Jumbo Boost

[Chinke82]

yes you would still have the tune after the turbo install. It would be used to mainly clear codes and "help" with idle.

 

[jbaker1121]

EXACTLY what I was thinking. Gotta keep it in the family.

yeah dude..... also was doing some abstract thinking.... R34 engine swap into the FX? since our AWD is the same.... lol

but really,,,, I was looking at some 240s and 180s and the like....to have something to play with and so i can start to keep miles off of the FX lol Im planning on keeping the FX until it dies

 

[fx35ky]

hahah yeahhh i always dream about going boost but just dont have the money for it at the time but hopefully soon.

hope you enjoy it.

 

[shadow191]

If you're worried about noise, definitely have the wastegate recirculate into the exhaust. I had an open wastegate dump on my old car and though it sounded cool, the noise was crazy when it was wide open under full throttle. Plus it'll be better for the environment if you pipe it back in before the cats. Also, since you're maintaining a luxury feel, you'd probably prefer not to smell raw gas inside the car which is what sometimes happens if you don't plumb the wastegate back in.

To answer your concern about the cats - he suggested we custom Y the cats together (starting with 3" downpipe) - using both O2 sensors like stock. Every connection on the hot side will use V-band clamps. Cold side will be silicone couplers.

Also suggested controlling noise by piping the BOV outlet into the exhaust. This idea was from his experience with the supercharged FX he did. He thinks the BOV would be too loud for my build philosophy - it crosses the luxury line I'm trying to maintain. The price he quoted is inside my limit, meaning I can do this as soon as the details are ironed out.

These are starting points in terms of ideas for the build, but I'm posting them to get some opinions. I can tweak this up until he/we start buying parts.

Did I mention the dyno tune is freakin awesome???

 

[yoogene]

Also suggested controlling noise by piping the BOV outlet into the exhaust. This idea was from his experience with the supercharged FX he did. He thinks the BOV would be too loud for my build philosophy - it crosses the luxury line I'm trying to maintain. The price he quoted is inside my limit, meaning I can do this as soon as the details are ironed out.

These are starting points in terms of ideas for the build, but I'm posting them to get some opinions. I can tweak this up until he/we start buying parts.

Did I mention the dyno tune is freakin awesome???

He may have confused a couple terms for you here. The purpose of a BOV (blow-off valve) is to prevent large pressure spikes in the intake pipes when the throttle plate is closed while boosting, preventing the turbo from surging. Therefore, your excess boost will be plumbed back into your Intake track, not your exhaust.

The Wastegate's purpose is to allow exhaust gas to go around the turbo instead of through it, which allows the turbo to stop making more boost. In other words, the wastegate is what allows you to control the boost level. This is what's typically routed back into your exhaust downpipe to maintain a level of sanity when driving.

However, I'd like to add that an external wastegate does sound wicked while driving...for the first few miles. Then it gets obnoxious and old real quick. The blow-off sound, however, doesn't really get tooo old unless you get a BOV that makes an obnoxious sound when it vents straight to the atmosphere compared to routing back to the intake tract.

If you're worried about noise, definitely have the wastegate recirculate into the exhaust. I had an open wastegate dump on my old car and though it sounded cool, the noise was crazy when it was wide open under full throttle. Plus it'll be better for the environment if you pipe it back in before the cats. Also, since you're maintaining a luxury feel, you'd probably prefer not to smell raw gas inside the car which is what sometimes happens if you don't plumb the wastegate back in.

Dang, I guess i should have read the entire thread? good info!!

 

[jumbosrule]

Got advice from a guy I know that runs a shop in Australia:

"Ok well having 3.5 litres engine capacity you can really get away with a quite large turbocharger without causing too much lag. I would recommend a garrett gt3582r with the largest 1.06 rear housing. It will be on boost by around 2500rpm at the latest, more than likely closer to 2000rpm. As for wastegates there is a lot more to it than just the size of the gate, positioning is critical to get good results, a well placed 38mm gate will work better than a poorly placed 60mm gate. Being a v6 engine you will have 2 separate sides of the manifold coming into 1 at the turbo collector, it is easier to have a single 38mm wastegate on each bank of the manifold rather than use a bigger single gate trying to feed of both banks. So my recommendation is a single gt3582r with twin 38mm tial wastegates and make sure your fabricator puts the gates in a good spot that gets a lot of flow ie. on the external radius of a bend AFTER the collector so all cylinders have a good chance of venting."

