[Mk2] [Turbo] Compression ratios and head gaskets

[gavinda]

Because by adding high octane fuel or installing lower compression pistons the engines then start to perform the way they should do, See jimGTS post above.

Still waiting for some evidence that lowering the compression ratio makes a engine perform better...

What do you mean by evidence?

Will Garrett's word do?

http://www.turbobygarrett.com/turbobyga ... with_boost

you are taking what he is saying out of context, he is suggesting properly intercooled mr2s are not retarding ignition from knock (as they are not overly knocking) and so will perform better then at lower CR, he is merely asking for back to back dyno or some other evidence of the low C/R vehicles vs stock C/R

he is in agreement with garrett quote 'Generally, compression ratio should be set as high as feasible without encountering detonation at the maximum load condition'

[Marf]

How will a simple dyno run tell you that the ignition is being retarded?

[bobhatton]

How do you know they are all running on the knock sensor?

Because by adding high octane fuel or installing lower compression pistons the engines then start to perform the way they should do, See jimGTS post above.

Still waiting for some evidence that lowering the compression ratio makes a engine perform better...

Having the right compression ratio for the fuel and boost being used so the ECU is not running under the control of the knock sensor will make the engine perform as it was designed, this is all common sense something I think you lack.

[bobhatton]

in regards to engine knock,preignition. The cooler intake air lowers in
cylinder gas temperatures at the end of the compression stroke. Reducing the
gas temperature at the end of a compression stroke reduces knock.

what were your intake air temps on track? chargecoolers tend to be less effective for longer durations of wide open throttle depending on if the system is large enough.

The lower the inlet temperature the more volume of air there will be in the inlet. So under compression there will be more air to compress, this will give a higher pressure and a higher temperature

[jon]

Data-log of my Rev 3 on the dyno with a stock CT20b turbo, ECU and intercooler running Tesco 99 RON fuel.

Blue line is ignition timing, green line is injector pulse-width. At around 4000 RPM something triggers the ECU to dump extra fuel and rapidly adjust ignition timing.

I haven't figured out the exact trigger yet, but I'll bet it has something to do with the knock sensor....

[kev8611]

in regards to engine knock,preignition. The cooler intake air lowers in
cylinder gas temperatures at the end of the compression stroke. Reducing the
gas temperature at the end of a compression stroke reduces knock.

what were your intake air temps on track? chargecoolers tend to be less effective for longer durations of wide open throttle depending on if the system is large enough.

The lower the inlet temperature the more volume of air there will be in the inlet. So under compression there will be more air to compress, this will give a higher pressure and a higher temperature

I always thought hotter air has more volume than colder air

[Marf]

in regards to engine knock,preignition. The cooler intake air lowers in
cylinder gas temperatures at the end of the compression stroke. Reducing the
gas temperature at the end of a compression stroke reduces knock.

what were your intake air temps on track? chargecoolers tend to be less effective for longer durations of wide open throttle depending on if the system is large enough.

The lower the inlet temperature the more volume of air there will be in the inlet. So under compression there will be more air to compress, this will give a higher pressure and a higher temperature

I always thought hotter air has more volume than colder air

You thought wrong.

[kev8611]

Obviously I did which is why I said it

[Marf]

[jimGTS]

so we want to run no intercooler then

[Marf]

Replace it with a heating element.

[bobhatton]

in regards to engine knock,preignition. The cooler intake air lowers in
cylinder gas temperatures at the end of the compression stroke. Reducing the
gas temperature at the end of a compression stroke reduces knock.

what were your intake air temps on track? chargecoolers tend to be less effective for longer durations of wide open throttle depending on if the system is large enough.

The lower the inlet temperature the more volume of air there will be in the inlet. So under compression there will be more air to compress, this will give a higher pressure and a higher temperature

I always thought hotter air has more volume than colder air

Yes you are right, the hot air has a bigger volume but less weight because it has expanded from the heat.

