Supercharged air temperature
Discussion
I've been struggling in the past few weeks on and off with a misfire, it was quite pronounced on the return from BBWF, as I neared home I could barely get above 3500 rpm. However when the engine is coolish it pulls quite cleanly all the way up to 5,500 no problems.
I suspected the air charge temp so I stuck a thermocouple in the air stream between the s/c and the plenum, and it's getting up to 80C, but only when the engine is fully hot.
I think I need to duct cool air into the intake because it's gulping the stuff that's been past the rad.
Any of the other s/c guys out there, Jasper, Tony, Steve, have you measured the charge temperature and what does it get up to?
I suspected the air charge temp so I stuck a thermocouple in the air stream between the s/c and the plenum, and it's getting up to 80C, but only when the engine is fully hot.
I think I need to duct cool air into the intake because it's gulping the stuff that's been past the rad.
Any of the other s/c guys out there, Jasper, Tony, Steve, have you measured the charge temperature and what does it get up to?
With charge cooler only highest temp I have seen is 42 and that was on a 30 deg day. With water injection, I can get it around ambient or sometimes even below!
But I have a centrifugal blower which doesn't raise the charge temp so much as a screw type. At 80 deg the ecu will be backing everything off or it should be to preserve the engine.
But I have a centrifugal blower which doesn't raise the charge temp so much as a screw type. At 80 deg the ecu will be backing everything off or it should be to preserve the engine.
Thanks for that Steve.
Just to recap it's a flapper with a 4CU ECU.
I imagine that the air temp sensor is in the flapper for the ECU, but anyway it's pulling in quite hot air to start with (I will soon be putting a thermocouple in the air filter to check that too.)
The ECU will probably be putting in less fuel I suppose because it's hot air going in, which probably doesn't help matters, as there will be less cooling from fuel evaporation.
When I spoke to Dennis Priddle he did say that the Sprintex blowers we one of the more efficient screw-type ones, with less heating effects than others, but I take your point, centrifugal ones may be even better.
Another reason for not using an intercooler except as a last resort is that it wastes energy, you have put all that work into pressurising the air going in, and yes it does rise in temp according to Boyle's Law, but if you cool it in an intercooler some of that energy is going back into the atmosphere. I think it's far better to cure the air intake temperature first, if that sorts it then great. Unfortunately I don't have the luxury of a flattened Westfield bonnet with all those slats in it!
Looks like a trip to Mackay's for me to get some thin sheet ally to box off the air supply.
Just to recap it's a flapper with a 4CU ECU.
I imagine that the air temp sensor is in the flapper for the ECU, but anyway it's pulling in quite hot air to start with (I will soon be putting a thermocouple in the air filter to check that too.)
The ECU will probably be putting in less fuel I suppose because it's hot air going in, which probably doesn't help matters, as there will be less cooling from fuel evaporation.
When I spoke to Dennis Priddle he did say that the Sprintex blowers we one of the more efficient screw-type ones, with less heating effects than others, but I take your point, centrifugal ones may be even better.
Another reason for not using an intercooler except as a last resort is that it wastes energy, you have put all that work into pressurising the air going in, and yes it does rise in temp according to Boyle's Law, but if you cool it in an intercooler some of that energy is going back into the atmosphere. I think it's far better to cure the air intake temperature first, if that sorts it then great. Unfortunately I don't have the luxury of a flattened Westfield bonnet with all those slats in it!
Looks like a trip to Mackay's for me to get some thin sheet ally to box off the air supply.
Yep, the run back home sort of confirmed some of this.
The temperature just kept steadily building over the 20 mile run until it reached 86C. It then dropped a bit after I came off the motorway and cruised at 50, to 82.
The intake temperature is definitely a big factor as that's the main way the supercharger cools - the intake air can reach 50C when stationary, so this definitely needs sorting.
The supercharger itself also get very hot. The compression of the gas doesn't affect the temperature half as much as what I expect the vanes are doing to the air as it passes over them - heating the air because they are hot themselves. So I think some mild water injection will help here, by cooling the internals of the supercharger. I'll probably rig it up gated by output air temperature and throttle opening, no need for it on cooler days.
Time for somre real engineering (I do software by day!)
The temperature just kept steadily building over the 20 mile run until it reached 86C. It then dropped a bit after I came off the motorway and cruised at 50, to 82.
The intake temperature is definitely a big factor as that's the main way the supercharger cools - the intake air can reach 50C when stationary, so this definitely needs sorting.
The supercharger itself also get very hot. The compression of the gas doesn't affect the temperature half as much as what I expect the vanes are doing to the air as it passes over them - heating the air because they are hot themselves. So I think some mild water injection will help here, by cooling the internals of the supercharger. I'll probably rig it up gated by output air temperature and throttle opening, no need for it on cooler days.
Time for somre real engineering (I do software by day!)
Hi,
I put a scoop at the front, just behind the rad to avoid speed bumps but sticking underneath so picking up cool air, the scoop is a bit like a vacuum attachment in shape and has a 80mm hose connection on the back, I then have a cold air box which is fed by this hose and which houses the filter. It is all wrapped in air con duct insulation.
Intake temps stay within 2 or 3 degrees of ambient air - proven as the air temp sensor sits just inside the air filter (running MS). Obviously your intake is a bit different but can definitely recommend a pick up in cooler air. I was toying with the idea of putting it below the headlight pod and just cutting a louvre to feed it into the undertray that sits from the front splitter back under the rad - mine's sheet as the grp original was missing. One either side feeding a twin plenum would be neat !
I put a scoop at the front, just behind the rad to avoid speed bumps but sticking underneath so picking up cool air, the scoop is a bit like a vacuum attachment in shape and has a 80mm hose connection on the back, I then have a cold air box which is fed by this hose and which houses the filter. It is all wrapped in air con duct insulation.
Intake temps stay within 2 or 3 degrees of ambient air - proven as the air temp sensor sits just inside the air filter (running MS). Obviously your intake is a bit different but can definitely recommend a pick up in cooler air. I was toying with the idea of putting it below the headlight pod and just cutting a louvre to feed it into the undertray that sits from the front splitter back under the rad - mine's sheet as the grp original was missing. One either side feeding a twin plenum would be neat !
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