independant throttle bodies

[barneybrendan]

would they work?

 

i dont know

[Rob_Mitchell]

i dont know

 

[Kirk]

Not at all, just a wait of money just for 'noise'. I could understand if it was for performance build. Comeon dude think about it, you are willing to pay 2k+, having to have alot of custom work and wiring done then a standalone 1k on its own new plus mapping just for some noise?

 

They would probly work but it will take alot of work to do it properly.

[-Welsh-Stealth-]

ITB's mixed with a supercharger!? thats like xxx illegal car porn! ha ha!

hmmm?still phoning and looking into it just might have to sack the re-spray and do a bodge-spray myself

and the whole uprating the internals sounds like a good idea

and by the way just curious...but do we have a fastest NA in the UK? or are us lesser beings not weighed up?

[Kirk]

The only NA on record which was built by a individual rather than a company was a guy in the states with a fully built engine, cams higher CR pistons etc and netted about 270 rwhp max. From a performance stand point the GE isnt easy to work with as it was never designed with NA performance in mind.

[-Welsh-Stealth-]

cool cheers was just wondering

[-Welsh-Stealth-]

if i can remember correctly from what i was reading earlier paul_mac used the m3 tb's.check out the link further back that martin posted

[Swampy442]

That does sound superb. Ive linked this before but this guy used AT Power for his custom ITBs. Its also a cracking build thread so have a look as well

 

http://www.driftworks.com/forum/drift-car-projects-builds/108245-team-driftmoto-ae86-1uz-fe-itbd-nosd-nissan-killer-3.html

[paul mac]

it is a hell of a lot of work and if your paying someone else probably not worth the gains, mine are on hold at the moment as i'm busy divorcing my wife

[Neil-NA]

it is a hell of a lot of work and if your paying someone else probably not worth the gains, mine are on hold at the moment as i'm busy divorcing my wife

 

If and when you finish your conversion do you fancy sharing a bit of knowledge.

 

I will be building an NA motor next year and really want to run with throttle bodies but will need a wee bit of help

[Nodalmighty]

it is a hell of a lot of work and if your paying someone else probably not worth the gains, mine are on hold at the moment as i'm busy divorcing my wife

 

It will be interesting to see what effect this has on a turbo motor. It is a generally held belief the GTR's ITB's are what give it such good throttle response.

[Kirk]

FFS paul

 

You would be right to say that about skylines plus tuned properly you can still have great response even running something like 272 or 280 cams, well from my understanding anyway. I have a set off an R34 at home although it may take a little more work to make then fit.

[Digsy]

As ITB's have come up a few times recently I thought I'd just put down a few lines about what they actually do (and don't do).

 

 

 

Consider a standard intake system with a single throttle between the plenum and the intake ducting / intercooler / air box or whatever. At wide open throttle the whole system should be designed so that no single point is a restriction. Its perhaps easier to think in terms of an NA engine at this point. The air outside the engine bay and everything on the "dirty" side of the air filter element is at atmospheric pressure. However, as soon as this air passes the air filter the pressure will start to drop because of losses in the system. The air filter is probably the biggest contributor, but every bend and twist and shape change in the air intake ducting will drop the pressure further. Even a straight pipe has some pressure loss. Therefore by the time you get to the intake manifold, the air is slightly below atmospheric pressure.

 

 

 

This has two effects. Firstly, the air will be slightly less dense, so you have slightly less air to mix with fuel to combust, and correspondingly slightly less power. Secondly, the engine will have to work harder to suck the air in on each induction stroke (think of how your eyeballs bulge out when you try to drink a McDonald's shake really fast through a straw). This increases what are called "pumping losses", and the net effect is again a loss of power.

 

 

 

Continuing with our NA engine, the way to reduce the WOT intake depression as much as possible is to make your entire intake system as non-restrictive as you can. Let's go straight to the extreme and chuck it away all together and just have some intake trumpets and a massive F1 style air box on top (or maybe even nothing if you are feeling chavvy and don't care about filtration at all). Now, you obviously have to have ITBs otherwise there would be no way to control the airflow at all. The trade off is that because you no longer link the runners in any way you have no way to take advantage of pulse tuning, variable geometry intakes and the like. In fact it also becomes a but silly having long intake runners to improve low down torque because they now have to stick straight out from the engine rather than curling around a plenum. IMHO this is why people associate ITBs with power increases - purely because cars engineered mainly for maximum power tend to use them.

