Zero R

iTrader: (1)

I would say it would depend on what your referring to as common sizes, I think that alot of people come on here with little or no experience, read threads about how they should use what most people would say is a fairly large turbo for the size motor we run because of alot of the more drag oriented people in this section. Then loose alot of streetablity which is fine for guys that just want a fast street car. I understand what you say about the power band, though I think it is a little misleading to some. I would say the power band is closer to each than you say just one is shifted a little more upwards.I do agree it's all about application though.

-Sean

rx7tt95

Was that the inducer or exducer diameter for your turbo, Roro? That sounds fairly small. The 40R I've chosen uses an 88mm wheel (exducer). Looking at the Garrett catalog, that's smaller than a 30R compressor at 76.2mm.

carx7

iTrader: (31)

Sorry, I'm used to inducer sizes. It's a 66.7mm inducer with a 84mm exducer... not sure which GT compressor that is.

Slightly larger than a T66.

-Chris

IGY

66.7/84 is a TO4R blade.

Carl Byck

also known as a PT67GTQ the Supra guys run this turbo non-BB in a .68AR, or P Trim .68, or .81, The Q trim .68 is good for low 700s on a 3.0L Supra @ ~2.3Bar, nice flat torque from 4000-7000 rpm right around 600ftlbs.

crispeed

Well guess what!
You can't really tell the A/R of a housing just by looking at it. Believe it or not the A/R on the turbo is bigger than the one on the T-78.
The housing/wheel combination on that turbo was good to about 650 rwhp at 25psi at which point back pressure became a problem.

rx7tt95

I understand that a/r is a ratio and isn't comparable across turbo models but looking at the actual physical size, that's what shocked me. The bellmouth on the front of the turbo makes the compressor side look a bit bigger as does the heat shield for the turbine. It's led me to a rethink about turbos on RX7's if nothing else :-) I'm not saying it's a bad choice (I don't have the knowledge for that) but I don't understand why that turbo works so well on a rotary (as a combination with engine porting?) when it looks like it would choke off the exhaust path. It obviously does work. What's the principal at work? Why did you choose this turbo? What else needs to be present for this combo to be effective? What type of engine porting, etc...?

I also didn't realize you were even at the dyno session. I was the guy stroking the keys while tuning Eddie's red third gen. until you saw the fuel leak. Had I known it was you, I probably would have asked you about a gazillion questions the rest of the afternoon.

rx7tt95

Isn't it a .81 rear a/r?

Roro

Forgot about this one. My definition for this is the fact that I have 30%-40% blockage as I transfer from the manifold to the turbine housing. I build the manifold before I had the turbine housing... my guestimates on the entrance area for the turbo were way off.

So right now the manifold air hits a huge wall before it makes it into the turbo. I can't fully port match the turbine housing without breaking out of the shell. Oops. So I'll be fixing that, as well as some intake track issues.

I'm also not 100% satisfied with my manifold... amazing what you learn/realize after your first manifold design, so I'll probably be re-doing that as well.

-Chris

crispeed

Nope!
Keep guessing!

BTW. There are many rotaries that I know of that are making close to 800 rwhp using .81's and .96's.!
From my experience with rotaries the turbine wheel size plays more of a roll on back pressure than the A/R of the housing.

chuck8313BTSDS

If we are guessing a/r size, my guess would be a .7# a/r with a Q-trim wheel clipped 15deg.


chuck

rx7tt95

Eh, I heard through the grapevine it was a .81 :-) Interesting about the turbine vs. A/R. I'll chew on that one for a while.

Ranzo

Ok I had an interesting conversation with a Japanese Tuner the other day about this very subject and his statements kind of reflect what Rice Racing is saying.

I was shown a graph in the Power Excel software mapping Exhaust pressure vs Manifold pressure. Basically to create maximum driveablity and horsepower there needs to be a balance struck between these two. In some cases turning the boost down will give greater results.

After discussing this for a while I think the only way to talk accuratley is to talk in terms of CFM ........ How much air can your engine flow in and out as well as how much will your intake can put into it. If you are running a bridgeport with a large exhaust port then a .84 AR is too small to acheive the boost and power levels you want because the exhaust pressure will become much higher than the manifold pressure, so in this application you need a larger backside. The opposite is alslo true if you have normal ports then a .96 might be a little large . Speaking in terms of How much air the engine can move is more scientific and accurate then just saying a rotary should use a particular A/R.

SPOautos

Dont forget about the wg....not all your exhaust goes thry the turbine housing. In addition it depends on the turbine wheel like Chris mentioned. Imagine if there was NO turbine wheel in the housing...how restrictive would it be then? There is going to be a very fine balance between housing a/r, wheel, and wg. I dont think you can cut it all up to a "one theory fits all" type applicatoin cause it just depends on spacific parts and how those parts with interace with other parts.

