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 Post subject: Re: Boost creep
PostPosted: Thu Aug 17, 2017 10:18 am 
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Bazross wrote:
Deffo make a huge difference put the KnN back on and it hit fuel cut again and peaked at 17.9 psi

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Took off the turbo and smoothed out the flow path of the waste gate.
Once the gate was opened you could feel a step/ridge in both ports one was worse than the other so rather than die grind it and risk taking out to much because there looks as though there isn't much on the sidewalls to start with and I did have some cracking in the ports
I opted for some fine needle files and filed down the lumps and bumps and reduced the steps took some time and graft but the end result was a smooth bore into the waste gate, hopefully curing the boost creep I've had since fitting the 3inch exhaust
I have yet to test as I'm still waiting for the belt kit to arrive once fitted ill give it a blast and report back on the creep situation.
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 Post subject: Re: Boost creep
PostPosted: Thu Aug 17, 2017 8:25 pm 
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I have some theoies on waste gate porting, but I should really test them unless people fancy a theoretical discussion.

It's worth looking at the shape of the downpipe round the wastegate area and making sure there's a good smooth flow out of the wastegate and downwards, and also check that the wastegate can open fully when the downpipe is fitted.

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 Post subject: Re: Boost creep
PostPosted: Thu Aug 17, 2017 8:29 pm 
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Yep it's now solved the issue it's running at slightly above 16psi.
Nibbles what would the effect of being a tooth out on the valve timing I'm thinking it could be slightly out if it was would it be pronounced at idle or whilst running


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 Post subject: Re: Boost creep
PostPosted: Thu Aug 17, 2017 9:38 pm 
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Depends on which way it's out and which cam.
Inlet cam out will have a knock on effect on ignition timing, usually leaves the distributer on one end of travel to get it right.
I would expect exhaust cam opening early would have a similar effect on turbo as retarded ignition - the mixture is still burning when it comes out through the valves, leading to loads of boost but no go.

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 Post subject: Re: Boost creep
PostPosted: Thu Aug 17, 2017 11:26 pm 
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Ok I cannot time this up it seems as it's half a tooth out on the cams does anyone know what the part number is for a genuine Toyota belt I'm thinking this is the wrong belt the part number is 13568-yzz04 and searching comes up as 89-93

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 Post subject: Re: Boost creep
PostPosted: Fri Aug 18, 2017 1:47 pm 
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Ok so it's the correct belt 177 teeth so I redone it again but still the same
Turns out it's the crappie marks on the cam cover for the cams
I stripped out the rocker cover and used the marks inside the cams lined up these marks and Tdc removed the inlet cam sprocket and slipped the belt on
Made sure that the tension was between crank and exhaust cam
Held the exhaust cam in position and tensioned the belt to the inlet cam
All marks lined up and released the tensioner hand cranked it 4 times and all the marks spot on
In all honesty it was probably correct first time round but just didn't feel correct and I had a feeling so it had to be redone.



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 Post subject: Re: Boost creep
PostPosted: Fri Aug 18, 2017 2:49 pm 
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I was about to tell you to pull the cam cover off and check the marks inside. It's very easy to get paralax error with the engine in-situ as it's not vertical.
It's also not unknown for the rubber to come unstuck on the crank pulley and allow the timing marks to be out, especially if it's removed with a 2 or 3 leg puller tool rather than the correct one which pulls the middle. This can be cross checked with a long rod down the No. 1 plug hole.

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 Post subject: Re: Boost creep
PostPosted: Fri Aug 18, 2017 4:43 pm 
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Yeah I've seen that done with the pullers
I made my own which bolts to the crank pulley and draws it off
The best way is as you described with cam cover off and a rod down number one, the amount of times I checked the crank position and it looked out reset it and rechecked slight different position and it looked worse
Started to doubt where to look

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 Post subject: Re: Boost creep
PostPosted: Mon Aug 21, 2017 12:17 pm 
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Nibbles wrote:
I have some theoies on waste gate porting, but I should really test them unless people fancy a theoretical discussion.
.


Yes please :-)

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 Post subject: Re: Boost creep
PostPosted: Mon Aug 21, 2017 9:20 pm 
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Diceman wrote:
Nibbles wrote:
I have some theoies on waste gate porting, but I should really test them unless people fancy a theoretical discussion.
.


Yes please :-)


First is more of a question. Looking down the ports from the manifold (direction of gas flow), it's quite a sharp turn into the wastegate port. I'm sure there is some merit in putting a bigger radius on the inside of the turn to aid flow out through the wastegate, the question is how much would it reduce flow down to the turbo at the lower end where turbo efficiency is most needed.

Second one is probably more controversial. Being a dual port turbo, the gasflow in each port isn't steady. Alternate cylinders send pulses into alternate ports. If a substantial part of the metal in between the 2 ports were removed, this would create a single, much bigger, port. Each pulse of gas would then have a much larger exit path as it can spill across into the other port which would be in it's 'off' phase. Removing this metal shouldn't lead to cracking, unlike increasing port diameter and reducing wall thickness.

ANy thoughts ?

