So this weekend was drivin around with a PSD'er from Nebraska, and he was intrigued by my truck's turbo flutter..said he had never heard anything quite like it.

So I did a little looking online, with some mention that turbo flutter can potentially be a sign that there's something wrong.

My flutter has always seemed harmless enough, and I assumed it was due to the fact that I have 4" turbo-back and that the lack of muffler just "allowed" me to hear something that was always there.

She only flutters when I am just rollin around town 30-40" MPH and barely touching the throttle. She seems to flutter when the truck is just idling around town. My turbo boost and EGT's are great, no complaints. By flutter I mean that cute little hummingbird noise the turbo makes that is most easily heard out of the exhaust.

Turbo experts, any thoughts? I've seen you guys speak of flutter before but I never recognized it as something that can be harmful. Perhaps an expert explaination of how and why, exactly, turbo flutter exists would be helpful.

 

The flutter is just a result of the straight pipe you are running.

Enjoy the sound

 

2nd what pocket said normal sound w/straight pipe

 

Can anyone here (ahem, Kris) anyone at all (i.e. Kris) possibly explain what causes turbo flutter, not the basic explaination but the extended complicated one. Someone here (uhh, Kris) must be able to explain in detail.

 

It isn't harmful, but it's very inefficient. The engine has to constantly work against those pressure waves to keep the exhaust moving out the tailpipe.
They could have done better with the firing order.

 

I'll give it a try. Kris has a way with words, doesn't he?
BTW my wife spells her name Kriss.
Exhaust flutter is caused by an exhaust system that is not "tuned" to have all the passages be of equal length and taking the exact same amount of time to travel from the exhaust port to the turbo inlet. Some take less time than others to arrive at the same spot. When you have two pulses arriving at the same time you have a pressure spike and the inverse of that situation is that there is a "vacuum" of sorts that needs to be filled. Well, you get the engine turning over at 1500 rpm and all those uneven pressure waves start to work off of each other and you start to hear that fluttering noise.
Hope this helps.

 

Ahem, Ahem. Like kwikkordead mentioned, the reason you hear the flutter is because of the exhaust pulses out of the cylinders at different times and it is not a smooth wave of pulses leading into the turbocharger. Vacuum and pressure spikes. When the pulses hit the turbine wheel, they are chopped up and only small bits of "sound" are "let out" at each vane of the wheel. It is perfectly normal and i can notice it on a completely stock-exhaust truck too. Just the fact that you have an opened exhaust is the key factor to hearing it better. Tell your buddy he is wrong. Once you delete the EBP Valve in the exhaust, the flutter is alot more apparent, as the exhaust can exit the turbine wheel, still spinning in the same direction, the valve is not there to break up the spiral flow and straighten it out. I believe it could also be the cause of the drone, spiraled exhaust flow reverberating in the pipe. The exhaust keeps spinning in that same direction, and when i had my straight piped horizontal exhaust i could even see smoke spiral out of the pipe. I love the sound and it is one of the reasons i went to stacks. You can hear it really good in the better version of my stack video. When its idling

Oh and Kwikkordead, im pretty sure with a different cam, jody can change the firing order. That might be something to look into. Custom headers will also help channel exhaust gasses to "pulse spool" the turbo, and make a smooth wave of exhaust pulses... like you hear the pulling Cummins soopsoopsoopsoopsoooooooooooo spooling the turbo at the beginning of a pull.

 

I get a kick out of Kris. Very bright kid with a bright future. I thought he'd get a kick out of my bid for his attention.
Kwik you should know I appreciate your explaination just as much.

So...flutter is esentially backpressure pushing back up against the back end of the turbo? you say it's caused by an inefficient exhaust system. My brother is an exhaust man and has been extremely enthusiastic about building me a new exhaust. Perhaps a well engineered system will help this?

Edit- I think I understand now. And now it makes sense as to why it makes that particular noise..the sound waves as being "chopped" up by the spinning turbine wheel. Cool. I don't mind the sound at all but dislike the word "inefficient".

Thanks guys!

 

Only an exhaust system between the cylinder heads and the turbocharger will help this. Doing a system after the turbo will have no effect, no matter how many curly-ques and loops you have in it. It's not an easy task generating a "good" header and exhaust system without knowing ALOT about the exhaust pulses and the firing order these engines have. Most all of us just have to live with it, and i can.

 

Well, I can live with it if it's harmless, no problem. As I said before, I think it's kinda cute (what a chick thing to say, isn't it?).

I really wanted to understand WHY it happened. Now I do, in an elementary way at least. Thanks Kwik, Kris...Pocket and Mudrat.

 

I think a set of equal length headers would be about as far as I would go for this. That ought to negate the poor firing order problem with the stupid, but very durable cast iron log style OEM units. Having said that, I am living with my current setup as it does not bother me that much. $$$$$

 

I guess the engineers had to make due with the room they had available in the engine compartment. Think of it this way:

The engine firing order produces exhaust pulses in the exhaust stream very unevenly. However, it's the ONLY way to make a V-8 run. EVERY modern v-8 out there (gassers incl.) utilize a Left bank (L) and Right bank (R) of cylinders. It matters not how the cylinders are numbered be it 1-2-3-4 on the right bank and 5-6-7-8 on the left or 1-3-5-7 on the left and 2-4-6-8 on the right, or ANY variation thereof, the crankshaft only allows 2 cylinders on any given 90 degree rotation to be at top dead center at once because ALL 8 cylinders NEED to fire every 720 degrees of crankshaft rotation. The camshaft only decides which of the 2 cylinders at TDC at that time is on the compression stroke or exhaust stroke.

I guess back to the reason the exhaust is choppy.....
The firing order of the v8 engine causes the exhaust pulses to exit the cylinder heads in a "R-L-R-R-L-R-L-L" pattern. Any modern V8 will have a similar pattern. It's not possible to have a smooth L-R-L-R-L-R-L-R pattern (or I"m sure it would have been done by now). It's all due to the crankshaft design and camshaft corellation. Now, take these exhaust pulses and pipe them through unequal length manifolds and unequal length up-pipes to a turbocharger that has an inlet biased toward the driver's side (in the case of the 7.3L). During the 180 degrees of crankshaft rotation that has either two exhaust pulses or a huge gap in the exhaust flow, you get an uneven pressure pulse from each cylinder head. Pressurize the pre-turbo system and that just adds to the harmony...or lack of.

Cody

 

To add to what Cleatus said, I heard somewhere that it's possible to make an even firing V-8 engine, but it requires a flat crankshaft and then it's hard not to make the engine shake from it's own vibration. F1 racing engines had that design for a while.
But this is all just rumors that I heard, nothing documented.

Ferrari makes an even firing V-8 or at least one that sounds like one. I had a chance to lean over one at school one time and it sounded like a straight eight. It completly lacked the typical V8 rumble that we are all accustomed to. It sounded a very similar to an inline 6, but with more cylinders.

 

ahem, ahem
My EBPV went bye bye, AND MY FLUTTER WENT WITH IT.

Want a sound clip?

 

My EBPV went bye bye, and now i have more flutter. i also have a 1.15 housing.