ITBs and turbos?

[jmc330i]

Im sure Ive read somewhere that ITBs are not really suited to a turbocharged engine, which is why Im guessing some of the S38 turbo cars Ive seen (from PPF etc) are running one big TB instead.

Is it the case that the advantages of ITBs are not as great on turbo engines and so you can get just as much power/torque etc using a single large TB?

[Turbo-Brown]

ITBs are generally suited to engines with high lift on overlap cams and these cams are less suited to turbocharging which I guess is why ITBs aren't usually used with turbo setups.

However, look at it in terms of flow area:

A Zone BBTB is 65mm diameter (I think?) and has a free area of 2800mm^2 on WOT assuming an 8mm spindle.
The ITBs I made for my engine have a free area of 5628mm^2 on WOT with their 8mm spindles.

So the potential to make more power is there with the ITBs on the turbo setup, and the effect of the more efficient inlet (the ITBs) is amplified by the turbo, in the same way that you get proportionally more power from a ported head on a turbocharged engine when compared to N/A.

Then, there's the throttle response you get with ITBs which is another great reason to have them on a turbo motor where the greater lengths of inlet tract tend to dumb it down a bit.

Wouldn't say the advantages aren't as great, they're just different

Of course if you make your own plenum you can get as large a TB as you like which is what PPF do I guess.

There have been various engines over the years that have used ITBs and turbos, I believe some Skylines had ITBs (stand to be corrected on that though) and there was the Bugatti EB110, the little 3.5 V12 quad turbo which featured ITBs

[e30_Turbo]

and there was the Bugatti EB110, the little 3.5 V12 quad turbo which featured ITBs

Thats one of the best sounding turbo'd engines ever!

Wastegate chirp like nothing on earth, four of them too

[jmc330i]

So really its just down to what you want from the engine in terms of power delivery/response etc?
For example an S50 turbo with its ITBs wont necessarily be any better than an S50 turbo with a single large TB, they will just have different characteristics.

However, look at it in terms of flow area:

A Zone BBTB is 65mm diameter (I think?) and has a free area of 2800mm^2 on WOT assuming an 8mm spindle.

How do you work that out then?

[Turbo-Brown]

65mm dia TB without spindle has a free area of:

(32.5*32.5)*3.14=3316.625mm^2
very roughly the spindle has an area in the bore of the TB of 65*8=520mm^2

so total free area is (roughly) 3316-520=2796mm^2

As an after thought, one drawback of giant throttle bodies is that a tiny angular movement of the throttle spindle off closed throttle leads to a relatively large increase in flow area which could make it a little difficult to drive at low speeds and make the resolution of a throttle pot a little less fine.

[Gunni]

Using TPS with ITBԚ´s is better then MAP, as you can adjust the load signature in the EMS,

for instance, if you have 2% throttle at idle, and at regular at driving 7% ,
25-70% is strong accelaration and 70-100% is WOT,

itԚ´s obvious that you need to adjust the low TPS settings alot more then the higher, so having the load as follows would be best,

2%
4%
6%
13%
18%
40%
70%
100%

this assumes 8 loads sites and the EMS interpolates the values from 70-100% anyway so you should be fine,
ie. 70%@3000rpm [300] 100%@3000rpm [500], at 80% throttle you get 80%@3000rpm [366]


Also Nissan Sunny GTi-R has ITBԚ´s and turbo as a stock setup,

[Turbo-Brown]

That's great if you can bunch up the load sites as you see fit, but I'm not sure you can on all aftermarket ECUs.

There's also the issue of how accurate / consistant the pot itself is, and that can't be adjusted out in the software.

Agreed that Alpha-N is better than Speed-Density for ITBs, although if you're using a turbo you'll need corrections for positive manifold pressure which is what I've got

[Gunni]

And so shall I ;)
using a perfect power XMS unit,

If you canԚ´t adjust the resolution on surten areas then one should look at other EMSԚ´s if your going to run ITBԚ´s

The pot obviously needs to be 100% functional and reliable,

[tim_s]

fwiw I didn't like alpha-n mapping with so little difference between sites. I had a brand new TPS carefully set up, and close sites, admittedly I have pretty large ITBs though. It would be fine if you don't demand impeccable light throttle behaviour etc, but for a daily driver i prefer MAP or MAF, although both also have their negative points too.

[320Touring]

will the luvvery sound of ITB's be lost due to the FI?

[Turbo-Brown]

will the luvvery sound of ITB's be lost due to the FI?

Fraid so Can't hear anything but the turbos on mine

If you canԚ´t adjust the resolution on surten areas then one should look at other EMSԚ´s if your going to run ITBԚ´s

The pot obviously needs to be 100% functional and reliable,

Fair comment!

but for a daily driver i prefer MAP or MAF, although both also have their negative points too.

Only problem I can see with Speed-den on ITBs is that the vacuum signal is pretty wavery, certainly is on mine and that does read off all the cylinders.

Having said that, for my mate's engine I'm making up a much larger vacuum tank than I've used on mine to see if it helps to smooth out the signal so the jury's still out on that one.

