Is The Hot Weather To Blame?

[Godzilla32]

Logical physics, interesting stuff!

[mad082]

i know that the act of compressing the gas is what heats up the air, but the question is, does a gas compressed at 1 temp go to the same temp as a colder gas.

the reason why it could go either way is that boiling water freezes quicker than warm water. its called the Mpemba effect.

[Godzilla32]

What gas? Its air..

[mad082]

air is a gas.

[Cubes]

Apparently for every degree you reduce the intake air temperature you gain 1 Hp. The pod filter shroud is probably more beneficial on a non turbo engine as they dont have/need intercoolers.

Just because the turbine is stinking hot doesnt mean it will directly heat the charge air to the same temperature. The air rushes through there so fast it would barely be heated by the turbine next door. Its the compression of air that causes friction between atoms which in turn causes alot of the increased heat.

The issue with hot air isn't the turbo heating its the air passing through the radiator.

A 30degree day... The air exiting the radiator is hot enough to feel as if its burning your hand. Just out of school and working at the end of a glass furnace we saw air temps of 70degree's... The air I felt out of the radiator on a 30degree day felt pretty damn close to the furnace air.

Mad082... I know what you are saying.. But I have NFI.

[Godzilla32]

The intercooler is normally placed in front of the radiator. Air will pass through it first

[Munkyb0y]

i think he means the air being sucked into an unshielded pod is basically radiator air, which by the way, might be as hot as furnace air

[Cubes]

i think he means the air being sucked into an unshielded pod is basically radiator air, which by the way, might be as hot as furnace air

Yep, the post was in reply to..

Apparently for every degree you reduce the intake air temperature you gain 1 Hp. The pod filter shroud is probably more beneficial on a non turbo engine as they dont have/need intercoolers.

Just because the turbine is stinking hot doesnt mean it will directly heat the charge air to the same temperature. The air rushes through there so fast it would barely be heated by the turbine next door. Its the compression of air that causes friction between atoms which in turn causes alot of the increased heat.

[700HP-GTR33]

On a hot day ,fuel evaporates in the injectors.

When you go to start up the engine it needs to crank a few times before it fires up.

If you have faulty injectors, they may also play up , this can also be your problem.

Run some injector cleaner through the petrol tank a few times to see if this works.

When you have driven the car for a while and stop the engine, manufacturers recommend you

press on the gas when you go to start it up again.

I too have had to wait for the thing to turn over on a hot day before it fires up.,

Your tune is also at fault....if you have had one.

Tuning a car on a cold day then driving it on a hot day plays a big role in your problem.

Don't go to much into new radiators ,fmic etc if your not over-heating.

[mad082]

if 30 degree air is heated to 110 degrees in the process of being compressed, i don't think the 70 degree isn't going to be heated to to 150 degrees, just because it started off 40 degrees hotter.

also cold air is denser, so when it is compressed it will expand more. this would mean a higher pressue in the intercooler pipe. the wastegate then sees this higher pressure and opens the wastegate further, slowing down the turbo, so it pumps less air.

which means pressure on the air coming out of the wastegate.

[Cubes]

if 30 degree air is heated to 110 degrees in the process of being compressed, i don't think the 70 degree isn't going to be heated to to 150 degrees, just because it started off 40 degrees hotter.

Is that a think or a know from a physics point of view? Just curious so I know if I have to do a little research in my spare time or not.

-----------------

Hotter air is thinner air. A turbo must work/spin harder to produce the given boost level; boost build will appear lazy and outlet temps will be higher due to lesser turbo efficiency. Remember its not just the air compression that throws heat in to the air; its also the compressors efficiency.

Notice that lazy turbo on those hot 35degree days.

No matter what its always best to have the absolute lowest inlet (pod) temperature, it not only slows the heat soak of your fmic but allows the turbo to do its job easier resulting in a lower outlet temp.

Sure one may say that the larger the temperature difference the greater the heat transfer efficiency.

I don't see this as a valid argument for thinking its ok to have higher turbo inlet as a result outlet temperatures. No matter what, the air entering your motor is ALWAYS going to be hotter; as a result thinner with a greater ability to aid that nasty detonation and make less power. But hell slap it on a DD Dyno and shove an IT sensor to bump that figure up so its inline with a car that runs a good cai sucking air thats 20degree's cooler.

