To change oil, or not to change oil?

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I'm paritipating in a online race series where 550PP race cars are being used that are all power limited. I am using the Honda NSX-R Prototype LM Race Car (standard car) with very dirty oil. I bought it this way in the UCD. Currently I am able to run a 1.20.1 with it on Trial Mountain. It's very competitive at the moment.

The car currently has 397 BHP @ 550PP. Performing an oil change would give it 417 BHP @ 558PP. Now, if I change the oil I would have to limit the engine even further down to get it on 550PP again.

I am wondering if I should change the oil or not. I have read in the seasonal events forum that there's an advantage in using dirty oil when a TT is limited to PP alone. It there any truth in this statement? Does changing the oil only affect engine power or are there other subtle changes in behaviour of the car after a change?

Looking for some insight on this, as this is my only NSX-R Proto I am reluctant to just experiment on it.

Any info is greatly appreciated.
 
Hi Voxalizer,

I've not experimented with the power limiter in a while, but I think if you change the oil, the engine's power across the whole rev range will increase by x%. When you then apply the power limiter, the powerband will get flattened at the top end. Overall you will have gained some power a little lower down. Now if you were tuning to meet a BHP restriction, I'd say go for it - you could get a flat power curve at the top end, all at exactly 400 BHP or whatever your limit was. High average power over the rev range you're using = win.

The complication is that you're tuning to a PP limit. I'm not sure how PP is calculated with regards to engine power i.e. whether it's based on peak power, average power, or what.

Suggest you buy a cheapo used car (dirty oil), max it with engine mods, and look at peak power and PP. Run a few quarter miles and max speed tests.

Then change oil, note new power, and detune with engine limiter to the "dirty oil" PP. Run the speed tests again - the you should be able to see if it was worth the oil change and detuning.

Cheers,

Bread
 
Also, Remember the Power limiter only affects HP not torque so your car will have higher torque too.
 
Interesting,

So when I change the oil and limit the engine back to 550PP I will have more torque than before. Am I correct in assuming that on tracks with a lot of turns the car benefits more from having more torque than on tracks with fewer turns and more long straights?
 
^ to some degree, a different gearset will be needed to utilize the most of your torque.
 
In most cars a few HP will not cause an effect on torque numbers. give me a minute to get pics of the changes made in a full tuned Tempest Lemans GTO.

Uploading pics of power torque curves at 706,600, 500(70.8 and 70.9) 400 and 353(50% total power). It shows that torque is not affected in the same manner as HP, So small changes in the limiter in most cases do not have a large effect on torque with the exception of the 2 500 hp graphs.
 
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Torque and power are really two sides of the same coin (link if you fancy a read)
http://craig.backfire.ca/pages/autos/horsepower

Getting more torque at a given RPM also means more power at that RPM. Engines which make a decent torque (and hence power) across a range of RPM are sometimes more "usable" than ones which make loads of torque & power at high RPM, but less lower in the RPM range.

I think the confusion about power limiter not affecting torque comes from reading the peak torque number. Limiting power at a given RPM will by definition also limit the torque at that RPM. Often, the peak torque occurs lower down the rev range, where the power is already below the limit being set, hence it is unaffected (though the torque higher up in the rev range will be limited).

Cheers,

Bread
 
I apologize for the fact that this will be a pic heavy long post.



First we have the 100% no limiter full tune Tempest. 706hp with 821ft/lbs of torque


Now, limited to 600hp a loss of over 100hp but a loss of only12ft/lbs of torque putting it at 809. at 3/4's


The next two exhibit an anomaly at the 500hp mark in this car where a 0.1% difference yields a change only in torque but not in PP or HP.

70.9% 500hp and 752ft/lbs
70.8% 500hp and 750ft/lbs

Still, despite the anomaly the torque still hasn't been decreased near as much as the HP which the power torque gap has widened meaning although power has been lost a large portion of torque remains intact.


At 400hp the torque is at 663ft/lbs so at this level hp is at roughly 2/3's
the torque number


Now finally the full limited car sitting at 353hp and 618ft/lbs. Total hp loss is 353hp (50% obviously) but torque only lost a little over 203ft/lbs (just under 25% loss) now, given My initial statement isn't entirely true, but that was because of poor elaboration on my part. If the HP loss is under a certain percentage (in this cars case it was 13.5% losing 1 ft/lbs between 610 and 611hp) torque loss is non existent. So if you are able to make your PP requirements with going over a certain amount of limiter used you can infact retain 100% torque.
 
bread82
Torque and power are really two sides of the same coin (link if you fancy a read)
http://craig.backfire.ca/pages/autos/horsepower

Getting more torque at a given RPM also means more power at that RPM. Engines which make a decent torque (and hence power) across a range of RPM are sometimes more "usable" than ones which make loads of torque & power at high RPM, but less lower in the RPM range.

I think the confusion about power limiter not affecting torque comes from reading the peak torque number. Limiting power at a given RPM will by definition also limit the torque at that RPM. Often, the peak torque occurs lower down the rev range, where the power is already below the limit being set, hence it is unaffected (though the torque higher up in the rev range will be limited).

Cheers,

Bread
Click to expand...

In real life this is true but in GT5 it isn't as my previous post shows.
 
fbccars924
In real life this is true but in GT5 it isn't as my previous post shows.
Click to expand...

no, he is correct - real life or gt5.

your examples cite peak hp and peak torque which sell cars but dont tell the whole story. notice how dramatically the torque falls off past peak torque in a car that has a lot of engine limiter.

what you are failing to realize is that hp = torque * rpm / 5252

and torque = ( hp / rpm ) * 5252

so a car with 706hp @ 6500rpm, makes 570 lbft at 6500
a car with 600hp @ 6500rpm, makes 484 lbft at 6500

no ifs ands or buts.

sure, at peak torque the difference is only 12lbft but look at the difference over the entire curve.

in PP limited racing it is ALWAYS better to NOT use very much engine limiting.

...and to answer the OPs question, in most cars found in gt5 you will gain a slight advantage by running dirty oil in PP limited rooms.
 
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^That.

Unfortunately I am at work and whatever image host you are using seems to be blocked, but I would bet large amounts of money that right under the flat part of your HP curve on your GTO you see the torque plummet. As you said, changing the oil will raise the overall numbers slightly but backing them off again with the limiter will affect both HP and torque in the limited part of the curve, which is most often in the effective/usable part of the RPM range, hence esoxhntr's advice.
 
^ After a certain point the torque does plummet. But, the amount of limiter that he'd be using wouldn't be to the point of messing with the torque enough to make an issue if it affects it at all.
 

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