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Boost pressure in 2nd


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Hi guys, my bike has seemed a lot slower over the last few days. I've noticed if going wot from first into top of second, I'm only building 10 psi. (Wastegate set to 14) This is with +1 -1 longer gearing BTW. This seems low, and the bike feels a lot lazier too. In 3rd to 4th I can tickle 13.

My current suspects are small boost leak, boost controller, or failing turbo. When I disconnect the charge pipe before the plenum with the bike running and cover the side that connects to the turbo housing with my hand, the bike dies. If I blow into the plenum, it comes out of the pipe that goes from the compressor to the plenum. I thought it would go through the turbine side of the turbo, not the compressor side. Is this a sign of a fucked seal? Thanks.

Edited by rerb
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Not sure what you are trying to say in the lower bit?

If you block the compressor discharge, you effectively stall the compressor and by connection the turbine which produces large backpressure hence why engine stalls.

'Blowing into the plenum' - how? Via the charge pipe or the WG pressure line? There is no physical air pathway between the hot side and the cold side unless it circumvented multiple seals and bearings through the core!

In lower gears, engine acceleration can be fast enough that next gear is required before desired boost is reached - this is the balancing act between turbo sizing / boost required / turbo response / power output required / V max required. There is never one solution that satisfies everything!

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If your manging to hold WOT in 1st or 2nd then somthing is seriously wrong with it.

Your not likely to see full boost in the lower gears due to the short time you spend in them due to them being shorter, and not being able to use full throttle due to wheelies.

Best bet get it on a dyno and see what its doing, not only can you check fueling you can have a good look/feel round for boost leaks etc whilst its running and under load as long as dyno operator is cool with that.

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Think my turbo blew a seal, started spewing oil into the charge line. I'll check compression too but I think there's crossover between the hotside and coldside because just the day before it was a total rocketship. Motor feels the same before boost but I'll still check compression.

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18 hours ago, rerb said:

Hi guys, my bike has seemed a lot slower over the last few days. I've noticed if going wot from first into top of second, I'm only building 10 psi. (Wastegate set to 14) This is with +1 -1 longer gearing BTW. This seems low, and the bike feels a lot lazier too. In 3rd to 4th I can tickle 13.

My current suspects are small boost leak, boost controller, or failing turbo. When I disconnect the charge pipe before the plenum with the bike running and cover the side that connects to the turbo housing with my hand, the bike dies. If I blow into the plenum, it comes out of the pipe that goes from the compressor to the plenum. I thought it would go through the turbine side of the turbo, not the compressor side. Is this a sign of a fucked seal? Thanks.

You have the balls to go WOT in 1 and 2?

When I had the TD05 on it I only had the guts to go WOT in 3rd above 100km/h, and still it did some fish tailing..

Damn I'm a sissy..

Edited by Reinhoud
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3 hours ago, Reinhoud said:

You have the balls to go WOT in 1 and 2?

When I had the TD05 on it I only had the guts to go WOT in 3rd above 100km/h, and still it did some fish tailing..

Damn I'm a sissy..

When it was running great I didn't lol. That's how I knew something was up. I could lift the wheel in 3rd but now it stays down in all gears :(

Doing a lot of headwork this winter and hopefully switching over to a td04, what would you guys recommend for a td04 capable of 250 hp? I see 14t is a common choice but not sure.

Edited by rerb
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On 9/23/2021 at 10:44 PM, rerb said:

Think my turbo blew a seal, started spewing oil into the charge line. I'll check compression too but I think there's crossover between the hotside and coldside because just the day before it was a total rocketship. Motor feels the same before boost but I'll still check compression.

You also can have a restrictor what doesn't restrict enough..

I also had a leak from somewhere I couldn't find. Turned to come from the up pipe, smaller hole in the restrictor solved the problem, and the oil pressure stabilzed a bit.

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  • 2 weeks later...

Well I'm partly an idiot.

I took another look today and noticed the wastegate actuator actually managed to get stuck against the frame, propping it open about 1/2 of the way.

I guess boost pressure was enough to open it fully, but on the return the friction must've held it in place somehow, I have no clue. 

Readjusted the mount and now it clears by a few hundredths, bike runs a lot better now. 

Still not sure how that even happened unless the manifold sagged with the weight of the turbo 

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