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Discussion Starter · #1 ·
Ok. I've got sumthing to say here for all of you who upped boost. I feel that upping the boost on the stock turbo is actually stupid. Here's why. We have a tiny tiny compressor housing stock. If you check the flow charts it's maximum effiency is probalby around the 70% area. Seeing how small it is already, we'll say that it's probably tuned for it's peak effiency right at a pressure ratio of around 1.5, not 1.5 bar, but a pressure ratio of 1.5 or about 8 psi of boost. 8 pounds of boost equals about 270 cfm's on our engine at 5500 rpm. Pretty straight forward so far. Now, if we'd look at a compressor map (can't find ANY for the rbh5.. someone help!), we will notice the stock numbers would match up to a nice effiency. Now, plug in 15 psi of boost which would require 360 cfm's. I can promise you that this turbo with those numbers is far too low efficiency to be considered an upgrade. When you lower efficiency, heat goes up, and therefor your density ratio goes down. What we really want here with turbo charging is high density not high pressure. They can go hand in hand, but according to the law of thermodynamics, we cannot increase the pressure ratio the same amount as increasing the density ratio. So, by upping the boost, and loosing effiency, you're probably gettin the same density ratio as a lower number of psi. My advice would be to stick it to around 10-12 psi. Because we're intercooled we do have room for the turbo to be ineffiecent, but still to an extent. And on top of all that, Mazda does KINDA know what they're doing. YES, there's room for upgrades, but upping the boost on the rbh5 much might not be one of them. They wanted a car that's quick, and responsive at low rpm. If they wanted to up the boost, and make the car overall quicker, I'm sure they would of chosen a bigger turbo. That's all I got for today! Let me know if you agree! Peace out.
 

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here is the answer to your question. show me a map on stock turbo then we continue from there.judging the turbo performance due to his size is not a way to figure out performance.
here is an example.
a tdo5 18g turbo is a small turbo compare to an hybrid t3/t4e,bvut the 18g flow a wooping 600cfm,while the t3/t4e flow around 400cfm-500.check out force performance.net. they build my turbo.
 

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Discussion Starter · #3 ·
Yeah... I totally agree. BUT.. there's one small thing that makes think this turbo can't produce effienctly above 9-10ish psi. They use it on the b6t. The b6t is a 1.6 liter engine with a 7.3:1 CR putting out 130 hp. The community of users complain because it's too small for their engine! I can't hardly imagine what they'd think for the f2t. I WOULD LOVE TO SEE compressor maps. But, I've seen similiar maps and what i've said is right for them. So, anyone got RBH5 maps?!? That'd solve whether I'm fact or fiction. Thanx guys!
 

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TIMSmx3 said:
Yeah... I totally agree. BUT.. there's one small thing that makes think this turbo can't produce effienctly above 9-10ish psi. They use it on the b6t. The b6t is a 1.6 liter engine with a 7.3:1 CR putting out 130 hp.
sure thaey use the same compressor housing but different wheel.the stock turbo wheel has 10 fins while the b6t has only 8.also the exhaust side of the turbo is also different.so thats make the vj11 rhb5 bigger and flow better

[Just fixing formatting]
 

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also remember b6t has 7.3.1 compression which without a turbo makes 60hp,so its safe to say the turbo itself make up for the extra 70hp,to make it 130hp rating.at 7psi.thats 10hp/1psi.so they are close to maxing out the turbo efficient already.if if you running 15psi on that motor.thats another 8psi different and 80hp .so basically the tiny turbo is producing 150hp extra.I think thats pretty good for that turbo.
 

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Discussion Starter · #6 ·
YES BUT>>>!!!!

