Boost falls below wastegate pressure after the out lap
07-18-22, 07:32 PM
#1
Eats, Sleeps, Dreams Rotary
Thread Starter
Boost falls below wastegate pressure after the out lap
My boost falls below the 0.8 bar (12 psi) wastegate pressure after about one lap and settles at about 0.58 (8 psi) for the rest of the session.
Once I stop and let the intercooler cool, it will temporarily boost to wastegate pressure again.
I suspect this is a heat soak issue, but what exactly causes it? High IATs > retarded ignition timing > less exhaust pressure > less boost?
Previously I had an FRP hood with a huge cutout paired with a modified stock bumper. I then moved to a carbon hood with a much smaller cutout and an aftermarket bumper with massive inlet.
The V-mount intercooler would practically be cold to the touch after a session.
Due to....reasons..... I moved back to the stock bumper but kept the same carbon hood. Now the intercooler is too hot to touch after sessions.
At first I thought it was mostly the bumper, but then it occurred to me that the previous owner had enlarged the hood cutout for a reason.
The cutout on my new hood is probably far too small for the size of the intercooler.
I pulled the mesh off the outlet and that sees to have made a bit of a difference. I'm going to try enlarging the hole next.
Is it the IATs, or am I barking up the wrong boost tree?
Once I stop and let the intercooler cool, it will temporarily boost to wastegate pressure again.
I suspect this is a heat soak issue, but what exactly causes it? High IATs > retarded ignition timing > less exhaust pressure > less boost?
Previously I had an FRP hood with a huge cutout paired with a modified stock bumper. I then moved to a carbon hood with a much smaller cutout and an aftermarket bumper with massive inlet.
The V-mount intercooler would practically be cold to the touch after a session.
Due to....reasons..... I moved back to the stock bumper but kept the same carbon hood. Now the intercooler is too hot to touch after sessions.
At first I thought it was mostly the bumper, but then it occurred to me that the previous owner had enlarged the hood cutout for a reason.
The cutout on my new hood is probably far too small for the size of the intercooler.
I pulled the mesh off the outlet and that sees to have made a bit of a difference. I'm going to try enlarging the hole next.
Is it the IATs, or am I barking up the wrong boost tree?
07-18-22, 08:48 PM
#2
Arrogant Wankeler
Probably a combination of the intake density reducing (and supplying less exhaust energy as well) and general heat soak. Retarded ignition will bias more energy to the turbine all else being equal.
Is the turbo drawing ambient air or from after the radiator or intercooler?
Is the turbo drawing ambient air or from after the radiator or intercooler?
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Howard Coleman (07-20-22)
07-18-22, 08:56 PM
#3
Eats, Sleeps, Dreams Rotary
Thread Starter
Probably a combination of the intake density reducing (and supplying less exhaust energy as well) and general heat soak. Retarded ignition will bias more energy to the turbine all else being equal.
Is the turbo drawing ambient air or from after the radiator or intercooler?
Is the turbo drawing ambient air or from after the radiator or intercooler?
I don't really have anywhere to pipe a cold air intake because of my V-mount setup. The carbon hood has a small vent for air intake, but I don't think it's doing much work.
Now I wish I hadn't bought the carbon hood and sold the (modified) Jun FRP hood.
If I had a bit of money to spend I would get an RE-A-style six vent hood and a 99-style aftermarket bumper for the cooling and aerodynamic benefits.
Now I wish I hadn't sold my 99-style corner lights...
I have a boost controller, but it's really only there to decrease turbo lag, according to the previous owner.
07-18-22, 09:26 PM
#4
Triple check for boost leaks.
Boost leaks will increase air intake temps and make it harder for your turbo(s?) to make full boost.
Boost leaks tend to be worse when everything gets really hot as well since the silicone or rubber couplers get quite soft.
But, yes- just heat soak alone can limit boost due to lack of intake air density. Especially on the primary turbo boost of stock sequential twins.
