Let me explain what I think, and you correct me if I'm wrong. Power adders, like blowers and nitrous, actually add horsepower to an engine. In contrast, bolt-on modifications free-up horsepower by using aftermarket parts that are more efficient than the cost-effective factory parts. For the intake, this may include a cotton air filter, true-flow inlet pipe, and larger tb and plenum. By using these aftermarket intake parts, you are not adding horsepower but reducing the amount of horsepower used by the engine to draw air. This horsepower can then be used to move the car forward more quickly. For the exhaust, you can install headers, high-flow mid-pipe, and cat-back exhaust. Again, you are not adding horsepower, but reducing the amount of horsepower that is used to push the exhaust out of the engine. And again this horsepower can be used to move the car forward more quickly. Therefore, aftermarket performance parts are more efficient than stock parts. But, rather than adding horsepower they free-up horsepower that is wasted by inefficient factory parts. If this is true, then the horsepower was already there but wasted on drawing air and pushing exhaust. This also means that bolt-on modifications should not put greater stress on your internal parts than was already there. What do you think of my explanation? What am I missing?
How do bolt-on modifications work?
- Thread starter 01mgvert
- Start date
I suppose that's one way of looking at it. I always went with the engine is an air pump explanation. The more air the engine can process (along with the correct amount of fuel) the more power the engine will make.
Since its doubtful you'll break 400HP@ 6700+RPM (upper stock piston/rod limit) you won't hurt anything with bolt ons as long as you properly tune it. The only way you could kill the engine would be to over-rev.
Since its doubtful you'll break 400HP@ 6700+RPM (upper stock piston/rod limit) you won't hurt anything with bolt ons as long as you properly tune it. The only way you could kill the engine would be to over-rev.
Redfire03GT
New Member
01mgvert said:
That's essentially correct. Which is why the term -power adder- is commonly used with superchargers, turbo's and nitrous. It's adding power that the motor wasn't capable of by itself. Efficiency is basically all it is, as far as bolt on mods are concerned. If they're more efficient than the stock parts, you'll more than likely see a positive benefit from having it in place.
This goes from having general stuff like, plenum's and exhaust components all the way to having a more efficient drivetrain.
With bolt-on modifications, your car does not require as much power to draw air and push exhaust. This saved power can now be used to turn the crank. My point is this: the power was there all along; you simply changed what the power was used for. This means that bolt-ons do not put additional stress on the internal parts (e.g., crankshaft, pistons, connecting rods, etc.).
I think the way it works is all based on Volumetric Efficiency, or how efficiently the cylinders can fill compared to their max volume. If you can increase the VE by allowing the engine to freely pump air in and out without restrictions, you will allow more fuel to burn and increase power, not to mention the reduction in parasitic loss as the piston/rod doesn't have to pull as hard when pumping air in/out...I have heard of some N/A engines with really well tuned intake/exhaust systems that can exceed 100% VE, which is normally reserved for power adders.
You are the man 
Thanks for a great explanation 
01mgvert said:
I don't think this is true. By increasing VE you have increased the amount of fuel and air in the chamber and therefore get a larger explosion when the plug fires, which means you are putting more stress on the engine internals.
I'm there for ya man! NasaGT said:
Let's say that you add 50 rwhp through bolt-on modifications. How much of that horsepower was due making the engine more efficient? How much is due to the larger explosion in the chamber? Most of my power gains have come from exhaust modifications. Rather than increase the size of explosion, these mods remove the exhaust more efficiently. Again, it seems to me that bolt-on modifications create little additional stress to the engine.
I think the part your missing is that ANY power increase comes from a larger/more efficient burn in the chamber, and will result in increased stress. It goes back to the VE thing, if your engine is effient enough to have 95% VE through bolt ons, there is that much more fuel/air going into the engine and igniting, which is what really increases power. The only power increase I can think of that wouldn't add stress to the engine would be due to reduction in friction and/or weight of the rotating assembly...
using your example, exhaust modifications allow power because they remove the spent exhaust from the chamber quicker, allowing the engine to fill more of the cylinder with combustibles. Same thing happens when the exhaust is extremely free flowing, the backpressure at the exhaust ports is reduced, so the engine has less to overcome when bringing in fresh air.
using your example, exhaust modifications allow power because they remove the spent exhaust from the chamber quicker, allowing the engine to fill more of the cylinder with combustibles. Same thing happens when the exhaust is extremely free flowing, the backpressure at the exhaust ports is reduced, so the engine has less to overcome when bringing in fresh air.
Similar threads
