Modern Engines & Static CR vs. Boost Levels?

[4vpc]

An overview of the BMW engines here discussing the differences and modifications needed to make it work: http://youwheel.com/home/2016/03/27/det ... er-engine/
It has a mechanical water pump and additional electric one. The invention of the electronic wastegate has made boost control much more manageable in recent years.
N54 piston differences here: https://www.n54tech.com/forums/showthread.php?t=20322

[jacksoni]

The old school way (think WWII bombers) of combating high cylinder pressure and heat, was more octane. I’ve read that fully loaded bombers were using leaded fuel in excess of 150 octane. Yikes!

No different than 60s muscle cars.. the knowledge and computational / engineering ability wasn’t there to know how to deal with higher cylinder pressures other than a lot high octane leaded fuel. 50 years later.. engineers have figured out how to improve combustion efficiency (and cycle to cycle repeatability) that raises the detonation threshold, and thus high cylinder pressures can work with a given octane.

It’s still a function of compression vs. boost pressure, but again, a lot of thought needs to be put into lowering compression without disrupting the combustion efficiency of a modern engine design.

Check out the cooling system on the new CBR1000 (214bhp/L in full emissions garb): https://www.cycleworld.com/2021-cbr1000 ... cati-v4-r/

I have quite a few books on WW2 engines and aircraft....
All US 4 engine bombers used dual stage supercharging, a turbo that maintained seal level air pressure to maybe 25,000 feet, and a mechanical blower to provide boost for engine power. All of them had intercoolers to reduce intake heat and fuel was 100/130 octane...Normally bombers only used full power for take off, about 50 inches of boost max, about 10 psi....The fighter aircraft mostly used dual stage supercharging at much higher levels..War emergency power, allowed for maybe 5-10 minutes ,could see over 80 inches in liquid cooled engines and a bit less for air cooled radials...Sometimes 150 octane was used but lead flouling spark plugs was an issue...Some used water/alcohol to limit detonation, others used various types of intercoolers..Limited use "sprint" engines used 100 inches of boost , intercoolers, water injection and exotic fuel blends like Tripane to control detonation...

You have to remember that the numbers for Avgas (100LL, 80/87, 100/130, 115/145 etc) do not represent octane numbers the same way we usually think of them nor directly the MON/RON numbers published by autogas suppliers.

[peejay]

The old school way (think WWII bombers) of combating high cylinder pressure and heat, was more octane. I’ve read that fully loaded bombers were using leaded fuel in excess of 150 octane. Yikes!

No different than 60s muscle cars.. the knowledge and computational / engineering ability wasn’t there to know how to deal with higher cylinder pressures other than a lot high octane leaded fuel. 50 years later.. engineers have figured out how to improve combustion efficiency (and cycle to cycle repeatability) that raises the detonation threshold, and thus high cylinder pressures can work with a given octane.

It’s still a function of compression vs. boost pressure, but again, a lot of thought needs to be put into lowering compression without disrupting the combustion efficiency of a modern engine design.

Check out the cooling system on the new CBR1000 (214bhp/L in full emissions garb): https://www.cycleworld.com/2021-cbr1000 ... cati-v4-r/

I have quite a few books on WW2 engines and aircraft....
All US 4 engine bombers used dual stage supercharging, a turbo that maintained seal level air pressure to maybe 25,000 feet, and a mechanical blower to provide boost for engine power. All of them had intercoolers to reduce intake heat and fuel was 100/130 octane...Normally bombers only used full power for take off, about 50 inches of boost max, about 10 psi....The fighter aircraft mostly used dual stage supercharging at much higher levels..War emergency power, allowed for maybe 5-10 minutes ,could see over 80 inches in liquid cooled engines and a bit less for air cooled radials...Sometimes 150 octane was used but lead flouling spark plugs was an issue...Some used water/alcohol to limit detonation, others used various types of intercoolers..Limited use "sprint" engines used 100 inches of boost , intercoolers, water injection and exotic fuel blends like Tripane to control detonation...

