HOHN

OK fellas, some questions on how to setup an external gate:

-- Can I weld the V-band flange to the cast iron manifold? I was thinking I could torch weld it and it would turn out better than with a MIG. TIG I don't have access to, so that's not really an option unless I can talk someone into trying it with TIG. Can you weld dissimilar metal to cast iron with decent results? Maybe brazing is more appropriate?

-- Any problems with weld cracking on the external gate meeting the manifold? How sturdy are those flanges?

-- Anyone have any experience with the new 60mm Tial? Looks like a great piece for a CTD twins application where you are gonna bypass a LOT of hot gas around the small charger.

Thanks-- my brainstorming is continuing.

jh

2500superram

i've seen it a few times.the weld didn't look to good on either of them.maybe you could bore out the mani enough to insert the pipe.then possibly weld it on the inside for a little more strength.
i've also seen people remove the internal gate and mount it on the flange that exit's the turbine.kinda of like a divorced down pipe.the only problem with that is the restriction in the turbine housing,which has been known to cause boost creep.the whole reason for external over internal is to have better control over the boost spike's
i run a 44mm tial on my supra,nice quality gate.

HOHN

I've looked at all the different "divorced" downpipes for the internal wg holsets. None of them will fix boost creep because none of them can bypass enough flow.

I figure that the WG has to flow as much as the small charger's housing, maybe even double that. Hence, I think the external gate should be very large, and that leads me to the 60mm Tial.

I don't think a basic butt weld of the V-band flange to the manifold would be strong enough to do what I want.

But if I had a short section of tubing in there, I could lap weld the tube to the manifold, then the flange to the tube AND manifold, I think it would be stronger.

Idaho CTD

I have welded tubing to manifolds with both the tig and mig. You need a lot of penetration with either method. The make both mig and tig wire for welding mild steel to cast. Make sure the cast is clean and it's best to heat it before and find a way to cool it slowly if possible.

For big wastegates I would look to a JGS. It uses a piston ring type of seal instead of the diaphrams the Tials use. Their 50mm is massive and uses a billet SS base. They are set up for 2" pipe and v-band connections like the Tial 44's.

HOHN

Thanks, Nathan.

I only wish I had the $$ to just call you up and spec the BB instead of dreaming up ways to pull off the system of my dreams with little to no experience or skill.

jh

2500superram

i don't really know much about diesel yet.on a turbo gasser you use a big wastegate to run less boost,smaller can be used for more boost.then the wastegate spring would need to be sized right.
i don't think you could weld the v-band flange to the manifold.you wouldn't have enough room for the clamp.you would deffinatly need a peice of pipe.

Idaho CTD

You could weld it directly with one exception. The curves of the manifold need to be compensated for. So what ever you are welding to it needs to be contoured. With a big v-band there isn't enough meat below the clamp for that. The JGS gates have about 1/4" of the flange below the clamp but you'd probably need closer to 1/2" or 3/4" to compensate for the curves. You could always weld additional steel to the flange to use for contouring before welding the flange to the manifold.


Justin,

One good thing about Garrett is they are making BB center cartridges without the water cooling now. It knocks about 50% off of the cost difference between the TB and water cooled BB. The water cooling is only really good to prevent coking of the bearings. It you cool them off well before shut down there is no need for water cooling.

cyric

I think BigBlue was running a similar setup with his old turbo. I have seen pictures of it on here. My only question is won't you only be gating 3 cylinders with this setup? I don't think there would be room to center up the gate over the center divider in order to gate all 6 cylinders. When I was researching my twins I found alot of info on using to big a gate. If the gate is to big it is constantly opening and closing almost a like a shuddering. I am by no means trying to discourage you from this just thought I woulod toss that out there for you to consider. I must give you Kudos for always thining outside the box Justin. (Even though I have to reread your posts 3 or 4 times to absorb what you are saying) I hope this helps
Joe

HOHN

Thanks, Cyric. Your post on fabbing twins is really inspiring me!

An external gate can do all 6 cylinders, but the manifold will have to have the hole drille on center and have the divider cut down.

I'd anticipate having a machine shop mill a flat area just before the exit flange, then welding the gate flange to that machined flat.


As for gate fluttering, this is a real concern. It has a lot to do with how progressive the gate's opening is. This is why most wastegates use a spring and they actually crack open well before that actual boost limit. In other words, when set to limit boost to, say, 30psi, they might start bleeding off gas at 20-22 psi or so. They don't bleed off enough to stop the boost from rising until they hit that 30psi spec.

With a very large gate and a soft spring, it's possible that even if the gate just cracks a little, it still bleeds off so much pressure so fast that boost comes crashing down and then you set yourself up for a flutter scenario.

