Saxo VTS Turbo, std compression?

[Bim]

So i got my head skimmed 0,15mm and bought an repair gasket which is 0,20mm thicker (1,7mm gasket)

So i wont be lowering my compression, im curios if anyone done this before, high boost Saxo VTS? (standard compression).

Its a std engine aswell.


Instead of lowering comp and have more boost, could'nt i have std comp, and lower boost, to get about the same power?

Maybe doesn't work like that..

Im more curios, so i dont blow up my engine the first thing i do, when its ready.. :wall:

[AdamH]

i know its suitable for low boost, but I wouldn't recommend past 6psi. Normally its a uber tight budget way rather then a decomp or going lowcomps.

what psi are you looking at?

[blackie_2k5]

You can run oe compression, but are limited to what ignition you can run

You could run 8psi and decent ignition mapping and get a good nice feel,

But on the other hand,

You could run more boost but have to retard the timing to stop it knocking and it'll feel flat and boring, it's a trade off really

Nothin sayin ^^ those are figures set in stone either, just have to have your mapper work with what he can come mapping time

[Bim]

As its my first turbo conversion, and a little bit of budget/diy build, i prolly would be satisfied with about 0,5bar (7,5psi) to start with, you will always want more :).

Is there any type figures, what hp that would give me, or is that impossible to say?

[jones91]

It's impossible to say really as you haven't said what turbo your using lol, 0.5 bar on a k03 turbo would easily be fine, but 0.5 bar on a gt34 and the standard internals would struggle lol

[axsaxoman]

0.5bar is 0.5bar no matter what turbo it comes from --std internals will be fine at that with correct ignition+ fuelling

[tweeqd]

The pressure is the same but the volume of air will be different

[yr51ocw]

0.5bar is 0.5bar no matter what turbo it comes from --std internals will be fine at that with correct ignition+ fuelling

Compressor dependant, the plenum temp could drastically change which will change the engines knock limit.

[luthor1]

The pressure is the same but the volume of air will be different

Not sure that's right, 0.5 bar is measured in the intake, what does it matter if it's a big turbo turning 80,000rpm or a small one moving at 120,000rpm?

Mass of air is represented by volume, pressure, and temperature, I can't see how what turbo is pushing it makes a difference to that equation?

It will affect surge, spool time, tail-off and temperature (if you're spinning a tiny turbo too much)

EDIT: I would never use a decomp plate either, because that puts the cylinder head face further from the piston crown reducing the gas speed at the point of 'squish' therefore, quite ironically, *increasing* the chance of detonation!

[tweeqd]

while the pressure (psi) may be the same when comparing two different turbos, the surface area (air the turbo can hold and thus blow) is completely dependent on the size of the wheel, housing etc (for simplicity's sake we'll just say dependent upon the size of the turbo, period).

So at a given pressure, a large and small turbo will move different amounts of air b/c their surface area is different. And if one has a much larger surface area, the resultant force from the turbo is greater, which leads to greater forced induction of air into the IC --> more cold air --> greater density of O2 into the motor --> greater combustion --> greater power.

[gazza808]

The reason you get pressure is there's a restriction,

Imagine a 1inch pipe sealed one end with a 1mm hole in it,

Now pump air through that pipe, using a small compressor, to a point you see 10psi pressure, then do it with a massive compressor, if you put air flow meter both will be flowing the same amount of air to get that pressure in that pipe, it's just the fact the bigger one has less work to do per rpm, and has a much bigger range to go higher.

No idea if that applies to engines though lol!

[luthor1]

while the pressure (psi) may be the same when comparing two different turbos, the surface area (air the turbo can hold and thus blow) is completely dependent on the size of the wheel, housing etc (for simplicity's sake we'll just say dependent upon the size of the turbo, period).

So at a given pressure, a large and small turbo will move different amounts of air b/c their surface area is different. And if one has a much larger surface area, the resultant force from the turbo is greater, which leads to greater forced induction of air into the IC --> more cold air --> greater density of O2 into the motor --> greater combustion --> greater power.

tweeqd, I'm afraid I think you're just wrong there :( Sorry - not wanting to start a row!

