New pistons, higher compression?

[Allch Chcar]

Originally Posted by jakobnev

You'd get a theoretical efficiency improvement of ~5%, with a price hike of only 2-3% and if you already had the parts and enjoyed the labour, it would just about be worth it.

^This.

Regarding E10. If they're not spec blending it locally to 87 Octane, then it is 89 Octane already.

[beatr911]

I seem to remember that some of the benefit of two intake valves weather on 3 or 4 valve heads was that they can provide for tumble as opposed to swirl.

If I recall this correctly, I think it was that at higher intake velocities say over 2500 rpm or so, swirl was detrimental as the heavier fuel droplets would centrifuge out near cylinder walls causing a lean area in the center where the sparkplug is. Tumble, with the injector putting fuel near the middle of the charge keeps the richer part of the mixture near the plug and leaner parts to the sides, aiding in more consistent combustion events. Sort of a stratified charge idea.

Didn't the VX (D15B?) motor operate with mostly one intake valve under 2500rpm and then both above 2500rpm for swirl at low speeds and tumble at high speeds?

[Ecky]

Originally Posted by beatr911

Didn't the VX (D15B?) motor operate with mostly one intake valve under 2500rpm and then both above 2500rpm for swirl at low speeds and tumble at high speeds?

That's exactly what it did. In fact, that's what nearly all VTEC systems do.

So the trick is to drive my car at 2500 to 3500rpm I guess?

[IsaacMTSU]

I'm wondering the same thing... Higher compression on regular gas is fine for hypermiling because you are going to be driving easy anyway right? Would it help to put some HC pistons in?

[serialk11r]

Originally Posted by IsaacMTSU

I'm wondering the same thing... Higher compression on regular gas is fine for hypermiling because you are going to be driving easy anyway right? Would it help to put some HC pistons in?

Would depend on the engine. A fully variable duration intake valve equipped engine would do fine on low octane gas, since the temperature at ignition will be considerably reduced. A throttle plate can be thought of as adding the pumping losses it induces to the intake charge in the form of heat, so the amount of extra detonation headroom you get when running at part load is smaller. I don't know how much you have to restrict your load due to running lower octane fuel, but if it forces you to remain at very low load levels where the engine isn't very efficient, then it might be better to buy higher octane fuel and just burn less of it. If you're just sitting at part throttle on the open highway, no pulse and glide, then regular gas would probably save you a bit.

[trooper Tdiesel]

running 12/1 comp or better, with E85 being 105 octane, err better to say, 100+ octane year round....

high compression would work in a dedicated E85 fuel, daily driver auto.
granted E85 cost compared to 87 octane is a major factor in making it worth it. the other thing is, is the fuel even in your area
let alone the cost of doing the compression change.....

making a dedicated E85 fuel auto is something that's on my bucket list, not any day soon....

with a much more common un modded, 9/1 comp engine running 100% 87 octane gas with no ethanol in it, will get you the best cost per mile.

9.25 to 10 compression, is for the most part, the limit of 87 octane in most engines. but there are getting to be more and more modern VVT engines now days.

[Allch Chcar]

I've heard of people running 12:1 with Premium Gasoline. Depends on the engine.

BTW E50-E85 is between 95-96 AKI Octane. I'd like to build an E85 build too but it's expensive and beyond my current skills.

[wagonef8]

I run close to 13:1 on 91 octane on my Gsr motor all forged internals and a good tune
Here is something to play with
Honda B-Series Compression Calculator by ZealAutowerks

[trooper Tdiesel]

odd.
the local E85 pump says 105 octane

and in winter its a 70% blend.

[IsaacMTSU]

Good info here! I was asking about my CRX. It's a 91 HF with the D15B6 1.5L with a stock CR of 9.1:1.