Outer Limits 4x4 Board

Hi all,

I have been reading with interest in the Nissan X-Trail Forums about a throttle body spacer going between the throttle body and the inlet manifold.

This has the effect of seemingly giving more power and better response due to the alteration of the length of the throttle body assembly. In reality, its suggested that the increase in power is because the effect of the part is that it moves the "power band" of the engine to the more useable rev ranges, much like tuned extractors (4-2-1) being for more torque at lower revs, and (4-1) being for more power at higher revs.

The X-Trail guys seem to think there is quite a noticeable difference and their part costs US$90 shipped.

This got me thinking, seeing as I'm an EFI Vitara (J20A presently, but most likely V6 in the not so distant future) driver, as to whether anyone has mucked around with these on Vitara EFI motors, and if so, has there been any success?

I look forward to anyone's input on this issue.

Having done a search, I found that there has been brief mentions of TBS's in previous posts on other issues, but it was usually only a mention, and then it seems to have not been persued as a dedicated post in any way.

Rocky Road have this one for EFI Sierras (Samurai's), but nothing for Vitara: http://www.rocky-road.com/zukpoweraid.html

FYI, the thread I refer to (unfortunately quite a long one, but interesting and logical nonetheless) is here:
http://www.runboard.com/baustralianxtrail.f17.t124959

I've heard of the apparent power gains on throttle body spacers but have always wondered if it'd work on a carby aswell? I had a spacer mounted under my 3k carby but never really noticed any difference. That spacer from rocky road has a Hiclone twist affect on the air aswell it'd definatley work then in getting more power

I ported and polished my ashtray, and now I can fit more coins...

I think this is a very hit and miss way of tuning the car. Effectively, as far as I can see, the biggest effect is a small increase in plenum chamber volume, which may or may not have an effect on performance (either way) but I can tell you, if adding 20mm to the length of the plenum was going to achieve "noticeable" (meaning >10% at the wheels) gains, the factory would have been all over it.

I'd be wanting to see some dyno numbers.

Steve.

Some vehicles respond to this and some don't and as Steve said, it is a very hit and miss affair. People have played around with phenolic resin spacers to insulate the manifold from the heat of the engine which also slightly space it but personally I think there are better ways to spend your money. Have a look at fitting an adjustable cam gear for instance from occracing.com

i believe that the spacers allow better atomisation of the fuel and air molecules before combustion allowing the fuel to burn easier.
I have seen drag cars with carbys pick up 1-2 tenths down the quarter mile with large carby spacers, this is the theory behind longer runners on the manifolds ect...
however this is on highly tuned dragcars the results on a 4x4 with a small capacity may be nil

MrRocky - for carby motors they may be something in that, but for RFI to achieve the same effect the spacer would have to be between the manifold and the head because the injectors are in the runners.

There is something in that though - race EFI tends to put the injector a long way from the port.

Steve.

Maybe so the fuel has enough time to fully atomise and fill the air with fuel...

lump_a_charcoal wrote:Maybe so the fuel has enough time to fully atomise and fill the air with fuel...

Injectors are at the port - spacer is way before so makes no difference to atomization - its simply a plenum volume/resonance tuning mod.

The plenums on many vehicles can be re-tuned for what we perceive as "better" performance. The manufacturers design meets their needs and goals which may not be the same as ours - so gains are "possible"

However doing this professionally is a very large task and requires equipment and expertise very few people posses. Even a flow bench isn't going to help as this is a resonance phenomena - very difficult to guess and get right. Computer modeling is the most common tool and thats a big buck exercise

You do see applications where this has been used - a single engine used in both a passenger car and 4WD for example... the 4WD might have a large plenum before the throttlebody - which can make a worthwhile addition to low/mid range torque.

However this is hard to determine with the "seat of the pants dyno", its so easy to be fooled by changes in induction noise or wishfull thinking. Unless you have made more than 10% power difference you just wont detect it without a dyno.

And whilst on intakes don't be confused by Helmholtz resonators on intake tracts - there are there to suppress undesired intake system resonances for noise reduction purposes - not power gains

Gwagensteve wrote:MrRocky - for carby motors they may be something in that, but for RFI to achieve the same effect the spacer would have to be between the manifold and the head because the injectors are in the runners.

There is something in that though - race EFI tends to put the injector a long way from the port.

Steve.

I wonder if it is worth playing round with spacers on a TBI serup. The jeep 6cyl guys love the throttle body spacers.

Layto....

i put one on my new ba 5.4 pursuit ute, just seemed like the in thing to do, didnt notice the 5-10 rwkw as claimed by herrod motorsport $249 well spent NOT

mrRocky wrote:i put one on my new ba 5.4 pursuit ute, just seemed like the in thing to do, didnt notice the 5-10 rwkw as claimed by herrod motorsport $249 well spent NOT

BUT...if its anything like my mates Helix Spacer on his XR8 ute, they do sound kool!

It can have alot to do with velocity and holding that velocity like in custom headers etc. Carbied drag cars gain because of a combo of the single plane manifold design and spacer causing an increase of air speed velocity by somewhat extending the runners. Cars with full trumpet manifolds are a good example of using long runners for more top end power. My group A VN intake manifold incorporates very long cross ram intake trumpets in a large plenum and is primarly designed for high rev power, as are single plane carby manifolds. Smaller duel planes have smaller runners and are suited to lower revs.

Therefore I don't see an efi spacer that increases plenum volume helping bugger all unless it somehow allows for longer intake runners, and even then without any other mods the gains would be insignificant.

Thanks for your opinions and input, guys.

As was said, possibly some vehicles respond to it, whilst others don't. I'm interested because it seems a fairly cheap & easy mod, and we're all DIY'ers to some extent or another on this forum.

Steve, the point you raise about the spacer being between the inlet manifold and head is a good one. This is evident in the difference between the 86kW and 103kW versions of Toyota's 4A-GE engine in the 1990's Corollas.

The X-Trail (as mentioned in the thread I quoted) is this set-up too, but despite that, the guys are pretty much all reporting increases in performance from spacing the plenum from the manifold.

It seems contradictory, as the spacing the manifold from the head is proven (by Toyota, and I'm sure many more), but maybe someone who has done such a mod to their Zook will see this thread in time and throw their findings our way.

So if I spaced out the intake manifold from the head by about 2inchs I could possibly get more HP out of my carbied 1.3? Or would it be so minor it wouldn't make any difference?

The spacing of the manifold from the head with plastic spacers is more of a heat soak preventative, alot of cars come out whole intake manifolds made of plastic for this reason.

i surface ground my wheel nuts for better aerodynamics...but these work better.

Kitika wrote:So if I spaced out the intake manifold from the head by about 2inchs I could possibly get more HP out of my carbied 1.3? Or would it be so minor it wouldn't make any difference?

I'm so going to do that, run the air filter through the bonnet.By making a bigger spacer for the Weber.

Kitika wrote:So if I spaced out the intake manifold from the head by about 2inchs I could possibly get more HP out of my carbied 1.3? Or would it be so minor it wouldn't make any difference?

I'd be amazed if it was detectable by dyno or "seat of the pants."

Steve.

boner59 wrote:

Kitika wrote:So if I spaced out the intake manifold from the head by about 2inchs I could possibly get more HP out of my carbied 1.3? Or would it be so minor it wouldn't make any difference?

I'm so going to do that, run the air filter through the bonnet.By making a bigger spacer for the Weber.

if you mean like this don't bother its a crappy idea.

That pic brings the funnae