Look at it from the Manifold's point of view, that's what the engine is sucking on - in the manifold we measure 30degC, 0.5bar positive pressure and have a known volume. How/why does it matter whether the turbo it small/fast or big/slow? the engine is sucking from 30degC air which is at 0.5bar.

If neither the pressure nor the temp change, then the mass of air remains the same irrespective of the turbo.

The 'larger' turbo, given our 0.5bar of manifold pressure, will simply be spinning slower. It won't be moving more air, it will be moving the same mass of air, but the blades will be turning slower.

when the manifold is full of 0.5 bar of pressure, it will send a signal to the larger turbo to open the actuator and stop increasing pressure. The same with the smaller turbo, one just spins faster than the other, but it amounts to the same thing.

Have a think about the exhaust side - on the big turbo it has lag because the exhaust gas only turns the blades slowly, on the little turbo the same MASS of air turns them more quickly. Now reverse that and pretend the blades are being turned and the gas is being forced, now you can see that for the same pressure, MASS stays the same (temps being equal).

[axsaxoman]

air temp rise will be the same as temp rise is a function of compression ,so same pressure rise will heat air by same amount

[tweeqd]

ok i was wrong on the volume but my point is valid with the density

the statement of ''5 psi will be fine'' is rubbish unelss you know the size of the turbo used

[axsaxoman]

density is pressure .
your intercooler effiency is not variable but fixed as a function of core size +type ,
so if the engine eats "x" cfm @0.5bar then the volume of air flowing through it is the same no matter what is providing the pressure
only thing that can change the outlet temp of air that flows through it is temp of air being drawn through the core to do the cooling,so if you have a big turbo right close behind it ,its possible the radiated heat from it or from the manifold could drop the effiency of the intercooler ,or maybe impede the flow by just being close to it
in thruth the slower the air flows through the intercooler the better temp drop you get ,which is why bigger intercoolers work better.
the downside with turbo,s is a larger than needed intercooler gives more lag.
the intercooler core i use for the s/c cars is actually good for well over 600bhp ,if it were a turbo -but as lag is not a problem with s/c I will go for lower induction temps every time ,which is why i can get what seem like big fugures from lower boost levels than with turbo,s .
I don,t have the luxury of being able to just wind up the boost as you can with a turbo to make up for a poor flowing intercooler.
if you want to check how good your intercooler is measure pressure drop by taking a pressure reading from the input end of intercooler and compare with what the inlet manifold is seeing--it is easy to by fooled into thinking the actuator spring is not correct pressure it is rated at ,just because of the pressure drop across the intercooler

[luthor1]

ok i was wrong on the volume but my point is valid with the density

the statement of ''5 psi will be fine'' is rubbish unelss you know the size of the turbo used

Yes totally agree with that! Once you choose the power required, that really defines the pressure required, and from that, defines the turbo given the flow map.

If you want 165bhp on a 16v you are never gonna choose a Disco Potato, you'd be insane, it'll have so much lag - you'd have the GT1752 and it'd come in hard from around 2200-2500rpm and hold that power right through easy without becoming a hair-dryer

[Bim]

TD04HL-13T from a Volvo. I can't find any info about the compressor/turbine Wheel tho..

[yr51ocw]

air temp rise will be the same as temp rise is a function of compression ,so same pressure rise will heat air by same amount

Nope, thats why different compressor designs have different efficiencies. Yes you may see 5psi at the inlet manifold, but the but a 5psi/30degC inlet air condition will have a different effect as a 5psi/70degC inlet air condition. The pressure and temp of the compressor out air is a function of its efficency.

