Engine Question-Torque vs. Horsepower

[rychi1]

I am looking at 2 engine options and I am trying to figure out if it is worth it to pay up for horse power. Both have basically the same torque, but one has more horsepower. How much difference would I notice between the two driving it on the street?

350 HP @ 5200 RPM, 410 ft. lbs. of torque @ 4000 RPM
390 HP @ 5400 RPM, 410 ft. lbs. of torque @ 3900 RPM

[NAZ]

Both are mild for a 350CI SBC and not really much difference in seat of the pants dyno on the street. Both would be good choices for a street rod and unless you plan to race it, you should be happy with the power levels of either on the street. I'm building mine with a SBC that has significantly more HP / TQ but my build is primary a race car first.

[Gromit]

It would be hard to make a true recommendation without seeing the torque / HP curves. a single point for HP and a single point for Torque really doesn't tell you much about drive ability or real world performance.

Unless you plan to set the motor at that fixed RPM and never change it... ;)

Chris AKA Gromit

[GoDadGo]

Here is a cool little tool from Spicer that might be of use to you.

http://spicerparts.com/calculators/horsepower-torque-calculator

If nothing else, it is fun to play with.

[erlihemi]

Without considering drivability, idle quality, and sound preference, maybe at less than 400hp you should consider dollar/hp. Should be under $20/hp, so is the other 40hp in your budget? most street time wants good torque at 2000rpm so does the 390hp version make better torque under 2500 rpm? At $15/hp it becomes a mute point based on economics. At $10/hp just make sure it pulls off idle and get the 390.

[Papa]

HP is a lot less important if you have a nice flat torque curve across the power band. Here is a plot of the curves for my BMW's engine, a 2.0 liter turbo 4-cylinder:

72404

The car is a four-door sedan and feels very nimble with the torque coming up at very low RPM and holding pretty flat across the power band. If the torque curve was closer to the HP curve, the car would feel like a slug.

[boBQuincy]

Which brings up an interesting point: few dyno runs show torque at 2000 rpm. Even lower would be worthwhile to see if there is a steep dropoff or wild fluctuations at engine speeds where we spend most of our time.
The engine with 350 HP would have about 350 lb*ft of torque at 5200 rpm since at that rpm (actually 5252) HP and torque are equal.

[rychi1]

Here is the chart of the two. It would cost about $500 more for the higher HP.


72422

[NAZ]

For a pure street car that is used for cruising and occasional car show / cruise night events, I wouldn't pay more for either of these based simply on a dyno chart that shows two very similar curves (discounting the spike & dip anomaly of the one). However, I'd pay $500 more for aluminum heads vs iron or for forged internals vs cast as these are tangible improvements. Use that $500 for more chrome and putt along in the lower cost engine that nobody at the car show will be able to tell is different than the one with a claimed 40 HP more. Either one will smoke the tires when you dump the clutch in a light little car like you're building. Forty extra horsepower (~10%) over a small RPM range is really not significant unless you're running against a clock or another car in serious competition. I can take away 40HP on my engine by simply adjusting the timing and without a clock it's very hard to tell the difference.