A simple heatshield dividing intake from the radiator waste heat can make a huge difference in AITs.
If you post pics of your set-up we can try to provide more ideas to help.
Boost leaks will increase air intake temps and make it harder for your turbo(s?) to make full boost.
Boost leaks tend to be worse when everything gets really hot as well since the silicone or rubber couplers get quite soft.
But, yes- just heat soak alone can limit boost due to lack of intake air density. Especially on the primary turbo boost of stock sequential twins.
A simple heatshield dividing intake from the radiator waste heat can make a huge difference in AITs.
If you post pics of your set-up we can try to provide more ideas to help.
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gracer7-rx7 (07-20-22)
07-18-22, 09:34 PM
#5
Eats, Sleeps, Dreams Rotary
Thread Starter
Triple check for boost leaks.
Boost leaks will increase air intake temps and make it harder for your turbo(s?) to make full boost.
Boost leaks tend to be worse when everything gets really hot as well since the silicone or rubber couplers get quite soft.
But, yes- just heat soak alone can limit boost due to lack of intake air density. Especially on the primary turbo boost of stock sequential twins.
A simple heatshield dividing intake from the radiator waste heat can make a huge difference in AITs.
If you post pics of your set-up we can try to provide more ideas to help.
Boost leaks will increase air intake temps and make it harder for your turbo(s?) to make full boost.
Boost leaks tend to be worse when everything gets really hot as well since the silicone or rubber couplers get quite soft.
But, yes- just heat soak alone can limit boost due to lack of intake air density. Especially on the primary turbo boost of stock sequential twins.
A simple heatshield dividing intake from the radiator waste heat can make a huge difference in AITs.
If you post pics of your set-up we can try to provide more ideas to help.
Hopefully there isn't an exhaust leak that only shows up when the engine is hot... since that will be much harder to fix.
This is the only relevant picture I current have on hand. The intake is sucking air from the intercooler.
07-18-22, 11:30 PM
#7
OK, I think you have a really good starting point for the track driving you are doing (assumimg the radiator angle is reversed from stock into a "V" mount).
Airflow under the hood has some unusual eddies/currents/flow paths and it is probably the case that the vents on the old hood were influencing the currents in a manner benificial to getting cool air to the airfilter.
Like you allude to with cutting holes in your flat undertray, you have to work on underhood airflow to make it work for you.
You need a cooling panel between the bumper and the front of the IC so more air goes theough IC.
You can seal the sides of the radiator and IC "V" better. I see sheetmetal there, but gaps that should be filled with foam.
Make sure the back of the "V" (nearest the engine pulleys) is sealed off too so all airflow gorles through rad. & IC cores.
Looks like you have a gap on the far Right of rad. & IC (like stock) you can get air for your airfilter from. Build a shroud that blocks IC and Rad. Waste heat and guides air from this slot to airfilter.
Try it out of cardboard and gumtape 1st and when you get something working make it out of sheetmetal so its not a fire hazard.
If you still have windshield squirters you can use that instead to spray water on the IC to cool the core when its heat soaked.
What is the hood? Might be some light trimming you can do to make it work better and still look OK.
Airflow under the hood has some unusual eddies/currents/flow paths and it is probably the case that the vents on the old hood were influencing the currents in a manner benificial to getting cool air to the airfilter.
Like you allude to with cutting holes in your flat undertray, you have to work on underhood airflow to make it work for you.
You need a cooling panel between the bumper and the front of the IC so more air goes theough IC.
You can seal the sides of the radiator and IC "V" better. I see sheetmetal there, but gaps that should be filled with foam.
Make sure the back of the "V" (nearest the engine pulleys) is sealed off too so all airflow gorles through rad. & IC cores.
Looks like you have a gap on the far Right of rad. & IC (like stock) you can get air for your airfilter from. Build a shroud that blocks IC and Rad. Waste heat and guides air from this slot to airfilter.
