Exhaust size???

[Wolfe]

right its about volume not flow speed

[Wally]

Originally Posted by efdup_booby_job

i see where your coming from... although ive owned two previous turbo'd applications im more familiar with n/a engines. with an n/a engine the smallest point on the system is the choke point so the whole system might as well be the same size (before the choke point that is...) so thats why i said the exhaust inlet size should be relative to the pipe size. i failed to mention i meant between the turbo and the engine.
that would create velocity up to the turbo then the dramatic pressure drop from the smaller diameter pre-turbo to the larger after would spool faster per what wally said?

this is how i understand it now so am i right? please correct me if im still dim the the head, lol. im doing a custom remote build on my 02 blazer (starting at 6 psi and moving up from there) so id really like to make sure i understand the dynamics before i mount this thing

The two biggest gains on any stock turbo engine are:
1: larger throttle body
2. larger dump pipe

While it seems to be common sense that the velocity of the gas into the turbine will make it spin faster, the fact is that the work done by the turbine relies on upstream pressure being a high as possible and the downstream as low as possible. If the exhaust runners are too small they will impose a pressure drop and thus lower the upstream pressure: in your own words the runners will choke the supply and take authority over the flow, rather than the turbine.

It is the job of the infuser to accelerate the gas into the turbine inducer, not the exhaust runners. Likewise it is the job of the diffuser to make sure the gas exits the turbine exducer in an orderly fashion not the dump pipe.

When you select a turbocharger there is more to the process than looking at a compressor map. The backend also needs to be selected and this is where you calculate the expansion ratio (ER). In essence you make an educated guess on what net pressure drop you expect to encounter.

[efdup_booby_job]

sweet, i understand... now my setup will be an almost stock 4.3 vortec in my 02 blazer. relevant upgrades include 22lb/hr @ 48psi injectors, turned up to about 55psi to emulate a 26lb/hr injector (give or take), underdrive pulleys, k&n cool air intake (for now), wait4me performance pcm (by jesse bubb, Warsaw, IN), magnaflo 2 1/2" w/turndown (for now), tps sensor adjusted for a higher fuel curve at wot, for pics go to
Myspace.com - efdup booby job Photo Albums

and click my truck or turbo build. will update soon. sorry i have no engine pics or wheel tub pics. like i said, ill update them.

the turbo is a little overkill for now but its a starting point since i got it free. it supposedly makes (on a 404ci bigblock, lol) 45psi @2300rpm so im thinking it might be able to make (given that i have a 262ci sb) either 22psi @2300rpm or 45 psi @ 4600rpm...

my downpipes (y-pipes on a v-6) are 2" from manifold to collector and from the collector through the cat to the muffler is 3", id like to put a 2 1/2" y-pipe on it and leave the 3" pipe through to the turbo then maybe a 3 1/2" (size decided after reading this thread) turndown or exhaust out the side before the rear tire.

sorry if this post is like a mile long.

[ebxr8240]

If turbo is spit pulse ? One side can be slightly restricted which actually reduces your A.R.. I may have to make a flapper system like intergrated wastegate on my Celica 1UZ turbo project to quicken spool..

[efdup_booby_job]

hmm, thats the first time ive heard of a split pulse system, maybe ive heard of it but it was refered to as a savaging header setup. the runners are made so that each cylinder gets its own turn to expel exhaust so it creates a savaging effect or by the exhaust further down the pipes "pulling" the burnt gas out of the cylinder instead of the piston pushing it out. thats not exactly how it works but you get the idea. it makes the engine think its bigger than it actually is.

i can understand how this would be beneficial to an N/A engine but might decrease back pressure in a turbocharged setup.

but im still not sure what exactly makes a split pulse turbo what it is... i have a split inlet on my turbine housing... is that what your talking about?

[Wally]

I think he meant to say siamese (dual inlet) turbine housing. I think you knew that too.

[ebxr8240]

Yep on split palse, dual tang.. Restrict one side and your effectively halving turbo's A.R... While manifold is under pressure or boost.. The N/A scavenge theory doesn't really come into play.. Just good flow. In most cases the exhaust size from head to turbo can be smaller than N/A..
My V8 has 1 1/4 primaries where when it was N/A they where 1 5/8..
But after the turbo the dump pipes and exhaust need to be much bigger..
I could be absolutely silly and run 6" dump pipes and not loose any power on turbo engine...
Smaller primeries help turbo spool, effectivley letting the gasses EXPAND in turbine.. Which is where the turbo has an advantage over supercharger.. It helps burn the fuel twice..

[efdup_booby_job]

so by blocking one side of the inlet its like putting a spray nozzle on a garden hose? velocity over volume... so you think my 3" head pipe to the turbo then a 3.5" dump pipe is acceptable?

[ebxr8240]

Originally Posted by efdup_booby_job

so by blocking one side of the inlet its like putting a spray nozzle on a garden hose? velocity over volume... so you think my 3" head pipe to the turbo then a 3.5" dump pipe is acceptable?

D
o you have pics etc?? Download on Image hosting, free photo sharing & video sharing at Photobucket and link pics from here..
Give me engine size etc..
On a 5.4 V8 I'm runing 1 1/4 primeries as said into 2" just before turbo's..
I don't require a crossover pipe as I have twin turbo..

If I did have a single turbo?? I would have a 2" crossover again letting exhaust expand in turbo [there are two of them remember?] ..
In a high end [power wise] I would run a 2 1/2" but for street use and the odd strip use its not worth it..
If engine is over 400ci ?? Then bigger size is required.. There is not much point in having pre turbo exhaust too much larger than turbo flange..
What would be fabricated for std early Supra engine for example would be quite different to 2JGTE engine as well..

[efdup_booby_job]

well ive got a 4.3l vortec (262ci) with a Schwitzer 3LM-39 (overkill i know but a free place to start). from the manifolds there is a 2" downpipe to a collector before the cat. it then opens up to 3" up to the muff. the muff i installed is a magnaflo 2.5" (but that wont matter after the install anyhow)

pics:

the turbine housing during the rebuild...


the turbo after the rebuild...


a pic of the truck its going on...


and the new wheel tubs i installed (if anyone cares)...