I am learning turbo stuff still, so bare with me. Yes, I have searched and searched and found a lot of old topics but none really answered this. I'm about to have the engine back and ready to start figuring out the piping.

What I am trying to learn or get info on, is what the difference is going to be or might be between a set of 1-5/8 shorty headers and 1-3/4 up and forward header. I have a set of Sanderson shorty's right now that could be used that have 1-5/8 primaries. Both sets have 2.5" collectors. I also have a set of truck manifolds but I really don't want to use them due to the weight.

If I use the 1-3/4 primary, I would most likely run 2.25 pipe to the turbo flange. I am trying to find out what running the 1-3/4 will do to it compared to the 1-5/8. So does it take a bit more rpm to reach full spool? If so, about how much more? What rpm should I anticipate to reach full spool? Lag, how much estimated lag will there be for the 2 sizes or maybe a difference in total lag?

I am sure the larger primary will have a touch more lag, and might need a bit more rpm to spool. I'm just curious on how much more. If its going to be enough to cause issues or not. This is a race truck that will be driven on the street to shows, meets ect. But not a DD.

My setup.
6.0 LQ4. SBE except for a set of 4.030 Diamond pistons which will net me about 10.25 cr. 317 heads with no port work. TU2 cam. Victor Jr. intake with elbow. S482 turbo T6 divided with race cover 1.25 AR. Not billet. 5" exit pipe.

Trany is a powerglide. Stall to be determined based on what is calculated I will need. 3.90 rear gear.

If more info is needed just ask, I'll let you know. Appreciate the info.

 

Honestly it's not going to make a difference in the two primary sizes... A 370ci motor is going to spool that turbo pretty quick! And I would do 2.5" off each collector to a merge at the turbo. I have pretty much the same setup as you, I went from a log type setup where I couldn't build boost off my footbrake, to a header style with 1 3/4" primaries that merged into 2.5" tubing at the collectors then 2.5" all the way to the turbo flange, the header setup spooled my turbo a considerably amount sooner and I could build boost off my footbrake! This was all on a 370ci 6.0 setup as well.

 

On a 438" going from 1.75" to 2" made a noticeable difference. Optimal size on that combination was 1 7/8" with a 2.5" crossover. Keep it on the small size and you will be fine. 1 5/8" with 2" crossover or 2 1/8" if you can find the piping should be good for the power your trying to make.

 

PHIL !!!! welcome man. LOL I read the entire thread you were in and it confused me more than anything. I went ahead and bought the 1-3/4 primary 2.5" collector up and forward set. Its a nice set for the money. And I didn't think it was going to kill me. I plan to use a cone right off the collector to get me down to 2.25". This way its a smooth reducer, basically extending the collector some. I'm also looking for a cam. The TU2 is going to be an issue for my engine from what a couple of others are telling me that know about cams and turbos. I have another thread on cams where I am looking for racer input. So your input would be good there too.

 

I would call Shawn at Precision Race Technologies and let him get you a camshaft.

 

That's one I haven't seen mentioned. I'll look into him. Does he grind yours?

 

Yes, your in good hands.

 

I looked at his build thread on Yellowbullet, and yea, that Nova is impressive for sure.