I was on another forum and was recomended here.
I just want to post what was said in the other forum to find out what you guys thing. Here was my thread.
It started basicly as a engine life thread but went a bit off topic.
Just wondering since Im changing to the y8 mani and 70mm tb will I have to change injectors or anything?
Also Like I said in another post. Im trying to get the car to just run right.
Am I going to have to worry about grenadeing the engine or anything since im doing all this to a car with 220,000 miles on it??
I only drive the car back and forth to work. And it seems a little late in the engines life to be doing drastic things to it to gain more power.
I would almost rather buy another engine and start building that and run this the way I have it so it last's longer.
Any thoughts?
Without going too far off-topic, I would recommend selling the 70mm throttle body and going back to a 56mm or maybe 58mm one.
When you boost an engine, you increase the mass flow of gasses passing through the engine since the compressor raises the air density entering the intake manifold. However, due to the increased backpressure caused by the turbine, the volumetric flow of gasses usually drops a little, and that's what matters for throttle body selection. Pressure variations in the intake manifold also have an influence, but a boosted engine doesn't have as much variance in manifold pressure between cycles as an atmo engine. If it wasn't for the slightly increased pressure drop across the throttle plate, you could actually use a slightly smaller throttle body when you boost an engine. Most people think they need a larger throttle body when they're boosted because they're flowing more air mass. It might seem like a logical conclusion, but it's not really true.
Good nfo right there ^ also correct me if iim wrong but does it also have to deal with the fact that it takes more to pressurize a bigger area then a small area
It takes more time to pressurize a larger volume, all else being equal. However, the increase in volume between a 70mm throttle body and a 56mm throttle body isn't that large, so the difference will be pretty small. Charge tubing diameter will have a big influence though, which is why you want to keep the tubing small but not small enough to add a significant pressure drop between the compressor/intercooler and the throttle body.
The main reason for using a small throttle body is for drivability. Here is a graph of the theoretical airflow through a 56mm and 70mm throttle body:
Assuming the 56mm is not a restriction, look at how far you need to open the 70mm throttle body to flow the same amount of air that the 56mm throttle did at WOT - it's a little over half. That means almost everything above half throttle is useless, and you're not flowing any more air by opening the throttle more. It makes modulation more difficult.
You might hear that a larger throttle body will improve throttle response. This is possible, but it's misconception 99% of the time. What people think is better throttle response is really the engine becoming less throttled faster. Less pedal throw will allow the engine to flow more air, and it takes less pedal throw (and time) for the engine to effectively be at full throttle.
Throttle response is primarily dependent on the volume of air between the throttle body and the valves as well as the transient fueling calibration. The throttle diameter has little effect with one exception: if too much fuel is injected during throttle transients, the response actually will improve with a larger throttle since the engine will run relatively leaner and will make more power. However, this is only true while the average airflow through the engine is still increasing. Once you exceed the angle at which the larger throttle no longer restricts air, pushing the throttle pedal down more will just make the engine run richer - especially if you push the pedal down fast. It will therefore make less power (if it was properly tuned before the throttle body replacement).
This is a bit to in depth for me. I was just wondering if this guy is correct. Should I save my money and not go with a 70mm tb? He said later on in the post (don't want to put everything here) That it's best to just get the factory tb bored out 3mm
Thanks for the help and info.
Ohh and the car is a 98 civic lX boosted 7psi.
Thanks again!!
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