[Streetwize]

The best of both worlds would be to build using a smaller higher velocity port that flows as well or better than the R in the .200-.450 lift ranges and port the intake manifold to excced the flow of the heads. Combine that with a smaller cam in the 235I/242E range and you will make near equal top end power to the R with a flatter less peaky torque Curve. Even if the engine seems Under-ported for racing, big cube motors have no trouble drawing harder than the simulated flowbench depression so power doesn't suffer anywhere nearly as bad as many would imagine.

so....I would be tempted to run the SR but run it with a ported (tapered) single plane intake manifold in order to extend the powerband and improve the peak power even with the smaller cam....and this can be accomplished without negatively impacting part throttle or low speed drivability.

The Roush motor has a very carefully selected combination of parts and is guaranteed it will hit the advertised numbers. But that said it is (for want of a better word) still a "crate" motor, so there will be little to no consideration or attention given to massaging the ports for enhanced flow as with a custom engineered combo. A bigger cam will act smaller and come in sooner by advancing the intake centerline 2 to 6 degrees in order to trap more cylinder pressure (dynamic compression) at lower engine speeds.

I've made between 25 and 40 horsepower from just porting the intake manifold, I would go with the SR and probably look at doing just that.

The smaller the cam is that will get you to the desired HP goal will almost always give you the highest average torque and part throttle "linear" responsiveness....and torque is what you feel at part and roll-on throttle.

Opinions vary, but you don't drive an engine on the street the way you load it on either an Engine or a chassis dyno. A cobra will accelerate faster than the standared 300 rpm per second an dyno cell loads the engine. And as a result, Most cobras will easily blow off the tires if you apply the power too quickly anyway. So build it for tractability and part throttle responsiveness, so you can tune your driving skills to the car and more easily/predictable apply power to the track.


My own 427 I believe accomplishes this very thing, Roush SR type drivability with R Type peak power, It idles with a nice chop at 800-850 RPM, never loads up at idle, Cruises on the highway smoothly at under 2000 RPM and makes over 500HP. And I can promise you no-one who'se ridden in it ever felt like it lacked for horsepower or face ripping torque in any gear. Optimizing the port velocity and cross section is the key to a great combination.

The joy to me of a big torque motor is the pleasure of having grunt and acceleration in any gear virtually everywhere in the powerband, if I added 100 hp (and I could with a bit more cam and head flow) and 1000RPM to the power peak the car would ET quicker but I doubt it would be anywhere near as fun to drive. To me it makes very little sense to take a big engine and cam it where it's only happy at engine speeds higher than a light nimble car really needs it to be.

to me the best combo would be a 357" big bore 8.2" deck (4.185B x 3.25" stroke) high rpm capable engine with modestly sized turbos that would give you a nice linear boost curve so it feels exactly like a big block off idle though 5500 rpm but keeps boosting all the way to 7500.