interchangable throttle body?

[needaride]

hinew to this forum and wondering what the vh45de throttle body maybe interchangable with more particularly if it is with an r34 rb26 looking for minimum modifications if i grab a throttle body off another car so suggestions will help thnx

[mtcookson]

I think those RB's have ITB's stock. I'm not much of a RB fan so I'm not positive. I do know that there aren't many other stock engines out there with throttle body the size of the Q's. Its a common "upgrade" on many cars these days.

[gs14racer]

You are correct the rb26dett has individual throttle bodies stock.

[needaride]

kool thanks for your replies, so fitting a skyline throttle body shouldnt be a problem? correct me if i misunderstood :Sthanks

[gs14racer]

The skyline gtr has 6 throttle bodies. The code for that motor is rb26dett.

The regular skylines have 1 throttle body. Engine codes rb20det and rb25det.

They are all much smaller than the q45 throttle bodie.

Pretty much anything you put on the q45 would be a down grade from what it comes with stock.

[SSDwellah]

Here's some info for you:

KA24DE 60mm TBVG30DE 51mm x 2 TBVH45DE 90mm TB

Guess which one flows the most? The Q45 90mm TB. It flows even more than two of the KA24DE TBs. Remember area is proportional to radius^2. Now that being said, if you made a dual plenum IM for a naturally aspirated VH I would say that two TBs sized 65mm-70mm are a good setup (I don't know what car you can get these from though). This should allow more flow due to the larger cross-section, but have a higher air velocity due to the smaller diameters. Think if it as one step closer to ITBs. Plus the separate plenums would result in less contention for air among the cylinders.

I apologize because I know this is slightly off topic, but its related and good information none the less.

[ch187]

i had planned on fabricating two aluminum plenums with two 90mm q45 tb's. think that would flow any better...? haha

[mtcookson]

One thing you want to be careful of when going with a large throttle body is if you do something like that, your throttle positioning will be way off. Basically, at low throttle it'll flow enough air for the engine to have max acceleration so opening the throttle any more than that will yield no changes. It'll basically make throttle modulation non-existent unless you make a very odd throttle cam to try and correct it.

[SSDwellah]

Right, I think that the idea here is that many other substantial substantial power-increasing mods should be done long before you worry about throttle upgrades. In a nutshell, on most cars the throttle should be upgraded only when it becomes a significant bottleneck. Particularly in an NA car where throttle sizing, runner sizing, and plumbing sizing in general is more important since the air is being pulled in by vacuum rather than forced in by a compressor (turbo or SC).

What I suggested was to use two smaller throttle bodies and do a dual plenum setup on V-engines like ours. That way you can size the two TBs so that their cross-sectional area is the same (or slightly larger for an upgrade), but the bores are smaller, allowing faster air velocity -- rushing air goes faster in a smaller tube, I know this is a simplification please don't flame me

but I think mtcookson was right in that throttle modulation will be harder with a big honkin' throttle and the car may become even less drivable -- bogging down at first and then a sudden surge of power, albeit not nearly as drastic as having a late spooling turbo

[mtcookson]

It shouldn't really cause any bogging or power issues that I know of. The major issue is it'd basically be like turning your throttle pedal into an on/off switch with an over sized throttle body. You barely move the pedal and it'd be like going full throttle with a smaller tb.

For drag racing that probably wouldn't be all that bad but for anything else it would be a bit of a pain, especially any street driving.

[ch187]

can you explain that in more detail man? i think i see what your saying though. my second plan was to take a single 5 inch aluminum pipe and lead all 8 runners into that and use one tb. but with that, all the runners wouldnt be the same length. with the dual throttle setup i was going to do what i saw on a twin turbo vk45 where he had the cable on one pulley in the center connected to 2 solid linkages connected to the 2 throttle bodies. i dont know my goal is to get rid of the spider all together.

[mtcookson]

Not a problem.

Say you have a 2 inch throttle body and a 3 inch throttle body. Lets just say hypothetically that the 3 inch flows as much air at 50% open as the 2 inch at 100% open.

So, say the 2 inch isn't a restriction but you put the 3 inch on. Pushing the gas pedal only 1/2 way down would basically give you 100% flow going by our ratio. So, if you were to push the throttle anywhere from 51% to 100% open, there would be little to no difference in power and acceleration.

Say your pedal has 3 inches of movement from idle to WOT, now that you have the larger throttle body on and it only needs to be opened 50% for the same flow you now only have 1.5 inches of pedal movement from idle to "full throttle".

Now, driving on the street it doesn't take much throttle to keep a steady speed. With the larger throttle body it would take even less throttle to keep a steady speed. So, you'd pretty much have to breath on the throttle to keep a steady speed.

My whole explanation is basing everything on the extreme side (and of course with incorrect numbers) just to explain it clearly but hopefully it'll help with the idea.

[SSDwellah]

My point was with a very oversized throttle, the pumping losses would be greater, think about an exhaust which is too big for the application. It's the same concept: even though a larger pipe diameter allows more air to flow when forced, the fact that there is more air in the pipe which must be forced out of the way in order to cause a flow -- either by the pumping of a vacuum or the expansion of hot gasses in the intake and exhaust cases respectively.

[ch187]

you both have made your point. and its true. so i think im leaning towards itbs.