does anyone else notice the same thing? when i start my car and the engine is still cold, it definitly has more power, but than it warms up and goes back to normal. funny, cause most engines are slow when cold and need time to warm up. why is this?

 

I definately get the same feeling. In the middle of the night when i take my car for a spin around the block to bring it in the driveway, its pick up is alot faster than when i would drive it when the engine is warm.

 

ever since my first 95 max, i've felt this as well. I dont know why but it feels stronger

 

well when it is cooler outside i notice it has more power, however when i get off the interstate i also notice it has plenty of power since it is all warmed up and ready

 

its pretty simple actually, cold air compresses better = bigger explosion= more power... when the engine is cold the air stays cold till it gets to the cyclinders.... exactly why a cold air intake is a must.

 

i get this feeling too...dunno if its the placebo effect or what not, but it indeed is there...i thought I was crazy at first, then read many other owners sayin the same...

 

Engine runs lean when the engines cold to warm up the car faster thats why your cars faster when you first start it.

 

You don't tax(floor) your engine when its cold, I hope?

 

A few factors: as mentioned above, running lean, intake parts are still cold -> colder air coming in, oil is still cold (thick) -> higher compression

 

VQ engine running lean when hot, rich when cold. A rich running VQ has more power.

 

Please don't beat on your engine when it's cold.

 

Amen to that!

I let it warm up to its operating temp before I step on it and give it a minute or two before I put it in drive...

 

I guess this is true, but I don't try to beat on it when it's cold. I do usually rev it up to around 4000, very rarely but *sometimes* 5000 at least once in the first few minutes when I'm moving, usually around 1/2 throttle. It warms up pretty quickly after that.

 

this is my first nissan i've ever owned and seem to react better than my other car (2000 accord v6) when engine is cold...on my other car when engine is cold and i drive slooowly the car jerks around but the maxima feels super smooth hehe

 

sounds more like a honda problem than anything...

anyway... the car runs RICH for a short time to light off the cat on cold start, and then runs richer than normal until ECT comes up to temp. the reason the car performs better is because the intake manifold and cylinder heads arent yet dumping heat into your intake charge, as i believe was already stated.

 

lol ok this is a really stupid question but why is it bad to beat on the engine when its cold....I mean i always heard about warming up the car since i was little but i mean it was understood. I never really questioned it.

 

One reason is that most of the oil is in the pan- bad lubrication= too much friction=warped walls(over time)

 

if you cant beat on the engine cold, its a weak engine to begin with... most of you will disagree, and thats fine but consider this...

give your car one minute of idle time and one minute of easy driving before getting on it. this is in florida weather... if youre up north, give it longer. this is for lubrication and charging system issues.

high performance valve springs HATE being pushed at high RPM when cold. if you have h/p valve springs, wait a little longer.

if you have a higher mileage car, wait until its ocmpletely warmed up before going WOT.

turbocharged cars should wait a bit longer as well...


other than that, you should be alright.

if anyone can show me otherwise, id be more than happy to listen..

 

Every owners manuel I have read tells you not to rev your engine when its cold. Has nothing to do with how strong an engine is.

 

so.... what are you saying? two minutes is too little?

 

Read my post carefully I know there are alot of big words...NOTE what I qouted.

 

Acutally 1st thing that WILL go on a engine that is beat on when cold is the rod bearings. Engine runs RICH at start up and then it settles down to normal stoich mixture after it goes into closed loop operation. Spining a rod bearing sucks, it can be fixed with new bearings sometimes, but sometimes the crankshaft will get damaged also- and a price of a new crankshaft is as much as a used VQ.

 

Dang, and to think I have been lied to all this time by a five different dynos.

 

Those dyno's don't know anything....all they do is measure how much hp and tq a car has....nothing to do with how fast it is

 

indeed, which is why i said what i did about higher mileage, high clearance engines. OBD-ii and LEVs and their cousins only stay in open loop on a cold start for about 30 seconds in normal weather.


and yes, once you get too rich, power starts falling off. SR20DEN, id like to see the dyno plots youre talking about.

