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Discussion Starter #1
What’s a good A/R for a basic GT40 top ended Fox? The A/R on my 70mm On3 is .70. The new turbo I was looking at is still a 70mm but had .81 or .96. A/R, They are out of the .81 and I’m wondering if the .96 is going to be too much for my setup. What do you all think? Any first hand experience? My car is also 90% street.


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Is your motor laggy? When does the boost kick in?

If it's street, I'd want it as responsive as possible but still pull to about 6000 which also depends on your camshaft.
 

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Discussion Starter #3
That is where I don’t know. I’m putting stock cam back in, the boost before would start pulling at like 2500 rpm depending on throttle position. I guess my only fear was the .96 A/R would be too much and wouldn’t kick in until way later. Or if I was just over thinking this all together lol.


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Discussion Starter #4
These are the specs on the turbo I was considering:


PTE's PT7075 Turbocharger features the following:
• 70mm inducer compressor wheel
• Compressor cover - "H" compressor cover 4.0" inlet/3" outlet
• 75mm, 84 trim turbine wheel
• Turbine housing: - T4 Tangential .96 A/R with 3 5/8" V-Band discharge
• Hydrodynamic 360° thrust bearing system


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I've spent some time reading about different combos running different A/R's.

I've never seen anyone post results on .70/.81/.96 on the same engine. I have seen more than one post where the poster had an "all stock" 302 and their turbo has a .81 and the A/R is "perfect".

I have also spent a bunch of time watching and studying the setup on the Roadkill Rotsun. Everything about it screams it shouldn't work very well. From the sketchy hot side setup to the Powerstroke turbo. Yet it works really well on the stock 302 they have it on. I saw that they put a Banks turbine housing on it and I was able to find confirmation that the Banks housing has a 1.00 A/R online.

Why care about that? They use the E7TE heads and stock cam and they make peak torque at around 3800 rpm and the engine falls on it's face at about 5200-5300. I believe that's the heads fault.

In the Engine Masters video on the dyno the setup made over 600 ft-lbs at 3300 rpm at the crank running 14-15 psi. Set aside the numbers and boost level and consider that to double the factory torque at 3300 would require at least 14psi and you can surmise that the 1.00 on that setup was not an issue.

Also in this article Economical Turbo Kit - Wind Of Change - Muscle Mustang & Fast Fords Magazine they ran a .96 A/R turbo and it didn't seem to hurt boost performance even down at 2500 where it resulted in just over a 2:1 boost ratio (which is 14.7 psi).

So....1.00 A/R or 0.96 A/R..... let's say they are basically the same. And if it's not what you need, you can always buy just the 0.81 turbine housing and swap it to fine tune it later.

Either way I would like to ride in your car next summer. Hopefully my car will be up and running by then.
 

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Discussion Starter #8
I know he had an E303 and was on the factory block before.



He lifted a head gasket and is rebuilding now.


True story lol. E cam was in my stock block with my s trim and the car ripped. The e cam wasn’t as fun with the turbo. I could tell that I was leaving a lot behind and I felt that I’d be better off with the stock cam and 1.7 rockers. Lots of success stories with that combo. That’s actually all I want from this. 4-450hp at the tire and something I can run mid 11s in with better drive ability than the e cam. I know I can make a custom cam blah blah but I have a stock cam and a brand new set of crane 1.7RR. I seen Power Added solutions sells the “upgraded” On3 kit and used that turbo. I already bought the precision wastegate so I figured if I had some extra cash a new turbo might put me a little ahead of what I want.... the turbo I have is used but seems tight. I may just finish working out all the bugs on this car and buy the turbo this spring or summer after I see how the new combo works. But I was wondering when purchasing the turbo what disadvantages I would run into with that.


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Discussion Starter #10
I mean, the car was fun with the S trim, it sounded mean at idle, it sounded even better when you hammered on it but I bet it only had maybe 375rwhp. And to be honest I was tired of the V1 whine. It was only cool at a cruise in lol other than that it started to get old. The E cam would buck though parking lots when you were trying to creep along. So now with my “new” combo I’m hoping to reclaim what I had lost with drivability and still have a fun street cruiser. I’m putting ARP studs in place of the bolts I had and I’m probably going to have the boost around 11-12psi.


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The 7075 with a .96 will be lazy down low on a 302.
 

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Discussion Starter #14
Are you running a 7075 or something different? I think I’ll definitely go with the .81. Thanks


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Discussion Starter #16
"lazy" wouldn't be an issue with a 4R with a proper convertor. Just sayin'......


Lol I don’t want to give up my TKO just yet....... one more season and then I’ll decide.


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The 7675 bb will spool a few hundred rpm sooner than the non bb. It will still spool slow on a 302/306 with a stick.
 

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Ya I'm looking at a used [email protected] guy has a presishion turbo I beleave the best you can buy at the time kit is about 3 or 4 years old about 3000 miles. Turbo is a T76 GTS billet wheel turbo says full boost by 2700 with a stick he had TFS Heads .wants 3 grand plus shiping with .its a quality kit but if the turbo is going to suck on the street then not worth it.
 
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