Here is the math:

Inlet Air Temp = 25degC
Inlet Air Pressure = 1000mbar (abs)
Therefore inlet density = 1.17kg/m3
Compressor out pressure = 1500mbar (abs) (7PSI)

If the compressor efficiency = 60%, then:

Compressor out temp = 86degC
Compressor out density = 1.45kg/m3
Static Pressure Ratio = 1.5
Density Ratio = 1.24

If the compressor efficiency = 80%, then:

Compressor out temp = 70degC
Compressor out density = 1.52kg/m3
Static Pressure Ratio = 1.5
Density Ratio = 1.30

So you can see that the compressor efficiency controls the density of the air in the inlet manifold, even in the pressure is the same. It is the increase in the DENSITY of the inlet manifold air that is the purpose of the compressor.

[yr51ocw]

density is pressure

NO NO NO. Basic physics states:

P=(nRT)/V

[luthor1]

This math is going to confuse some people, and I'e realised we are talking about different ends of the intake system. You are talking about just before and just after the turbo itself, and John and I are talking about what's actually in the intake manifold.

PV = nRT therefore for a pressure and temp in the manifold, the MASS of air is the same irrespective of what turbo the air passes through.

Your maths is talking about how much the turbo heats the air up, well that doesn't really matter, this thread is about pressure, and pressure in the manifold. The OP is taling about 0.5bar of pressure in the inlet manifold, and the turbo STILL doesn't make a difference to that air MASS unless the air is at a different temperature

[Ross]

Although (just to throw my oar in the mix)... of course the temperature does matter. It's critical in fact - as you're talking about running standard compression, and (presumably) standard pump fuel.

Detonation is therefore a factor because of the temperature - remember the OP's actual question before we get bogged down in the science. :)

[yr51ocw]

thanks ross!

Andy - yes you and john were talking about the inlet manifold, my point was if you are getting very hot air coming out of the compressor then you are most likely going to have hot(ter) air in the inlet manifold (assuming the same I/C system and boundary conditions)

Therefore the turbo size can have an effect on mass flow and performance for the same static manifold pressure.

[yr51ocw]

This math is going to confuse some people

I know that, but it was used to prove a point. And hopefully if more people actually put some thought/math into their turbo selection rather than using the opinion of forum users then hopefully the vehicle would perform better.

[luthor1]

thanks ross!

Andy - yes you and john were talking about the inlet manifold, my point was if you are getting very hot air coming out of the compressor then you are most likely going to have hot(ter) air in the inlet manifold (assuming the same I/C system and boundary conditions)

Therefore the turbo size can have an effect on mass flow and performance for the same static manifold pressure.

But not at half a bar, with even the cheapest universal FMIC on the car?

If he was trying to push 240bhp / 17psi out of a GT1752 then yes, maybe a GT2554R would be better, but half a bar, that's nothing really!

[atspeedracing]

https://i.chzbgr.com/maxW500/4668978432/h9AB69F8E/

[blackie_2k5]

Back to the original post.. Get your mapper to start about 7/8 psi and see what it's like, if it'll take a little more then try it, but don't susbstitute more boost at a cost of less ignition

As it'll feel better and quicker with a lower psi and more ign :y:

[axsaxoman]

I know that, but it was used to prove a point. And hopefully if more people actually put some thought/math into their turbo selection rather than using the opinion of forum users then hopefully the vehicle would perform better.

thats what i have been saying for years turbo match is important --so would the right turbo not be one from a modern 1.6 litre engine ?

then lag and all the other bad bits won,t be a problem --

[luthor1]

Anyone know what turbo the new Fiest ST 1.6 EcoBoost turbo has? That's probably a good one! 1.6 litre, makes 182PS in stock form and still does 57-some-odd mpg!

[yr51ocw]

so would the right turbo not be one from a modern 1.6 litre engine ?

then lag and all the other bad bits won,t be a problem --

I agree, OEM turbos are usually very well spec'd for the intendent performance while still taking into account transient response, efficiency etc...

The problem with OEM turbos (especially modern ones) is that they are getting more complicated to adapt to use in an aftermarket situation, such as intergrated manifold, pressed stainless turbine housings, electronic actuators, twin scroll, compressor by-pass. None of which is impossible to work around but it can add more complexity to what is already a complexed project (turbo'ing a N/A engine). Hence off the shelf turbos with known interfaces are still the most popular choice but this does require some thought put into the match.