 

 

 

Open trumpets also have no place in a road car in stock form because of drivability, noise, emissions, and packaging issues. Bringing the turbos back onboard you also need to run some kind of plenum if you want to pressure charge. So what kind of plenum to have? All the powwwweeerrrrrrr junkies will cry "let's have a big one!" and that's absolutely correct if all you are interested in is peak power. However, ask someone who has to calibrate (that's the OEM-world term for mapping) an engine so its drivable and they will say "as small as possible please". So why is this?

 

 

 

Let's bin the ITBs and put a plenum and single throttle back on our imaginary NA engine again, but this time think about what happens at part throttle. If you measure the depression in the plenum you will find it to be large because the engine is having to suck all the air past the partly closed throttle valve. You may think "ah, but the engine will be spinning much more slowly" but this is actually irrelevant. What we are talking about here is engine load. If you are cruising down the motorway at 70 doing maybe 3000RPM with your foot resting very lightly on the throttle you are sitting at a "low speed / low load" point in the map. Now mash your right foot into the floor and what happens? Your throttle opens to 100% but at that instant your engine revs have not risen at all, so it is possible to have the same engine speed for almost any engine load. You are now asking the engine to move to a "high speed / full load" point in the map. This cannot happen instantly because the engine has to develop sufficient torque to increase the engine revs from 3000 to whatever you want against the resistance of the car. How quickly this change happens is affected by many things like engine inertia and gear ratio but the size of the plenum also plays a part.

 

 

 

As mentioned earlier, when you are at part throttle, the plenum will be running a heavy negative pressure. This means it is not actually full of air at all. When you crack open the throttle, you expect an instant surge of torque but in fact what happens is the first gulp of air the engine takes at WOT is still weak because the plenum acts like a reservoir of rarefied air. You may think that an engine spinning at 3000RPM would empty the plenum pretty quickly so the effect would be hardly noticeable, but think of a misfire. On the 2JZ that only lasts 1/3 of an engine revolution, but you sure as hell would feel it. By comparison emptying a nominal 3 litre plenum would take a minimum of two whole engine revolutions before the effect started to tail off, so it would take the edge off the crispness of your throttle response.

 

 

 

I mentioned a 3 litre plenum because that's the rule of thumb for plenum design: 1 x engine displacement. I would imagine the NA Supra is more than this when you include everything between the back of the valves and the throttle butterfly. So those massive high plenums that the max power boys want will increase the effect discussed in the previous paragraph. The bigger the plenum, the worse the effect.

 

 

 

Now imagine that the road car we are discussing is not the regular model but a rip-snorting M-sport GTi Type R version. The designers will want to have big lumpy cams running massive overlap to improve breathing and also they will have to have a regular intake manifold because they want to tune the runners and have some fancy variable gubbins to spread the torque curve out. They will also probably want a massive plenum. Now, those lumpy cams may work fine at the max power or max torque speed, but come back to cruising and that big overlap starts to hurt throttle response.

 

 

 

While both valves are open, if there is not enough inertia in the air column, or pressure difference between intake and exhaust, then instead of the intake air "blowing down" the cylinder to chase the exhaust residuals out, the opposite can happen. The exhaust residuals flow the other way and start to fill up that lovely big plenum. The situation thus created is now even worse that the engine breathing less then a full charge of air. Now, the gas mixture that the engine breathes when you suddenly go from part throttle to WOT is only partially combustible, as some of the air has been replaced by exhaust gas. This will truly mess up the throttle response of your sporty engine.

 

 

 

Now consider the same engine with ITBs. When running at part throttle it will only draw a vacuum in the part of the runner between the back of the valve and the throttle butterfly instead of the whole plenum. This is a huge difference in volume. Because the plenum remains at atmospheric pressure and the volume of rarefied air is tiny by comparison, the engine is much more "prepared" to jump from part throttle to WOT. Also, if you run your lumpy cams, you will only fill up the same small volume with exhaust residuals while the plenum remains uncontaminated.

 

 

 

So in summary, ITBs improve throttle response but they don't usually give you more performance on their own. An exception might be if the stock throttle body was very restrictive. In this case the extra area per degree opening afforded by ITBs might make the car feel more alive and may also improve performance a little. However, ITBs do allow you to do the other stuff that improves power and torque but would ordinarily make throttle response unacceptable in a road car. Hence why cars like the M3 have them.

 

 

 

Remember, a throttle's job by definition is to restrict airflow. You could improve part load throttle response by simply changing the gearing of the stock throttle valve linkage so it opened faster. At anything less than WOT this would be the same as increasing the total area of the throttle. I once drove my old 3 series BMW to a computer repair shop, amazed at how alive the car felt. When I got there I remembered the I had had to move my seat forwards about 2 inches to get my PC on the back seat behind me, and I was simply pressing the throttle harder than I realised...

