Write-Up: Custom CAI

Abaddon wrote:

LOL you were reading IAC counts

d'oh!

Did some driving around town. Ambient temp was 80*. IAT was reading anywhere from +9* - +18* over ambient. It didn't go past 98*.

Stopped at advance for a MAF on a 93 Riv, came out and IAT was 119* before starting. Some more driving (heavy throttle) I saw the IAT move up to 129*, then slowly came back down to the 110* range.

Didn't drive the Riv much this weekend so I'll take some more measurements later this week.

Anyone know the chart for IAT heat ranges matched with timing retard? (Does one exist)?

If Scott doesn't post anything, I'll try to capture the data from the PCM's timing maps. I can't remember exactly how it's mapped, but I think there's a curve that varies base timing using IAT values.

AA wrote:

If Scott doesn't post anything, I'll try to capture the data from the PCM's timing maps. I can't remember exactly how it's mapped, but I think there's a curve that varies base timing using IAT values.

Thanks AA! That would be very helpful!

The IAT vs. spark timing map is as follows, according to a stock PCM file from DHP PowrTuners:

("0" indicates no effect on timing, a "-" value indicates timing retard, shown in red)

IAT (ºF) = Spark (º)

176ºF = -3.0º
158ºF = -2.0º
140ºF = -1.5º
122ºF = -1.0º
104ºF = 0º
86ºF = 0º
68ºF = 0º
50ºF = 0º
32ºF = 0º
14ºF = 0º
-04ºF = 0º
-22ºF = 0º
-40ºF = 0º

Looking at these values suggests there is no added timing advance from cooler IAT temp for our cars in stock form. The timing retard begins at 122ºF and up. This is a little surprising, as I always assumed there was hotter timing to be had with cooler intake temps, as my PCM is set up to add 1-2º at cooler temps. One of many advantages of a PCM tune, and it makes you question GM's logic from a performance standpoint. The more I learn about the "brain" controlling the engine, the less credit I give to the Buick programmers for robbing us of potential power, performance, and even longevity.

Also this info would seem to prove that the $25 "chips" sold all over the web, claiming to add HP by bumping resistance on the IAT wire, would be useless and 100% ineffective when installed on a Riviera, and likely the same with any SC 3800 engine.

Thanks so much! Great info!

AA wrote:

Looking at these values suggests there is no added timing advance from cooler IAT temp for our cars in stock form. The timing retard begins at 122ºF and up. This is a little surprising, as I always assumed there was hotter timing to be had with cooler intake temps, as my PCM is set up to add 1-2º at cooler temps. One of many advantages of a PCM tune, and it makes you question GM's logic from a performance standpoint. The more I learn about the "brain" controlling the engine, the less credit I give to the Buick programmers for robbing us of potential power, performance, and even longevity.

If you think about it, it makes sense. Your IAT isn't realistically going to be anywhere near your true intake temps, since we are FI. Once the air hits that SC, its going to get super hot...so I don't think GM wanted to rely on the intake air temp pre-sc for timing advance. Even if your IAT reads 30*, that compressed air is going to be super hot...on the other hand, if your IAT temp is high, that would certainly increase the compressed air temps once it hits the manifold.

It must use other sensors (besides the IAT) to determine timing advance...that or base timing is already at its most advanced state.


Also, what is the potential HP loss per 1* timing retard? 5hp per 1*?

It also uses MAF to calculate Mg of air in the cylinder. Based on that vs. RPM, timing advance is adjusted accordingly. The IAT adjustment is in addition to that calculation. There is also a separate table in there for folks who think the car takes 87 gas, lol.

But the superheated air charge should be irrelevant, because the PCM is programmed to work around that variable, so it's all relative. We know compressing the intake air heats it a certain amount, say +100ºF for a stock engine at WOT. When that air enters the intake, the MAF meters it, calculating Mg/cylinder. The fact that the blower heats the intake air shouldn't matter, because the PCM's fuel and timing maps take that into account. Also, for a given amount of boost, the heating is constant +/- the IAT value. Therefore, IAT can be relied upon for setting timing adjustments.

