Long story short, the jackshaft bearing on my vortech kit went out on me when I was 8 hours away from my house. The bearings fell out and was literally throwing sparks down the road. I got the car towed back and ordered a new jackshaft and cog drive pulleys. Since my vortech now has 70,000 miles on it, I figured I just pull blower as well and send it to vortech for an inspection on whether I need a rebuild service or not. Since it will be at vortech I am considering an impeller upgrade from my Sci to an Si impeller. If I do this upgrade, will I need to get the car retuned straight away for it drive properly? I know that ideally I would get it re-tuned since that would be the purpose of the the impeller upgrade in order to make more power, but I just don't know if doing an impeller upgrade would affect the drivability of my car with the current tune. I wouldn't mind doing the upgrade if I can drive my car safely the way it is and get the tune at a later date. Just not sure if adding a stronger impeller means it will perform differently as is.

Also, for those familiar with the SCi and Si units, is it even worth it?

By the way, my engine is fully built with upgraded supporting mods and has been dyno tuned with Uprev so it can handle more power.

Thanks in advance.

 

The Si flows more cfm so yes it's going to pump more air and thus need more fuel. Just watch your AFR gauge initially to see how it's doing, it's a roughly 10% increase in total flow as long as enough air can be pushed through your intercooler. If you have a lower flowing intercooler than you might not see hardly ANY extra air going into the engine though.

Also use some kind of logger like torque pro and see what kind of correction the ECM is making for fuel trim.

Typically though, as long as you aren't getting hard on the throttle and have an AFR gauge you can watch then a change like that is something that you can still safely drive for a short time until you can get retuned. It's hard to say though EXACTLY how your car will respond because a lot of that depends on which intercooler you have and if it can even handle a higher flowing compressor.

 

Hey cleric670,

Thank for posting on my thread. I wasn't sure if there was much traction on the site these days considering the various facebook pages people are using these days. I really wasn't sure if the Si upgrade would push more air without a tune, but what you said about the cfm make sense with the way I am reading it anyway. It seems my possible decision of upgrading for a $400-600 impeller upgrade just jumped to $1500 if it needs a tune. Now, I'm not running a larger intecooler. I am using the standard one that come with the Vortech kit, so do you think even upgrading to a Si impeller is worth the cost considering that gains could be hindered to the standard size of the intercooler? If I need a larger intercooler to see any potential gains with the Si impeller and a tune to top it off maybe its best to keep the Sci impeller. Thanks again for you help.

 

You'll see SOME gains yeah because you can always push more air through something via pressure until it finally explodes. However on the stock intercooler you will certainly be leaving power on the table.

Just to verify you are already running the smallest pulley yeah? How much power is the car currently making? What duty are the injectors running from your last tune? What fuel pump are you using?

These are the important questions, making sure there aren't other limiting factors like injector or pump otherwise you're still hitting a performance wall.

 

Hey Cleric,

Thank you for your reply. My engine was built back in 2013, which is also when I had my Vortech installed. Since I was living in the UK at the time, the tuners there were not comfortable tuning anything other than a Vortech, hence the reason for going with a supercharger over a turbo despite having a fully built engine. I did not go with the smallest pulley which was normally the 2.87 size at that time. Instead I went with a 3.12 since I was also using a Fluidampr Harmonic balancer which is larger than the standard crank pulley. That combination of 3.12 and the harmonic balancer makes the Vortech spin faster and actually overspins the blower to 56000 at 6600 rpms which is 3000 over the max impeller speed of 53000. If I'm not mistaken, going with an even smaller pulley, would give me further low range torque, but my powerband would shorten as I would be hitting max impeller speed much sooner, maybe around 5000 rpms possibly. This reason has led me to considering a Si impeller upgrade rather than trying to get the blower to spin faster, which it is already overspinning somewhere between 6000 and 6600 rpms currently. Of course, I did not consider the air-to-air cooler that is currently installed as you had previous mentioned. In addition, I'm running Injector Dynamics 725cc injectors, CJM Stage 1 Fuel return, and an Aeromotive 340 fuel pump.

When I lived in the UK, dyno numbers were always printed in engine bhp rather that whp like here in the US. I don't know where to find what duty my injectors are running at or if it is even on the dyno sheet. My bhp numbers before I replaced my Motordyne TDX2 exhaust with a Tanabe Medallion was 452hp and like 345 tq. Since being back in the US for a few years now, I have been considering getting a re-tune anyway since I changed my exhaust and since I'm now using US fuel. Also, with the current set-up I had the car dyno'd at a local garage on a dynojet and hit 370 whp. After seeing what others are achieving with a Vortech on stock block, I feel I should be getting more out of my set-up.

 

Check exactly which Fluidampr pulley you are using, the part number is stamped on the front of the pulley. The typical one used on the VQ35DE is just an OEM replacement diameter, 6.5 inches. If that's what you're using then it's not actually overdriving the SC.