FD Rey

I asked this same question on another thread and I figured I'd make a separate thread. Why does the manifold for the GT35R kits have two wastegates? The reason I ask is because I'm having a local shop build me a kit for a great deal. I'm getting sponsored and I was planing on using my current wastegate (TiAL 38mm). Is it ok to use just one? What could be the advantages/disadvantages of using one/two? I'm sure I can guess you use two to prevent overboosting and whatnot, but I would think just one would do the trick. Thanks.

the_glass_man

iTrader: (2)

Because two is better than one.

FD Rey

Please back up your answer with some explanation. Like I mentioned before, I know two would help with overboosting but I see plenty of kits out there that only use one wastegate. I just don't see why one couldn't work with this kit.

the_glass_man

iTrader: (2)

You've answered your own question.

gfelber

First, some kits offer one, others two.

If your desired base pressure is 15+ PSI, then the smaller 38 mm gate may be fine, i.e., it depends on how much boost you want to run. A bigger gate, assuming correct plumbing) is better for venting more exhaust gas. This is more advantageous for controlling boost/venting exhaust at lower pressures. Two gates offer a similar advantage in that they offer more flow than the largest available single gates (46MM TiAL [yes, I know they offer a 50mm race gate] or 50mm HKS, etc.). Of course, the manifold design/plumbing is a critical factor as well. WG runners placed in suboptimal locations may require a larger gate(s) to control boost. I'm not suggesting that this is a common occurence among the FD vendors who offer single kits, but I've seen at least one that has a problem with wastegate plumbing.

Newer, efficient turbos like the Garrett GTR series typically require less exhaust energy than older units. Thus, controlling boost at lower levels may be more difficult than before. I've personally witnessed manifolds created for T04 turbos that do not work well for 35Rs in this regard.

I've no problem controlling boost with my A-Spec single 46mm TiAL gate at 10 PSI. If you wanted to run less, then dual gates MAY be required, though I've yet to see anyone wanting to run, say, 8 PSI or less on a single.

Gene

FD Rey

I'm planing on running 10psi on low boost, and 15+psi on high boost. Do you think my 38mm Tial would work?

RETed

There's no real reason to HAVE to run dual WG's on a GT35R, since the GT35R is not a divided turbine housing...


-Ted

LT1-7

There are some safety advantages. If one doesn't work, like say it gets stuck closed or one of the hose pops off, the other will still work decreasing the chance of overboosting.

Two 38mm wastegates are more effecient than one 45mm or even 50mm wastegate. Both of them combined will have a larger area of flow resulting in less chance of boost creep.

There are some disadvantages though. Space, two wastegates obviously take up more room than one. And that leads to a harder setup to build

RETed

I dunno if boost creep is an advantage with just one 38mm WG opening.

Um, that's questionable.
Efficiency of the WG(s) are highly dependent on placement and WG pipe angles off the main turbo exhaust manifold pipes.
I think in terms of pure airflow (not expanding hot gases) a single 50mm orifice might flow the same a twin 38mm orifices.
I need to go find that potential airflow formula, but I do remember something about increase in radius is ^4 in (fluid dynamic) flow...?


-Ted

LT1-7

Well, I'd rather have one wg open than none. I think 100% of people here would agree.

RETed

Well, if no WG(s) are working, then the boost will shoot through the roof - I think it'll be obvious on the boost gauge.

Boost creep is a whole nothing matter, and you might or might not catch it on the boost gauge?

I think a single 38mm WG out of a pair might make the boost creep barely noticable?

It's a hard call, but have two of them means you have twice as many chances for a WG to fail.


-Ted

Zero R

iTrader: (1)

Twin 38mm gates will in general not offer more flow than one larger gate 60mm hks gate, there could be chances of this not being true but as Gene stated, you would need some pretty poor flow to the 60mm. I had this little arguement with someone in the past. We were both saying the same thing yet I wasn't being clear enough as I should of been. With two 38mm gates the surface area equals just over 50mm at around 54mm, however (and this is where we were saying the same thing only differently) you will have a much better valve to diaphram ratio and this will offer even better control than the said 60mm gate, confused

With that being said running it on a undivided manifold offers no real benifit as the main reason for doing it on rotary manifolds other than the better control is being truly fully divided.

-Sean

Zero R

iTrader: (1)

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LT1-7

You obviously have never driven in a high hp car than. Yeah, if you driving a 400rwhp, you might be able to catch the boost gauge if it creeps. Try driving in a 500-600rwhp car and keep an eye on the boost gauge. It's hard enough keeping an eye on the road when you're *** is going sideways at over 60mph let alone looking down to make sure you're not over boosting. One 38mm wg might not completely eliminate boost creep, but I'd rather overboost a 15psi tune to 20 psi than 25-30psi.

You could say that. You could also say having two wg means you have twice as much insurance

I'm not arguing there. 60mm gates will outflow twin 38mm for sure. I did my comparing on 45mm and 50mm. But to take full advantage of a 60mm gate, the wg runner must be at least 60mm ID. That is if you want to take full advantage. Most kits I've seen with interchangable wg size keeps the runners the exact same size, they just change the wg. The biggest wg can only flow as much as the point of choke. But yeah if you have the 60mm gate along with the right size runners, that'll more than outflow twin 38mm gates

FD Rey

This thread has gotten good. Finally some educated answers to my questions.

Zero R

iTrader: (1)

Creep and spiking can also have nothing to do with size and be more a issue of wastegate position/location.

DCrosby

Chances of manufacturering flaws are greater with two, since you have 2X the moving parts. And I'm not saying that one is better, just that the reasoning that it will work more reliable is weat at best, since you also set the wastegate controller up for two gates, if one shuts off it'll try to compensate, with the other I suppose by trying to open both, but it all depends on how smart the controller is. My Manual wastegate controller, I'm nor sure how it would handle it, I would immagine it would not be able to let off the pressure or vacuum on one, and therefore increase the opening closing of the valve on the other.... but I'd hate to find out the hard way

RETed

Please, drop the superiority complex and the insinuation down.
I have a customer with a GT3540 (same thing as a GT35R) running an HKS GT 60mm WG.
There are ways to "catch" boost creep or spiking.
We had to do this trying to figure out the stupid Haltech E11 boost control.
We've had NO problems trying to catch runaway boost.

Having a "500-600rwhp" 13B is not something 99.44% of the people on here have experienced.
I'd rather leave that kinda power levels out of a 2 rotor to the "professionals" that are willing to guarantee their work.
I have the humility to say that I would not be comfortable trying to tune a 600hp 13B.



-Ted

Sesshoumaru

iTrader: (1)

https://www.rx7club.com/showthread.p...6&page=1&pp=15

only reason i can see an advantage to two is for a divided manifold like mentioned earlier.

I agree with what Reted said.....what's the point with a gt35r?