2008 AP2
SoS with Novi 1220 SL
3.8" Pulley
Racing (larger) heat exchanger

The car dyno'd at 355 rwhp, with boost levels peaking at around 7k rpms at 7 psi.

The chart on the SoS page indicates that I should be seeing 9 psi, and I honestly expected something more like 375-385 rwhp using the 3.8" pulley over the 4.2" stock pulley.

Am I possibly losing boost somewhere, or does this seem about right?

 

you must have a boost leak. Your boost should keep climing all the way to redline.

 

Yep if boost is peaking at 7k RPMs than there is a problem. Check to make sure there are no leaks and make sure your belt is tight and not slipping

 

I already checked the belt, which seems arguably too tight by the 90 degree twist test.

What other locations could possibly leak boost on the SoS kit? Is there any easy way to actually test for this? Soapy water on the transition points?

Do the SoS kits really not build peak boost until 8k?

 

Thats the nature of centrifugal superchargers. The blower is connected to the crank pulley, so the faster the engine spins, the faster the blower spins. Therefore peak boost will be made at peak rpms. If your boost climbs steadily up to 7k and then flattens off, you are getting belt slip. Boost should climb steadily with rpms, so peak boost and peak torque will be at peak rpms (redline)

 

Hmm... the dyno's on the SoS site both show peak torque at 7500 rpms. My dyno shows it more up around 7900 or so, but it's maybe 5 ft/lbs more than at 6900 (where I appear to be peaking on boost).

Is it possible to have a minor boost leak that's only evident at the 7+ lbs mark... or the recirculation valve dumping some of it over that mark, or does this seem to only point to belt slippage? Again, trying the 90 degree twist test, I can maybe tweak it to 80 degrees or so.

Thanks for all of the responses so far! I've been going back and forth on this with the SoS guys as well, and they also believe I should be seeing more than 7 lbs, but I also read a few posts on this site seeming to imply that the boost figures on their charts may be a bit high. <shrug>

 

Agree with liquid. In my experience its always belt slip unless you can see literally a clamp blown off one of the couplers. If the couplers look secure and lined up at the TB and after cooler then you should be fine. Also its not typical that the recirculation valve would be failing at such low boost. Ive held 20psi through one of these. Bite the bullet and tighten up that belt more and see if you gain anymore psi, if you do then you will know, if not then back off the belt tension and continue to look elsewhere. Also make sure your belt isn't contaminated with oil or anything that could cause slippage even though the tension is proper.

and you are still on a aftercooler right? Not an FMIC?

 

Peak torque does not equal peak boost. The torque curve will typically flat-line or start to drop off in the top-end, even though the SC is still increasing in pressure.

I'v always seen higher actual boost ratings than what the SOS charts show on their site. I saw 7 PSI on a 6 PSI pulley, and 13 PSI on an 11.25 PSI pulley. So from my experience the SOS charts read a bit low. Note that I'm only about 700 ft above sea level, so YMMV.

 

It sounds like I should at least be seeing 9 psi then (Atlanta is only 1,050 above sea level), and even SoS seems to feel that way as well.

I'm going to go with the suggestions here and see if I can shake something out. I intend to hook up a mechanical boost gauge and re-verify the results seen on the dyno. Then I'm going to double check the all connections, and probably fully loosen, press together, and re-tighten the coupler between the blower and after cooler, check the results again. Then finally if that still doesn't do the trick, I'll Hercules the tensioner and give it another go.

Thanks all for chiming in! I'll post back results (hopefully good ones) soon.

 

Is the belt new? Is it the one that SOS sent with the kit? I think they sent me a Gatorback??? But I would have to agree with the slip thought process...I had the same problem with mine. I would get up to 14 psi at 8k and then it would flat line or on some runs just drop off.

Also, did you do a compression test prior to the install as well as a leak down test? I am assuming the kit is new so your probably have no blower issues.