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#43596 - 16/06/02 06:51 AM does SC have knock sensor, mine never rarely knocks, regardless of gas used
husky fan Offline
Member

Registered: 27/10/01
Posts: 63
I have always dicked with timing on cars I own, as an inexpensive way to get a bit more HP. Generally the thought is increase the timing until knocking is heard, then back off just a tad.

When doing this I have noted that my it is difficult to get any real knocking going, regardless of my gas or the timing settings. 87 octane or 92 octance, it seems to have little effect on the knocking, or the power output.

I have noted that when I rotated my distributor counterclockwise (which I think is advancing the timing) too much, then i get a huge drop off in power in the upper RPM band. It basically feels like the power has completely flattened out above 4000 rpms. Ugh.

OK, you guys note any improvements based on adjusting the timing?

thanks

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#43597 - 16/06/02 10:51 AM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
*paul Offline
Member

Registered: 16/08/00
Posts: 822
Loc: New Zealand
Perhaps the knock sensors are detecting a knock (which is not audible at higer rpm's) and the computer is backing off timing and boost to compensate.

I'm sure you know you're playing with fire. I would suggest setting it to the max allowed by Nissan (using a strobe light) and leave it alone before something expensive breaks. I found a slightly noticible improvement going from 15 to 17 degrees (spec is 13-17 for my 2000 non-sc.)
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2007 Nissan X-Trail
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#43598 - 16/06/02 11:07 AM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
bethterra Offline
Junior Member

Registered: 16/06/02
Posts: 4
Loc: Phoenix, AZ
The engine ( as almost every new car) is equipped w/ a knock sensor. The SC has a pretty low compression ratio so use of lower octane ratings is okay even with timing pushed. However, unless you are using a ecm chip for performance, adjusting the timing may have little effect as the other sensors in the ecm system will make a compensation for what the stock chip recognizes as out of the ordinary state of tune. You most likely will not hurt any thing but may make the engine performance suffer at different areas (low end torque, economy and emmisions) Unless you have a programmable eprom chip or access to a dyno, I really see no advantage in meesingwith the timing of a modern vehicle.
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#43599 - 16/06/02 10:00 PM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
ChuckH Offline
Member

Registered: 27/02/01
Posts: 5206
Loc: Seattle, WA
Must be nice! My 2000 is set at 16 degrees and knocks like a Mofo regardless of gas or throttle position. Needless to say I have an appointment at the dealer Tuesday to have it looked at. frown
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#43600 - 16/06/02 11:20 PM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
OffroadX Offline
Member

Registered: 17/08/00
Posts: 13692
Loc: Baltimore, MD
You bet your ass it has a knock sensor.
It will detect the knock before you do and back off the timing if you run 87 octane.
Don't dick around with regular gas. There's a reason your manual says if you must use it only add enough to get you to a pump with premium, avoid heavy throttle, and top off with premium to dilute it at the first opportunity.

Brent
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#43601 - 17/06/02 04:52 AM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
DaveDatsun Offline
Member

Registered: 16/08/00
Posts: 1421
Loc: Sahuarita, AZ
Brent -
I just can't wait for one of these geniuses to use 87 octane gas *and* a high boost nose pulley. I doubt the knock sensor has enuf range to compensate for that much stupidity.

dave and xtoy - but someone said it was OK...duh

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#43602 - 17/06/02 06:47 AM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
husky fan Offline
Member

Registered: 27/10/01
Posts: 63
So Dave Datsun what makes you a car expert?

I build and race motorcycles. My current bike is a Suzuki GSXR 750 with Carillo rods, Cosworth pistons and a bunch of other modifications. It turns 14,700 rpms, reliably, and makes 165 HP out of a 750cc.

I know what ping sounds like. If it doesn't ping at high load, low RPM, then it won't ping at high RPM, low load. That being said, if I hear/heard ping, then I would either change the gas to a higher octane, or retard the timing to an appropriate amount.

You are probably one of the fools that uses high octane gas in an engine that will see no benefit, because you think it will help your performance.

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#43603 - 17/06/02 07:04 AM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
OffroadX Offline
Member

Registered: 17/08/00
Posts: 13692
Loc: Baltimore, MD
Hey husky fan, how does that shoe taste?

Dave knows his stuff...

