Clipping refers to removing the trailing edges of the turbine blades to allow less restricted airflow to pass. A clipped wheel has a machined angle on the turbine wheel exducer. Clipping causes an increase in the wheel's flow, but it also reduces the turbo efficiency. This reduction in efficiency causes the turbo to come up on boost at a later engine speed ie increased lag.

 

If anyone has a dyno graph comparing clipped to unclipped power bands please post it!
When I upgrade I think I'll go for unclipped since most of my driving is on regular
roads and not the track.

 

A dyno won't show you lag or threshold, which are the two detrimental characteristics of clipping, if that's what you are looking for. A compressor map can help decide on the best low, mid, and high RPM performance characteristics for daily driving.

 

Thanks Bob. You are an amazing source of information.

 

I just wanted to see what the effect on the power band was, but yeah it wouldn't show lag.

Cann is right, you are encyclopedic!

 

This is very good info. I need to get some clarification from my tuner. i dont know if his proposed upgraded VTGs have only modified exducers, or if they only have modified turbine wheels (induder and exducer).

 

Most tuners modify both compressor wheel and turbine wheel. TPC racing and Protomotive do another modification which gives another 50WHP over modded VTGs. I don't know if they published what they really do so i wont post that.

Maybe TPC can give some info

I'm getting a set soon

 

stock GT2 VTGs already clipped from the factory.

The clipping will make u loss littel bit on low-end but got more top-end!!

I didn't feel the loss on low or midrange on modded 997 VTG's since we saw 6.7sec from 60-130 ON 93 OCTANE

 

what, are you saying that TPC and Protomotive versions of upgraded VTG will give you 50whp more than others, like Switzer, Works1, ect.? that's quite a difference.

 

I think milou is referring to wheel clipping that Shotcaller also mentions.

 

There are different version( more then one company that makes the hybrids)... thus the differences are in the detail... and price....

 

No this is not what i was referring to, there is another thing that can be done to VTGs.

Mike at TPC holds the 60-130 record i think, i'm changing my VTGs soon so i'll let you know how they compare to my already modded VTGs

 

Out of curiosity, what is the 60-130 record for vtg 997t 6speed?

 

From 6speedonline list :-

6.55 - Acicchelli / 997TT AWD TIP <-Fastest tip car ( on racegas ) by Switzer

6.60 - Adam Bowles / AWD / 1-shift
6.66 - 996ttalot / AWD / Tiptronic
6.69 - Shotcaller / 997TT AWD/ 1-shift <-- Fastest 6peed car ( on pumpgas ) by Protomotive

 

I've been out of the loop here for months and need to catch up. Who has the turbo mod that minimizes lag, has huge power gains and is offering a great price deal to boot. I guess I need IC's too?