You have to remember that the numbers for Avgas (100LL, 80/87, 100/130, 115/145 etc) do not represent octane numbers the same way we usually think of them nor directly the MON/RON numbers published by autogas suppliers.

They had compounds "rated" at 270!

What is telling is that the octane ratings were for "severe" and "mild" engines... aircooled were severe, liquid cooled were mild, as far as detonation was concerned.

[BLSTIC]

Read these. Logan is a combustion engineer for an outfit that does a lot of work with OEMs, F1, etc.

Why is it beneficial to transfer heat from the cylinder walls, piston, and combustion chamber roof into the charge on a pump gas, knock limited engine? This is not a rhetorical question.

Hot spots act like a spark plug. Controlling hot spots is more important than an increase in pre-combustion air temp. On modern high-BMEP production engines there's also the issue of material longevity, this is an issue particularly on the exhaust side.

This is the same reason they use oil squirters on pistons.

Ok, so if the problem is low speed preignition, I can see how more tumble is better. If the problem is spark knock, then more tumble is not necessarily always better.

If so, for downsized passenger car engines, or engines running very high octane fuel, more tumble the better. For a "tuner engine" running on pump gas and making power at higher rpms, there may be a point where more tumble is no longer better.

This used to be the old thinking, and it was based on the fact that as RPM rises charge motion naturally gets more chaotic so you don't need to design a port specifically for tumble at high RPM. Now we know you want to control that charge motion and design it to do things deliberately, this involves designing the entire intake system correctly.

This is how you've got Ferrari and McLaren turning 8500+ RPM with turbocharged engines making 200hp/L on 91 octane.

The new quote display for this forum sucks hairy scrotum.

With port-injected engines, the "old thinking" certainly looks it has been the dominant thinking. Maybe the solutions have changed. My impression was that in the port-injected engine era, the idea was to get a lot of tumble at low rpms or low loads such that the burn would be fast enough in those conditions even with a lot of EGR. In the port-injected engine era, the high rpms and high loads would take care of themselves. At high boosts and high rpms, sometimes charge motion was considered excessive and an intent was to slow it down.

That McLaren is a low compression, port injection engine "relic" so it's of particular interest to me. What's inside there? It has long intake runners and I am guessing very much a tumble port feeding a conventional four-valve head. But that's just a guess. Another guess is that the variable valve timing and using them right with turbos is largely responsible for the wide power band. With those log exhaust manifolds, the narrow bore spacing is going to allow it to rev higher, especially if the VVT takes out the valve overlap, I am guessing.

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.

So does anyone have a recipe how to cost effectively modify an oversized, small cam, early 1990’s dump port into a more modern tumble port? Or is that “go straight to the foundry with passing go” sort of proposition?

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.

and...


This is all just a refinement of what Keith Duckworth figured out with the Cosworth DFV.

So that's interesting. It looks like on an oversized 4v port (which is a thing on lots of 4 cylinder car engines) you could achieve that port shape by filling the ports with resin. You don't have the direct injection but the tumble benefits remain.

Makes me wonder how much detonation resistance you'd get from it by modifying an older design engine. Modern turbos are certainly capable of more boost efficiently so it's not like losing inlet flow is going to matter that much. Could something like an EJ20 or 4G63 be brought up to nearly modern standards?

[ptuomov]

So that's interesting. It looks like on an oversized 4v port (which is a thing on lots of 4 cylinder car engines) you could achieve that port shape by filling the ports with resin. You don't have the direct injection but the tumble benefits remain. Makes me wonder how much detonation resistance you'd get from it by modifying an older design engine. Modern turbos are certainly capable of more boost efficiently so it's not like losing inlet flow is going to matter that much. Could something like an EJ20 or 4G63 be brought up to nearly modern standards?

That's a very interesting question for a four-valve turbo engine running on pump gas. My thinking is that it's important to get the exhaust valve face to work as a guide or diffuser for the air flow, which means that the intake port angle has to be close to the exhaust valve face angle. With the engines that we play with, one would want to put in a new oversize seat insert, install 39mm intake valves (stock 37mm), sink the intake valve a little more than stock, and weld the port roof a little bit before shaping the long side to be a straight shot.