[axsaxoman]

looking at the majority of turbo conversions it seems the off the shef ex manifolds have the biggest influence on turbo choice .
there are lots of simply modern turbo,s about but they do not use the common gt flange .
thats the other point you make quite well ,which forums gloss over ,
fitting a turbo and getting it right is not any where near as simple as it first looks.

add to that most expect too much power ,too cheaply and are repeated told on forums that you can make turbo conversion from s/h bits for bugger all and get huge bhp figures at the same time
the std type evo turbo,s are small, spin up quick ,but don,t have same flange
I,m pretty sure they would be a far better match for most mid to higher powered conversions ,std unit spools at less than 2k on a an evo and can make 360 bhp .
they are physically small ,
the cost of course is the other usual factor -- they are not as cheap as the old style turbo,s

[SeniorGT]

Evo turbo's are a good match, used an 80 series before on a 106, helps being a twin scroll design and makes good power low(ish) down, also found the subaru turbo's work well (our preferred choice), and give a good range of possible upgrades if you start fairly low in the range with a td04, aswell as the possibility of using a standard location Scooby Clinic billet turbo, more for the big power builds though and presumably out of the OP's price range.

[SeniorGT]

You can run oe compression, but are limited to what ignition you can run

You could run 8psi and decent ignition mapping and get a good nice feel,

But on the other hand,

You could run more boost but have to retard the timing to stop it knocking and it'll feel flat and boring, it's a trade off really

Nothin sayin ^^ those are figures set in stone either, just have to have your mapper work with what he can come mapping time

Just worth a mention you dont need to be as sympathetic as you'd think with timing even at reasonable boost levels on std compression, 1 bar is easily doable nowdays with proper management and mapping.

[blackie_2k5]

I know mate :) I wouldn't have said 1bar, I'd have said ten psi from my experience, but you'll have seen/done more then me,

Post was mainly to show that he shouldn't add too much boost and have to retard the timing to compensate, better to run lower boost and nice advance

That's why other one ^^^ sais start 8ish and get the mapper to work with it to get what he can :)

[SeniorGT]

I know mate :) I wouldn't have said 1bar, I'd have said ten psi from my experience, but you'll have seen/done more then me,

Post was mainly to show that he shouldn't add too much boost and have to retard the timing to compensate, better to run lower boost and nice advance

That's why other one ^^^ sais start 8ish and get the mapper to work with it to get what he can :)


No worries, just mentioning whats possible, agree completely with the part about letting the mapper sort final boost level, its whatever they are comfortable with at the end of day.

[blackie_2k5]

Yeah they're strong engines tbh

Better to find someone with experience in them than someone who wants to be conservative

[axsaxoman]

I agree but what you can,t get way from is the design and stregthen of std pistons --the std units will eventually crack or compress top ring land and unfortunately the only off the shelf pistons are very lom comp .
remeber owssner comp ratio quoted is with no head gasket ,so you add that and the comp is alot lower than you think
I had a btach of higher com postons made --but took along time to sell them as most are looking for the cheapest parts
I would do it again IF i thought they would sell .
yes you can get specials made but they will cost £600+ a set +vat

the only way to get them down to a lower price is to get at least 10 sets made at a time

[blackie_2k5]

Thing is these days, most wil be happy with 200-250bhp which is daft quick in A Saxo and it can be done on double head gasket

If you're doing the work yourself you can go through 4 engines before a forged lump could even be considered

I got 14 months out of my first engine before I though I had issues and replaced it, turns out it was t even the engine lol

If they lasted a year each, most won't even keep the car 4 years

[SeniorGT]

Thats exactly the reason i personally think going for a standard engine is the best choice for going boost ( on a reasonable budget), as it cuts the cost hugely by not having to have the engine built in the first place, gets very good power, stays within the limits of what the ma box can take ( with some sympathy ) and makes for a very driveable car off boost. While still keeping a good level of reliability. Even if something was to go wrong, its only the cost of a good low mileage engine.