I'm thinking that's actually a bigger turbo than I really need as it will make up to 25psi no problem. Since I'm aiming for 8-10psi, I wonder if I can go smaller and get full boost even before 2000rpm. Also - what do you think about the suggestion to run twin wastegates?

 

[yoogene]

A GT35 would be great for power if you want to strengthen your internals (rods, pistons, etc), but I'm not as familiar with the stock VQ strength and I've heard stories of G35/350z guys pushing the limits on these motors with a GT30-GT35 without issues.

That being said, I think a twin GT2860 (GT28RS - disco potato) setup would be ideal for this application. The problem with getting smaller turbos is the addition of a torque spike or the placement of torque on your RPM range. For example, you could use a smaller turbo and get the subaru STi surge of power with a 16G turbo, but you would run out of efficiency at the upper rpm. If you wanted a smoother delivery, then a bigger turbo is the way to go.

I've contemplated this the other day, but it would be badass if someone were to do a twin-scroll setup on this motor. The cost of the exhaust manifolds alone would scare most away from it, but the delivery of power could make stock STi's shit their pants....

I'm thinking that's actually a bigger turbo than I really need as it will make up to 25psi no problem. Since I'm aiming for 8-10psi, I wonder if I can go smaller and get full boost even before 2000rpm. Also - what do you think about the suggestion to run twin wastegates?

twin wastegates is fine for this application since it'll help reduce the amount of work on a larger wastegate; just be prepared to handle the extra plumbing required for the twin setup.

Honestly, i think you should just say F-it and go balls out; built internals, bottom end, and do twin GT30's and call it a day!

 

[turbocad6]

when he is saying "on boost at 2,500rpm or closer to 2,000 rpm" he is NOT talking about being at full boost at that kind of numbers, he's talking about starting to see boost IE: going into the positive pressure range, starting at 1psi. to make full boost at 2,000 rpm you will need a very small turbo with a small A/R, & it in turn will not supply enough cfm's for upstairs really. trying to get full boost at 2k rpm is not too practical really, only way your going to do that & not have it choke upstairs is going to be in going with a dual stage dual turbo setup using one small & one large, not very practical unless you want to get really really complicated...

far as wastegates go, the less boost you are looking to make the bigger your gate(s) will need to be. a guy looking to run 15-18psi for example can be fine on just one 38mm gate where someone looking to run 8psi or less on lower boost conditions will want either 2 38's or even one 44, & yes, it is very important that the piping is done correctly to allow the gates to flow well. only a butcher will attach the gates at a 90deg angle to the exhaust, although it is not uncommon to see so called pro's even do that too. ideally your going to want it to be more like a Y, where one branch feeds the turbo & the other feeds the gate, so best place to create this situation is on an existing bend. another just as important thing is the wastegate feed back into the downpipe, as I'm sure you are not going to run just dumped, the wastegate inlet back into the downpipe should be downstream from the turbo itself at least 8-12" & should also be done in a way to allow very good flow while no impeding the exhaust flow from the turbo itself, again on a natural bend & as a Y is best. bad piping will require a much larger gate to make up for flow inadequacies of a bad design. some guys will use larger gates to make up for inadequacies in there piping design, not the best way to go though.

far as a larger turbo than really necessary, I will kinda agree with this to a point. being a large heavy awd automatic vehicle, having the boost come on a bit later & come on at a less aggressive slope can go a long way towards not breaking things & giving a more even torque curve. keep in mind that engines are under the most stress & usually break at the higher end of the rpm range, but drivetrain breakage is the opposite, drivetrain breakage usually occurs where it is under the most stress which is on launch, or low speed high loading... even when you see a guy blow his tranny or rear at higher speeds it is because he actually damaged it & started the break at the lower speed higher stress load, only he didn't break it all the way, then, it let go at higher rpm, but it is very hard to actually break a drivetrain while under higher speed. for these reasons I'd say I agree to using turbo(s) on the larger size, but, there is such a thing as too large too.