Toyota-Dynamic-Force-engine-tumble-flow.jpg

[BLSTIC]

I see what you mean with the diffuser angle. But wouldn't the inlet valve act as a kind of turning vane to make the mixture follow the roof anyway? It is still a flat plate at a 40°-ish angle to the port. That same screenshot you've shown shows a degree of mixture following the exhaust valve face on the standard port too.

Also on another beneficial note, without any of this bowl throat and short side radius to deal with trying to get maximum flow around the circumference of the valve, you could make the port a lot smaller in CSA without affecting flow. Effectively you've gone from the (unobtainable ideal) venturi with a valve at the end of it at 90° to airflow, to a very obtainable tube with a valve at 40° to airflow (and a dead zone that exists when the valve open, unfortunately)

The modifications done to the original port in red should be achievable and at least mimic the scratch-built design.

Also you'll have to excuse my epic paint skills on the second pic, but you can see my thinking regarding minimum CSA and actually being able to build a port, rather than the unobtainable ideal port. Sucks about the dead zone around half the valve but that's unavoidable.

It should be noted that I can't see this port shape working with high valve overlap. I couldn't think of a better way to throw clean mixture down the exhaust than this inlet port with an open exhaust valve.

[Truckedup]

You have to remember that the numbers for Avgas (100LL, 80/87, 100/130, 115/145 etc) do not represent octane numbers the same way we usually think of them nor directly the MON/RON numbers published by autogas suppliers.

Yes, and for instance the 100 is lean burn octane and the 130 is rich burn...No matter what, 30 psi boost in a 1700 cubic inch engine at sustained full throttle requires a lot of octane..

[ptuomov]

I see what you mean with the diffuser angle. But wouldn't the inlet valve act as a kind of turning vane to make the mixture follow the roof anyway? It is still a flat plate at a 40°-ish angle to the port. That same screenshot you've shown shows a degree of mixture following the exhaust valve face on the standard port too.

Also on another beneficial note, without any of this bowl throat and short side radius to deal with trying to get maximum flow around the circumference of the valve, you could make the port a lot smaller in CSA without affecting flow. Effectively you've gone from the (unobtainable ideal) venturi with a valve at the end of it at 90° to airflow, to a very obtainable tube with a valve at 40° to airflow (and a dead zone that exists when the valve open, unfortunately)

The modifications done to the original port in red should be achievable and at least mimic the scratch-built design.

Also you'll have to excuse my epic paint skills on the second pic, but you can see my thinking regarding minimum CSA and actually being able to build a port, rather than the unobtainable ideal port. Sucks about the dead zone around half the valve but that's unavoidable.

It should be noted that I can't see this port shape working with high valve overlap. I couldn't think of a better way to throw clean mixture down the exhaust than this inlet port with an open exhaust valve.

Toyota has a whole paper about the angle of the intake port relative to the angle of the exhaust valve face and, from memory, they seem to say that it works the best with 5-10 degree angle between the two.

Another thing that I'd consider is installing an oversize valve seat and intake valve. This will allow shaping the roof straighter on the long side with less welding required.

In terms of the low lift flow, I wonder if there's a way to shape that intake valve seat such that it wants to flow over the short side only at low lifts. Some sort of steeper cuts on the long side and shallower cuts on the short side? I don't know what I am talking about, just wondering about it.

Normally aspirated and on race gas, the old-school port on the left has a lot going for it in terms of air flow. Turbocharged and on pump gas, the high tumble port on the right seems like the better solution.

[hoffman900]

Toyota is also using a laser clad seat, which allows it to use a larger valve and not run into problems like you would with a traditional seat. The Honda F1 white paper about developing them 10 years ago mentioned it allowed them to get the water jacket closer to the seat, which was interesting.

Tumble is briefly mentioned here on the Mercedes Formula One engine white paper (circa 2010, like the Honda): http://www.heron.co.at/_lccms_/download ... nglish.pdf

It also sounds like they were going to explore it further.

