I need 250hp @ 4000ft msl. Turbo or NA?
 

Trying to formulate the engine setup for the rally project. As a general rule, around 250 hp is a good number for a RWD car on a loose surface. Traction is difficult to get as it is. Seems like an easy number but i am stuck in the route i want to go. Its right at that point where a turbo can do it easily and an NA engine can do it with some effort.

Truthfully, i would much prefer a naturally aspired engine. Simple, less heat, simple. etc. BUT the car has to be able to crank out the power at high altitudes. It really seems to be looking like a peripheral port might be the way to go if i decided to take the NA route. But at that point a turbo engine might be easier and cheaper, but certainly more heat is generated and far from "basic" in design.

Turbo, stock ports, maybe a little exhaust porting. Clean up the runners, bowls, make things as smooth as possible. Run an ECU that has a boost trim function (or two for that matter) that you can base off of atmosphere. That way the ECU will automatically increase boost as altitudes, temps, etc change so you can maintain that same hp whether you're driving around my neighborhood - right on the water, sea level, or cruising around the Rockies. I know Motec can do that :rofl:

I would go the turbo route becuase while it is more complicated, a stock turbo can make that power and an aftermkt turbo or hybrid can do it without breaking a sweat which means less strain. I would think you would have to rev the hell out of an n/a to get to those power levels.

that is a good point. Ill probably use something aftermarket for the turbo setup so i can attempt to minimize turbo lag without use of something like anti-lag. I think external wastegate would work well unless i can make something like this cosworth turbine housing work...too bad its for a 2.3 engine, its a real nice design.

http://img.photobucket.com/albums/v2...housings02.jpg

The NA option is not that hard either. I have about $750 in mine and it gets 270 Hp at 800 ft (almost enough) with 8.2:1 compression ratio and poor ignition above 6,000 rpm.

Peak power is at 7,500 rpm.

This s4 block, planetaries and rotors has no problem revving to 9,000 rpm

Honestly, I'd go NA. Less weight and less to go wrong. A turbo is going to put more stress on the engine, between the higher combustion pressures and more heat, etc. And you should be able to reach your power goals without much trouble with peripheral ports and EFI.

heat is still my biggest enemy. Im not taking a run down a dragstrip and the added inclines and extended time on a track is going to just build up heat. While turbo does seem "easy" i am still concerned about HOW the power will be delievered. There is alot to think about here. I would still like to get some input from a few vetern racers.

When you say 250 are you looking for wheel or crank? P-Ports generally do 310-315 which is 267ish crank

i think you mean 267 wheel? Im looking for wheel. 250 is about the magic number for what you can maintain some traction with on dirt.

yup, meant wheel... Absolute drivers :rofl:

Yikes, 250 WHp is going to be tough NA. I thought you meant 250 Hp (200 WHp).

I will get back to you after my first 9.5:1 and 24V ignition dyno run. I think I can get that (250 WHp) at 800 ft, I really doubt that I can get it at 4000 ft.

Still, I am convinced that the intake manifold is where the secret to rotary power lies.
I have a manifold Idea, but I don't have any good drawings of it on my computer.

I'll make you a deal. If I get 270+ WHp, I will send you all the intake measurements, Port cross-sectional area profiles and port templates used in my engine, then you can do the same (it uses all stock parts - slightly modified). Otherwise, I think that you are looking at a turbocharged car.

PP is not a bad option (although it will guzzle fuel). Really the PP and the turbo will have similar power bands and similar power levels. The fuel consumption will likely be comparable too. (The turbo is easier to do, the PP will run cooler and be lighter)

well see how things go. PPort isnt out of the question.

Wow! I should be more careful with my wording. Obviously, the turbo will not rev as high as the PP, and will make more torque down low (once the turbo spools). By power band, I was meaning that you will experience a low-rev power deficiency with both configurations.

I think that if you keep the PP downshifted, your throttle response would be better than with the turbo. You will probably have to shift less frequently with the turbo.

I think that a NA streetport would be fun on a hillclimb, mine makes pretty good torque from about 3,000 rpm to 9,000 rpm (good broad rpm range is better for racing as you are not always in the wrong gear).

I sure hope I get those rotors changed before the snow flies. (It is not currently looking good).

for now, im just gonna focus on the chassis. ill have to mull over the engine for awhile. I can probably offset lag with the turbo sizing and final drive gearing and build a cheaper engine with simple street porting as long as i can manage the heat.

I am in Utah, elevation 4350 ft. I have a TII, mostly stock, mild porting on the intake and exhaust. I am about to install a Rtek 1.7 ECU and 720cc injectors all the way around. Anyhow my dyno run on the stock ECU at this altitude was 242 Whp at 6700 RPM.

not to shabby on a stock turbo