TB swap and lower boost

[HSKR]

Not sure if this is normal or not. All I did was install a throttle body that came off a '93 3.3L V6. It's visually bigger and larger than the port on the intake manifold. I trimmed the gasket to fit the TB, but there is still the lip into the intake manifold. Since the intake manifold itself didnd't change I wasn't expecting the boost levels to really change. So with stock TB is hit 10lbs of boost by 3500RPMs and pulled nice through the gears. After the larger TB was installed it struggles to hit 7lbs of boost and it obviously down on power. I put the stock TB back on for now, but is that to be expected? I know guys with superchargers when you open up the intake side the boost levels usually go down due to better flow but the power goes up as the overall volume of air increases. That didn't happen in this case.

[cordes]

That is unexpected. Do you have the ports on the TB blocked off, or are they still running to the charcoal cannister and whatever else is hooked up there? I'm not sure if the ports on the 52mm TBs are the same or not. I would suspect that could be an issue, but I still don't see it causing a 3lb reduction in boost unless your WG was somehow involved in that.

[GLHNSLHT2]

if it hits that lip and causes enough turbulence to slow the air into the intake it could, Though i would think it would be temporary until the ECU relearns to adjust the wastegate and spins the turbo faster to compensate. Though that's just killing hp as you now have to keep the wastegate closed more to get the boost level back to stock, also you're running in a less efficient part of the compressor map now too causing increased heat.

Superchargers spin at a rpm directly tied to the engine. So if you increase flow on the intake side then yes boost will go down. Turbo's don't operate like that. The wg will just stay closed longer to get the desired boost level.

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That is unexpected. Do you have the ports on the TB blocked off, or are they still running to the charcoal cannister and whatever else is hooked up there? I'm not sure if the ports on the 52mm TBs are the same or not. I would suspect that could be an issue, but I still don't see it causing a 3lb reduction in boost unless your WG was somehow involved in that.


3.3 V6 TB's have the same ports as Turbo 46's.

[cordes]

Well that eliminates the ports on top idea. I'll say that I've installed larger TBs without any problems even when the manifold wasn't matched for it.

[HSKR]

I thought it might be a ECM thing and just needing to relearn it, but the stock TB was doing fine so put it back on until I can get the intake opened up to eliminate the lip. It does have the two vacuum ports on top of the TB but they are hooked back up the same way they were on my stock TB. Everything on the bigger TB is the same as my stock one other than the bore size and the "cams' for the linkage cables. Which now that i think about it could be part of the problem. The linkage has smaller "cams" on it so it might not be opening up all the way. Which if the TPS isn't seeing full WOT and the blade isn't fully open could be a problem.

[GLHNSLHT2]

On a side note, if you still have the stock 1 piece intake installing a bigger TB is pointless. Even if you try and port the opening to match. Why? Well because after the turn it necks down to an opening that is smaller in area than that of even the stock 46mm TB. It just does nothing for performance on a 1 piece as that is NOT where your restriction is. Now if you had a 2 piece or a cut and modifed 1 piece, that's a different story.

[HSKR]

On a side note, if you still have the stock 1 piece intake installing a bigger TB is pointless. Even if you try and port the opening to match. Why? Well because after the turn it necks down to an opening that is smaller in area than that of even the stock 46mm TB. It just does nothing for performance on a 1 piece as that is NOT where your restriction is. Now if you had a 2 piece or a cut and modifed 1 piece, that's a different story.

Well, guess I'll keep the TB around for down the road if i ever change the intake manifold.