Beyond_Redline

hello all,
Over in the racing forum I have built a s2000 for NASA ST3. This year I was running about 2 points off my power to ratio limit. I was way down on power but the amazing grip combined with aero allowed me to post similar lap times to my competitors.

This next season im throwing in a few radical tricks because its fun and im always trying to find new ways to go faster. Ive been studying some CFD models of diffusers and im currently building a convex diffuser for drag reasons against concaved and straight angled diffusers. ill get to my question soon enough. Lol. just filling you in on my reasoning. The diffuser is a 4 to 1 foot incline from the front of the sub frame. (1 inch incline for every 4 inches) the cfd model says this will create air separation half way down the diffuser without vortex generators see http://www.f1technical.net/forum/vie...p?p=257224&f=6 . I was going to make a double diffuser but before I do im going to try out a “blown diffuser”

So to my question.
Ill be running a Supercharger wastegated down to 275 whp. Am I correct in saying that there will be a fair amount of air traveling though the wastegate? If there is I need to dump it back into the exhaust. This is a supercharge mind you not a turbo so if its possible, and if there is enough air worth doing something with, can I dump it back into the exhaust. Reason being is it makes a huge difference running blown diffusers on boosted cars (that much air traveling through the exhaust). But these were all turbos and im trying a supercharger to get around high heat levels.

Do you think the super-heated air pressure in the exhaust would be higher than that in my charge pipe? If so it wouldn’t work…
How much boost would be dumped back in?

CoolGuy094

You need to talk to 99SH about wastegates on an SC setup and look over his old threads for info.

Ian300D

Wastegate or not exhaust gasses alone should yield benefits. Just remember that you loose this on throttle lift, but your wastegate may supply a little bit to offset this, but i wouldnt count on it a lot.

Are you already a full under tray. Also how do you test your aero setups?. You should get on time attack forum, there are some engineers on there that are great at sharing info.

Also will this even be allowed in your classing, typically i thought this tech was not allowed on most classes.

Beyond_Redline

after reading though this https://www.s2ki.com/s2000/topic/971...#entry21928379 (awesome read by the way) it sounds like ill be bleeding off 9 or so lbs of boost and the pressure behin the wastegate has to go somewhere. only way out would be through the exhaust so there is no way it could make it back up into the charge pipe. so im thinking this boost would help with constant flow.

yes the diffuser will be installed with a complete undertray. I test my aero parts with with string, tape, highway, and a cam car lol. that and 3d modeled CFD. aero is open in ST3 it just cant be active aero (moving parts) I posted here looking for some answers on boost. i got the aero side of it in the box!

RAIN H8R

I must be confused. What exactly are you trying to do here? Use the air from the wastegate to cool down the header?

Sent from my Samsung Galaxy S4

benes2k

When the wastegate opens at X psi the supercharger itself keeps climbing in psi resulting in more heat from the supercharger. So you are actually making your engine temp, egts etc. go up. it will be more hot than you were previously.

for the air coming out the wastegate, it will steadily increase once the wastegate opens up and you will get more air the higher the rpms at WOT. however whenever you let off the throttle at all your changing the amount of air going through the diffuser no matter what rpms you are at. I dont know if that could really harm your high speed handling though. just some thoughts.

benes2k

he bascially wants to know if its worth it to recirculate his wastegate to the exhaust to benefit his rear diffuser. on his supercharger set up.

Beyond_Redline

More so than a Turbo? the supercharger will have to be wastegated no mater what I do... if that's going to cause temps to go up to the same levels as a turbo then its a no brainer. id install a turbo instead.

as far as boost for the diffuser, am I wrong to say that there will be a constant flow even off the gas? the crank is always spinning. even in between shifts boost would flow through the exhaust correct? I didn't think about the blow off valve though.

if so what is the cfm through a supercharger at on avg. of 16 psi(7-9000rpm)

with 300hp there is never a time where im off the gas but to brake. there are few corners that I brake to the apex (slow corners) so the diffuser would not be in effect anyways. im 90% on the gas just after turn in unless Im tryn to get the rear to rotate trail braking.

lleron

I think the real answer that needs to be known here is what is the actual maximum pressure seen from an exhaust pulse? The pressure differential between that and your wastegated boost pressure will determine how much air will flow from the wastegate (along with piping diameter from the wastegate). It will definitely flow (significantly I would think) less than the wastegate opened to air. I also think that heat transfer from the exhaust could be an issue.

Could you not just dump the air somewhere else (behind a wheel or something) with a longer dump tube if you're so worried about aero? I would imagine the amount of air being dumped out of the wastegate is negligible compared the the mass of air flowing over the car at 70+ mph, although I'm certainly no expert in aerodynamics.

benes2k

I cant say if it'd be more than a turbo, but I know it will be more than you previously had. All turbo set ups are different and can be coated, wrapped etc. For longevity I would say it would be very similar to a turbo, much hotter than before as the supercharger is constantly being overworked. I would look into that issue I know most people running wastegates on blowers have low mileage blower failures from the blower being overworked.


yes theres always a constant flow but unless your on the gas the blow off valve will be open venting to atmosphere.


like lleron said I would be worried about exhaust gas heat, and look into dumping it under the car. As long as the underflow of air is steady dumping it under the car and out the exhaust seems to minimal effect on overall airflow.