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Hey all, I am looking to bounce some ideas/diagnosis off some forum members regarding a boost taper/turbo efficiency/on-track elevated IAT issue I have been fighting.
Relevant Build Specs:
MS3pro
Fully forged decked and balanced BP4W (84mm 9:5:1 ST Pistons//Manley Rods//ARP Studs//ST Valve Springs//Fluidampr//Re-route)
R8 Coils
VICS Manifold
Garrett 2560R (Now a 2871R, keep reading for context)
CX Intercooler Kit (2" hot side//2.5" cold side, IAT sensor installed in cold side end tank)
Log-Style Manifold
2.5" Bell Tuning Downpipe (divorced wastegate pipe that dumps back into the DP)
2.5" stainless exhaust all the way back, no resonators, no muffler
Car is a purpose built drift car. It gets driven hard and absolutely shreds. The power goal this year is around but definitely not more than 300hp/280 ft-lb at no more than 18psi on 93. Put down 288/275 before I noticed the efficiency drop off and called it quits and lowered boost a smidge for the next few events I had lined up. Here are the symptoms I am dealing with -
If I set duty cycle to yield around 14-15 psi, I can hold it to redline no problem. If I increase duty to reach my power goal (17-18 psi) I get a very noticeable drop in kpa (14 kpa or so) over the course of the pull to redline, this is also why my power was falling off on the dyno. Just can't hold that 17-18 to redline. But will never drop below 15psi. IATs ambiently and over the course of a pull looks standard. However, once I hit the track, and start pushing the car hard (2 hot laps max//45 second laps//Lots of WOT) my IATs climb to uncomfortable levels. First event was 86F ambient super humid and max IAT saw 180F with the MAT just steadily rising over the course of the lap. TOO HOT. Yes, my MAT based retard map is configured to combat this and my link knock light never detected det.
I suspected the 2560R with a year and half of events on it was getting tired and blowing hot air and running out of its efficiency range at 18psi. So, I cost effectively upgraded to the 2871R (13 psi internal WG) which I knew would leave me with plenty of headroom. The problem still persists and presents in the exact same fashion with the 2871. So there must be a weak link in my setup causing this. I can only imagine the boost taper and the unacceptable IATs on track is connected? Turbo blowing hot air due to some sort of efficiency problem? Boost leak test did not locate any obvious leaks hot or cold side. I would also imagine that a boost leak would show itself at 14-15 psi as well...but is it possible that a small enough leak might not present itself up until a certain air pressure and then slowly starts bleeding off whilst trying to maintain the target and over spools the compressor? Could the 2.5" exhaust diameter cause these symptoms? what else might cause this? I'm always happy to upgrade components to meet goals, but I would rather find the weak link and identify it and learn vs. just buying new parts/taking shots in the dark. I have attached the tune, a log from a brief road tuning session, and a day on track.
Keep in mind, with drift, the car is sideways under lots of load at typically slower physical speeds for the vast majority of the lap so the air front doesn't hit the intercooler fins quite the same way as a track car. I have no idea if this affects IATs dramatically or not. Not a lot of data on turbo drift miatas yet. Water temps were great. What do you guys think? If you've gotten this far, Thanks for listening!!
Car is in the follow position
Last edited by Nick Stacy; 06-28-2022 at 01:55 AM.
My guess, after reading hours and hours of posts here, is that you have removed all ducting on the front of the car, and air is going around the heat exchangers vs through them. I would put the bumper back on, and an undertray, and see if you still have the issue.
My guess, after reading hours and hours of posts here, is that you have removed all ducting on the front of the car, and air is going around the heat exchangers vs through them. I would put the bumper back on, and an undertray, and see if you still have the issue.
J
Probably not the case here. I have great on track water temps and extremely good cruising temps. Also my buddy with the purple NB2 is running acceptable IATs for the conditions and has no ducting either. However he is running only 13 psi peak pressure and has a different exhaust setup
High level guesses based on info above. Log style manifold and 2.5" exhaust are a potential hot combo for exhaust backpressure no matter the turbo. Red hot exhaust manifold radiating to inlet area. Retard strategy for high IAT is then magnifying the issue and potentially taking you on an ever increasing hotter journey. Hotter it gets, more retard, more exhaust heat, more IAT heat, rinse and repeat.
I would try is getting your air filter out in the cold. I'd do it by bringing it out into the inner wing - in your case it will be in direct cold air at the front of the car as you have no front bumper. Your friend's looks like he may already be doing this. Easy to enlarge the air hole in the inner wing to get a pipe through it.
I double check all your clamps etc. for a boost leak as well. Worm clamps like to loosen off with heat cycles. Anything in the intake side could be leaking - if so your turbo will be spinning harder and hotter to make your targeted boost.
I'd probably drop the boost so you are not utilising any material retard strategy until you bottom out your issue. Otherwise you are probably sending yourself round in circles for the sake of making hot air and not power anyway.
High level guesses based on info above. Log style manifold and 2.5" exhaust are a potential hot combo for exhaust backpressure no matter the turbo. Red hot exhaust manifold radiating to inlet area. Retard strategy for high IAT is then magnifying the issue and potentially taking you on an ever increasing hotter journey. Hotter it gets, more retard, more exhaust heat, more IAT heat, rinse and repeat.
I would try is getting your air filter out in the cold. I'd do it by bringing it out into the inner wing - in your case it will be in direct cold air at the front of the car as you have no front bumper. Your friend's looks like he may already be doing this. Easy to enlarge the air hole in the inner wing to get a pipe through it.
I double check all your clamps etc. for a boost leak as well. Worm clamps like to loosen off with heat cycles. Anything in the intake side could be leaking - if so your turbo will be spinning harder and hotter to make your targeted boost.
