LS folks,critique this manifold.

[Fabrik8]

I'm mostly talking about optimizing piping sizes and things like that. Can't see if there's an intercooler, but I assume there is one form the piping path.

 

[Loganwayne]

Ya there is I think everything is 3" but not 100% but please share any hints you have. We're about to do a 4.8 with a similar set up in a Fairmont and then I'm gonna build one this summer

 

[Fabrik8]

Don't go too big between the manifolds and turbo because you'll lose velocity and increase spool time, don't go too small between the turbo and intercooler and intake because you'll lose flow, and make everything on the turbo outlet and exhaust as big as you can to reduce back pressure as much as possible. Specific sizes are related to power output obviously, but the relationships are the same. Choosing the proper turbo and intercooler is crucial; its nice to grab something cheap you got from a buddy but proper turbo sizing and intercooler effficency is worth spending extra money on if needed. Depends if you're going for lowest budget cheap thrills or best bang for the buck.

And think carefully about cam choice. What works well for big naturally aspirated power is not usually good for making the best use of a turbo. Turbos often like a milder cam with less overlap, etc. That's one really good thing you can usually get used for cheap from someone who has bumped up to a bigger bumpstick.

 

[Fabrik8]

Ya there is I think everything is 3" but not 100% but please share any hints you have. We're about to do a 4.8 with a similar set up in a Fairmont and then I'm gonna build one this summer

I'd say you probably want smaller than 3 before the turbo (at least before the 2-1 merge) and larger than 3 for the downpipe and exhaust, especially with a single exhaust. I'm just going off the cuff based on the current power level. A lot of this is more geared toward transient response on the street rather than somewhat steady state power on a dyno.

If you want the best transient response, stick with 2 smaller turbos instead of a big single. Depends on whether you want fast response and low end torque or the biggest possible power numbers.

 

[Fabrik8]

I knew it was only a matter of time before someone made a completely sleeper EFI system that looks like a carb. Holley did it, and it's really cool looking.