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im getting my turbo next month and want to order the correct size... I am going to get a GT3076RB but I have seen A/R range from .48 (slimjim) to .82 (peanutbutter)... what differences would this A/R make on spool time and or max hp numbers? would the .82 spool slightly slower than the .48 but make higher HP numbers? im interested in knowing...
I posted this on another thread but it off topic so I'm making my own thread so we can discuss this further...
The A/R sizing impacts the spool time, but more importantly, it has a huge effect on where the compressor's efficiency range relates to engine speed speed. If I had a 0.63 or 0.82 A/R turbine housing, I might see a spool time increase of 300-600 RPM, which might be considered moot in a race since the engine speed would always remain high enough to keep the turbo spooled. But since my A/R is really small, it creates a restriction, and forces the exhaust gas to speed up a lot as it hits the turbine blades. Faster gas movement = faster turbine spinning = faster compressor spinning. A larger A/R won't accelerate the flow as much, but at exhaust gas flow rates (corresponding to higher engine speeds) the exhaust gas speed will reach a similar speed to what the smaller housing creates at a lower RPM.
Take my setup for instance. I have a well of torque at 4500-7500 that falls off big time up top. A 0.63 A/R housing would decrease spool time only slightly, but it would move the torque "mound" over maybe a 1000 RPM. The mound is dictated by the compressor, and the location of that mound is dicated by the turbine.
Ideally, we'd all have variable vane technology turbines. At 4500 RPM, the vanes would be highly restrictive and force the air to speed up a lot to spin the turbine with less exhaust gas (what my 0.48 does). As the revs increased, the vanes would slowly turn and open up the restriction inside the housing. The exhaust gas speeds would remain the same as before, but would now be caused more by the increased revs than the confining housing. At max revs the vanes would allow maximum flow and the result would be amazing. We'd all have torque "mounds" that started at 4000-4500 and wouldnt quit until redline.
These turbos are a few years off from mainstream production, at least affordable mainstream production...
Here is a turbine map for various housing options with the GT3076R from Garrett's website. The Precision housings used by Inline will differ only slightly from these.
These maps show the maximum flow capabilities of each housing. Anything flow over this value will need to be vented out a wastegate.
Notice that the 1.06 A/R allows almost 30% more flow than the 0.63 housing, meaning is is 30% less restrictive. Without more data its hard to say for sure, but 30% more restriction roughly correlates to the turbine reaching it's maximum speed with 30% less gas flow at the expense of a higher pressure delta.
I would not use the 0.48. If I was that worried about response, I would just use the 3071 with a 0.63 a/r housing. I have personally run both the 0.63 and 0.82 a/r housings. There was a VERY minor difference in spool time, but the 0.82 appeared to be more efficient at high RPM. It needed more fuel to maintain the same a/f ratio. For the 3076R, I personally think the 0.82 a/r is the one to have.
I'd like to be able to tell you that it wouldn't matter which you chose and that there would be minimal differences between the various selections, but thats far from the truth.
There are a lot of variables to consider and when it all boils down, the best insight we have is dyno results from other turbocharged engines. Inline has experience with using my turbo specs and the larger F22C and the results were not good. If I had a Full Race or Lovefab manifold instead of the InlinePRO cast iron one, my turbo might not be a great selection.
The best thing to do is to pick a power delivery characterstic that suits your needs. High end peaky power, broad mid range, powerful low end, etc. What exactly are you looking for?
looking to have a strong upper midrange simular to yours but trying to reach the 500whp level... I am going to be running the InlinePRO cast iron mani and the 3076RB turbo... I'm going to be using an aquamist system with direct port 50/50 meth/water injection and a 5th injector pre-turbine intake to increase my turbo efficency map... so I dont need the immediate spool that you have slim but I want midrange and still wanna hit the 500hp club if possible... I am just after a quicker spool and midrange than a GT35R would allow and have no need for the HIGH 500-600hp numbers they make... 475-515 is my optimal range...
The question is do you want a dyno queen or a capable street racing car.
Go with the larger flow if you just wanna shoot the sh*% with the boys and say you have 600hp but if you actually want to drive down the street and race either from a dig or from a roll get something wit ha smaller a/r. I feel that the .63 is great for our cars. But again this is just my opinion don't get upset over it.
Originally Posted by SPECIAL-OPS-S2K,Aug 2 2007, 01:34 PM
looking to have a strong upper midrange simular to yours but trying to reach the 500whp level... I am going to be running the InlinePRO cast iron mani and the 3076RB turbo... I'm going to be using an aquamist system with direct port 50/50 meth/water injection and a 5th injector pre-turbine intake to increase my turbo efficency map... so I dont need the immediate spool that you have slim but I want midrange and still wanna hit the 500hp club if possible... I am just after a quicker spool and midrange than a GT35R would allow and have no need for the HIGH 500-600hp numbers they make... 475-515 is my optimal range...
I have yet to see a 3076R make over 480whp. Regardless of a/r size.
For a 3076 to hit 500rwhp with an inlinepro kit, your going to need an aggressive tune + all supporting mods (aka single exhuast, etc) + some luck. You could easily hit it on race gas but most would find that inconvient.
I would venture to say you would probably need a built motor so you can run over 20psi safely to hit the desired goal.
Originally Posted by AirborneS2K,Aug 2 2007, 10:51 PM
I have yet to see a 3076R make over 480whp. Regardless of a/r size.
I'm with you. Even with the largest A/R turbine housing, I seriously doubt you will be able to reach 500 rwhp with a GT30R, certainly not with the Inline manifold. 2NR Werks came pretty close with a tubular manifold, but to give you and idea of what happens when a turbo runs out of steam, check out the plot below...
The compressor cannot move the amount of air needed to reach your goals. You'd need 62+ lbm/min and a GT30R is going to max out in the low 50s. You'll need a GT35 sized turbo.
Turbo shopping... please explain A/R