 

not that this thread is conducive to intellectiual input, however, any, and yes any internal conbustion engine running on gasoline will make the most power for it's displacement at the stoichiometric figure of 14.7:1. Now.....any engine in any car anyone here would have rarely if ever see's a 14.7:1 mixture. So in theory, the leaner you COULD GET the VQ to run would make the most power. However, going leaner than the stoichiometric figure for gasoline would not only lose power but cause engine damage through detonation,and pre-ignition(which are different things, but that's another tale). So in short, yes a leaner running VQ will make more power, but only relative to it's factory tune. In long, running leaner than necessary to make efficient power(which is what we're all about here) will damage the engine, and not make power. Look at it how you want, just remember, once you add air, you need to add some fuel.

 

14.7:1 is a stoich figure for emissions only, not for power output.

id also like to see a dyno plot where a 4stroke car is making more power at 14.7:1 than it is at a figure below (richer than) that

 

in a controlled environment it would, but at 3500rpm with a full load, in 90 degrees with humidity you're correct. take the dyno plot's out of the equation, if you want to discuss practical power production by means of altering mixtures.....well that will be different for every engine in every maxima, and my neighbour's may be different than mine if it's slightly drier air across the street

 

yes, i understand the variations between different engines. if a 'real world' measurement is what youre after, run a a/f program that keeps the target afr at 14.7:1 at all RPMs and load ranges, make a WOT pass and record with an accelerometer, then run a proper tune (i.e. richer than 14.7 at WOT) and i bet the richer mix wins.

and why is the dyno not good enough for a power output measurement? its not exactly a controlled environment. besides, everythign else remains constant of can be accounted for aside from what were testing... a/f ratio.

 

you misunderstood everything...... the fact that you thought i said at WOT, or full load that it will make more power when it's leaner, tells me all, because i clearly stated that under full load or any load for that matter, the engine will require more fuel......if you want to talk about internal combustion engines, that's cooler, if you want to talk about making a street car faster, those are two different things. I'm talking about engines, an engine on a stand for example, or on your lawn mower, or your moped. Yes, in a street car under load, you will want anything from 13.3:1 or so all the way down to perhaps 10.5:1 or so, even richer in forced induction. make it as complicated or simple as you want, i chose the simple route with this medium.

 

so the below statement is in regards to part throttle only, correct?

 

no that's an engine on a stand with no throttle that runs at a constant rpm, such as a compressor, water pump, jet pump. this is getting rediculous, just ask any nitro RC car owner if you want to understand what i'm saying. Until then find your magic fuel ratio that makes you the most power in all conditions at all rpms.......good luck

 

lol... nitro cars are 2stroke. different animal. i know that nitro cars make more power when theyre lean. youre comparing apples to...

...elephants



were talking about 4 stroke gasoline engines, and more specifically, the VQ.

go ahead and post a dyno plot or two... ill consider it accurate if its the same vehicle within 5000 miles of dynos and its a corrected SAE plot on the same brand dyno.

and ill say again, 14.7:1 is an emissions target afr.

 

Acutally your AF readings are all wrong here, let me tell ya something (SR20DEN feel free to chime in at any time). Bone stock VQ30DE or even a VQ35DE will run around 11.9-12.4:1 AF mixture - with dips in the powerband - especially at top end on a 3.5L- where it tends to run richer than it should.
My car runs 13.4:1 AF for optimum performance, in 100F heat, with AC on, with 93 octane Mobil gas in the tank. At 10.5:1 AF ratio these cars would run like azz, they would polute quite alot, get **** for gas mileage and this is NOT something you want for POWER. On my turbo car I try to keep the AF around 11.8 when boost onsets to 12.3 through the rest of the RPM range- with NO detonation even when its 100F outside. Your information was somewhat a little bit off, and it kinda bugged me to see wrong info being posted to people here- so I took the liberty of clariffying it. 10.5:1 AF ratio would make the EPA cry !

 

and foul your spark plugs with a quickness...

