inlet plenum

Rowdy36Sc

Registered User
I have an 89 with the stock blower and 75mm tb and want to know if it is possible to cnc machine the inlet plenum to 75 mm to match the tb and if this will accomplish anything? I am a cnc programmer/machinist and might as well save myself some money with my knowledge! anyone ever try this and get anything out of it? Thanks
 
Zach,
Your blower has a 60 mm TB on it so unless you purchased a 75, don't bother.

A 75 will require the inlet be opened up to matched or there will be a large obstruction to flow.

Unfortunately, you will break through the inlet in several places by doing so. I hand ported mine and "found" several thin areas in the process. These had to be rewelded and "thickened" so that I can finish.

I can post some pics as you should preweld to beef up those areas as it is easier to weld when the casting is thick.
 
No, if you can afford it, the MP will eat a ported stocker alive. It is designed for continuity of flow through out. The problem is that they ain't cheap.

A huge gain can be made by porting the stocker and adding the bigger TB but generally other power adders are in the mix.

I will try to take the pics and post them as soon as time allows. I have not worked on it since the welds so the thinner areas will be obvious.
 
short of splitting the plenum down the middle and adding in material all you can do is flare the opening so there's a smooth transition from tb to plenum.
 
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If you buy the MP inlet you are gonna be upset when it doesn't fit your early style blower.

They fit the 94-95's but really are designed for the MP2 blower.
 
Good call Scott,

I upgraded both of our cars to new square sport M90 and just assumed he did as well when he mentioned the MP inlet.

nickle,
You are wrong there. I removed a huge amount of material in the throat and throughout the inlet. This is approximately 3/8". The mounting flange was matched to the blower which was about 2mm smaller all the way around.
 
At it smallest point...the best your going to do with porting an early style plenum is about 68mm, so installing a 75mm TB doesn't accomplish much. It can be improved by cutting and welding but will still fall far short of the MP inlet plenum.

David
 
Wrong David. I am currently at 71 mm at the narrowest spot on one wall on my rectangular port inlet. The weld end a little too soon to allow me to maintain continuity through out the inlet.

I will have it touched up a bit and am sure it will hit at least 73 mm and this is just one small area with the bulk of the inlet being 75 mm or greater. I will post pics of the finished inlet and still have a second brand new inlet to use as a comparison.

It may not flow like an MP or allow greater than a 75 mm TB, but it will eat a stock inlet and doesn't cost $400 for those of us that can't buck up for an MP.
 
Oh puleeze, David was talking a out an oval outlet.

A 60mm TB & late model SC is sooooo much better than a totally pimped out early model SC its not even funny.


Just my opinion.
 
nickle,
You are wrong there. I removed a huge amount of material in the throat and throughout the inlet. This is approximately 3/8". The mounting flange was matched to the blower which was about 2mm smaller all the way around.

like i said WITHOUT ADDING MATERIAL you can't expand the throat much. in another thread you say that you added extra material, read what your writing son, the throat is too thin to expand more than 5 or 6mm.
 
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David was talking a out an oval outlet.

True...I was talking about early model....I wouldn't even bother with porting a late model since you can bolt on an MP inlet plenum. Going from a heavily ported and welded late model plenum to an MP plenum on Chris Wise's car gained something like 25 rwhp. It's well worth the money.

David
 
There is no doubt that the MP inlet will be better. I have said that. That is what it was designed for.

Unfortunately, a lot of us cannot afford extravagant goodies and especially not all at once. So what is better, leave a stock inlet and TB or mod the inlet to improve flow and add a larger TB.

Better some gain than none at all.
 
David I did a search for the comparison you described and couldn't find it. Do you have a link?
 
So basically I need to buy a mp2 blower in order to use a bigger throttle body?!? who the hell made these cars? they are too expensive!
 
Not the blower, just the inlet plenum is the suggestion as it will bolt up to a the 94/95 rectangular blower.

A cheaper solution would be a 94/95 factory blower. They were supposed to come with 70 mm TB's and had coated rotors.

Even the stock inlets apparently flow better.
 
so I have a 89 sc with 89 blower. I need to get 94/95 blower and plenum and mp plenum will bolt to that?
 
Yes. The 94/95 come up on Ebay or on the boards. I bought a new one for $350. The MP plenum will bolt to it, but not needed unless you are after major power.
 
the inlet of the late model blowers is rectangular in shape with a significantly larger cross sectional area to flow through. The earlier model blowers inlet port were oval in shape, with less cross sectional area in flow. This is why the MP inlet plenum will not fit the early model blower.

Is it worth it? that is up to you.

Oh yeah, the 94/95 rotors are coated and have tighter case to rotor clearance allowing it to move more air at the same RPM, and therefore generate more boost.
 
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