So....
I poured over how to figure out the math for turbos, and plot points on a compressor map.
http://www.enginelogics.com/read-a-turb ... essor-map/Only lousy part of that sight is they used a bad color scheme. The examples for each section are a grey that blends too easily with the background - so there was a lot of highlight/copying/pasting.
And either I royally messed up my math, or I plotted out the following information - go me! (apparently, excel formatting does not carry over well. Sorry for the hypenated spacing replacements). I've got a lot more numbers I wrote down and typed up in notepad... but I didn't make great notations at the time, so... not sure what it's all for, or if anyone is interested in other numbers. If there are, just let me know, I'm sure I have them!
RPM----------------------------------1000---3000---3750---4750*---5625---6500
VE-------------------------------------88-----89-------91------90-------89--------87
Intake Temp-------------------------89-----90------105----135------138------140
Boost----------------------------------0------1-------10.6----20.1------20.1-----20.1
Pressure Ratio----------------------1------1.07----1.72----2.37------2.37-----2.37
Corrected Airflow (pounds/min)-6.5----21.1----42.3----66--------80.4-----91
The 4750 is where my current HP plateaus till the near-end of the run, and also where my torque starts to drop off.
I ran these numbers assuming .55 for BSFC (what I read said that turbo engines are usually between .55 and .60)
So I took that stuff and started plotting out the points on compressor maps I could find, that article said to try to get the area you'll be operating in most often in the highest efficiency point of the compressor table. The trouble I ran into was that my other points after the 3k, were all higher and to the right on most compressor charts, pushed well outside peak efficiency.
Chug said that there's also a way to read these compressor maps to see how it'll lay over your power curves, but I haven't quite figured out how to do that yet, so right now, just working on getting stuff in the right section of the compressor map (highest efficiency, and avoid the left hand side where there is surging).
Mapping out the GT4708 108mm, 56 Trim, .69 A/R and the GT4718, 118mm, 56 Trim, .69 A/R seems to be the best options so far given my limited knowledge.
When reading up on these turbos, it seems like I'm going to be leaving a lot of this turbo "on the table" (the 4708 is good for over 1000 HP, way more than I need or want), but it has a peak 79% efficiency. The 4718 peak efficiency is 78%. In both cases, a good number of my mapped points are in, or very near, this efficiency level, and all a good ways away from the surge line.
All that aside, I gave up trying to get the correct pressure plate from Clutchnet, ordered a Spec 3+ off-the-shelf clutch, and filed a BBB complaint on Clutchnet.
FieroGuru hopes to have the car all done, tuned, and ready for pickup by the end of the month - assuming my new clutch/pressure plate shows up as quickly as promised.
Sadly, won't be ready in time for Chugfest, but that is by no means FieroGuru's issue, that's due to parts issues/delays.
1986 Pontiac Fiero GT, 355 cubic inch small block Chevy putting down 371 HP and 381 ft/lbs torque at the wheels, with more to come!