What was the tq?

 

I don't think the torque is a fair comparison. The supercharger did 571 ft-lb at 3700 rpm. The turbo would flash the converter much higher on the dyno, so peak torque didn't register until much later, more like 4800 rpm, where it made 530 ft-lb at 11 psi. If we could have started the dyno earlier in the rpm range, I'm sure it would have topped the supercharger by a bunch.

 

So when are you going to build a tubular header?

 

I would agree with that; mine at only 6 psi did 513 at 3400.. with a T350 and 3400 stall. At 12 psi you should see well over 600.

 

I'm not. At 680 rwhp, based on the old times, it should pull around 142 mph in the quarter which will accomplish my goal of owning a truly streetable 9 second car. By truly streetable, I mean cruise control, A/C, full interior, reasonably quiet, etc. . .

My plans are, in order:
1. Replace the Vortech aftercooler with a homebuilt aftercooler with approximately 50% more flow capacity and 80% more cooling capacity.
2. Port the intake and install a 58 mm throttle body. Current is 52 mm.
3. Consider intalling a different cam, something like 226/226-114 using slower ramps. Mine is the Comp 224/236-114 and has some stability issues above 5800 at 19 psi.

 

Good call, mine had the same problems...

 

Care to explain on the above 'stability' issue?

Slower valve accel. solve this?

Thanks,

-Scott.

 

Quick ramp rates take more spring pressure to control valve motion. For instance, the Extreme Comp lobes require more spring pressure to run the same rpm as slower ramps. Also, the Extreme 4X4 lobes have even more aggresive ramps since their aim is for low-end torque. Slower valve acceleration will require less spring pressure.

My problem is this:

The valve effective spring pressure is reduced on a boosted motor since boost pressure is trying to open the intake valve.

The amount the spring pressure is reduced is:

19 psi x pi/4*(2.08")^2 = 65 lb

With a hydraulic camshaft, I'm running 145 lb seat pressure and wouldn't really feel comfortable higher than that.

So, at 19 psi boost, my seat pressue is 145 - 65 = 80 lb. 80 lb of seat pressure is not enough to control an Extreme hyd roller cam lobe with 224 duration and .605" lift at 6000 rpm.

Since I'm sort of stuck with 145 lb seat pressure, my other option is to go with less aggresive lobes. I like the Crane HR1 lobes (used in the GM 847 cam) and have had good luck with them in the past a low spring pressures. Furthermore, turbo motors don't seem to respond to quick ramp rates like NA and blower motors.

Crane makes a 226 lobe with 288 adv (.004), 145 at .200, and .552" lift, versus my current 224 intake lobe with 276 adv (.006), 152 at .200, and .605" lift.

For instance,

Crane says "HR1 Hydraulic roller series created for high lift applications with good stability."

Comp says "The high lift versions are more aggressive over the nose and will require more spring or less RPM."

 

The turbo makes more power, but is it more streetable?

What about maintenance and dependability?

Exhaust leaks?

One good advantage I can think of is that it takes no load on the front of the crank like a blower.

Glad to see the 224/236 cam kicks butt. I just stuck that one in my 355 along with additional head/manifold porting, beehive springs, billet timing chain, and some other stuff. (Stock LT1 chains suck!, believe me)

 

The turbo is quieter than the supercharger on both ends (no whine and less exhaust noise), plus the engine runs cooler and gas mileage is better since there is less load at idle and cruise.

Maintenance/dependability/leaks have gotten worse, probably becaused I designed a built my own kit. I used a few flanges I probably shouldn't have in pressure service. Those will be fixed soon, though. Accessiblity has pretty much stayed the same.

 

Why would the engine run cooler? With the exhaust restriction and the extra piping in the engine compartment i would think heat management would cause higher engine temps.

 

The engine runs cooler because it isn't having to work to drive the compressor at all times. A centrifugal can take 5 hp at idle and 20 hp at cruise, which will make temps go up. If you measure exhaust backpressure with a turbo, it's nearly Zero at idle and cruise. Sure, the turbocharger adds heat under the hood and increases temps there, but that doesn't affect coolant temp much.

Mike