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Discussion Starter #1 (Edited)
Just thought I'd post some pics of what I've been working on in my spare time over the past few weeks:






I ported/ground out all the manufacturing defects including all the mold seams, etc, and smoothed out all transitions. After considering grinding out the "trough" that is in the bottom, I decided against it because of the way the unit was cast, I would have ground a hole through. The plenum was then subsequently sanded (by hand) to a smoother and smoother finish and ultimately polished and sealed. You can still see slight scratches in some places (like on the sides) that I could have sanded away with more hours of work, but come on! I doubt what little gains could have been had by completely eliminating all minute scratches was worth continuing on.

What do y'all think? :zdunno:
 

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PostSlut
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looks real good!
I feel you on the "with more hours of work, but come on!"

Thats everyday for me with my car....just hours upon hours....:D
 

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WOT Junkie and avid corn burner
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How much of a gain, if any, could be expected by doing this? Also, is that the OEM air elbow?
 

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How much of a gain, if any, could be expected by doing this? Also, is that the OEM air elbow?
put a vacuum gauge in there, and compare it to a stock one immediately afterwards.....if vacuum is lower, then there is some kind of gain
 

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Discussion Starter #7 (Edited)
put a vacuum gauge in there, and compare it to a stock one immediately afterwards.....if vacuum is lower, then there is some kind of gain
You mean just hook a vacuum gauge to one of the ports on the stock setup the way it is right now, then replace the plenum and take another vac reading from same place right after and compare with the TB butterfly closed? Is that accurate? I can do that - I'll do it tomorrow afternoon and let you all know. I'm also gonna get a Crown Vic upper next (I've read it is 3/4" taller) and clean it up.

Where should I hook the vac gauge? Does it matter?

How much of a gain, if any, could be expected by doing this? Also, is that the OEM air elbow?
Yes, it is a stock 1996 Thunderbird elbow it started life as. I have another elbow here off a 2001 GT, but believe it or not, it is much WORSE than the 'Bird one I started with and is going to take a lot more work to look good.
 

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put a vacuum gauge in there, and compare it to a stock one immediately afterwards.....if vacuum is lower, then there is some kind of gain
How would the vacuum change by just porting and polishing the intake elbow?
 

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Discussion Starter #11
at idle it wont....I obviously mean @ WOT
I wondered about that. What, you want me just to let it rev to limiter and watch the gauge? Sounds hard on the engine with no load. Or do I try to hold the brake and rev in gear? I've never done such a test, so you're gonna have to walk me though your "homemade plenum test", gm. :D
 

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PostSlut
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I wondered about that. What, you want me just to let it rev to limiter and watch the gauge? Sounds hard on the engine with no load. Or do I try to hold the brake and rev in gear? I've never done such a test, so you're gonna have to walk me though your "homemade plenum test", gm. :D
you would need the gauge in the car with you.....I actually have in one in my daily driver that I keep an eye on....for gas mileage.

 

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How can any vacuum be generated at WOT with the throttle blade wide open?

Al
Suction. IIRC, the vacuum drops to 0 inHg, or at least close to 0 inHg, when the throttle is snapped open, but when the throttle is left open, vacuum is created by the air being drawn into the engine. This is due mostly to the resistance of the air being drawn in. Less resistance (smoother air passage), less vacuum created. Am I right...somewhat? This vacuum reading should probably be taken at below or at the bottom of the intake elbow.
 

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Discussion Starter #15
How can any vacuum be generated at WOT with the throttle blade wide open?

Al
Yeh, I totally agree. I know for a fact that those vacuum activated heater controls do NOT work at WOT. We once were towing a load WAY too large for a Dodge van and the controls would not work because we had to keep standing in the throttle to keep the vehicle moving and obviously didn't have vacuum to work with.

you would need the gauge in the car with you.....
I like that idea better. Gotta go test after lunch. I'm wondering how little vaccum is going to exist at WOT with ANY intake, but we will find out!
 

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Well of course you'd need to have the gauge in the car when you go WOT when you actually DRIVE IT......come on guys, snap out of the ricer mentality......do some real world testing....the smaller the scale on the gauge, the easier it will be to discern the differences, if any
 

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Discussion Starter #17 (Edited)
Well of course you'd need to have the gauge in the car when you go WOT when you actually DRIVE IT......come on guys, snap out of the ricer mentality......do some real world testing....the smaller the scale on the gauge, the easier it will be to discern the differences, if any
Yeh, I found that out! LOL Anyways, the car idles normally about 22" of vacuum with all vac lines, a/c off. With all vac lines plugged, it rises to about 23". Not that idle matters, I'm just saying it looks like it loses about 1" with all the vac lines hooked up.

At 65, it runs about 19" of vacuum. At WOT, it runs about 3"-3.5" of vacuum. I tried removing the air cleaner filter and the numbers dropped to 2.5"-3". What raised my eyebrows was I could feel the difference when I removed the air filter; if 0.5" of vacuum can be felt, I should REALLY be able to feel ~3" of vacuum! BTW, with all the vac lines hooked up, it had like 1" of vacuum at WOT.

I haven't put my new elbow on, but I can see already that with my stock engine (except for the PI intake) and full exhaust, it probably isn't going to do much but who knows? Now I'm also wondering how much of that 3" of vacuum could be recovered with a bigger throttle body such as a 70 or 75mm? The hole in the elbow is 73mm (~2 7/8") which didn't increase much from before I started; what DID increase was inside where I bored out the sides. So what I'm getting at is with better flowing heads & exhaust, the difference will obviously be much greater.

I'll get that new plenum on in the next couple of days and tell you the results...

Oh, and GM, I have like no experience with any Jap hot rods, but I do like rice, boiled, fried, whatever! And I just stuck the gauge under the wiper blade where I could read it easy.
 

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It's amazing what a little grinding, when done right, will get you in the HP department. Lots like nice work.
Actually, that has yet to be determined if you read his post carefully
 

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Yeh, I found that out! LOL Anyways, the car idles normally about 22" of vacuum with all vac lines, a/c off. With all vac lines plugged, it rises to about 23". Not that idle matters, I'm just saying it looks like it loses about 1" with all the vac lines hooked up.

At 65, it runs about 19" of vacuum. At WOT, it runs about 3"-3.5" of vacuum. I tried removing the air cleaner filter and the numbers dropped to 2.5"-3". What raised my eyebrows was I could feel the difference when I removed the air filter; if 0.5" of vacuum can be felt, I should REALLY be able to feel ~3" of vacuum! BTW, with all the vac lines hooked up, it had like 1" of vacuum at WOT.

I haven't put my new elbow on, but I can see already that with my stock engine (except for the PI intake) and full exhaust, it probably isn't going to do much but who knows? Now I'm also wondering how much of that 3" of vacuum could be recovered with a bigger throttle body such as a 70 or 75mm? The hole in the elbow is 73mm (~2 7/8") which didn't increase much from before I started; what DID increase was inside where I bored out the sides. So what I'm getting at is with better flowing heads & exhaust, the difference will obviously be much greater.

I'll get that new plenum on in the next couple of days and tell you the results...

Oh, and GM, I have like no experience with any Jap hot rods, but I do like rice, boiled, fried, whatever! And I just stuck the gauge under the wiper blade where I could read it easy.
I'm confused....at wot do you have 1" or 3-3.5" of vacuum?
 
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