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Old 01-25-2013, 09:40 PM   #1
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plenums

Are all plenums 75 MM? I'm looking to get a throttle body and plenum combo the 70 MM setup but every plenum seems to be a 75 would this be ok to get with a 70 MM without FI?

---------- Post added at 09:40 PM ---------- Previous post was at 09:39 PM ----------

Get with a 70 MM throttle body**
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Old 01-25-2013, 09:55 PM   #2
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Yeah get 70 if your not going FI
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Old 01-25-2013, 10:01 PM   #3
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Would that be ok to run even with a 75 MM plenum?
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Old 01-26-2013, 12:25 AM   #4
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IMO I'd get 70 both
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Old 01-26-2013, 06:00 AM   #5
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IMO I'd get 70 both
Where can I find both 70? I can only find the tb 70
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Old 01-26-2013, 06:01 AM   #6
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Have you checked LMR? AM or CJ
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Old 01-26-2013, 06:16 AM   #7
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Have you checked LMR? AM or CJ
Both AM and CJ don't put in their descriptions what size the plenums are and lmr offers a 70 combo but the plenum is a 75.
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Old 01-26-2013, 11:38 AM   #8
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On AM the accufab 70mm tb and plenum are both 70mm and it's what I run on my gt. definatly gained some go and throttle response. Can really feel it after 3k rpm.
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Old 01-26-2013, 12:40 PM   #9
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On AM the accufab 70mm tb and plenum are both 70mm and it's what I run on my gt. definatly gained some go and throttle response. Can really feel it after 3k rpm.
+11 after 3k rpms I can definitely feel my car pull harder
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Old 01-26-2013, 03:11 PM   #10
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On AM the accufab 70mm tb and plenum are both 70mm and it's what I run on my gt. definatly gained some go and throttle response. Can really feel it after 3k rpm.
Damn that would be an awesome feeling.. to bad its way out of my price range lol
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Old 01-26-2013, 08:12 PM   #11
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The Accufab is what I used to have on my 04 and it has been proven to make more power the all other setups available. There was a bunch of dyno comparisons in muscle mustangs and fast ford years ago.
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Old 01-26-2013, 10:41 PM   #12
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The upper plenum, stock or aftermarket, has a 75 to 78 mm opening at the TB--there is no such thing as a "70 mm plenum". Also, the stock plenum is the weak link in the intake tract, if you examine Accufab's flow bench tests you will see that any aftermarket plenum, with the stock 65 mm TB, will out flow the stock plenum with any size TB.

After market plenums are 3/4" to 7/8" higher than the stock unit which allows a wider (internally) passage through the 90° bend. Ford should have replaced the upper plenum when the PI upgrade was introduced--they did not as it's only real effect on the PI 2V is to roll-off the power a bit faster after 5500 rpm. If you were warrantying Mustang GTs you might not consider that as being a bad thing either.

Also and as stated by others above, 70 mm is the optimal size for any n/a 4.6 L 2V build--this is also spoken to on my Accufab flow data page.

In the last, the OP make want to read the "Beginner's guide to bolting-on power gains" sticky...
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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq
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Old 01-27-2013, 01:24 PM   #13
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The way I see the prices are that you get what you pay for.
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Old 01-27-2013, 03:29 PM   #14
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The Accufab is the prettiest and most expensive, they all perform basically the same with no particular brand having any significant advantage. Some of the B&K throttle bodies have throttle plate shaft binding problems due to a weak design...
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Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq
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Old 01-27-2013, 07:00 PM   #15
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I bought a 70mm tb and just ported my stock plenium. Plenty of air flow
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Old 01-27-2013, 08:33 PM   #16
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I bought a 70mm tb and just ported my stock plenium. Plenty of air flow
I like that idea better.
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Old 01-27-2013, 08:35 PM   #17
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I bought a 70mm tb and just ported my stock plenium. Plenty of air flow
How did you do that?
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Old 01-27-2013, 09:09 PM   #18
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With a port and polish kit of jegs and a few carbin bits with a air drill
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Old 01-27-2013, 09:21 PM   #19
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With a port and polish kit of jegs and a few carbin bits with a air drill
Any tips for the process? Or is it pretty simple..
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Old 01-27-2013, 09:27 PM   #20
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Pretty simple. Just be careful
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Old 01-28-2013, 03:35 AM   #21
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Please, I say what follows not to offend anyone or cast aspersions on anyone's diligent work (I have ported and polished more than one intake/head in my years).