if you don't want a lot of lag with a larger turbo def go with a good ball bearing turbo over a cheaper journal bearing design... those combined with a good blow off valve setup will minimize lag & the larger turbo will bring the torque on a bit more progressive which helps in the drivetrain durability. I went a step further with my build & I'm using tial stainless steel exhaust housings... these help even further with fast spooling because of better heat retention over the stock ductile iron exhaust housings... if your using tubular manifolds & piping to your turbo's then a good ceramic coating can also help with heat retention & faster spooling.

if you are not designing your own turbo install then hopefully the person who you are going to trust to do your setup will of course know all of this & then some, just communicate your desire to use a larger turbo & bring the boost on more progressively & to gate it in a way that you can run very low boost when you want to without having boost creep upstairs.

also, a lot of how you spec a turbo will depend on what compression ratio your motor will have... at stock compression ratio, boost lag is no where near as much of an issue as say building a motor that is 8.5:1 compression, just because the motor itself will not be as much of a dog before boost, so a higher compression motor can afford a little more lag just because it is already peppy before boost.

also, now seeing yoogenes post, he has a very good point about using a twin scroll. if I was to do a single then I would def use a twin scroll for sure, manifold design will not differ much because you are already collectingfrom 2 banks into one, so the only difference in building it is going to be in the collector feeding the turbo...

---------- Post added at 03:06 PM ---------- Previous post was at 02:57 PM ----------

ha, yoogene says twin gt30's... that's good for like what, 8-900hp?

my recommendation to at least look into for twins if you were to go that way on a DE would be to use a pair of gt2860r, not rs... mainly because that particular turbo is stock replacement for the sr20's & you can get a really good deal on NOS from a nissan dealer at say 700 a turbo, which is a great price, I know a few places you can get hem at that price. I was originally going to go that route but upped to the gt28RS turbo's in my build...

 

[jumbosrule]

Actually I think I mention the twin scroll in the middle of this thread? Maybe it was in my blog or something. Definitely a consideration, but as you said - fabrication intensive. There is no existing manifold for the FX, but it seems to me a twin scroll manifold could be done with what is pretty much a custom Y pipe and a slightly modified set of good quality headers (like turbo is doing with his HR).

View attachment 200164

I've decided to stay with a single - not twins. Given that assumption, what turbo size would you recommend?

For my lower horsepower and boost goals, is an intercooler even necessary? Wondering if I could route from turbo directly to intake?

 

[turbocad6]

a bigger turbo can create more cfm's at a lower boost level than a smaller turbo can, so you can make the same HP at say 7psi with a large turbo that a smaller turbo which might need to see maybe 8.5- 9psi or so to make the same hp... the pressure increase is what raises charge temps, so ~7psi with a larger turbo I guess you can get away without an intercooler maybe, but your sacrificing efficiency & increasing chance of detonation too, the only good thing about no intercooler is the turbo will need to make less boost overall too, in other words to see 7psi at the manifold you won't need to make 9 at the charger & then loose 2 psi to the intercooler, but the trade off of higher charge temps kinda narrows the gap in benefit there too. personally I'd intercool any turbo setup really, especially anything in the 8psi & better range. a centrifugal supercharger can get away without an intercooler more easily at lower boost levels because they don't raise the charge temps as much as a turbo... that being said I guess many builds have been done without an intercooler really, to me if your going that far though the intercooler is only a small expense compared to everything else...

size would probably be something in there gt35 range, more specifics would take more research & I haven't done much at all for larger singles to be able to really pick an actual suggestion, but again, I would think the person who is designing your setup would be the best to really choose a specific turbo. I'm assuming your looking to mount the turbo in front of the engine?

 

[jumbosrule]

Yes - front of the engine, but lower in the bay, to try to minimize all runs.

So this might just be crazy, but it's also fun to think about:

What if I stuck with a larger turbo, no intercooler, but added water/meth injection to keep the temperatures down? I've seen injection kits that go for less than it would be for an intercooler + custom piping, for sure.

