BC847

True.

The science of it all it is that all mediums as such have a pressure/temperature map. Ex ~ contain any gas in a sealed vessel. Add heat to it (energy), and you'll see the pressure go up. Remove heat from it, and the pressure goes down.
When we look at EGTs from the standpoint of where the probe is located (pre-turbo versus post-turbo), we typically see an approx 300*F temperature difference. The 300*F represents the energy being converted from heat to actual mechanical work.
You'll also note the shape of the exhaust housing. If we were to unroll the housing so to speak. It'd be in the shape of a trumpet . . . .sorta. Small at the inlet, increasing in size till the outlet. It's there that the exhaust gasses expand. There's a bunch of Chinese math going on, but it's there that the energy transition takes place as far as converting the heat to work.
In that shade of light, it is the pressure that drives the turbine. Said pressure is a result of the heat.


Tuckerdee, as the exhaust gasses emerge from the turbine, they are moving pretty-much like the turbine. In a spiral motion. Centrifical force compels the gasses to emerge in the fashion you describe.
Certainly, leaving the exhaust housing open to the atmosphere would offer the best flow, barring that, we're stuck with the TOP. I suppose adding something like the TAG (turbine air guide) to the outlet would clean up the motion of the flow, but it would be at the expense of increased back pressure. Perhaps there would be subtle benefit in increasing the pipe size gradually as suggested above, but it'd be pricey for the results IMO.

johnny5.9

You bring up a great point about the tuned length exhaust. You're totally right. I simply didn't touch on that because to my knowledge nobody makes a tuned length header for the cummins. I've thought about if there'd be any benefit to a header, not for scavenging (because that also requires a tuned length collector to be really effective) but for reduction in backpressure. If you wrapped it, it would probably transmit heat energy to the turbine very well. But maybe heat would crack it, and it wouldn't be any better than ATS.

BC847

Three inch galvanized ~ http://store.airflo.com/galv3.html

Three inch stainless ~ http://store.airflo.com/ss3.html

BC847

I can't find it now but at least one individual has custom fabricated a stainless, equal length header for his twin set-up. It looked extreamly sweet. Still looking . . . . . .

johnny5.9

I can only imagine how edit that would look when you open the hood. You'd have to lay a towel down to catch the drool from your jealous buddies. LOL

90firstgen

If you don't get it from airflo.com then go to a semi truck parts store or salvage yard. They'll have it there or at least be able to order it in.

whereswaldo250

Hey thanks BC847 and 90firstgen you guys are awsome

Ben

wannadiesel

The turbo is THE main restriction in the exhaust. A header would be a waste of effort. You want those hot exhaust gases getting to the turbine as rapidly (and as warm) as possible. The ATS and HTT manifolds accomplish that very well, and the stocker doesn't do half bad either.

You do want to do everything possible to free up flow after the turbo.

jrussell

Wow, guess I'm in a club of my own!

I posted about this shortly after installing my full 4" kit from Stans. I noticed absolutely no change in EGT's. It sounded a little better and might have added a few HP, but not the EGT reduction others claim or I had hoped to see. Prior to the Stans kit I had a 3" Magna-Flow muffler on the stock system with it cut off just behind the muffler.

BigWaylon

I didn't see much of a drop at all, either...

from stock DP to Stan's 4" DP...no exhaust past the DP either way...

Greg

Fergavs

I did a bunch of other mods while installing my exaust so I can not say how much it helped but I have done quite a few down pipe/exaust swaps at the shop and always notice quicker spooling turbos and lower egts.

flashgordon

Hmmm..... so if you rapped the ex manifold with some thing like, header tape(High temp ) would it makes the turbo more efficient(gain more power) or would it just make it spool faster!

If you weren't turning enough boost to require a waste gate.....would it increase you boost?

if you had a waste gated turbo, would it just come up to boost faster or would there be a HP advantage to it?

What about some sort of heat sink after the down pipe, or on the down pipe? the faster the ex.cool the less restriction there is in the pipe......Right?

johnny5.9

I've always heard that the hotter the exhaust is the faster it exits the system. Remember, the hotter the air the less dense it is so therefore is easier to move. As was mentioned earlier, the temperature difference between turbine in and out is a good indication of what the turbo is doing, however, artificially reducing the outlet temperature is going to do nothing for the turbo's effieciency.

flashgordon

if hot air is easer to move then would it make sense to rap the ex from the turbo alls?

mhuppertz

The best thing would be to coat the exhaust turbine housing and the down pipe with ceramic (like JetHot). The second best thing would be to wrap the housing and downpipe with thermal wrap, but the wrap can cause premature erosion of an uncoated downpipe.