Turbo Surge

[rkreigh]

my current combo is a TE45, 72 lb injector, Trans + with Extreme chip (love it!!) and an older easern front mount. 3.5 MAF, GN1 heads, 206 billet roller, TH dp, XP dbl pumper

at above 10 psi at part throttle, turbo surges pretty bad shifting into 3rd. car studders and then picks back up. doesn't seem to do this at WOT, but with as much power as this combo makes, I can't hook up very well with street tires at WOT so I end up with the car surging quite a bit. it's especially noticeable going into 4th gear (boost gauge flutters down and picks back up).

I need to get some direct scan readings, and talk to the mad scientist (bob) more but is there anything I could do to keep the car from surging???

changing the intercooler or plumbing??? or is this just kinda a side effect of the front mounts and the larger turbos.

would a blow off valve help this condition???

I posted this a while back but didn't really get any ideas on what to do to fix this.

thanks!!

 

[blackbuick87]

One of the bad side effects of a front mount and all the piping, along with a big turbo. Just go WOT all the time

A blow off valve will not help at all, if you set it to activate at 10psi it would be constantly activated

What kind of wastegate are you using, and what kind of boost controller?

 

[TurboDave]

Blow off valve will absolutely NOT help surge.

About the only thing I can think of right now, is to make a change to the post turbo volume. That means, maybe some changes to the intercooler plumbing. Either going up in size or down. It's tough curing part throttle surge, some times it only takes subtle changes, other times more drastic.
You may not be able to cure it 100%.

 

[turbosam6]

My car does the exact same thing, and we have very similar setups. I haven't got to play with it much, but I hear its pretty normal with this turbo.

 

[Steve Wood]

It is fairly common with larger turbos. If we had access to all the various compressor maps, we could make a pretty good prediction as to the affect.

In essence, as turbo size increases, it grows increasingly likely that compressor surge may be encountered at cruise or part throttle acceleration. If one looks at the compressor map for a given turbo, any condition of operation that ends up to the left of the the surge limit line may create surge. It should be noted that various compressors have different slopes on the surge limit line and some are more vertical than others so making blanket statements with regard are not guaranteed to be right.

Also, techically, the phenomenon of compressor slam which occurs when the throttle is suddenly closed at high boost (and which a bov can help if it can handle the volume) is very similar to what happens with compressor surge when the throttle blade is open only slightly at cruise and the compressor gets confused trying to make boost against a restricted passageway (except, a bov is useless in this case)

If you don't have Hugh Macinnes' s book, "Turbochargers" or Corky Bell's book, "Maximum Boost", there is a very good write up by John Estill in

http://www.gnttype.org/techarea/turbo/turboflow.html

I don't know if it is fact, or observation, but I have noticed in my own case that the larger the IC volume, the worse the problem. Again, this is my observation and may, or may not, be relevant.

I have also noticed, again on my own cars, that fuel mixture may move the point of surge around a bit. Might be coincidence. I know of nothing that supports this observation.

 

[Reggie West]

Just a thought here.

Check to see if the motor is surging where the second fuel pump kicks in. If this is the case then you are doubling the amount of fuel going to the injectors which will cause some surge problems.

Usually surging is from the fuel map being way out of whack at certain points.

The reason I am suggesting this is your surging is happening at 10 psi and that is where the double pumper could be set too.

Hope this helps

 

[TurboTR]

You just usually learn to drive around it. There is no good fix for it really. You could make it less likely or reduce it by increasing the volume flow through the compressor at a given boost level. You may find that a more restrictive MAF sensor reduces it for example, but the reasoning is not immediately obvious- has to do with decreased inlet density (from lower inlet pressure) = higher volume flow But it's usually not a big deal in practice though, avoiding part throttle surge. Exactly as Steve said, closing the throttle or otherwise reducing flow while maintaining boost just moves the compressor operating point towards/past the surge line.

TurboTR

 

[blackbuick87]

How much of a factor is the partially closed throttle blade in the equation? Would a larger throttle body help to eliminate the surge, since it would allow more airflow at a given throttle opening?

 

[Steve Wood]

If you look at a compressor map...you find air flow across the X axis and boost ratio up the Y axis.