For example, if the IAT = 100ºF, + 100ºF heating from boost, the result is 200ºF. Based on the fueling and timing maps, the engine will safely burn this mixture at 200ºF without knocking. But if IAT = 20ºF, +100ºF heating, the result is 120ºF into the cylinder. The fueling and timing maps are still going to burn the mixture safely (adding more fuel to the denser air), but there is some added potential now - heat in the combustion chamber has been lowered 80ºF because IAT was lower to begin with, keeping knock well below zero. Boost can be added, and/or timing can be advanced without penalty. This is why I once ran a 3.2" pulley in the winter months. There was a clear HP increase, and KR was in check.

The PCM cannot change boost levels, but it can change spark timing. Correctly programmed, a little hotter spark when intake temps are cooler could give some added HP. I can definately feel mine kicking in below 40ºF. It's not huge, but it's something.

I think I read somewhere it's between 2-5 HP per 1º degree of KR, which is roughly equal to 1º timing retard. This is on a stock 240 HP engine.

Interesting....


I wonder if it advances timing in the Pontiac, or another performance car with the L67. I don't think GM had performance in mind when they built the Riv. (not saying the Riv cannot perform) I just don't think they had planned it that way, so maybe that's why there is no advance over base when the IAT is at a lower temp....just a guess

So what you are saying is, if we can keep the intake temps under 122*, we wont lose anything

It seems they did and it seems they didn't have performance in mind. It's like some areas were taken seriously, while others were ignored, or thought they wouldn't get noticed. Take the aluminum hood for example. Here is a list of some cars with OEM aluminum hoods:

Acura NSX
Subaru WRX, STI
Dodge Charger SRT-8
Honda S2000
Mazda RX-7
Volvo S60
'82 Trans Am (option)
'91-92 FireHawk
'11-12 Camaro ZL1
'11-12 Mustang GT

That's quite a group there. There are probably some non-performance cars with alum hoods as well (I think Ford puts them in a few of their trucks), but it's an expensive part that must customers wouldn't notice, and GM didn't have a habit of putting them on very many cars.

Why did they put the battery under the rear passenger seat? Could be to offset some of the driver's weight? Could the faux dual exhaust system support the same kind of purpose? It's hard to say, but both of these things do in fact help balance the front heavy nature of the car.

At the time Riviera was introduced, hydroforming was an expensive process, reserved for building Corvette frame rails, yet GM decided to hydroform the Rivera's cradle in order to achieve "Dramatic increases in torsional stiffness - to best-in-class levels at 23-Hertz - improve the performance of suspension components." There were very few cars in the world at the time that could match the rigidity of the Riv's chassis. The target spec was to match Mercedes Benz.

Bill Porter called the Riviera "sporty", the same term Audi has used to describe their current line of sedans. The seats were called "state of the art" by the interior designer during a Riviera product information video - whatever that means, exactly, I'm not sure.

And we take it for granted now, but 4-wheel ABS disc brakes and 4-wheel traction control in 1995 was not as common as it is today. The Riv's stopping power was impressive, and they beefed up the discs even more in 1998. They tightened the steering, too. GM also created modified Rivieras that were track tested against the European touring cars. Why? To me it seems to indicate that performance was important to some degree.

But there is evidence they slipped up when you look at the details. The PCM programming was one of these areas. It's as if Buick ignored everything else they had set up the car for, making the powertrain as quiet and as numb as possible, giving the perception of very smooth, powerful thrust. This was thought to be more appealing to the 50-up target market I guess, and maybe they were right. Anyhow, the positive efforts are still evident if you look - there is some very strong performance car under the graceful skin of the Riv. It only needs some relatively minor tweaking to wake it up.

Dang! ya gotta ring the dinner bell to wake the 95 up!

hummm ive been thinking about designing a cray scoop on the fender around the headlight not sure thought the lines of the car are nice .... wither that or a sealed box with maybe like the early 90s ram air trans ams with the tubes going from the front valance to the air box....

Alright!
I started off with the desire to simply gut the factory air box and drop in a K&N filter. While I was removing the top half of the intake box to remove the red plastic non-sense, I noticed that the top half seemed to be loose, almost not quite fitting the bottom half of the air box. I slid my fingers along the side of the bottom half (prior to removal) and I could feel there was a piece missing!
I proceed to remove the lower portion of the air box, only to confirm with my eyes what my finger had felt a few minutes earlier. The right side of the lower air box was broken off, allowing for air (read DIRT) to enter the air box from the side and bypass the paper filter by traveling OVER the filter.

