ecms171 wrote:Hey, quick update since last time.
Tony:
thank you so much for your post, i really appreciate advice from someone who has been there and done that.
In regards to TQ i should be good to go past 300 WTQ if i have new pistons and more specifically new rods?
Mechanically i understand how the trim affects boost and response, but I havent found any mathematical ways of working out these effects, even vague ones.
I know the larger GT28XX and smaller GT30XX are the right size compressor for our engine but i still dont know how to factor in the trim and turbine into my calculations.
Im sticking to some nice new ball bearing turbos just for better response, which im hoping will cut down on lag. A nice large exhaust should minimize backpressure, and i have the FMIC and Meth both reducing intake charge temps. I have hopefully a double headgasket to bring down the compression ratio. With the new 2GR rods being good for nearly 500lbft of TQ i think i have most of my bases covered with the engine. Anything else i may have forgotten?
Also, in terms of the ratings on the turbos, should i be paying attention to the manufacturers rating? Is it really significant at all? And any suggestions on how to do the calcs for trim and turbines?
With pistons and rods, you can go well past 300 lbft of torque... Our motors aren't that great in terms of head and combuston chamber design, so on pump fuel (91 or 94 oct), it will depend on your compression ratio to determine what's the safe limit. When I had 9.0:1 CR, I ran it at 460 lbft of torque on 94 oct, and there were no problems. I went higher later on, and plugs showed signs of light detonation. Mechanically the motor will take it, so we have to worry about detonation again in terms of finding the limits.
For turbo sizing, the wheel trim is the ratio between the inducer and exducer... You don't have to worry about trim numbers for either compressor or exhaust, just because the trim affects the flow and pressure ratio of a certain wheel. The result is the full compressor map you see on Garrett's website, so just base your flow and sizing on the compressor map because that's all you'll need.
For the exhaust housing and turbine wheel sizing, for example, like a GT2871R, or a GT3071R; these two turbos have the same compressor wheel and HP rating, but the GT30 series has a larger exhaust wheel. The 1MZ isn't too efficient in making power based on fuel consumption, and it means that for the same amount of mass air flow from the turbo compressor, our motors uses more fuel for the same given power (higher BSFC) versus a more efficient engine. So a GT2871R compressor rated for 42-45 lbs/min allows for roughly 400 WHP, but the 1MZ motor needs a lot of fuel to do it. More fuel means more exhaust energy, more heat and more flow out of the exhaust.
The same air going inside a 11.5:1 CR Honda 4-cyl engine for example, requires much less fuel to support the same power. It is due to efficiency. Higher revving, better overall VE, better burn, higher compression ratio are factors contributing to efficiency. So the same given 400WHP worth of flow, the Honda uses much less fuel. Lesser fuel means lesser exhaust energy, lesser exhaust flow, thus, requiring a smaller turbine wheel and housing.
So that is why the GT2871R is really designed for smaller 4-cyl engines. If you run the GT2871R on the 1MZ, you will be fine until about 350 WHP, until the exhaust energy maxes out the turbine side and begins to choke based on the turbine maps. This just simply mean that the turbo was improperly sized. There is no point to run a 400 WHP compressor wheel if the turbine side chokes at 350WHP. So a better turbo (GT28 series) for a 1MZ, is actually the GT28RS. It is the same GT28 turbine wheel and housing, but a 350 WHP rated compressor wheel. Perfect match for that power level. But if you want 400-420 WHP, you have to step up to a GT3071R for a 1MZ-FE
I know you are probably wondering how do I determine that the 1MZ-FE uses a lot more fuel than a Honda engine at the same power? You have to tune the motor to find out. The power my engine makes, versus the amount of injector duty in relation to injector size and rail pressure, lets me know how much fuel I am burning based on the power I was making at a certain RPM.
There is no "clean" way to calculate this. You have to go by prior experiences with other engines. I would tune a Honda Civic B16A with a GT2871R for example, and I notice it starts to choke right at 420 WHP (maxing out the compressor). So in this case, the turbo is well matched. I would go back to the fuel maps and determine the BSFC for the given HP. From there, I have useable a figure to work with. Then I would crunch in some numbers for my Camry and check out the amount of fuel used when I was making 420 WHP, and right away, I have found a useable figure and can determine the BSFC as well. With BSFC and amount of airflow consumed into the engine, you can get the exhaust flow figure just using some online calculators.
But I did all the research for you already.. Your best turbo for maximum spool per HP output (and within Garrett GT-series) is:
560-680 WHP --> GT4094R 0.85 A/R hsg;
The GT4088R ideally has the best comp flow sizing for this power, but the wheel does not have a high enough pressure ratio to make it there on a mildly built 1MZ. It needs bigger valves, port work, etc.. Goodies that allow more power at a lower PSI.
420-560WHP --> GT3582R 1.06 A/R hsg.
300-420 WHP --> GT3071R, T3 0.82 A/R hsg.
260-300 WHP --> GT28RS, T3 0.82 A/R hsg.
230-260 WHP --> GT28RS, T2 0.86 A/R hsg.
by stringbean » Fri Nov 26, 2010 9:44 pm 
