ECS

When people make mods for more power, they seem to always go the route of turbos, superchargers, more cubic inches etc. No one ever talks about modding the engine to increase RPM capacity. I am assuming this is a more expensive mod but is it that prohibitive? Why wouldn't someone want to go the small displacement high rpm route (e.g. F1). I am surprised that I have never seen someone try to mod the Porsche dry sump for 11K or 12K rpm.

Thoughts?

Geoffrey

The higher the RPM, the lighter the components need to be and the more frequently the rebuilds will occur. Anything is possible.

bruinbro

In another life I was in the process of modding my 914-6 2.0 with 2.8 pistons, modded crank, modded 2.2 heads, custom Garretson cam and forged followers. The setup would have been good for around 11k rpm, but it was hideously expensive. Had to punt when I moved from NorCal. Not sure I would go that route again.

Bro

Steve Weiner-Rennsport Systems

LOL,..Thats precisely what racing engines are since these are all constructed to comply with specific displacement regulations.

Current GT-3RSR engines can safely rev to 10K but the air-cooled ones do not make power at those rev ranges due to limitations in head flow and valve train design.

Ultimately, it comes down to how long you expect an engine to last. In some cases, complete rebuilds can be required after 10-15 hours of running time, depending on compression ratio and peak RPMs.

Rassel

All it takes, is a lot of green.
The knowledge and machinery to make it exists.

In general you've got the combustion to play with. Either make:
- more of them (rpm)
- increase the size (displacement)
- increase the energy in them (air/blown)
Building an engine by power, you try to reach an optimal combination. Reaching too far in one direction will cost you unnecessary. So you'll try to go the optimal route.

Add finance, technology, durability, efficiently, emissions and racing regulations and you end up with something. Now, racing regulations often give different displacement regulations, restrictions and turbo coefficients, so you get different paths to choose from. Actually, it usually works the other way around. You got a few contestants (Ferrari, Porsche, Aston..) and the regulations are mostly to even out the possibilities.

333pg333

Well obviously the turbo route is the easiest way of getting a big increase in power. You can also increase capacity without trying too hard either. That should give you more and earlier torque. Then you deal with the VE making everything bigger and better flowing by which you're starting to change all the components to the nice, light, and expensive ones. You can do some or all of these. Increasing the revs will decrease your engine time as mentioned too. What's the application?

ECS

No application. I was just curious as to why there was so little discussion as to mods associated with higher rpms. I thought it was cost, but wasn't sure. It would be really great to hear some higher revving track cars out there during DE.

DWalker

RPM kills engines, period. Spend whatever you want, but the laws of physics will only bend so far.

Given the choice, I always prefer to make the power as low in the RPM band as I can. More displacement helps, and boost is lot like adding displacement. There is a lot more to this of course, things like rod ratio, piston speed, etc etc., but given the advances in engine management, boost control, engine dynamics and fuel quality makes boost possibly the safest way to add horsepower to small to medium displacement engines. This is immediately evident by the large number of manufacturers who are offering more boosted cars than ever before.

mark kibort

rpm doesnt alone, give you HP and I assume that is what you are talking about.

if you look at most rpm/hp curves, they fall off torward the end pretty abruptly.
maximizing HP maximizes acceleration.
Only if you have a rising hp curve, would it pay to contiute to rev the engine up past its designed redline.
by redesigning an engine for higher rpm (only a portion of the battle), you then need to design the engine to breath at the higher rpms. intake, cams, compression, oil flow, spark, exhaust, all have to work as a system to be able to have a high hp, high rpm engine.

mk

Geoffrey

Actually that is not true, increasing the RPM with all else constant will give you more hp. An engine that produces 100ft/lb of torque at 5252 will give you 100hp. Keeping that same 100ft/lb of torque, but increasing the RPM to 6000 will give 114hp.

The engine is most efficient at peak torque with the highest volumetric efficiency occuring there. After that, the engine cannot breath as efficiently and the torque will fall off. This is often accompanied by a reduction in the manifold absolute pressure (increase in vacuum). The slower you can make the torque fall off, the more HP the engine will produce.

An engine's Redline will be determined by a number of factors, some mechanical (rotating component strength) and some where the engine's power falls off. Assuming that the engine mechanicals are sufficient, typically the redline is set several hundred RPM past peak HP.

ECS

Really interesting discussion guys. Learning a lot. Did F1 go the high RPM route because of regs or given the costs/performance ratio at that level, high rpm was the obvious choice. Or....was the high rpm route just a matter of circumstances driven by regs. Or....if the goal was to get 800hp in a car with the performance characteristics to win races (no regs) would they still go high rpm or go the boost route?

333pg333

You just can't ignore boost for free power (well relatively of course). However if you had a set power limit that was easily attainable via n/a means, then that would probably win out due to heat, weight, less moving parts, reliability factor I would assume.