I agree.....

Another problem with the rule that you quoted...
The calculations would suggest that it's the exhaust that's limiting your HP, which isn't the case. The thing that limits a stock 911's head flow is the intake flow, which your equation suggests should be good for 320 HP. I also find it curious that the calculation doesn't have a term for the number of cylinders in an engine. A hypothetical 12 cylinder engine with these heads (a street 917 motor???) should make about 2x the HP of a 6 cylinder with these heads, but the formula doesn't reflect that.

Was the flow chart that you posted from a stock 2.2E head or a ported 2.2E head? The reason that I ask is because I plotted the flow against a bunch of other data that I have which I've collected from different sources. While it's generally not a given that head flow data from one flow bench will correlate with data from another, so far the data that I've collected seems pretty consistant. But the data that you posted (the light-blue line) is something altogether different.

http://forums.pelicanparts.com/uploa...1200510231.jpg

Specifically...

1) The 2.2E head that you have graphed flow awfully good at .1", in fact it flows better then all of the other heads, including the 3.3 liter turbo head which has a bigger 49 mm valve. If you look at the difference between the '66 head with it's small 39 mm valves, and the 2.2T head with it's substantially larger 46 mm intake valve, you can see that at low lifts the valve size has a lot to do with flow. Once the valve is well off the seat (~.2"), it's the port diameter combined with the valve size which seems to have the biggest impact on the flow. You can see this when you compare the 2.4TK head with it's small 30 mm ports to the 2.2T (32 mm ports) and the '66 head (32 mm ports). (Note that the Turbo data came from a different source the other heads. Never the less, it correlated really well.)

2) Above .2" in lift, the head in your data seemed to consistently draw about 40 CFM more then what should be an identical 2.2T head. :rolleyes:

This brings me to the other concern with the formula that you were using. It would seem to be very susceptible to "garbage in = garbage out". Flow benches are renowned for not correlating with each other. But an engine's HP won't change just because you bring your heads to a different flow bench to be tested. Curiously, the exhaust port flows listed on that sheet map very closely with the data on my spreadsheet, it's just the intake flows that seem suspect.

BTW -- do you know what the "explosion sleeve" is that is mentioned in the notes? Head flows can be greatly influenced by what the head is attached to. For example, was the head flowed while attached to a 911 cylinder or not? If the "explosion sleeve" is some sort of a bell-mouth, it could have a huge affect on the data compared to a cylinder. This is because the proximity of the cylinder wall to the valve can have a big impact on the flow.

Just my $0.02. SmileWavy

I'm no expert, but here's what I did which is very simple. Bored my 2.4 case for 2.7rs pistons. Added E cams and had the mfi pump recalibrated by gus at PFI. I did nothing to the stacks and heads, and kept the dizzy the same. I did a few other internal mods like chain tensioners, etc....
I run 87 pump gas and I dial timing in by sound and seat of the pants-what works for one car sometimes does not for others in regards to these old cars. In other words I advanced the crap out of timing. The car is fun as hell around town and does great at auto-x events.

2.2S pistons are actually 9.8:1, used with the 2.4 crank will probabily get you about 10.4:1CR. The 2.2T piston will get you somewhere near 9.1:1CR, but with the small valve pockets you might be limited to cam selection.

How about a 71 T? Can the 2.4-2.7 crank and rods drop in w/o machining? Do any of you on the list have any experiences, either good/bad on modding the 71t 2.2?

Reddog928

Several years ago, I built a MFI 2.4S up from my '72 2.4T engine. Did the porting, using S cams, stacks and pump. I am still quite pleased with my MFI 2.4S. Whoever said that an 2.4S motor is no fun below 5K really meant that the fun gets piled on above 5K. And I can burn cheap gas as its only at 8.5:1 but I live at high altitude. Swapping out to 2.2S pistons has crossed my mind but it is not really needed. YMMV

John
The head was flowed by a friend that runs a race shop and is also the head engineer for Kobelco Superchargers.

http://www.dmpeinc.com/

Redline was his previous partnership before he went solo.

Anyway, I understand that flow benches are only a tool and are not a predictor of power. Every tuning website will tell you that flow benches and dynos can only help with tuning, and the only real test is on the track. That being said, I was able to come across the formula stated above with a few google searches. I thought I was being helpful. I'm sorry the data does not fit your spreadsheet. I do not know what the explosion sleeve is, as I was not present during the test. The heads are stock 2.2E heads.

When I got the head back from Darren, I asked if it would make 200Hp without porting it. He said yes. He pointed out that there was only one real dead spot in the exhaust port, but that was several years ago and I simply don't remember where he made his marks inside the port.

On to the claim of power up to 200hp... Please open the dyno sheets that I attached above and look at the power outputs. I think the max was 172 RWHP. Multiplying by 1.15 = 198 crank HP. Multiplying by 1/.85 or 1.17 = 202 crank HP.

Two years later (the second set of graphs on the LM-1 thread), the car made 165 RWHP with smaller venturies. This equals 190-193 Crank HP. I'm sorry if this engine makes too much power. In fact, you were on my original dyno post. You didn't like my numbers then. You still don't like my numbers. What gives?...

