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fiat22turbo
Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR
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 Posted: Sun Oct 25, 2015 3:04 pm Post subject: |
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Have you ever ported a cylinder head?
How about an intake?
Did you have the equipment to test the CFM rate before and after?
How about dyno tests?
No?
Have you read any books on fluid dynamics or even cylinder head and intake porting?
There's a lot of thought, skill and training that goes into properly porting an intake or a cylinder head. The people that do it for a living live and die by their data and their skills. It's basically an art form. So why would they give this hard earned information out for free when they need to run a business?
You can permanently damage a cylinder head very quickly with a Dremel tool.
Now if you really want to DIY, by all means go for it. There's been a lot of discussions on the cylinder head ports, including molds taken as well as CFM tests on a flow bench. Adding material requires using material specifically engineered for aluminum cylinder heads. Knowing where to add material and remove it, isn't as easy to know.
There's information available online on how to build your own flow bench. Go for it, DIY and break out your Dremel.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose) |
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nickthompson
Joined: 26 Mar 2013
Posts: 873
Location: Central Georgia
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| Posted: Sun Oct 25, 2015 6:48 pm Post subject: |
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| chris79 wrote: | | I do not understand why a free forum is always pushing to spend so much money instead of proposing soforlutions. |
Speed cost money especially on an engine like the 2.0 Audi lump that's in the 924. The engine wasn't really designed for performance if you want it to run you jave to bust out thewallet. |
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morghen
Joined: 21 Jan 2005
Posts: 8879
Location: Romania
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| Posted: Mon Oct 26, 2015 3:41 am Post subject: |
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But it was designed for performance, in the late 70s when the 911 had 160hp.
And at 125hp the 924 was not that slow.
Everybody keeps compairing the 924 to modern standards when it is actually a 70's car that stretched production into early 80s.
Thats a good sign that says that 924 is a timless figure 
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unheardofinstruments
Joined: 15 Sep 2011
Posts: 71
Location: Nimbin
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| Posted: Wed Nov 04, 2015 11:26 pm Post subject: supercharging |
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I am planning a supercharged setup for na using a sc14 from a toyota, If the stock head gasket is used and euro spec pistons as we got here in australia what kind of boost levels will start to cause detonation on 98 and a hot day? Don't you drop compression for boosted setups to account for the extra air forced in? When does this become necessary?
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There is more to heaven and earth than is dreamed of in your philosophy... |
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ideola
Joined: 01 Oct 2004
Posts: 15548
Location: Spring Lake MI
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| Posted: Thu Nov 05, 2015 12:10 am Post subject: |
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You should consider a thicker Cometic head gasket to drop compression. Much more than 6PSI on ROW 9.3:1 CR will cause detonation, especially with the inefficient roots style blower you are considering.
You can play around with different combinations here:
http://garage.ideola.com/top-DL-CompressionRatioCalc.html
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erstwhile owner of just about every 924 variant ever made |
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morghen
Joined: 21 Jan 2005
Posts: 8879
Location: Romania
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| Posted: Thu Nov 05, 2015 12:15 am Post subject: |
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In Australia it will detonate as soon as you get the supercharger closer than 50m to the car 
There are so many things that will make it grenade or not.
Will you use an intercooler? what kind? what size..?
Will you still use CIS or go EFI?
If still using CIS, i would use a big enough intercooler, dial back the spark advance and start with 0bar....then probably would not run more than 0.4-0.5bar anyway...and gently bring the advance back on carefully listening for detonation with propper instrumentation.
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Lefty
Joined: 14 Oct 2013
Posts: 61
Location: Sydney, Australia
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| Posted: Thu Nov 05, 2015 7:43 am Post subject: |
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Dan,
That's a great tool.
I have a 1982 na row
Changing to a .27 head gasket will increase cr to 9.7, from 9.3.
How will this feel, or what will this mean to,
Power increase
Reliability
At .27 is that a reliability issue.
Is this a simple swap out or is there other mods required?
Cheers
Lefty
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unheardofinstruments
Joined: 15 Sep 2011
Posts: 71
Location: Nimbin
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| Posted: Thu Nov 05, 2015 5:26 pm Post subject: supercharged na |
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Thanks guys, I was considering thicker gasket rather than having to swap or shave pistons, great to have a ballpark boost figure to work with and know that it is sufficient for some significant boost. Love the calculator.
