194/204 or 204/214 for rebuild

[deezdad]

Motor is being rebuilt and need to decide on cam. t-44/ rjc pp / 36# blue tops/ champion irons / extrude honed intake.... Any thoughts on what would work better between the Speed-Pro 194/204 vs. 204/214? Thank-you

 

[frankg]

Use the 204-214. Frank

 

[Ed Valvo]

Smog friendly?

 

[SouthernCal GN]

Shouldn't be a problem- these cars have been known to pass emissions without a cat AND plenty of mods.

 

[VadersV6]

You could probably run as high as 210 on the intake and still pass smog.
Whatever the stock duration is, add 10 degrees duration for every 300-500 rpm you want to shift the powerband up.
Heads and cam have to match. Say you add 40 degrees to the stock duration. You've moved the powerband where the cam is happy, 2000 rpm higher than before. But the heads and intake arent very efficient at that speed. The cam will start to come into effect, and then runs out of speed right away. It ends up peaking at 4500rpm like before, but weaker. Then people say the duration theory is bogus. Its cause of the heads and intake, not the cam.
The cross sectional area of the intake manifold runner, and head port, need to be of a size that allows the torque to peak right where you want it to. There are formulas for this. It reaches peak torque cause thats where the intake charge reaches supersonic speed. Runner length is very important, but you cant do much with it on these cars.
So find one of those runner calculators online. Measure the X and Y of the runner. Calculate cross sectional area. Run that through the other calculator which will tell you what rpm, torque will peak at.
Then choose a cam that will match that number.
Flow numbers will determine the flow potential.
Cross sectional area will determine what rpm the air will reach supersonic speed. (this is why you should increase flow without hogging ports out).
The duration should match an rpm where the air reaches supersonic.

 

[Ormand]

Cross sectional area will determine what rpm the air will reach supersonic speed

Good stuff, Vader. But...Don't think you will ever get anywhere NEAR sonic. That's about 1,200 ft/sec, and mostly intake runners should be in the range of 200 to 300 ft/sec. The only place that gets close to sonic is the venturi of a carb that's at the limit, and between the intake valve and seat when the valve is close to the seat.

 

[VadersV6]

Good stuff, Vader. But...Don't think you will ever get anywhere NEAR sonic. That's about 1,200 ft/sec, and mostly intake runners should be in the range of 200 to 300 ft/sec. The only place that gets close to sonic is the venturi of a carb that's at the limit, and between the intake valve and seat when the valve is close to the seat.

I re-read what I wrote, and I said intake charge...sorry thats not what I meant. When you're dealing with resonant tuning, you're dealing with sonic speeds. The actual intake charge, no. But the wave produced by the valve slamming shut, it at sonic speeds. That wave is what is used to tune the runner lengths to provide passive supercharging. The intake charge comes in, the valve slams shut. There is a sonic wave produced, and at the same time, the intake charge compresses behind the intake valve. The sonic wave reflects back toward the plenum. After the air charge compresses, it reflects back toward the plenum, and in a sense, it stretches and then bounces off the pressure of the plenum...kind of like a pillow. Think of the plenum volume as being a pillow of sorts. Too much volume will cause the returning wave to be dampened...just like it would be with a big pillow. Too little volume, the reflective power will be high, but plenum volume will be too small to provide the balanced air supply the runners need. There are 2 waves moving at different speeds. When you start calculating runner lengths, the formulas are based on timing resonating sonic waves which help to push the resonating intake charge back into the intake valve the next time it opens, The air speeds are more or less a function of a pressure differential, (air density plays in here) the runner cross sectional area, piston acceleration, cam timing...a whole bunch of things. The old school of thought with forced induction and runner lengths, was that tuned runner lengths were no big deal when under boost. Turns out to not be the case at all. Resonant tuning will provide the same benefits in boosted applications. The runner lengths on these cars are tuned for very high rpm. The torque curve would be much stronger with longer runners, (about 12" for a peak hp at 6000rpm) but they still do fine. These motors have to rely on sheer airflow and doesnt really use resonant tuning to boost the torque curve.
Ive done a huge amount of work with this stuff in the past, and the difference runner lengths make is astounding. I used my old car as a testbed, and tried about 20 different variations of runner lengths, plenum volumes, etc. Based on the TR runner length, if it were ever built in N/A form, the TR runner length would be terrible for providing a useful torque curve. On my N/A 99 cobra, between a 12" runner and a 7 inch runner, there was about 100 lb ft of torque lost at about 3000rpm. Peak torque was down about 50lbs. Peak hp increased about 8 hp, but the engine didnt even reach the stock hp curve until about 6000rpm, and then peaked at 7000, vs. 6000 before. The car was a DOG. This is just one out of about 20 different combos.

 

[deezdad]

I re-read what I wrote, and I said intake charge...sorry thats not what I meant. When you're dealing with resonant tuning, you're dealing with sonic speeds. The actual intake charge, no. But the wave produced by the valve slamming shut, it at sonic speeds. That wave is what is used to tune the runner lengths to provide passive supercharging. The intake charge comes in, the valve slams shut. There is a sonic wave produced, and at the same time, the intake charge compresses behind the intake valve. The sonic wave reflects back toward the plenum. After the air charge compresses, it reflects back toward the plenum, and in a sense, it stretches and then bounces off the pressure of the plenum...kind of like a pillow. Think of the plenum volume as being a pillow of sorts. Too much volume will cause the returning wave to be dampened...just like it would be with a big pillow. Too little volume, the reflective power will be high, but plenum volume will be too small to provide the balanced air supply the runners need. There are 2 waves moving at different speeds. When you start calculating runner lengths, the formulas are based on timing resonating sonic waves which help to push the resonating intake charge back into the intake valve the next time it opens, The air speeds are more or less a function of a pressure differential, (air density plays in here) the runner cross sectional area, piston acceleration, cam timing...a whole bunch of things. The old school of thought with forced induction and runner lengths, was that tuned runner lengths were no big deal when under boost. Turns out to not be the case at all. Resonant tuning will provide the same benefits in boosted applications. The runner lengths on these cars are tuned for very high rpm. The torque curve would be much stronger with longer runners, (about 12" for a peak hp at 6000rpm) but they still do fine. These motors have to rely on sheer airflow and doesnt really use resonant tuning to boost the torque curve.
Ive done a huge amount of work with this stuff in the past, and the difference runner lengths make is astounding. I used my old car as a testbed, and tried about 20 different variations of runner lengths, plenum volumes, etc. Based on the TR runner length, if it were ever built in N/A form, the TR runner length would be terrible for providing a useful torque curve. On my N/A 99 cobra, between a 12" runner and a 7 inch runner, there was about 100 lb ft of torque lost at about 3000rpm. Peak torque was down about 50lbs. Peak hp increased about 8 hp, but the engine didnt even reach the stock hp curve until about 6000rpm, and then peaked at 7000, vs. 6000 before. The car was a DOG. This is just one out of about 20 different combos.

Alrighty then.

 

[VadersV6]

Alrighty then.

I was bored that night, lol.