Can An external wastegate be too big?

[TTV8RA23]

Im looking at buying a couple of external wastegates for the 1GZ I was wondering if you can go too big? Im looking at 2x 60mm wastegates so thats 1 per 2.5 liter motor basically. Is this too big? I know its wank wank but that is a bit what im after
Any info would be appreciated.
Cheers
Simon

[midnight_purple_GA70]

i would think if you go too big any minimal opening of the gate could release exhaust too quick for your turbo/turbos to produce it... resulting in bleeding boost off

i have always thought gate choice is more related to turbo size rather than engine capacity

i could be completely wrong though...

[Draven]

turbo choice and boost/power goals are important for wastegate choices, but that said going to small is usually a much bigger issue than going too big.

I think anything 48+mm would suit you fine, but a big blingy 60mm gate should have minimal/no impact - just choose the spring correctly and get a good boost controller

[Duk]

If you want/need to be able to run low boost pressure and are using a small A/R ratio turbine housing, then bigger(ish) wastegates will allow more exhaust gas to bypass the turbine wheel(s).
But think of it in terms of, eh hem, 'valve curtain area'. A 60mm 'gate opened only 1mm has 188.5mm squared surface area to bypass the turbine housing. That is the same as having a 15.5mm diameter bypass hole before the turbine wheel. At 2mm it's 377mm square or just under a 22mm diameter, pre-turbine hole.
3mm lift = 565.5mm squared or a pre-turbine 26.8mm diameter hole.
So, do you think that you will have smooth boost pressure behavior with 2 massive (60mm) wastegates on a 5 litre V12? I think you'll find a case of constantly chasing boost pressure, where once the waste gates crack, the boost pressure will drop rather than being maintained. Followed by an increase in boost pressure to the cracking point........ It's your car/engine, but bragging writes may not be all that they are cracked up to be.

[TTV8RA23]

Im not gonna do it just for wank if it has a subverse affect on the performance thats for sure. The turbos are not huge. Should be seeing full boost by 3500 Nissan Skyline Turbo DSR430 360 GEN2 | Trade Me The other option is twin 44mm gates. I have 38s at the moment but am thinking they are gonna be a bit small And i reckon screamers always sound better with a bigger diameter pipe with less velocity so its more of a bark than a scream.
Cheers
Simon

[JustenGT8]

I reckon 38s will be fine at the hp (exhaust gas flow) you'll be making. 44's for a bit more piece of mind wouldn't hurt though. As for the 60mm, you don't need that large but it's more how they are controlled than their total flow capacity.

You need them to open in a fashion that the control of boost isn't faster than the control system can keep up with. As Duk was explaining....if there initial opening allows too much exhaust gas to bypass too quickly, boost will drop before the system can control that rate of drop. What you end up with is a turbo chasing it's tail trying to maintain the set boost level.

The initial install of my 44mm gate on the 3SGTE did exactly this. I was stuffed for room and didn't use the bevel plate that seats the WG valve...i just used a thinner flat shim. When the gate cracked at all, the initial opening was large, causing the turbo to slow suddenly and lose boost...valve would snap shut at revs and boost would build almost instantly...and then drop again as soon as the valve opened. On the dyno, this produced such a violent surge it almost threw the car off. On the street the effect was less and only under certain throttle conditions....bad enough that i revised the whole WG piping to find the room and get the beveled valve seat back in there...problem solved.

I would say that a huge 60mm gate is more likely to suffer this with only 2.5 litres of exhaust gas to work with, so WG control will be very important.

BTW, my 38's to atm don't scream...or bark so much. They just add more deep V8 rumble when they open. The pipes are quite long, which might be the reason?

[SHEPPO3930]

if it were me, i'd be looking at what people are using on other turbo 2.5L motors, then just double the hardware for each bank of your V12. i can't see there being a more simple way of getting started.

[Donmik]

As enticing as it may be to have the big shiny 60mm's sitting loud and proud,
it will deffinatly be an over kill for your set up.... I do custom turbo set ups on a daily basis at work and can tell you right now from experience, unless your out to make 1000+hp you will be doing more bad then good....

I totally agree with some of the earlier posts, that the pressure inside your turbine housing will drop dramatically when the 60mm gate opens even the slightest, causing a boost loss on the compressor housing side (Boost drop), once the pressure is lost on the turbine side the gate will shut, then crack back open and so on, causing a "poping effect" rather then a nice consistant steady flow of presure!!!

Reagardless of the spring used in the 60mm gate, it will not change anything, as the problem is not going to be the spring holding the right pressure, but more the area of the 60mm valve bleeding too much pressure too quickly....

the biggest thing you MUST keep in mind with turbo set ups is dont just look at the smaller picture....
Everything feeds everything in a turbo system, so, everything must be calculated in your idea, right from the air clean through to the exhaust tip....

[skin]

I'm running a 38mm on a 1jz big single set up and it happily held 12 psi

[TTV8RA23]

Sheppo this is what i have done mate thats why i was looking at 44mm gates but i was just wondering if a 60mm would be too big, if it would still work fine though be unnecessarily big i would not mind. But seen as it will have a detrimental affect i wont be using 60mm gates it was just out of curiosity that i asked the question. Thankyou all for your replys.
Cheers
Simon

[Supra967]

You could try mounting the gate where it wouldn't have ideal flow? Point the gate inlet pipe at the turbine wheel on the collector? Or even use a 60mm gate with a smaller diameter opening, or perforated opening. Might still get the sound effects you're after and damp the initial surge of flow out the gate.

[TTV8RA23]

I hadnt actually thought of this. Fitting a restrictor on the pipe to the gate might work. If i just run a 50mm pipe to wastegate but then fit with 38mm restrictor or something. The reality is though that im probably not gonna have enough room in the engine bay. 60mm gates are Farken huge from memory and things are fairly tight as it is. Will probably just run the 44mm gates and just use 63mm pipe for the screamer and keep them as short as possible this should give me the effect im after. I really love the sound of a big gate barking while bouncing off the rev limiter.
Cheers
Simon

[Toy77]

hahahah funny concept...

I had enough trouble fitting one 44mm in my celica bay in a manner i was happy with.... they look plenty big and bling lol......

cheers
Stew

[SHEPPO3930]

i wonder if a 38mm gate with a screamer pipe that expands to 60mm would sound the same, or similar?

[JustenGT8]

Like i said, 38mm gate and no scream from mine