You cannot by any means just divide horsepower by psi to equal a number that each psi is worth. THE WHOLE POINT IS, by spining a compresser faster (to create a higher psi number) you automaticaly create MORE heat. MORE HEAT lessens the density ratio. The density ratio is what really makes power! There's no way on completely stock everything you can simply crank the boost to 15 psi and go from 130 hp to 210! That's CRAZY. (on a b6t) And I do understand that the F2t has a different version of the RBH5, but everything still applies. I had a friend with a talon and he had a knock reader thing on his palm pilot, going from 13 psi to 16 psi there was LITERALLY no change in power according to his 1/4 at all, CEPT with 16 psi of boost he was creating knock at the higher rpms. BECAUSE he was creating more heat! Like I've been saying, increasing the boost has drawbacks. Luckily our engines are properly intercooled and have a low enough CR that this severe heat is bearable, but isn't benifitial. ANYONE HERE agree?!?! Thanx.
 

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Discussion Starter · #7 ·
if you running 15psi on that motor.thats another 8psi different and 80hp .so basically the tiny turbo is producing 150hp extra.I think thats pretty good for that turbo.
I would LOVE to see a 40 dollar boost controller give any stock engine EVER 80 hp. That's simply unheard of. Company's do research when putting a turbo in a car. If they could get 80hp outta the same engine with ALL the same components on it, don't you think they woulda done it stock?!?! If they wanted a higher HP rating, they woulda fitted a bigger turbo. But this bigger turbo wouldn't help their LOW rpm driving and therefor would of been less like-able by the general public. A bigger turbo would be more efficient for high boost/ high hp numbers. A small turbo is efficient for low boost and low rpm driving.

BUT if you've upgraded intercoolers, compressors (housing and/or wheel), or done anything to handle the higher intake charge temps of high PSI from a stock turbo, then you will see a noticable gain in performance. BUT, stock everything will not gain much horsepower with a simple boost contorller. At least not above 12 psi i'm guessing. But, boost above the stock numbers will give you noticable gains, but not 15psi. And the gains WILL NOT BE 80 hp.

And once again, does ANYONE have any maps? THANX!
 

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well im assuming they make the same amount of hp/psi as gt.my gt dyno 200+ hp @17psi.I have been running 18psi for almost 6 month now and the car pull like crazy,i have runs a comparison test against a lot of 1st gen i have come in contact with and did a lot better that i though.so that make me wonder when people talk about the ihi turbo and there efficiency.untill i see the map.i will continue to boost higher boost on my turbos:)
 

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Ok, if raising the boost on the small vj11 rhb5 isn't effective than why does everyone run lower e.ts when they raise the boost? I for one am a prime example of this. Completely stock I ran a 15.7, I raise the boost to 12 psi and I ran a 15.3 with just added boost and an adamturbo chip. This was on my old 1988 GT, I know own a 1990 GT with a Zombie chip and 10 psi and have ran a 15.0 with a 2.1 60 foot time. I wish I could find time to get a dyno on different boost levels to show you how effective raising boost on any turbo is.
 

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SixSick6 said:
TIMSmx3.......YOU DON'T EVEN OWN A TURBO.....WTF ARE YOU TALKING ABOUT? THEORY? you can shove your theory
man relax. no need to get worked up. he does have one thing right, the stock turbo sucks ass. regardless, more boost makes more power. it's the same thing I've been saying for a long time.
 
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SixSick6 said:
TIMSmx3.......YOU DON'T EVEN OWN A TURBO.....WTF ARE YOU TALKING ABOUT? THEORY? you can shove your theory
Pointless attack.

TimsMX3 has a very good point, and one that I partially agree with (And I own several turbo's).

Example, 5 psi on the 15G I put on my MX6 easily outpulled 14 psi on VJ11.

Even though we don't have a compressor map of the RHb5 VJ-11, there is a point on all turbo's were the compressor has reached its peak effiecency and going any higher does not benefit at all. Look at the guys at the dodge garage for some good turbo effieciency articles.
 

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I admit, I didnt read the whole post, I was on a quick break at work and briefly scrolled through it with the thought that he meant raising boost produces no gains with the RHB5, or no gains worth anything. sorry man, you are somewhat correct in your theory, although most people who up their boost are also upgrading exhaust, intercooler and piping.
 