I'd probably drop the boost so you are not utilising any material retard strategy until you bottom out your issue. Otherwise you are probably sending yourself round in circles for the sake of making hot air and not power anyway.
These are the easy things to try first IMO
See my air filter location. It sees quite a bit of direct ambient air. I definitely believe the cause of the high temp is coming from the turbo outlet, not the air entering the filter. My buddy’s filter placement is straight off the turbo further back in the engine bay and he has no louvers and his idle MAT temp is a good deal higher than mine. My underhood temps are solid, hot rad fan air goes straight out of the hood. I have never seen the manifold or turbine red hot, but I have also not looked at it seconds after pulling off track.
I definitely agree with you, I will be lowering boost pressure on track until the cause is found. I am going to do a proper and thorough boost leak test over 20-25 psi and confirm there are no small leaks. Vacuum at idle is right at -20 so I don’t suspect an intake leak but if it’s small enough it could be possible that it bleeds enough boost to cause this. I would need to do something fancy to find an intake leak that small. I also may try pulling the exhaust off the downpipe and taking the car for a pull or two and see if it holds the higher pressure to redline to rule out the straight 2.5” to the back being a restriction. I don’t see that being the issue though.
On another note, I have seen widely varying MAT based retard maps. Can anyone chime in on what is too conservative/too aggressive for a racing application?
Last edited by Nick Stacy; 06-28-2022 at 02:30 PM.
Restrictive air filter
Hot air going into air filter
Blowing wastegate open (high backpressure pre-turbine)
Boost leak (test entire system to +10 psi above expected boost level)
Dying turbo (check for any shaft play)
I've seen all of the above cause tapering boost at high RPM.
Restrictive air filter
Hot air going into air filter
Blowing wastegate open (high backpressure pre-turbine)
Boost leak (test entire system to +10 psi above expected boost level)
Dying turbo (check for any shaft play)
I've seen all of the above cause tapering boost at high RPM.
I have seen the same issue with a quality K&N so can probably rule filter out. Will report back with a proper boost leak test. New 2871 so turbo is happy, no shaft play, same issue with the 2560. I thought about the wastegate as well. It’s a 13 psi internal. What’s the best way to test for this? Watch the wastegate arm visually on the dyno when trying to maintain the target psi?
Alright y’all problem most likely identified. There is an o-ring that goes around the bov piston and it has slipped off the piston/plunger. You can see the slow leak in the video. The o-ring is in good shape and has probably been off the plunger for a long time. This seems like a design flaw so I will probably switch to a new different bov. I’ve actually seen the o ring slip off like 2 years ago and I reassembled the bov. Thanks for everyone’s input. I don’t have a good way to test this without getting a new bov and sending it so I will update the forum when I know for sure so people in the future can hopefully get some insight.
yeah, checking wastegate on dyno would be good. Or try upping the spring pressure, swap from a 13 to 17-18 psi spring and see if anything changes.
I'm running a 6258 but can confirm with other turbos that sometimes even though the WG spring rating "should" work doesnt mean it always works.
FWIW i have 0 issues hitting 22psi with a 14psi spring but i can barely hold 13psi above 6000 with a 8lb spring. all things being equal besides the spring.
Nonetheless boost leaks are always an issue.
On a drift related note, how long do 5 speeds last ya around those power levels? and what tire grip level? I've lost 2nd gear and 3rd gear in a different trans and i'm turning it down for the track to find a reasonably lasting setup. that and because of temps.
I'm running a 6258 but can confirm with other turbos that sometimes even though the WG spring rating "should" work doesnt mean it always works.
FWIW i have 0 issues hitting 22psi with a 14psi spring but i can barely hold 13psi above 6000 with a 8lb spring. all things being equal besides the spring.
Nonetheless boost leaks are always an issue.
On a drift related note, how long do 5 speeds last ya around those power levels? and what tire grip level? I've lost 2nd gear and 3rd gear in a different trans and i'm turning it down for the track to find a reasonably lasting setup. that and because of temps.
Legit FV Greddy BOV ordered and on the way so diagnosis should be confirmed in a few days. My 5 speeds 3rd gear blew after about 3 events. I have been on the six speed for a little over a year/8 ish events now and it’s holding up great 🤞🏻 the idea is to run as much power and torque as possible without going through six speeds every season. I don’t have any issues with temp. Even when it was 101 ambient at the last event. But I have no bumper, water and wetter, re route, double fans and shroud, and louvers. I am running 205/50/15 Hankook Ventus for burners and a 195/50/15 200tw up front. The kookies are a cheap 500tw rated tire and are affordable, have great life, are easy on the drivetrain and keeps up with C6s, LS 350s, SR20s, and 2Js with 200tw tires no problem. I love this chassis.
I would try is getting your air filter out in the cold. I'd do it by bringing it out into the inner wing - in your case it will be in direct cold air at the front of the car as you have no front bumper. Your friend's looks like he may already be doing this.
If anyone is curious, both the boost taper and high IATs were resolved by upgrading to a non-shitty non-chinese intercooler and moving the wastegate reference point to the new intercooler end tank. amazing IATs and dead flat boost curve now.
I was seeing huge IAT rises on my CX cooler, now my IATs only rise 5 degrees over the course of a 5th gear pull and my on track IATs dropped 60-80 degrees. Also, i am seeing less pressure drop over RPM now. However, I have a tubed front end. So if you try to fit this cooler on a stock car with stock metal/frames up front, it probably won't fit. Hard to say, this thing is pretty huge.
Looks a lot like the FM unit that I have. Unfortunately, the FM unit is also painted silver which reduces its heat transfer. I have been contemplating going to a tube & fin design over the bar & plate.
06-27-2022, 07:50 PM
Built BP4W Turbo Boost Taper/High IAT Diagnostics
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