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Author Topic: Need help with low airflow/power 1.8t  (Read 1548 times)
maxwell_ck
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« Reply #15 on: February 29, 2024, 01:04:38 AM »

Update.
I have replaced the old shitty onesided intercooler with two-side 600x300 one, and placed the new BAM intake manifold.
It has made a slight difference in airflow at higher rpm range but CFs stayed at the same levels.
Please find the new logs attached
I get the idea of reducing the CR, but it seems to be worth the deal when trying to get over 370-380HP, not past 320HP.
I have seen some projects doing more than 360HP with 9.0:1 CR, so I am afraid that there is another problems.
What do you think?
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prj
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« Reply #16 on: February 29, 2024, 03:05:40 AM »

You were already told what the problem is.
If you choose to ignore that and believe in fairytales then that's on you.

Your CR is probably even higher because the head was off the car and most likely was skimmed.
Certainly when building the engine you never measured the actual chamber sizes by filling with liquid, so you have no idea what your real CR is.

You can either keep the boost at 1.5 bar or you can:
a) Drop CR
b) Increase quality of fuel - WMI, race fuel, octane booster, E85 - pick one.

We have seen guys like you on this forum come and go many times, who believe that their engine is magic and they should make 1000 hp with 10 CR because they read something on a forum somewhere.
I call them CR deniers. Welcome to the club.
« Last Edit: February 29, 2024, 03:09:54 AM by prj » Logged

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maxwell_ck
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« Reply #17 on: February 29, 2024, 04:57:04 AM »

Take it easy prj, I understand what you mean, thank you for your help with that.
Even though there are 9.0:1 pistons the head was skimmed two times and that may be the cause.
Can you recommend the proper head spacer to fit in
« Last Edit: February 29, 2024, 05:00:51 AM by maxwell_ck » Logged
aef
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« Reply #18 on: February 29, 2024, 05:20:45 AM »

Start by measure your current head gasked.
How thick is it when it was compressed?
Measure your combustion chamber volume with a spark plug in there and measure your piston volume in TDC.
Add the compressed head gasked to your math.
now you have your current CR.

Easiest way is to buy 2 of your last used head gaskets (because you know how thick they will be after everything is torqued down)
and just use 2 or disassemble them and mix until you have the correct CR.

No need to buy expensive laser cut pieces or something.

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prj
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« Reply #19 on: February 29, 2024, 08:06:58 AM »

Best would be to change the pistons for proper 8.0:1 ones.

Alternatives:
https://www.bar-tek.com/de/1.8t-dicke-metall-zylinderkopfdichtung-bar-tek
Of course they don't say how much it drops CR. Height is quoted as 1.92mm.

https://www.turbozentrum.de/Dicke-Zylinderkopfdichtung-VAG-18T-Metallkopfdichtung
They say 0.5-1.0 and the price is very good. Height is quoted as 2.35mm.

https://www.034motorsport.com/head-gasket-compression-dropping-multi-layer-steel-20v-1-8t.html
Drops 0.5. Height not quoted.

Here's a website that uses a plate and they let you customize it:
https://www.turbo-concepts.de/motorenbau/audi-vw-seat-skoda/1.8t/rumpfmotor/verdichtungsreduzierung/149/verdichtungsreduzierplatte/spezial-kopfdichtung-1.8t-20v
And here is another one, that is cheaper:
https://www.lspeed-racing.de/product_info.php?info=p1603_audi-1-8t-20v-zylinderkopfdichtung-mit-verdichtungsreduzierung.html

I would just get the thickest one. The only thing the compression ratio is beneficial for on a turbocharged car on pump fuel is fuel economy, at least as long as it is higher than 7 or so.
So maybe you will lose 0.1L/100km, but you will easily and safer make more power. Which is the point I think?!

If your CR is now closer to 9.5 then the thickest variant will drop it around 8-8.2. I recommend using ARP studs with the proper torque too...
Alternative is the Turbozentrum multilayer, but the effect will not be that big. You probably need around 0.1-0.3mm extra thickness just to get back to your original CR. It depends how badly your head was warped when it was skimmed. And the Turbozentrum one gives you about 0.8mm over stock.

Keep in mind that whole timing map will need re-tuning on dyno, not just WOT. If you do not take advantage of the CR then the car will be slower off boost.

Also the 9.0:1 CR is ok for a standard K04, not for a turbo that can give 1.5x the output. The 9.0:1 is already a tradeoff between fuel efficiency and performance/reliability from factory.
You should be aiming below 8.5.
VAG dropped the CR by 0.5 going from 180hp to 225hp, which is only a 25% power increase.
« Last Edit: February 29, 2024, 08:28:39 AM by prj » Logged

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fknbrkn
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mk4 1.8T AUM


« Reply #20 on: February 29, 2024, 09:53:28 AM »

What is the common practice with the timing at low end range with ~8.5 CR ?

iirc ~25-30 btdc at the underboost levels was the best for driveability but impact on the boost buildup is noticeable
stock ~10 deg building boost faster but lacks of response

btw id say 9.0 with k04 is the pretty good choice with proper fueling for a daily use, but at the limit of CR
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prj
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« Reply #21 on: February 29, 2024, 01:41:20 PM »

btw id say 9.0 with k04 is the pretty good choice with proper fueling for a daily use, but at the limit of CR

He has TTE 480, not a K04...

Timing you have to find on dyno, my experience is that torque is always better when you get on the throttle, because with 9.0:1 CR knock limited absolutely everywhere at WOT, even if turbo is not spooled.

You can do tricks with spool, like using lambda 1 for quicker spooling as it creates higher EGT and so on.
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