Upgraded VTG opinion please
#151
04-24-2013, 02:02 PM
As stated, those 68s will make big power. But the engine needs to be rebuilt to hold it. So if you dont ever plan to build the engine, the 65mm would be better IMO as the slight loss in power up top is less important to me than the loss in spool down low. Tom has a chart in one of these threads showing a 65mm car overlayed w/ a 68mm on stock engines. It was very informative for me to help make a decision.
Last edited by G911; 04-24-2013 at 02:06 PM.
#152
04-24-2013, 02:09 PM
Thats crazy #'s. Thats why i said im not the expert. Thanks for chiming in!
#155
04-24-2013, 08:33 PM
Here you go. There are two attachments. The first one has 3 graphs on it. A stock 997TT, our 65mm VTG's, and our full 68mmVTG kit. All three of these are cars with stock engines, never running more then 23psi.
The second graph shows our full 68mm VTG kit on a car with a built 3.8L engine at higher boost levels (28psi). No other hardware was changed except the modified engine and increased boost.
The second graph shows our full 68mm VTG kit on a car with a built 3.8L engine at higher boost levels (28psi). No other hardware was changed except the modified engine and increased boost.
Could you run the 65mm VTG's on C16 or E85 at 27-28psi safely on a stock motor since the fuel is better?
#157
04-25-2013, 07:18 AM
Former Vendor
I would not recommend it. During our early testing of the 68mm VTG's on our own shop 997TT a couple years ago, we did run 28psi with C16. The car made 775 AWHP....but it also bent the rods. That's why we typically do not recommend any more then about 22psi, which turns out to be around 650 AWHP.
#158
04-25-2013, 12:32 PM
I would not recommend it. During our early testing of the 68mm VTG's on our own shop 997TT a couple years ago, we did run 28psi with C16. The car made 775 AWHP....but it also bent the rods. That's why we typically do not recommend any more then about 22psi, which turns out to be around 650 AWHP.
#160
04-25-2013, 01:08 PM
I worded that wrong. I meant 68mm makes 775 on 28psi how much less would the 65mm produce at the same psi? Also you can run 700whp and limit the torque to 650.
#162
04-25-2013, 07:13 PM
So speaking only from my experience with other platforms (though in the same power range), the smaller turbo pushed hard is actually worse than the larger one. High tq down low is what kills rods (and knock....), and the 65mm spool ~500rpm sooner, with similar tq as the 68mm. The advantage of the 68 is they can hold that high tq up higher in the rpm range due to increased flow, thus more hp.
So, if the 68mm at 28psi (775whp) is too much for the rods, the 65mm at the same (~700+whp probably) would also be too much for the rods as the torque figure at 3500-4k rpm would be essentially the same. In fact, the 65 would have that tq 500rpm lower per Tom's charts.
Basically, stick to lower boost without a built engine. 600whp is really the sweet spot where most cars feel dangerous and fast with that thrill we love, without being so bat**** crazy you're crossing the line into massive $$$ to keep it running. And our cars seem perfectly happy in that 600-650whp range.
So, if the 68mm at 28psi (775whp) is too much for the rods, the 65mm at the same (~700+whp probably) would also be too much for the rods as the torque figure at 3500-4k rpm would be essentially the same. In fact, the 65 would have that tq 500rpm lower per Tom's charts.
Basically, stick to lower boost without a built engine. 600whp is really the sweet spot where most cars feel dangerous and fast with that thrill we love, without being so bat**** crazy you're crossing the line into massive $$$ to keep it running. And our cars seem perfectly happy in that 600-650whp range.
Last edited by Chkmgnt59; 04-25-2013 at 07:15 PM.
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