99kon

iTrader: (6)

I got a 99 2 door 2 wheel drive yukon. I would like to put headers and have a set that would fit, the only thing is that the headers dont have the small pipe that goes back to the intake like the manifolds have. Can i just plug it off at the intake? I would hate to pay over $200 for headers if I dont really need that pipe.

James B.

iTrader: (1)

The pipe is EGR. (Exhaust Gas Recirculation) You can plug the EGR inlet on the manifold if you are not in a state that does smog inpections. You will get a code and SES light for "EGR system inefficiency" or something like that, can't remember the number. You'll need to find someone with TunerCATS or have a custom program done for you that disables EGR diagnostics.

99kon

iTrader: (6)

Thanks James!

What exactly is tunerCATS? and should I really put that much money into reprogramming or just get the right headers?

My truck has a weird y pipe, it is the one that has the two cats on it (split 2 1/4" pipes or 2"??????????) I just dont like it, I want to go true dual with long tubes, but for know, Can i just get a y pipe that has one cat from another truck and tap the o2 sensors? Does this fit?

99kon

iTrader: (6)

Anybody else has this type of stock exhaust? What have you guys done? What type of exhaust do you run JamesB?

James B.

iTrader: (1)

TunerCATS is the only Programmer available for the L31 Vortec Generation of OBD-II PCM. Check it out here: http://www.monodax.com/

The exhaust you have is the standard emissions system for a 2WD. I'm going to guess you have a crossover pipe that runs under the bellhousing to individual catalytic converters staggered under the passenger side floorpan. Most of these systems go into a dual-inlet muffler. Right?

Going to true dual on your truck is easy because the fuel tank is behind the rear axle instead of between the frame rail and driveshaft on the driver side like 4-door Tahoes and pickups.

If it were me, with all the room you have under that truck, I'd go for some Hooker Comps or even Super Comp Long-Tube headers. The Comps have a 2.5" collector which is going to be better for your engine than the Supers which have 3". Even the headers you have are sure to be an improvement over the stock manifolds. You need to keep the pipe size down to Single 3" or Dual 2.25" and no larger. The stock cam needs a little backpressure, so you'd lose torque if you go too big.

Your headers have some type of flange on the collector. They probably do not have the O2 bung in the header if they are shorties. O2 bungs are standard and can be purchased from Summit or Jegs to be welded into a custom exhaust. From the downpipes I would go straight into a cat, each side. Directly after the catalytic converters it's a good idead to run a balance pipe. Make it 2" in diameter. The other option is running an X-Pipe underneath and behind the transmission tailshaft housing, but this would require a lot of angles since it would have to rise quickly again to clear the structural crossmember just a short ways rearward. Mufflers will fit on each side forward of the rear axle and aft of the structural crossmember. From there you can dump them or do side exits in the stock location. It's a little bit tight with the fuel tank, axle and frame in the back but even the stock exhaust finds a hole. I've gotten to a point I can't stand looking at exhaust tips any more. Mine have been removed for dumps right now, but I want to build some hidden turndowns right behind the rear bumper like a Caprice. For whatever reason any exposed tips just look like **** to me now - and that's coming from someone who's bought 3 different pairs of $tainless $teel for the same truck tyring to find something that looks good.

Here's a few pics of what I've done for my exhaust, keep in mind forced induction needs a lot more flow, hence the dual 3" plumbing:













Here's a friendly work of advice about Magnaflow:
- I love their mufflers, they sounds and flow great.
- Their Catalytic Converters, however, are JUNK. They break up and fail.

Re-use the stock converters if they are still in good shape. Just hack them off and weld them into your new system. I am back to running my stock cats now based on the expensive lesson learned with Magnaflow cats.

Here's a pic from the converter swap I did three weeks ago:


Hope this helps.

99kon

iTrader: (6)

Thanks alot James.
That exhaust looks real good. You are right about the dual inlet muffler, and the gas tank in between the rails ( I love that but hate the muffler). What if just tapped the headers and weld the egr pipe on there? That would work right. I am planning to put a cam in, nothing radical. Something that won't need more than 1500 to 2000 stall, i really dont want to get into the motor to much other than the cam. I guess all iwant to do is all the bolt ons and the cam with the custom tune (any recomendations). Will cams from camaro or corvette with the 5.7L motor worck? Because my cousin has a cam from an89 corvette with the roller lifters. Thanks for all your help

James B.

iTrader: (1)

You need a cam machined for a factory roller block. These are different than aftermarket roller cams. Aftermarket roller cams rely on a timing cover with a cam button to keep the cam from walking forward. The factory rollers have stepper drive snout on the cam and a hardened trust plate that bolts into the block. The timing cover is plastic and cannot have a cam button. (Aftermarket timing sets and covers do not work on the L31 because of the crank position sensor.)

The LT1 and LT4 cams are factory rollers but you have to be carful not to exceed the lift capabilities of the stock Vortec heads. Also, the stock valve spring are good for only 5000RPM maximum. They actually start floating even lower than that. 1.6:1 ratio rocker are a pain on stock heads. Best to stick with 1.5:1 and get the durationn and lift you want with the cam instead of the rockers.

You can tap and put a bung anywhere it's convenient, but I would not recommend putting it in a primary. It needs to be past the collector. As far as EGR, it has a funny fitting. If you can find that, go for it.

99kon

iTrader: (6)

Somebody else had suggested a 208/214 cam. I guess putting in some new springs that can handle the lift would work. Right?

James B.

iTrader: (1)

It's not the springs that limit lift, they limit RPM. Lift is limited by clearance between the valve seals and the retainers.
Changing a cam in these engines must go hand-in-hand with programming or it won't idle right.

litreddevil

iTrader: (4)

THE CRANE 210/224 IS ALL SO GOOD CAME WE HAD THAT IN A 99 X-CAB WITH 3.42 AND A LITTLE TRANS STAR 2200 STALL AND THE SUPER COM HEADERS ALL BOLT ONS
AND WAS RUNNING MID TO HIGH 14.s.I WOULD NOT GET ANY HEADERS WITH BIG THAN 1 1/2 PRIMES THE 3" COLLECTOR IS OK.