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PostPosted: Tue Jan 07, 2020 9:20 am 
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Location: Denver CO
Al Seim wrote:
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.


Talking to others, DI has certainly helped, but that doesn't explain the 13:1 compression ratios in Sportbike engines, some with bore sizes in excess of 4.5" (Ducati twin). They all have higher specific outputs than the naturally aspirated automotive engines (220bhp/L+, pump gas, emissions, and warrantied)

Check this Honda white paper out on the Development of High-Pressure Fuel Supply System for Formula One Engine and the gains found by increasing fuel system pressure from ~175psi to the then rules capped 1450psi. It's a good read and should get you thinking..
https://pdfs.semanticscholar.org/838d/3 ... 752c07.pdf

GDI engines are in excess of 5000psi+.

In addition to the knock sensors, and everything else, individual timing of ignition for each cylinder helps. A Runoff winning A-Series builder (not Huffaker) shared publicly that he used different ignition curves for the center cylinders than the outside. He said it didn't so much produce much more power, but widened the tuning safety window. Jay Wiles of Hendricks shared that they lost quite a bit of power switching to FI from the carburetors on the NASCAR engines (a lot of that has to do with how the system was spec'ed, but a big bit of it was the lost in charge cooling due to the injectors being closer to the cylinder than the carburetor. NHRA Pro Stock had the same loss/cause), but were able to gain most of that back by having full control of the timing curve by ditching their distributors. Even with FI, they are still using a common plenum intake, with runners of different lengths, cross talking between cylinders, etc.

This can be figured out with in-cylinder pressure sensing equipment. Not cheap, but it's out there, even in the vintage racing world.

Here is a screenshot from the NASCAR Engines 101 video showing this on a carburetor NASCAR engine:
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PostPosted: Wed Jan 08, 2020 9:02 am 
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Interesting stuff - thanks!

Very surprising that the cylinder to cylinder mixture varies that much on a presumably well developed NASCAR engine! ~11.5 to ~13.5 is a pretty wide range.


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PostPosted: Wed Jan 08, 2020 9:57 am 
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Location: Denver CO
Al Seim wrote:
Interesting stuff - thanks!

Very surprising that the cylinder to cylinder mixture varies that much on a presumably well developed NASCAR engine! ~11.5 to ~13.5 is a pretty wide range.


Keep in mind that's with a carburetor, but with a the center mounted manifold (single plane), even with the FI, the runners aren't equal length. Furthermore NASCAR requires the 1-8-4-3-6-5-7-2 firing order: Image
so you have cross talk between cylinders. Scavanging isn't as even on a bent crank V8 either. Lastly, you can see the wetting issues with the carburetor: https://www.youtube.com/watch?v=7Iq1B-2paCs - then add Gforces on top of that.

It was mentioned by a few of the Pro Stock builders that with the change to EFI they lost power (spec system, with rules mandated injector location / size, ecu, and throttle body location, plus rpm cap), but they had faster 60' times due to the fact that the Gforces effected the FI system less than the carburetor set up (like seen in the Kaase video).

Looking at the firing order, you can see why Chevrolet finally went to a cross plane crankshaft for the C8R, since each bank has separate restrictors and now it will pull on each one more evenly.

As far as fuel wetting goes, you can see from the earlier white paper that even F1 designers struggled with it some as recently as ten years ago. Here is a paper on measuring AFR on a F1 engine and the effects of the airbox inlet shape, also AFR conditions under part loading:

Combustion Diagnosis of Formula One Engine Using Micro-Cassegrain Sensor
http://www.f1-forecast.com/pdf/F1-Files ... P2_12e.pdf

This gets into fuel wetting, intake harmonic (cross talking) interference, and exhaust system scavenging:
Development of Induction and Exhaust Systems for Third-Era Honda Formula One Engines
https://pdfs.semanticscholar.org/5b69/d ... 38d1ae.pdf

The exhaust port information and choke conditions on the single cylinder test engine vs. multi cylinder engine is the most interesting part for me, but it's all interesting.

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PostPosted: Fri Jan 10, 2020 4:41 pm 
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Joined: Sun Oct 08, 2017 2:58 pm
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Location: Dousman, WI
I'm not saying DI is the whole thing, just that it helps. Sport bikes and F1 are kind of a different kettle of fish in that 13:1 compression with cam timing that will support 10+k RPM has less cylinder pressure than a grocery getter engne. Also, I think the V-twin Duc maxed out at around 4.4" bore, with a claimed 205 with the track exhaust out of 1.2L. Still impressive.

Tumble is hugely important, and it's interesting to me how long it took people to figure out what Duckworth was doing.


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