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3" cross-over

turbonator

turbonator

Member
Messages
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Location
Lac Superieur, Quebec
hi guys, has anyone ever used a 3" cross-over? i was thinking of making one, but i think it needs special custom flanges that bolt up to the outlets on the manifolds, what do ya'll think?....:)
 
What size are the manifold openings where it bolts up? If they are 2.5 or less, wouldn't 3" be overkill?

I know with my 3" down pipe, the 2.5" cross over barely has clearance on the passenger side anyway. I have to be carefull to ensure the two don't make contact as it is. The fight is the clearance between the cross over, the down pipe and the fender well. I kept hearing a metal clanking noise thinking it was injector lines, injector or worse...nope. Just the two knocking each other around.
 
Paveltolz said:
What size are the manifold openings where it bolts up? If they are 2.5 or less, wouldn't 3" be overkill?

I know with my 3" down pipe, the 2.5" cross over barely has clearance on the passenger side anyway. I have to be carefull to ensure the two don't make contact as it is. The fight is the clearance between the cross over, the down pipe and the fender well. I kept hearing a metal clanking noise thinking it was injector lines, injector or worse...nope. Just the two knocking each other around.
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i think the openings are 2.5" ? i was just wondering if it would flow better, but maybe it is true that the opening is only 2.5" so 3" would be over-kill, as for the D-P hitting, i was already thinking to run the down pipe out side the frame on the pass. side, 3" down 3" exhaust.... to be honest i have never even looked at a 6.5l cross-over and d-p under a truck yet... our first truck is a 6.2l N/A, and the other 2 trucks are custom center mounts..... for our 35004x4 i want to start out with a side mount and change it after to our center mount set-up, when i dig it out of the ashes of our shop...LOL
 
Even though you may have choke points, larger pipe could still be advantageous. I dont believe it is in this case, due to the inefficient nature of running all exahust through the passenger manifold and up into the turbo and back out, all sorts of flow resitrictions and inefficiencies. The donut gaskets are choke points even for the 2.25" pipe. With more preturbo volume spooling and holding drive pressures could be impacted.
 
buddy said:
Even though you may have choke points, larger pipe could still be advantageous. I dont believe it is in this case, due to the inefficient nature of running all exahust through the passenger manifold and up into the turbo and back out, all sorts of flow resitrictions and inefficiencies. The donut gaskets are choke points even for the 2.25" pipe. With more preturbo volume spooling and holding drive pressures could be impacted.
Click to expand...

Yes I would think that the larger diameter would lower the exhaust pressure and thus impact turbo spooling. From turbo back, bigger is better.
 
3 inch pipe also has larger surface area. It's possible that this would cause you to lose some heat energy in the exhaust that would normally be exerted on the turbine wheel.
 
I'm planning on trying different sizes,starting with stock size and going smaller for better spool up. Probably wouldn't hurt to put a drive pressure gauge on both banks,to make sure it don't get off balance with rpms ?
 
If someone was to make fully custom headers and wrap it up would a 3in crossover be worth the effort then? Just thinking out loud....

I would also like to combine the 2 banks differently and not have the driverside coming in at the #8 hole. Possibly a Y under the turbo? But then there is the space issue.
 
no i dont think so. theres guys with cummins and dmax headers running a lot smaller diameter pipe and making big horespower. but i dont know anything about thermodynamics so i really dont know for sure
 
That is a good point, I don't know what size pipe d-max or a p-choke uses. I don't know that a cummins needs a crossover pipe being an inline engine but i'm not an expert on them, I know my neighbor doesn't run factory manifolds though.
 
Small restriction into a big pipe then forced through a small straw restriction on the other end of the pipe... You are loosing with having to re compress and speed up the exhaust when it hits the restriction on the end of the crossover. The restriction can also reflect pulses back down the pipe.

The only way to be sure is dyno it.

Then change things like custom doughnuts and other restriction removal tests.

I have not had luck with the header wrapping staying on the crossover. The wrap falls off easy even with stainless straps. Possible a better job could keep it on or less furry things going bump on a dark road... It is worth it for keeping the turbo drive energy and general exhaust hot and up to speed.

In any case I imagine you have a budget to stick too...
 
Matt Bachand said:
Guess its possible you'd have lower EGT's too then :)
Click to expand...

EGT being lost inside the crossover pipe won't help your engine any in the grand scheme. You want to get it out and away from your engine. In that regard, the larger pipe is better. However, you want to hold on to heat as it makes a big difference in spooling turbos. I have a 2.5" CO pipe and i definetly wouldn't go any bigger. Mine doesn't start really building boost til 16 or 1700 rpm. IMHO, a good mandrel bent 2.25" CO would probably be just as good for flow and not lose as much heat and DP. It's only 4 cylinders worth of exhaust going through it.
 
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