Yes I was planning on intercooler as I am using an inefficient and hot air blowing s.c. hence my concern about being within 50m when/if it does detonate.
I was planning a front mount air intercooler, currently reading corkys book but wanting to know where to start with the 924 specifically as far as sourcing the right bits goes. So far I have volvo 850 injectors, neon fuel rail, bigger throttle body, high lift cam and larger valves in the head but wondering if I can get my head around the magasquirt or similar platform for the efi. I might enlist some help there at the end on a dyno to get it right as it looks very complicated from my research so far. I still need to source a suitable dizzy, 02 and knock sensors, MAF?MAP?EDIS? dunno yet (but I liked the thread on cheap efi using VW golf GTi bits), fuel pressure regulator, intercooler and pipes and fit the oil cooler. For now I am swapping the head over as I need a new head gasket anyhow and after buying it found the previous owner learned the CIS wouldn't work due to the cam making waves in the intake so EFI it is...sometimes I wonder why I get into these things but I suspect when it comes together the seat of my pants will know why. |
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morghen
Joined: 21 Jan 2005
Posts: 8879
Location: Romania
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| Posted: Thu Nov 05, 2015 5:45 pm Post subject: |
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Before you read further, learn that i'm a CIS die hard guy
Waves in the intake are normal, CIS can cope with that, the original 924 cam is a sporty cam too.
Depending on how experienced are you with EFI conversions and how long do you want the car off the road i would suggest to choose to go EFI right away or delay that and just use the supercharger with CIS.
Then that blower is not going to be a very efficient thing so it might not be worth the effort to convert to EFI if you are happy with the blower sound and the amount of extra torque&power it safely gives in conjunction with CIS and the NA engine.
If i would have not bought my second 924 turbo last year i would have taken on a CIS & supercharged/turbocharged 924 NA project.
Honestly the 931 power levels of 170hp are enough for me and i think 170hp and reliability can be had from a lightly boosted 924NA still using CIS.
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ideola
Joined: 01 Oct 2004
Posts: 15548
Location: Spring Lake MI
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| Posted: Thu Nov 05, 2015 10:46 pm Post subject: |
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| Lefty wrote: | Changing to a .27 head gasket will increase cr to 9.7, from 9.3.
How will this feel, or what will this mean to,
Power increase
Reliability
At .27 is that a reliability issue.
Is this a simple swap out or is there other mods required?
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With a proper build and correct fueling, there should be no issue with reliability running upwards to 11:1 CR on a naturally aspirated car. Swapping the head gasket on an NA is a relatively straight forward job. However, it is highly advisable to have the head and the block mating surfaces "clean cut" to ensure straightness and a good seal with the Cometic gasket. On a non-boosted application, this step is probably not quite as critical, but I'm not sure I would want to just swap in a Cometic gasket without properly prepping the head and the block. You get what you pay for, and short cuts like just swapping in the gasket without doing anything else are usually a recipe for more expensive repairs later.
As for the power gain potential, as originally posted in this thread:
| ideola wrote: | From this article (using the code tag to preserve the table spacing...):
| Popular Hot-Rodding wrote: | CR Power Gains
The theoretical thermal efficiency (E) at any given CR can be predicted by the following formula:
Where E = the Otto cycle (thermal) efficiency, R the compression ratio and k the coefficient of adiabatic expansion for air, which is nominally 1.4. Rather than flogging through a lot of calculations, the quick reference chart (Figure 2) has been made up. To use this chart locate your original CR horizontally. Next, locate the new CR down the first column. Where the two intersect is the gains that can be expected. For instance if the CR is raised from 9:1 to 12:1 we find the two values intersect at the box with 7.7 in it. This is the percentage increase that can theoretically be had by raising the compression from a lower to a higher level.
