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Discussion Starter #1
Built and forged 4.6 with 8.5 compression , stock heads and cams , pac stage 2 valve springs , 76mm on3 turbo , all the needed fuel system upgrades to make tons of power.

One of the rookie guys at my tuners shop told me 600rwhp would be max on,setup with pump gas. I don't believe that as I see way higher numbers with 4.6s with 76mm turbos.

What do you guys think? Should I upgrade to a bigger turbo for my goal or what ?
 

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I'm not an expert on those heads and all I can do is compare your combo to mine but I would be concerned about the stock heads and stock cams holding it back. But if you cram enough air down it's throat it's bound to make the power so it may come down to how much boost you will need.
Maybe someone else can chime in but I'm guessing that the 60# inj's will be pretty much maxed out.
 

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Honestly that low of compression, stock heads and cams, and pump gas...I think 600rwhp will even be a stretch. A bigger turbo will not necessarily net you more hp. For your power level a 76mm is actually probably even overkill the way it is
 

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You have an ON3 turbo. It isn't like you have a race turbo or something like a Precision.

My car is a 363 with good heads that flow mid 300's. With a racing class legal Precision 7675CEA it made well over 1000.
 

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I don't have much history with 4.6's. But I ran an On3 70mm on a pushrod 302 and could get 600 out of it. If I pushed it hard enough I don't see 700 unrealistic out of an On3 70mm. Perhaps not ideal, but not unrealistic either.

A 76mm on a 4.6 is large enough to hit your goal. I don't see the turbo manufacturer being a limiting constraint. However there might be other things in your combo that limit the power?
Did this "rookie tuner" say 600hp limit due to solely the On3 76mm?? If so I'd take that guy's advice with a grain of salt...IMO.
 

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The turbo will PROBABLY cause an issue.What size is the exhaust turbine on that turbo? My buddy had a built 2v with heads and cams and an on3 kit with a precision 7675 and that was a stretch with his t56.Think it made mid 600s on tons of boost for pump gas with the 7675.His compression is also 9.5 i beleive.

Also he had a real nice intercooler that held his IATs way down.My previous on3 turbo on a 302 based car didnt mske the power thr higher end turbos did
 

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Discussion Starter #7
That's what I'm worried about as the 7565 turbo basically. it's only got a 65mm exhaust wheel. I've contemplated going to the 7875 turbo that is offered now because it's got the bigger exducer
 

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Am I missing something or is your car not a 4v? I think it'll 700 pretty easily with a better turbo. Not saying it couldn't be done with the on3 just would need more boost. Might need a larger injector.
My 5.0 made [email protected] with gt40 heads and 14psi out of the 70mm on3 kit. Lifted the heads so never went higher.
 

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Am I missing something or is your car not a 4v?
That's a great question! I assumed it was a 2V mod motor but if it's a 4V then I change my opinion. Making 700hp from a 4V should be easy.

ks
 

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Discussion Starter #10
Yes , sorry it is a 4v cobra 4.6. I was hoping for at least 650 to 700rwhp range with it using the on3 76mm but if not I'll go a little bigger or better quality 76mm.
 

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My comment was based off a 2v as well. 8.5 compression and 93 octane are going to be the dampers on your goal
 

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93 octane and 700 RWHP has been done, how long it will live is the question. You will have zero room for any fuel or injector issues. On my turbo 3V I could not get past 600 RWHP on 91 without knock at 12 psi. Anymore boost or timing and I had knock.
 

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Discussion Starter #13
91 would be a killer. 93 at least has a little room to grow .
 

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Just saw this is a 4v...I still think a meth kit should be in the cards if your planning to go crazy on 91 octane.
 
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Never had one issue with my on3 turbos. Not sure what a "race" turbo is and precision is a brand just like on3.
If you don't understand the general idea, the jist, the fundamental principle behind that comment. Then you've just shown your background on this subject matter.

Cliff Notes: yes there is a difference between a $300 turbo and a $3,000 turbo...

I enjoyed using On3 turbos. They were ok for what they were. From a Cost to Fun factor, they were the cheapest fun I've ever had in this hobby. However it's a big beautiful world out there. When your ready to transition from "just having fun" to "I'm ready to make power." You will absolutely understand the comments you quoted.
 

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If you don't understand the general idea, the jist, the fundamental principle behind that comment. Then you've just shown your background on this subject matter.

Cliff Notes: yes there is a difference between a $300 turbo and a $3,000 turbo...

I enjoyed using On3 turbos. They were ok for what they were. From a Cost to Fun factor, they were the cheapest fun I've ever had in this hobby. However it's a big beautiful world out there. When your ready to transition from "just having fun" to "I'm ready to make power." You will absolutely understand the comments you quoted.

Yea, your probably right I wouldn't now what its like, Maybe some day. I took Precision Turbos off my Twin Turbo Gallardo, and The owner of ON3 Sent me some new billet wheel turbos they just came out with, and the car made the same power 12xx AWHP with a set of On3turbos that cost a 1/16th of the price. Ive Ran Garrett, Precision, On3, Borgs ETC. Thats the great thing about the aftermarket world, you have options and not one of them is right or wrong.
 

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Nothing is against the quality of the turbo,its just not all "76mms" turbos are the same...

The On3 turbo he has is a mild street turbo and will run into back pressure issues if he turns the boost up to start trying to make power.Depends on hos goal.I assumed as well it was a 2v

That car would be more happy with the 7675 or similiar.When you start pushing more boost to make power and the small exhaust wheel causes back pressure it generates tons of heat and the turbo blows hot air due to this which increases IATS as well.Properly sized turbo are very important.

I just took a s366 t4 .88 Borgwarners off a Windsor and put an s475 t4 1.10 and it feels better everywhere.Spools faster ,comes on way harder,and pulls all the way to red line.I assumed the smaller turbo was ok due to the low stall converter and i didnt want a laggy turbo until I swap converters...boy was I wrong.The car is stronger on 10lbs then it was on 15 before.
 

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Discussion Starter #20
I ended up buying a 7875 turbo and will be selling the 7665 lil guy , ha! Now just waiting for the engine to get done...some time this millennium
 
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