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Discussion Starter #1
Looking at the on3 kit. I have 331 stroker with forged internals, ported tfs heads, ported rpm intake, blower cam (any negative issues keeping it?) however running 68' block with girdle and canton 7qt. road race pan. This is pretty much a street driven car so I don't need the biggest turbo I could get as I will be keeping the a/c and leaving 130 amp alt on the passenger side. I wouldn't mind spending a few bucks to upgrade to ceramic ball bearing for reliability however I don't understand the options available for turbo sizes. I visualize running about 7 to 10 lbs of boost which I don't know hp wise where different sizes would take me hp wise, thinking 600rwhp. Are the larger turbos only effective when running more boost such as am I doing wrong to get a larger turbo for down the road (when going to dart block and more boost) or at the boost level better off having a smaller turbo? Also if one could also recommend injector size/brand to use. Let me also know what has worked for tuning as I was thinking about switching from pms to microsquirt.
 

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The cheap 70mm journal that comes with the kit was a great turbo for my stock block 347. If reliability is an issue, the 70mm is relatively dirt cheap to slap a new one on. It’s literally 4 volts, that are easy to reach. To swap a T4 turbo on a Fox On3 car is at most a half hour of easy work.
People go with larger turbos for a number of reasons. More power, less back pressure are the 2 most common reasons. But there are also downsides to going larger. Fitment and being more lazy are 2 common downsides. There are ways around those issues. But for your build it’s pretty much a simple build. The basic 70mm journal is cheap and sized pretty well for your build.

When you move from your 331 into an aftermarket block. Then start trying to over think it. For now, there is no valid reason to create a mountain from a mole hill.

For injectors, I went with Injector Dynamics. I needed high Z’s.
There are a slew of 80# injectors on the market now and they are low buck. Mine were nearly $2k but drastically overkill for your build.
I’d look for a deal on some Ford 80’s and call it a day.

The basic On3 kit is a solid starting point. Don’t worry, it still packs enough to split your block in 2 with relative ease. Save your money in upgrades and spend it elsewhere on the car. Transmission, rear end...suspension, tires, ECU, fuel system...the list never ends.
 

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A 76mm with a small A/R like a .68 will do well with the proper cam. You could then upgrade to a .96 later on when you step things up for more power. Ball bearing will help spooling time as well.
 

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Discussion Starter #4
would that size with a blanket still fit my 130a alt? I still want to keep a/c. I would sacrifice low end torque as I already need drag radials on the street.
 

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Is this an auto or manual car? Thats a big thing as well as what gears you have.

I personally for that power range liked the master power t70 turbo.I had all the housings (.68,.81.96) as well as 76mm turbos and s475 etc. I really liked the car with a .81 with a mild 600whp set up.The boost came on instantly and didnt choke like the .68 did. This was a c4 with a tight converter and 3.27s .I didnt like the .68 really at all...I eventually switched to a .96 for more flow and i had a transbrake so it didnt matter,i could make full boost on launch with the brake.

The .68 with a 5 spd and 3.73s was in boost cruising on the highway and spooled way to fast
 
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