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Discussion Starter · #1 ·
These are my oppinions only, and not based on experience with my Saab, but rather with other turbo cars I've had the opposrtunity to work on. (Chryslers, Hondas, etc.)

Here I'll lay out what I think are the pros and cons of each design, and please feel free to give input!!

Journal Bearings

My Conclusion:

For power levels below 300 bhp, the rotational inertia of the compressor wheels and turbine wheels is such that transitory response is not a problem. Twin scroll migh help some with flow, and if you are already having a custom exhaust manifold made, it may prove a relatively cheap and effective way to get what most users have described as "instant-boost" ... but otherwise, stick with traditional turbos. They're cheap, effective, and reliable.

For power levels above 300 bhp it depends on your wallet. Ball bearings should be a must at this point. But at this point you need to do what an accountant would call a "cost/benefit analysis". If the cost of a twin scroll setup causes you to be unable to afford another upgrade which would be more effective, then forget it. As for VNT, forget it unless you have an unlimited budget. You'd need to mix and match turbo parts, and have many custom things made to do this effectively as most are designed for the low-EGT world of diesels. (like the Saab and Volvo diesesl, which have a VNT turbos) However, for those who have nearly unlimited budget, and want a 400 hp car which is also drivable, VNT is the ultimate setup, period.

Hopefully this will be useful ... and by all means these are just oppinions of my own, and oppinions of others (like Corky Bell and Hugh MacInnes), and every application will be different. Even the best ideas implimented poorly can give poor results. Only experimentation can give proven results, and until a kit has been made to take advantage of these ideas, much cost will be spent in th experimentation.

The reason I made this post is to start discussions and get people to start experimenting! If no one ever tries anything new, no improvements will ever be made. So let the experimentations/discussions begin!!

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