if i change the 60mm throttle body to a 75mm do i have to change plenum?

no

No, the plenum is fine but you will need to gasket match the opening. I did mine by stuffing it with rags then placing the the new gasket on the studs and marking the excess with a black sharpie. then dremeled it into compliance. Shop vac out the shavings before pulling the rags then vac the plenum too.
 
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holes?

The four holes at each corner? Those should be the same. The big center opening is only 60mm to match the stock throttle body. so when you put the 75mm tb up to the plenum you will see a big step or restriction that needs to be opened and blended to match the 75mm tb. you will see how much needs to be removed when you place the 75mm gaskets onto the studs up to the plenum. If your not comfortable with gasket matching there might be a member on here near you who has done it and willing to lend a hand. Im in SC. ?
 
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?

If you dont have it apart to look at then it might be a little confusing. you dont drill or dremel "through" anything that woud be bad. basically there is a 60mm hole in the center of the plenum for air to enter the supercharger. what ever size larger throttle body 65,70,75,ect, you have match that 60mm hole in the plenum to tthe TB. there is plenty of aluminum there to grind and blend using the larger gasket as a guide. Basically you grind that 60mm hole out to a 75mm hole to match the TB you are installing. I suggest getting some help. There are also books for pointers too.
 
They usually leak no bueno. I had one and sent it back and they sent me back the one Id returned. Whistled it leaked so bad. BBK are okay but the one I had would stick then pop open. Got an accufab. spendy but flawless.
and would a 75mm professional products brand is it a good throttle body?
 
I could post you some pictures if you still are not clear. I have used 6-12 BBK throttle bodies without issue. Accufabs are nice but they are a rich mans tb.
 
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Alright, the first picture is of the late model rectangular inlet. I have several of these left over so it was easy to dig one up. You can see that the throttle body opening is fairly small. It was designed to accomodate the factory 60mm tb.


In the next picture, I have installed a BBK 75mm throttle body that I had lying around. Looking through the throttle body's throat, we can see the "ledge" that would be present if the throttle body was installed on the factory inlet as it is. The result would be a disruption in airflow as the rushing air tried to push its way past the obstruction.

I traced through the throttle body to obtain the last picture but tracing around a gasket will be better as it will making the opening the correct diameter in order to maintain a constant width from the throttle body to the opening in the inlet.

The inlet can be ported while it is installed on the the supercharged while still attached to the motor, but you will not get the best results. For the minor extra effort to remove the supercharger and then the inlet, the job will be completed much better. Inexperienced porters will most likely end up with shavings everywhere including inside the engine. If you do decide to do so, stuff the inlet with clean painters rags. They are cheap and easy to work with. Make sure they are back about 1.5"'s from the opening. If a burr catches one at speed, it could hurt. I would recommend covering the rest of the engine to make sure nothing sneaks itsway inside. Carefully fold up those covers when done and dump them away from the engine bay. Vaccum the shaving from inside the inlet before pulling the rags as suggested.

Working on the inlet while of the car and removed from the supercharger would be the best approach. This not only eliminates the posibility of contamination into the motor, but it allows you to be manipulate the inlet as you work on it. To get the best results, you do not just want to "wedge" the opening sharply, but you should blend into the throat for about an inch or more with a gentle radius. The best approach is to remove material with an aluminum burr until you attain approximately 85% of the final desired shape. Then use a large flapper wheel to smooth everything out.
 

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Alright, the first picture is of the late model rectangular inlet. I have several of these left over so it was easy to dig one up. You can see that the throttle body opening is fairly small. It was designed to accomodate the factory 60mm tb.


In the next picture, I have installed a BBK 75mm throttle body that I had lying around. Looking through the throttle body's throat, we can see the "ledge" that would be present if the throttle body was installed on the factory inlet as it is. The result would be a disruption in airflow as the rushing air tried to push its way past the obstruction.

I traced through the throttle body to obtain the last picture but tracing around a gasket will be better as it will making the opening the correct diameter in order to maintain a constant width from the throttle body to the opening in the inlet.

The inlet can be ported while it is installed on the the supercharged while still attached to the motor, but you will not get the best results. For the minor extra effort to remove the supercharger and then the inlet, the job will be completed much better. Inexperienced porters will most likely end up with shavings everywhere including inside the engine. If you do decide to do so, stuff the inlet with clean painters rags. They are cheap and easy to work with. Make sure they are back about 1.5"'s from the opening. If a burr catches one at speed, it could hurt. I would recommend covering the rest of the engine to make sure nothing sneaks itsway inside. Carefully fold up those covers when done and dump them away from the engine bay. Vaccum the shaving from inside the inlet before pulling the rags as suggested.

