maxxdamigz

iTrader: (1)

There are plenty of turbos out there that would meet or exceed the amount of CFM a renesis would be moving at 9k rpm at any number of pressure ratios. For some reason, people would rather have boost at 3k rpms (where the car is fairly anemic N/A) which requires a smaller hotside. A normal piston engine making boost at 3k rpm doesn't usually have to worry about a redline that can be over 3x as high.

Wanganrx8

that's something i don't understand, everyone here wants a turbo that's not laggy. but just because a turbo is bigger than an 18g doesn't mean it will be laggy. I much rather have a gt35r that spools around 4k and pulls until redline then my "hunk-o-junk greddy" that spools around 3k and stops at around 8k.

Red Devil

Speaking to many Renesis owners with GT35Rs, they're not spooled until around 4.6k. For the boost levels this car allows with its compression and using only pump gas, I think that's way too large.

maxxdamigz

iTrader: (1)

That's probably just a dynamic of the accountant, sales guy, and engineer all working together. The accountant knows he can source lower performance turbos for less money. The average deep pocket joe is not going to be overly familiar with compressor/turbince maps. The sales guy knows he can sell more turbo kits if the kit price is cheaper and when you punch it at cruising RPMs, you get that quick spool and boost. The engineer just sits quietly in the corner mumbling about his stapler and how he could make more power at 8k rpms if they had a larger turbine.

I think SFR is willing to adapt their kit to different turbos so if you want to work with them to pick your own, you can do that.

Given the operating range of a Renesis and something like a track application where you are 5k+ rpms all the time, you could probably get very good results with something as large a GT35R that spools at 4.6k. However, you would still need to downshift to 4rth to pass on the highway.

Red Devil

Well, for 10psi and under something like a GT30 would pull to redline and spool much sooner. But whatever, if someone is willing to wait longer to get into operating range to get more compressor efficiency up top than that fits their parameters. I wouldn't use a GT35 unless I was looking for like 1 bar or more on the Renesis.

chickenwafer

iTrader: (9)

I like how on the 350 forum they are bitching about torque. Maybe if their cars went on diets we could talk.

Oh yeah, a 350 boosted at a low 9psi (like the RX8 they are talking about that makes 320-rwhp), a 350 wouldn't make more than 400-rwhp, so it would be a REALLY close drivers in a straight line. Throw in a track, stock suspension vs stock suspension, and the 8 would spank the Z with that kind of power. Not to mention the 8 costs more, so take the price difference and upgrade the suspension for the 8, now it's all over.

silverstripes

Is there anyone on the forum with a gt35? I would think with a 9k redline that it would be the perfect turbo for the 8. It would spool later like mentioned which would be great for daily driving since you wouldnt get into boost often, and better for gas mileage, which we all know is a factor for the 8. And having power between 4.6k-9k rpms sounds like a fun ride to me.

mysql101

If you don't mash the throttle, you aren't going to enter boost. So your statement isn't valid.

What you're going to get is WOT that doesn't do squat till 5k rpm. That is just going to make your car feel anemic and give you a narrower powerband to play with.

silverstripes

Not sure about shifting in a 8, but where do your rpms fall to when shifting? As in say straight line acceleration... I would imagine that with a bigger turbo that will be holding boost to redline would be more ideal for a 9k redline car. I wouldnt want to have a smaller turbo that would spool at say 3k and falls flat on its face at 7.5-8k rpm. To me it seems like a slightly larger turbo or turbine upgrade would be more ideal, at the track or the strip, you would have more constant power to redline which is what you need. Why would you want boost so far down on the powerband? For what? Its not like it takes 2 days for a 8 to get to 4.6k rpms...

mysql101

just because you can go to 9200 rpm doesn't mean you should. You have to also consider where the range that engine is most effective at. In stock form, the car peaks around 8600 rpm range.

silverstripes

But, I am just assuming here, wouldnt a good tune correct that? Im sure that with a tune you could have full power from 4.6k rpm and up. To me it just seems like if you tracking your car or taking it to a strip a gt35 would suit better for power standards. From what videos ive seen of rx8's at tracks it seems like you stay 5k rpms and up, so isnt that where you would want most of your power? What good would it be to have full boost at 3k where you would never see it, and then have it drop off at say 7k rpms where the engine is still "effecient" to 8600rpm? I just dont see your explaination as to how my input wasnt "valid". Im trying to learn as much as I can about the rx8, so if I seem like I am going no where with this then just say so. I am just trying to understand why everyone buys a smaller turbo for a car that can easily spool a larger one that can make more power toward the top of the powerband where it is most used for a car like this...

swoope

iTrader: (5)

could someone that is a member on that site ask them where the got the power mod ecu?

phantom?

