High compression on low octane

[BongoBennie]

It's been a while but this seems to be the place to ask "dumb ass questions" per FB K series groups.

I have a K swapped Insight with the goal of power AND economy, I've had a K20a3 with 11.5: compression and 5psi of boost, 3.4 final drive and while its a blast to drive I average 30mpg with 40mpg being my tank record. Meh

I now have a K24a4 on the stand and will be swapping it in next year. No turbo, well muffled. Stock compression is 9.7:1 and made for 87 octane.

I'm interested in running higher compression on 87. TSX engine is 10.5:1 which seems possible. what about higher?

My thought are that the car is almost half the weight of the original Element/Accords the engine came from so the load will be less.

My other idea is to add EGR to the system and control it with Kpro or maybe another means.

Also FWIW I fully expect less power than my current setup and I'm cool with that, I have other cars for that.

[Gasoline Fumes]

The original Insight engine was 10.8:1 and only required 87 octane. But I don't know how that translates to a K-series.

I've driven a manual K24 CR-V and really enjoyed the engine. It's gotta be awesome in a lighter car! Cheap and torquey! But I think I'll be sticking with the 64 MPG 3-cyl.

[JRMichler]

Originally Posted by BongoBennie

I'm interested in running higher compression on 87. TSX engine is 10.5:1 which seems possible. what about higher?

Also FWIW I fully expect less power than my current setup and I'm cool with that, I have other cars for that.

The engine in my previous GMC Canyon had, if I recall correctly, 10:1 or 10.5:1 compression. It ran well on 87 octane. The best ambient temperature for gas mileage was about 70 deg F. It lost about 1 MPG per 10 deg F at lower temperatures. The mileage did not improve at higher temperatures. I think that the knock sensor was retarding ignition timing at temperatures above 70 deg F.

I saw timing as retarded as 2 deg after TDC at high manifold pressure and low RPM, and as advanced as 45 deg BTDC at low manifold pressure and higher RPM. That engine would slowly and smoothly accelerate from 21 MPH in fifth gear, which was about 600 RPM.

Your higher compression should be possible. Pay careful attention to ignition timing vs RPM, intake air temperature, engine temperature, and manifold pressure to prevent detonation. You may need a knock sensor to get your timing fully dialed in. I would not be surprised if getting smooth running at low RPM required ignition timing a few degrees ATDC at higher manifold pressures.

If you are happy with less power, try a camshaft with delayed intake valve closing to get some Atkinson cycle effect.

[Logic]

BYD serial hybrids with direct top gear have an ICE running 16 to 1 compression,
I posted about it here"
https://ecomodder.com/forum/showthre...6-a-41587.html

The only other place I have seen talk of successfully increased compression without ping is here:
https://turbobricks.com/index.php?th...y-tried.66779/

I would say low hanging fruit is you want your intake charge as cool as you can get it.
In a dry climate; using an Ultrasonic Mist Maker (or Pond Mister) or 10 to produce max mist for per 'space required' for evaporation in the intake may work.

https://www.youtube.com/watch?v=jekXeBRZnGY

[Ecky]

I tuned a few high compression K24's to run on 87, but it absolutely guts their low end torque, and they're very temperature sensitive. Best I can tell, OEMs get away with high compression on regular (without resorting to Atkinson cycle) by having very sophisticated knock detection, and very high resolution ignition tables. The ND Miata knock control is done via ionization detection through the spark plugs, and ignition control down to a tenth of a degree, just as an example.

There's very little downside if you're keeping revs up. Most of the ignition advance is lost below 2500rpm.

[Logic]

"...The Skyactiv-G[7] is a family of direct injection petrol engines. The engine compression ratio is increased to 14.0:1. To reduce the risk of engine knock at high compression, residual gas is reduced by using 4-2-1 engine exhaust systems..."
https://en.wikipedia.org/wiki/Skyactiv

Tuned length 4-2-1 exhaust system calculators are available online.
NB that the ...-1 pipe length and diameter is also important.
You can fool the exhaust into thinking it's exhausting into the atmosphere with David Vizard's Pressure Wave Termination Box, discussed in my other posts here.

Videos of the design how and why are available on his Youtube channel.
Videos of systems built by enthusiasts too.

[Ecky]

There isn't really a magic bullet to solving the compression / knock issue. Adding a point of compression gives a few percent thermal efficiency, but unless you can run Atkinson cycle, you then lose that efficiency through retarding ignition timing, or you lose the monetary gains through high octane fuel. Turbos are just another way to get more compression, and come with the same set of issues. There are combustion chamber tricks, such as Logic's quoted tuned headers, changes to piston design or valve timing or combustion chamber shape, but these are largely outside of our control as lay people.

I'd wager the best engine swap might be one of the Toyota Dynamic Force engines. Honda never mated their highest efficiency engines to a manual transmission; the L series in Honda's hybrids were 13.5:1 CR in the automatics, but only 11:1 in the manuals. Mazda did Atkinson Cycle + manuals right, but due to cheaping out on materials, their efficiency is only mid 30's %, similar to the non-Atkinson Honda engines. A Toyota 3- or 4-pot Dynamic Force engine can reach 40-41%, they have manual transmissions available, and make decent power. Nobody else, other than perhaps Mercedes, seems to be building maximum efficiency gasoline engines.

[Logic]

Originally Posted by Ecky

There isn't really a magic bullet to solving the compression / knock issue. Adding a point of compression gives a few percent thermal efficiency, but unless you can run Atkinson cycle, you then lose that efficiency through retarding ignition timing, or you lose the monetary gains through high octane fuel. Turbos are just another way to get more compression, and come with the same set of issues. There are combustion chamber tricks, such as Logic's quoted tuned headers, changes to piston design or valve timing or combustion chamber shape, but these are largely outside of our control as lay people.

I'd wager the best engine swap might be one of the Toyota Dynamic Force engines. Honda never mated their highest efficiency engines to a manual transmission; the L series in Honda's hybrids were 13.5:1 CR in the automatics, but only 11:1 in the manuals. Mazda did Atkinson Cycle + manuals right, but due to cheaping out on materials, their efficiency is only mid 30's %, similar to the non-Atkinson Honda engines. A Toyota 3- or 4-pot Dynamic Force engine can reach 40-41%, they have manual transmissions available, and make decent power. Nobody else, other than perhaps Mercedes, seems to be building maximum efficiency gasoline engines.

This is an interesting read once you get into it:
https://turbobricks.com/index.php?th...y-tried.66779/
All sorts of testing and reporting back by engine builders.

Headers... Id just take it to someone reputable and ask for the equal length system and a pressure wave terminator. Plans in hand.
If I could afford it..

I had this in a tab:

https://www.youtube.com/watch?v=5nKDNrUz5to

Cams: Same story.
If I could afford it!

Fuel and spark:
There I'm light.
pgfpro will know for sure. And about most else here.

And don't forget the water mist. As long as the vehicle is in a dry climate it will help.
I fill the house cooler up daily already. It's quite affordable..

Shot for the engine info. Interesting!

That 16-17 to 1 BYD engine; I'd love to see stripped down.
What do you think we'd find?
Sodium-filled engine valves?

[Logic]

https://www.youtube.com/watch?v=jextyKc2UN4

[arcosine]

lot of swirl and quench, retard the cam