 

Now this is for Nissans---when an engine is cold it is running in "Closed Loop" which means that there are programmed parrameters for the engine so it can get the engine up to temp quick. thats why it seems like it runs better cuz you have more fuel at hand than you would when its warm. and you want to get the oil in the engine nice and warm so that it gets thinner to lubricate what it needs to. and for you guys arguing about Lean or Rich runs better--this is my opinion now--but I think you'll get more power at 14.7:1 cuz thats what these cars are programmed to run at its best--thats why we have o2 sensors to keep the a/f ratio as close to that as possible---But if you have a overly rich running vehicle it means that your dumping a lot of fuel in the engine and more than likely you are not burning all of it--cuz you need the correct amount of air to effectively burn it all--you arent doing anything but ruining the cat. and if your car is running to lean your starving the car of fuel and you are wasting your power stroke cuz there is not enough fuel to get it done. So thats what I think

 

Wrong- OPEN LOOP is when the engine is cold, it goes into closed loop operation around 160-180F coolant temp. On German cars- its around 15-20 seconds and then they have already warmed up the cat enough (air injection pump) and the 02 sensors are heated enough- my car uses the same Bosch wideband 02 sensor that is used on a few VW/Audi products- and it is fully functional within 20 seconds.

Closed loop means- its using all the feedback sensors to determine the correct AF mixture for proper emissions, fuel economy and power. Open loop is when the ECU runs off the set parameters to determine the correct AF mix to get the engine up to temperature quickly and still efficiently. At the same time they run more timing advance when cold since they are runing richer and cooler engine temps. The timing alone is what makes the car faster feelin than anything.

14.7 AF is too lean for maximum power, especially since all WE care about is wide open throttle performance. You will detonate, and kill power with 14.7 mixture at wide open throttle, it is not possible to run that mixture on street gasoline or even C16 race gas. I have done quite a bit of tuning on cars, like my own and others and others will also tell you- 14.7 is NOT what you wanna see when you dyno your car, sure you can tune it to that, but you will not be making any power- knock sensor will be killing your timing advance by retarding the timing to a safer runing condition.

Incorrect AF can also take toll on piston rings by washing down the walls with gasoline and creating too much friction- this usually happens when the engine is REALLY runing rich. After you score the cylinder walls, you will have MAJOR oil burning going on, and at the same time you will be deluting the oil in your crankcase- killing its viscosity and protection levels, do you really want gasoline lubricating your crank bearings and rod bearings ?

This theory here applies to ANY car, not just Nissans. If you have any scientific data, or dynos to prove me wrong- please do, and I will eat my bannana.

EDIT-I forgot to add that your stock 02 sensors are NOT able to controll AF ratio like you make it sound. They are only able to controll it over a very narrow window, they are only good around 12-16 A/F ratio and they respond too slow to any changes. Wideband 02 sensors that are used nowa days in many cars from the factory- they stopped calling em 02 sensors, its called a A/F sensor- they are able to controll the A/F better due to their ability to read anywhere from 8:1 to 22:1 AF ratios, they respond quicker- but they do cost alot more. You see these AF sensors on VWs, Hondas, Toyotas and probably many more cars- you can actually read the real time A/F ratio via scanner without going through the hassle of installing a standalone WideBand 02 sensor with little read out to inform ya what the A/F is- like I have on my car.
02 sensors wear out due to age and they are not able to compensate for oxygen in the exhaust to controll the A/F, do you still think you are right ?

When going to WIDE OPEN THROTTLE the ECU no longer relies on the sensors that are sending it the input- but it reads off its memory what the AF and timing should be- it goes into OPEN LOOP under WOT.

I thought U where a tech over at a Nissan dealer ?? How can you not know this ? Ya guys have em little computers at the dealer ?? uhh they are called Consults, learn how to read and use it properly !

 

Considering that everyone else just beat around the bush on answering your question (although th fuel portion is part of reason). The major reason you dont want to rev the engine high or beat on it is because the the oil is a lot thicker at ambient air temp. Thicker oil means abnormally high oil pressure at a lower RPM. So if you rev the engine too high the thick oil doesnt flow through the oil pump as well as if it were at opperating temp. Since the pump isnt flowing oil as well your motor isnt as well lubercated, and that can lead to expensive repairs if you do it a lot.

 

If you guys think the 3.5 is bad when hot...It is nothing compared to the power loss on a heat soaked LS1

 

cristobal, after two minutes of driving, how hot do you think the oil really is in normal weather?


and good post, blackbird. the only thing i dont fully agree with is that closed loop comes a bit quicker on newer vehicles. when the coolant temp is above a relatively low number, like 60ish degf, and then engine has been run for 30s-2m, or thereabouts (different for each car/engine), its early enough to get closed loop status.