I blew my turbo a few months ago and I'm shopping for a new one. I'm running an S4 Half-bridgeport motor with all supporting mods (cooling, injectors, etc.) in my FC. I used to have a T04R with a 0.70 A/R on the compressor and a 1.00 A/R on the turbine side. Now, I met a guy that's selling a T04S with a 0.70A/R compressor side and an 0.84 A/R on the turbine side.

When I was looking for a turbo in the first place, I was told that for a bridgeport motor you absolutely need a large A/R for the turbine side. I was told a 1.00 A/R would be perfect for bridgeport and an 0.84 would be good for a stock port motor.

Has anyone here experimented with an 0.84 A/R on a bridgeport or can someone explain to me what would be the difference ?

 

Depending on the compressor with a half bridge I wouldn't run below a 1.15. To function properly they need very low exhaust back pressure. I would also be running a Q trim turbine with the To4R on your setup.
The more power and rpms you plan on the bigger the turbine and a/r should be.

 

I plan on 450 whp and my old T04R had a P-trim. So if I understand correctly the larger the A/R on the turbine housing will be giving more power, right ?

 

I've got a .96 on my t70 half bridge setup and do admit that I've heard from some people that it's a bit small so I may go to 1.15 however I tell you that thing spools very quickly

 

definatly dont go smaller than 1.00 and stick with your t04r

 

my understand,, big turbine A/R makes HP,,, small A/R makes torque.

some place you have to chose a happy medium, for what you gonna use the car for!

 

I've got a question. What causes higher increases in exhaust back pressure? Smaller a/r sizing or smaller turbine wheels? Also with the increased back pressure from a smaller turbine housing what are the major side effects of this? Very hot egts? I really need to get an hks or greddy log manifold instead of my ebay knockoff. I'm sure it won't beable to hold up to the heat.

 

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A/R is just a calculation between Ratio and Area. You can only compare A/R in same turbine family, and still only 8 out 10 times you will find the calculation to be linary with size. It is useless as measurement across different turbos, and can be misleading within same family.

Area ((cm2) is much more relevant. Saddly not all suppliers list the figures (ratio and area) behind the A/R calculation.

Example of confusion within same turbo family:
Area of 13cm2 and A/R 0.96
Area of 14.7cm2 on A/R 0.7
Same turbine wheel

Which of the two above turbine housing do you think is the largest turbine housing .... the high thin or the lower fat one?











The 14.7cm2 is largest in overall volute volume

 

Is your motor oversized studded or still retaining the stock tension bolts? What’s your internal work if you don’t mind me asking?

 

This Borq Warner turbine section flow chart shows the relationship between exhaust wheel size and exhaust housing A/R well in regards to overall flow.

 

Anyone know what the deal is on the 70mm range inconsistency. Goes 0.83, 0.92, then blank, 0.80 (???), 1.22. Seems like a typo or general error, but it’s been that way for at least 5 years or so. Hard to believe they wouldn’t fix it if it was.