Just like Chris already pointed out he knows people making right at 800rw with .81-.96 a/r's and there are people on here running well over 1.0 a/r and only making half that power.

STEPHEN

Zero R

iTrader: (1)

Thank you for saying this. I have had discussions on this before with people who don't seem to want to believe me.

-Sean

rx7tt95

But obviously if you're relying on the wastegate to relieve backpressure, you're wasting potential energy from the exhaust no? So as some were saying, this sort of thought would work up to a point. But that point is obviously dependent on a lot of different things and as Chris/Sean say, it also depends on the size of the turbine. Obviously there's no cutoff point because this guy is making over 500hp. Are there any general "rules of thumb" on this one?

Ranzo

This is exactly the point I was hoping to make. Turbine choice should start with how much air can the engine flow. Then when tuning on the Dyno look at the exhaust pressure in relationship to manifold pressure and try to create the best balance. Obviously to make big power you need a larger compressor which will increase resistance and spool time to trying Different A/R's on the backside can aid in making the best balance.......as well as Manifold design and Exhaust size and the wastegate.

Cory Simpson

OK, I've only skimmed over this, but I thought it was bad to have a small exhuast on a large intake, because it would surge.

Is this not true?

crispeed

[QUOTE]Originally posted by rx7tt95
Obviously there's no cutoff point because this guy is making over 500hp. Are there any general "rules of thumb" on this one? [/B][/QUOTE

Every combination is different and that's why there are no 'rules of thumb' when it comes to high horsepower.
Another thing to consider is exhaust manifold design. The manifold also plays a role in backpressure. I've seen the same motor with different manifold designs get the same backpressure with different turbine housings. In the worst case there are a lot of manifolds out there that have very poor low rpm velocity and are also very restrictive at high rpm. The normal and most popular manifold designs of late are only good at one end of the power band. Most of these manifolds are mass produced compromised designs. These manifolds/kits are developed if at all, around stock porting etc. so 'rule of thumb' may apply here. When you get get into aggressive porting and custom turbo kits these so called 'rule of thumb' combinations don't apply.
Like I said before every combination requires a different setup to make reliable, efficent, high horsepower.

rx7tt95

So in other words, get out my wallet and hand it to the pros who know what they're doing :-) Are you still at S. Florida Performance?

Zero R

iTrader: (1)

Cory when sizing a compressor and turbine there is a very good formula to go by.Measure the compressor wheel exducer diameter and divide it by the turbine inducer diameter. This gives a wheel diameter ratio. A good wheel diameter ratio is between 1.1 and 1.20 (good boost response and low backpressure). Mediocre is 1.20 to 1.25 (decent boost response and moderate backpressure). Anything above 1.3 is horrible (bad boost response and
very high backpressure). Anything above 1.4 is shitty (doorstop material).
This rule of thumb is invaluable for turbo sizing, you would be suprised how many are made that are doorstop material and people run around thinking they have great a turbo, though it's not really common in the rotary community because we tend to gravitate to larger hotsides.

-Sean

suganuma

going by that...I ran some #s

compressor - P trim - Q trim
T61------------ 1.21 -- 1.14
T64------------ 1.26 -- 1.18
T66------------ 1.23 -- 1.15
T70------------ 1.32 -- 1.24

I'm using previously posted sizing information from Maxthe7man.

MODEL TRIM INDUCER MAJOR INLET SIZE MAP

T-SERIES TS04 58.42 83.92 101.60 TS04
T-SERIES T-61 60.96 89.92 101.60 T-61
T-SERIES T-64 63.25 93.22 101.60 T-64
T-SERIES T-66 65.53 91.03 101.60 T-66
T-SERIES T-70 69.09 97.79 101.60 T-70
T-SERIES T-72 72.14 102.36 101.60 T-72
T-SERIES T-76 76.71 102.36 101.60 T-76


MODEL TRIM EXDUCER MAJOR

T4 N 52.60 74.22
T4 O 58.32 74.22
T4 P 64.62 74.22
T4 Q 68.40 79.02

SPOautos

Does a T76 have much more lag than a T72? Has anyone compared the 2 directly? I was thinking of trying out a T72 but the only diff in it and a T76 is the ompressor inducer is 4mm larger on the T76.

If there isnt that much difference in getting the power to build on it I might try that instead of the 72

Directfreak

iTrader: (2)

He's not part of SFP. His shop is next to them, and they have a professional relationship - but they are NOT the same entity or company in any way.

rx7tt95

Gotcha...so I can go directly to him for say an engine build or advice on my current turbo setup?