Brent
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#43604 - 17/06/02 08:45 AM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
DaveDatsun Offline
Member

Registered: 16/08/00
Posts: 1421
Loc: Sahuarita, AZ
This is wrong folks:

"I know what ping sounds like. If it doesn't ping at high load, low RPM, then it won't ping at high RPM, low load. That being said, if I hear/heard ping, then I would either change the gas to a higher octane, or retard the timing to an appropriate amount."

OK, not all together wrong, on a normaly asperated engine you could do this in most cases. With a *forced induction* engine things are very different. You have to take boost into account. That's the point Mr. Husky is missing. Typical SC or TC systems do not tax the engine until higher RPM's. With all the noise occuring, it is difficult to detect detonation - and often too late.
Now take a stock Xterra SC and add a smaller pulley and do it without damaging the bearings or gears in the Eaton. You've got more air(boost) than before. But what about extra fuel to go along with the air? Lean mixture = detonation. Spin the SC faster and the air from the SC is hotter too. Hotter mixture = detonation. How about the ignition advance curve? You better back down a few degrees or you guessed it, detonation.
Let me make this real clear - detonation at high RPM's with forced induction can turn an engine into a boat anchor before you can lift your foot.
Don't take my word for it, read the 'power' forums.
Think the stock ECU will magically make all the adjustments for you? Go ahead and find out. How will you know? Got a boost guage, air/fuel ratio display, SC output air temp read-out, injector duty cycle display? Then add some 87 octane gas.

dave and xtoy(87 octane), miatank(93 octane)@ 6+psi

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#43605 - 17/06/02 10:50 AM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
Paco Pico Offline
Member

Registered: 16/01/02
Posts: 673
Loc: Gig Harbor, WA
Quote:
Originally posted by DaveDatsun:
This is wrong folks:

"I know what ping sounds like. If it doesn't ping at high load, low RPM, then it won't ping at high RPM, low load. That being said, if I hear/heard ping, then I would either change the gas to a higher octane, or retard the timing to an appropriate amount."

OK, not all together wrong, on a normaly asperated engine you could do this in most cases. With a *forced induction* engine things are very different. You have to take boost into account. That's the point Mr. Husky is missing. Typical SC or TC systems do not tax the engine until higher RPM's. With all the noise occuring, it is difficult to detect detonation - and often too late.
Now take a stock Xterra SC and add a smaller pulley and do it without damaging the bearings or gears in the Eaton. You've got more air(boost) than before. But what about extra fuel to go along with the air? Lean mixture = detonation. Spin the SC faster and the air from the SC is hotter too. Hotter mixture = detonation. How about the ignition advance curve? You better back down a few degrees or you guessed it, detonation.
Let me make this real clear - detonation at high RPM's with forced induction can turn an engine into a boat anchor before you can lift your foot.
Don't take my word for it, read the 'power' forums.
Think the stock ECU will magically make all the adjustments for you? Go ahead and find out. How will you know? Got a boost guage, air/fuel ratio display, SC output air temp read-out, injector duty cycle display? Then add some 87 octane gas.

dave and xtoy(87 octane), miatank(93 octane)@ 6+psi
As well I must agree with Dave...I have tuned/built many engines and with and without boost you are definately playing with fire. No matter what the computer does (and most people don't even have a clue what it does and does not do...) it still cannot stop the laws of Physics. I am not saying to be scared of and SC or TC but be aware of what you are doing or your wallet might suffer the consiquence. Check out Dave's last two paragraphs - it is exactly right. And don't just take my word as a shade-tree mechanic...I work in the business.

Personally I intend to add the pulley...but I never use anything other than 91 octane. Period! As well I have blown up enough expensive toys to know how to drive things responsibly.

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#43606 - 17/06/02 11:33 AM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
SpenceJT Offline
Member

Registered: 31/03/02
Posts: 164
Loc: Madison WI
Thanks DaveDatsun & Pacopico!

Now you've got me pretty paranoid about this pulley modification that I was planning.

I had purchased the ASP 2.35" pulley and had hoped to install it in the next few weeks. Now, other than merging onto a busy highway from a metered on-ramp, I consider my driving "moderate" (average local highway cruising speed between 55 - 65 mph, with interstate driving between 70 - 75 mph).

