I decided finally to start a thread about this.

Someone got his intake manifold pressure to drop significantly after installing the Bad Mad header. I'd like to know the results of the other people who have it installed. The question is, and it is really important that you read it FULLY:

How much PSI did you loose after installing the Bad Mad header with A STOCK CATBACK SYSTEM?

Thanks in advance for all the responses!

 

i need to know the same exact thing, i just ordered mine on the gb. also, whats the problem/gain with this happening?

 

Try it and see for yourself??

It is pointless to compare one person's "results" to another. Every car and setup is a little different. He could have had an IC pump that wasn't working right causing increased boost and it decided to start working properly for a while now.

There is usually some drop off of boost when you lower restriction, but using a stock downpipe will not allow a header to do much. I saw decent gains by just porting the stock exhaust manifold and did several of them for other people with solid gains. Biggest key on these cars to a good working exhaust is getting rid of the stock DP, it's got a funny kink in it where it turns to go under the car and is crushed down to create a flat spot for the O2 sensor. Even the stock cat isn't that bad, it's the pipe as a whole that sucks.

Cat-back isn't that important either, we've had tests showing almost no gain from a 2.25" to a 3", even on a heavily modded car. I ran a GMPP exhaust and made a ton of power, others have as well.

 

i'm amazed that people freak about a boost drop when they change the exhaust on a supercharged car.. yes thats a good thing, it means theres less restriction and you are making more power...

 

Best way to put it, and straight to point!

 

I agree with joe, a real choke point on the lsj is the dp, if you have ever had yours off to look inside or the ouside design even you would know exactly what I mean.

 

yea i'll agree a chokepoint is the dp,

now alot of ppl claim a 10ish hp gain with just the bad mab, is this true or is that with a dp as well? in other words, there is still a considerable gain just doing the header right?

also, idk how it sounds does anyone have an opinion on that or a link to a vid with just the header?

 

I had an LSJ up on a lift at an exhaust shop way back in '05 and saw it, that made the decision for me. The pipe design is terrible, it looks like an afterthought. One of the guys at the shop that looked at it told the owner that the cat wasn't the problem, it was actually a pretty solid flowing design, such a large frame cat for such a small pipe can't be that restrictive, actual open flow area is similar.

First real mod after the basic stage kit for me was a catless dp and it made a very noticeable difference. These cars do not need any real type of scavenging effect under WOT when you have fairly strong pressure forcing the charge in, so there is little loss even with a very large DP and the only place you might feel it is part throttle and lower rpms, not where it matters.

 

why would you put a stock downpipe back on? its the same amount of work... and a downpipe is cheap...

 

agreed, i use cats on aftermarket dps more as resonators then for emissions

 

my ZZP 2.5 catted DP made a big difference when the stock flex broke. now i'm S3 and can't wait to couple my Bad-Mab with it. should be here tomorrow.

 

Exactly thats why I asked!!!

I just find that too amazing that the Bad Mad header can drop the pressure down to 15 PSI on a stock catback and 3" downpipe (2.8" pulley).

With my stock catback, when I installed my CTI Header and 3" catted downpipe, I saw a drop of only 0.5 psi...

Now someone said 3 PSI once the Bad Mad header is installed... I'm like... WTF! This is 6 times more of a drop... I wanted to know what other people experienced, that's it!

 

Nice to hear some common sense talk here.

Italian Joe. I used to hot rod Quad 4's. The predecessor to the Ecotec. The stock manifold responded well to porting at the outlet. Not so much at the inlets though. That cast iron grinds slow doesn't it?

For the stock downpipe being horrible, a guy with welding skills and some stainless mandrel bends could use the stock cat and simply rebuild the whole thing. You could even modify the inlet flange to better match the Bad Mab header. (Which I think has too large an outlet to begin with)

I used to do just that with the Quad 4. Although finding a good stock cat was impossible so had to use Magnaflow which was dead after about 1.5 years.

Also agree with the better exh flow will reduce boost a bit. I have been hotrodding cars for 30+ years, but never dealt with blowers. So I asked my engine builder friend who has done countless blown engines, and he said yes, the boost will drop, but the power goes up.

Ron

 

What ItalianJoe was trying to say is there are too many variables to really compare with others. There are so many things that can play a factor to say well why did he dropped 3 psi and I only dropped 0.5 Wtf. You dropped boost, be happy haha.

 

It made me invest in some carbide bits and a new die grinder, but the resulting speed upgrade was worth it Helped out with the cyl head porting I do as well. I do TB's and lots of other aluminum stuff too, so I had to have two sets of bits, but the cast iron isn't bad. Some of the alloy stuff like the LNF manifolds are nasty, the carbide bits barely touch them.

There is quite a bit of room to expand on the stock LSJ header, it cramps down pretty bad at the collector and outlet, and there is a lump on each primary where the header is clearanced for the bolt on the top of the flange, that has to go

 

AAAAHHH! But I want it to drop more! hahaha! I guess that I will have to port the head in order to be satisfied with more boost drop!

 

Boost will not be at 15 psi on a 2.8 with the stock head/cams. I was seeing mid 16's with the intake and exhaust manifolds ported well and a good working I/C system. Once I went to the GMR cams and a CIA header, I was getting around 15 at most and making a ton more power.

Don't worry about the number. The stock boost gauge isn't that accurate anyway