 

 

 

On a turbo engine filling the plenum during a transition will be less of an issue as long as you are on boost. As long as the ECU closes the wastegate fast enough you should have all the air you need on demand. However, if you start running longer cam profiles and increasing overlap you may run into exhaust gas reversion issues at part load because the exhaust backpressure will possibly be higher than the inlet pressure during the overlap period, because of the turbine, which might mean ITBs would be an advantage.

[Gaz6002]

Good postings

[Robzki]

As ITB's have come up a few times recently I thought I'd just put down a few lines about what they actually do (and don't do).

 

 

 

Consider a standard intake system with a single throttle between the plenum and the intake ducting / intercooler / air box or whatever. At wide open throttle the whole system should be designed so that no single point is a restriction. Its perhaps easier to think in terms of an NA engine at this point. The air outside the engine bay and everything on the "dirty" side of the air filter element is at atmospheric pressure. However, as soon as this air passes the air filter the pressure will start to drop because of losses in the system. The air filter is probably the biggest contributor, but every bend and twist and shape change in the air intake ducting will drop the pressure further. Even a straight pipe has some pressure loss. Therefore by the time you get to the intake manifold, the air is slightly below atmospheric pressure.

 

 

 

This has two effects. Firstly, the air will be slightly less dense, so you have slightly less air to mix with fuel to combust, and correspondingly slightly less power. Secondly, the engine will have to work harder to suck the air in on each induction stroke (think of how your eyeballs bulge out when you try to drink a McDonald's shake really fast through a straw). This increases what are called "pumping losses", and the net effect is again a loss of power.

 

 

 

Continuing with our NA engine, the way to reduce the WOT intake depression as much as possible is to make your entire intake system as non-restrictive as you can. Let's go straight to the extreme and chuck it away all together and just have some intake trumpets and a massive F1 style air box on top (or maybe even nothing if you are feeling chavvy and don't care about filtration at all). Now, you obviously have to have ITBs otherwise there would be no way to control the airflow at all. The trade off is that because you no longer link the runners in any way you have no way to take advantage of pulse tuning, variable geometry intakes and the like. In fact it also becomes a but silly having long intake runners to improve low down torque because they now have to stick straight out from the engine rather than curling around a plenum. IMHO this is why people associate ITBs with power increases - purely because cars engineered mainly for maximum power tend to use them.

 

 

 

Open trumpets also have no place in a road car in stock form because of drivability, noise, emissions, and packaging issues. Bringing the turbos back onboard you also need to run some kind of plenum if you want to pressure charge. So what kind of plenum to have? All the powwwweeerrrrrrr junkies will cry "let's have a big one!" and that's absolutely correct if all you are interested in is peak power. However, ask someone who has to calibrate (that's the OEM-world term for mapping) an engine so its drivable and they will say "as small as possible please". So why is this?

 

 

 

Let's bin the ITBs and put a plenum and single throttle back on our imaginary NA engine again, but this time think about what happens at part throttle. If you measure the depression in the plenum you will find it to be large because the engine is having to suck all the air past the partly closed throttle valve. You may think "ah, but the engine will be spinning much more slowly" but this is actually irrelevant. What we are talking about here is engine load. If you are cruising down the motorway at 70 doing maybe 3000RPM with your foot resting very lightly on the throttle you are sitting at a "low speed / low load" point in the map. Now mash your right foot into the floor and what happens? Your throttle opens to 100% but at that instant your engine revs have not risen at all, so it is possible to have the same engine speed for almost any engine load. You are now asking the engine to move to a "high speed / full load" point in the map. This cannot happen instantly because the engine has to develop sufficient torque to increase the engine revs from 3000 to whatever you want against the resistance of the car. How quickly this change happens is affected by many things like engine inertia and gear ratio but the size of the plenum also plays a part.

 

 

 

As mentioned earlier, when you are at part throttle, the plenum will be running a heavy negative pressure. This means it is not actually full of air at all. When you crack open the throttle, you expect an instant surge of torque but in fact what happens is the first gulp of air the engine takes at WOT is still weak because the plenum acts like a reservoir of rarefied air. You may think that an engine spinning at 3000RPM would empty the plenum pretty quickly so the effect would be hardly noticeable, but think of a misfire. On the 2JZ that only lasts 1/3 of an engine revolution, but you sure as hell would feel it. By comparison emptying a nominal 3 litre plenum would take a minimum of two whole engine revolutions before the effect started to tail off, so it would take the edge off the crispness of your throttle response.

