OK---I know this subject has been hashed out several times. I've got a 2006 XKR and am thinking about using the 2.6" pulley which as I understand adds an extra 3lbs of boost. I've read WhiteXKR's write up which is well written and very informative. I've also seen the statement from Count Iblis about how the M112 is under it's max speed of 14,000 rpm which lends itself to additional boost. I'm looking for feedback on how much bang for the buck this offers. It appears that adding 3lbs of added boost does help with off the line power which I would like to have and probably does a bit better in the mid range which is nice for going from 70 to 100 mph??? Do I really need to consider upgrading the I/C radiator or changing out the thermostat to a lower temp rating? I don't want to modify the exhaust system since I do like the nice quiet ride on the freeway. Oh yeh, what does this do to the existing gas mileage any data on this? Thoughts appreciated.

 

I'd like to add to the original question- does anyone have A/F data on a stock car running the smaller pulley? Is the additional airflow manageable within the stock MAF tables or would it lean out? I'm aware a number of people run the smaller pulley, but am wondering about the figures nevertheless.

 

There is plenty of room for fuel; you will not come close to the boarders with such a pulley change.
Fuel consumption goes up when you spin the Eaton faster, but don’t know what it is for this ratio.
For the price you get a good bang for the buck, but the extra power is also limited, so all depends on what you really are looking for. The faster you spin the Eaton the more heat/power consumption you generate (the line is not linear, it will be more exponential), and anything you can do to cool down the charge will aid in keeping the power levels. Even though the maximum advisable speed may be 14.000, the maximum efficiency is way before that.
So if you use the power only occasionally for only a couple of seconds there is no need to uprate the intercooler circuit. But if you use the power for longer than that, or quicker short bursts after another, you will lose power quicker as the ECU will retard timing due to the extra heat. So then getting either a larger buffer (so increase the coolant capacity) or better intercooler radiator will help you counteract the power losses.

 

I have not done it yet, but I am still planning on the Nameless Performance intercooler upgrade to help to counteract the heat soak.

To my butt dyno, performance is noticeably stronger in cold weather vs. hot. Running the A/C also reduces the effectiveness of the intercooler.

I know a couple of folks have installed a killer chiller Home Page to have the A/C compressor cool the intake air with reportedly good results.

 

Thanks for the feedback. How about belt wear with the smaller pulley? I was also looking at the Nameless I/C radiator. Heat is always the factor when dealing with rotating machinery and electrical circuits---makes life fun.

 

The general wisdom that I have heard is to go with a steel, not an aluminum pulley to minimize slippage. Also Goodyear Gatorback belts are supposedly the best. (Search 'Gatorback' for details and to get the size for the 4.2 engine).

 

White XKR, I noticed you have that awesome XKS scanner installed. That puts you in a pretty objective spot to comment on its effects! Few questions if you don't mind:

How have the IAT and coolant temperatures changed since you upped to the 3lbs pulley?

Do you have a boost sensor hooked up? If so, how much real boost change did you see with the new pulley?

Are there any other changes that you've noticed/logged since the pulley change, such as retarded timing, knock warnings, etc?

 

Unfortunately I swapped the pulley before I installed the gauges, so I do not have before and after data .

I have a supposed 2.5 to 3 lb pulley. My recollection is that our factory boost is supposed to be about 11 PSI. So far, on my boost gauge the max I have seen is about 13-13.1. So I am coming up a bit short-I do not know if I was a little low to start with, or it is the pulley.

There are no warnings or faults.

I do have an open issue that the cat converter efficiency test never seems to run, but this could be due to one or a combination of the other mods I had made. I also have some reason to believe it might be an EGR issue...this is something I need to look into. (Fortunately, most states have an exemption allowing for one of the several required emissions test to be incomplete).

I monitor both the coolant temperature and the intercooler fluid temperature. It is clear that their thermal isolation is quite good, even though the systems are connected by a very narrow tube.

It is also clear that the intercooler temps rise very rapidly when using significant boost, and cool off very, very slowly when letting up on the gas. So there is a definite need for additional cooling. The intake air temps at the MAFS generally remiain just a few degrees over ambient, so there is no problem there.

As Avos mentioned, the ECM in these modules has a wide range. Others have run much higher boosts without problems, other than heat soak.

I do think there is some finite risk of weakening the supercharger snout which could lead to fracture when milling to acccmodate the 3 lb pulley, but so far no issues of that sort for me.