It's not that I "don't like" your numbers. I don't harbor any preferences for one piece of data over another. It's just when you have a large set of data which has a lot of consistency, and then you are presented with a new piece of data which is inconsistent the rest, the analytic in me asks "Why?". Why is the exception different from the rest? Is there something fundamentally different about it? Was it measured accurately?

When it comes to HP claims, I'm a skeptic if the claim doesn't fit within the known data. This is merely because 911 motors (and motors in general) are known commodities. 911 motors have been around for over 40 years. I've got a data set of over 50 different 911 configurations -- some factory spec and some not. In general the data hangs together real well, not matter if I'm talking TE's or RSR's. I've also got the overall numbers compared to a set of over 200 different race and performance engines. There's some overlap between the two sets of data in regards to the Porsche race engines and in general the two sets of data agree with each other in regards to valve flow capacity and BMEP's.

I'm not picking on you, it's just that you periodically pop up with these claims about how to make big HP based on your engine, and I just can't help to point out that your numbers lay way outside that entire set of data. My point is that there appears to be something different about your numbers. I don't know if it's a measurement methodology, secret fuel, special porting or just plain BS. To be honest, I'd rather not even venture a guess. Being intellectually curious though, I would be interested in understanding it.

Incidentally, when I plugged your data into my spreadsheet, this is what I found...
- Your peak HP RPM is about where I would expect it for an 2.4 engine with E cams.
- Your peak torque RPM is a little higher then what I would have expected given a 2.4 with 32 mm intake ports, but within normal variation.
- Your peak torque of 152 lb-ft off of the chart results in a BMEP of 158 psi (essentially the torque divided into the engine size so that engines of different capacity can be compared). So straight off the dyno the number are nuts-on with other 2.4s with E cams. If I apply the 15% drag factor for the transmission (152/.85) I come up with a peak torque number of 178.8 lb-ft. This bumps the BMEP up to 185 PSI which at least 5 PSI higher then every other E-cammed engine that I've seen, and about 18% higher then all of the other 2.4s' with E cams. That's curious...
- When I look at your peak HP BMEP on the other hand, the 202 HP number results in a BMEP of 180 PSI, as opposed to the other 2.4's with E cams which are consistently putting out 148 PSI. That's a big difference -- almost 22% more torque from your engine at peak RPMS! To put it differently, this would suggest that you're getting 22% more mixture into your cylinders at peak RPM, using the same port size, cams and valve size as other 2.4's.

The funny thing is that if I were to exclude the 15% transmission correction factor, your numbers would be nuts-on with the other engines. This would lead me to hypothesize that the the transmission losses are being double-counted. I believe that many dynos can explicitly measure transmission losses, and then calculate them into the numbers. Just looking at the numbers I would suspect that this was happening on the dyno used for your engine, and then you're making the correction a second time which results in the numbers being inflated.

As far as the port flow numbers, I listed my questions about those numbers earlier.

John
Well stated.

Couple questions...

What is BMEP?

My engine runs about 9.6:1 compression. How does this info change your data? I believe the 2.4E was about 8.1:1...

I read through some discussion about the Dynojet 248C, which is what my car has been run on several times, in several locations. Each has been corrected to SAE numbers.
This one is from Rennlist:
http://tech.rennlist.com/performance/pdf/dynosexplainedDubovskyWeinerFerch.PDF

One thing it mentions, and it is something that I mentioned in my 2002 thread, is that a lightened flywheel can have an influence on a chassis dyno. Perhaps this is an additional factor that elevates the printed HP output.

I welcome further discussion. The data collection that you have for power output, is it all from chassis dynos, or from a mixture, plus factory data?

I will be going to a dyno day within the next month. If you have specific question that you would like me to ask before/during/after my runs, I would be happy to bring back the information to the board or to you personally.

BMEP = Brake mean effective pressure.

BMEP at peak HP in PSI = (Peak Power * 13000)/(Capacity (liters) * (Peak Power RPM))

BMEP at peak torque in PSI =(Torque*150.8)/(Capacity (liters)*62)

Where do those equations come from? It all comes from the average pressure within the engine which is pushing on the pistons.

Torque = "Mean Effective Pressure" * displacement / ( pi * 4 * 12)

Note that the denominator is a constant (~150.8), so MEP * displacement correlates with torque. The more pressure you have in an engine, the more torque which is generated. This is why doing nothing else then bumping the CR on an engine will often increase the specific torque number, as well as basically bump the torque numbers up across the whole torque curve. This is why bumping a CR has less of an impact on the peak HP number generated then it does on "seat of the pants" acceleration across the engine's rev range. Alternatively, if you have two different sized engines which generate the same MEP, the larger engine will generate more torque. (duh! :rolleyes:)

If you want to do it from the HP, the equation is...

HP = mean cylinder pressure * (Stroke in ft) * (surface area of one piston) * (number of power strokes per minute) / (33,000 which is the number of lb-ft/min in 1 HP)

If you simplify the equation, you'll wind up with...