Try it out of cardboard and gumtape 1st and when you get something working make it out of sheetmetal so its not a fire hazard.
If you still have windshield squirters you can use that instead to spray water on the IC to cool the core when its heat soaked.
What is the hood? Might be some light trimming you can do to make it work better and still look OK.
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07-18-22, 11:54 PM
#8
Eats, Sleeps, Dreams Rotary
Thread Starter
OK, I think you have a really good starting point for the track driving you are doing (assumimg the radiator angle is reversed from stock into a "V" mount).
Airflow under the hood has some unusual eddies/currents/flow paths and it is probably the case that the vents on the old hood were influencing the currents in a manner benificial to getting cool air to the airfilter.
Like you allude to with cutting holes in your flat undertray, you have to work on underhood airflow to make it work for you.
You need a cooling panel between the bumper and the front of the IC so more air goes theough IC.
You can seal the sides of the radiator and IC "V" better. I see sheetmetal there, but gaps that should be filled with foam.
Make sure the back of the "V" (nearest the engine pulleys) is sealed off too so all airflow gorles through rad. & IC cores.
Looks like you have a gap on the far Right of rad. & IC (like stock) you can get air for your airfilter from. Build a shroud that blocks IC and Rad. Waste heat and guides air from this slot to airfilter.
Try it out of cardboard and gumtape 1st and when you get something working make it out of sheetmetal so its not a fire hazard.
If you still have windshield squirters you can use that instead to spray water on the IC to cool the core when its heat soaked.
What is the hood? Might be some light trimming you can do to make it work better and still look OK.
Airflow under the hood has some unusual eddies/currents/flow paths and it is probably the case that the vents on the old hood were influencing the currents in a manner benificial to getting cool air to the airfilter.
Like you allude to with cutting holes in your flat undertray, you have to work on underhood airflow to make it work for you.
You need a cooling panel between the bumper and the front of the IC so more air goes theough IC.
You can seal the sides of the radiator and IC "V" better. I see sheetmetal there, but gaps that should be filled with foam.
Make sure the back of the "V" (nearest the engine pulleys) is sealed off too so all airflow gorles through rad. & IC cores.
Looks like you have a gap on the far Right of rad. & IC (like stock) you can get air for your airfilter from. Build a shroud that blocks IC and Rad. Waste heat and guides air from this slot to airfilter.
Try it out of cardboard and gumtape 1st and when you get something working make it out of sheetmetal so its not a fire hazard.
If you still have windshield squirters you can use that instead to spray water on the IC to cool the core when its heat soaked.
What is the hood? Might be some light trimming you can do to make it work better and still look OK.
I actually already used the windshield washer to squirt water on the intercooler. I had this idea years ago and finally got around to installing a spray nozzle a few months ago.
Actually, yesterday was the first time I actually tried it. It definitely made a difference, combined with removing the mesh from the vent.
No idea who makes the hood. I should be able to double the size of the primary vent pretty easily without affecting rigidity too much. I think I can buy a knockoff RE-Amemiya-style hood for about $400.
Simply going back to an aftermarket bumper (another couple hundred bucks for a used one) would instantly fix the problems and provide other aero benefits, especially with some side skirts to match...
07-19-22, 07:13 PM
#9
Eats, Sleeps, Dreams Rotary
Thread Starter
By the way, does pressure testing the intake system work on rotaries? A friend says that the engine would be so leaky as to make such a test completely futile.
07-19-22, 10:49 PM
#10
Yes, I have sucessfully boost leak tested my rotary by making a plug for turbo inlet with an air compressor fitting-
BUT
You have to also use a plug to seal your exhaust tip, make sure you dont have exhaust leaks and rotate engine by hand till leaking out exhaust port is minimal.
BUT
You have to also use a plug to seal your exhaust tip, make sure you dont have exhaust leaks and rotate engine by hand till leaking out exhaust port is minimal.
