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PostPosted: Sun Jan 05, 2020 7:55 am 
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Does anyone have any insight as to how Mazda is able to get away with using pump gas on a 13 and 14 to one compression ratio? A friend bought a new MX5 and was claiming that it could run on 87 octane pump gas and had a 13 to one C/R. I checked and he was right, and in Europe it goes to 14 to one and the spec calls for 91 octane but states 87 as a minimum. When I ran 13 to one in a race motor I had to use at least 110 octane if I wanted to have any pistons left, and if we didn't take some special measures we blew head gaskets. Is it the VVT that allows them to get away with it? That seems like a really high C/R for a street motor.

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PostPosted: Sun Jan 05, 2020 11:22 am 
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Ron Bartell wrote:
Does anyone have any insight as to how Mazda is able to get away with using pump gas on a 13 and 14 to one compression ratio? A friend bought a new MX5 and was claiming that it could run on 87 octane pump gas and had a 13 to one C/R. I checked and he was right, and in Europe it goes to 14 to one and the spec calls for 91 octane but states 87 as a minimum. When I ran 13 to one in a race motor I had to use at least 110 octane if I wanted to have any pistons left, and if we didn't take some special measures we blew head gaskets. Is it the VVT that allows them to get away with it? That seems like a really high C/R for a street motor.


Ron,

The sportbike engines have been over 12:1 compression on the street for years now. Ducati has gone as high as 13:1 on a 4.5" bore, with a redline north of 13,000rpm (single plug) on their twins. If you look at the newest batch of high performance NA engines (like the Porsche GT3 engine), they're all north of 12.5:1 on pump gas. Talking to people in the know, this has to with manufacturers having a better understanding of mixture motion and having a better grasp of tumble (4 valve cylinder heads). Here are some quotes from a combustion engineer at AVL on what is happening:

Quote:
You don't want swirl in a gasoline spark ignition engine. If you're seeing combustion efficiency improvements with the introduction of swirl then the system simply didn't have enough charge motion to begin with. Tumble is what you want in a gasoline SI engine. High swirl rates produce fuel/air separation and move the fuel away from the spark plug (centripetal acceleration) producing a localized lean zone by the spark plug....and that's the exact opposite of what you want.

This is why you've seen the move away from steep valve angles in 4-valve cylinder heads to much shallower valve angles without a major change in port angle. The amount of tumble in a new 4-valve cylinder head (anything post 2018) is crazy, and this is how they're getting 32 bar BMEP on 91 octane.

This WAS a debate for a long time, but it turned out that the steep valve angles and large ports in 90s 4-valve heads, particularly those from Honda and Mitsubishi, just didn't have any charge motion at low pressure drops. Modern heads to not have this issue. You do sacrifice some flow for any charge motion, so some manufacturers have compromised with moderate valve angles and some sort of flap that will help charge motion at low pressure drops. Ford did this with the Coyote V8, it has "CMCV" plates or charge motion control valves.

We measure this now with a flow index. We have a tumble meter on the flow bench and we rate the heads by (flow*tumble)/valve size. You're looking to maximize tumble while still utilizing as much of the valve curtain area as possible with a given valve size. Mercedes are the absolute leaders in this, it's borderline witchcraft how good they've gotten at balancing this.


Quote:
Modern turbocharged engines run a huge amount of tumble. Not only does this help with mixture uniformity, it actively cools edges in the cylinder and prevents hot spots. It's like....having a fan on the inside of the cylinder before combustion starts.

This is true even for port injected engines, probably the best production example is the Ricardo designed McLaren V8. Those heads rate very high on the tumble index. The reason you don't see DI on superbikes is that they need all the valve area they can get and it's not possible to package central DI with their valve sizes and cooling jackets. As was stated earlier, superbike engines have quite a bit of tumble, although not as much as say....the new Civic Type R engine or A45 AMG engine.

If you want to see radical cylinder head designs for swirl, look into the Supertruck project. There were some very interesting designs and they reached 50% thermal efficiency with a conventional turbodiesel.


