Went for a bit of a blast yesterday. Nowt too fast (just got to the limit quickly ) But when I opened the bonnet to see what got hot, the standard IC was cold yet the inlet manifold was very warm! My car is completely standard bar a different backbox but I'm interested in what can be done to reduce the temperature of the manifold. I've read about header tank insulators and phenolic spacers but not sure what works best in the real world... What have other people done?

 

What problem are you trying to fix?

 

Good question, i've got what feels like retardation (it's not a miss-fire) which I'm assuming is knock, so I was hoping to fix that, but also just make it generally safer as I'm interested in a remap next year. Reliability is paramount so am going through making everything as good as possible!

 

Paranoia will send you insane though

Measure your inlet temps and if you do actually have a problem then look at ways to resolve it. I suggest borrowing a thermocouple setup from someone as they're fast acting (depending on probe used) and accurate, compared to these 'ACT' gauges you find dotted around. You can buy cheap digital multimeter now which accept thermocouples, so that might be a cheap method.

 

You know what assumption is? In practice genuine knock can rarely be felt, or heard, the likelihood is that there's another explanation for your problem. Might help you pinpoint it if you could tell us more about the specific symptoms - what it feels like, when it happens, and so-forth.

If you have a standard-ish car at the moment there will invariably be other ways of spending the same amount of money that will have a more beneficial interest on reliability and stability than going out of your way in this area.

Your inlet manifold is getting hot because it is absorbing heat being radiated up from the engine, and also the header tank (and the heated throttle body, unless you've disconnected it). However, it is debatable how much of an effect this has on the temperature of the charge air itself, which, don't forget, passes through very quickly.

When you're shoeing it the air volumes passing through the engine are huge - in the hundreds of litres per second area at times, so each molecule of air is exposed to the heat of the manifold for hundredths of a second. That just isn't enough time to absorb significant amounts of heat energy, especially when you remember that only the molecules closest to the aluminium will be affected at all.

Even if you do fit insulating spacers and disconnect the throttle body, your manifold will still warm up in use due to absorbing heat radiated from beneath, it'll just warm up a bit less, so you could end up spending a lot of money on spacers and shims and feel as though you haven't actually achieved much.

While you can't always apply racing techniques to road cars, a possible clue to the potential advantages of thermal insulation in this area could be found from a peak under the bonnet of a WRC car. If there was a significant advantage, chances are you would see insulating spacers between the heads and the inlet manifold.

As above, best way to look at your problem at the moment is probably to put assumptions to one side for a minute and tell us all about it - and your car

 

Can see what you're getting at but I'm not sure you're answering Si's question there.

He's concerned about the possibility of the warm inlet manifold heating the air on its way into the cylinders. There's no easy way of measuring that using a simple standalone thermocouple, because you have no easy way of putting it in the right place.

In order to do so you'd need one sensor in the throttle body (to measure the air temp on its way into the manifold), and then find a way of positioning a second in one (or more) of the manifold branches, immediately above the fuel injectors.

Subtracting the temperature at the throttle plate from the temperature above the fuel injector will show exactly how much (or how little) the air is being heated as it passes through the manifold. Finding a way of putting that second temperature sensor in position is the difficult bit - for most people anyway.

 

I didn't bother going into detail due to it being, on the whole, unnecessary (it being a non-problem in the first place). It was just the basic concept, which you have now described in detail so no confusion should be apparent.

 

The mother of all f ups?

It wasn't the knock I was feeling (or hearing), more the feeling of timing being pulled. But like you say, assume nowt! I'll get a boost gauge on there and see if that's the problem. I've already cleaned the boost solenoid but i'll do it proper

I'm interested to hear what others would suggest. It's done about 95K with LOADS of history but no clutch change. I've done the timing belt & tensioners recently. Currently ploughing through cleaning things out (IC etc) just to get rid of 95k's worth of crud.

Sure. I agree but with the IC doing such a good job (it was stone cold to the touch) I don't see the point in running it through a hot manifold.

I was planning on powder coating the manifold too whilst fitting the insulators and then applying some heat foil to the base of the manifold to reduce the radiation effect. I was also looking to refurb the injectors whilst they are off to ensure correct spray etc etc. It's done 95K, so I'm sure they aren't perfect...

