Hi all,

Since I like to learn something new, I thought that this can be a good topic of discussion since I am not able to find nothing specific online and here on hondatech.
I asked this question on my build thread but I think that this could be helpful and needs to be separate from my build thread.

So I ask the turbo tech guys present in this forum to chime in and help me / us to understand.

How is it possible to calculate the correct AR size based on a specific engine ?
Even on the Garrett website the answer to this question is superficially covered, and multiple times the average answer is “just pick one in the middle”.
I would like to go a bit in depth and understand the process behind this choice.
Sometimes is possible to choose between a smaller turbine wheel and a big AR housing, or have the same flow going with a bigger turbine wheel and a smaller AR.
I don’t want to pick a specific turbo for this case but I’ll leave it to whom know this topic better than me.

Thanks for your attention!

 

You, like me, are overthinking a lot of this. The reason it is superficial is because there are many variables involved and not just a simple equation. Your engine displacement, goals, use, efficiency, modifications, all play a factor. If there was a solid answer, my friend, it would have been posted!

 

You almost cannot calculate it. Its a guess/ experience thing. Ill tell you tho. On the evolutionm forums i found 2 reports back in the day of people that had gtx3076 .82 and went to gtx3576 .63.
Those hotside combinations flow the same but both reported it was a very little bit slower on spool on the gtx3576.63 but when it came full boost it was better. It makes sence since turbine wheel is the powermaker not turbine housing.

 

I'm not very knowledgeable about turbo sizing, but from my experience and from seeing what others are doing, I agree with Txdragon and Balor_Gr. Most guys that are serious about racing will have the funds to try one and if they don't like the performance, go up or down in AR. Us weekend warriors or street guys just usually go off the reports and experiences of those with similar setups to ours. Maybe one of the gurus will step in and learn us all something good!

 

Ah, young people. Same question, different year.

But yes, there's some equation to it, but it's more of a differential calculation between turbine wheel diameter, compressor wheel diameter and profile, desired behaviour, engine displacement, max rpm, Volumetric Efficiency and exhaust back-pressure.

Come to think of it, more like 4 calculated equations, not just one.

Side note. What would you guys think if I did a recorded Zoom videocast on Turbochargers in General? From Billet wheel materials to "Rules to Grow on?".. Any interest?
I'm thinking of posting it on Skillshare, and make a little coin while I'm at it. Took me a while to put it together, but would like it to do some good.

 

Sounds awesome. One question: Dafuq is Skillshare?!

 

Learn something.