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X-Over Pipe on 6.5td

FellowTraveler

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Thread starter #1
I've been digging into the benefits or lack thereof a larger diameter x-over pipe I run a 2.25" flowmaster and have not found any real information on gains from a larger diameter x-over pipe.

According to Corkey bell 2" can flow 300 cfm in a N/A application and up to 500 cfm boosted application so I suspect the velocity loss of larger diameter x-over must be considered when running a non-gated turbine in that the max cfm flow for any given 6.5td divided in half along with drive pressure indicates 2" is all that is needed for most 6.5td x-over's then 2.25" for a highly modded 6.5td.

So a properly sized x-over on a 6.5td running a non-gated turbine housing we should see the benefit of faster spooling using 16/18 or larger cm2 units.

Input and thoughts are welcome.
 

Will L.

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#2
The only way I can think of to figure the best size is use of flow meter and pressure sensor on the turbo side manifold output, then match the flow and pressure through swapping sizes and testing output of crossover to match.

The you need to compare pressure advantages vs lower restricted flow into the turbo. Then there is the whole heat loss thing, which still puzzles me. And it all changes slightly with different turbos.

Hopefully the research has already been done somewhere. I think that's a big reason so many twin turbos are used when power is more desired than low input costs. Perfect balance and flow, minimal heat loss, etc.

If I could have figured how to protect twins under my truck with the off roaring and water crossing I do, that's what I would have done.
 

FellowTraveler

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I'm thinking the big factor is that the GM IDI 6.5td can't take much boost as compared to more modern diesels so if my thoughts are correct it's flow is limited to an average +- 40 lbs of air flow however Heath has made +- 500 hp w/his land speed truck and that would equate to around +- 50 lbs of total air flow out of twins using the calculation of 1 lb of air for every 10 hp.

Will L.; I suspect the best setup for you would be a blower which would pump way more air than a turbo at much lower boost levels so latent heat would not be an issue w/water crossings as you know parasitic loss is there but I've seen some interesting blower installs on 6.5's down under and in other places around the globe.

I'm still mining for any information of research that has been done w/x-overs on 6.5td's.
 

WarWagon

Well it hits on 7 of 8...
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#4
One look at the mess of the passenger side manifold flowing 90 across to exhaust ports... Well the crossover losses/gains are lost in that mess. Just saying fix the big airflow issues before looking for the small gains.
 

FellowTraveler

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One look at the mess of the passenger side manifold flowing 90 across to exhaust ports... Well the crossover losses/gains are lost in that mess. Just saying fix the big airflow issues before looking for the small gains.
So true, that choking point issue GM designed into it what do think % of loss really is there?
 

Will L.

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#6
When I turned my hummer from n/a to turbo, I put on the turbo, but did not turn up the ip yet. I did not have enough fuel to light the turbo, but noticed going up a hill I do all the time the engine got to 215 in the same time it used to get to 210. After fuel increase it only gets to 205-207 in the same location.

It was also slower accelerating as well until I turned up the fuel. All from the exhaust restriction.
 
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