Hi Ash! :-)
First I want to say that I appreciate the work you do and want to congratulate you on your successes!
I do believe you are leaving out some very important differences between Seb’s and Dee’s car when presenting your resent data though and I feel
People need to see what I believe is a more complete picture of some other dynamics taking place in the two different cars being discussed.I believe that both cars have restrictions in different places and both cars could offer more overall power if both cars incorporated the gains each car has seen from
there respective better breathing areas.
In short, Seb’s engine has a better VE with the head work and cams and also has the potential for more top end with the larger A/R housings.
Dee’s car on the other hand offers before and after engine breathing mods resulting in net better overall power over Seb’s set up with restrictions in those areas. Basically Seb's car has major restrictions in his intercoolers and exhaust for what his engine and turbos are capable of.
Seb had 2.5” exhaust and stock 2” intercooler pipe with stillen intercoolers that have more restrictive inlets and outlets than stock.
The casting on the stillen intercooler inlets and outlets are 2” outside diameter and are very thick resulting in about a 1 ¾” inside diameter. Just cutting the inlets and outlets off and welding on thin wall 2" pipe connections nets huge CFM gains with the Stillen intercoolers.
The restriction in the intercooler tanks has the same effect as opening the throttle plate less.
Here is info Dee posted about the difference on his car between Stillen intercoolers and just changing to 2.5” intercoolers and pipe. Keep in mind this was also with 3” downpipes and midpipes on Dee’s car. [ http://twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1672666&words=massive%3a%3adyno ] Now it would seem Ash knows the difference that the larger intercoolers and pipe made and since he has dyno data on Dee’s car with Stillen intercoolers that a more fair comparison when trying to look at the difference in VE or turbine A/R to Seb’s car would be to use the data with at least the same intercoolers and pipe?
This is still not a good comparison with what I now know about the differences in exhaust size with proper downpipes at this turbo level given Dee has 3" parts. We have done lots of testing on the Exhaust end and found amazing gains from the time you touch the throttle all the way to red line without even addressing the intercooler end tank restriction issue, let alone going larger as well on the intercoolers and pipe. So the bottom line is that Seb’s car did make similar top end power with the larger a/r housings on his turbos and head work cams at lower boost levels even with significant restrictions going in and out of his motor.
In my mind you cannot begin to justify that the A/R housings are the biggest difference in the two set ups. In my mind with the before and after engine mods that Dee has done he would see substantial gains going to larger cams, adding head work and going to the .86 A/R. Seb’s engine and larger A/R on the other hand was severely restricted by the Stillen intercoolers and stock pipe as well as the smaller exhaust and his set up would shine with larger intercoolers and pipe as well as a larger exhaust. We are not ready to release the exhaust data we have collected yet, But I will share this much…….On Seb’s car going to 3” exhaust with a properly made down pipe to make the 3” work best, his set up makes 2 psi more boost at every setting level on the boost controller as well as 2 psi more max boost with the 3” exhaust over the 2.5” exhaust. Even with the restriction from the Stillen Intercoolers on the intake side.
Higher engine VE = less resistance= more power at the same boost level.
If you have a bottleneck anywhere in the entire system it will decrease the max efficiency any of the parts are capable of. In closing I will say that I am still pro ,86 housings. I have had both housings on my own car and my car is quicker and faster at the track as well as more fun to drive on the street with .86 A/R housings over the .64’s.
The turbo works on a pressure and heat differential, So with the .86 housing it becomes more important to have larger exhaust after the turbo to see the benefit.
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