This leads me to the idea of a "bypass ratio" for a twins setup with an external gate. In other words, you need to figure out what percentage of the gas flow is going out the gate versus through the small turbo's turbine. There are two variables here: wastegate size and spring tension. Unfortunately, the spring assortment with many gates isn't as good as you'd like, and you're limited to the highest spring tension they sell.

This ratio is also going to change as boost levels rise. For example, you'll start at very low boost with the small turbo making all the boost, and the external gate is closed. Your "bypass ratio" is zero, because there's no bypass happening.

At some boost level, the WG starts to crack, and you start bypassing gas flow around the small turbine and directly to the big turbine.

As boost climbs, you hit a point where the wastegate is wide open. This is your final "bypass ratio" and it's determined by wastegate size relative to the turbine size (both wheel and housing A/R).


So the the spring tension determines WHERE the transition happens as far as boost pressures. But the size of the gate determines HOW MUCH transition occurs.

This is also related to turbo choice and relative sizing. If there's a big difference in turbo size, then the WG will have to bypass a lot more. The twins setup ends up resembling a "sequential" turbo setup more than a "compound" setup because the big charger ends up seeing more workload.

Say I want to build a twins setup with lightning fast spoolup and I only need the airflow that a turbo like a Silver bullet 66 would give at my hp level, but I don't want the lag. I could run a small turbo (HY35 or smaller) and a massively huge WG that would bypass up to 75% of the flow to the SB as a primary. The pressure ratios would reflect this, as I might be running the silver bullet at a 4:1 PR, and the little turbo at only 2:1 or less. This is more of a "sequential setup".

But in a "compound" setup, I want the small one staying in the game a little longer. Hence the "bypass ratio" will be a little lower, and the gate should be smaller. In this scenario, the difference between the turbos is not as substantial, and the small charger's hot side can flow a lot more. Instead of having a handoff from the small turbo to the big one, what we are going for here is essentially one big turbo, with two stages of compression. Thus, in this type of setup, you'd want to run a larger A/R and hot side on the small turbo, so that hopefully your primary and secondary would spool fairly close to each other.

In fact, I think with a setup like this you could probably get by with just the internal gate on the top charger (assuming it's high flow, like the HTT turbos) because you're not bypassing nearly as much flow.

An example of a setup like this would be an HTT 62/71/16ss over a B2 or S400 type of bottom turbo with a fairly tight housing. Note the large 16cm housing on the top charger.

From what I can gather, this is how the BD twins are setup. The turbos are both S300 variants, and fairly close in size to each other. They are more like one large, two-stage, compressor. In a setup like this, you give up a certain measure of spoolup in favor of efficiency.

As a general rule, it's more efficient to enlarge a housing and have more flow go through it then to have a small one and bypass a bunch of flow. All the flow that's bypassed doesn't do any work on the small turbo-- just the big one.

If you were seeking max efficiency, the twins would would probably only need a WG on the big turbo, and only to limit peak boost. This is more appropriate than putting the hot water pressure relief valves in the crosstubes as is commonly done.

So even with twins, you have a similar compromise as you would with regular turbos-- you can have spoolup, or you have efficiency, but not both.


..at least until we get VGT!!

R.T.D.H.S.P.

It can be welded with a TIG fueled by Argon with wire with no internal flux. This gives better penetration as well as a prettier weld. JMO

HOHN

Sweet! Now I just need to spend lotsa money on a TIG machine, teach myself to use it, and get my garage re-wired for 220.

Since I don't even have a garage, I'm guessing this might be awhile

Anyone wanna teach me to weld?

cyric

Glad I could inspire you. I think I even understand your post on sizing the wastegate. I have to agree the spring selection out ther for these gates leaves alot to be desired. I haven't put the external gate on my primary yet. I have a 50mm but the heaviest spring I have is 12lbs. I am going to use a boost controller and hope the drive pressure doesn't blow the gate open. I am hoping that opening up the gate on the 35 to 38 mm and allowing it to open farther will bleed of enough pressure on the secondary. Keep the good information coming.
Joe

XLR8R

Justin, you can buy an inverter-based TIG for less than $1K; it will be easier to use and produce better welds than any other process.

HOHN

What would an example of such a machine be? All I've looked at were the Lincoln and Miller TIGs in the 175 range. 175 is more than enough for the kind of work I'd want to do.

Justin

Idaho CTD

Something like this is what I think they are talking about. A econo tig is another cheaper tig welder.

http://cgi.ebay.com/MILLER-907135-MA...QQcmdZViewItem