After getting my boost gauge installed today, I gave the car about 10 hard runs for some measurements. During the early runs, I was hitting 8PSI at 6000RPM consistently. By the end, I was hitting a little over 7PSI.

What could cause this? The car felt noticably slower so I don't think it was human error in the measurements. I've experienced the degraded performance in the past too so I don't think it's a boost leak (although I'll run her hard tomorrow after she's cooled down to verify).

Is this the car pulling timing?

 

It could be one of many things, but your issue is most likely related to heat. The blower flows much less when the air is hot and the stock ATI setup comes with a nice heated air box that gets nice and toasty after you have driven the car for a while.

The PCM will also pull timing as the IATs go up above 95* or so.


Like I've said many times before, I can't imagine owning a boosted car without a scanner. If I were you I would purchase EFI-live and do some logging. It's absolutely required for anyone trying to figure out an FI setup on their own.

 

Agreed, EFILive is my next "mod"... But I guess I'd like to find out if my problem is in the programming or just the heat? It was 80 degrees outside, would I really lose a full pound of boost after 6 runs back to back (just runs in 1st gear up to 6000RPM)? I am using the stock ATI plumbing (including air box and filter). I'd like to eventually get my dual fans back since this is a Florida car but I want to get everything running right first before I start "improving" things.

So would timing being pulled actually slow the blower down or does timing have nothing to do with the belt RPMs (and hence blower RPMs)?

 

:iagree:

BTW, Quicksilver, where did you purchase the scanner? I'm looking to get one myself. :cheers:

 

I'm no expert, and I really don't know much about what the timing will do but I would venture to say that heat would affect your boost a lot more than you would think. As the air gets hotter it gets less dense, which would actually decrease the efficiency of the blower. It may be enough to drop a full pound of boost. I assume you were using a fan do get some airflow over the intercoolers?

Edit: Just reread your post and it sounds like you weren't on the dyno but on the street so airflow wouldn't be a problem. I really think that if there's no signs of belt slippage (dust in the engine compartment, etc.) then heat is probably your culprit. :cheers:


[Modified by SleepieAce, 12:27 AM 10/25/2003]

 

This is difficult to answer.

Timing has everything to do with cylinder pressure. More advance = higher cylinder pressure and thus a faster ramp in RPM. But I don't think it will impact the amount of boost at a given RPM.

I have found that heat is the #1 factor impacting boost. I've seen 3 psi swings with a change in weather.

1st gear is a tough gear to track data in, things are just happening too fast and traction is a big issue.

Try higher gears and you may get more consistent results.

Autotap actually sells EFI live. I purchased autotap not knowing any better and I lucked out when EFI live started targeting the Autotap cable.

I think they sell it for $300 (cable and software).



[Modified by QuickSilver2002, 11:31 PM 10/24/2003]

 

IMO, if they were back to back runs, you may have heated up the lines from the S/C to the TB. Those rubber lines will expand under heat and you could loose boost.. Though I could be wrong... I think this may be the problem.

VR :cheers:

:chill: Chillin in San Jose... ;)


[Modified by vetterdstr, 9:30 PM 10/24/2003]

 

There is no connection between the mechanics (rpm, flow rate) of your blower and your car pulling timing due to any condition. Your blower is a dumb device. At any given RPM, the same amount of air is coming off that impeller. It's what happens at your MAF that matters. Density, temperature, etc. Driving the car in boost back to back is very likely to produce lessened performance due to heat. That would be less pronounced on a night that is 30 degrees than it would be on a day that was 90 degrees outside.

When your intake ambient temp goes up, you are more prone to enter into a KR (knock retard) condition. More aggressive timing also raises cylinder pressure. Higher pressure demands a better mixture (fuel grade, air quality), and without the engine will start detonating. Your ECM detects the detonation, and pulls timing at a rate and frequency you can specify using LS1Edit. Pulling timing keeps your car out of detonation, which is your best safeguard against "BOOM!"

Less dense air (think hotter, or higher altitude) being pushed into the intake will show less boost on the gauge, and you'll also be making less power. It's not a coincidence that I leave my supercharged car in the garage on really hot days...but I can't resist driving it when that temp drops in the fall and on cool evenings.

That's when I enjoy the boost the most!

Mike M


[Modified by LS1 Bird, 9:38 PM 10/24/2003]


[Modified by LS1 Bird, 9:41 PM 10/24/2003]

 

Thanks! :thumbs: That's not a bad price at all. I'll be getting it in the next couple weeks. :cheers:

 

Just posting an update --

I ran the car hard again today and once again it's hitting 7.5 to 8PSI, so it was not a boost leak and is most likely due to the heat issues mentioned earlier in this thread.

I guess soon I'll be lowering the radiator to get my two fans back and changing out the stock ATI air box...

 

The stock BOV has been known to stick too.