Thanks for the info. I REALLY didnt want to change turbo's but looks like I may need to now.

Can someone explain to me though why my 76mm turbo ISNT a 76mm since its a q trim?

 

Try it and see if the current turbo makes enough to keep u happy. I was just throwing a better match. Wont hurt anything to try yours.

 

Im going to have to for cost reasons now. I still dont understand why my 76mm isnt a 76mm?

 

Same reason a small block is just a small block.

Need to consider both sides. You’ve got a 76/68. Look at it form a leverage perspective. The smaller the turbine is the less leverage it has to turn the compressor. This causes slower spool and more back pressure. All these “upgraded” larger wheel compressors don’t do much if you’ve exceeded your power limit on the turbine side. Turbine and AR housing play a big roll. That "S475" (really a 74.5mm) would beat the pants off your current "76mm" turbo IMO.

 

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This is the one forcefed86 is talking about.

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Alright I'm picking up what your puttin down now.

 

I'm going to say something different... although a bigger turbine may be better, I don't think a Q trim on 347 cubes with the 170's, and the right cam is a bad choice. If he has the t76, still wants to keep rpm down, wants to keep a smaller frame turbo, or its more of a street car, i'd go Q trim, before a 96mm.... What is the intended use?

 

Have to remember that BW lists the major diameter of the exh wheels. Its not really a 96, its an 87. IMO if the car was to run a quarter mile the big s475 would run a quicker et and trap on 350+ cubes than his current turbo.

 

I understand that, i'm just saying that given the choice of a Q trim, or 96mm for a given combo, and usage i'd rather under turbine than go too large. I'm not saying a 83, 87,92,or 96mm turbine won't make more hp, just that the Q trim was used on plenty of hp combos before the Bw's, and large turbines became the rage, and wouldn't be a horrible choice for 347 cid given it fit his intended use.

 

I think it fits the intended use well now. Since its a street car it doesnt turn a lot of rpm's anyway. I also have a 3 inch hotside so Im getting plenty of volume to the turbo. I AM going to do some testing at the track and see if I might need a spool valve to help get up on the brake sooner.

 

You dont' want volume going to the turbo you want velocity. 3" is way to big and will perform poorly compared to a properly sized system. The turbo scroll necks down well under 2". It is the restriction in the system, not the hotside. Your 3" hotside adds volume and slows velocity. (adds to lag) A 2" hotside will support 900hp and would spool a larger turbo much better.

4.8's are spooling the big S475 without any problems using the right converter and hotside.

 

Interesting post. I never looked at the leverage point but see where you're coming. What do you think about an off the shelf s366 .88 ar on a 260ci motor? Upgraded from a 6262 .63 but still managed 103mph traps in the 8th on 16psi and 3500lbs.

 

I don't know the S366 wheel sizes off hand. Less restriction on the exh and larger wheels always have an edge performance wise if you can get then into boost quickly enough. If you can't spool a turbo until 6k and your redline is 6800... obviously you need to step it down a few notches. It's all a balancing act. The hotside size plays a huge roll.

 

91/66 and 80/73 turbine. Another 4.3l like mine is spooling a turbonetics 76mm unknown turbine 96 ar full spool is 4500rpm. I'm thinking 4000rpm on mine with a 6500rpm shift point.

 

That is a big change in turbine... 366 is 80x73mm. Like forcefed posted, if you can spool it when you want, a larger turbine is the way to go. He is also right on the larger turbine making more hp, and the balancing of the two, I just wanted to point out there are always multiple ways of doing things, and some are better suited to some goals, and to parts you may have..... cost being one of the big ones.

 

That's what this engine needed, a lot more exhaust flow. The 6262 was originally intended for a mild 3.8l but you know how things can change. This engine was intended to make power past 6000rpm but fell way short with the tight housing. The 6262 would spool with 2600rpm part throttle going down the highway, well before the shift kick down is programmed at 3v on the tps. On 15psi manifold I logged 38psi pre turbine at 6000rpm. The cam was spec'd to make 700rwhp and the heads have some trick work done to them to increase flow. I have a build thread I'm going to post some pics in. Sorry for getting off topic in this one.

 

The 6262 turbine is quite small, and the 366 turbine sounds like it should work good for you. I ran what was basically a s366, but was in a s400 frame (goofy Mack turbo) with a t6 1.10 a/r on a stockish 5.0 on e85, and it spooled great. It was going positive before 3k, and ramped up quick.