Q45 Throttle Body Help

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MardiGrasMax
Posts: 2
Joined: Wed Jul 24, 2002 2:19 pm
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Q45tech,

I have a 98 Maxima and would like to know if the Q45 throttle body is similar so I can upgrade. It is my understanding that the 96' year generation Q's TB is ~70mm, is this so? Here is a link to my web page that has some pictures of the Maxima TB and intake manifold, can you please take a look and let me know what you think? I am concerned with the two TPS connectors and throttle and cruise linkage mounts, do they look similar on a Q?

http://members.cox.net/matchou/TBProject.htm

Thanks for any help!

Matt


Q45tech
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Posts: 14365
Joined: Tue Apr 30, 2002 3:19 am
Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl

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The 90-96 Q throttle body is ~ 3" [77mm], from the pictures of the Maxima unit it appears significantly different [not in function ] but lay out. 3" [7 sq. "] is suffucient to flow 350Hp of air.

Commetary:Nissan always uses a larger than normal TB vs air flow requirements [unlike domestic designers] which makes the programming of ecu kind of critical..the closed vs WOT MAF voltage and how this relates to engine demand [load]. Notice that even at 60 mph the throttle is barely opened.

The point is: even 5% more area will upset drivablity [ability to make fine linear increments with the accelerator pedal].Generally the whole intake tract is a balanced system of components and each component is allowed only so much restriction [the Nissan limit for air horn through filter, MAF, connecting hose and throttle body is around 21" WC in total] with the TB flowing around 7" of the total restriction at the rev limit [roughly the same as the MAF] and the air box, filter, and input as a system [7,7,7].

On NA engines [like Q, G20, J30] changing the TB has resulted in some power increase [usually only 1-1.5% ......because the runners and plenum are also a tuned system [volume, diameter, and length to match the cylinder] at the expensive of drivability!

Measuring the plenum vacuum at WOT tells you the restriction. Unfortunately the typical vacuum gauge is designed for idle [18-22" HG = 9.8 negative PSI] and 28" WC. is only 1 psi] so you need to measure [with accuracy] the range between 0 and 1" HG which requires the Dwyer Manometer or taking the TB to a flow bench [which Nissan spent time on to pick the one you have].

Before you go changing, measure your differential vacuum [of the existing TB].A cheap trick is to smooth the throttle plate center support and the screws which hold the plate on. This curve bump in the middle causes 20% of the restriction. Careful as you don't want to remove too much of the mechanical strength.

Doing any mods to the TB forward is an exercise in minute improvements, much like working on the cylinder heads [port matching] as hundreds of engineering hours have been spent already to squeeze as much as they can out.

Stillen use to sell a massaged TB for the Q it yielded 3-4 HP at best and had funky linearity except at WOT.

I really don't think dropping the [TB] restriction by 10% or 0.7-1.0" WC is worth the effort unless you are supercharging or running NOX

If a mod doesn't create 10 HP [5%] it is probably unnoticeable especially if it only occurs at the peak of the rev band.

Q45tech
Moderator
Posts: 14365
Joined: Tue Apr 30, 2002 3:19 am
Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl

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Much like the injectors, range is the problem: in that from idle to WOT peak flow is a ratio of 12 to 15. Create 12-15 HP to idle [overcome frictional losses and auxillaries] and then progressively make 200-300 HP.On a Q the air flow mass varies from 15 grams per second to 230 grams per second.The air speed [in the runners and into the cylinders] varies from almost zero at idle to 250 feet per second.The trick is to keep the air flow speed as high [within the ideal range 200-250 feet/sec] as possible [the function of the restriction of the throttle body.Transient acceleration demands a small TB and WOT peak power wants a larger one.

It appears that a 3 liter engine would be optimized with a 4.65 sq" thtrottle body area or 2.4-2.5" diameter~~62 mm not 76 mm.

reggiegsd
Posts: 419
Joined: Tue Jul 23, 2002 9:51 am
Car: '94 Q, '73 240Z

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I wonder if anyone has tried a dual progressive TB arrangement? You would probably have to own a dyno to pull it off.

Q45tech
Moderator
Posts: 14365
Joined: Tue Apr 30, 2002 3:19 am
Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl

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The best situation is no throttle body at all, using variable cam timing and variable valve lift to act like a throttle body.BMW has this currently in Europe on one engine [maybe more] they are able to improve HP by 4% or 7 HP .......about twice what you can get by enlarging a throttle body.

The important thing is better cruise mileage 0.06%, hey every hundreth counts!

reggiegsd
Posts: 419
Joined: Tue Jul 23, 2002 9:51 am
Car: '94 Q, '73 240Z

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If you are talking about the new 7 Series, it looks like it also has a variable intake runner length. When you hire good engineers and then give them a blank check to work with, you get some interesting stuff.

I'm thinking of a small TB in parallel with a large TB and run them in a progressive arrangement. It could give the light throttle control that one big TB just can't do. Well, maybe.

Some early Bosch TBs used an adjustable bypass air passage for engine idle control. Same idea, only throttle controlled.

Q45tech
Moderator
Posts: 14365
Joined: Tue Apr 30, 2002 3:19 am
Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl

Post

But why go to the trouble if the vacuum created by the factory TB is only 7" WC or so at WOT. That's about 1/4 psi surely less than 1.7% or 5 HP at 6900 rpm. And no matter what you do you can't cut that in half

Now if you supercharge a stock engine obviously the TB will be more restrictive but you can always spin the charger faster by 3% much less expensively than playing with the TB.

If all you have is a hammer everything looks like a nail!

Interesting to note that after 12 years of work by all the companies a 4.4-4.5-4.6 liter engine still creates the same peak torque [330-333- [337 lb/ft 90 Q with ecu]-340 at best by any one.

Physics gets in the way of bragging rights and advertising.

MardiGrasMax
Posts: 2
Joined: Wed Jul 24, 2002 2:19 pm
Contact:

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Thanks for the help guys!!!

The Q TB is way to big and wont work. However the 01'+ Pathfinder TB looks to be a good candidate. Its 70mm and the linkage closely matches as do the TPS plugs. I found one in a junk yard for $150 shipped.

As to why I want to do this, BOOST! I am running 13psi now on a stock VQ30DE. I am spinning the V1 charger at its max rpm (actually a bit more) So I am running out of things to do :) The 60mm TB on the Maxima is a bit small, I am also changing to 3" intake tubing. I will have to do some major grinding and hoaning to get the 70mm to fit the Maxima intake.

Realistically I dont expect more than 10hp at best, but every little bit helps!

Matt


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