Working on the inlet while of the car and removed from the supercharger would be the best approach. This not only eliminates the posibility of contamination into the motor, but it allows you to be manipulate the inlet as you work on it. To get the best results, you do not just want to "wedge" the opening sharply, but you should blend into the throat for about an inch or more with a gentle radius. The best approach is to remove material with an aluminum burr until you attain approximately 85% of the final desired shape. Then use a large flapper wheel to smooth everything out.

I guess Crash and I are up to the same thing. I have a spare stock plenum I'm going to be porting with my die grinder. I don't have any burrs, just some harbor freight stones for my die grinder. I have a feeling they will clog pretty quickly, but I've got a few. By flapper wheel, do you mean one of those cloth polishing wheels?
 
Don't waste time with stones. Three days with stones or 10 minutes with an aluminum carbide burr. The small ones are $15 to $25 bucks.

A flapper wheel looks like a drum and has small "flaps" of sandpaper epoxied into the center. You can prevent both items from filling up with aluminum by coating them in beeswax occasionally. I can post some pictures if this is still unclear.
 
I'll agree with Flex on that. (How much aluminum do you think you have turned into shavings by now, buddy? :D)

Get a good carbide burr. The aluminum is pretty soft, so you have some flexibility with speed. You can use a hand drill if you don't have a proper grinder. A 1/4" burr can take material away faster than a 1/8" burr, but bear in mind that the tips move faster with the bigger diameter burr. To smooth things out and get the final shape, you can use a flap wheel or those mini sanding drums that have sandpaper around a rubber cylinder.
 
Don't waste time with stones. Three days with stones or 10 minutes with an aluminum carbide burr. The small ones are $15 to $25 bucks.

A flapper wheel looks like a drum and has small "flaps" of sandpaper epoxied into the center. You can prevent both items from filling up with aluminum by coating them in beeswax occasionally. I can post some pictures if this is still unclear.

I'd gladly buy a burr, I just not sure where to buy them around here. Something tells me I'm not going to find one at Sears, or auto-zone. I could buy one online, but I'm hoping to tackle it this weekend. Grainger sells them, but they are expensive there.

I know what you're referring to now on the flapper wheel. I was reading where a guy suggested using permatex silver anti seize (I have copper i might try) to prevent clogging as well as beeswax (that I don't have).

I'll be using an air powered die grinder, it has both eighth and quarter inch collets, I'd much prefer to use quarter inch tools. I'll have to do some research to find a place that sells aluminum carbide burrs tomorrow...there's gotta be some place in RI that sells them.

Thanks for the tips!
 
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I'll agree with Flex on that. (How much aluminum do you think you have turned into shavings by now, buddy? :D)

Get a good carbide burr. The aluminum is pretty soft, so you have some flexibility with speed. You can use a hand drill if you don't have a proper grinder. A 1/4" burr can take material away faster than a 1/8" burr, but bear in mind that the tips move faster with the bigger diameter burr. To smooth things out and get the final shape, you can use a flap wheel or those mini sanding drums that have sandpaper around a rubber cylinder.



At one point I had three large plastic coffee jugs full of them. I stopped collecting.


How are you and the family? How is your bro doing?
 
I'd gladly buy a burr, I just not sure where to buy them around here. Something tells me I'm not going to find one at Sears, or auto-zone. I could buy one online, but I'm hoping to tackle it this weekend. Grainger sells them, but they are expensive there.

I know what you're referring to now on the flapper wheel. I was reading where a guy suggested using permatex silver anti seize (I have copper i might try) to prevent clogging as well as beeswax (that I don't have).

I'll be using an air powered die grinder, it has both eighth and quarter inch collets, I'd much prefer to use quarter inch tools. I'll have to do some research to find a place that sells aluminum carbide burrs tomorrow...there's gotta be some place in RI that sells them.

Thanks for the tips!


Ebay is your friend for this buddy.

http://www.ebay.com/itm/3-CARBIDE-B...ultDomain_0&hash=item3cd0b8fee3#ht_469wt_1125

http://www.ebay.com/itm/New-Carbide...ultDomain_0&hash=item4d0b97c904#ht_337wt_1125

http://www.ebay.com/itm/4-CARBIDE-B...ultDomain_0&hash=item3cd0e2a3b8#ht_431wt_1125




Regular steel carbides are not as agressive on aluminum and allow for better control and a smoother finish.


http://www.ebay.com/itm/New-Carbide...ultDomain_0&hash=item35c6772b11#ht_407wt_1125


http://www.ebay.com/itm/over-1-and-...aultDomain_0&hash=item2a2ba790bf#ht_44wt_1125
 
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