Got tired of no good options for exhaust on my 2000 K3500 CCLB 7.4L truck. Previous owner hacked it up pretty good. Gonna use factory down pipes since they are 3" until I get long tubes...need suggestions on that too.
Diamond Eye single 4" turbo back exhaust. Going to cut off the downpipe socket and use a 3-4 merge. Brackets and hangers all look good to go. Will update tomorrow when I get it hooked up. (3" Turbo downpipe not pictured)
You must be registered for see images attach
Dave
In reference to your comments on headers, I opted for the Gibson "shorty" kit. Why shorty? I have read more negative stories about getting full long tubes all set up in a 4x4 than my comfort level accommodates. Also for me its emissions, the Gibson units have C.A.R.B. #. Will they give up TQ from off idle to the engines TQ peak when compared against a long tube?, yes that is likely, but the question then comes down to how much? Will they give up HP from the TQ peak till redline?, the data out there suggests not enough to be concerned about, single digit numbers. I have read through many header dyno comparisons and what I consider be to the best comparison for a big block with apples to apples comparison linked below, however the cam in the comparison is huge relatively speaking to what a L29 might run. I am no scientist and certainly no expert, but if you run the numbers in that article through a spreadsheet, on average the shorties gave up 17 ft lbs vs the same size 1-3/4 primary long tube from where the cam started until peak TQ, the rest of the headers were huge primaries and made more TQ but unlikely units we would ever shop for, basically race headers, and nothing you could find off shelf for L29 truck application. Now an average # ultimately masks the highs and lows, and that being said there was a 500 rpm band range where the long tubes made 30 ft lbs greater that the shorty, which is pretty dang big right?, or if you break it down in alternate terms it is a 6% increase of an average value of 475ft lbs, but where would that lie in our world and much different RPM band? If you back in to the slope of the chart the data suggests it very well might fall right where our cruise rpm is depending on whether you have 3.73 or 4.1 and whether you tow in 3rd or 4th gear, so it starts to get skewed far as real world usability is concerned, again the gain was 6% of nearly 500ft lbs. Now for me, if that data isnt confusing enough, we now consider that dyno session was performed on a true dual ultra high flow exhaust with no cross over pipe involved. In our world we are running what is advertised as a higher end scavenging y-collector, the flowmaster product. Maybe this scavenging effect will lend itself to evening up the low end loss of the short tube headers, or maybe it is irrelevant, I dont know. Its ultimately hard to say or prove without a controlled test environment. Just speculation.
Here is what i do know. For my application I have 3.73 gears and tow a max of 11,000lbs with a ton of wind resistance in 3rd gear at 2700ish RPM, and that is real deal with my bumper pull tow hauler hitched up. Running 2700rpm in full factory trim with 130,000 miles i had no real issue on flat interstate hauling that load, sure I dont pass a gas station at 2700rpm but I tow for recreation. Pulling my boat or RZR at 3500-4000lbs doesnt break a sweat and I tow in 4th, over drive, 4l80e. I live in Arizona and I also pull from elevation starting at 1,200ft climbing up to 7,000ft and I will say that running 6% grade for a 2,000ft dead rise that the L29 just bogs and dogs and kills my factory L29 configuration to where parsing hairs over headers will be of no consequence when the toy hauler is hitched up, but in all reality that is a few and far between like a once or twice a year event, but we still get to the top of the mountains, change load to pulling my boat or RZR at 3500-4000lbs with nominal wind resistance in grade and no real issue as it just runs good enough above factory peak TQ 3200rpm, but becomes totally gutless above 4,000rpm due to smog cam and castrated factory tune and factory exhaust. Now that being said, the extra TQ from the long tubes below the TQ peak are meaningless when a gas motor pulls grade as the motor needs to be in in max power pulling rpm band above the TQ peak where the data suggests the header power difference is insignificant . The data suggests the improved TQ from long tubes will be of benefit at cruise RPM almost exclusively. Now for a small block that cruise RPM benefit might be huge or if I was pulling weight well over factory limit for a living, but for me I have a 454 Suburban and will not be hitching up a ton of weight over and above the factory max rating and it already performed satisfactory on flat interstate in cruise from the factory in stock trim, which in all reality stock trim just sucks.
SO MY THEORY OF IGNORANCE is as follows, the Gibson shorty setup includes a fantastic mandrel bent full 3inch "crossover and connection down pipe" setup in the box. That will then dump into the dual 3inch in and single 4 inch out high end flowmaster y-pipe to the 4inch mandrel bent diamond eye exhaust and give me a great benefit right where I need it when pulling above the peak TQ rpm when I am pulling in the power band in mountain grade. Alot of internet bench technicians also like to comment on how a huge exhaust will give up low rpm TQ and driveability? I dont know and can not comment on that, maybe it will...? I just cant imagine though that the setup I will be running will be worse at cruise rpm then the factory which adequately hauls my loads. Science does however prove that temperature of the exhaust with that single 4 inch exhaust will be so dramatically lower when pulling in power band than with smaller dual factory 2.25 pipe that there will be nothing but additional benefit of keeping the engine cool and reducing knock retard in the ecm.
Frankly I dont really know whats best either way as this is the first BBC I have ever invested $$$ in. I have already bought the headers, Summit had a sale of 10% off and a factory rebate of 75$, so I was pleased and assumed I could pipe it through the factory duals and upgrade the muffler. The more i laid under the truck the factory setup became garbage and Google then led me to your thread here, THANK YOU. As a note I am building this exhaust as a necessary requirement to the motor that I just built for this truck, nothing wild, .020 over on my factory bock and decked, L29 heads milled and rebuilt with performance valve job, mild porting, and adjustable Comp valve train, Comp 212/218 cam, ported L29 intake, upgraded fuel system, and BlackBear tune.
My end goal is POWER when pulling grade at 3500-4000rpm, I purchased my Gibson Headers with that in mind but did not sacrifice my goal just for ease of install, I hope it all plays out well.
https://www.hotrod.com/articles/headers-dyno-test/
View media item 31703View media item 31704View media item 31705