Do you see the spacers there? I dunno

Good call Feel like I'm telling a story here Reliability here is the key, it's my wife's car so if it breaks, I get grief So, without spending a chunk of cash, I want to refresh it as easily as possible and avoid having an engine rebuild bill. I do all my own work on the car, so parts are the only real cost. Box oil is being done soon for some good stuff, new o2 sensor is on it's way, have already reconditioned the calipers all round with new pads, will take a look at the selector bushes whilst I'm there. Got cam cover gasket to do. Basically, I want to get it at fit as possible in case I remap it next year. Lowering the charge temperature (in theory!) without replacing it for a STi IC is never going to hurt I thought but i'm open to suggestions as to what I could fix / improve.

 

just fit some inlets maniflow spacers to drop the temp ...prob solved

 

I was going to use the one about making an a** of u and me but the other one works. It would have to be pulling a hell of a lot of timing for you to actually feel it. There are any number of explanations for flat spot or hesitation. If you have the option, having it looked at by someone who knows will likely get to an explanation and fix quicker than a blind process of elimination. if you are going to do it yourself, the more you know and the less you assume, the better so the gauge is a good move.

What is "it" (i.e. type and model year)? Will be easier to make suggestions for things to look at if we know the above. However, again nothing beats having an experienced eye look it over and spot things that are in need of maintenance or replacement.

In an ideal world you wouldn't, but the engine bay isn't an ideal world and everything is a compromise to some degree or other. If you conducted the temperature measuring experiment as I described it earlier I strongly suspect you would realise that the there was little if any measurable heating effect on the charge air as it passes through the manifold.

If you wanted to sort this "properly" you'd make one with a coolant jacket and run an aux rad and pump. That's clearly total overkill so it's a case of finding a compromise that works. To be honest even the measures you're looking at will be unlikely to make a significant difference to anything that matters. The average air molecule spends something in the region of a few hundredths of a second passing through the inlet manifold. There's minimal opportunity for appreciable heat exchange there.

The other thing you haven't considered at this point is that the manifold will, naturally, run cooler when the car's in motion than it does when at a standstill due to airflow through the bay. As things stand you are assuming (that word again) that there is a problem here that needs fixing.

The only things I would bother with in your position are disconnecting the throttle body water (something you can do at no net cost) and possibly decoupling the coolant header tank from the manifold. Anything else is likely to be expenditure and unnecessary complexity for minimal if not non-existent advantage. Getting the injectors checked, cleaned and matched though is a good idea.

Without wishing to flog the point to death, if you're watching the pennies, throwing some in the direction of inlet manifold spacers is not likely to give you value for money.

On a 99MY and onwards the MAF sensor insert is (relatively) cheap. If you're interested in reliability and are replacing on a precautionary basis, you should probably do the MAF before the oxygen sensor. Other than that, as above, it's impossible to make sensible recommendations to you without actually looking at the car.

The only two things that will affect charge temperature in any meaningful way are either changes to the the intercooler itself, or making the flow of air through the IC more effective - which you can do easily on a bugeye or classic by fitting a splitter to the undertray beneath the scoop.

You don't.

 

Cool. Thanks. Ordered one night so I can deal with some facts rather than theories

MY00 Turbo 2000, UK spec.

I would say I'm thinking there's a problem, more I want to improve on where it stands right now.

Yup, have already pondered the TB water lines. I have a theory that some engine failures are affected by a injector not flowing right, running a cylinder lean. So that's where I started - pull the injectors to flow test them, ahh, I might as well, pull the manifold to do that and whilst that's off, I'll paint / powder coat that, then I might as well add insulators whilst I'm there

OK, thanks for the advice

Yup, MAF already replaced I'm also mid-way through building a leak testing kit to pick up any failed gaskets etc

I'll look into that. Thanks.


Nice one, ta.

Cheers for the advice fella

 

if your wanting to cut down on the temprature under the bonnet heatwrap your headers and downpipe make sure youve got the heatshield on the turbo unless you can get a turbo blanket.
thats prob best part of £100 where as the spacers are circa £30 i think reposition your headertank off the inlet as that can get HOT!
throtle body coolant bypass About £10
maybe look at swapping your hoses over to some silicone as some of the oe ones can perish pretty quickly
thats what ive done on mine and the temps are noticably lower
hth jon