HP = ( MEP * displacement * RPM ) / 792,000

This makes sense since HP is nothing more then a certain amount of torque applied within a certain period of time.

Now MEP occurs within the cylinders and generally can't be measured directly without special equipment. However, you can back into it by knowing the brake HP or brake torque at the flywheel and rearranging the earlier equation. So the...

(B)MEP = HP * 792,000 / (displacement * RPM).

The short form is that once you know the BMEP of an engine, you can compare different engines of different sizes, or even which develop their HP at different engine speeds. In my database of engines, the engine which developed the lowest peak BMEP was the... (wait for it.... )

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Triumph TR8 at 101 PSI at peak HP, and 110 at peak torque :( - Not much of a surprise since this engine existed in the 70's with 2 valve heads, a single 2 bbl carb, poor fuel and low Compression ratios. The low BMEP also suggests that this engine might have considerable opportunities for tuning since it's so lightly stressed. Notice how the peak HP BMEP is always less then the peak torque BMEP. This is because the engine is actually working at it's peak at the peak torque engine speed. After that point it's all down hill for cylinder pressures as the intake charge can't keep up with the increasing engine and valve speeds. For a while the engine gains more in engine speed then it loses in cylinder pressures, so the HP continues to increase until the torque curve falls off the edge and HP starts to drop. This is also why detonation is a major issue near the peak torque engine speed, but rarely near the peak HP engine speed when cylinder pressures are actually lower!

The engine with the highest BMEP... (drum rolll!)

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The Nissan 2.0 liter Super Touring engine from the BTCC of a few years ago. The engine has a peak HP BMEP of 248 PSI and a peak torque BMEP of 252 PSI. Under the rules, the engine were limited to 2 liters and 8500 RPM, so the only way to squeeze out more HP was to increase the cylinder pressures. So the peak torque was developed at 7500 RPM and the peak HP at 8250 and the very narrow rev range was compensated for by a semi-automatic, very close ratio transaxle. As opposed to the street legal TR8, the super touring engine ran with modern, high-octane fuel, computer controlled injection and ignition and with 4 valve heads with compact combustion chambers.

It doesn't really change anything if I'm calculating the BMEP off of a dyno chart. Generally increasing the CR will increase cylinder pressures with the following caveats:
1) If the cylinder pressures peak too high (keep in mind that we've been talking about mean pressures as opposed to peak pressures), you'll get detonation and everything goes to hell in a hand-basket since the pressures won't be effectively turning the crank, and will be increasing temperatures, which increase pressures, etc.
2) If the increased CR compromises the combustion chamber design, it may not help. If you have a compact "penteroof" combustion chamber like most modern 4-valve engines (thank-you Keith Duckworth!), this isn't a major issue. If you have a great big "hemi" head like 911, the only way to increase the CR is to increase the piston dome,which actually makes the combustion chamber spread out more, which means that the flame front has further to travel in the same amount of time (near TDC), so you may wind up losing peak HP, or having detonation issues near the peak torque engine speed. I suspect this is why 911's seem to be somewhat unresponsive to CR changes

The data was collected was from published dyno numbers (in the case of the Nissan engine), data tables from R&T articles, Porsche factory manuals or internal data charts (Coventry Climax racing engines) or just published numbers found in Racetech Magazine or Race Car Engineering. There are also a few dyno results from people on this BBS.

Great around town good at the track
 

Years ago when he ran the best shop in LA Pete Zimmerman at Redline rebuilt my 1971 911t with E cams and an E P&C set from Mahle. It ran Webbers but was otherwise stock.
That car was just a treat to drive everyday in LA traffic and a blast on the open road, docile and well behaved but willing to fly right up to 7200 rpm which it did often as I was only 27 years old and got on it pretty much all the time. At a rough guess we felt it made between 160 and 170 HP.

I kept asking Pete during the rebuild if there wasn't more we could do. Walt, now at Competion Engineering, built the motor and they both told me to relax, this was the best setup for the car with everyday driving in mind and the occasional day out at Riverside. They even made me remove the cool looking Anza exhaust and replace it with stock.

I sometimes think we all act like the actress at the plastic surgeon getting new breasts; we opt for too big.

That car went to high and low desert, skiing, PCH and as I lived off of Mulholland it got battered everyday, about 15,000 miles a year. It started first time everytime and never once broke down. Probably the best Porsche I ever owned and I foolishly sold it for a new Euro Carrera in 84.

One thing became pretty evident: although few cars could keep up with it through the canyons those were pretty short bursts. At the track it was humilating to get out front early and then get passed as the brakes faded and cars with better suspension setups late braked and passed in the inside. Once you finish your motor you are only a 1/3 of the way ready for the track so build your motor with everyday street driving in mind and you will be MUCH happier and quite a bit wealthier too.

Or you can spend twice the money and sit in the car while it hunts for idle, lopes with too much cam, backfires on decel and won't start when hot. Your call.

Pete just loves these cars and posts over at Rennlist, why not ask him for some more details, he would be only too happy to help.