Is there anyone running the T78 turbo on any 13b utilizing a custom-made divided, equal length runner (~18inch runners) manifold? If yes, are you able to compare spool characteristics to the manifold that comes with the Greddy kit?

Thanks in advance!

 

Is there are particular reason you want 18" runners?

 

A couple people have suggested 18" is the optimal exhaust runner length for bottom end power. I'm curious as to how they arrived at that particular number.

 

I chose roughly 18" to designate a longer runner manifold than most japanese companies design theirs to be. Looking at pictures of most SS manifolds that come with the turbo kits from HKS and Greddy, it looks as if the manifolds have runner lengths of around 8-12 inches. I figured a slightly longer runner turbo manifold might help spool turbos as big as a T78.

 

Why do you think longer headers would improve spool?

Kevin T. Wyum

 

I could see the longer runner length maybe helping at lower rpms from scavaging, and tuning for pressure waves, ect ect ect. There is a lot of math used to figure out the correct runner length for those things and if someone has crunched the numbers I'd like to see the results of it. In reality my understanding is when you tune headers/manifold length for pressure wave tuning its for a pretty narrow rpm range.

I really dont see how having a long manifold would help with spool, I've heard it does from a few people on here (probably all reading from the same source) but I just dont see how. It seems like the longer the runner the cooler and slower the exhaust is going to get.

I guess a theory could be formed that if you use scavaging and pressure wave tuning designed to help with low rpm VE then you will increase low rpm air flow which would help spool the turbo. I wonder what effect that would have in the high rpms? Rice Racing used to suggest 13-16" but I dont think I've seen anyone suggest more than that. But I wonder at what point the longer running created lower egt's and lower velocity at the turbo would offset any benifit in the better low rpm VE?

I guess what I'd like to know form you guys that decided longer is better what theory are you working off of and what are you guys trying to achieve?

Please explain, I always enjoy a good tech discussion. Its the best way to learn

 

Honestly, I have no understanding as to why I think longer runners might help for an earlier spool. This is just information that I have come across from members such as Rice Racing and turbostreetfighter and members alike who have had more experience than I. I was asking because I thought it might be interesting to couple a better-designed manifold with a comparatively late-spooling turbo.