Restricted Flow

[Wogan]

what turbo were you using on your rb20?

isn't all turbo air hot? .. i thought that was the point of having the huge intercooler out front........

[MBS206]

what turbo were you using on your rb20?

isn't all turbo air hot? .. i thought that was the point of having the huge intercooler out front........

Sometimes you get to a point you're not actually forcing more air in to create more pressure, you're just heating the air up and creating more pressure...

Hence, you're running out of flow, it'll still boost higher, but it's just doing that by heating the air up only, not heating it AND forcing more air in...

[bubba]

Edit: what he^^ said

s1 25 turbo..

Well.. air leaving a turbo is hot due to it being compressed but turbos have efficiency ranges, this is where compressor maps come into it. Turbo compressors have an ideal range, below or above and it's losing too much efficiency which could be in terms of excess heat but not much more airflow.

That was a VERY simple explanation but if you want something more indepth, check out www.turbobygarrett.com as they have some good articles that attempt to explain how to read compressor maps discopotato might also chime in

Edited November 11, 2008 by bubba

[Wogan]

true.. but power did go up 15hp with an additional 1psi.. so it's still doing better with the extra boost.

[rob82]

The difference in boost potential between bubba's setup and your is about 750rpm. As in it take your car 750rpm longer to get to the same boost point using the same ramp rate and very very similar setups at WOT. Usually boost on single turbo charged vehicles comes on allmost exponentially with rpm but yours just seems to slowly come up to pressure. Hence why I would be looking for a leak. All you have to do is plug the intake pipe -ie pull off you pod filter and jam something in the end and then pressurise the intake and listen for leaks. Failing that I would then look at dropping the exhuast to see if there is a restriction.

[bubba]

Wogan, was there a tune in between those runs? I noticed you have a nistune board in there but I'm surprised at the lack of response compared to my old RB20 which was an untuned laggy POS but when it actually got on boost it went alright

[Tex Willer]

Is your cam timing correct?

[rev210]

Why? we have already discussed this. Would be nice to substantiate what you are saying.

Sure, should have added...

Manufacturing of the pipes I have seen ( about 5) and subsequently had to spend hours with a die grinder on has been nothing short of 'rushed'. They aren't taking the time to align anything. Which is fine for the very low price you are paying. If you don't clean them up, they may give you some issues like this one. I've been lucky enough to get them to work for myself and others but, with more effort than is worth it.

They are only $250 but, if you have overlap on the flange where the turbo bolts on, it may well bolt on but, you may also wind up with a top end restriction that makes the stock dump pipe look good. Also, there are a number of people who have had the wastegate foul the product. A few others have had warped flanges that won't seal. Granted you can have the product exchanged if it really doesn't work but, a number of punters who don't know any better won't go checking the quality of the work and making sure there isn't any alignment issues. Hey it bolts on! Wait a minute whats this weird restriction in power?

Having said that it could be something else causing the issue.

[Wogan]

Wogan, was there a tune in between those runs? I noticed you have a nistune board in there but I'm surprised at the lack of response compared to my old RB20 which was an untuned laggy POS but when it actually got on boost it went alright

both sheets are from when i took it to hyperdrive for a tune ... so it should be tuned... unless they just took my money and printed out a new sheet.

[bubba]

Sure, should have added...

Manufacturing of the pipes I have seen ( about 5) and subsequently had to spend hours with a die grinder on has been nothing short of 'rushed'. They aren't taking the time to align anything. Which is fine for the very low price you are paying. If you don't clean them up, they may give you some issues like this one. I've been lucky enough to get them to work for myself and others but, with more effort than is worth it.

They are only $250 but, if you have overlap on the flange where the turbo bolts on, it may well bolt on but, you may also wind up with a top end restriction that makes the stock dump pipe look good. Also, there are a number of people who have had the wastegate foul the product. A few others have had warped flanges that won't seal. Granted you can have the product exchanged if it really doesn't work but, a number of punters who don't know any better won't go checking the quality of the work and making sure there isn't any alignment issues. Hey it bolts on! Wait a minute whats this weird restriction in power?

Having said that it could be something else causing the issue.

There we go, some substance! Thankyou Many people are too quick to come out with "oh you've got such and such, there's your problem". I wasn't aware that top end restriction was an issue with some JJR split dump, how bad is the overlap you've seen? would it be a flow restriction or the result of gasses bouncing back against the turbine (if the overlap was that bad)?

both sheets are from when i took it to hyperdrive for a tune ... so it should be tuned... unless they just took my money and printed out a new sheet.

