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Old 8th August 2004, 08:31 PM   #1 (permalink)
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single throttle body and plenum

anyone on here removed the 6 throttle bodies and replaced them with a plenum and a single throttle body.

it has advantages - when remapping the car with an aftermarket ecu and using a map sensor instead of mass airflow meters
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Old 8th August 2004, 11:21 PM   #2 (permalink)
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Hi Gadget

Nice to see that you are on a more technical forum (The dark side, is the best side)
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Old 9th August 2004, 12:03 AM   #3 (permalink)
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You can still use a MAP sensor on throttle bodies, so the need to change to a big single is at quite high power outputs, like 800+.
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Old 9th August 2004, 08:37 AM   #4 (permalink)
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I thought the whole reason for having the throttle bodies was to control more evenly the air / fuel mixture to each cylinder
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Old 9th August 2004, 09:01 AM   #5 (permalink)
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Single throttle body is good for all out power, at the exspense of driveability. It is also possible to replace the 6 45mm bodies with 6 50mmm bodies if you are chasing big power and would like to retain driveability.

As to remapping with, or without AFM's it makes absolutley no difference.
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Old 9th August 2004, 09:49 AM   #6 (permalink)
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I would go with individual throttle bodies for anything but a pure drag car. I believe there is a solution for MAP based ECUs using a mini-plenum that links all the cylinders and provides a pulse free MAP signal.

Paul
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Old 9th August 2004, 09:59 AM   #7 (permalink)
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All the parts needed for going MAP based are present on a standard engine.
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Old 9th August 2004, 12:39 PM   #8 (permalink)
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Hi Guys - throttle bodies are great for throttle response, but can cause problems when using a map sensor for air/fuel metering

The throttle bodies do not have a plenum as such - so there is not one place to read the manifold pressure -( a problem off boost ) Pavlo mentioed a mini plenum - this works by balancing out the 6 single throttle bodies into one reading

an other solution would be to use the maf sensors or the tps to drive the car off boost and then use the map sensor once it comes on boost

as Pavlo mentioned its probably not worth the effort unless its for a big bhp car.
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Old 9th August 2004, 12:47 PM   #9 (permalink)
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Hi Guys - throttle bodies are great for throttle response, but can cause problems when using a map sensor for air/fuel metering

The throttle bodies do not have a plenum as such - so there is not one place to read the manifold pressure -( a problem off boost ) Pavlo mentioed a mini plenum - this works by balancing out the 6 single throttle bodies into one reading

an other solution would be to use the maf sensors or the tps to drive the car off boost and then use the map sensor once it comes on boost

as Pavlo mentioned its probably not worth the effort unless its for a big bhp car.
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Old 9th August 2004, 01:03 PM   #10 (permalink)
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on the standard engine there is a "collector" (can't think of it's proper name) that is fed from after the butterfly valve on all 6 throttle bodies. This sees full vacuum and is pulse free.

Cord
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Old 9th August 2004, 01:10 PM   #11 (permalink)
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cord - that sounds ideal

have you got any pics of it ?
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Old 9th August 2004, 01:30 PM   #12 (permalink)
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Gadget,

What cord is talking about is standard on the throttle bodies.
The system uses this 'mini-plenum' to distribute the air from the idle valve, and also for supplying throttle closed vacuum to the brake and clutch boosters. Every GTR engine has them.
So to fit a MAP sensor, you only need to tap into this 'mini plenum'. Job done.
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Old 9th August 2004, 01:57 PM   #13 (permalink)
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Under the plenum, above the oil filter and heat exchanger. Basically follow the pipe from your brake servo back inot the engine.
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Old 10th August 2004, 03:53 AM   #14 (permalink)
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Quote:
Originally Posted by Cord
Single throttle body is good for all out power, at the exspense of driveability.
Since I have a single throttle conversion I can tell you first hand that the driveability is not affected in the least. The single throttle allows less obstruction in the air flow which in turn increases the potential for top end power, and coupled with a better aftermarket plenum (we all know about the "less than ideal" charge distribution provided by the factory GT-R plenum), you can realize better mid range torque also. Having said all that, I would agree that you won't get significant return on going single unless you are making some big hp numbers (read above 700hp).

The only thing that I can "complain" about is that when I have the aircon blaring, the idle is weaker and can stall the car after coming off the accelerator and letting the revs drop fast out of gear (unless you catch it early by blipping the throttle). This is also influenced by having large cams. When I don't have the air con on (ie. loading the engine under idle/vaccum conditions), there is no issue with the idle at all.

Hope this helps.

Cya O!
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Old 10th August 2004, 07:41 AM   #15 (permalink)
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I've made/driven a few with single throttle bodies, and I don't mean there is a major bug with having the single body, just slightly less smooth on a very very light throttle, i.e. when cruising. And also just a drop in throttle response. It may be hard to spot this very slight differences as your engine is a good chunk far away from standard but I've driven similar spec engines on 6x50mm and single throttle bodies, and there is a difference (however it is small and I'm a fussy git!!!!)

At risk of going off topic,
What cams are you running?
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Old 10th August 2004, 08:20 AM   #16 (permalink)
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MILDLY off topic, is there a different plenumn available that gives equal amounts of airflow under boost to all 6 cyls, as the std one does a **** poor job at that...

And is it worth it?
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Old 10th August 2004, 09:18 AM   #17 (permalink)
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Yep - the Nismo one is supposed to correct the air flow mismatch - esp. on No. 6.

Other choice is the Greddy plenum but not sure how well it evens out the flows.

Good discussion here

http://www.skylinesaustralia.com/for...ad.php?t=25803
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Old 10th August 2004, 09:45 AM   #18 (permalink)
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There's a few of them,
Jun
Greddy
Veilside
Nismo
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Old 10th August 2004, 05:22 PM   #19 (permalink)
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Has anyone created a plenum that has trumpets inside it ?

trumpets are used on n/a cars to increase the mass of air using a venturi effect

they can be used on turbocharged cars too - with some very impressive results
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Old 10th August 2004, 06:19 PM   #20 (permalink)
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The one I fitted to Keiths has bell mouth trumpets inside it.
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