There's alot to be said for MAF in that you can map a brand new engine on it and then largely forget about the mapping, whereas with both Speed-density and Alpha-N, you need a map that'll work whilst the engine's still new and all tight, and then a re-map once everything loosens up, which is probably why production cars use MAF.

[320Touring]

will the luvvery sound of ITB's be lost due to the FI?

Fraid so Can't hear anything but the turbos on mine

Aww bugger

difficult choice, eh

slow and sounds good

or fast, silent and deadly....

[Turbo-Brown]

As I say, the benefits of razor sharp throttle response outweigh the drawbacks

[tim_s]

Only problem I can see with Speed-den on ITBs is that the vacuum signal is pretty wavery, certainly is on mine and that does read off all the cylinders.

Having said that, for my mate's engine I'm making up a much larger vacuum tank than I've used on mine to see if it helps to smooth out the signal so the jury's still out on that one.

There's alot to be said for MAF in that you can map a brand new engine on it and then largely forget about the mapping, whereas with both Speed-density and Alpha-N, you need a map that'll work whilst the engine's still new and all tight, and then a re-map once everything loosens up, which is probably why production cars use MAF.

yeah I had to make a restrictor and plenum to stabilise the vacuum signal, it was quite a bit better then. I had further difficulties because the manifold pressure was static despite big changes in throttle position (and fuel required).
MAF is working well for me though, its proved the best for my setup.

[Turbo-Brown]

I had further difficulties because the manifold pressure was static despite big changes in throttle position

Now that is odd, I get a definate trend of signal movement on the MAP with mine, but you can see the pulsing as individual cylinders take their turn to draw breath.

The signal's much smoother once the boost comes in, and there is a damping factor control in the ECU software, but it does still jump around a bit, even with a restrictor.

Other than that though I'm more than happy with running Alpha-N

[Gunni]

with the xms system I will be using I will have a long term wideband support for the ecu so
as time goes by the afrԚ´s will steadily be perfect for what I want,

MAF has almost NO bad points,
itԚ´s function is so clever that itԚ´s almost perfect in every way,

IAT doesnԚ´t matter as itԚ´s built into the MAF
boost doesnԚ´t matter as the MAF just calculates mass anyway
itԚ´s almost non restrictive and available in many sizes,

[Turbo-Brown]

Wouldn't agree that it doesn't need to know IAT as it uses a heated element to magically calculate air flow and therefore needs to know how hot that air is so the mass can be deduced. Certainly the S50 has an IAT sensor.

MAF can unfortunately measure the same air twice too if you've a situation where air's bouncing out of the engine

But agreed that the pros by far outweigh the cons

[Avner]

I think that alfa-N isn't suitable for turbo application; you can be at any throttle opnening both under boost and under vacum and the fuel/spark requirments for each condition are totally different of course.

BTW - both the Nisaan Skyline GTR and Sunny GTI-R use ITB in a boosted engine (with MAF).

[Turbo-Brown]

Quite right, but you can set your system up like I have mine where you have an Alpha-N map and then a seperate correction table for fuel and ignition which used manifold pressure as it's input so that everything off boost is purely Alpha-N, and once you get above atmospheric pressure, it runs Alpha-N+MAP

[tim_s]

I had further difficulties because the manifold pressure was static despite big changes in throttle position


Now that is odd, I get a definate trend of signal movement on the MAP with mine, but you can see the pulsing as individual cylinders take their turn to draw breath.

Sorry that was unclear, you could get manifold pressure at high 90s KPa at not very much throttle and still accelerate faster by putting your foot down, resulting in either overrich mixtures at part throttle or lean at full throttle.

[jmc330i]

will the luvvery sound of ITB's be lost due to the FI?

Fraid so Can't hear anything but the turbos on mine

Aww bugger

difficult choice, eh

slow and sounds good

or fast, silent and deadly....

Thats almost made my mind up - S50, one big TB, one massive turbo

[Gunni]

Quite right, but you can set your system up like I have mine where you have an Alpha-N map and then a seperate correction table for fuel and ignition which used manifold pressure as it's input so that everything off boost is purely Alpha-N, and once you get above atmospheric pressure, it runs Alpha-N+MAP

Even more is that the MAP comp section of the standalone can also comp for off boost, from 0bar - 2bar (1bar boost)

for instance when at 5k and WOT and no boost (0bar) and you donԚ´t adjust the throttle but boost rises, the MAP map compensates by adding numbers % wise to the injector pulses, now obviously 1bar boost requires pretty much 100% more fuel then at 0bar, but it can be adjusted to find the optimum value,

same with ignition , you can base the ignition map on alpha-n and then retard ignition based on MAP values as well,

too me that is the optimum of both worlds,

[Ant]

resulting in either overrich mixtures at part throttle or lean at full throttle.

could be cured with better tps based accel enrich settings Tim ?

turn off the accel enrich, map for load to target AFR( in theory you could target for stocih, but safe not sorry ), then trim the accel enrich (and time) to get the best (12.5 ish) AFR, I use no accel enrich over 100Kpa though, map to boost from there on, using accel did cause bucking issues as the mix went 9:1 rich on a good bootful.

