Header sizing
Thread Starter
Teching In
Joined: Jan 2021
Posts: 26
Likes: 1
From: Grew up in Manhattan Kansas, live in Saint Louis
Header sizing I want some opinions on sizing headers for an LQ4. I’m thinking about building my own. There will be no exhaust after the header. I have a good idea what to do for the N/A build, but not sure how the nitrous effects primary/collector diameter selection.
basic information - pretty standard N/A setup:
403ci
trick flow 225 heads
236/244 cam
fast LSXrt intake
11.4:1 compression.
NX direct port kit.
looking to spray as much as 400 on race day, if I can tune my way up to it. Keep it under 7200 rpm.
basic information - pretty standard N/A setup:
403ci
trick flow 225 heads
236/244 cam
fast LSXrt intake
11.4:1 compression.
NX direct port kit.
looking to spray as much as 400 on race day, if I can tune my way up to it. Keep it under 7200 rpm.
The exhaust side of the event is extremely critical with big nitrous hits…similar to a build with big boost levels. Your gonna want a very robust exhaust valve, ample exhaust port/valve seat work and a well built header setup. Your going to want to run some exhaust pipe behind the header, to keep the o2 sensors in check. O2’s don’t like open headers. The pipe max software advice above is solid, unless you’ve got an engine builder with YEARS of big N2O experience. Ring package and piston design must be on point with that much Nitrous also. I cannot stress what tuning means in this application also. That’s a huge amount of Nitrous.
Staging Lane
Joined: May 2023
Posts: 90
Likes: 71
Having a similar-ish engine spec..
1 3/4 killed power and took 3* of timing less to run right, engine just wasnt overall happy.
1 7/8 made good power and kept the RPM band going, supported 700hp no problem.
Like Scott said, shooting that much nitrous through an engine isn't something someone does on a whim. It is a well thought out game plan. Whomever is building the engine etc. Should know what size headers you will need more than anyone. The exhaust valve, port size etc. Will be a big factor to get all that "dirty" air out. You're going to want 16-18" of pipe coming off the headers though. It's been Dyno tested to produce the best HP results over just open pipes.
1 3/4 killed power and took 3* of timing less to run right, engine just wasnt overall happy.
1 7/8 made good power and kept the RPM band going, supported 700hp no problem.
Like Scott said, shooting that much nitrous through an engine isn't something someone does on a whim. It is a well thought out game plan. Whomever is building the engine etc. Should know what size headers you will need more than anyone. The exhaust valve, port size etc. Will be a big factor to get all that "dirty" air out. You're going to want 16-18" of pipe coming off the headers though. It's been Dyno tested to produce the best HP results over just open pipes.
Thread Starter
Teching In
Joined: Jan 2021
Posts: 26
Likes: 1
From: Grew up in Manhattan Kansas, live in Saint Louis
PipeMax is good advice. I’ve got the equations from school, but without experience it’s hard to say that those theoretical answers line up with what people see in the real world.
It sounds like I should do some more research on the exhaust valve before I spray that hard. Good news is that the heads are off the motor, so it’s a good time to slow down and get it right.
I should have been a little more clear on the headers themselves - I can build in some amount of collector length without an issue. They are going to be up out the hood, tractor-pull style headers. So they just won’t have anything after the collector.
For O2’s - i planned to put a bung in the collector on each side. I am running OLSD on the N/A tune so I won’t be using them during the run to change fueling, but I’d still like the data as a check piece to make sure the Wideband agrees with what I see on the plugs.
this probably belongs in the nitrous forum, but it pertains to building headers. What about bungs for EGT sensors?
400 shot is a goal to strive for, it’s possible I start turning it up and find that maybe 250 or something in between is the limit on this motor as-is.
appreciate all responses
It sounds like I should do some more research on the exhaust valve before I spray that hard. Good news is that the heads are off the motor, so it’s a good time to slow down and get it right.
I should have been a little more clear on the headers themselves - I can build in some amount of collector length without an issue. They are going to be up out the hood, tractor-pull style headers. So they just won’t have anything after the collector.
For O2’s - i planned to put a bung in the collector on each side. I am running OLSD on the N/A tune so I won’t be using them during the run to change fueling, but I’d still like the data as a check piece to make sure the Wideband agrees with what I see on the plugs.
this probably belongs in the nitrous forum, but it pertains to building headers. What about bungs for EGT sensors?
400 shot is a goal to strive for, it’s possible I start turning it up and find that maybe 250 or something in between is the limit on this motor as-is.
appreciate all responses
