View Full Version : Northstar intake manifold

Harry Yarnell
12-16-05, 01:38 PM
1997 code Y motor.
At the end of the intake manifold, next to the power steering pump (opposite end from the throttle body), is a large flapper device that opens directly into the inside of the manifold. It's spring loaded closed. Looks like the flapper in a toilet tank. What is this, and what purpose does it serve?

12-16-05, 05:30 PM
It is for relieving pressure from the intake manifold in case of overpressurization.

12-16-05, 05:36 PM
Provisions for Supercharging??

12-16-05, 06:32 PM
This looks familiar... I'll say it again just in case anyone missed it.
It's called a "backfire valve".
When the engine backfires the pressure has to have somewhere to go.
This valve lets the expanding gasses escape rather than exploding your intake.

12-16-05, 07:17 PM
Ok, you are likely right, but I have to ask. GM went to the effort to design this in. Is backfiring REALLY a problem on a modern computer controlled V8 engine??

12-16-05, 08:57 PM
Not often but it is possible and when it occures there better be away to relieve pressure or your manifold may become a grenade.

12-16-05, 09:27 PM
Back when the Northstar was in it's infancy it really was common.
It really doesn't sound like a backfire anymore when it happens.
Just a big "poof" sound. If it wasn't for the valve it would be a loud explosion followed by a shower of small black plastic pieces.

It's been redesigned a couple of times, now it's more of a springloaded plunger. Usually you'll hear this in action when you crank it for a short period and let go of the key but it doesn't start, at the last instant it will go "poof"!
That's the valve in action!

12-17-05, 09:55 PM
I have seen it posted here before. It does happen apparently.

12-17-05, 10:18 PM
It really doesn't sound like a backfire anymore when it happens.
Just a big "poof" sound.

I've got the flapper, and I had a backfiring problem caused by a leaking injector. Let me tell you - it's not a "poof" sound. It's a gunshot. Anyone in the vicinity will turn around to see whether they have to run. It was fun. :rolleyes:

12-19-05, 11:52 AM
As engines have gotten more sophisticated, backfires certainly aren't a "normal" occurance, but they can still occur. Recall also that the Northstar's intake manifold is a composite (plastic), unlike steel or aluminum that you'd traditionally find. Plastic is a good choice for many metrics, but backfiring resistance isn't one of them...so they included a valve for the engine to relieve itself in the event of overpressurization...so you don't ruin your expensive intake manifold.

12-21-05, 06:13 AM
How hard is it to replace the intake manifold? Anybody know what they cost? Thanks.

12-21-05, 06:35 AM
Not sure about prices, but replacing a N* intake is not really that hard.
How long it takes depends on what kind of tools you have and what kind of skills you got.

12-21-05, 07:27 AM
The LSx engines use a similar composite intake, and prices in the aftermarket for performance versions are in the thousands of dollars. If you needed to, I'm sure you could find a used intake manifold from a salvage yard for not much money. It'd probably be awfully expensive to replace with a new GM part. Physically, it's easy to replace. No draining of coolant -- it's a dry manfiold. Thank you GM!

12-21-05, 08:06 AM
The lSX intake is performance intake for the LS1.Normally the intake for the LS1 is around 200 from GM! I would say a Cadillac Northstar is around 200 also for the Northstar! I will check today.

12-21-05, 08:48 AM
When I said "LSx", I meant the LS series of engines, like LS1, LS2, LS6, LS7. There are performance intakes for those. Here are a few examples of aluminum LSx intake manifolds:


The LSx intake from FAST you speak of goes for almost $1000:


It would be interesting to know how much these intakes are, new, from GM.

12-21-05, 08:59 AM
For LS1 which is 1997-2000 price is 189. 2001-2004 which all LS1 motors use the LS6 intake are 200. I had to replace mine on my 2001 Supercharged LS1 Corvette. I had a lean pop! :thumbsup: The metal intakes for the LS1 hold way too much heat and are heavy. The LSX intake is no more power increase then the LS6 intake for third of price!