| Code: | ORIGINAL CR
NEW 8:1 9:1 10:1 11:1 12:1 13:1 14:1 15:1
9:1 3.5
10:1 6.5 2.9
11:1 9.2 5.5 2.5
12:1 11.5 7.7 4.7 2.1
13:1 13.6 9.7 6.6 4.0 1.9
14:1 15.4 11.5 8.3 5.7 3.5 1.6
15:1 17.0 13.0 9.8 7.1 4.9 3.0 1.4
16:1 18.6 14.5 11.3 8.6 6.4 4.4 2.8 1.4 |
Now anytime we use the word "theoretically," it usually implies that there is not much chance of achieving as much in practice. Here the good news is that because intake valves do not close at BDC, the gains computed in Figure 2 tend to be a little on the low side. |
From this table, you can see that a full point of CR increase will yield about a 3% gain on our motors. 125 BHP (Euro-spec) x 3% = 3.75BHP. Pretty measly, eh?! You'll have to decide if half a point of compression is worthwhile to take a chance on losing the non-interference aspect of your engine.
For me, because the timing belt is so easy to do on our cars, I feel that the issue of interference is way over-rated. Most modern cars are interference design. To achieve the biggest possible HP gain, I'm going more radical, and going to 11:1 on my NA project (120 BHP [US-spec] x 5.5% = 6.6BHP). Of course, it also involves additional stroke, Stage 1 cam, Cometic gasket, big valve head, free-flowing header, etc. so I expect the gains to be multiplied. I'm also encouraged by the fact that the stock motors went from 120 BHP at 9:1 in US-spec to 125 BHP at 9.3:1 in ROW-spec. That's a 5 BHP gain, or ~4% increase from .3 increase in CR... |
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erstwhile owner of just about every 924 variant ever made |
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gegge
Joined: 27 Jul 2007
Posts: 1124
Location: Sweden
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| Posted: Fri Nov 06, 2015 2:04 am Post subject: |
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"...stock motors went from 120 BHP at 9:1 in US-spec to 125 BHP at 9.3:1 in ROW-spec."
Ceteris Paribus - NOT. The petrol and ignitioncurve wasn´t the same.
Agree that increasing CR is a marginal theroretical power improvement of decreasing value and backing ignition in order to fight off pinging is a lot worse. But in order to keep the dynamic compression with a cam with more duration, you need to increase the static CR. Simple trigonometrics my friend.
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Carl Fredrik Torkildsen
924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs |
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chris79
Joined: 29 Jan 2014
Posts: 551
Location: milan
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| Posted: Fri Feb 05, 2016 8:07 am Post subject: |
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For reach 200cv is better to sell my na and overbust a 931 with intercooler or bust my car?
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Porsche 924 2.0 na 125hp (1979) euro
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Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro |
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JjyKs
Joined: 05 Oct 2015
Posts: 114
Location: Finland
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| Posted: Fri Feb 05, 2016 10:22 pm Post subject: |
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| chris79 wrote: | | For reach 200cv is better to sell my na and overbust a 931 with intercooler or bust my car? |
As far as i know (currently doing my own na to turbo efi conversion), getting 200hp from 931 would be a lot easier. Stock CIS is able to hand 0.5bars (not 100% sure about this?). No idea how far it's possible to get in terms of hp, but there was that one guy strapping 2 fuel distributors in one car, and it's also possible to use one from some other car (931, 928, bigger Mercedes engines, etc. with k-jet. Going to be a lot of DIY work anyways).
EFI conversion is all about DIY, and not an easy job either, but once you get it running it should be pretty easy to scale your setup.
I have no idea about 931:s either, but if you can afford getting one, i'd definitely go for that. You can always do same mods for your turbo car if you'd want to, but you'd have a lot of work done already. |
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chris79
Joined: 29 Jan 2014
Posts: 551
Location: milan
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| Posted: Sat Feb 06, 2016 12:36 am Post subject: |
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but for bust over 200hp is better 924 or 931 engine ?
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Porsche 924 2.0 na 125hp (1979) euro
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Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro |
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JjyKs
Joined: 05 Oct 2015
Posts: 114
Location: Finland
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| Posted: Sat Feb 06, 2016 10:15 am Post subject: |
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| chris79 wrote: | | but for bust over 200hp is better 924 or 931 engine ? |
Both of them will be able to hold that power easily if they're well maintained and in a good condition.. |
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