 

[yoogene]

a bigger turbo can create more cfm's at a lower boost level than a smaller turbo can, so you can make the same HP at say 7psi with a large turbo that a smaller turbo which might need to see maybe 8.5- 9psi or so to make the same hp... the pressure increase is what raises charge temps, so ~7psi with a larger turbo I guess you can get away without an intercooler maybe, but your sacrificing efficiency & increasing chance of detonation too, the only good thing about no intercooler is the turbo will need to make less boost overall too, in other words to see 7psi at the manifold you won't need to make 9 at the charger & then loose 2 psi to the intercooler, but the trade off of higher charge temps kinda narrows the gap in benefit there too. personally I'd intercool any turbo setup really, especially anything in the 8psi & better range. a centrifugal supercharger can get away without an intercooler more easily at lower boost levels because they don't raise the charge temps as much as a turbo... that being said I guess many builds have been done without an intercooler really, to me if your going that far though the intercooler is only a small expense compared to everything else...

size would probably be something in there gt35 range, more specifics would take more research & I haven't done much at all for larger singles to be able to really pick an actual suggestion, but again, I would think the person who is designing your setup would be the best to really choose a specific turbo. I'm assuming your looking to mount the turbo in front of the engine?

All good points. An alternative to an intercooler is to use water/methanol injection to cool your intake temps as you're getting boost. This has been used as an alternative to Intercoolers for many superchargers and some turbo setups, but depending on the size of turbo you're going to use, I'd use it as a supplement to an intercooler rather than a replacement. This way, you can have the added benefits of running a lower intake charge and thus adding timing which in turn equates to more power.

Yes - front of the engine, but lower in the bay, to try to minimize all runs.

So this might just be crazy, but it's also fun to think about:

What if I stuck with a larger turbo, no intercooler, but added water/meth injection to keep the temperatures down? I've seen injection kits that go for less than it would be for an intercooler + custom piping, for sure.

Looks like we're already on the same page

Another thing to think about is your ambient heat; are your summers extreme? Being in Vegas, a FMIC for my setup was insufficient for any power on a bigger turbo so I had to implement water/methanol injection just to prevent detonation on a +1* timing advance. If you reach temps of 95*+ WITH high humidity, then I'd spring for both to maximize the set up.

 

[turbocad6]

chemical intercooling can def help, but yeah, I'd also look at that as suplimental... if you only have chemical intercooling then it's a good idea to use a very low psi wastegate so if for any reason the tank is empty or any other reason it happens to not be available at any given point you can turn the boost way down...

have you had anyone look at it & say they can do one large single in the place your thinking? room for the downpipe & all? will be a bit tight. I forget, are you awd? if not then theres room on the right side for a downpipe, if awd it's going to be tight & tricky, especially with the DE having all the water pipe stuff on the right side upper & the diff & stuff lower...

 

[shadow191]

A GT35 would probably work well. I used to have a VQ30 with a custom turbo setup and I had a T3/T04S turbo on it. That was basically a journal bearing version of a GT35; I actually thought about swapping to a GT35 since it would have reduced spool time, but I sold the car. Even with the smaller motor, it started spooling by ~2800 rpm. Given that the FX is ~1000 lbs heavier than my old Maxima and it has the extra .5L displacement, I'd think that a GT35 would spool quickly. Nothing like a heavy car to load a turbo.

And if you're going to do this, I'd highly recommend intercooling it. What are your reasons for not? Is it a fitment issue? If you're only running a single turbo, an IC setup should be pretty simple. It would be harder with twins. I'd personally never trust a set up where you had to ensure that the meth tank was full or that all the pumps worked. An IC can't really fail.

FWIW, for most mild street setups, running the wastegate at a 90 deg. angle won't make any difference. Yes, properly running a Y off of the downpipe is the optimal way to do it in order to avoid boost spike. But that's usually when we're talking pretty high boost levels. I did 3 custom turbo setups back in the day and all ran the wastegates at 90 (due to space constraints) and none of them saw any boost spike. However, on a few higher boost cars, I did see boost creep that was resolved by better wastegate placement. If you don't plan to run 25+lbs of boost, you'll probably be fine.