Colder air has less volume but more weight. The more air by weight that an engine can breath the more power it will give.

[bobhatton]

so we want to run no intercooler then

It is all a balance, change one thing and other things change, it is understanding how everything works together.

No intercoolers when I started turbocharging so anything can be done, it is just getting the maximum pressure in the cylinder just before tdc without the temperature going too high and giving detonation.

[MR2 Rich]

Because by adding high octane fuel or installing lower compression pistons the engines then start to perform the way they should do, See jimGTS post above.

Still waiting for some evidence that lowering the compression ratio makes a engine perform better...

Having the right compression ratio for the fuel and boost being used so the ECU is not running under the control of the knock sensor will make the engine perform as it was designed, this is all common sense something I think you lack.

I have common sense Bob. I just like messing with you. What I don't get is your logic that Toyota designed this engine to run on 100 Ron Japanese fuel and they made it 8.5 compression ratio. You think when using 99 V Power the engine compression ratio needs dropping to 8!

[MR2 Rich]

Because by adding high octane fuel or installing lower compression pistons the engines then start to perform the way they should do, See jimGTS post above.

Still waiting for some evidence that lowering the compression ratio makes a engine perform better...

What do you mean by evidence?

Will Garrett's word do?

http://www.turbobygarrett.com/turbobyga ... with_boost

Thanks for proving my point Peter.

"Generally, compression ratio should be set as high as feasible without encountering detonation at the maximum load condition. Compression ratio that is too low will result in an engine that is a bit sluggish in off-boost operation"

"Factors that influence the compression ratio include: fuel anti-knock properties (octane rating), boost pressure, intake air temperature, combustion chamber design, ignition timing, valve events, and exhaust backpressure. Many modern normally-aspirated engines have well-designed combustion chambers that, with appropriate tuning, will allow modest boost levels with no change to compression ratio. For higher power targets with more boost, compression ratio should be adjusted to compensate."

[bobhatton]

Still waiting for some evidence that lowering the compression ratio makes a engine perform better...

Having the right compression ratio for the fuel and boost being used so the ECU is not running under the control of the knock sensor will make the engine perform as it was designed, this is all common sense something I think you lack.

I have common sense Bob. I just like messing with you. What I don't get is your logic that Toyota designed this engine to run on 100 Ron Japanese fuel and they made it 8.5 compression ratio. You think when using 99 V Power the engine compression ratio needs dropping to 8!

Nothing wrong with 8.0:1 compression ratio at all. Would you notice a 1.5% drop in power from 8.5:1?

What is your logic in running a high compression ratio?

[Draven]

Ron rating isn't the best way to gauge fuel.. MON is.. Tesco has a 87MON rating which isn't bad. I'm still struggling to find a spec sheel for Vpower or BP Ultimate (rubbish)

On the face of it seems that Tesco 87Mon fuel is the best you can buy in the uk.

For that fact I cannot find any specs for the so called Japanese 100ron fuel.

It seems on lower MON fuels the Knock sensor does a lot of work to prevent pinking. The MR2 does run very rich from the factory and I believe Bob is correct in saying that UK fuel doesn't quite cut it.

[MR2 Rich]

If you are building a high power engine you would personally drop below 8, wouldn't you? If it was that important why are there no pistons for the 3SGTE that are below 8 and most are 8.5 or 9?

[Marf]

My first turbo car ran 7.8:1 and 25psi boost, but the car was a homologation special designed to take bolt ons to get big power.

[bobhatton]

If you are building a high power engine you would personally drop below 8, wouldn't you? If it was that important why are there no pistons for the 3SGTE that are below 8 and most are 8.5 or 9?

Pistons are made to any compression needed, you just have to order them.

In the USA the pistons are 8.5:1 and above because racers use high octane fuel, in the EU we have to race on road fuel so piston made in the EU are 8.0:1, just common sense again.