Quote:
Well, I guess it depends on what you consider "old". You have to be careful because an engine released in 2005 had the combustion system designed at least 5 years earlier, so there's a time lag. Basically any engine with the combustion system designed in the last 15 years is going to have very high tumble due to shallow valve angles. So that would basically be any production engine after 2010. In the late 90's and very early 2000's high end CFD was still so expensive that it was being used sparingly and time-dependent CFD was virtually impossible with automotive development budgets. It was also pretty impractical from a time perspective, what used to take 6 months to run now takes 2 weeks and can be done on computers that are 1/100th the cost you would have paid 20 years ago.

I guess what I'm saying is that the drastic increase in speed and drastic reduction in cost for high end CFD has caused us to change a lot of our previous perceptions about engine design. The new Mercedes M139 is a perfect example, 20 years ago if someone were going to design a 2.0 turbo 4-cyl to make over 400 hp on pump fuel they wouldn't make it heavily undersquare (83x92) with almost no valve angle. That engine revs to 7400 RPM and makes 370 lb-ft from 121 ci.

It makes a lot of sense if you think about it. If you're knock limited and not airflow limited, which most is the case for most heavily turbocharged engines, it makes sense to design the entire engine around reducing knock instead of just trying to make it flow more. This is where the aftermarket is behind, a Coyote or LS head doesn't need more flow to make 1000 hp on pump fuel, it needs more knock resistance.

This thinking spilled over into naturally aspirated engine design. They now give the engine just enough airflow to make the RPM/power target, and then they design the rest of the engine around maximizing efficiency and cylinder pressure. That's why the new GT3 engine has 13.5:1 compression and pretty shallow valve angles for an engine that revs to 9000 RPM. They spent a great deal of time making the large bore engine very knock resistant, and that's a hard thing to do.


Quote:
This is going to be completely counter-intuitive for you, but the answer is to lower the roof. You want the angle of the port generally to be more out of line with the angle of the valve. You also want to get rid of any "turn" into the valve, you actually want the port exit to have an angle relative to the valve. This will absolutely reduce your bench flow readings, the key is to minimize that loss while still getting the tumble.

This is the exact opposite of what race heads do, they always raise the port and try to bring the port more in line with the valve angle. This is very, very bad for tumble. Part of the reason this is happening is that CFM sells heads, in the aftermarket it's always more more more bigger bigger bigger. Unfortunately combustion efficiency isn't an easy sell.


Mazda does things a little differently for sure. Watch this video from Toyota: https://www.youtube.com/watch?v=cWHq-Qr903g

Also, check out the Honda Research Paper site: https://www.hondarandd.jp/ - for those interested in motorsports, they have all their white papers from their last N/A Formula One efforts, some motorcycle, and IMSA stuff. It's free to sign up.

Lastly, this is all just a refinement on what Keith Duckworth started with the DFV.

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PostPosted: Sun Jan 05, 2020 2:13 pm 
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Also direct injection even on the NA motors helps


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PostPosted: Sun Jan 05, 2020 3:10 pm 
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Wife's 2011 Mini Cooper S grocery cart has 91 or 93 octane rating but the variable cam timing and 4 valve head allows for 87 octane for running around town. Don't have the specs handy but put your foot in it and the turbo does wonders for getting down the road. Going to try the higher octane one day to see how it really runs. After all these years running 16.1 race engines it's weird to sit behind something that won't blow up if you abuse it just because of the technology.

Bob

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PostPosted: Sun Jan 05, 2020 4:34 pm 
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Bob Hess wrote:
Wife's 2011 Mini Cooper S grocery cart has 91 or 93 octane rating but the variable cam timing and 4 valve head allows for 87 octane for running around town. Don't have the specs handy but put your foot in it and the turbo does wonders for getting down the road. Going to try the higher octane one day to see how it really runs. After all these years running 16.1 race engines it's weird to sit behind something that won't blow up if you abuse it just because of the technology.