Actually I think I mention the twin scroll in the middle of this thread? Maybe it was in my blog or something. Definitely a consideration, but as you said - fabrication intensive. There is no existing manifold for the FX, but it seems to me a twin scroll manifold could be done with what is pretty much a custom Y pipe and a slightly modified set of good quality headers (like turbo is doing with his HR).



I've decided to stay with a single - not twins. Given that assumption, what turbo size would you recommend?

For my lower horsepower and boost goals, is an intercooler even necessary? Wondering if I could route from turbo directly to intake?

 

[jumbosrule]

Just exploring the world of possibilities - besides my goals, I have no set notions of how this system should come together. That being said, it's gotta take shape before I can reason through changes. I'm working within a certain framework based on my discussion with the installers I have been talking with.

I have taken a shot at the layout - assuming the turbo will be between the engine and the radiator, low in the engine bay. Aftermarket headers, modified to mate up to a custom Y pipe for a twin scroll turbo. Hot side will be a custom downpipe that Ys into the stock Cat location. Cold side is a super short run to the intercooler, then custom piping from IC to intake. Filter will be in the same general location as now - or moved into the bumper in front of the driver wheel well. I realize I'm going to need to nail down routing much better than this concept, but I wanted to start with a sketch. Still need to place the wastegates and BOV.

I see the wastegates placed about where the modified headers mate up to the custom Y-pipe. For this set-up I want to size the twin scroll turbo, twin wastegates and BOV. Still need to route the wastegate exit to the exhaust as well.

Question - does the BOV go before or after the intercooler?

 

[StuLax18]

Those are really cool little sketches. Not sure about the BOV. From just a quick search, there was no definite answer.

 

[tchuck]

This may be getting too specific for this stage of development but wouldn't you want to run the hot and cold sides on opposite sides of the engine? I mean if your air filter is going in the drivers side fender (+1 BTW) and your plenum inlet is angled to that side as well, wouldn't you want the exhaust plumbing to be on the passenger side of the engine?

 

[yoogene]

You can put the BOV either before or after the IC, but i'm sure there are specific reasons for each.

edit:

put it on the hot side, as close to the turbo as possible. also run the vacuum line from the bov directly to the throttle body- if you T it off to something else, response is diminished. Use the correct size line too.

Reasoning:
Your bypass valve is supposed to bypass unwanted pressure in the plumbing. If the bypass is on the cold side, then all of the high pressure from the turbo to the bypass has to flow through the intercooler to get out, which means it the venting will be slower, more gradual, not as sharp and not as quick. People will say this "keeps the air moving in the right direction"- however, air is always flowing into the engine, even at idle or after you let off and the throttle body shuts, the engine still breathes. The purpose of the bypass isnt to keep the engine breathing its to prevent COMPRESSOR SURGE. By placing the bov on the hot side:
the turbo gets a fast-as-possible response for relief of compressor surge
the release is more sharp, and faster, which on a maf car, is a large benefit (Due to the way the ECU cuts fuel) you will note that cars with bovs on the cold side, even a ssqv, will tend to backfire under light throttle conditions... because the ecu cuts the fuel but idle falls low enough for it to come back in with the bov still hanging open... and POP!
Air density at constant temp is related to pressure. whether the plumbing releases pressure on the cold side or hot side doesnt make a difference- the turbo still has to re-compress the column of air when you step on the gas. the air doesn't "keep moving" any more or less whichever side its on- the engine is always breathing, and unless you are shifting with the throttle body open, the column is going to lose its increased pressure ratio. oh, i still put some bov on the cold side, just for looks though. they looks cool right there by the throttle body. And they are quieter, more subtle. And the vacuum line is shorter, which means it opens even easier. Yes it backfires unnecessarily and yes the compressor surges slightly more than it should but... LOL it still serves its purpose.

 

[turbocad6]

if your running a MAF sensor you have to put it before the sensor too, you don't want to bleed off already metered air, because the ecu will add fuel for that air & if that air doesn't make it's way into the motor then you'll wind up creating a rich condition...

 

[shadow191]

You could always recirculate the air from the BOV. But then you'd lose that "cool" BOV sound.

if your running a MAF sensor you have to put it before the sensor too, you don't want to bleed off already metered air, because the ecu will add fuel for that air & if that air doesn't make it's way into the motor then you'll wind up creating a rich condition...