Stroker build

[Wizard-of-OD]

Kind of late to the party and did not get a chance to read the rest of the thread but just thought Id shed some light on Wossner pistons from my own discovery and ask a few questions:

Measuring piston volume for cr calculations

1. Do you mind sharing what you got for piston dish volume?
2. What head gasket did you use? AAN is 82.2mm max bore @ 1.60mm thickness fully compressed so did you take an AAN head gasket and bore it out?
3. Were you ok with your pistons sitting above deck?

From dealing with Mahle Motorsport , I have discovered (the hard way) that Wossner publishes incorrect data on there website.Lets assume they did publish correct data though:

http://www.wossnerpistons.com/produc...e?cookietest=1
Dome Volume = -19.7 cm³
Compression Height = 30.2mm

TDI Block = 236.5mm deck height (not 236mm as often published)
TDI Crank stroke = 95.5mm
Connecting rod Length = 159mm

So you would need a piston that a Compression Height of : 236.5 - (95.5/2 + 159) = 29.75mm
So by using the Wossner pistons , your pistons are now sitting 30.2mm - 29.75mm = 0.45mm above deck.
Not a huge issue if you are running a 1.6mm thick head gasket when compressed (which from the images they are) however lets work out your CR.

Cylinder head CC = 44cc (for a 4V/cyl stock size valve pockets)
Cylinder head gasket CC (AAN head gasket bored out to 82.5mm and a max thickness of 1.6mm) = 8.49cc . with pistons sitting 0.45mm above deck means that cylinder head gasket volume is reduced from 8.49cc to 6.09cc

Vc = 6.09cc + 44cc + 19.07 = 69.69cc

82.5mm bore x 95.5mm stroke = 2552.5cc : Vh = 510.50 cc / cylinder

Based on my math a 82.5mm bore piston (for me) will yield the following:
E (compression ratio) = (Vh + Vc) / Vc

= 510.50 + 69.69 / 69.69 = 8.3:1 CR

Kind of low CR no?

[diesel des]

So when it came to compression ratio selection I was torn in 2 directions. As I run 95 plus % on lpg gas which has an octane of something like 110 it made sense to go with a high cr. But the issue I have is that the lpg system falls back to petrol if it has any issues. As the lpg tank isn't baffled very well if at all I find that if I'm below half tank and pull lots of g in a series of bends I get vapour and not liquid from the tank and the lpg ecu falls back to petrol. All I notice while driving is a slight glitch or hick up when this happens and a few seconds latter the lpg ecu goes back to gas automatically.

It's quite hard when this happens to get a definite signal from the lpg ecu that it has switched fuels that I could reliably tie into vems to switch maps. So to be safe I needed a setup that was safe on cheep petrol 95 Ron.

I worked with a guy called Brian who did his PhD in internal combustion engine development and was very interested in this type of thing. We talked about compression ratio and it's effects on power and efficiency. In a normally asperated engine cr has a bigger effect on power and efficiency than boosted engines. The reason being that a high static compression ratio on a boosted engine will mean loads of timing retard when boosting and a big drop in efficiency. There is an optimum timing advance for any combustion chamber design and retarding beyond that hurts efficiency. Prj Dmitri has also stated that 8: 1 is ok on normal pump fuel and 8.5 is a bit high. Again JP has a 7.X : 1 compression on his stroker.

I talked to Brian about compression and turbo spool. I told him that Internet wisdom was that high compression spools turbos faster that low cr. His response was a lot of mathematics that prove the opposite. With high compression you have a high expansion ratio in the cylinder. This high expansion ratio is how extra efficiency and some more power is obtained from the fuel. BUT as the gas has expanded more in the cylinder driving the piston there is less energy available to drive a turbine and the egt will be cooler. This means slower spool.

Now to counter this he did say that if you were planning a low boost engine higher cr would be benificial as despite the lower exhaust energy the engine would do more with the low boost than a low cr engine. But to make my power and torque target I need 2 bar boost on my displacement to flow the required air so low cr was a necessity.

So I set 8.25:1 as my target compression ratio. I did the same calculations as you and the wossner pistons you linked looked perfect. I got them and measured the volume to be more than what wossner stated! Also the compression height is a little less too. So I did a dry build of the engine and measured were the piston was relitive to the deck. I was able to skim 0.45 mm from the deck to get the piston out of the block 0.65 mm. I'm using a machined victor rinze gasket from iroz motorsport in the us. This can be machined to use 83mm pistons if required. Anyhow that gave me a squish height of 0.95mm. I like to run an engine just below 1mm and over 0.85 so it's about right. It should be good for knock suppression as the wossner have a nice combustion chamber with a squish ring round the edge.