07-20-22, 03:01 AM
#11
Eats, Sleeps, Dreams Rotary
Thread Starter
Yes, I have sucessfully boost leak tested my rotary by making a plug for turbo inlet with an air compressor fitting-
BUT
You have to also use a plug to seal your exhaust tip, make sure you dont have exhaust leaks and rotate engine by hand till leaking out exhaust port is minimal.
BUT
You have to also use a plug to seal your exhaust tip, make sure you dont have exhaust leaks and rotate engine by hand till leaking out exhaust port is minimal.
how tight does the exhaust plug need to be?
07-20-22, 11:10 AM
#12
RX-7 Bad Ass
iTrader: (55)
Yep, start with boost leaks. You can plug the exhaust but you don't have to. Typically I pressurize to like 15psi and it will bleed down but you can typically feel and hear the air escaping. Many are in weird spots - a cracked vacuum nipple, a tiny tear in a silicone coupler, etc. If you pressurize to around 15psi that should show anything major. Don't really have to get the car hot, if it leaks cold it will leak hot too.
I would try to at least duct fresh air to your air filter so it's not getting SUPER hot air. That's definitely not helping. Doesn't have to be perfect, just anything you can do to get some clean fresh air to it and maybe shield it from the radiant heat from the IC will help.
Could also be worth hacking 3" or so out of the core of the IC and having it re-welded, then you can move it over to the left side of the car and have a good area for a duct or air box or something.
Also worth doing water injection. Makes a HUGE difference in air temps.
Dale
I would try to at least duct fresh air to your air filter so it's not getting SUPER hot air. That's definitely not helping. Doesn't have to be perfect, just anything you can do to get some clean fresh air to it and maybe shield it from the radiant heat from the IC will help.
Could also be worth hacking 3" or so out of the core of the IC and having it re-welded, then you can move it over to the left side of the car and have a good area for a duct or air box or something.
Also worth doing water injection. Makes a HUGE difference in air temps.
Dale
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Howard Coleman (11-26-22)
07-20-22, 11:38 AM
#13
Is the beer can filling up? I mean, besides the drop in boost are you getting any other symptoms of too much heat?
It's hard to tell if you've dealt with it from the pic, but for me, proper ducting made a difference on hot days. I've also seen a few V-mount set ups that place the intake in the V so it gets fresh air.
It's hard to tell if you've dealt with it from the pic, but for me, proper ducting made a difference on hot days. I've also seen a few V-mount set ups that place the intake in the V so it gets fresh air.
07-20-22, 07:20 PM
#14
Eats, Sleeps, Dreams Rotary
Thread Starter
Is the beer can filling up? I mean, besides the drop in boost are you getting any other symptoms of too much heat?
It's hard to tell if you've dealt with it from the pic, but for me, proper ducting made a difference on hot days. I've also seen a few V-mount set ups that place the intake in the V so it gets fresh air.
It's hard to tell if you've dealt with it from the pic, but for me, proper ducting made a difference on hot days. I've also seen a few V-mount set ups that place the intake in the V so it gets fresh air.
I haven't gotten around to checking how much blowby is in the catch can. Hopefully less than before.
Other than low boost, I don't have any temperature issues. That said, when I had an aftermarket bumper the car would basically overcool on the highway due to the 70C thermostat.
07-20-22, 07:57 PM
#15
Rotary Freak
How long is a lap, heatsoaking completely in an out lap seems very odd unless it's the Nordschleife.
For exhaust and intake leaks, usually a smoke test is good enough - even a fracture should produce a telltale completely cold. WG removed and checked?
For exhaust and intake leaks, usually a smoke test is good enough - even a fracture should produce a telltale completely cold. WG removed and checked?
07-20-22, 09:43 PM
#16
Eats, Sleeps, Dreams Rotary
Thread Starter
Pulling the wastegate would be a huge job for me, since it costs money every time I need to take the car to the shop (because it's not street legal).
I also don't have electrical power (or water, for that matter) where I store it. Maybe I should buy a generator...
