James' Civic Rebuild Thread + High Power ER Motor Theory
Posted: Tue Sep 04, 2007 10:10 pm
Hey all,
Ive been thinking about what an appropriate turbo to make 200HP in a street driven city motor is. I think 200hp is a realistic goal for a moderately worked street driven car with a good tune.
I recon due to the special characteristics of the city motor it needs a reasonably special turbo choice.
Firstly it has a very low bore to stroke ratio. What this means is that piston speeds are relatively high, which in turn means high intake velocities meaning good low RPM torque. The offset is that there is not much room in the bore for valves, so the engine can't breathe very well in the high revs because of this (lowering the volumetric efficiency).
This decrease in volumetric efficiency can be offset to a certain extent by running a higher lift and longer duration cam (or bigger valves but you cant go much bigger at all). More camshaft lift is a good thing, gives you more torque over the board, is just harder on your valvetrain. Having more duration hurts your low RPM torque, something turbo motors don't particularily like so we won't go there.
SO all this means we are never going to make much power over 6000RPM, its just the physics of it. With a decent cam and some headwork we might be able to stretch it to 6500 but not a lot furthur.
This all leaves us with a relatively narrow rev range in which to make some decent torque, say our target zone is about 3500-6500 rpm.
I have a lot more to say about increasing volumetric efficiency and will do so tomorrow , (actually today, its past 12)
I have been playing around with online turbo calculators all night and I have found a turbo which I think is perfectly matched to a 200hp city motor. Its a TD04-09b from a twin turbo Mitsi GTO or legnum.
Todays lesson shall end there
Ive been thinking about what an appropriate turbo to make 200HP in a street driven city motor is. I think 200hp is a realistic goal for a moderately worked street driven car with a good tune.
I recon due to the special characteristics of the city motor it needs a reasonably special turbo choice.
Firstly it has a very low bore to stroke ratio. What this means is that piston speeds are relatively high, which in turn means high intake velocities meaning good low RPM torque. The offset is that there is not much room in the bore for valves, so the engine can't breathe very well in the high revs because of this (lowering the volumetric efficiency).
This decrease in volumetric efficiency can be offset to a certain extent by running a higher lift and longer duration cam (or bigger valves but you cant go much bigger at all). More camshaft lift is a good thing, gives you more torque over the board, is just harder on your valvetrain. Having more duration hurts your low RPM torque, something turbo motors don't particularily like so we won't go there.
SO all this means we are never going to make much power over 6000RPM, its just the physics of it. With a decent cam and some headwork we might be able to stretch it to 6500 but not a lot furthur.
This all leaves us with a relatively narrow rev range in which to make some decent torque, say our target zone is about 3500-6500 rpm.
I have a lot more to say about increasing volumetric efficiency and will do so tomorrow , (actually today, its past 12)
I have been playing around with online turbo calculators all night and I have found a turbo which I think is perfectly matched to a 200hp city motor. Its a TD04-09b from a twin turbo Mitsi GTO or legnum.
Todays lesson shall end there