been forever since ive been on here.... first off i started with the OEM cats.... hated it robbed me of about 15-20 hp.... changed to catless downpipes and a larger Y pipe with a single midpipe exhaust and i went from around 425 to about 510 rwhp on E85.... im not sure if the power gains are different if you decided to go with just a straight 93 pump tune or not but i have had great success with the catless downpipes and larger Y pipe and E85 tune... secondly whats up everyone and hows the car running diego??

 

The lower end torque gains are from exhaust scavenging due to the increased velocity of the exhaust gasses in the pipes. It may very well be that the Stillen kit is engineered with this in mind.

 

Ok… I'm going to take a run at this with an analogy.My background is electronics so you will have to forgive an example from that field.An electronic amplifier is much like an engine translating AC line current to audio power.When viewed in a static manner (measurement with an Ohm meter) some components will appear like either a dead short or infinite resistance.When the circuit is energized however (dynamic alternating current) those same components will display some resistance (reactance actually), and these values are balanced carefully with design to optimize the amplifier for the most gain.
The way I understand the need for some back pressure is that the engine operating dynamically is a system that presents a certain resistance to the flow of air.If the SC sees very low resistance I don't think it will have the capability to build 8 PSI on the intake, thus producing sub-optimal results.
A turbo is totally different and relies on exhaust gas velocity to power the pump for the intake pressure. So in this case low exhaust resistance is good… but there is also a trade off as other posters have mentioned.Low back pressure does not always translate into exhaust velocity… if the pipe is too big velocity goes down… it's just physics.

 

If the engine had no valves, you'd be correct. However, intake valves block flow for some 500 degrees of the 720° of crankshaft rotation. Granted, there can be overlap when both intake and exhaust valves are open but the vast majority of cars with catalytic converters minimize overlap to limit the amount of raw gasoline going to the cats. So, there is plenty of opportunity for pressurizing the intake whether using positive displacement or centrifugal pumps.

You're obfuscating the discussion by introducing turbo-supercharging. You're right, though, different animal.

When I hear back-pressure "helping", that tells me the ECU maps and/or fuel injection system are insufficient for the flow capability of the engine.

And +1 for Stanford's guess. It could be the back-pressure is just an unfortunate artifact of developing a low-rpm solution to emphasize low-end power at the expense of high-end power.

 

"You're obfuscating the discussion by introducing turbo-supercharging...."


Huh? I never mentioned turbo-supercharging.


I was simply suggesting that a turbo uses exhaust velocity to power the pump. A SC does not and looks at the overall "load" or resistance. All I care about is an optimized tune and max HP, and from what I have read from guys who have this SC have better gains without the test pipes... that is good enough for me.

 

From your previous post in this thread: "...A turbo is totally different and relies on exhaust gas velocity to power the pump for the intake pressure. So in this case low exhaust resistance is good… but there is also a trade off as other posters have mentioned..."

Alrighty then. I'll drop this subject but I sure would like to know more about the discrepency.

 

Just a quick update... finally got my build completed and even though I had a whole lot of issues I am very happy with the end product. I took some screen shots of the dyno after the final tune and am pleasantly surprised with the performance of the car. Peak power was 443HP and torque of 323. Those numbers are a huge improvement over my previous NA numbers (284HP and 243TQ).

I have a bit of a low end bog, but the high end performance is very impressive. I think the real story here is the TQ curve and the difference between NA and SC is huge.

 

Looks like the "Par" Numbers for the kit great work, Just dont mod the kit for more WHP leave it and be happy

OH Just change the heat exchanger. The Stillen one is not any good, Frozen Boost on is WAY better,

 

Thanks for the tip on the intercooler. I was wondering if the Stillen one was any good... it looks small. I am pretty happy with the the way the car is performing right now so I'm going to leave it alone. My gas mileage is way better than when it was NA. I can't figure that one out, but i'm not complaining. Did you find any way to resolve the rough transition when you come off boost? It is a bit nerve wracking when you are cornering and back off the gas a little and there is this huge "adjustment".

 

I didnt have any issue going off throttle. Whats it doing. The heat exchanger I would change sooner that later you wont be able to make 3 runs without losing HUGE WHP. After 2-3 runs my car would feel like it was towing a boat, LOL Heat soak FTL

 

When I go off the gas even slightly it feels almost like I am hitting the rev limiter... a pretty abrupt loss in power. I'm guessing that all that boost pressure gets vented when you go off the pedal and it is a rough transition. Not a big deal in a straight line but I don't like that on corners.

I hear you with the heat soak issue... I was concerned about that. The water to air cooling system is great in theory but you need the system to be large enough to dissipate the heat that spirited driving generates.