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wanna-be subaru killer.
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Alrighty, So as I have postponed or rejected the turbo idea due to the fact that I want this car to remain as a fun daily and don't want to really risk it's functionality. I am back to bolt ons. I know the headers are the top pic for the 6g75 but I have been doing some thinking.

I was thinking through N/A power increases and thought about a throttle body diameter increase. I ran a search and didn't dig too deep into the forum but I figured I'd like to get the fresh responses to this question regardless...

Has anyone found a larger diameter throttle body that is suitable for this motor?
 

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The Evil Wizard
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367 Posts
Alrighty, So as I have postponed or rejected the turbo idea due to the fact that I want this car to remain as a fun daily and don't want to really risk it's functionality. I am back to bolt ons. I know the headers are the top pic for the 6g75 but I have been doing some thinking.

I was thinking through N/A power increases and thought about a throttle body diameter increase. I ran a search and didn't dig too deep into the forum but I figured I'd like to get the fresh responses to this question regardless...

Has anyone found a larger diameter throttle body that is suitable for this motor?
Check previous postsabout TB swap..worth the swap, better when pair with headers and tune.
 

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Basically Stock
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5,677 Posts
Nobody has ever done a before and after dyno test between changing throttle bodies, and the science supports that there would be a loss in overall power. It's just been a longstanding rumor around here, and has been disproven on other platforms.

You're trying to accelerate air into the engine to give increased VE. That's how NA power increases. Changing to a larger TB port does not do that, it would only allow for a maxed out airspeed to be slowed down in order to allow for more maximum flow. That would be important if displacement or head flow are increased beyond the capacity of the current inlet
 

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The Throttle bodies on the 4g are drive-by-wire. There is no specific aftermarket throttle body explicitly designed for application in our vehicles. Sabertooth is also correct, a larger throttle body will not necessarily improve performance of the vehicle; if the size of the throttle body isn't a restriction on the intake, then all a bigger throttle body will do is slow the air down.

That being said, there are options. Boomba used to make a throttle body for the Evo X that is plug-in and bolt-on compatible, but to my understanding, you need a modified tune to work with it or else the car will surge. While Boomba no longer sells this specific product, OBX sells one that is basically a knock-off of this design and works the same way with the same limitations.

A throttle body for a WRX can be made to work as well if you rewire the connector for pin compatibility, but I don't know what work would need to be done, nor do I know if they have a throttle body bigger than the stock GT body in their aftermarket.

Finally, in theory, any electronically controlled throttle body could be adapted to work on the GT if you rewire the harness for pin compatibility, but will likely require custom fabrication of some sort to mate it to your intake manifold.
 

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The Evil Wizard
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The Throttle bodies on the 4g are drive-by-wire. There is no specific aftermarket throttle body explicitly designed for application in our vehicles. Sabertooth is also correct, a larger throttle body will not necessarily improve performance of the vehicle; if the size of the throttle body isn't a restriction on the intake, then all a bigger throttle body will do is slow the air down.

That being said, there are options. Boomba used to make a throttle body for the Evo X that is plug-in and bolt-on compatible, but to my understanding, you need a modified tune to work with it or else the car will surge. While Boomba no longer sells this specific product, OBX sells one that is basically a knock-off of this design and works the same way with the same limitations.

A throttle body for a WRX can be made to work as well if you rewire the connector for pin compatibility, but I don't know what work would need to be done, nor do I know if they have a throttle body bigger than the stock GT body in their aftermarket.

Finally, in theory, any electronically controlled throttle body could be adapted to work on the GT if you rewire the harness for pin compatibility, but will likely require custom fabrication of some sort to mate it to your intake manifold.
I understand that especially using a larger TB like Boomba 75mm, only like three members had use them and all of them required a tune. A tune is required to get the most out any upgrades anyway. But using a ported TB (68mm) compare to the stock 65mm, is an improvement. Its been documented. Only those who do 6g75 swaps in 3G and Mirage have been using 70mm+ TB with success, again, documented. Go check out the builds in Puerto Rico:timja:
 

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I understand that especially using a larger TB like Boomba 75mm, only like three members had use them and all of them required a tune. A tune is required to get the most out any upgrades anyway. But using a ported TB (68mm) compare to the stock 65mm, is an improvement. Its been documented. Only those who do 6g75 swaps in 3G and Mirage have been using 70mm+ TB with success, again, documented. Go check out the builds in Puerto Rico:timja:
Hang on let me check real quick...yep, you aren't the guy who asked the question, so I wasn't responding to you. I don't understand spanish, so why don't you explicitly translate all those things the PR guys have done and explain it to everyone here so we understand, since you seem to know it all so well but have twice failed to provide details?

Or is it that you don't really know either, and you're just talking out your ass based on what you saw someone else do on YouTube?

You're like one of those assholes who responds to any technical question on this site by posting a link to the service manual without being able to cite where in the manual the answer to the question is. If you don't know, don't say you know and tell others to go look it up; what you're really saying is your full of shit and don't know a damn thing about what's being talked about.
 

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Basically Stock
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Having a rough day? That's a bit of an over reaction Kevin. I get where you're coming from, but even so.

I'd like to see him back up his claim with an example as well though, as it's against the science. A GS throttle body should actually increase power on a GT as the GS TB would flow air faster, yet still below the speed of sound in that airmass, so the plenum would have higher pressure between intake valves opening, allowing for a higher VE.
 

