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      01-08-2013, 10:30 PM   #55
jdbretz's Avatar

Drives: '07 E92 335i, '07 E70 X5 4.8i
Join Date: Dec 2010
Location: Florida

iTrader: (9)

Originally Posted by Vargasturbotech View Post
Bottom line of what he was saying is you are not correct in saying twins will run out of air up top. Which I 100% agree with, your thinking is flawed. You have TWO compressor wheels that will flow as much as a big SINGLE compressor will. You will hit a wall up top based on your turbine A/R and turbine wheel sizing much before your run out of air if you have sized your wheel combo correctly.
Once more a post generalizing about turbos was applied to specific situations. I never said all things being equal the single would flow more air. I know you know turbos much better than I do, but what would be the benefit of twins over a single if the twins took just as long to spool? You are then paying for 2 turbos to accomplish what a single can do, and a simpler set up at that. You choose the turbo(s) based on power goals, and what spool characteristic you would like. There are compromises for each. You give up a little low end power for more peak power, but as far as I know there isn't a turbo out there that will spool at 1500 RPMs like our stock ones and hold power to redline. I bolded the key part of your statement which is the whole basis of what I explained originally.

I am in no way saying the current single is or will be better than the Stage 3 set you are building. I honestly think your twins will be great for this platform. That being said, I have a hypothetical situation I would like to know the answer to if you don't mind helping me better understand this. If the N54 was revving to 8000 RPM, there were no concerns of fueling, and the block would handle it, would the specific twins you are planning on using on your Stage 3 produce as much peak power as a 62mm single in the same car assuming perfect tuning on both? I would guess that twins that spool much quicker than a larger single, would be out of their efficiency range at a high boost/high rpms scenario where as the single would still be doing fine. Is that incorrect? I know you could put larger twins and run the same power to redline so that is not what I am asking. I am asking if twins that spool by 2500 RPMs will run out of air before a larger single that spools at 3200? I am generalizing once more, so if it is possible to answer this question as it is without specifics I would really like to know (not trying to be a dick or anything, I am genuinely curious and would like learn more about turbo configurations) Also I am not in any way trying to turn this into a single vs twins battle, so please don't take it as such. I don't have the money to buy either of them, but I would like to learn more.

Last edited by jdbretz; 01-08-2013 at 10:47 PM.