Bob


The sportbike stuff is most impressive. A 1000cc Superbike is making ~240bhp and can run 24hr events with the right mapping. Just a change in exhaust, ECU, porting, pistons, and camshafts.

Example, the 1100cc Ducati V4R makes 221bhp from the factory, 14:1 compression on pump gas (has shower injectors), and meets emissions. With a just an aftermarket exhaust, it makes 234bhp. It's also making 1.23lb-ft/ci over a wide rpm. This also has standard road service intervals of 15,000 miles. In race trim it is destroked to a 1000cc for homologation .

The new BMW 1000cc and Honda 1000cc sportbike engines are 220bhp engines from the factory as well.

When compared to something like a BMC 1275cc engine, it's clear how far technology has come. Imagine a 1275cc engine, that rev'ed to 14k rpm, made 280bhp and 95lb-ft of torque over a wide range, met emissions, on pump gas, and just needed oil changes and valve adjustments every 15k, and that's what you have.

As an aside: For reference, the the fastest MotoAmerica and WSBK Superbikes (so production based) are faster around Laguna Seca than a Runoffs winning SCCA Formula Atlantic.

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PostPosted: Mon Jan 06, 2020 8:36 am 
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Ron,

Here are some more things to ponder:
Kevin Cameron
Quote:
British racing singles of the 1930s started life with flat-topped pistons and compression in the 4.5 - 6-to-one range. This allowed them to pretty much copy the hemi 2V chamber pioneered by Fiat in their 1922 GP car engine, setting the two valves at a 90-100 degree included angle. But fuel octane number rose through the 1930s as Britain legalized use of the violent poison/antiknock tetraethyl lead and combined best available leaded gasoline with 50% "benzole", which was a by-product of coke production. Benzole was a catch-as-catch-can mixture of benzene, toluene, and xylene - all highly anti-knock aromatic compounds. With all that new ON, compression ratios could go up. It was a lot cheaper to make a new piston than a new head, so up, up went piston domes. Combustion had never been all that fast in OHV engines - there was no way to have squish as in flatheads/sidevalves. Along came Harry Weslake with a little help from the tangential intake port, which converted high intake velocity into rotary swirl around the cylinder axis. THis "stored" intake energy for later use as turbulence to accelerate combustion. Now a little math - making a true hemi chamber exactly doubles the surface area of the combustion bowl, as compared with the area of a disc whose diameter is the cylinder bore. And adding the matching piston dome did something similar to piston crown area - increased it a lot. This put piston temperature up, discouraging people from increasing bores and decreasing strokes for a long time. In 1950, here came Pole Leo Kuzmicki, working for Norton. If you imagine the tall piston dome as being made of fudge, he essentially pushed it down, forcing it outward, closer to the head surface everywhere except where valve clearance was needed. In those regions he brought the piston as close to the head as mechanically possible, creating OHV squish for the first time. As he pushed the top of the piston dome down, he created room above the now-flat piston top in which intake motion could persist all the way to TDC without being damped out by friction between moving gas and close-by metal surfaces. He transformed the old, slow "half an orange peel" combustion chamber into a faster-burning, much more compact chamber that was basically just the valve cutouts plus spark-plug area. The greatly improved Norton would have defeated the new Gilera-4s in GP racing that year, but Dunlop tires came apart on a couple of fast tracks and prevented what would otherwise have been runaway wins. Norton came back in 1951 and did the job - beating a potentially much more powerful Gilera. People today, in the 4-valve era, forget this great lesson - that just cramming a bunch of mixture up into a tight, badly-shaped combustion chamber and setting it off does not equal power. Or, as the late Keith Duckworth put it, "People are mesmerized by airflow, never reflecting that they must burn all that air and fuel they are getting into their engines." When Duckworth applied the 4V version of Kuzmicki's concept, the result was a flat-topped piston, a narrow valve angle, and a strict separation between as-close-as-possible squish and the most open, roomy combustion space. When Duckworth applied this concept to his DFV V8 GP car engine of 1967, it was able to defeat higher-revving V-12s. In place of Weslake's tangential intake, he biased his intakes to produce downdraft so that air flowed from the intake valves, across to the far cylinder wall, then down to the pison, across its crown, and back up the near cylinder wall. This, which he called "barrel motion",, is now called "tumble". The problem today is that too few builders realize there must be room in the combustion chamber for the turbulence needed for fast combustion. They just add material to the piston wherever it is easiest until they get the 13.8-to-one or whatever ratio their buddies told them they had to have. The piston now comes so close to the head that there really is NO combustion space. Any tumble-generated turbulence is damped out as the piston rises close to TDC, so they are having to use very long ignition timings for best torque. To a certain extent, this compromise must be tolerated, but the Kuzmicki/Duckworth idea has to be kept in mind at all times; make room for combustion turbulence. In some cases, like the truly terrible 5V Yamahas, the compromise really bites, so you can have either acceleration (from high compression that kills flame speed on top, causing weak peak power) or top-end (by lowering the compression enough to get back some top-end flame speed), but not both. When I asked Claudio Domenicali at Ducati how they have been able to shorten stroke again and again and still have competitive engines, while both Suzuki and Kawasaki have made new, shorter-stroke models that were slower than previous longer-stroke versions, he replied, "I cannot speak for other manufacturers, but in our case, we use a device like a small anemometer, placed in the cylinder. Then we vary the intake downdraft angle and port sizes until we get the tumble motion that our experience shows to be necessary." Sure, nothin' to it! Anyway, that is the modern combustion chamber conundrum in a nutshell. It really hurts in F1, where bore/stroke is 2.5, and they end up with ignition timings up in the 60s. Another problem is a social one. Racers don't mind being considered "advanced", but no one like to be thought "retarded". But where combustion is concerned, the more ignition timing your engine needs, the worse its combustion is revealed to be. Some people just can't get past the old idea that needing a lot of ignition advance is good. The reverse is true. A classic example of a bad engine is the old Honda 450 twin of the 1960s. Its tall piston dome and 78-degree valve angle made it into a heat-gatherer, and air just hates to go into a burning hot cylinder. It is delightful to be rid of air cooling at last! I have to go on another trip weekend after this, but am resolved to write the vaporization article you have asked for thereafter. I've just finished writing a "50-engines book", so there is more time available for other things. KC