[axsaxoman]

so you are saying a std vtr which is 90bhp can be lifted to a REAL 250 bhp on std internals,nearly 3 times std bhp!!!! and that will be at least 1.5 bar of boost
i think your rollers are enthusiastic to say the least .
200@ wheels is not for std pistons --
I,ll leave you carry on this thread

[blackie_2k5]

Mine was 185atw's

Never mentioned it for vtr but plenty have done it and ill be pushing mine further

Plenty vts running 220+ atw's on oe pistons,

Nothing wrong with the rollers impulse either, they're the best in the north east and have been proven time and time again

[jones91]

As blackies just said, with the right mapping and low enough compression vtr/vts pistons can take mega power

I'm not the best example of saxo reliability with boost lol, but I believe Ropers gti lasted 5 years with 250bhp @ the fly on a standard engine, and i think that only gave up because a standard rod bolt gave way

[SeniorGT]

so you are saying a std vtr which is 90bhp can be lifted to a REAL 250 bhp on std internals,nearly 3 times std bhp!!!! and that will be at least 1.5 bar of boost
i think your rollers are enthusiastic to say the least .
200@ wheels is not for std pistons --
I,ll leave you carry on this thread

282bhp at the fly, and 240-odd at the wheels, wouldnt call it generous tbh. Running 1 bar flat from spool to limiter, on a 16v engine, for over a year and a half, i'd call that reliable.
Very easy to slag rollers off.

[blackie_2k5]

Last post was meant to say I use* not impulse


It's been done time and time again, don't get me wrong John.... I wouldn't want To lash it round track all day, most are road cars

They can and do last

[Ross]

282bhp at the fly, and 240-odd at the wheels, wouldnt call it generous tbh. Running 1 bar flat from spool to limiter, on a 16v engine, for over a year and a half, i'd call that reliable.
Very easy to slag rollers off.

Saxo Vtr johns talking about tho not c2 Vtr - so it's missing 8 valves :D

[axsaxoman]

not wanting to get into the old rollers debate again ,but i had to have one more say on this thread
just post up a video showing a car with std pistons holding 240@wheels for more than 5seconds with std pistons
It takes longer than that for the inlet + exhaust temps to stabalize.
if the engine cannot hold the power for at least that time then its not a REAL figure
dyno run should take at least 12 -17 seconds to be a REAL figure from say 2k to 7k--not 6-7 seconds--thats jsut not enough load on the dyno


and that is the test to show relaibility and true figures.
I am not saying that the car won,t go well ==it will,
but lets not get carried away with the actual numbers.

If I put a seat /vw or renault or any std turbo hot hatch I expect to see it hold the real number and it will -- and they will have forged pistons as std

I wonder if most appreciate the difference between cast + forged , If they did I don,t think they would be making such definative and all encompassing statments about the sutability of std pistons + high boost.

forged pistons expand at a different rate to cast pistons and the ring gaps are totally different for a boosted application ,maybe up to 50-60% larger gaps -- to allow for the expansion due to heat ,especially on a bock where you only have 4mm between the bores and no water cooling between them.

those of you that have stripped tu engines will have noticed the blackening between the bores on the block and the "distortion" of the head --its not the head that distorts but the block expands up wards deforming the head due to excess heat where there is no cooling --and thats on std engines --not boosted. which is hwy the jp4 head is thicker and a thinner gasket ,to transmit heat better to the head where there are cooling passge ways full of water
Iti s also why the latest "ep" series of engines have gone to alloy block with sintered liners and a smaller bore --77mm to allow engough space to have water circulating and suprise suprise the pistons in these engines are noe round at the top ,not 00.6 oval across the piston pin as the tu engines are ,it is also why the ds3 turbo versions are 230-260 from the factory --the block can now get rid of the heat

the 5 seconds is about the length of time a dyno with a big cooling fan will hold the tmeps down -- after that unless you have a huge cooling fan it will not and temps will rise and power will drop away,but engine will stay in 1 piece
to get enough cooling in a dyno
eg. make an envelope of air over and under car to equate to 100mph road speed you need a 100bhp fan ,

