How many cubic inches do you need?
How many cubic inches do YOU need for your combination? I have spoken to a number of individuals lately that wanted the most inches they could fit in a stock block but did not do anything substantial to increase the engine's breathing. In fact, one guy was afraid he was going to make too much torque so he wanted to "tame it down" with the addition of a longer duration camshaft. Now, anyone that follows my blogs or reads my postings on Twitter or FACEBOOK will know I think that is the wrong thing to do. If you want to REDUCE torque, then build a smaller engine.
Take a look at the dyno sheets below where driveability was of paramount importance to the customers...
The first one is a typical 4.25" stroke combination with our RPM (round port) Edelbrock heads ported to what would become our Stage 2 spec, ported RPM intake, owner specified 274 X/E Comp Cam and 750 cfm Quadrajet carb. This combo was tested with cast iron Ram Air exhaust manifolds. I regret not testing with 4 tube headers as well for advertising purposes but we made the power we needed quite easily and the customer was satisfied. 500hp was the stated goal and as one can see, 500hp was attained by a lowly 4,900 rpm. Game over--- right? No. Valve float was seen a mere 200 rpm higher and if changes were not made, I would consider the dyno session a failure. Obviously, we moved forward and decided to change valve springs and IMMEDIATELY recorded a clean pass to 6,000 rpm where over 500lb-ft of torque were produced through 5,800 rpm!
On this build, VALVE SPRINGS were directly responsible for an additional 60HP. On a combo that shows peak torque around 4,700, how much HP is being lost when peak power is seen at 1,000 rpm away at 5,700 rpm?
Was that remarkable output? No. Was the fact that power was still increasing at 6k remarkable? Yes. Torque and HP peaks were on the extreme ends of the rpm range. That camshaft was the 274X/E that some have said, would not make power above 5,200 rpm. We have proven that to be untrue. Is it a coincidence that we ran into valve float around 5,100 rpm and others said "you can't make power above 5,200 rpm"? Far be it from me to tell someone else what to do...
Take a look at this next dyno sheet....
This combo utilizes a 4.5" stroke, D-port E-heads ported to a Stage 1 spec, hydraulic roller, and 1 3/4" four tube headers. The common thread between the builds is the desire for a broad torque curve--- not peak power. Granted, this engine being a Torque Monster, GOOD TORQUE was a priority on this one!
Generally speaking, we make TORQUE, make it at a low rpm, and then carry the rpm so good power is realized. Simple. In other words, "let the HP fall where it may". Even with a longer cam, 242/248 vs. 230/236 for the 461, the 488 only made about 20 more HP than the 461 (580 vs. 560). Neither engine utilized cam timing specifically tailored for peak power or torque, but instead, a good balance between the two. Lobe separations were 112 and 110.
So how come the 488 didn't make more power?
It will become obvious that horsepower is not dependent on displacement. It is DIRECTLY related to V/E and RPM though. The displacement of the 488 and conventionally sized ports (conventional meaning "non-wideport") dictates a higher airspeed in the ports at a lower rpm, giving you a "built-in" torque monster where airspeed is so fast, the engine actually becomes choked. This is where a single plane intake and larger ports would extend the horsepower curve and make more power.
We make torque with displacement, V/E, and compression. If we want to maximize torque, we apply the appropriate cam timing. If we want less torque, we build a smaller engine. If we want to make more power, we increase the airflow through the engine. You cannot simply increase the size of the engine WITHOUT INCREASING ITS BREATHING and think you will make significantly more horsepower, you WILL make more TORQUE.
Stay tuned, we will be getting some dyno numbers for our 3" main 455's using our CNC Stage 2 heads and one of our custom ground cams.
