Emap (Exhaust backpressure) data

[redrkt]

I thought there was a thread already on this but I I could not find it. Would like to gather emap data on different turbo setups.
I have been running a sleeper 20g with a large clip (20*) 5h turbine wheel in a ported 6cm turbine housing. Generally emap is about 10 psi higher than manifold pressure except at higher boost and rpm. Above 6k rpm higher boost will start to drop off from 25-28psi to 20ish psi by 7.5k but e map will stay steady around 35psi. If I just run 20 psi it can hold that pretty steady and e map is 30 psi it the top.
I plan on swapping back to a 9 blade 6h turbine in the future and compare that data. I didn't monitor e map when i ran the 6h the first time.
If anyone else has data they would like to share or link to the thread I couldn't find that would be appreciated.

 

[danl]

I don’t have data to directly support your question but from memory Robert discussed this a bit here:

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Hopefully this helps you out. From memory, if you have a race car getting emap closer to 1:1 is ideal. For street cars with a wide power band 1:1 may not be the way to go. Just listen to Robert’s comments on it. He really is a treasure for the turbo and DSM community.

 

[biglady112]

I live at 6000ft. So things vary a lot compared to some.

However, I generally see turbos give up(dyno proven) in the 1.4-1.6:1 range here in Colorado. That is from td05 stuff to 80mm. And this is not car or engine specific. I see the same data on every platform.

I have yet to see a car actually continue to make power past that. And seen cars actually lose power as they creep closer to 2:1.

The only way to know is to put the car on a dyno and turn it up until it stops making power. Then back it off a hair. My experience I feel is quite solid as I monitor back pressure on as many cars as I can.

It is pretty easy to tell when you are out of turbo. The back pressure will continue to rise the whole time and your boost will level off or start to drop. Which you are experiencing. When you loose control of the turbine is when you have gone too far.

You won’t see any actual gains with the larger turbine on that small of a turbo. I built a max effort 14b car. It ran a 10cm T3 housing, GSC S3 cams, sheet metal intake and a very serious I beam engine. The car would spike to 19psi and be down to 12psi by the end of a run. I think turbine pressure was right near 30psi but, held the entire way. Anymore and it would sky rocket.

It was so bad at top end power production you could feel the car lay over. I shifted that thing at 6300 in first, 6100 in second and 5600-5800 in third. Any more rpm and the car would slow down.

 

[redrkt]

Appreciate the replies. Yeah I remember FP sharing a lot of data during their turbo testing back in the day. Some might still be on evom I will check it out too.
Your experience with the max effort 14b is crazy thanks for sharing that. Good stuff.

The response is much better even with a heavily clipped 5h vs a 6h specially for a street car. For drag race I am curious if the 6h may get the emap closer to 1 to 1 at higher rpm. Basically wondering if the 6h would make more power above like 5500 compared to the 5h. It will lose midrange on the street but may run a better 1/4 mile. Like I said currently my emap stays roughly 10 psi over boost no matter the rpm, unless I try to run 25-30psi then boost drops off to 19-20 psi at high rpm and the emap just holds 10 psi over the peak boost until redline. Emap ratio is usually about 1.5 to 1 until boost falls off then it climbs to about 1.75 -2.0 to 1 by redline.
Still stock engine and cams, stock intake manifold. Would also like to try retarding the exhaust cam or swap in some fp2s with a jmfab smim to see how that affects things. Also would like to try swapping in a higher flowing comp wheel eventually.

 

[redrkt]

Just stumbled on this. More good info from Kiggly.

Anyone *know* ex. mani. backpressure number?

I've heard that a crude estimate for backpressure in the collector or just upwind of the turbine is roughly 2xboost. I have some guesses as to why this might be, but I wonder if anyone knows what it is, either from theory or from direct measurement. I read a post a long time ago and forget...

www.dsmtuners.com

 

[Kevin Jewer]

Older thread but some quick numbers. On 16g type turbos I usually settle in around 2:1 on EMAP:IMAP. 1.7 at least. When the back pressure starts to climb way faster than boost you've generally found the compressor limit. Being just at the beginning of where it takes off is a good place to be for max effort stuff. Any higher you just hurt parts. I can wipe out a thrust bearing in a 16g in one pass if back pressure is too high. Or set it to where I run 9.9 to 10.0 second quarter mile ETs and it lives forever. The numbers vary with displacement and whether or not it's intercooled, but a simple example, intercooled 2 liter I run 20 psi boost and 45 psi back pressure max.

Getting into the 35R sized stuff, which I have a lot of experience with, the older tech turbos or Chynese stuff I often run in the 1.5-1.7:1 range in T3 housings. Older HTA turbos do better at around 1.4:1, and the more recent Xona Rotor stuff does extremely well at around 1.2:1.

On my 7169S I have to work pretty hard to get back pressure over 1:1 even in the little T3 housing and smaller X3C cover. Being non intercooled I'm over 70 psi max effort and the back pressure is still less than 80 psi with all the nitrous and M5.

I've run turbos between 0.6:1 and 3:1 and will say that wherever the turbo in question maxes out (back pressure curve turns skyward, minus a couple psi boost), is where it runs the best ET. You can optimize the combo to make use of high back pressure turbos, or low back pressure turbos, just have to set it up accordingly.

 

[redrkt]

Thanks for the info I know you have a ton of experience. Stoked to see you reply.

I think i remember you talking about using the e map pressure signal to the top of the wastegate to help keep it closed? I was thinking of trying something like that but use the e map as the pressure source for the stock wg instead of the intake manifold or compressor housing. I'm not sure how well it would work with the BCS bleeding it off things might start to get hot. I could use a bunch more coiled copper tubing to try to keep it cool.

Track opens soon I plan on testing the current 20* clip 20g then maybe back to the 9 blade 6h then to the old PTE gt35.
How is the spool/ response of that 7169s and what a/r is it? That emap is impressive in a t3 footprint. I always kinda thought response is going to be somewhat proportionate to e map.

 

[Kevin Jewer]

I've used exhaust pressure on the side port, since it's already spent it won't contaminate the O2 reading when it leaks past the WG valve stem. This is really only a problem on my compound setup where the HP gate is recirculated before the LP turbo and eventually meets the O2 sensor.

I DO use boost pressure to the top of the gate though, usually with a mini-regulator, to basically make for an adjustable WG spring. Dome pressure control with an ECU or dedicated boost controller that can do it is a fancier version of this, but I like simple mechanical shit whenever possible.

It's always hard for me to judge the spool up of a turbo the size of the 7169s since I need nitrous to spool it no matter what. On the 35R stuff I can still spool without nitrous and at least judge relative changes, even though I can't generate an RPM number that people are accustomed to. But it's still a pretty small turbo and still responds well to having to pedal it etc. The T3 housing is either a .82 or .85, I forget which one I have. There is a 1.06 available but I have to assume that will only slow the turbo down and keep me from maxing it out. Might be useful on larger displacement engines though.

 

[redrkt]

Thanks for the info. I might have to try to use e map for the wg boost control source on the stock wg actuator. I know its is minor thing but I figure way that way would eliminate the boost leak created by the wg solenoid. I like to try to keep things simple too.

That 7169s turbo is sick. Turbo tech has come quite aways since early 2000s.