[gtst25]

What about water methanol injection fellas??

Can't wait to see how mine goes next tune - you can't get anything over an 8 knock now with the newly fitted kit.

Your car shouldn't be hard to start in the hot weather - there's something else amiss there - your fuel pump will prime the injectors before you start your engine so it won't be the old fuel evaporating, and your injectors are closed anyway unless powered up unlike an old carby.

Unless you get an intercooler spray kit or water meth your line will be sluggish in the heat, 'specially the rb20's - the rb30 boys probably don't notice it as much.

Pushing your car in the heat isn't too smart regardless and fellas running un-shielded pods in the engine bay can only expect stinking hot intake temps.

Cheers

[Cubes]

3ltr you don't notice it off idle/boost but still feel it if you want to bring it up on boost; still feels just that little bit lazier.

The best part is the a/c I can't even feel.

I remember the old rb20 in hot weather with the a/c. I used to have to rev the thing on and slip the clutch (dipping it in slightly as rev'd dropped) to get it off the line just to keep up with traffic..

Felt like it was hard work just to get it off the line.

I agree; no matter what it should just start, hot or cold. If it doesn't it has issues. Its not the ecu remembering the prior day (skyline ecu's are not this smart, they are dumb 1990 ecu's) or fuel evaporating in the fuel line.

[gtst25]

3ltr you don't notice it off idle/boost but still feel it if you want to bring it up on boost; still feels just that little bit lazier.

The best part is the a/c I can't even feel.

I remember the old rb20 in hot weather with the a/c. I used to have to rev the thing on and slip the clutch (dipping it in slightly as rev'd dropped) to get it off the line just to keep up with traffic..

Felt like it was hard work just to get it off the line.

I agree; no matter what it should just start, hot or cold. If it doesn't it has issues. Its not the ecu remembering the prior day (skyline ecu's are not this smart, they are dumb 1990 ecu's) or fuel evaporating in the fuel line.

There's nothing like driving through an icy winter night in a high performance turbo car! We really suffer up here in QLD.

The rb20's don't do it for me anymore either. Dad and I fitted one to my old commodore 8 years ago and torque was such an issue. With boost etc it still managed to see off plenty of v8's though!

If anything happens to my 25 bottom end I'll be building the 30 hybrid.

Cheers

[mad082]

There's nothing like driving through an icy winter night in a high performance turbo car! We really suffer up here in QLD.

but that has more to do with the intercooler getting nice cold air than the intake.

we need someone with an intake temp sensor to do some testing. plenty of people have done it on the pod, but that only proves that it is going into the turbo colder, it doesn't show what happens once it has been compressed.

[Cubes]

but that has more to do with the intercooler getting nice cold air than the intake.

we need someone with an intake temp sensor to do some testing. plenty of people have done it on the pod, but that only proves that it is going into the turbo colder, it doesn't show what happens once it has been compressed.

Are you sure? Back in the good old VL days with no IC the cool nights made a hell of a difference.

[Munkyb0y]

what i'd like to know is if the flow restriction of boxing the pod for a few degrees cooler temps provides benefits that outweigh a higher temp unsrestricted flow to an 'open' pod.

i want results damn it !!!

as for the starting, the car starts fine now and always, but had the issue during the recent hot days.

a tuner messed with my idle. i put it back to ~725rpm. but even then after the stinking hot saturday, on the much cooler sunday morning the engine turned over for quite a while before starting. havent seen this before or since.

[Godzilla32]

also cold air is denser, so when it is compressed it will expand more. this would mean a higher pressue in the intercooler pipe. the wastegate then sees this higher pressure and opens the wastegate further, slowing down the turbo, so it pumps less air.

which means pressure on the air coming out of the wastegate.

This makes no sense..

[quiksta]

"what i'd like to know is if the flow restriction of boxing the pod for a few degrees cooler temps provides benefits that outweigh a higher temp unsrestricted flow to an 'open' pod".

I too want to know the answer to Munkyboy's question.

[Godzilla32]

Unless its in direct air flow it won't reduce any extra possible flow.

Edited October 20, 2006 by Godzilla32