Also, start to watch this around the 35 minute mark: https://www.youtube.com/watch?v=rBZCnG1HwDM&t=1362s and think of cycle variability in the ability maintain the threshold from detonation to controlled combustion. More variability, the larger your safety of margin.

I have also attached some screenshots from some of the Honda white papers.
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Some more food for thought...

Dave Calvert (the "C" in "CP Pistons")
Quote:
Well I suspect that this will be many pages long but I have some piston experience that may be of some help. Because the inlet is started by the last of the exhaust cycle it gets some pull in that direction and then it has to get around the intake valve, were OK to this point but now there's a huge dome in the way. I know the piston is moving downwards at this point and ignition IS going to happen but you may not be getting the best burn possible. We've proven this time after time that once you've achieved adequate compression the rest is just bragging rights and you've narrowed up the tuning window as well. A SBC can get a .600 dome but almost every time a .400 dome will make the same or more power and with less timing and maybe less jet.
I have a customer that builds Cosworth v8s which has an ugly little dome in the very center, we borrowed from our 4 valve Power Sports technology and pushed the dome out to the chamber walls and then adjusted for CR with a 6 inch radius bowl in the center, so that there is a dome with a radiused dish in the center. This got the fuel further away from the plug and I think it kept the mixture more "excited" especially with the tighter dome to chamber.And more uniformly spread across the piston top. I forgot that the main point about the Cosworth dome change was that the motor picked up 12 hp which is significant for a motor that's been around for decades.