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You're like one of those assholes who responds to any technical question on this site by posting a link to the service manual without being able to cite where in the manual the answer to the question is.
You talking about me when I want to help and know where it is in the FSM but don't have time to post it all when it's already explained by the people who made the car?
 

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A larger TB is beneficial when using forced induction, or different cam profiles. Otherwise your velocity will drop and the engine is still using the same amount of air as the stock TB.
 

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Basically Stock
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With forced induction, as you increase the pressure, so does the speed of sound. So you can move the air at a higher velocity. The problem then becomes more on the inlet side of the turbo.

From what I've found, 70mm throttle bodies on an Evo seem to be the largest that anyone needs, even on 800hp builds. Many go larger, but there doesn't seem to be any gains.

The 6G75 I still say only needs about a 62mm, unless you have a super restrictive intake, which nobody would who's looking to upgrade throttle body
 

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The Evil Wizard
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Hang on let me check real quick...yep, you aren't the guy who asked the question, so I wasn't responding to you. I don't understand spanish, so why don't you explicitly translate all those things the PR guys have done and explain it to everyone here so we understand, since you seem to know it all so well but have twice failed to provide details?

Or is it that you don't really know either, and you're just talking out your ass based on what you saw someone else do on YouTube?

You're like one of those assholes who responds to any technical question on this site by posting a link to the service manual without being able to cite where in the manual the answer to the question is. If you don't know, don't say you know and tell others to go look it up; what you're really saying is your full of shit and don't know a damn thing about what's being talked about.
Having a rough day? That's a bit of an over reaction Kevin. I get where you're coming from, but even so.

I'd like to see him back up his claim with an example as well though, as it's against the science. A GS throttle body should actually increase power on a GT as the GS TB would flow air faster, yet still below the speed of sound in that airmass, so the plenum would have higher pressure between intake valves opening, allowing for a higher VE.
I don't have time to dig up every results, every pm, every email, every chart for you or anybody else to prove something. Go, take your time, and comb through the posts. I was here way before you join this forum, here when everyone was actually into wanting HP for their cars with bolts on and such, pushing for aftermarket support. Experiencing the trial and error. I was there when I told my PR friend about using the Pajero Evoluation rom for speed density for 6G7x swap, and from there it snowball into the tuning/swap scene it is today. All or most of the old heads on this forum move on from this platform. Why would Mitsu underperform the Eclipse GT because it was selling their "flagship" the Evo, their made it run a bit richer and put on a decent size TB so i can go toe to toe stock with the Evo. Give me a break, get hands on and see for yourself.
 

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Basically Stock
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They even put it in their original ad for the 4g that it wasn't going to be a competitor for the evo, so that's not it. And the richness was for emissions reasons, and is a very common practice.

But seriously, it's been shown thousands of times (not just on the 4g) that too large a throttle body for the airflow amount just reduces power, and works in all the science of how an intake manifold works to give maximum air velocity

Nobody has ever actually shown on here any data to back up that a larger TB helps, not for the GS or GT, and the science says it should not. I could definitely see it being useful on ones with a head build, or revving much higher than stock motors do, but otherwise, no, and there's no data to support it either. I won't claim to be an expert on the GT, but the science remains the same as working on my GS
 

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The Evil Wizard
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But seriously, it's been shown thousands of times (not just on the 4g) that too large a throttle body for the airflow amount just reduces power
Yes, too large can hurt given the circumstances but a small increase does not such as the ProFlow TB mod. A small increase from 65mm to 67mm will be beneficial especially in the upper RPMs. If you are not after high HP, especially you are not going to rev near redline, then no a bigger TB is not a bolt on part for you.
 

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Basically Stock
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Could you share at least 1 dyno before and after of this? I keep searching but can't find anything on the 6G75 engine

What the issue is, is that the stock size has been calculated out to already be too big to be optimal for stock power, making it a great size for a lightly modified (bolt on) car. The intake manifold limits the rev range significantly, as do the cams, so without changing those, it's tough to get the engine up into the rev area where airflow volume is high enough that the velocity into the plenum would require a larger throttle body, and whenever you reduce velocity into the plenum, you lower volumetric efficiency as the plenum air charge density drops as well.

Even MAP and MAF data in equal weather conditions or stating temperature and barometric readings would work to compare if it's a benefit (more peak MAF and higher MAP, more air in, more ability for power, generally speaking)
 

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Basically Stock
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He's also running leaner, which we know adds power and is something we do when tuning these NA

You really can't compare non tuned stock vs non tuned lean. You need to keep the parameters the same. Otherwise you could use a slightly larger MAF housing and argue that that adds power too, because it'll run leaner as well without being tuned properly.


I maxed out my MAF and leaned out (~15:1 when I lifted) and made huge power increases over running at 12.8:1 AFR with a larger MAF housing that can measure the air and add proper fuel
 

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The Evil Wizard
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367 Posts
He's also running leaner, which we know adds power and is something we do when tuning these NA

You really can't compare non tuned stock vs non tuned lean. You need to keep the parameters the same. Otherwise you could use a slightly larger MAF housing and argue that that adds power too, because it'll run leaner as well without being tuned properly.


I maxed out my MAF and leaned out (~15:1 when I lifted) and made huge power increases over running at 12.8:1 AFR with a larger MAF housing that can measure the air and add proper fuel
No, he is running rich...near 10.1:1 near redline with no tune...did you read the whole thread?
 
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