TIMINATOR

I've got a 2002 2500HD 8.1, extended cab short bed GMC. Mods so far have been minor: K&N air element, 4" tailpipe after the muffler (keeping the stock 2 into 1 mini collector and opening it to 4"), Flashpack tuner(which makes the truck run like it should have from the factory). For the next go around I have the Stainlessworks 1 7/8" diameter, long tube headers ready to install, and since I own a machineshop, I will bore and flow the throttle body too. AFTER I quantify the headers impact. In all of my years of experience I have noted that a crossover about 16"-18" after the collectors raises the torque and HP output. Has anybody done this with the SSW headers and the 8.1? My plan is to stagger the x-over to keep the collector lengths closer to the same length. If no-one has any input on the x-over deal, I will do the headers first, then do the x-over. After that will be a cam or at least 1.8 rockers. Also, with the stock muffler, the one pipe has very little exhaust flow from it. Anybody drill the inside baffle? or have a pic of one of these mufflers cut apart? or got one laying around the Phx,Az. area that I can cut apart? I will, lacking any feedback, put the muffler on the flowbench and modify accordingly, as this truck is too quiet to begin with! or, install my favorites: a pair of the 3" long body Dynomax Super Turbo mufflers. But I like to modify parts rather than purchase new, and Dyno max does list the free flow CFM and HP ratings so I have a comparison there. My Nova Ran 9.68@141mph with those 3" inlets reduced down from a 3 1/2" collector and x-over. So I know that those work! Thanks for any info! TIMINATOR

Vortec350ss

iTrader: (20)

I'll be excited to see your results! We have a few 8.1 members on here, but they arent nearly as present as the LSx based trucks.

My understanding is that the intake manifold is a fairly large restriction on these.

TIMINATOR

Headers should go on this week. I'll keep posting the results. Timinator

TIMINATOR

As promised, here is the latest on the header install: Vehicle: 2002 GMC Sierra 2500 HD short bed, extended cab, 8.1 engine, and Allison 5 speed automatic trans.

All of the bolts supplied to secure headers to head are too long, and bottom out before tightening the flange to the head, being metric, they are not readily available. Solution: Shorten by 1/8" or use two AN washers under each for spacing.
No header gaskets supplied, Really? on a $920.00 set of headers? Round 2 1/8" inch hole size high temp gaskets for a regular BB Chevy 454 work best.
No EGR tube flange gasket, it is required in all installs and is a dealer only item. See above.
No upper exhaust pipe flange gasket included, and it will be needed since you have to remove this tube to shorten it.
Need to cut out the pre-cats and lengthen the head pipes accordingly, see above. The instructions make no mention of these pre-cats, and the factory has "never seen them" We sent them pics.
O2 sensor extension cables were supplied incorrectly for my truck application, we sent pics to the factory of my plug and their cables, "we have never run across that type of plug in issue either" was their only reply.
EGR supply tube flange is about 4-5" away from where it is located on the stock manifold and because of this the factory Stainless steel EGR tube can just BARELY be finessed to work. Use care, these tubes aren't cheap, nor are they stocked by anyone that we called!
Header/collector diameter is 2 7/8", factory exhaust pipes are 3", and in our application a standard "U" clamp or a stepped wrap around style clamp would have worked better. Non-stepped clamps were supplied. We welded thick 3 bolt flanges to the headers and head pipes as our solution.
The above are facts, the below is my opinion!
Pluses: good quality headers, quality welding, good design, good performance.
Minuses: Poor packaging (cosmetic damage in transit), I feel that the required gaskets should be supplied in the kit. I was disappointed that the factory didn't do more homework on possible vehicle variations or fitment issues. I was also disappointed that I never received any return calls regarding resolution of the incorrect O2 extensions.

I will post the results of the next batch of planned mods: Porting the factory throttle body, mods to the air box, mods to the air inlet tube. These will be accompanied by flow bench figures of the foregoing, and of the factory Mass airflow sensor.
TIMINATOR

DEWFPO

Thanks for the update.

