M20B25 Twin Turbo Setup Question

[ariel]

Hi there guys.
Im runnin atm single turbo setup t4 i think.
Quite massive turbo and lagy.Didnt realise will
try to go profi drifting route and for my purpose is usless.
Dont get me wrong engine prepared for easy 2bar of boost (thats what im running now)havent blowe up for the last 2000miles abuse.When i mean abuse 100mph power slide full
boost no probs.
Problem is im getting boost at 4000rpm which is CRAP for my purpose.

Question to guys who have some expirience:
What setup is better:
2 x k03 (like passat 1.8 turbo) or
2 x k04

any other options more than welcome.
Thanks

[b12rlw]

what spec u got for 2Bars boost?

[ariel]

Smallest (thinest) Commetic headgasket
ARP Studs,All fresh genuine bearings and piston rings,later type pistons (supost to be forged)
130mm con rods wich is give me around 7:1 compression ratio.
And aftermarket head that is much stronger AMC-i think is made in spain.
Does the job.Maximum boos ive had was 2.3bar ant that thing was flying.
Also 044 fuel pump.walbro 255 in tank and swilr pot.Ajustable fuel regulator and 5bar fuel pressure(7.3 bar under full boost).MAF conversion as well.

Has been abuse a lot and not a single puff of oil thru exhoust.

[ross2009]

your problem is really running the compression way to low ideally you want it about 8.0:1 yep its alright for big boost which is what your doing but for that sort of boost you need a big turbo which is also what your doing
if you go smaller then obviously it will choke at higher boost your engine is pretty gutless at that sort of compresssion so you need some thing with near enough instant spool up to compensate
your later type pistons as in facelift model arnt forged there just a lower compression piston that the preface lift
just cast ali

as for the k03 and k04 dont really know much about them best guy to ask is geoffbob hes the turbo guy on here

[GeoffBob]

Hmmm,

Detonation, that nasty phenomenon that has a habit of displacing head gaskets and destroying valves and pistons, is a function of the absolute pressure and temperature of the air/fuel mixture in the cylinder. One way to bring on detonation is to raise the pressure in the combustion chamber by pressurising the intake manifold beyond some critical value (whose definition I will not go into here). Another way is to raise the compression ratio. Either way, its the absolute pressure and temperature that bring about detonation. Take note that while the pressure in the cylinder is undoubtedly a function of boost pressure, lowering the compression ratio will, as expected, offset the effect of pressurising the intake manifold. For example, 2bar of boost at a compression ratio of 7:1 is roughly equivalent to 1.3bar of boost at 9:1. At least in terms of peak combustion pressure that is.

So what's the difference between the two? Simple, a 2bar 7:1 CR engine inducts more air and fuel than a 1.3bar 9:1 engine. Why? because it is physically flowing a greater mass of air into the engine (assumedly mixed with the prerequisite amount of fuel courtesy of the ECU). Why is this important? Because actual hp has f*ck all to do with boost pressure and everything to do with the mass of air and fuel flowed into the engine. Hence the supreme importance of the intercooler due to the fact that is raises the density of the inducted air, and thus increases the mass of air drawn into the engine. So what's the downside if any? Well, the lower the CR of an engine the lower its thermal efficiency (thermodynamics 101). Hence, less hp for each gram of fuel combusted. So why build a low CR engine? Usually for drag racing. On boost a low CR engine has the potential to make high hp (albeit at low thermal efficiency) due to the greater volume of air and fuel that can be inducted without the onset of detonation. The downside, however, is that the car will be a slug off-boost and fuel economy will be appalling. Definitely not a car to be stuck in traffic with.

Ariel, at the very least you need to raise your CR if you want to get away from the lag you are encountering. This will no doubt require that you also lower your boost pressure to avoid detonation. As it stands your engine isn’t making enough hp off-boost to get its revs up fast enough to be able to induct more air which is required to further spool up the turbine, etc... You’re stuck in a vicious circle that is the product of a large turbo and a low CR engine.

