Trade offs

[Turbo11T]

Is there a tradeoff backpressurewise to running a smaller turbo that is sacrificing low speed driveability for trying to accomplish a turbo that will spool super fast? Turbos create more backpressure and if you run a larger turbo you would think that would mean less backpressure and likely slightly slower spool. But I wouldn't call it lag because the engines of today are very torquey. So I would assume that if the engine was allowed to flow well with backpressure very close to stock in regards to intake pressure then it would run well preboost?

Anyone understand my thinking?

I think must turbo sleds run good when on boost. But it is the slow speed driveablity that suffers. Especially on a 2 stroke.

 

[Turbo11T]

Just thinking outloud

 

[hobbes]

Just thinking outloud

There are definitely back pressure issues no matter what size turbo you run on a two stroke. Almost all turbo kit companies run a stock stinger size with the same diameter turbo inlet pipe. So by sticking a turbo on the back of that pipe system you are increasing your backpressure by quite a bit. I'd love to see what the pipe pressures are just off idle with and without a turbo kit with the stock diameter stinger. It has to be a huge difference IMO. Some companies have found that by moving the turbo to the expansion chamber portion of the pipe or increasing the diameter of the pipe outlet, they are seeing closer to stock backpressure and increasing throttle response by a ton. I'm just a layman, but a sure seems like sound science to me. I rode a kit with increased pipe diameter for 2 years, and it was light years ahead of the stock diameter kit I ran before for both throttle response and spool quickness.

 

[gmustangt]

First off , I think we all understand we need X backpressure for Y boost. Even NA we need backpressure.

I've ran a backpressure gauge on my sled and it was nothing alarmingly high. Its dependant on your exhaust housing and wastegate setup. Understanding how the pipe works is also important

 

[Turbo11T]

First off , I think we all understand we need X backpressure for Y boost. Even NA we need backpressure.

I've ran a backpressure gauge on my sled and it was nothing alarmingly high. Its dependant on your exhaust housing and wastegate setup. Understanding how the pipe works is also important

Agreed obviosly. But it would be interesting to know what stock back pressure is compared to back pressure with a turbo before the turbo spools. Once the turbo is spooled the system evens itself out. I am talking off boost back pressure.

 

[brycter]

back pressure changes hourly on the hill. we have done a tone of testing here. and made quite a few adjustments over the year, adjustments that you would not see unless shown. we do see huge gains with no silencer or can. if back pressure get to high and you go above one to one to soon. you will burn the exhaust side of your pistons off. we always try to stay about 2.5-3.5 lbs of back pressure at idle and then stay as low as we can. on my kits your back pressure will be a constant 5 lbs over boost at 12lbs. on a 0 degree day.

I have built bleed pipes with a rave valve on it that would bleed pressure off at a certain pipe pressure. it works great. but not repeatable on every sled. I think it is because manufacturing allowances.

I will tell you if you can control back pressure. your sled will run better and your tune will be more stable.

 

[gmustangt]

Agreed obviosly. But it would be interesting to know what stock back pressure is compared to back pressure with a turbo before the turbo spools. Once the turbo is spooled the system evens itself out. I am talking off boost back pressure.

I don't think there would be much difference stock vs turbo in this case. The pipe is not seeing enough cfm at the lower rpm for it to effect back pressure. Your not on the pipe yet. This is the job of the exhaust valves on the bottom end, until you have enough cfm flowing in , then valves open and its up to the pipe from there.
I know on the sled I built (pro rmk) from a fueling standpoint it was happy with oem duty cycle on the bottom end and it ran good...wasn't a need to pull any

 

[Turbo11T]

I like the rave valve idea.