Hey guys, i've got a spare plenum chamber sitting here and am looking at the throttle bodies in particular. I was wondering if there is anyway you can modify the throttles by increasing the size of the butterfly thus so they can flow more air. Can it be done? Would it make much of a difference in power output? Are there such things as largers throttle bodies you can buy that will bolt on to the existing ones?? This is in relation to a NA VG30DE Any help or ideas would be appreciated! Cheers Nathan
It wont do anything, especially on an NA. Until you're talking about big Q45 90mm throttle bodies a few mm isn't going to have any significant benefit at all. Some people might disagree, those people would be wrong though. Spend your money and time elsewhere mate.
I have a Q45 throttle in my shed at the moment, attached to my Q45 engine It is HUGE! 90mm To be honest the standard ones are big enough for a NA. Go and look at the great 4 banger NA's and have a look at the size of their throttles, they are normally a tad smaller than the Z32 ones. I wouldn't bother... Z1 make 55mm throttles, definatley not worth the money without a bucketload of money being thrown at the NA, and it you've thrown that much, you should throw some more and get some ITB's like I had planned for my monster NA VG that I never finished...
would the Q45 90mm throttle bodys bolt onto a vg30 plenum ? What mods would have to be done apart from opening up the holes behind the throttle bodys in the plenum ?
Yeah, thats what I was wondering. I was thinking though if it would be possible to enlarge the size of them myself I'd save money just mucking around. I wasn't expecting huge increases in power but if I could do it myself to get one or two cheap horsepower then why not.
A completely custom intake plenum would be a good start! Having big mofo throttle bodies mated to a small stock intake will just be a huge bottleneck rather than an upgrade and wont do anything either. There's no point having a huge buttlerfly valve flowing into the same restrictive intake path. The tapered log style plenum is a popular choice, like this. It will be slightly more difficult cramming two of them in there though but I'm sure you could with some clever fabrication!
Actually, I was wondering about this also, because z1 in the states sell massive throttle bodies as an upgrade (around 30% larger than stock), but wouldn't the stock plenum still be a restriction, as you said? I ask because I was wondering if this would be a good way to increase throttle response / pickup. Cheers, -Kirill
I know it's pointless having a bigger throttle size if the plenum is at its maximum flow capabilities. But is the vg30 plenum at its maximum flow in its standard form or would the increase in size of the throttles make a difference. Is there any way of working that out??
Going larger throttle bodies will not increase throttle response at all, it does the opposite Regards Trev
Yep, intake manifold flow test. Take stock intake, test. Take custom intake, test. Give the winner a gold star. It's a safe bet that a tapered log plenum with a big 90mm throttle body will flow better overall than two smaller throttle bodies. That's just speculation though until it's proven, but the majority of high powered drag cars go with a tapered log plenum so there is definately some truth to it. We're moving away from the subject at hand though and getting into some sticky business now, i.e single turbo vs twin turbo etc. You do realize "30%" is just a few mm? You would definately have to port match the neck of the intake itself to fit the larger bore of the TB otherwise it really would be a complete waste of time. If they dont recommend that is done when installing larger throttle bodies then they're just taking your money. Having the intake diameter SMALLER than the throttle body itself could infact hurt performance because the air flow path is interupted by the protruding edge of the intake. You wont "feel" anything anyway, on the dyno I'll eat my hat if you see more than 1-2hp difference after installing throttle bodies just a few mm larger. And on an NA? Probably none at all...
Yeah i realise 30% is a very small increase, but an increase none the less, a few mm is still tangible when the whole opening is only 35mm. I don't care about what it does on an NA because I don't drive an NA. It does say that you'll have to modify the plenum for it to fit. Maybe you're not sure about my question, what I meant is that even though the throttle body is bigger, the plenum itself isn't, so will it be effective to get the throttle body or not? As you say, I'm not expecting anything great on dyno, just wanted to see if I could improve throttle response. Cheers, -Kirill
It won't , it will move the power band up a couple hundred rpm. Thats the last thing u want, a street car needs all the low down torque it can get, these larger throttle boddies are a wank, but if ur running giant turbo's high lift cams, ported mani's hed work , shure go ahead fit them and u "might "get a few more top end ponies, but thats after uve spent 10-15g to get there. Nissan engineers would of spent countless hours matching the throttle body size to work with the plenum design. my 2 cents, Trev
It doesn't "move" your powerband as such. That's not really the right way to describe it. A larger throttle body will lower air velocity therefore slightly decreasing throttle response but providing more flow up top. But a few mm wont do dick either way...
On other cars it is a cost effective and worthwhile mod. Ive seen a few cars benefit from a bored throttle body, a Mx5, v12 jad and a v8 commodore. No point on a VG30de.
30% is 15mm, seems significant to me, remember that it's the cross sectional area that is important, not the diameter. In area it's a increase of Stock throttle: 7,854mm^2 2 of = 15,708mm^2 65mm throttle: 13,273mm^2 2 of 26,546mm^2 My Q45 throttle: 25,446mm^2 So a 15% increase in diameter will give nearly double the flow. As for the velocities, not sure it will have that much of an impact, once the air is past the throttle it's into the plennum which is practically a 'volume' of air for the engine to draw on, the length, diameter and shape of the intake ports would have a much larger effect. Only real positive I can see from the larger throttles is the reduction in losses past it, slightly slower velocity may reduce the chance of turbulance and create a more laminar flow, but I doubt that the flow would be fast enough in the first place. Larger throttles are also harder to modulate as a small change in throttle angle can allow a large amount of air to pass through, doesn't do your tune anygood since the maps are directly related to rpm, airflow and throttle position In my humble opinon, not worth the trouble on a relatively stock car. Rob's car, yes, Pete's car, yes, your NA, no.
Nathan, You could give this a go: http://s95014253.onlinehome.us/63104/182732.html I don't think it will do that much for you but. Next things on your upgrade path are: but nothings free i'm afraid
test the air pressure along different places in your intake then you can work out where the greatest restriction is , if there is none over the trottle bodies it wont be worth it if there is alot you will probably get a decent gain
that's a good comment, of course only valid at WOT, because when you're not WOT then you want the TB to be a restriction, as that is it's function!