I never fill with anything less than 93 octane purchased from either local Mobile, or PDQ (a very large regional chain of convenience stations).

Would I be just "plain stupid" to do this modification (can you be somewhat nice when you tell me how stupid I am)? I'm just looking for that "little extra" to push my X a bit closer to it's limit.

...of course I don't want to end up buying an engine in 2003.

My reasoning for going ahead was this. Even when merging into heavy traffic, my automatic transmission shifts between 5000-5500 rpm. Since the Eaton is rated to 16,000, and the pulley mod brings it up to 15,880 at 6000 rpm, is it really pushing the engine that hard?

Given my driving habits, and 93 octane "pledge" would the modification still run into the category of "stupidity"? I may have a nice "never installed" ASP pulley for sale.

Thanks,

Spence

Edited - to correct a couple of typo's. Is there such a thing as too much caffine?
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#43607 - 17/06/02 11:58 AM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
Paco Pico Offline
Member

Registered: 16/01/02
Posts: 673
Loc: Gig Harbor, WA
Quote:
Originally posted by SpenceJT:
Would I be just plain stupid to do this modification (can you be somewhat nice when you tell me how stupid I am). I'm just looking for that "little extra" to push my X a bit closer to it's limit.

...of course I don't want to end up buying an engine in 2003.

My reasoning for going ahead was this. Even when merging into heavy traffic, my automatic transmission shifts between 5000-5500 rpm. Since the Eaton is rated to 16,000, and the pulley mod brings it up to 15,880 at 6000 rpm, is it really pushing the engine that hard?

Given my driving habits, and 93 octane pledge do would it still run into the category of "stupidity"? I may have a nice "never installed" ASP pulley for sale.

Thanks,

Spence
Spence,

As long as you drive reasonably there probably is nothing to worry about. Though you must concider that everyone has a different opinion of reasonable.

Here are some of the factors to take in account when it comes to engine operation: Load %, engine speed, ambient air temperature, coolant temperature, oil temperature, intake charge air temperature, fuel temperature, humidity, A/F ratio, knock, emissions, and barometric pressure. There are alot of factors that your engine must compute to get the correct operation from your engine.

That said; if you use 93 octane, and don't go to redline every time you drive the truck I doubt you would ever see a failure. Adding two pounds of boost without changing the fuel map/timing is likely not going to cause a big problem, especially if you use premium fuel.

The point I *believe* that Dave was making is that there is a point of knowing what you are playing with and the potential for damage that may occur. If someone modifies to get more boost, over-advances the timing, and then proceeds to drive the thing relentlessly under poor conditions (poor fuel, high temperatures/loads) with the rationale that the ECM can compensate for everything in any situation then that person is sadly mistaken.

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#43608 - 17/06/02 12:37 PM Re: does SC have knock sensor, mine never rarely knocks, regardless of gas used
SpenceJT Offline
Member

Registered: 31/03/02
Posts: 164
Loc: Madison WI
Thanks for the calm reply Pacopico. Some are quick to point out ignorance rather to help guide and educate the new and uninformed. I fit into both of the aforementioned categories and I'm grateful for your patience.

I'm not planning to race the Xterra, but living in Wisconsin, our ambient temp can range from -10 to 97. I adhere to a strict maintenance schedule, running Mobile One 5w-30 which I change every 3,000 and only run 93 octane.

Ian and a few others have drilled into me the fact that experts have engineered the Xterra. I admit that I know little about auto mechanics, and even less about SUVs / off-roading. Who am I to change what the experts have deemed as optimal? My main reason for buying it was to get away from the 4 cylinder “economy cars” that I’ve been driving for the past ten years. I wanted the Xterra for it’s for cargo capacity, towing ability, style, and driving in Wisconsin a winter.

While I may be a lower risk with the pulley modification, it is still not something that I should go into without a greater deal of research. Upon further thought, I think I'm going to take my time on this modification in order to wait and see what happens to others before I attempt it.

I'm a computer nerd, not a motorhead but even I know that replacing an overclocked a CPU is far less expensive than replacing an over driven engine!

I’ll stick with my plans to install my boost gauge and get to know my engine for a while wile I monitor others who perform the modification.

Thanks again!

Spence
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www.spencesplace.com

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