PetroleumJunkie412 asked me some things in a pm, but I'm choosing to answer publicly, in hopes of helping others:
>>>
Hey, was re reading that thread again. You mentioned you didn't like most turbo sizing formulas? Been reading on that area for a few months, and still trying to figure out if the one I have here is correct for a 2.9. 13T off a volvo 2.4/2.5L - they call it a 2.4, but it's 2496cc.
<<<
I DON'T like turbo sizing formulas. Because
Here's why:
1 the people that use them, don't need to.
2 they make people stick to a particular number
3 ergo limiting their choices
here's a formula:
.... hell I cant even find one now!
but it was basically engine displacement x max rpm x boost
or something like that. whatever..
rpm: I'm not gonna run at max rpm. A 2.9 in a truck does not need to be spun at 6500 rpm. period. so why should it figure in my calculation? It shouldn't.
boost: who in the hell picks almost any number and then sticks to it? no one.
CId: is not gonna change, but it is practically the most important variable related to turbo sizing.
For me, here is how I picked the turbo I used.
I'm very familiar with Ford's various turbo offerings of the 80s; 2.3 Thunderbird, SVO, XR4ti, and Aussie Capri (Mazda).
So the 2.3 Turbo Coupe had a smaller faster boosting turbo in 87/88. They did that to make it spool faster and earlier.
2.3 x 6500 rpm = 14,950
14,950 / 2.9 = 5155 rpm = good enough for me.
I had previously built a Merkur XR4ti with a Turbo Coupe turbo.
It made over 300 lb/feet torque at 3000 rpm at 17psi of boost.
In fact THAT very turbo is THIS very turbo.
I already had it, and it cost 50 bucks = good enough for me.
Speaking of which, 2.9 / 2.3 = 1.26 x 300 lbs tq = 378 lbs tq. This is a valid guess at what's it's making at 8psi. I think it's more like 450+ lbs tq at it's current 17 psi.
On a great flowing cylinder head it is a rule of thumb that at 8psi you will double the original horsepower. 8psi is actually inverse equal to standard atmosphere, so this makes sense. IOW 8 psi is as far from 0 ATM as 14.7 inches of water is. Look at the combo gauge in both directions. You can make good guestimates at power using this. In most cases the cylinder head is not awesome enough to double the horsepower, but it does flow enough to double the torque which is at a lower RPM. So at 8psi it should double the torque. Anyone here would LOVE that improvement.
Back to sizing. You want to turbo you vehicle for an increase in power. Anything that stands in your way is a negative.
Is it not better to be turbo'd with the wrong size, than not turbo'd at all?
You said your goal is 30 extra horsepower. Good luck keeping the improvement THAT small.
More important considerations will probably be turbo mounting and exhaust connections. You can familiarize yourself w various turbos by joining enthusiast groups for various car manufacturer turbo model sites. or haunting a junkyard.
If you look at a turbo, there are 4 necessary connections: air in and out, oil in and out. In fact, my turbo is water cooled and it's not connected.
With a turbo, every improvement that you make to the flow of the engine, every gain will be magnified.
Also, the cost of every improvement you might make to increase power can be deducted from the cost of turbo'ing the engine, by NOT doing it. It's usually cheaper on an absolute (dollars spent) basis, but more importantly, it's ALWAYS cheaper on a $ per hp basis.
The 2.9 has a broad flat torque curve, perfect for turbo'ing. Mine additionally has necked down SS valves, and World Products improved casting brand new heads.
So quit thinking and get to doing. Mine took about 6 hours to be operational, then probably another 10 to get reliable. There's more room for refinement, but honestly isn't worth doing.
View attachment 37227