I wouldn’t recommend either the KKK K03 and K04 for your engine.

[Ant]

dig out turbobrown's ( Alex) original twin turbo build in the FI section, lots of useful info there !

zero lag on that , and 270 hp on a stock 9.75:1 bottom end @ 7 psi iirc.

search for all posts by username turbobrown in the FI section, it will get you there

[Kos]

I was told His car kept shitting it self

Proper twinn turbo setup took up 'bootymans' car

[Ant]

more for guidance than empirical data Kos

more info on that one that Bootys on here iirc.

[pacerpete]

I was told His car kept shitting it self

Proper twinn turbo setup took up 'bootymans' car

I heard Bens was just lots of Samco and Mirage tat and not much gristle. All show and not much go . I'm still waiting for the 800 BHP dyno print out

[E30BeemerLad]

I think the last i saw of Ben's car was in PPC magazine when it was on the rollers at Dave Walker's place and the only reason it hadn't done big power was because it was on stock injectors still. Not heard of what the car has done since then though, but I think the comments of Mr Walker were that it was a properly sorted setup.

[CHR1S1990]

ariel, I seem to remember you are running LPG? I assume you figured a low compression, big turbo, high boost motor running on LPG octane would be a good idea when you built it? I would take heed to Geoff's advice, your (very very) low CR is the main problem here. Hopefully you wont have to lower your boost pressure much due to running on LPG and you would see some nice gains. Shame you said you've fitted the thinnest cometic headgasket and not the thickest as it would be a simple fix!

[Gunni]

Hi there guys.
Im runnin atm single turbo setup t4 i think.
Quite massive turbo and lagy.Didnt realise will
try to go profi drifting route and for my purpose is usless.
Dont get me wrong engine prepared for easy 2bar of boost (thats what im running now)havent blowe up for the last 2000miles abuse.When i mean abuse 100mph power slide full
boost no probs.
Problem is im getting boost at 4000rpm which is CRAP for my purpose.

Question to guys who have some expirience:
What setup is better:
2 x k03 (like passat 1.8 turbo) or
2 x k04

any other options more than welcome.
Thanks

What boost control are you using?

Have you made sure you have as leak free intake system after the compressor as possible? Same on the exhaust side.

You might be in the market for antilag for drifting.

[e301988325i]

your problem is really running the compression way to low ideally you want it about 8.0:1

8:1 would be achievable with a small piston skim, a thick head gasket and 135mm rods.

If you're running LPG then detonation surely can't be an issue, as well as the high octane rating LPG doesn't pink as it needs a spark or flame to start combustion.

Correct me if I'm wrong here guys?

[HairyScreech]

Lpg comes up at about 104 research octane.

I think the crevice volume created by the use of a thicker head gasket and skimmed piston may be worse than the effect of the higher compression. detonation Is not just a result of mechanical compressing but also the pressure built during combustion a large crevice volume can lead to the mixture being forced into the gap and remaining unburned until very late in the cycle, which can result in that mixture becoming over pressurized.
another effect of q large crevice volume is the mixture can remain trapped in there and not bun at all resulting in high consumption and poor emissions.

If heading for large crevice volumes inthe squash band then it may be better going for an open chamber design. this would be do-able on the m20 by using flat pistons and opening the b25 head up similar to the alpina. its still compromised but it will be less nasty than large crevice volumes.

Can't really write a lot here as important on the smart phone but whats the exact spec your current build, as it maybe something simple causing the lag.

[Gunni]

Depending on the gasket thickness you may or may not run into det problems with less compression.

larger then 3mm gap will not cause issues.

[Phill172]

dig out turbobrown's ( Alex) original twin turbo build in the FI section, lots of useful info there !

zero lag on that , and 270 hp on a stock 9.75:1 bottom end @ 7 psi iirc.

search for all posts by username turbobrown in the FI section, it will get you there

That set up is now in france, there is a link to it somewhere but I cant find it