Exhaust wheel/housing comparison

[turbows6]

Does a new billet Precision turbo with the "65" Exhaust offer lower backpressure compared to a Turbonetics P-trim? (P-trim was a 65mm exhaust wheel from what I understand)

I was mulling a Turbonetics 70 s-trim, but now am considering a 6765bb too. I'm just not really sure how these different brands compare.

I think the exhaust pressure on my cpt66 p-trim .63 was fairly high because at 28#s the boost could not be turned any higher (I'm assuming exhaust pressure was just pushing the puck open)

How would a T'netics s-trim .85 compare with the precision billet "65" turbine with a .85?

I'm thinking on my combo a good hot side will help a lot because the TTA heads after porting really flowed almost as much as the intake, AND my camshaft favors the exhaust side (210/215 roller). It's also got a little over 9:1 compression, so I'd say the "put" leaving the cylinder has a little more force than stock. I'm just feeling that the hot side on my ctp66 was a major bottle-neck on my particular setup. Car went 10.3s with too tall gears for 275/60's, so it was running pretty good for what the turbo was, but In my minds eye the car will wake up with better exhaust and a lower rear gear. (The engine would rev to 6000 with ease, but was going through the traps at around 5100, so I'm going from 3.31's to 3.55's)

 

[forcefed3.8's]

They are the same. Precision's "new" 10 blade 68,65,62,etc are Turbonetics F1 wheels. As far as housings go, I am unsure if the Turbonetics are any better/ worse.

 

[bison]

Did you have a 65 trim or a 76 trim? I easily made 600whp with a 6665 last month at 26psi on a 7.5:1 engine It had at least another 50whp in the tank. The 66 compressor is at the edge of the map at 750hp and 2.5:1 pressure ratio. The 65 trim will not see too high backpressure till around 700whp.

 

[turbows6]

I'm sure those numbers are probably correct, BUT engine dynamics must also play a role.

For example. An engine with a stock camshaft isn't going to loose major amounts of horsepower by a high ratio of exhaust pressure since you have no issues with reversion of exhaust into the cylinder. (The engine won't do jack squat past 5000rpm either, giving up 20% horsepower to an engine with equal torque at 6000rpm)

If you apply those high backpressure ratios to an engine with a larger camshaft with some overlap it would be an entirely different story since exhaust would actually push back into the cylinder with both valves open. It may also reverse air flowing down the intake port, so from a flow standpoint its not allowing the port to work and who knows how it effects the fuel leaving the injector.

The Full Throttle hydraulic rollers favor the exhaust and they are ground on a slightly tighter LSA than most of the others I've seen. That is why I would theorize those camshafts would like a bigger hot side. Also on my TTA heads after porting the exhaust port flowed 95% of the intake port All I can do is find try it and find out. I know that the engine actually felt stronger in the mid range with the old 212/212 flat tappet, but I did not run the car at the track with the old cam. I might even go with another CPT-66bb except it would have the new S-trim and .85 hot side (6668).

On a side note I'd also assume high amounts of backpressure would make the motor more sensitive to knock issues. That's just based on what I've seen on N/A motors in older cars with small exhaust systems, catalytic converters, and restrictive exhaust manifolds (like an early 80's dodge full size car etc) Those baby's loved to blow headgaskets, but if you ditched the converter and/or put a small tube header on they wouldn't spark knock on 87 octane.

 

[bison]

I'm sure those numbers are probably correct, BUT engine dynamics must also play a role.

For example. An engine with a stock camshaft isn't going to loose major amounts of horsepower by a high ratio of exhaust pressure since you have no issues with reversion of exhaust into the cylinder. (The engine won't do jack squat past 5000rpm either, giving up 20% horsepower to an engine with equal torque at 6000rpm)

If you apply those high backpressure ratios to an engine with a larger camshaft with some overlap it would be an entirely different story since exhaust would actually push back into the cylinder with both valves open. It may also reverse air flowing down the intake port, so from a flow standpoint its not allowing the port to work and who knows how it effects the fuel leaving the injector.

The Full Throttle hydraulic rollers favor the exhaust and they are ground on a slightly tighter LSA than most of the others I've seen. That is why I would theorize those camshafts would like a bigger hot side. Also on my TTA heads after porting the exhaust port flowed 95% of the intake port All I can do is find try it and find out. I know that the engine actually felt stronger in the mid range with the old 212/212 flat tappet, but I did not run the car at the track with the old cam. I might even go with another CPT-66bb except it would have the new S-trim and .85 hot side (6668).

On a side note I'd also assume high amounts of backpressure would make the motor more sensitive to knock issues. That's just based on what I've seen on N/A motors in older cars with small exhaust systems, catalytic converters, and restrictive exhaust manifolds (like an early 80's dodge full size car etc) Those baby's loved to blow headgaskets, but if you ditched the converter and/or put a small tube header on they wouldn't spark knock on 87 octane.

You can theorize about these things all you want but ill tell you one thing for sure is that they are not what they seem. The most powerful LC2 engines out there with extreme back pressure (60+psi) are running a lot more overlap than the 212 grinds have. There are ways around the backpressure issue. There are several things that come into play with the valve open/close timing and the CR that allow you to run high backpressure and still make power up to 6000rpm or even higher. Im not going into detail about what to do to get around this either. Another thing is that the 212/212 small ductile roller grinds will easily make 9 sec power installed straight up with a 6680(superceded by 6668) at under 30psi boost with less than 8.5:1 CR on a 231ci. If your ex is flowing 95% of your intake flow then you will never be able to maximize the mass flow through the engine. You would be surprised at how far the stock cam will pull with the right selection of parts and a lot of boost thrown at it.

 

[turbows6]

Then why don't you see any race cars running small hot sides if all that backpressure helps out so much?

I'm assuming you're talking about TSM cars or some class that requires a buick style turbo, but I'd say they would make more power without the 3 bolt hot side.

Hey, what do I know, I've run faster than most anyone else on this board with a cpt66 p-trim and thats even with factory irons with the stock valves/stock intake/ stock throttle body.

 

[bison]

Then why don't you see any race cars running small hot sides if all that backpressure helps out so much?

Who said it helps out? Oh well im out of here. Some people ask the wrong questions. lol