Induction Route .v. Lag ? ?

[Steve W]

Watching all your replies/threads about the Infamous Mr. Mycroft

and his pals on the 'GTR' BBS.

 

They are going on and on about Intercooler efficiency and

pipework-mass-exchange-rates and what have you...

(all sounds technically correct and all that, BUT: )

 

It struck me as soon as I saw the induction route on my/our TT's:

 

Surely the EXTREMELY long route from Turbos down the long pipework

to the intercooler, along by the radiator and back up

by the intake manifold MUST contribute a LOT to the turbo-lag

? ? ? ? ? ? ? ? [ that is one LONG route ! ]

 

Is that why some cars (i.e. Sunny) have their IC on top of the

engine so that exhaust-IC-intake is as short as possible. ?

( Sunny's do seem 'quicker' , even if not as good at top end)

 

OR can the turbocharged induction route be as long as you like

(doesn't seem likely though).

[Steve Cargill]

Hi Steve, this was talked about a while ago. I did a bit of maths and at 6000RPM the 3ltr engine uses 150 Litres of air per second at atmospheric pressure.

 

Adding a few extra L of pipework looks like it would make no significant difference. What would though are the size of pressure drops through restricted flow.

[Steve W]

I don't suffer from much 'lag at 6,000 ! ? ! ?

( I haven't even been UP-THERE yet, problems etc.)

 

I was talking about lag at ~1,500/2,000

 

BUT, I see what you mean - large volumes = less 'time' (-ish).

 

Just seems to me that it needs to go from atmospheric UP TO

pressurised levels BEFORE you worry about volumes ?

 

( ie. turbo needs to raise pressure of ALL the air in the induction

system - ALL the pipework/IC etc before it starts 'boosting' engine.

Wouldn't it be able to raise that initial boost 'quicker' if it had

~1/4 of the volume to deal with. Once it's RAISED the pressure

then I can see that the volume wouldn't matter.

NO, I don't REALLY know what I'm talking about, that's why I'm

asking you clever chappies )

 

:stupid: :stupid: :stupid: :stupid: ( ? )

[Guest Martin F]

Originally posted by Steve W

 

Is that why some cars (i.e. Sunny) have their IC on top of the

engine so that exhaust-IC-intake is as short as possible. ?

( Sunny's do seem 'quicker' , even if not as good at top end)

 

 

I have heard of a reason for having the IC laying horizontally like that, in that pushing air through the IC at an angle is better for heat transfer. But my simplistic mind tells me that putting an IC on top of a very hot engine is just not good.

 

Guess that's why some of those Sunny owners go for FMIC's.

 

One of the worst induction piping routes has to be on the MKIII, all that nicely cooled charge comes straight out of your FMIC (yes the MKIII has a nice big FMIC as std!) straight up and across the top of your nice hot engine.

 

[Myles]

Steve , as I understand it , lag is caused by having a lowish compression engine breath through a strangulated exhaust (it's got a couple of turbos in the way)...I'm sure it is probably compounded a little by having a greater volume of air in the i/c pipework for the turbo to compress , but these losses may be preferable to the hotter air charge & increased risk of detonation caused by placing the i/c on top of the engine . I suppose it's a compromise between lag & heat-soak !?

[Digsy]

Lag is pretty much all to do with turbo impeller inertia. When you are on boost you can force the air through all sorts of weird and wonderful shapes with relatively impact on performance, compared to the sort of intake pipework you need to use on an NA engine.

 

I think the volume of air in the pipes would make a difference is there was an appreciable pressure drop across the intercooler. Otherwise I think more free flowing pipework with a larger diameter (and hence a greater pre-manifold volume) would be preferable.

 

I did read some of the GTR thread about IC mounting. Maybe I'm being over simplistic but I always thought the main reason for mounting radiators / ICs at an angle was jst so you could fit a bigger one in a given frontal area.

[Barry]

Standard Sunny intercoolers are nick-named 'Interwarmers' as they are above the engine. At standstill all the heat from the engine rises through the interwarmer. But once they are rolling the big bonnet vent soon cools things down.

 

How about fitting a chargecooler to the supra, Im sure one could be squeezed in if you moved a few bit & pieces around and that would make the pipework alot shorter.! ??

 

[Adam W]

Is a chargecooler an air/water version of an intercooler? I'm sure I read that they were less efficient than an air/air IC.

 

Do they use the engine coolant for cooling? That's at about 100 degrees isn't it?

[Barry]

Yep, its air to water cooling and no it doesn't use the engine coolant, its has its own seperate water tank, pump and radiator.

 

They are supposed to be better at keeping the inlet temperature lower for shorter bursts. I've never used one but would like to try and see what its like.

 

If you have a look on the Pace products web site there is a good diagram on there.

[Adam W]

I wonder if you could do something similar, but use your air con to cool the IC rather than the inside of the car? Or maybe adapt the internals of a freezer to get the intake air REALLY cold!

[THOR Racing]

I think you'd find the mechanical energy needed to drive the AC system far outways the gains you would see by cooling the IC with cold water.

 

I always ask if it's been done professonally (race team) before, then chances are there's a DIY version/way to do it. But I don't recall this being fitted to many turboed cars hence I think it may have crashed and burned as an idea.

 

I would have thought that the ideal intercooler would be 0mm thin but have infinite frontal area to get the max cooling/airflow possible and increase internal to external heat transfer.

 

Hence I think a typical FMIC size of 600*300*100 is less efficient than a 600*400*75 even though it has the same volume. The latter presents a greater surface area perpendicular to the air flow. The former suffers from heat soak across the 100mm thick core and the back of the FMIC end up hardly cooling the charge at all.

 

As to lag from pipes and size of IC I would have thought it would practically make very little difference, but then I've never experimented.

 

regards

Pete

just my 2p