DEWFPO

TIMINATOR

When I write for the magazines I keep everything as objective as possible, I will do no less here.
I flowed the throttle body, air tube and MAF. The airflow was significantly improved by porting the throttle body. BUT the inlet tube flows less than the throttle body now, so no gains there yet, although once I minimize the flat spot in the tube I expect the airflow will exceed the body again. My MAF flows about 15% less than the body did before the mods, even less now. I will try to remove the honeycomb inlet screen and see if the airflow is up to what the body now flows. We did that on many vettes, Camaros, and GNs before there were aftermarket MAFs available with no ill effects. I also did a bunch of work to the airbox and the feed holes to the airbox in the inner fender with good results. I'll report on the next go around. Meanwhile, IMHO I believe that to get the most "bang for the buck" on the cam, headers and intake manifold replacement (BIG BUCKS THERE!!!) one should do chip replacement first, then everything from the inner fender up to and including the throttle body next. Then the headers. You won't believe its the same engine! TIMINATOR "Modesty is a crutch for the incompetent!"

Raylar Engineering

You'll get good power gains from a camshaft swap (hp/trq depends on duration) and a bit more with a modified manifold (+20hp/0ft-lbs).

Here's a dyno of our 8.1L 540 stroker kit with ported iron heads, 203 cam with iron head spring kit, modified manifold and jba headers. You can see that even with our hot rod cam and extensive porting, stock heads won't let you make power past 4500.

Then we added our aluminum cylinder heads added to the mix. You can see just how much the stock iron heads are restricting breathing. I should probably note that this dyno isn't truly representative of our stage 2 540 kit as this engine is running a low lift camshaft (.530) and all of our stroker kits have the high lift 205 camshaft as the pistons have valve reliefs. You'll pick up another 20hp with a .600+ lift cam like the 205.

TIMINATOR

In the latest go-round, I flowed the air feed tube and found that if I taped over the hole to the Helmholtz resonator hanging below it, I gained about 40+ CFM. I then took about an hour and heated the air tube and removed the divot for shroud clearance, and gained about 60 CFM. Then I tested the airflow again after the divot was removed from the tube, but with and without the resonator taped over again. This time the airflow remained nearly the same. Apparently removing the divot changes the airflow pattern in the tube and makes the resonator less of an issue. BUT removing the resonator allows the truck to have a nice (to me anyway,) intake growl! It sounds good! Kinda like a 60s/ 70s muscle car! The not yet quantified, effect of the removal of the divot and resonator is not in the amount of raw airflow gain, but in the reduced swirl in the exit of the air from the tube. I found that out only after porting and reinstalling the throttle body. I will flow them together in the future. But this much is certain, if the flow from the tube is more laminar, and not tumbling/swirling it will be easier for the air to flow thru the throttle body and there will be more net flow. This is partially because the throttle blade acts as an air straightener and thus impedes the tumbling airflow by trying to straighten it. This better quality airflow will also act to speed the airflow in the manifold plenum feed tube behind the throttle body and into the main plenum. Next, I need to check the fuel pressure at the fuel rail while at RPM to make sure I have enough fuel volume/ pressure to the injectors. I also never meant that a cam and intake mods wouldn't make more power, but that the near free backyard gains would enhance the gains of the cam/intake when done. I want to see/report what and where the cheap gains are for the peeps that can't afford the good stuff. I have talked to one of the tech guys at Granatelli Motorsports at length about the restriction in the Mass airflow sensor and what to do about it. The MAF is still a MAJOR restriction in the intake air tract! It is so bad that when flowing the airtube and bellows, when the MAF is added to the end, the airflow will completely suck the bellows collapsed against the tube! GMS sells a recalibrated MAF with a higher top end airflow reading capability, and that will help the fuel flow curve, but not the raw airflow. Their 4" high flow MAF seems to be the ticket, but REQUIRES dyno calibration, as the unit is shipped with no calibration whatsoever. I will replace the muffler next, as it is a two 3" inlet into one 3" outlet unit. The other "outlet" seems to go to a resonator chamber only. The Magnaflow dual 3" in and one 4" outlet unit was just what we needed, (I thought,) until in research I found that it has ONLY 2 1/2" cores! I am setting up the exhaust with flanges so I can replace the muffler while on the chassis dyno, and will obtain the large uncalibrated MAF to do the same. TIMINATOR

TIMINATOR

Re: Nelson tuning. "Computer will be "locked", and can be unlocked at any time but will only have the "stock" tune." Does this mean that if I want to dyno or seat of the pants dyno compare what they did for $375.00 that I will lose my $375.00 tune? I am constantly in the process of upgrading everything that I own, and that sounds like a bad deal to me. Anybody have their stuff? What results? Did you make any more changes to your rig after the tune? TIMINATOR

Raylar Engineering

You might just want to remove your existing MAF, cut a hole in your intake tube and run an LS7 MAF. This will require dyno tuning to tell the computer that you have a different style of MAF, but its $80 for the LS7 MAF, not $310.