Phantom Menace

I goch'a Swoope! I'll post your question on the F/I section right now and let you know what I come up with....


This is the reason I made the whole, "I don't hate" thread. Why must we talk about cars as if they are intrinsically connceted with their owners and with so much animosity? ...And how do you put a car on a "diet?" Put in 89 octane?

maxxdamigz

iTrader: (1)

While the guess work is nice and all, you need to crunch some numbers to pick a turbo size. You need to calculate your CFM and pressure ratios and plot them on the compressor map. You want to have the right size turbo for the job. A turbo that holds 20 PSI to what the Renesis might flow at 15k rpms is probably too large. There are high CFM turbos. High pressure ratio turboes. High pressure ratio/CFM turbos and crappy turbos. Odds are, the GT35R would be the correct turbo for certain PSI at certain RPM applications. At other applications, it would be the wrong turbo.

SmokeyTheBalrog

silverstripes, mysql101 knows a lot about turbos, just FYI.

Aso, silverstripes I hate to say it but it's pretty obvious you don't know much about turbo/super chargers or engine tuning.

Just becuase you make 200 hp at 9000 RPM doesn't mean you will make more at 10,000, 11,000, or even 16,000. In fact you will almost definitely make less hp/tq. (BTW - The Renesis engine will destroy itself due to vibrations at 13,000)

1. Mazda did a great job building this car. I.e. it already has a good tune (That's why you don't get cheep HP boosts, anything that would give you HP has already been done.)

2. It is my understanding that a Turbocharger will only make boost when you have the gas peddle pressed down enough to "activate" it. You can start from a stop, merge onto a highway, slow down, speed up, get off, start and stop a bunch of times and NEVER "activate" your turbocharger(enter boost).

It will be almost like you don't have a turbo at all.

Read "Boost Threshold"
http://en.wikipedia.org/wiki/Turbo#Boost_Threshold

I believe we already have turbo chargers that will give you boost before 3K RPM and peak between 8K and 9K.

mysql101

I said your input wasn't valid in regards to your point that not getting boost till 5k would save on fuel. It's not valid because a turbo doesn't spool up at 5k automatically - you're thinking of a supercharger. A turbo is load based, not rpm based. So if I give the car throttle slowly, I can go way up in rpms without the turbo kicking in.

Also I don't think anyone here is arguing that the greddy is undersized. We'd all like for it to flow enough air to fill the renesis needs till 8k instead of 7k. But that isn't to say that you can't hit 8 or 9k with it. Just like you can hit 9k on the stock motor even though it's past the peak at that point.

SmokeyTheBalrog

Oops, I was wrong again. :<

Among other things, Boost threshold isn't what's being discussed. I think.

whoneedspistons

iTrader: (2)

well i have an interesting situation here... i have the kits pipes and i am modifing them to fit the turbo i have laying aroundhere (intake trim 70 and exhaust 63)... this should throw me right in the middle of both these turbos.... it should be interesting to see the response and peak of this turbo in this application.... its crazy that the kit take a 46mm wastegate.... that was a quick 500 bucks

maxxdamigz

iTrader: (1)

I don't know about that. You'd have to keep an eye on your intake air temps. The hotter they get, the closer you are to detonation. If you've peaked your power and are actually losing power compared to up shifting, I'd call it a day and not try to find out.

whoneedspistons

iTrader: (2)

i think he ment peak hp.... if you look on most hp curves after a certain rpm the motor does not peak in efficency

silverstripes

Im not going to quote every post before me but, did I ever state that a car would make more power through a larger rpm increase? I dont think so. All I stated was that if you where to add an increase of fuel along with the turbo kit, you should be able to make up a map that would hold boost to a higher rpm than 7k and have a little more power at the top of the powerband. I do realize that if you stay off the gas enough that you will not build up any boost but, if you start building at say 4.6k then you would be able to go from light to light a little faster without killing your gas mileage from going into full boost at 3-3.5k rpm. Im must not know **** about a turbo, considering my daily driver is a 266hp/340tq turbo'd car... There are many evos out there that are holding boost until 8.5k rpms and their power curve is great. So all in all, is the turbo that I mentioned a good one or not? Everyone on here has to swing there manhood around here and act like they know everything about a turbo besides answering the question that I stated and another person stated on the previous page. But atleast now I know how a TURBO works....

Red Devil

I think you're going too large. If we're talking about holding like ~10psi or a bit more (10:1 compression/pump gas) to redline, you can go with like a GT30 and get into operating range quickly and pull to 9K. Just my opinion.