It definitely added a lot of mid range and a little low end grunt. There wasn't any top end loss, but its not for those trying to add peak/maximum horsepower numbers. Even at the drag strip, I was more than a half second faster with 5-6 more mph trap speed over a stock STR with the pulley as my only modification. As mentioned, the downsides are shaving the snout to fit the pulley and more/quicker heat soak over stock (the 1.5# will heat soak more/quicker than stock as well). The 1.5# is not a bad choice, either, but if I did it again, I would go with the 3# again. I had 0 reliability issues or complaints and I did do a couple of full days on a road course and countless runs down the 1/4 mile strip.

 

Rasputin - do you have any videos/sound clips of your STR with the current exhaust set-up i.e. 11385 x-pipe and 59975 cats? Listening to how they sound would help me decide whether to go for them or a borla 400287, as I've heard how the latter sound on our cars thanks to goblue90.

Robinb - have you installed the exhaust parts yet? It seems that the 11385 is recommended and the 99675HM are also easier to install than the 599675 cats due to not having to run o2 extenders as reported by QuartzSTypeR. If you have installed them already, would you recommend them and how did they affect performance in your opinion? If you haven't yet, me and I'm sure other members would benefit and be grateful to sample their tone.

 

QuartzStypeR - are you certain the 3lb pulley takes off more than half a second from a quarter mile and adds 5-6mph more trap speed as 1320racer saw no gain in terms of times at the track over a 1.5lb pulley although 6 peak hp was gained? If that was the case, you would've certainly been running mid to high 12s at sea level with your mods however you've passed off DA calculations based on your altitude as mere speculation.

 

I can't compare to a 1.5# pulley. I did not run the car stock,so I can't compare my exact car from stock to the pulley, but I did talk to an acquaintance who said he was running around a 14.5-14.7 ~ 93-95 mph with a stock STR.

My worst time with just the pulley was a 14.1 @98 mph, and it was a little heat soaked then; I would typically run a 13.9 or 14.0 right around 99-100.

I added exhaust and intake after just a couple trips to the track, and my best run was a 13.6 (most runs were 13.8x) and I usually trapped 100-102 all depending on the DA which is typically between 8-9000 ft.

I have no doubts it would be a 12 second car at sea level, but pinpointing the real world time vs. a DA calculator does involve some speculation as more power=more spinning off the line and needing more driver control and ability.

 

any way to give me an idea of the amout of material you have to take off to get the 3# to fit? is it for the inner od of the pulley sliding over the end off the snout?

 

Its not a major amount. The "proper" way would be to pull the supercharger off and have it machined, but I just ground it down free-hand and took measurements with a micrometer at several spots around the snout to make sure it was somewhat even. I don't know the exact amount, but I would guess ~5mm. It is for the inner diameter to clear the snout, yes.

 

Thanks for clarifying QuartzStypeR, there was no doubt in my mind that your car is a 12 second car at sea level anyway, having established that 1320racer was able to run 12.9s with fewer mods yielding less hp and significantly less torque. If I am not mistaken there are at least 3 STRs which have ran 12s, not including your car which we know would do the same at sea level. Given the extremely low number of STRs which do see the track, I hope to be able set a sub 13 second time this winter after finishing my mods.

 

Should be doable. If it could stomp on cars like the Camaro SS, Charger/Challenger SRT, Mustang GT 5.0 and the like , I don't see how it would still be in the 13s at sea level.

 

No, not yet installed. Was waiting for the OEM cats to go, which could happen anytime soon at 76k miles. When that happens, I have new O2 sensors, extenders, hi- flow cats and the 11385 ready to go.

Did a lot of reading & research on the forum before deciding on the Magnaflow cats and 11385. Will definitely post results on the forum when the time comes...

 

Should I expect similar gains from my 2005 XKR coupe? I have x pipe and pre mufflers delete and hi flow muffs and K&N air filter. So with the lower pulley upgrade will I expect at least .3 1/4 et off?

 

Click here for my post with dyno results as my modifications were made ...

Correct. I purchased my 2005 STR used with 7K miles and I was not aware that a 1.5lb pulley swap had already been done by a previous owner until much later.

Installing a 3.0lb pulley on my STR made no improvement to 1/4 mile times and has reduced my trap speed slightly. This has been confirmed with many runs at multiple 1/4 mile tracks. With the 3.0lb pulley, there's an increase of power (primarily trq.) at low RPMs but at the expense of power at high RPMs. Since the 3.0 pulley installation I have not trapped at or above 109mph -- even in cold weather -- but every so often with the 1.5lb pulley, I'd trap at or slightly above 109mph.

Put simply, none of the STR modifications I've made increase the engines power as much as COLD ambient air (below 50F) and COOL intercooler/engine coolant (below 180F). If a unmodified STR raced me on a hot day, the outcome would be very close. But if an unmodified STR raced me on a cold day, I believe the minor mods would allow me to win most of the time.

If I knew this from the start this is the way I would have spent my money:

• I would have installed a wet nitrous oxide kit (post supercharger) active only in gears 2, 3, 4 and 5.
• If nitrous oxide is not your thing, I suggest a 1.5lb pulley and one of the forum "member designed" intakes located after the stock/OEM cold air intake.

For those like me who enjoy an aggressive V8 engine note, I suggest leaving the exhaust system stock except install a set of high quality 200 cell high flow cats. The Magnaflow 59975 high flow catalytic converters I had installed failed but I have not noticed if others have had the same experience. The power gain I achieved from high flow cats, x-pipe, resonator delete and high flow rear boxes/exhaust was again minimal.

Don't get me wrong, doing the modifications and testing the modifications has been a lot of fun and did increase the engine's power -- but they didn’t increase the engine's power a great deal.

It has been said by others and I agree, for those who really want a fast STR, go with a twin screw or nitrous oxide. If you do either, you will find the weakest link of the car. All my time racing this STR, I've only broken a $37 motor mount. Enjoy!!!