I’ve also attached a screen shot of Honda’s port shrinking for their Indy Car engine to be used in ALMS/IMSA/LeMans circa 2007 (12 years ago). Obviously a lot of what we’re talking about has happened since then. Notice they did fill in the roof a lot more, however.

8C57EC30-5812-4408-8C23-0249D95F6B7F.png

The newer Honda papers talk about this stuff a lot more.



On modern naturally aspirated side, I would be curious to see what the new Porsche GT3 heads look like, with their 13.1 compression ratio.

[modok]

Direct injected gasoline engines, the ports and pistons to me look all very familiar......
just like a diesel.
And I DON"T know much about the injection strategies, really never been my area of interest, but I suspect that how they are injecting the fuel is also very much like in modern "quiet" diesels. The fuel systems are VERY high pressure and that allows far more control of exactly when how much fuel is injected..how radically I don't know but probably pretty wild stuff. Maybe some is injected early and maybe some is injected right before tdc....or something like that.

And they need the high compression ratio to get high fuel mileage out of it, probably. And to get the fuel mixed FAST since it isn't already mixed.
You CAN do the same kinds of things, the high turbulance swirl and tumble ports, and piston shapes, to even a CARBURETED engine and gain knock resistance. But, at least until direct injection it usually NOT WORTH it go that direction. Would a hotrodder sacrifice flow for better combustion. never! unless at gunpoint. But, like I said it's very familiar, vw had IMo the MOST engines like that in the 80s, with deep dish pistons. May Fireball chambers, Widmer's stuff, even the chevy 235, clear back to Recardo and the offset head. Indeed they can handle higher CR, or more boost at the same CR as compared to normal designs, but power per cube not that good because the flow isn't there.
not to discount the "NEW technology" as being old, but, it's not that new either. it's a new combination. But for how to hotrod it, ask the diesel guys, Injectors and the injection timing and spray patterns and BOOST, head porting...not that much.
in case you didn't know, they run WOT at cruse, like a diesel, no throttle. Electric throttle anyway so you never know what ti's doing. Isn't that strange!

[BLSTIC]

Right. I'm gonna say Toyota knew about this for a while. I knew I'd seen that intake port somewhere before. This 4A-FE update was released in 1993. The 1998 1NZ engine has a similar intake port.

It's not *exactly* the super tumble port, but it's certainly comparable

[ptuomov]

I think that the high tumble ports with diffusing exhaust valve faces and raised center crown pistons became the norm much later than the 1990’s.

The following is from a 2016 Toyota paper abstract:

“This paper describes the key requirements for engine design to generate high tumble flow with high flow coefficient by using both simulation and experiment. It is important that the air flow of tumble is straight and runs along the wall of the combustion chamber near the exhaust valves for high tumble flow efficiency. As a result, better performance can be achieved by changing the layout of the valve angle and the intake port. The generated tumble flow improved by 10%.”

[hoffman900]

+1

A modern high tumble port is not the same as a tumble port from the 1980s and 1990s.

I think part of it is people struggle with that even 2010 is nearly a decade ago, which can be lifetime in development.

Going back further though, this kind of stuff is exactly what Keith Duckworth had an intuition for and made the Cosworth DFV so successful.

[ptuomov]

Where this modern high tumble port excels in my opinion is with long stroke turbocharged four valve engines. Long stroke compared to bore allows for a high combustion chamber without a piston dome, as does turbocharging and the associated lower compression ratio. The high combustion chamber shape in turn allows for a well-flowing and steep intake port while still preserving the exhaust valve diffuser arrangement and a great tumble. The “overvalved” four valve head allows moving the MCSA upstream of the valve and then flowing most of the air over the long side of the port/valve at the seat while still keeping the velocity high at MCSS. The valve clash might be a problem with a lot of overlap, but with a street turbo engine one doesn’t want or need a huge overlap anyway. That’s my thinking anyway.

[hoffman900]

What about the naturally aspirated, short stroke, big bore Porsche GT3 engine that Logan brought up. That engine is making 520bhp from a 4L flat 6, with 13.3 compression and a bore of 4.04”.