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 Post subject: Re: Boost creep
PostPosted: Tue Aug 22, 2017 1:07 pm 
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Nibbles wrote:

First is more of a question.
1) Looking down the ports from the manifold (direction of gas flow), it's quite a sharp turn into the wastegate port. I'm sure there is some merit in putting a bigger radius on the inside of the turn to aid flow out through the wastegate, the question is how much would it reduce flow down to the turbo at the lower end where turbo efficiency is most needed.

2) Second one is probably more controversial. Being a dual port turbo, the gasflow in each port isn't steady. Alternate cylinders send pulses into alternate ports. If a substantial part of the metal in between the 2 ports were removed, this would create a single, much bigger, port. Each pulse of gas would then have a much larger exit path as it can spill across into the other port which would be in it's 'off' phase. Removing this metal shouldn't lead to cracking, unlike increasing port diameter and reducing wall thickness.

ANy thoughts ?


1) Logic has suggested exactly the same thing to me Chris, it was interesting to see that this approach was adopted on the ATS racing CT27 (which still suffered boost creep IIRC all be it to a lesser extent). I doubt if any noticeable impact on turbine efficiency would result from this "low down" as the WG will be closed and the WG port already full of exhaust gas (although not at full pre turbo pressure all the time). I also suspect that a downpipe designed with the inclusion of a WG guide vane within the downpipe would assist in evacuating the wastegated exhaust into the downpipe without causing a whole heap of turbulence like I suspect the stock arrangement does. Interestingly it seems that soem Garretts have this.

The thing that gets me though is that a lot of the turbo/wastegate positioning on aftermarket turbo/manifolds seems much worse and relies on exhaust manifold pressure to divert exhaust gases to the external WG and yet seem to function!

2) The above IMHO is therefore directly related to part 2. By machining out the dividing plate you are effectively removing almost all of the effect of the twin scroll (as per Turbo Technics but still retaining the smaller A/R). The exhaust gases are likely to backflow through the WG port and into the non-active scroll of the turbine housing/exhaust ports. I think it would assist in reducing boost creep but have a far greater impact on boost threshold and mapping.

One thing that has been bothering me for a while is the exhaust manifold design, with it being unequal length (by a large margin) I wonder if there is an RPM range where you effectively have 2 pulses simultaneously reaching the same scroll and overwhelming the WG with flow (choked flow?). I wonder if an equal length manifold would serve to again reduce boost creep by spacing the pulses better or would lead to slower spool (depending on RPM range where 2 pulses happen together)? When I get some time I want to do a few tests on the stock manifold to see if the stock design promotoes flow reversion in some ports (as I have seen in other cast designs) or if Toyota actually did a good job of equalising flow between cylinders despite the nasty angles and unequal lengths.

I'm not sure how much you have looked into it but I found using the Borg Warner EFR Matchbot very interesting as it calculates the % wastegating & pre-turbo exhaust manifold pressure for each RPM band at your desired boost level/engine.

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 Post subject: Re: Boost creep
PostPosted: Tue Aug 22, 2017 10:24 pm 
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I was thinking of removing material between ports more at the wastegate end, so flow between ports would still be a fairly tortuous route and therefore not completely kill the benefits of the twin scroll. It's a case of looking at how big a notch, how far down and the compromise between boost creep vs. low down efficiency. Also, would it be a lesser evil than choking the whole thing with an orifice plate as is current practice.

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 Post subject: Re: Boost creep
PostPosted: Wed Aug 23, 2017 10:04 am 
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My understanding is that the main flow restriction will occur where the smallest port area is experienced and hence it all needs to be opened up equally. If there were anywhere that I would suggest has a higher restriction for a given port area it would be the entry & exit; in the case of the CT26 the entry point is commonly ported to provide smoother entry. The exit however is an abrupt (flat faced) exit and hence will generate turbulence/higher pressure drop/restriction than a smooth wall port and hence maybe your idea has some merit.

My gut reaction is however that regardless of where you join the twin scroll/ports most of the effect will be lost and boost threshold will be sacrificed. As the years move on and I'm reading more I am liking twinscroll more and more so seems a shame to be ditching it TBH.

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 Post subject: Re: Boost creep
PostPosted: Wed Aug 23, 2017 6:57 pm 
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We I'm out of my depth on those last 3 posts!!!
But after looking at the inner of my CT 20 I was impressed at the design and didn't want to mess to much with it
Looks like a lot of thought and work has gone into the design as regards the twin scroll I of course am just a layman but it did look purposely made that way If not the smoothest that wanted a little work with a file.
Reading about the twin entry and twin scroll it's purpose is to split the 1&3 2&4 chambers so it doesn't bottle neck is that correct
Baz

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 Post subject: Re: Boost creep
PostPosted: Wed Aug 23, 2017 11:28 pm 
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Something I often point out is that major manufacturers spend millions of pounds and thousands of man hours designing cars, yet the armchair experts think they can do a better job !!!.

The 3S engine was worked on by Yamaha who are experts at porting and resonance to get the best out of engines. Long gone are days of the old ford crossflow or mini engines where you could gain 10% by grinding away casting flash in the ports with ery little loss elsewhere. Anything changed on these engines will just change the parameters in the compromises - gains in some areas will be offset by losses in others.

Saying that, it's still fun to try :)

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