I called the local Buick dealer and asked for a quote for the lower portion of the air box (read them the part number on the phone). The woman on the phone said the replacement part was (are you sitting down for this?) - - - - $284! After picking up my jaw off the floor, I politely thanked her and told her I would be passing on the purchase.

So I ended up picking up a 9” long K&N filter w/ a 4” diameter base for $41 at the local Pep Boys. I decide I was going to use the factory rubber hose that comes off the top of the engine. I bought a $8 rubber adapter to go from the 3” factory rubber to the 4” K&N base. I used a Dremmel to make the hole for the AIT sensor in the odd-shaped box on the bottom of the factor rubber intake pipe (made a Newbie type of mistake here – to ensure the AIT sensor stays put, I put some Krazy Glue on the outer edge of the sensor). While the sensor is in REAL good, I dread the day it has to be replaced!

I took the car out for a test drive. Lots more supercharger whine, some nice wuuump sound from the intake, and seems to be more responsive through the entire range. The AIT temp was in the same range as I observed with the factory box (10 to 40 degrees above outside temperatures). While I have no idea what kind of HP gain this may be, I am quite pleased with the results. It looks clean (and dare I say, almost factory?), sounds great, seems to have added some power, and it was pretty easy to install (maybe an hour or so for the 2 nights I worked on this). I will get some pictures up tomorrow (as long as it is not raining too hard).

Since I was in the parts store the other day, I also picked up the 180 degree thermostat and the Autolite 104 copper plugs – these will be installed on Friday night! Next up will be the exhaust (this will probably have to wait until the spring time as I am expecting that it will be fairly expensive).

Ron's Rocket Riv wrote:

Alright!
I started off with the desire to simply gut the factory air box and drop in a K&N filter. While I was removing the top half of the intake box to remove the red plastic non-sense, I noticed that the top half seemed to be loose, almost not quite fitting the bottom half of the air box. I slid my fingers along the side of the bottom half (prior to removal) and I could feel there was a piece missing!
I proceed to remove the lower portion of the air box, only to confirm with my eyes what my finger had felt a few minutes earlier. The right side of the lower air box was broken off, allowing for air (read DIRT) to enter the air box from the side and bypass the paper filter by traveling OVER the filter.

I called the local Buick dealer and asked for a quote for the lower portion of the air box (read them the part number on the phone). The woman on the phone said the replacement part was (are you sitting down for this?) - - - - $284! After picking up my jaw off the floor, I politely thanked her and told her I would be passing on the purchase.

So I ended up picking up a 9” long K&N filter w/ a 4” diameter base for $41 at the local Pep Boys. I decide I was going to use the factory rubber hose that comes off the top of the engine. I bought a $8 rubber adapter to go from the 3” factory rubber to the 4” K&N base. I used a Dremmel to make the hole for the AIT sensor in the odd-shaped box on the bottom of the factor rubber intake pipe (made a Newbie type of mistake here – to ensure the AIT sensor stays put, I put some Krazy Glue on the outer edge of the sensor). While the sensor is in REAL good, I dread the day it has to be replaced!

I took the car out for a test drive. Lots more supercharger whine, some nice wuuump sound from the intake, and seems to be more responsive through the entire range. The AIT temp was in the same range as I observed with the factory box (10 to 40 degrees above outside temperatures). While I have no idea what kind of HP gain this may be, I am quite pleased with the results. It looks clean (and dare I say, almost factory?), sounds great, seems to have added some power, and it was pretty easy to install (maybe an hour or so for the 2 nights I worked on this). I will get some pictures up tomorrow (as long as it is not raining too hard).

Since I was in the parts store the other day, I also picked up the 180 degree thermostat and the Autolite 104 copper plugs – these will be installed on Friday night! Next up will be the exhaust (this will probably have to wait until the spring time as I am expecting that it will be fairly expensive).

...if you wanted an air box, probly could get one from moradpartscompany.com

...be careful oiling that K&N so you don' foul the MAF sensor

Albertj,

Thanks for the reference to Morad! I just checked the site out and the e-bay listings. Really cool.

Thanks again!