senior gt --282 on 1 bar I doubt thats a totally std 16v just with a turbo fitted --and at what rpm is it fully spooled 3-4k .so no real heat load until you get there and if it then takes another 3 seconds to get to max rpm --its not very long and not much heat soak to deal with .
as blackie has said= most ,if not all of the turbo cars go for very short blasts of power and not on a track going to max rpm every gear change . which again is not giving the heat soak that makes the std pistons + block expand .
most of the engines used will be very s/h and bores will be worn so it may help disguise +help the sitiuation --but to say catergorically you can run 1 bar on std pistons is incorrect at best and just asking for trouble.
add to that peoples dislike of paying for mapping on a home build turbo conversion and you have recipe for disaster --
just accept the limitations and run sensible boost on std internals is what people asking about turbo conversions on std internals should be told

[SeniorGT]

not wanting to get into the old rollers debate again ,but i had to have one more say on this thread
just post up a video showing a car with std pistons holding 240@wheels for more than 5seconds with std pistons
It takes longer than that for the inlet + exhaust temps to stabalize.
if the engine cannot hold the power for at least that time then its not a REAL figure
dyno run should take at least 12 -17 seconds to be a REAL figure from say 2k to 7k--not 6-7 seconds--thats jsut not enough load on the dyno

senior gt --282 on 1 bar I doubt thats a totally std 16v just with a turbo fitted --and at what rpm is it fully spooled 3-4k .so no real heat load until you get there and if it then takes another 3 seconds to get to max rpm --its not very long and not much heat soak to deal with .
as blackie has said= most ,if not all of the turbo cars go for very short blasts of power and not on a track going to max rpm every gear change . which again is not giving the heat soak that makes the std pistons + block expand .
most of the engines used will be very s/h and bores will be worn so it may help disguise +help the sitiuation --but to say catergorically you can run 1 bar on std pistons is incorrect at best and just asking for trouble.
add to that peoples dislike of paying for mapping on a home build turbo conversion and you have recipe for disaster --
just accept the limitations and run sensible boost on std internals is what people asking about turbo conversions on std internals should be told

John, not looking for a heated debate on this issue, but i think we will have to agree to disagree on this, as the car i mention time and again is used hard, whenever the owner feels like it, goes on trackdays ect.
The engine IS a completely stock J4, its never even had the head off in his 2 years of ownership, still running one completely standard head gasket, without a head spacer ect.

http://i199.photobucket.com/albums/aa41/senior520/IMG-20121210-WA0002.jpg
Dyno screens for ref... Showing repeated back to back pulls, with power increasing run over run thanks to increased ign advance. Can clearly see the boost trace aswell.

Said video... of the car doing 282bhp coincedantally.After a full hour of almost non stop back to back pulls.
http://i199.photobucket.com/albums/aa41/senior520/th_VIDEO0006.jpg (http://i199.photobucket.com/albums/aa41/senior520/VIDEO0006.mp4)

[blackie_2k5]

To add to that my VTR spent about 12 mins on the dyno last time with about 7/8 back to back runs, my arse was going like a rabbits nose about how hot it must have been, was ran until, it started decreasing in power due to heat as expected

And that's over spinning a t25 on 15psi, so more then a bar (just) and will obvs be giving more heat then it should really be subject to

Edit- also can't be arsed to get into the debate, but there are many ppl running decent boost on these engines, and they do last, if they're not run around a track all day

Was talking Tia Greek drag dude who is/was running 2.8bar on a 1.4 lump making 300+ bhp, obvs it was a drag car and will only ever get run up the strip

But it had been running over a year or two at that point doing doing full seasons

[SeniorGT]

Ohh, forgot to post that bit on the end, turbo is spooling by 2200, and on full chat by 2800, so not laggy by any means, Air temps in the dyno were a few degrees higher than it generally sees on the road but it still held intake temps under 35degreess even after many back to back runs.