Is it common to lose 1~2 psi of boost because of headers?
Thread Starter
8 sec potential, 12 sec slip
iTrader: (50)
Joined: Apr 2002
Posts: 4,092
Likes: 2
From: Savannah, GA
Is it common to lose 1~2 psi of boost because of headers? I just got my headers installed last night (mac mid- length & y-pipe), and today, driving around, it seems to have lost 1~2 psi of boost according to the gauge... I knew I'd lose a little boost, but going from 6~7 to 4~5 seems like a lot just from swapping from the factory manifolds. I haven't taken it all the way up to redline yet, but it seems like it was at least 1# lower throughout the whole RPM range from what it used to be. 
TECH Senior Member
Joined: Nov 2001
Posts: 10,341
Likes: 1
Yup that is perfectly normal. You need a pulley change and a retune if you want to bring your boost back up. 
BTW Boost is only a measure of restriction in the intake. You are still flowing the same cfm as before just with less restriction.
BTW Boost is only a measure of restriction in the intake. You are still flowing the same cfm as before just with less restriction.
Thread Starter
8 sec potential, 12 sec slip
iTrader: (50)
Joined: Apr 2002
Posts: 4,092
Likes: 2
From: Savannah, GA
So if I'm still flowing the same amount of cfm, then will I make any more HP? I'm supposed to get it dyno tuned again for the headers this friday, what kind of gains (if any?) should I expect??? Thanks for the info guys
Originally Posted by ChevyChad
Thanks... Any speculation on what kind of gain I'll get with my current pulley (call it 5 psi) just from the headers alone?
You should gain anywhere between 20-30rwhp giving the same pulley.
Trending Topics
Thread Starter
8 sec potential, 12 sec slip
iTrader: (50)
Joined: Apr 2002
Posts: 4,092
Likes: 2
From: Savannah, GA
Just an idea... Since I have a borla adjustable cat-back, and I am running the biggest insert (straight thru pipe pretty much) would it be to my benefit HP-wise to put a smaller insert in or completely block it off so that I could have some more back pressure since the exhaust would have to go thru the muffler and get maybe some of the boost back? 
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Originally Posted by ChevyChad
Since I have a borla adjustable cat-back, and I am running the biggest insert (straight thru pipe pretty much) would it be to my benefit HP-wise to put a smaller insert in or completely block it off so that I could have some more back pressure since the exhaust would have to go thru the muffler and get maybe some of the boost back?
With a SC setup you want the least backpressure possible... So i would say no dont do it.
TECH Senior Member
Joined: Nov 2001
Posts: 10,341
Likes: 1
Originally Posted by ChevyChad
Since I have a borla adjustable cat-back, and I am running the biggest insert (straight thru pipe pretty much) would it be to my benefit HP-wise to put a smaller insert in or completely block it off so that I could have some more back pressure since the exhaust would have to go thru the muffler and get maybe some of the boost back?
Thread Starter
8 sec potential, 12 sec slip
iTrader: (50)
Joined: Apr 2002
Posts: 4,092
Likes: 2
From: Savannah, GA
Originally Posted by WHPLASH
Swap that pulley now or push back your dyno appointment until you do. Trust me!!!
Guess I'll just have to find out what the headers alone will add 
If I did swap the pulley to regain the boost, would it be harder on my engine? It seems to me that it wouldn't because it did fine with the 6~7# before, so 6~7# with headers should be equivalent on the block? I dunno, that just sounds like it makes sense to me lol. I don't want to grenade my engine either. Its still all stock internally...
With less restriction you should be making the same/slightly more HP just at a lower boost # than before. Changing the pulley to get your boost # back up will gain even more HP, but more HP will equal more stress on the engine too.
Thread Starter
8 sec potential, 12 sec slip
iTrader: (50)
Joined: Apr 2002
Posts: 4,092
Likes: 2
From: Savannah, GA
Well, I got on it and took it all the way to redline coming home from work getting on the highway and it spiked right at 6# before red-line. Before in good air it would go past 6 and almost to 7 like 6.8ish or so. So turns out I only lost less than 1#. Not worth it to upgrade the pulley at this time IMO. Thanks to Bob at EPP tho for your help on the phone 
Originally Posted by CHRISPY
Yup that is perfectly normal. You need a pulley change and a retune if you want to bring your boost back up.
BTW Boost is only a measure of restriction in the intake. You are still flowing the same cfm as before just with less restriction.
BTW Boost is only a measure of restriction in the intake. You are still flowing the same cfm as before just with less restriction.
Originally Posted by ss1
This is probably a dumb question. How necessary is a retune after going to a smaller pulley? What would/could be a result of more boost and not changing the tune appropriately? For example, if I went from a 2.87 to a 2.75 pulley on my (cough...vortech), would I need to get it retuned right away? I'm not all up & up on the tuning aspect, so i'm just curious. Thanks!
Good luck
Originally Posted by LSs1Power
If you are running a MAF then you will most likely need a retune. The thing is with running a MAF is that most LS1 FI setups max it out between 3800-4500 RPM and then they add fuel manually via PE vs RPM table. So the extra air coming in from the 2.75 pulley is not accounted for by your MAF so the PCM doesn't have a way of adding fuel hence leaning out. The only way to do it is with a new retune.
Good luck
Good luck
Originally Posted by Dragframe
so your saying this is NOT the case with SD?