Nonetheless facts cannot be ignored and the issue with the stock upper plenum is not one that that porting and polishing will cure. Its fundamental design is lacking and it simply cannot flow as much air as any after market unit, this is shown in Accufab's bench test data here.

The best the stock upper plenum, with no TB and at 2.0 inHg drop, can flow is 505 cfm, less than the engine's 100% VE needs (528 cfm). The worst aftermarket plenum (the C&L which was at the tail end of the list) flows 569 cfm under the same conditions. The others all move 600+ cfm.

If you do choose to P&P the stock plenum then get an under plenum spacer (never thought I be recommending that), you can get them on eBay for $20 to $25 and it will to some extent fix the biggest shortcoming of the stock plenum by vertically extending the outlet end of the elbow.

All aftermarket plenums are taller than the stock unit, which allows a larger passage way through the bend. No amount of P&P can accomplish this as the stock unit doesn't have enough "meat" to support enlarging the bend...

Here is a photo (a crummy photo but the best I could fund) showing the height difference of a stock and typical aftermarket plenum:



The added height allows for a higher volume and less sharp 90° bend...
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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq
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Old 01-28-2013, 08:59 AM   #22
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Originally Posted by cliffyk View Post
Please, I say what follows not to offend anyone or cast aspersions on anyone's diligent work (I have ported and polished more than one intake/head in my years).

Nonetheless facts cannot be ignored and the issue with the stock upper plenum is not one that that porting and polishing will cure. Its fundamental design is lacking and it simply cannot flow as much air as any after market unit, this is shown in Accufab's bench test data here.

The best the stock upper plenum, with no TB and at 2.0 inHg drop, can flow is 505 cfm, less than the engine's 100% VE needs (528 cfm). The worst aftermarket plenum (the C&L which was at the tail end of the list) flows 569 cfm under the same conditions. The others all move 600+ cfm.

If you do choose to P&P the stock plenum then get an under plenum spacer (never thought I be recommending that), you can get them on eBay for $20 to $25 and it will to some extent fix the biggest shortcoming of the stock plenum by vertically extending the outlet end of the elbow.

All aftermarket plenums are taller than the stock unit, which allows a larger passage way through the bend. No amount of P&P can accomplish this as the stock unit doesn't have enough "meat" to support enlarging the bend...

Here is a photo (a crummy photo but the best I could fund) showing the height difference of a stock and typical aftermarket plenum:

The added height allows for a higher volume and less sharp 90° bend...
Thanks for all the great info cliffy!! Always great feedback, thanks. p&p prob isn't in my path due to I don't trust myself with that kinda cosmetic work... Lol
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Old 01-28-2013, 09:53 AM   #23
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Thanks for all the great info cliffy!! Always great feedback, thanks. p&p prob isn't in my path due to I don't trust myself with that kinda cosmetic work... Lol
As bottleFed04 stated it is much easier than the "wizards" make it out to be--buying the needed abrasives and tools is more difficult than actually doing the job. It is time-consuming, with frankly not a whole lot of "bang-for-the-elbow grease" unless your are a pro looking for that last 100th of a second.

Polishing is also a bit "old hat" as when fluid dynamics engineers entered the fray, when mandated fuel economy standards came along, they pointed out to the automotive engineers that a polished surface finish produces more drag than a stippled or dimpled finish.

A dimpled finish creates a turbulent boundary layer which separates the main flow from the surface both sooner and better, and behaves as a anti-friction bearing for the main flow. With a smooth finish OTH the main flow drags along the surface expending energy and slowing.

This is why golf balls are dimpled, and why ping pong balls seem to slow down faster then they should. And why stealth fighters have a matte finish...
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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq
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Old 01-28-2013, 10:12 AM   #24
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Straight genius didn't even cross my mind as such to a golf ball and ping pong ball for air flow I understand how it works just never took a second to think about it lol makes total sense! Thanks alot
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