I was initially hoping maybe a bicycle pump would be enough air to test for leaks. Hahaha.
07-20-22, 10:22 PM
#17
Rotary Freak
Imagine it's not the easiest thing over there to run a track only car!
One of the guys on a rotary forum down here made a smoke generator ages ago that was very effective and pretty simple. Probably a 12v cigarette lighter tyre pump would be good enough - wouldn't be surprised there's plans out there.....hard to justify spending mega bucks on a pro tool, when there's no power available, ha. Suspect you could hear the woof-woof noise of a bad leak, is the WG a bolted style by any chance?
One of the guys on a rotary forum down here made a smoke generator ages ago that was very effective and pretty simple. Probably a 12v cigarette lighter tyre pump would be good enough - wouldn't be surprised there's plans out there.....hard to justify spending mega bucks on a pro tool, when there's no power available, ha. Suspect you could hear the woof-woof noise of a bad leak, is the WG a bolted style by any chance?
07-20-22, 11:12 PM
#18
Eats, Sleeps, Dreams Rotary
Thread Starter
Imagine it's not the easiest thing over there to run a track only car!
One of the guys on a rotary forum down here made a smoke generator ages ago that was very effective and pretty simple. Probably a 12v cigarette lighter tyre pump would be good enough - wouldn't be surprised there's plans out there.....hard to justify spending mega bucks on a pro tool, when there's no power available, ha. Suspect you could hear the woof-woof noise of a bad leak, is the WG a bolted style by any chance?
One of the guys on a rotary forum down here made a smoke generator ages ago that was very effective and pretty simple. Probably a 12v cigarette lighter tyre pump would be good enough - wouldn't be surprised there's plans out there.....hard to justify spending mega bucks on a pro tool, when there's no power available, ha. Suspect you could hear the woof-woof noise of a bad leak, is the WG a bolted style by any chance?
It's a Trust external wastegate.
07-21-22, 08:27 AM
#19
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07-21-22, 07:41 PM
#21
Eats, Sleeps, Dreams Rotary
Thread Starter
07-21-22, 07:45 PM
#22
Eats, Sleeps, Dreams Rotary
Thread Starter
07-24-22, 07:18 PM
#24
Eats, Sleeps, Dreams Rotary
Thread Starter
Taking a closer look, there's enough space between the sheet metal ducting and the frame of the car to let a bit of fresh air into the engine bay.
I degreased all my pipe couplers and piping and checked for any tears. Hopefully the oil will be less of an issue now that the car isn't siphoning oil into the intake.
The U-bend hose from the compressor outlet to the intercooler inlet is actually a pretty poor fit, I wonder if I shouldn't get some heavy-duty snap ring pliers and adjust the angle of the compressor.
I just noticed that the new vacuum hose clamps I had on my vacuum hoses were too big, so they weren't really doing anything to hold the hoses.
Also, the big fat hose from the boost controller to the wastegate (I think this might actually be an air relief hose?) was a bit loose, and the zip ties on it had gone missing. So I'm going to need to get some proper hose clamps for it.
On an unrelated note, my car doesn't have a blow-off valve... I wonder if that's a problem.
I degreased all my pipe couplers and piping and checked for any tears. Hopefully the oil will be less of an issue now that the car isn't siphoning oil into the intake.
The U-bend hose from the compressor outlet to the intercooler inlet is actually a pretty poor fit, I wonder if I shouldn't get some heavy-duty snap ring pliers and adjust the angle of the compressor.
I just noticed that the new vacuum hose clamps I had on my vacuum hoses were too big, so they weren't really doing anything to hold the hoses.
Also, the big fat hose from the boost controller to the wastegate (I think this might actually be an air relief hose?) was a bit loose, and the zip ties on it had gone missing. So I'm going to need to get some proper hose clamps for it.
On an unrelated note, my car doesn't have a blow-off valve... I wonder if that's a problem.
Last edited by Valkyrie; 07-24-22 at 07:25 PM.