[size=13px]I have a 2010 camaro ss. Its a sbe ls3, m6, btr stage 4 na cam, arh longtubes and 3.91 gears. I am planning to use either an agp or huron speed twin turbo kit. Both kits have 2.25 inch hotside connection pipes and agp uses a t3 housing and huron uses vband housings. Because of the cam and gearing, i need to keep backpressure as low as possible. I will be using equal length shorties as opposed to stock manifolds as a means of reducing preturbine backpressure. My question is should i fabricate 2.5 or 3 inch connection pipes for the turbines or would 2.25 be enough and will a pair or 6266 .82 ar turbos be sufficient to keep backpressure at a minimum. The car currently peaks around 6800 to 7000 rpm.[/size]

 

The 2.25s will be fine. The turbo ar will be far more restrictive then that and the smaller pupe will help transient response. 6266 will be for sure large enough to keep back pressure down. Should be a pretty good running combo. I think there are much better cams out there to suit yhe new set up your planning on.

 

As an aside you dont need the shorty headers the stock exhaust manifolds are awesome for turbo and arent a cause of backpressure. All backpressure in your system will be cuased by the exhaust working to turn the turbine wheel. The cast iron manifolds will support the turbo better and keep the heat in to help spool the turbos.

 

I agree that the cam isnt suited to a turbo application , but i really dont want to go into the motor just yet. I will be using stiffer spring with the turbos however. I will most likely use a llsr with less overlap when i build the bottom end next year mainly so i can run a stiffer spring when i turn up the boost. Ive read that na cams will work fairly well if backpressure is kept in check which is why im leaning towards 6266. Will the .82 ar be enough or should i go .96. My turbo knowledge is very limited. Thanks for your help.

 

I dont think there will be a huge difference but id stick to the 82s personally since your manual. Your probably gonna hate that rear gear with turbos. Turbos dont really need the torque multiplication since they make crazy mid range torque. I tried 3.73 for awhile in my 12 and am now back to 3.27 since it was stupid how easy it would blast the tires off. Just my opinion.

 

I know what you mean. Its hard on tires now n/a and thats why i want to run the slightly larger turbos. I dont think ill need a system that makes a ton of torque right off idle. Ive been studying the forum and it appears that if back pressure is kept close to around 1 to 1 the na cam will work well and reversion wont be horrible. I actually like the power curve of the motor as it starts pulling like crazy around 3500 to 7000. So i basically just want to enhance that curve by about 350 additional horsepower. It would probaly easier to launch without too much bottom end. It runs 11. 70 now at 122 on street tires and id like to see low 10s or high 9s.

 

any pre-turbine pressure is dictated funnily enough....by the turbine sizing. Whether you use cast or tubular will make **** all difference to that.

But a n/a cam can and will hurt spool especially if it is what you could consider a bigger cam. And equally it can be a negative up top, or in some cases it will simply move the rpm band up a few hundred rpm, which may or may not be a good thing

 

My understanding was that the less backpressure, the more the system actually likes overlap. The cam is not huge. Its a btr stage 4. Duration is around 233 intake and 250 exhaust on a 113+5 lsa. Will it run horribly with mid-mount 6266 .82 ar twin setup.

 

Build it and run it as is. See how you like it. And install a simple backpressure gauge to monitor it. If you're unhappy, then change the cam. My bet is you'll be trying to figure out power management to try to get it to hook up.

 

Thank you. Im gonna try that. I saw a thread on camaro 5 where someone added a pair of arh shorties to an agp setup and picked up significant power everywhere. They attributed the gains to a loss of backpressure and iats dropped also. Ill let you all know soon.

 

I was always arguing that pressure will be determined by the smallest point in the system. Its physics and can't really be argued.( Bernoulli's principle) Now I'm thinking that applies to fluids and super heated compressible gasses are a totally different subject.

Smallest point is almost always the turbo housing exit. Then further restriction is caused by the wheel size and how difficult it is to turn. To me that meant I could have 2.125" primary long tubes with a 4" collector and 4" hotside and the exh. pressure will remain the same as it would with stock manifolds and 2.25" pipe. The velocity would just drop a ton pre-turbo. Which is bad for response in general. I'm not sure that's a completely correct theory. I'm betting there has to be a lot more going on.

Anything that improves VE/Flow NA will increase power in boost as well. (Assuming there's not tons of backpressure/reversion going on) So obviously the aftermarket exh. manifolds are doing that. Just not sure how exactly if the turbo is the "bottle neck". I'd think with the turbos being the restriction and BP remaining the same, aftermarket manifolds wouldn't show the gains that they do. There are just too many things going for me to grasp 100%. You have compressible gasses, heat, velocity changes, density changes and likely 10 other things I'm not mentioning.

Anyway, I agree with running what you have. That cam is likely fine, as are your stock exhaust manifolds and 2.25" pipe.

If it makes you feel any better I ran stock manifolds with 2" piping off each bank into the turbo. Thats 1.8" ID piping. I was making 1000ish crank on a 5.3, 4.8. and 370" motor with that hotside going by trap speeds VS weight. Back pressure was 1.4:1 on the 4.8 and 1.6:1 on the 370 at 20ish lbs of boost. That was with a single S480 1.32 T6. So with moderately sized twins I think you'll be MORE than ok.

 

I agree with Richard Holdener. Every cam is a turbo cam. The turbo just moves your torque and hp up. If you like where your torque and hp curves are. The turbo is just going move that higher on the graph.

 

Thats not really true. Richard wimps out on boost WAY before its necessary. Then does things like install a set of heads and runs the same baby boost to make more power. If back pressure vs manifold pressure remains relatively low...then an "NA style" higher overlap cam works fine with a turbo. But generally responsive street setups and oem turbo cars are at 2:1 or higher. This is why they run negative or low overlap "turbo cams". Run a high overlap "NA style" cam at 2.8:1 where my single t4 s475 was at running 26lbs and its going to cause problems. So every cam is not a "turbo cam".

 

It's a generic sweeping statement, which even Richard says isnt totally true.

A big cam can really make a turbo setup feel ****. It can hurt low end, it can hurt spool, and offer no benefit up top. In general, milder cams are more flexible and give better results everywhere.

Although once again, you'd need to do something pretty damn fucked up to make any LS really bad, as they just work.