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Hey guys, I'm starting to mortified my truck manifolds and building the crossover pipe . I think I've made a mistake. I used 2.5" pipe for the truck manifolds and was going to use the same 2.5" pipe to build the crossover pipe. After reading, most guys are using 2 or 2.25 " piping for the hot side . I don't mind redoing it I just want to do it right. This is for a 5.3,hp goal btw 500 and 650. ill be using a T4 flange
If you want the best spooling combo use 2" pipe to each side of the scroll with 2 38mm gates. Then use 2.5" cold size piping. You can adapt up at the TB and intercooler with a coupler. 650 HP is easily made with smaller diameter pipe. It's also easier to package and you don't need to run a merge. Making 900-1000 hp with a 370" and 2" pipe.
tucks nice and easy behind the oil pan.
Last edited by Forcefed86; 11-25-2016 at 01:16 PM.
My turbo will be placed on the passenger side, so the exhaust will be run thru that side , if I run 2 wastegates I would have to plumb the driver side wastegate from the driver side to the passenger side causing me to have 2 crossover pipes? I'm I thinking this correct ?
Why didn't you just leave the triangular flanges on the manifolds then put a triangular flange on your hot side piping? I see those flanges available at most turbo parts retailers. Space? I personally like the durability of the intact manifold, vs having the welds on it and the thinner exhaust pipe welded to it. If I were going to do that, I'd want to use something like .120 walled stainless pipe in 2 1/2" so the 2 materials I would be welding would be closer in both diameter and thickness? That would still give sufficient interior cross sectional area for adequate flow, and should enhance durability? I would think that will eventually crack with time and heat? How long, who knows? That seems like a lot more work than just using the triangular flanges.
I figured I was doing the right thing after seeing a few pictures here on how guys modify their manifolds . I had to change the angle the passenger manifold was facing to make it work .
I'm sure what you are doing will work, I've just seen it done both ways. I have my triangular flanges on still. I admit I bought a kit, mainly because my fab work is not as pretty as what the kit I bought is. I really do need to weld a few days a week to stay at my best. Right now I weld more like a couple times per month, and when I start a project my welds don't make me happy. As I go along it gets better. About the time I finish, my skills are back to where they should have been when I started a project. I understand needing to do the fab work on something unique, as parts are not readily available. Even doing a kit there is still quite a bit of modification required, for a really nice build. I've some guys with better quality fab work than the kits, but that's more the exception, than the norm.
I'm no expert here but I think that difference would be insignificant under the circumstances. Basically since it is a T4, and HP will be about 800 max looking at the turbo's your considering, either will work well. Possibly a slight advantage to the 2.25, to spool a little faster, but I don't think it will be significant. The longer you run the pipes, the more difference you will see. Shorter piping = less volume = quicker response to engine change(throttle opening or closing). The engine has to fill the hot side before it flows through the turbo, so a larger area to fill takes longer. A 2.5" hot side that is plumbed shorter, so less volume, could spool faster than a longer section of 2.25" pipe. We really are splitting hairs here. I'd just do with the one of those 2 sizes that's easier for you to work with.
What is the advantage in using larger pipe? It's heavier, more expensive, takes up more space, and doesn't work as well.
As mentioned above it's not going to be a crazy dramatic difference between 2.5 and 2". But performance will improve slightly and there's no good reason to go larger with your 500-650hp goals. Less volume helps, more velocity with the smaller piping is the major contributor. The velocity diff between 2" and 2.5" piping is pretty huge.
A 2.5" cross over will support 2300ish HP or so. Doesn't belong on a 500-600hp engine IMO.
Unfortunately when I switched from a 2.5" to a 2" I changed more than just the hotside. (went from a 5.3 to a 6.0) So i don't have an exact comparison. I will say compared to a few friends with 2.5" piping and similar setups, my 2" setup gets up into boost faster on the trans brake.
Last edited by Forcefed86; 11-26-2016 at 08:54 AM.
11-25-2016, 11:10 AM
Truck manifold & crossover pipe . What's to big? 