Randy Gillis. Then of JE Pistons now of Racetec:
Quote:
I did the first "tapered" or conical dish pistons for (then) Busch series engine builder Frank Leeson of Bill Davis Racing . He approached me with the idea and we made some test parts for him. Several dimensions were changed and those changes had a very clear affect on performance. One critical aspect was the width of the "perimeter squish band". Frank and I morphed the piston into the "spherical radius" from the conical due to the need for increased negative volume. After a couple of weeks I was contacted by Bob Fisher ( then of Ernie Elliott Inc) who was building engines for Bill. I gave both of them a 1 year exclusive on the design and development. Both did extensive back to back ( spherical to mirror image dish) testing . The spherical required at least two degrees less timing and always made a significant improvement to torque with a smaller improvement in HP. We figured combustion efficiency was responsible for that. There was also a stability condition. the feeling was the load was focused in the center and not offset by the mirror image dish. After the year was up , I offered the design to a west coast Craftsman truck ( then) engine builder. He was extremely skeptical and wanted no part of this "dumb design". I offered to ( and did) make two sets of equal pistons weight , rings, skirt profile, dish volume , etc . except for the dish design. The deal was to test the "conventional" design he was using first and then ( while still on the dyno)) pull it down , change the pistons and use the same used rings , and test it again. The result was a 10 hp 13 ft lb increase in power with 2*s less timing required. We didn't "invent" the concept , it was already out there on Hondas and other imports, we just adapted it to the V8 engine. There would eventually be a few cases where results were neutral as far as power increase but we did the design on all kinds of pistons. None made LESS power. I still use it today...

The "squish band" or flat around the perimeter had to be a minimum of .375. We tried and edge to edge radius and it was BAD. The piston had to have a flat on it . Let me also say this is not something that wasn't already being done. We couldn't patent the design because MANY import 4 cylinder pistons already were using the shape! Another thing we found was when the volume needed was greater than 20ccs, we could "step" the edge , effectively lowering the radius cut into the piston. We tried other odd shapes too with an upper and lower quench pad and a "V" shaped trough. They cost more in machine time but were no more powwerful than the spherical....

I will never say the spherical dish is 'the best" as there are too many different combustion chamber shapes and volumes. It worked where we tried it and caused guys to rethink what was happening inside the engine. MANY high end builders scoffed at the concept saying it was a fluke until they proved it by using it. One other piston company owner said to me "I think it's BxxxSxxx but when the customer wants it I'm damn well going to make it for him to keep him from going to you!" It was a fun time back then.


Anyway... there is plenty more out there, but that should get you started.

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PostPosted: Mon Jan 06, 2020 9:42 am 
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The short answer to all of Bob's great info: "because of 60 years of engine development".
:lol:

Even the Honda Fit, a grocery getting econo-box commuter car, comes from the factory with an 11.5:1 compression ratio, on regular unleaded. Meanwhile my 1990 Honda had to be built up from 9.2 to 11.5:1, and it gets 110.

The technology in modern ICE drivetrains is amazing. Too bad most major manufacturers are starting to cease further development of them.

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PostPosted: Mon Jan 06, 2020 9:55 am 
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My Hyundai Genesis coupe gt 3.8 GDI can run on 87,or higher CR 12.5 TO 1.Does knock a bit on 87 when cold tho.I :D run 91 or higher in it. i find it like highest octane you can get.Has variable valves and variable intake ,4 valves a cly ,ect. :D


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PostPosted: Tue Jan 07, 2020 7:06 am 
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All good info but like Dan I think that a big piece of the puzzle in modern road car engines is direct injection. It's my understanding that they can effectively shape the pressure rise curve by timing the addition of fuel, thus avoiding a detonation event even at high CR.

Knock sensors must help too of course.

Having said that, Bob's info is much more relevant to our "old fashioned" race engines!

On that tangent I'm idly curious as to how one goes about "race tuning" a direct injection engine? Although I've never done it, the concepts behind "tuning" port fuel injection are fairly simple, you are mostly just tweaking how long the injector stays open. I'd guess tweaking DI has more subtleties.


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PostPosted: Tue Jan 07, 2020 7:30 am 
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https://www.hotrod.com/articles/explain ... -theories/ i found this on GDI..Angelo :D


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