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Plus, lets not forget, that a lot of the people who stick with the stock turbo or variations thereof (t-bird hybrid, work to the exhaust side, yadayada) are stuck in california and can't go all willy-nilly with turbos. We gotta keep the stock look or get put on automotive time-out by the state. I had a hard enough time replacing the tube I had my bov wleded on to for smog, I wouldn't want to deal with replacing a turbo, manifold, and downpipe/exhaust whenever I had to smog it. I hate hearing the same damn thing every week about how no one should tune the stock turbo and such. We get it . It sucks. So does the government but everyone works through it.

It should also be noted that everyone will spend $1500 in engine mods but wouldn't spend that much on a custom torsen or quaife to handle it first. So I'm gonna start a "why you shouldn't mod your engine over the stock open differential" crusade. I'll be starting new threads on this at least once a week so that no one will forget. Be watching! :D
 

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I have dyno charts from my car at stock, 12 and 18psi....

The hp being... 122, 169 and 187hp respectively. I have mods to the piping, exhaust, pod etc... and also remapped piggy-back computer.

At 18psi, the intake temp is shockingly high, so I'm waiting to get a new IC to see a bit more of an improvement. But, with the remapped fuel, I'm hitting full boost at about 3000rpm and holding all the way until 6000rpm. Something that I couldn't get with the stock computer.

I haven't had time to take it for a 1/4 mile run, as I'm slowly building up a FE3 now. But, I would say that you are correct in theory, but in practice I can tell you that the car pulls like a scalded cat, and is definately quicker than stock.

I think what you should be saying is that, the higher the boost you run the less effecient it gets and the less hp gain you will get per psi. So if you run 18psi, you will still have more hp than 17psi... might only be 1hp, compared to 7hp from 5 to 6psi.... but it is still a gain. Understand?
 

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tripharn said:
I think what you should be saying is that, the higher the boost you run the less effecient it gets and the less hp gain you will get per psi. So if you run 18psi, you will still have more hp than 17psi... might only be 1hp, compared to 7hp from 5 to 6psi.... but it is still a gain. Understand?
I totally agree with this and maybe this is what is being lost. It's about effeciency, whether the turbo is putting the power out is a calculation and it should be correct. But the main concern is effeciency, IMO.
 

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So my rebuit t04 is better tehn the stock one I have now? I have it in 25 trim for a smaller engine, but I can "trade" it up from the guy who I bought it from. So what should I get if I am going to be setting up my GT for 18 lbs of boost. BTW I can get a bigger IC if I have to.
 

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gordmc said:
So my rebuit t04 is better tehn the stock one I have now? I have it in 25 trim for a smaller engine, but I can "trade" it up from the guy who I bought it from. So what should I get if I am going to be setting up my GT for 18 lbs of boost. BTW I can get a bigger IC if I have to.
It depend on the t04 you are getting,t04e or t04b.the t04 b is a little bigger than t04 b on the compressor side.but straight t04 will require a lot to spool the turbo on a sttock 7:8:1 compression.
you can get a t3 turbine side to mate with the t04 compressor.
 

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HotRodMex said:
Plus, lets not forget, that a lot of the people who stick with the stock turbo or variations thereof (t-bird hybrid, work to the exhaust side, yadayada) are stuck in california and can't go all willy-nilly with turbos. We gotta keep the stock look or get put on automotive time-out by the state. I had a hard enough time replacing the tube I had my bov wleded on to for smog, I wouldn't want to deal with replacing a turbo, manifold, and downpipe/exhaust whenever I had to smog it. I hate hearing the same damn thing every week about how no one should tune the stock turbo and such. We get it . It sucks. So does the government but everyone works through it.

It should also be noted that everyone will spend $1500 in engine mods but wouldn't spend that much on a custom torsen or quaife to handle it first. So I'm gonna start a "why you shouldn't mod your engine over the stock open differential" crusade. I'll be starting new threads on this at least once a week so that no one will forget. Be watching! :D
that's SO true :lol:
 

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Who cares. Why not get the most out of the stocker before you upgrade? If it can take you from a mid 15 to a mid 14 or better with some bolt ons, I don't see it as that bad. I could honestly care less if I just ran a [email protected] with a inefficent turbo. Its just the stocker, anyone who expects that much out of a stock turbo is asking for way too much.
 
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