Wasn't insinuating anything, just querying whether it was only a power run or it was in for a tune

[Wogan]

Wasn't insinuating anything, just querying whether it was only a power run or it was in for a tune

Yeah that's cool. I didn't mean anything by my statement.. i come across angry sometimes when i'm not.

well i've got 3 things to check out so far (which is good)

- Check for boost leaks

- possibly replace intake pipe

- check out and possibly replace/grind dump pipe

Thanks guys... hopefully get some progress updates this weekend. keep the suggestions coming though .. It's good going over the theory.

Edited November 11, 2008 by Wogan

[rev210]

There we go, some substance! Thankyou Many people are too quick to come out with "oh you've got such and such, there's your problem". I wasn't aware that top end restriction was an issue with some JJR split dump, how bad is the overlap you've seen? would it be a flow restriction or the result of gasses bouncing back against the turbine (if the overlap was that bad)?

Wasn't insinuating anything, just querying whether it was only a power run or it was in for a tune

No worries.

the overlap ranged from the weld protruding into the gas path to the actual flange plate bolting up crooked so that I had to cut into the plate itself. The wastegate welds were all 'lipped' really bad inside too. If you left them alone then no doubt much crapper performance than stock. The kicker is they all bolted up easy enough with the exeption of one, that needed material taken out around the flange weld as it stopped one of the nuts going onto the thread.

Locally you can't beat $350 - $400 for something custom from a good exhaust place, even if it's only mild steel.

[Wogan]

No worries.

the overlap ranged from the weld protruding into the gas path to the actual flange plate bolting up crooked so that I had to cut into the plate itself. The wastegate welds were all 'lipped' really bad inside too. If you left them alone then no doubt much crapper performance than stock. The kicker is they all bolted up easy enough with the exeption of one, that needed material taken out around the flange weld as it stopped one of the nuts going onto the thread.

Locally you can't beat $350 - $400 for something custom from a good exhaust place, even if it's only mild steel.

Would a JJR bell mouth fix the problem? .. obviously it wouldn't have the benefit of splitting the exhaust flows, but i'm not sure how big a help that is on lower-end modified cars like mine.

[rev210]

Would a JJR bell mouth fix the problem? .. obviously it wouldn't have the benefit of splitting the exhaust flows, but i'm not sure how big a help that is on lower-end modified cars like mine.

No the split isn't the issue it's the actual way the pipes are welded up. They aren't trying to line anything up, the china stuff gets done in a big hurry.

JJR belmouth would have the same issues no doubt. If the flange isn't welded on right your still up the creek. Just get a local exhaust shop to do a pipe. Should be about $400 or less.

Then again the JJR unit may not be the issue at all. Try the other things first and see how you go.

[Wogan]

yeah i get that it's not the split that is the problem.. just figured that with a bell mouth the flanges lining up would be less of an issue due to the bell mouth.

but point taken.. i will investigate possible boost leaks and also take off the dump and check out the pipe this weekend... wish me luck

[Cartman]

did you do the intake pipe mod to stop it sucking shut?

[Wogan]

not yet.. that'll be investigated on the weekend too.. seems least likely and hardest to test though.

is that a common problem?

[Fastrotor]

if you have no luck with your other things to try, and you have an adjustable boost controller, start winding the boost back off once it reaches peak HP.

You wont make any more power of course, however because you are asking for less boost to be maintained, the wastegate will stay more open, this keeps the exhaust Backpressure down (assuming the turbine housing&wheel combo is at its max flow, which is possible with std) and therefore power will roll off alot less dramatically. So technically you gain power in the top end, but wont increase Max power at its peak.

Gary

(I've proven this many times on the dyno by the way, not just theorising)

[Cartman]

not yet.. that'll be investigated on the weekend too.. seems least likely and hardest to test though.

is that a common problem?

very common in my experience. most people dont even think of it..

[Wogan]

if you have no luck with your other things to try, and you have an adjustable boost controller, start winding the boost back off once it reaches peak HP.

You wont make any more power of course, however because you are asking for less boost to be maintained, the wastegate will stay more open, this keeps the exhaust Backpressure down (assuming the turbine housing&wheel combo is at its max flow, which is possible with std) and therefore power will roll off alot less dramatically. So technically you gain power in the top end, but wont increase Max power at its peak.

Gary

(I've proven this many times on the dyno by the way, not just theorising)

My turbo and exhaust are not standard. If you look at the 2 different dyno tune sheets you can see that on higher boost the power actually starts dropping a couple hundred rpm later.. This makes me think it's not the turbo itself as it would have happened earlier if this were the case.

but thank you. If the other things don't work i'll give this a shot.