 

 

 

I mentioned a 3 litre plenum because that's the rule of thumb for plenum design: 1 x engine displacement. I would imagine the NA Supra is more than this when you include everything between the back of the valves and the throttle butterfly. So those massive high plenums that the max power boys want will increase the effect discussed in the previous paragraph. The bigger the plenum, the worse the effect.

 

 

 

Now imagine that the road car we are discussing is not the regular model but a rip-snorting M-sport GTi Type R version. The designers will want to have big lumpy cams running massive overlap to improve breathing and also they will have to have a regular intake manifold because they want to tune the runners and have some fancy variable gubbins to spread the torque curve out. They will also probably want a massive plenum. Now, those lumpy cams may work fine at the max power or max torque speed, but come back to cruising and that big overlap starts to hurt throttle response.

 

 

 

While both valves are open, if there is not enough inertia in the air column, or pressure difference between intake and exhaust, then instead of the intake air "blowing down" the cylinder to chase the exhaust residuals out, the opposite can happen. The exhaust residuals flow the other way and start to fill up that lovely big plenum. The situation thus created is now even worse that the engine breathing less then a full charge of air. Now, the gas mixture that the engine breathes when you suddenly go from part throttle to WOT is only partially combustible, as some of the air has been replaced by exhaust gas. This will truly mess up the throttle response of your sporty engine.

 

 

 

Now consider the same engine with ITBs. When running at part throttle it will only draw a vacuum in the part of the runner between the back of the valve and the throttle butterfly instead of the whole plenum. This is a huge difference in volume. Because the plenum remains at atmospheric pressure and the volume of rarefied air is tiny by comparison, the engine is much more "prepared" to jump from part throttle to WOT. Also, if you run your lumpy cams, you will only fill up the same small volume with exhaust residuals while the plenum remains uncontaminated.

 

 

 

So in summary, ITBs improve throttle response but they don't usually give you more performance on their own. An exception might be if the stock throttle body was very restrictive. In this case the extra area per degree opening afforded by ITBs might make the car feel more alive and may also improve performance a little. However, ITBs do allow you to do the other stuff that improves power and torque but would ordinarily make throttle response unacceptable in a road car. Hence why cars like the M3 have them.

 

 

 

Remember, a throttle's job by definition is to restrict airflow. You could improve part load throttle response by simply changing the gearing of the stock throttle valve linkage so it opened faster. At anything less than WOT this would be the same as increasing the total area of the throttle. I once drove my old 3 series BMW to a computer repair shop, amazed at how alive the car felt. When I got there I remembered the I had had to move my seat forwards about 2 inches to get my PC on the back seat behind me, and I was simply pressing the throttle harder than I realised...

 

 

 

On a turbo engine filling the plenum during a transition will be less of an issue as long as you are on boost. As long as the ECU closes the wastegate fast enough you should have all the air you need on demand. However, if you start running longer cam profiles and increasing overlap you may run into exhaust gas reversion issues at part load because the exhaust backpressure will possibly be higher than the inlet pressure during the overlap period, because of the turbine, which might mean ITBs would be an advantage.

 

I was just about to say that.

[Nodalmighty]

I was just about to say that.

 

I read all that and thought, that's why I let people who know what they are doing design manifolds.

[Kirk]

Great input digsy

[nevins]

lewis seriously fella, the saxo would have had quite a bit of a performance hike due to the other mods fitted and its alot cheaper to do due to being able to buy the kits off the shelf. If you want more power for your money TT is the sensible thing to go with. Or even sell yours and then the cash you would be spending put towards buying a TT supra.

[Chris Wilson]

Very thorough post, should be made a Sticky, IMHO. Well done

[Neil-NA]

Can some one, in real simple primary school talk please tell me what the big long post means

 

Or just answer throttle bodies........ yey or nay.

[Kirk]

For what your after YEY but the rest of the engine will want to be specced properly to take full advantage of them

[Neil-NA]

For what your after YEY but the rest of the engine will want to be specced properly to take full advantage of them

 

I'm on it buddy

 

Did i read it right you have a set of r34 throttle bodies?

[Kirk]

Somewhere, i would realy have to look hard for them

 

They are quite different to m3 type ones though

[Neil-NA]

Ahh okies, i have been searching and cant seem to find much at the mo, then again i'm just getting the ideas together.