discussion about overlap in a turbo cam
12-17-2012, 11:15 PM
#1
discussion about overlap in a turbo cam Ive been researching quiet extensivly and there are many proven turbo cams out there along with countless custom grinds that work like a charm. Most all of them somewhat follow the same reasoning for duration, split, lift etc. But one thing I have noticed though is that overlap tends to be all over the place. Ive seem proven cams with anywhere from -11 all the way into +20 or 30.
How does overlap play into a turbo cams performance and why the wide variation. I would love a great performing turbo cam that also has a great lope. But obviously overlap is a byproduct of choosing lift, duration and LSA that fits the needs of a particular build.
Thoughts?
How does overlap play into a turbo cams performance and why the wide variation. I would love a great performing turbo cam that also has a great lope. But obviously overlap is a byproduct of choosing lift, duration and LSA that fits the needs of a particular build.
Thoughts?
12-18-2012, 12:34 PM
#2
Overlap is in direct relation to the turbine to ci relationship.
More turbine you have, which gives you a better chance at achieving 1:1 backpressure to boost ratio or better, the more overlap it can tolerate.
For LS type engines in street car applications -3 to 14,15 is a range i work in. Thats at .050.
The most overlap the combo can tolerate is a good way to go.
I like more overlap in pump gas engines for the chamber cooling help it gives, and you can use it to set the dcr of the motor too.
More turbine you have, which gives you a better chance at achieving 1:1 backpressure to boost ratio or better, the more overlap it can tolerate.
For LS type engines in street car applications -3 to 14,15 is a range i work in. Thats at .050.
The most overlap the combo can tolerate is a good way to go.
I like more overlap in pump gas engines for the chamber cooling help it gives, and you can use it to set the dcr of the motor too.
12-18-2012, 02:09 PM
#3
Ok that makes sense. How does overlap correspond with spool time? Im looking to build a forged 370, possibly cathedral heads and pro flow intake. I know the turbo needs to be properly sized to your combo and goals. Since I want to be around 8-900 on the street ive heard an 88 matches up pretty well and offers fairly close to 1:1 backpressure. But I don't want it to be real laggy. Can this be solved with turbo selection or cam selection? Im assuming its a combination of both. Im fairly knowledgable in turbos, heads, cams, compression etc. But bringing it all together to a great combo seems overwhelming at times.
