I am new to turbocharging and have some questions. I'm thinking about hanging one on my big block.
I have a 468 BBC with GM steal crank, h beam rods and GM aluminum rect port heads, (320 cfm), and I'd like to achieve around 1000hp or so. I've been reading that a BW s475 would do it. What turbin a/r, what compressor size? Also, what is the inducer and exducer and which one matters when sizing?
What compression ratio?
Can I achieve this hp with a non roller cam?
What size carb for blow rough application?
Anybody here have any success with studded 2bolt main in high hp turbo applications?
I read Corky,s turbo and he says turbo engines aren't as brutal on bottom parts as n/a and blown applications. Any truth here? Anybody experience?

Or twins? What size? Cheap, eBay?
Thank you

 

Assuming you can make 500 hp n/a, a s475 compressor won't support 1k hp. You could step up to a s480, but even the 80mm will fall just short of 1k at a pressure ratio of 2. Imo the largest of the turbines (96mm) is still small for your goals. I would look at twins, or a single in the 85-91mm range.

 

If I go twins what would be a good choice? gt45's? What ar and comp?

 

Twin 68mm gt45's should be a decent fit. I don't believe there are any a/r choices with the gt45's. The 68mm's are 1.05, and the 76, and 80mm versions have a slightly larger turbine wheel, and a/r.

 

S480 would be the best budget turbo, with the 1.58 AR to meet your power goals.

 

I am with mnlx I think the turbine would be too small and pose a major restriction on this large of a motor.

 

So sounds like a pair of gt45's is the way to go but 68mm or 76mm?

 

Twin 68mm are good for roughly 13-1400 hp at 15 psi, and 76's will support about 1600 at the same boost level. I personally would go with the 68's.... they will make all the hp you want, spool quicker, and are much cheaper than the 76's.

 

x2 68mm gt45's they can be had for about 300.00 each

 

FYI I had a billet s480 with race cover and 1.58 are was told by 2 big time turbo builders it's to small for even my small ci bbc 440. I went with the gt45s. I put up a thread asking if any one has killed a gt 45 and no one has said anything that made me feel that I would kill one in my app .... For 1k hp I think 15lbs of boost should do it. I think those turbos on low boost would live for some time

 

Those or a pair if the on3 70 mm turbos. They are cheap too and seem to be decent quality from my experience.

 

an s480 matches a 383 cid pretty good for a rule of thumb

 

There's a big difference in turbine size between the ON3 70 and GT45. The little ON3 64mm turbine wheels are too small for a 468 BBC.

 

Inducer- 74.5mm

Exducer- 65mm

But that being said there have been 347 CI motors making 700 hp on a SINGLE 76mm turbo and like 600 something on a 70mm turbo.

 

I run 2 of the 70's on my 6.0, works great.

 

I agree that 2 p trims would be small for the op's setup. Twin p's seem to be a good match for 360-400 cid with a decent flowing head. There is a local racer here that runs twin p trim t70's 0n a 383 sbc with e85, and was over 2:1 turbine drive/ boost ratio with .68's. He went to .96's to get it in check.

 

How much boost was he trying to run on " E85 Race Gas"? How much backpressure is to much? Best case, worst case?

 

sorry to clutter your thread,,,,,,we should start a turbine size, turbine housing, cid, back pressure ,, thread if you guys think people would participate, i will see what Ken thinks

 

In the neighborhood of 14-15 psi iirc. The lower the the better, but 2:1 seems to be the cutoff for a decent setup.

 

It should also include cyl head, cam, fuel, and rpm info..... oh, hotside, and post turbine exh info as well. Many factors to consider when dealing with backpressure.