything.

28.00" H2O is the test depression that I use, along with the vast majority of people in the industry. Way back when, 10" H2O was the standard, only because we didn't have vacuum motors big enough to pull the big depressions.

One thing regarding head port flow, Porsche heads flow exceptionally well from the factory, across many castings and port/valve sizes. Even the small port heads will flow far more air than needed for any reasonable horsepower requirements. Will they make more power with higher flowing heads? Sure, but in the big scheme of things, they are not the restriction.

Superflow uses an equation to determine what horsepower a given port will support (MAX effort engine, NOT a street engine). 0.257 x cfm@max valve lift x number of cylinders. If you do the math on practically any Porsche engine that we see, the heads are not the restriction.

'78 SC · '78 SC's Garage

Quote:

Originally Posted by Walt Fricke

'78: a small port 3.0 with the stock 9.3 CR and stock cam, but EFI/ITB would give pretty useful data. Especially if outfitted with a race, rather than street, exhaust. Even with a street exhaust it should be suggestive, as one can apply various exhaust factors. Because the question here is whether this kind of change can compensate (or how much it can compensate) for the restriction the small port represents. By my calculations, a 34mm port has about 3/4th the cross section of a 39mm port.
...snip...
Walt

Walt, does this address the question? This appears to be a small port 3.0 with stock internals plus ITBs and EFI. The results are from a dyno session to fine tune EFI.
Car has SSIs; I saw no description of muffler.
Source thread is here.

Quote:

Big improvement! The first pull yielded 171hp at the wheels (appx 201 at the crank), after adjustments to the tables we got 193hp at the wheels (225 at the crank). I'm guessing this is about as much as one can expect from a 3.0 small port with stock pistons, cams, etc. It would be interesting to see if a big port with the same setup would fare any better.

Going back to my first post, I chose the mods I made thinking they would give me the best bang for the buck, along with making the car more serviceable, fuel efficient, and reliable. I'm sure some will have opinions about this, and btw I'm going with the understanding that a stock 1982 US was rated at 180hp (crank). This would mean the mods I've made improved power by 25%. Total cost for this improvement was around $8K for anyone interested. I suspect cracking the engine open, changing the pistons and cams and having some head work done will yield a similar improvement at a higher cost (around $10K), plus a lot more work. Just my guess.