kpjo4

Just in curiosity, I've been messing with timing lately and am going to be building up a motor soon. From what I've seen all the sr20det guys with 11:1 pistons seem to be using e85, same goes with that ka24det. In a turbocharged high compression motor I understand you run more of a risk of detonation vs a lower compression motor. What is usually the maximum threshhold on 93octane pump gas typically on these Nissan Motors with multi port fuel injection with low boost level around 7-12psi. I'm honestly thinking about building a KA24DE with 10.5:1 compression 2618 forging. I'm leaning towards using pump gas 93 octane rather than a e85 setup.

Kingtal0n

9:1 is the max you want for a turbo 4-cylinder engine in general, when using 93 octane.

E85 is race gas, or nearly so. Thats why you see people getting away with high compression ratio in addition to boost.

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RalliartRsX

With the current tuning technologies, 10:1 is very common ESPECIALLY in the Honda world.

My previous setup (Lowport SR20DE-T) included a 9.5:1 build on regular ol pump 93 octane gas. On a T3/T04E it made a healthy 340WHP @ 11-12psi and about 280 ft lb of torque. Powerband started from 4K all the way to the 7.5k rev limit (made a solid 270 ft lbs from 4.5K all the way to rev limit). Kept blowing couplers off at 15 psi before I parted it all out (just the single coupler that was around the pipe which wasn't bead rolled, so entirely my fault).

IMHO, any build from here on out is going with a minimum of 9.8:1-10:1 if I am going forged internals. The drivability it presents as well as allowing you to run less boost, coupled with the tuning technologies to maximize the burn of pump gas 93 Octane, means no looking bad and things are much easier to make work in the higher compression range.

9:1 in current standards is a VERY paltry number especially if you are going forge internals IMHO.

Seraphim38

Compression and boost are configurable based on the tune. More compression is going to give you more midrange power and torque of course, with less boost opportunity prior to knocking.

The AEM EMSv2 has the ability to tune the knock sensor frequency, which makes it more viable when pushing timing than a Power FC, which has a fixed frequency sensor configuration.

I have experience with a prior vehicle, being my Suzuki GSXR1000 street bike that ran 13:1 compression with a turbo charger set at 10 psi of boost, running on pump gas with no knocking. It did 255rwhp on pump gas easily, out of a 1.0 liter motor.

A lot of people seem to magically migrate to 9:1, but it clearly isn't a hard requirement to run compression that low.

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kpjo4

I'm actually trying to source some forged 9.5:1 pistons, but seem to be stuck between 9:1 or 10.5:1, thanks for the input everyone... seems I may be leaning towards a 9:1 but really want the 10.5:1 on pump gas

4x4le

Weisco will design custom pistons for you if you are willing to wait and pay.

Kingtal0n

There is a good reason many factory turbo engines are 8.5:1 (like the sr20det and 2jzgte). Don't you think that the manufacturer would have increased the compression ratio if they thought the rewards outweighed the risks?

Combined with the unfortunate fact that 99% of the "tuners" are useless, and still manage to [email protected]*# up the 8.5:1 engines often enough (...before anyone says 8.5:1 is "safe"), I would not exceed 9:1 unless you knew what you were doing and had experience doing it several times.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

4x4le

Today many turbo engines are 11:1 or higher. Their computers are a little smarter than old oem nissan ecus though and it is easy for them to deny a warrenty claim if they can blame it on fuel quality. One thing that really needs considered is the actual compression ratio. Cams have allot of influence on that.

RalliartRsX

............Those engines are also well over 20 years in design as well too (don't forget, an engine design takes 2-5 years, so tack that on to the oldest release if you will). And as mentioned, (actually, mentioned TWICE), the ECUs back then were simply not capable of the resolution and in addition, did not have the information stream as we have today from so many sensors, definable parameters, etc.

You just cannot use such a blanket statement of saying "the factory turbo cars of (key word) "YESTERYEAR" did it, so it must apply to today's standard". Just simply does not commute.

