This discussion came up in another thread...I think it is great to get it out there because so many folks do not understand how TQ and HP define an engine's abilities and how they relate to each other.
The comments were on task for the previous thread, but to getting too far into the topic was beginning to hi-jack another member's discussion.
I don't know alot of the minute details and formulas involved in computing the numbers, however I do know how to put the relation in 'layman's' terms.
We must first agree on a few things:
You cannot determine an engine's character or strength without using both TQ and HP. One measure without the other is meaningless.
To build an engine soley for torque will always lead to an over use of restrictive parts that hinder horsepower.
To build an engine soley for horsepower will lead to use of parts that generally do not have restriction enough for flow velocity and will produce unacceptable torque for street use.
For the purpose of keeping things in 'layman's' terms, torque should be thought of as an engine's strength or power... Though 'technically' torque is an equation that takes much more into account. The bottom line is that torque is an engine's 'grunt' or power.
For the purpose of keeping it simple, horsepower should be thought of as an engine's ability to apply that grunt quickly. Again, the technical math behind HP takes much more into account... Words like work, speed, time, ect...
When it comes to a rotating powerplant, HP describes how fast an engine can use torque. The 2 terms are inseperable when it comes to engines.
So...
When I see a thread where someone has bought so far into the torque end of things that they are using combos like:
RV cam
Performer intake (no better than stock except lighter, smaller ports)
Aluminum heads that flow like ported 351w heads
1.5" primary headers
Restrictive exhaust
Tiny carb
9:1 compression
Then...
They pair it up with stall converter
Low gears
and say they want to do 13 in the quarter...
I am not surprised.
Articles and rumor have everyone too focused on tiny carbs, dual plane intakes, and torque in general. Most of this stuff, while based in fact, is also based on larger engines than ours. Remember that most magazines start their thinking with 350+ cubes in mind. Our engines are quite a bit smaller at 289-302 cubes. We also have over-square engines with very short strokes... in layman's terms: they like to rev. They are strong making power at slightly higher rpms and when combined with torque producing parts, they will generally come up short.
Back to my example combo...
A small cube, short stroke engine as described, built for torque alone will underperform when paired with low gears (3.70-4.30) and a stall converter.
Think about it:
The low gears will put the engine out of it's very low power band before the power can be used. It will also cause a low traction situation to become unbearable.
The stall converter is a terrible idea. If you increase torque without raising the rpm capability, why do you want to raise the rpm that power is transmitted to the ground? A 2500 rpm stall, for example, is rated to go on an engine that starts to make it's best torque at 3000-3500 rpm if you follow manufacturer recommendations... 500-1000 rpm below where torque starts.
So my example engine will make it's best power from idle to 4000 rpm, while the gears and stall let you only use say 1000 rpm of that band. I am not saying the engine won't be viable and spin past 4k, but the power will be on an ever increasing downward slope from then on. Why would you want to lose 3k of usable rpm?
This combo will never see 13s at the track without giving some rpm and HP friendly parts.
My diesel engine makes around 500 lbs torque, but only 210 hp, so the fact that it would suck at the track illustrates my point. You have to build in some rpm and HP ability to balance things out. HP, in layman's terms, will give you the ability to use that grunt faster and therefore put you down the track faster.
The point that brought this whole discussion up is that you must build some revs into the SBF. The nature of the design just leaves you with that fact.
Side note: SBFs are very rpm friendly engines. The only thing that prevents them from being nearly indestructable in N/A applications to 7k rpm is the stock rod bolts. The large bore and short stroke make an engine that loves to rev. So don't be afraid of building an engine that makes power at 6k rpms.
Don't be afraid to vere away from dual plane intakes that make a little more power grunt at 1200 rpm, but fall off quickly after 4000.
Don't be afraid to use a 750 vacuum Holley... afterall, the 2 barrels that operate mechanically flow the same as your stock 2v. The back barrels don't open until your engine wants them... when properly adjusted.
Sorry so long.
Just want a sane discussion without a hi-jacking.
Dave
