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My 924 Turbo, up and running !
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Cdric  



Joined: 27 Aug 2004
Posts: 2077
Location: Sweden

PostPosted: Thu Dec 03, 2020 7:18 pm    Post subject: Reply with quote

jazz guy wrote:
Cedric wrote:
If you can aim for a twinscroll charger, it will make it much less knock sensitive. It made a big difference in EGT on joakims engine when he did that change, and makes it possible to accept more cam duration, you should at lest have a "stage 1" cam I think. For the head some rework of the inner radius and some filling in some areas would be good, do you plan on DIY or let an experienced head porter do it?

I'll leave the actual porting to a pro. I have a decent amount of engine building experience but not in head porting. I do want to have a firm concept and plan of attack in mind before I agree to any material being removed, so I've been digging into research on the topic. Still learning.

Thanks for your thoughts on a twinscroll setup. I'll be fabricating a manifold, so building it for twinscroll shouldn't be much more work. I guess it makes sense that it raised the detonation level on Joakim's engine. Less back flow/cylinder contamination when intakes are opening. Might also allow a larger overlap cam to function better in a turbo engine? I'm really not sure how far I can go on cam overlap and not give up too much low end.

Cedric wrote:
Its always fun with more tuned 931s, there are very few in the world in that gang so it would be fun if you would join in

True that! I've always thought these cars would be a hoot with horsepower in the mid-300's. Now I'm fixing to find out!


Yes, twin scroll drastically reduces the cross talk between the cylinders. Even if you have low mean pressure in the exhaust manfold (like in joakims case) if you look at it in a crank angle resolved pressure trace you will see that you have pressures interacting while one cylunder try to evacuate the eexhausts while the cylinder before it havent evacuated all of its gasses yet. With the twinscroll on a 4 cylinder you wont have that if you separate the banks correctly, and hence it will be possible to use longer exhaust duration, without getting alot of exhaust residuals getting trapped in the cylinder (creating high EGTs and knock sensitivity). A log manifold works great and give good turbine energy due to its low volume, but it works best with short exhaust cam durations or preferably with variable valve timing, which we have none of
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Cdric  



Joined: 27 Aug 2004
Posts: 2077
Location: Sweden

PostPosted: Thu Dec 10, 2020 9:42 am    Post subject: Reply with quote

Heres something for fasteddie and me, I know you want a solution aswell to get rid of the small restriction. The market for this pipe is small though since were only two that runs this kind of IC routing

I measured som areas, and the top of the short boost pipe is around 1700mm2, and the bottom of the boost pipe is only 40m diameter (where the turbo normally connects), so 1256mm2. So the restriction in the system needs to increase to at least 1700mm2 to not be the smallest part of the boost pipe system ( equivalent to a 47mm circular pipe). So a 2inch hose would probably be a smarter choice than the 2,5 inch that naturally goes on there, for packaging reasons.

Anyway, i forgot most of what i knew in cad, so its quite a challenge to get this complex part right, it will probably take a long time to get this done. But hopefully it will be wort it with better packaging and less restriction

Heres a draft of where im at, mostly to get the different measurements right.

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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2130
Location: MI

PostPosted: Thu Dec 10, 2020 12:31 pm    Post subject: Reply with quote

Ooh yes that..

C�dric wrote:
The market for this pipe is small though since were only two that runs this kind of IC routing

So far..

So reduce to 2” somewhere after the intercooler and it will about equal the inlet of the upper charge tube anyway?
Would fit past the cold housing easier..
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Cdric  



Joined: 27 Aug 2004
Posts: 2077
Location: Sweden

PostPosted: Thu Dec 10, 2020 7:10 pm    Post subject: Reply with quote

Fasteddie313 wrote:
Ooh yes that..

C�dric wrote:
The market for this pipe is small though since were only two that runs this kind of IC routing

So far..

So reduce to 2” somewhere after the intercooler and it will about equal the inlet of the upper charge tube anyway?
Would fit past the cold housing easier..


A 2 inch pipe is even larger diameter than the smallest area of the upper charge tube, so I think i will evaluate that aswell to see if I can get more space down there. I will have to redo my very special squeezed tube, but it might be worth it. Maybe i will print more pipes to get more clearance with the odd shapes needed.

