compression, how high is too high on 98fuel.

[jeffro ra28]

I have watched one of aussies better engine builders (has built the engines that won the past 2 V8supercar championships) throw together a Ex-stone brothers engine for a ski race boat and the attention to detail and understanding of the full dynamics of that particular block/engine was amazing..
He was like oh the 3rd main bearing needs a extra thou clearance becase at high revs the block deforms in a way which it clamps down abit

This is the sort of knowledge that only alot experience and development with that particular engine will find. Unfortunately, finding this sort of person for a 1uz is going to be alot harder then a V8 supercar engine. So lets be realistic here

They key is to finding the engine guy that has the most/best experience with the particular engine you wish to get built. Likely, the example merc blue has given is a guru with the ford V8's, but would he know what to do with an aluminium block 1uz with a cam belt yanking from the snout of the crank? i think not. Again, lets be realistic!
The little things like this are only picked up from working in industries such as V8 supercars, race teams or similar, where a whole bunch of the same engines are built very similar, had their necks wringed, then stripped down. This is the only situation where you will ever get the appropriate feedback needed to gain this sort knowledge and developments. So unless you are building an engine that needs to be similar to that of a raceteam. Stop dreaming!!!!

But what has this got to do with compression ratio honestly? The guy just wants to know some realistic figures of compression ratio's on 98 ron fuel .

Oh btw, Abently, increasing the Compression ratio is one of the only sure ways of increasing your power output throughout the entire rev range, without losing out elsewhere.
Im going to be honest and say i disagree with you. Many times iv seen and done a most important modification to an engine of increasing its compression ratio to yeild more horsepower.
Wild cams usually have more overlap resulting in losing dynamic compression compared to your static compression, thats why higher compression is needed when using wilder cams. Increasing static compression no matter what the combination will increase dynamic compression.

[abently]

Have you guys actually looked at what the "theoretical" power increase on any number after 10:1 is ?

You will also notice that most Engines are still maxing HP at piston speeds well under 20m/s and the 25m/s limit for most D.I.Y budget's.

So in most cases you will always see a better bang for buck return on just increasing the min CSA (Intake side) then you will for just a Compression increase.

But don't take my word for it, test both methods for yourselves.

[jeffro ra28]

Arent we arguing that more compression will infact increase your power output and IS worthwhile? And not what is a better mod and more bang for buck etc...... We are talking compression ratios ffs, not CSA.

[abently]

I realise the topic has sidetracked but this sort of question just isn't relevant anymore. It should probably be made a sticky as it is one of the first things considered by those looking for more power from an N.A Engine and probably on rotation yearly.

There are gains to be had but they are not worthwhile by any stretch of the imagination. Which is unfortunate given the cost of off the shelf high-comp Piston upgrades.

I dream one day buzzing 9000rpms (F1 stylez yo! ) will phase out the "cannon upgrade" so popular these days.

[oldcorollas]

it depends what compression you are coming from, and going to.

to be specific abotu the original question, you would have to phrase it like
"what is the peak cylinder pressure, or rate of increase in cylinder pressure, at which the burning of the fuel in the cylinder remains stable"

but that answer is of little use, since that sort of thing is not measurable.

what is useful, for the general backyard engine builder is:
for a given engine and good tuning, what is maximum compression ratio supported for that engines pistons/chamber, for a given cam and manifolding (ie, roughly comparable dynamic compression), either for NA, or in combination with a certain level of boost.

all of those things affect the stability and burn speed, which is what you are trying to control.

you also need to remember that most engines are not run with maximum cylionder pressure all the time... ie, not running maximum throttle/boost.

ANY TIME an engine is not running at max VE or max VExBoost, it WILL benefit from an increase in compression.

so then the question arises (as the thread was started) "at what compression ratio, assuming good tuning, will i start to have problems with a given fuel".
this IS relevant, as different fuels react to compression and boost and temperature differently.
ie, E10 burns differently to 91, which burns differently to 98, which burns differently to E85, different to ELF, different to Avgas etc etc...

apparently i answered 5 months ago
"cam duration/overlap combined with tuning will be other factors you should be considering in the equation."


what question do you think is relevant? and why?
do you think that 9000rpm buzzboxes will meet emissions?

[abently]

What is max V.E. ? You can actually achieve 120+% V.E. in N/A mode....