As far as your next statement is concerned, that is the SOLE reason why I tune every single one of my own vehicles. The problem is, in the "tuner" community, everybody's an expert, but 95% of the people have zero idea on what they are doing. My source of people for ideas consist of real engineers (I am an Aero Engineer myself) and people from actual race teams who I speak to and have related discussions. Not the hackjobs known as "tuners" on Zilvia

Kingtal0n

The newer engines have newer designs. Just because they exist doesn't magically improve our ancient engines.

likewise. Their computers are smarter and use more sensors as well. Just because they exist does not magically make our computers smarter.

not exactly sure what your point was. Did you know you can buy flat panel monitors now? So now all tube TV's magically become flat panels?


And camshafts do NOT influence compression ratio like you THINK they do. they only MOVE the peak torque around, and sometimes thanks to lift and design you get a little bit more of it. But that little bit is not going to give you anywhere near even a 0.5:1 dynamic increase to compression.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Kingtal0n

Again, the OP is not using a computer from 2014. not sure what the hell you guys are going on about. It's still a 20 year old computer, even if you do install taller pistons.

advice was directly at thread op, using OEM computer or standalone, and probably not tuning it himself.
Best to play it safe with 9:1 or less. (UNLESS HE GETS A COMPUTER/HARNESS/SENSORS FROM A NEWER VEHICLE AND RADICALLY MODIFIES HIS COMBUSTION CHAMBERS OF COURSE)

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

RalliartRsX

^^^ If you are building a high compression engine and NOT using a standalone, you are in for a world wind right.........

Also, new computers, NOT in the literal sense as you seem to want it to be defined, but the advancements in standalone computers.

I am not sure you are very aware of what we are referring to (yes, I DID see the S14 you built and all..........)

Kingtal0n

wait, which S14? because there have been quite few. picture time?

Stand alones are great but

1. there is no way I would ever rely on one to pull timing under any circumstance except for a bad tank of gas. And I would hope the driver notices the noise gradually dissapear and adds some toluene.

2. Stand alones are maybe 25% of what a factory ECU from 2014 is capable of doing. They work from the sensors already on the engine. Newer computers are "better" because there are "more/better" sensors. Adding a stand alone to an ancient engine does not give it "new and improved abilities". It just lets you have more control over thought process.

and finally there is still the issue of the ancient combustion chamber design which will directly limit the octane vs compression ratio. There is more to it than that of course; the way the air enters the combustion chamber, the way it leaves, efficiency of the fuel injector, piston design limitations, exhaust gas velocity and temperature, turbine size, overlap, the list goes on.

Nobody goes 10.5:1 on an sr20det with stock chambers, runs 93 octane (straight; no methanol, no water) runs 20 psi of boost and lives to tell about 100,000 miles of daily driver good ness. That is a gross, negligent, arrogant blanket statement that "nobody" should ever make but I've done it because it's probably true.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

RalliartRsX

Ok. I have my experience, engineers, stand alone, track time HPDE, PDX and Time trials) and my results, and you have your build results.........

.......And when did the gentleman ever mention this being a daily driver good for 100,000 miles?? Who said anything about stock chambers?? Who said prolonged amounts of boost at 20psi?? The only gross, arrogant and negligent statements being made are the ones you are assuming and fabricating........

Good day!

Kingtal0n

checking out already?

Who said anything about modern fancy electronics? Oh that was you. Where are your modern, fancy sensors? Not in your car. Not in the ops car. Its ok for YOU to make things up but when I do it you run?

we were having fun...

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Kingtal0n

An observation. IF you only intend to use 12psi then I would use a stock engine. Why throw thousands of dollars into a rebuild only for the 4% - 10% extra torque? increasing compression ratio is NOT a valid alternative to more boost on small displacement engines. Increasing compression ratio is ONLY considered when you have a very specific bracket to meet, or you absolutely need to squeeze every last drop out of a combination that you may not actually care about because you do not expect it to last.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240