Anyhow with this build I ended up with 8.05:1 compression ratio. Slightly lower than I wanted but within my 8 - 8.5:1 target range. The drop in compression will hurt fuel economy at cruse slightly but on boost the engine will be more efficient than a high compression engine with excessively retarded timing. Or so the theory goes...

[S2central.net]

Some proper science behind this build thread !

[diesel des]

Yea I suppose to sum it up having proper timing settings is more important to power and efficiency on boost than compression ratio. So better to loose some compression to gain timing.

[Wizard-of-OD]

Yea I suppose to sum it up having proper timing settings is more important to power and efficiency on boost than compression ratio. So better to loose some compression to gain timing.

2.5+ bar?

[diesel des]

The compressor map shows 2.3 bar through the mid range as a option.... [emoji1]

[kamuto]

The compressor map shows 2.3 bar through the mid range as a option.... [emoji1]

now try to upgrade to 1.2.23 maybe it will work too it has proper knock controll btw, check it with timing light after firmware upgrade btw, where are you from?

[diesel des]

I need to check timing with the strobe. Another thing on my to do list. I'm in northern ireland.

[quattro-nick]

is it realy possible,2 bar effective boost on 3000 rpm? or is it 2bar boost - 1bar atmosphere=1 bar effective boost
in vems you read the boost in kpa so if it's say 250kpa it is 1.5 bar boost but that will you probably know

[S2central.net]

Des will be talking about 2bar BOOST here - not absolute pressure... but it does seem kind of mad if that EFR turbo can make >2bar by 3000 on a 2.5 stroker !

[diesel des]

Yep I'm talking gauge pressure not apsolute. I have seen 2.3 bar gauge at 3k rpm on this turbo. It surges slightly at that point but surge is gone at 2.3 bar boost at 4 k rpm. Will probably end up limiting boost to 1.7 bar at 3k tapering up to 2.2 bar at 4 k rpm to stay out of surge.

[quattro-nick]

so,i have a gt3076r and full boost (2bar)at 3800-4000 rpm with 0.82 A/R on fuelpumpgas 98 oct
except by a 0.63 A/R,is there any other solution that the turbo spool faster?
maybe with water/methanol injection in the imtakepipe before throttlebody?
my c.r. is 8.0:1 and give a later spool correct?
i dont understand you can get so many boost on 3000 rpm

[diesel des]

Your cr is fine at 8:1 on normal non race petrol. I have 2 advantages. My engine is larger. 2550 cc vs your 2226cc and my turbo is smaller. Your turbo will make 25 to 50 bhp more than mine on your 0.82 housing approx. So you traded more top end power for less mid range with your turbo, and that's fine in a lighter car. My car is 1900 kg with me in it so I wanted torque and early spool more than power. I "only" want 450 bhp and this turbo can flow 52 lb min which is easily capable of 450 or push towards 500 bhp maybe... We will see.

[diesel des]

Looking at vems and knock control. My new firmware 1.2.11 is quite limited with knock control. It looks like version 1.2.15 is the one I need to use this tutorial.

http://vems.hu/vt/help/v3/v3_knock_control.html

On further reading of vems firmwares I should be able to upgrade as far as 1.2.19 without the bootloader being upgraded. What version do people recommend between 1.2.15 and version 1.2.19?

http://www.vems.hu/wiki/index.php?pa...irmwareChanges

Or as only version 1.2.20 says it needed the newer bootloader does that mean I could use say 1.2.23? So confusing. I have the bootloader cable on order...

[kamuto]

Looking at vems and knock control. My new firmware 1.2.11 is quite limited with knock control. It looks like version 1.2.15 is the one I need to use this tutorial.

http://vems.hu/vt/help/v3/v3_knock_control.html

On further reading of vems firmwares I should be able to upgrade as far as 1.2.19 without the bootloader being upgraded. What version do people recommend between 1.2.15 and version 1.2.19?

http://www.vems.hu/wiki/index.php?pa...irmwareChanges

Or as only version 1.2.20 says it needed the newer bootloader does that mean I could use say 1.2.23? So confusing. I have the bootloader cable on order...

for audis in Uk I use 1.2.23 but knock works from 1.2.15 anyway wait for cable, and use 1.2.28 or similar