A simply way to sometimes guage what CR would suit 98Ron Fuel would be to look at the Jap spec series Engines which are specified to run on 100Ron. Ideally you would also get a copy of the ignition table from that model but you could just re-tune it here on a dyno anyway. This is ofcourse assuming the camshaft duration/overlaps are the same which most times they are not... making things even more difficult.

Most other times you can find someone who specialises in your partciular Engine and either get the info for free or offer petty cash for it, espcecially if they are in another country. They won't give you the exact specifics but they will give you enough info to work from. If you really want an accurate answer to your question, its best you go and get it from first hand experience. Most of them are in the buisness of making a profit but $50/$100 for a quick 10min talk over the phone from someone who's never going to compete against them is too good to refuse.

You have to remember that these are the workshops whom have probably blown at least a handfull of setups at their own expense so naturally they will always be hesitant to give away good info for free.

[wombat]

At work here we run 98 on a direct injection v6 with comp of 11.70:1 so that might help, although with direct injection it does throw a whole new bunch of things to look at to decide the fuel used.

[oldcorollas]

max VE = max VE for that engine with the cam chosen and the intake/exhaust. not the total max ideal VE possible for a given capacity.... 130 is possible if you have high enough revs and enough energy.

A simply way to sometimes guage what CR would suit 98Ron Fuel would be to look at the Jap spec series Engines which are specified to run on 100Ron.

but.. their CRs vary widely, and almost all are tuned for fuel efficiency and drivability.. not for teh powah...
they are usually tuned well below the limits, so that any variation in initial production, and in subsequent running, does not have catastrophic effects..
i don't subscribe the the KM school of thought sorry.

100RON tuned cars must be able to survive without failure if the driver accidentally puts in 98 or 95 or whatever "regular" fuel is here"....

and specifically.. if we are talking about 1UZ.. it is primarily designed for 100RON.. at leats the later versions.. so to say "no, you can't increase CR becuse it cam from the factory like that"... is a bit.. misguided.

i guess the point is that the only thing that restricts the CR will be the last X% of throttle/VE/cylinder filling at whatever RPM... power has little to do with it.

[abently]

OC, I agree the Factory has built in safety factors such that the CR is not on the limit. Though they do have Knock systems and octane sensors additionally.

One thing that's important to remember in all this is that having a dome shaped piston does affect power at some stage. Dependent on each CC/Ports etc. You can get a general idea for this from the Honda guys running 12-14:1 CR.

Power is the end result not the constraint. Not sure why the amatuer Turbo guys think the other way around... lol

Anyway, I hope this enthusiastic discussion has given readers a better sense for the whole topic at hand.

I strongly recommend people who are serious about CR increases get first hand advice even if that means paying for it. Its cheap insurance. Especially with the internet these days, there is even less reason to find the limit on your own.

[oldcorollas]

hmm, perhaps you are missing the point of toymods, that being to generate and maintain a body of knowledge... no reason why CR should be exclude from that

not that many "paid professionals" know what they are doing either, and if they make changes, don't really understand why it does or doesn't work... so it is not a very safe option either.

i guess turbo guys think that becasue it is easy to change the pressure of air going into engine, rather than increase the efficiency of the engine.. but some know what they are doing.

knock detection systems yes... octane sensors? i wonder how a sensor can accurately measure the octane rating of a fuel going past it.
Please provide some information about these octane sensors.


(the only real octane sensor i know of is one based on spectroscopy, to determine the functional groups of the hydrocarbons themselves... i am pretty sure that no car is worth what they are..)

[af300e]

octane sensors? i wonder how a sensor can accurately measure the octane rating of a fuel going past it

Octane sensors are roughly spherical and are stuck in the head of the driver. They operate by reading the octane number off the fuel pump at the servo.

[Duk]

Octane sensors are roughly spherical and are stuck the head of the driver. They operate by reading the octane number off the fuel pump at the servo.

Some are better calibrated than others

[oldcorollas]

there may be an E85 sensor, but being able to tell between 91 and 98 or 100... when they are all comprised of basically the same chemicals, just in different amounts...

and.. different petrol companies using different recipes to each other etc...

but.. i will just wait until abently posts up the ones he knows about

[abently]

Sorry, yes octane sensor is more an R&D product than reality.

Anyway, I'll leave this topic back to the normal Users. People are bumping up my rep points and its contradicting my sig.... lol

[oldcorollas]

i can fix that for you.

americans seem convinced that their cars have octane sensors. but.. they are americans.. and wrong..