If you examine the position of the surge limit line, it becomes obvious that high boost, low air flow can kick you to the left of the line.

Therefore, I would think that the TB size is not the determining factor. It is the low airflow being passed versus boost.

If you read John's article on the mailing list tech section, he gives you the calculations required to turn the X axis into something more readily usable. Once you get up in turbo range, it gets hard to avoid. I guess a boost controller that keeps the boost down at low airflows would hide the problem? Not sure that is what we want for best performance, tho', in a race environment.

Todd is right...you just gotta learn to drive around it.... It can be a pain at times....such as coming up an on ramp and the guy in front of you can't get out of the way and your foot puts you into the surge zone....

 

[G McCall]

My "surge" is crusing in a 30-40 mph zone. Car acts like its hitting on 4 cyl. bla... bla.... bla. I'm told its characteristic of the big IC and PT 72 etc. My remedy is to speed up.

 

[TurboTR]

Wait- you're implying that you have boost at a 30-40 mph cruise condition? Hmmm.

TurboTR

 

[G McCall]

Originally posted by TurboTR
Wait- you're implying that you have boost at a 30-40 mph cruise condition? Hmmm.

TurboTR

huh ? .....Naw. My post may have gotten away from the real surge issue. I was just describing my surge problem.

Rkreigh's problem is different being he is under boost. I did not see him post what chip etc he was using, but I will offer this thought.
Years ago it was discovered you could not try a half throttle burst from certain speeds with some vendors chips (without race gas). Boost would come in before fuel and cause a momentary lean condition. Knock gage would peg the lights out. I learned no half punches with that chip. It was peddle to the floor or easy on the gas. ( Of course Vendor said the chip was not for the street, but I didn't want to drive the car without it). I don't remember surging though.

 

[J Banning]

I have INCREDIBLE compressor surge with my little PT51 turbo. I get a huge stumble, and it feels like the motor mounts aren't bolted up (they are though).

This happens at anything over 5# boost and doesn't matter what speed or grear I'm in. This is NOT dependent on my current combo (72's, ME16, ported irons, Powerstroke IC). It did the same thing prior to those mods (ATR frontmount, 009's, ME16, stock heads & cam). Only did it with the frontmount though... the problem went away when I took it off and put the stocker back on. The core on the Powerstroke IC is larger than the ATR, but the pipes are shorter in length.

What do I do?

-Banning.

 

[xlr8ngn]

Someone needs to build a solenoid operated inlet vane so that when the car is surging, you can program when in that condition (TPS voltage or specific PSI) that the vanes close, increase compression ratio, and help bring it back to the right side of the curve.

 

[325DR]

Originally posted by J Banning
It did the same thing prior to those mods (ATR frontmount, 009's, ME16, stock heads & cam). Only did it with the frontmount though... the problem went away when I took it off and put the stocker back on. The core on the Powerstroke IC is larger than the ATR, but the pipes are shorter in length.

,


ATR makes a front mount intercooler?

 

[J Banning]

Originally posted by AintGoinSlo
ATR makes a front mount intercooler?

Yep.

Not sure if they still have it in their catalog, but they did a few years ago. Rough dimensions (from memory) are: 30" wide, 12" tall, and 3" thick. Uses 2.5" pipes that are routed down under the car & back up to the motor (like most other frontmounts).

See a picture of it here:
http://banning.freeplace.net/ford_ic/images/atr_powerstroke_comparo.jpg

-Banning.

 

[rkreigh]

I thought about going to a different front mount intercooler (bigger) but this would probably make it worse. it does make sense that the "surge" is affected by the second pump coming on, I think it is set for 10 PSI.

its only annoying because on street tires, the car makes too much power to go WOT (which is great!!)

so I reduce the throttle, and it surges!! sometimes its a bit hard to drive around.

but I won't give up the big turbo for anything, the TE45 is still responsive on the street, and really pulls hard.

thanks for all the detailed explanations, I will do some direct scan runs and see if I can tune some of it out, but at least now I understand better what is happening.

thanks!!!

 

[TurboTR]

IME 10 psi is way too early and will bump the fuel pressure up and out of control. Heck I think 10 psi is still too early even for my 274"/GN1's combo ;-)

TurboTR