Its always interesting how much power you can actually push through that 40mm hole we have today, as we have seen. But it will cost you compressor capacity to keep that boost level with the restriction. So if you changed the pipe you would probably be able to get more out of your current turbo.
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morghen  



Joined: 21 Jan 2005
Posts: 8274
Location: Romania

PostPosted: Thu Dec 10, 2020 8:16 pm    Post subject: Reply with quote

Oh Catia
This should be good!


note: when designing my tubes, i always check the internal area in different sections. Catia has a way of blending surfaces in such a way that sometimes you get less cross-section area.

C�dric wrote:
Heres something for fasteddie and me, I know you want a solution aswell to get rid of the small restriction. The market for this pipe is small though since were only two that runs this kind of IC routing

I measured som areas, and the top of the short boost pipe is around 1700mm2, and the bottom of the boost pipe is only 40m diameter (where the turbo normally connects), so 1256mm2. So the restriction in the system needs to increase to at least 1700mm2 to not be the smallest part of the boost pipe system ( equivalent to a 47mm circular pipe). So a 2inch hose would probably be a smarter choice than the 2,5 inch that naturally goes on there, for packaging reasons.

Anyway, i forgot most of what i knew in cad, so its quite a challenge to get this complex part right, it will probably take a long time to get this done. But hopefully it will be wort it with better packaging and less restriction

Heres a draft of where im at, mostly to get the different measurements right.

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Cdric  



Joined: 27 Aug 2004
Posts: 2077
Location: Sweden

PostPosted: Thu Dec 10, 2020 8:53 pm    Post subject: Reply with quote

morghen wrote:
Oh Catia
This should be good!


note: when designing my tubes, i always check the internal area in different sections. Catia has a way of blending surfaces in such a way that sometimes you get less cross-section area.

C�dric wrote:
Heres something for fasteddie and me, I know you want a solution aswell to get rid of the small restriction. The market for this pipe is small though since were only two that runs this kind of IC routing

I measured som areas, and the top of the short boost pipe is around 1700mm2, and the bottom of the boost pipe is only 40m diameter (where the turbo normally connects), so 1256mm2. So the restriction in the system needs to increase to at least 1700mm2 to not be the smallest part of the boost pipe system ( equivalent to a 47mm circular pipe). So a 2inch hose would probably be a smarter choice than the 2,5 inch that naturally goes on there, for packaging reasons.

Anyway, i forgot most of what i knew in cad, so its quite a challenge to get this complex part right, it will probably take a long time to get this done. But hopefully it will be wort it with better packaging and less restriction

Heres a draft of where im at, mostly to get the different measurements right.
[img]https://rejsa.nu/im/user/1552/2020-12-09-23-32-38_boostpipe.pnb[/img]


Yeah that function really do take some work, one reason im using catia (except for that i worked with it 10 years ago, so I still remember something) is that i have friends who work in it on a daily basis. So its much easier to get help, one of them did actually design aluminum boost pipes for trucks for many years. I think he might be able to sort this out
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2130
Location: MI

PostPosted: Thu Dec 10, 2020 10:19 pm    Post subject: Reply with quote

To me it’s not just the size of the 40mm hole, but that god awful 90 degree step inside of it that just can’t be good for smooth flow..

I have almost thought about replumbing/replacing the entire upper charge tube, but I quite like keeping the original upper charge tube..

Do you think replacing the lower charge tube will make for a noticeable improvement?
I think it may..
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Cdric  



Joined: 27 Aug 2004
Posts: 2077
Location: Sweden

PostPosted: Thu Dec 10, 2020 11:32 pm    Post subject: Reply with quote

Fasteddie313 wrote:
To me it’s not just the size of the 40mm hole, but that god awful 90 degree step inside of it that just can’t be good for smooth flow..

I have almost thought about replumbing/replacing the entire upper charge tube, but I quite like keeping the original upper charge tube..

Do you think replacing the lower charge tube will make for a noticeable improvement?
I think it may..


Yes absolutely, that step is bugging me alot, its quite ironic that Ive been chasing people with the torch at work for many years to remove ugly designs and focus on pressure losses.. But now when it comes to my own personal engine i have that massive ugly restrictor in the pipe . That ugly step will make the actual diameter that the flow can use smaller than 40mm due to the flow separation that will occur around the edge, a more smooth transition will improve that( if you for example made an insert with a nice bellmouth shape (which is my back up plan), but its still limited.

I could try to replicate it in my simulation model, I would expect the difference for my engine to be smaller. Since I have a larger compressor that works at a lower target boost, so more margins. The more on the limit you are with the compressor the bigger the difference will be. But you would most likely need a dyno to verify it.

Btw, check your car thread, theres some #6 housings happening !

For me the upper charge tube is essential to keep, for estethic and originality reasons.
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