Yet to try a MAF on MS, Tim, stop tempting me dude , just did MattGs' touring on MS, Speed den/alphaN blended , tis quite lively

Induction noise is too

[tim_s]

Cool! I haven't tried the hybrid alhpa-n code very much. I tried it once and didnt' get on with it, but I had a bit of a dead spot on the TPS at very light throttle so it was never gonna work really.

As for MAP, accel encrich helped, but could not totally cure the problem. if you look at this red top VE table (haven't got my old MAP table to hand):


its the jump between 95 and 100KPa that is problematic and from 90KPa you can't tune very precisely because you get really similar MAP for different scenarios. mine looked more severe as I tried to be more precise with the sites, ending up with sites at 92, 94 and 96KPa. It's not the end of the world, but I knew I'd have to live with either compromising performance or economy.
See this post by phil ringwood:

It is my opinion its impossible to tune ITB's using MAP, well, the ITB's I have tuned certainly couldnt have been tuned in MAP as I hit 100KPa at 20% throttle and if I then put my foot down some more the engine would still accelerate some more, so obviously 100KPa wasnt full throttle, by opening the throttle some more I was altering the tuned length of the tube, this I guess was why it would accelerate some more, but the KPA didnt alter, so it wouldnt have worked using MAP unless, as I have discussed with Ken, it switched to Alpha when it hit near 100KPa,
Phil

I think he's probably hit on the solution, MAP until 90+KPa, then alpha-n.

[Gunni]

Perfect Power designed their systems to always be alpha-n and also MAP regulated,



As you can see as map changes so do the final calulations,

i.e 4000rpm@75%
Here you can see the effect of diffrent manifold pressures at that rpm and
load

MAP RPM
1,99 666,7
1,88 629,8
1,78 596,3
1,65 552,8
1,52 509,2
1,36 455,6
1,24 415,4
1,11 371,9
0,99 331,7
0,86 288,1
0,73 244,6
0,59 197,7
0,46 154,1
0,34 113,9
0,25 83,8
0,15 50,3

Now you can adjust the MAP comp values so you can actually have the fuel become more rich or lean in a unlinear way,
i.e at 28% you may want only 15:1 afr, but at the same TPS, RPM but at some other pressure you want 12.5:1 AFR for instance at 1bar boost

[jmc330i]

Having read and re-read this thread a few times now, I think I kind of understand what you lot are on about

My problem is that Im hopefully getting another S50 and its going to be force fed whatever happens Now I can either get it with the ITBs or tell the guy to keep the ITBs and get the engine a bit cheaper.

If Ive read all the above right, a turbo engine with a single large TB would be easier to set up but could have a few problems with regards to low speed driving etc, where as ITBs and a turbo would run better but be more difficult to set up.

I guess its 6 of 1 and half dozen of the other.

[320Touring]

I would have thought that ITB's would be harder to drive at light throttle openings, due to each cyl operating almost individually, hence the variation at idle that turbo-brown mentions?

[Turbo-Brown]

The opposite is true really, you get very fine metering of air with ITBs and there are no problems with one cylinder nicking the air meant for another (which is part of the problem with lumpy cams and plenum intakes) so you get extremely smooth progression off idle.

[Turbo-Brown]

Also, just to shake up the original debate a bit, that PPF M3 (PerformanceBMW Sept '06) with the 963bhp M5 engine still has the original throttle bodies, just with a revised plenum.

My guess for why PPF don't retrofit TBs to things like the M20 is that it's a pain in the arse to do, and the things are a real pain in the butt-hole to make!

[jmc330i]

It might not have been PPF, but Ive definitely seen a vid of an M3 with M5 turbo lump running a single TB.

TBH, if I do get this S50 engine, Im going to get it with the ITBs - it just wouldnt be the same really, oh and the turbo

[Turbo-Brown]

Good man! TBs rock!

[awx]

Can you use the Dbilas Multi-throttle intake with a turbo then?

[Turbo-Brown]

Don't see why not, it must be sealed if people use a MAF with them.....and for a variety of other reasons!

[awx]

What problems would i encounter if i was to use an m20b25 + MSnS + dbilas ITBs + turbo? Thought using MS you can throw away the MAF. Would i need to configure MS to work with MAF or just use Alpha-n pre boost then Alpha-n+MAP during boost?? You've got me interested in using ITB + Turbo

[Gunni]

I canԚ´t speak for MS but when using turbo and alpha-n
you need to have a specific MAP compensation map wich you adjust beforehand.

i.e at 0vacuum you can leave it at 100% , at 1bar you would leave it at 200%

ie if the pwm is 5ms at 0vacuum it should theoratically be 10ms for twice the air ,

if you put up a scale map from full vacuum to the max your MAP sensor sees (0-5v)
2.5 beeing half of the scale, it should be linear, when that is done and you have tuned the alpha-n map
TPS vs. RPM you can adjust the linear MAP map if itԚ´s not 100% on, but you must have configured your IAT map compensation before, as 1bar boost is almost definitly hotter (less dense) then 0bar boost and
1bar boost is only 100% denser then 0bar if itԚ´s at the same air temp

You can see this here in the picture