Holset HX35 - boost threshold

[sultan]

 gotasuby said:

My hx35 sees 25psi boost at 2500rpm

that's a lot of strain on the bottom end

[gotasuby]

 sultan']

[quote name='gotasuby said:

My hx35 sees 25psi boost at 2500rpm

/quote]

that's a lot of strain on the bottom end

Hence the hole in block haha

[funkytown]

so just split this off to carry on the conversation.. not holset specific but good to use as a working example

can someone explain to me the logical principles as to why there would be more strain on a block at 2500rpm than say.. 5500? (@25psi).

[Guest]

how do you make 25psi @ 2500rpm?

[funkytown]

not the point on his thread but he ran a 2.5l short block, with AVCS and twinscroll,

[MercuryFree]

I was under the impression that the stress on the rods/rodbolts/rotatingbits was an exponential of RPM? ie. 25psi at 2500rpm is going to stress the engine less than (say) 20psi at 5500rpm? (approximate numbers)

Although the amount of torque you're outputting at WXYZrpm is going to matter probably more than boost level

[funkytown]

inheriently the way i'd thought of it as well Rob, but Sultans comment eludes to the opposite ???

[Wiretap]

My thoughts on this issue are a wee bit complex.

Does more power lower down (forget boost, boost is just shoving more air in, that in itself isn't going to do anything strain wise) increase strain on rods/crank vs the same power higher up?

- At particularly low revs and high load the burn may complete before the crank angle has changed all that much, while at first thought one might think that it would put undue force on bearings and things, I don't believe so, since that force is still going to be applied higher up. It's the same force however the engine speed is high enough that the burn is not unduly fast.

- There's a psychological element to it since 'lugging' feels bad (and causes carbon buildup), but I am doubtful that lugging actually puts any significant extra strain on the bottom end unless the timing is unduly advanced where detonation takes over as the cause of trouble.

- In terms of strain vs RPM. The crank is definitely under greater strain at higher RPM as it is moving faster and therefore, while the _amount_ of instantaneous strain (or strain per revolution even) doesn't change, it is occurring more often/shorter time and therefore total strain for the same time period is greater.

Regardless of the above thoughts, is it anything to worry about?

- I honestly don't think so given that many modern turbo european cars (VW Golf, Audi A1 are the two I'm looking at in this instance) run compression ratios greater than 9.5:1 (2010 Golf GTI, 9.6:1 as per http://www.netcarshow.com/volkswagen/2010-golf_gti/ ) and spool to full boost by about 1800rpm. Subaru also have done this in the past, BC5 and BF5s equipped with the VF10 spooled to full boost by around 1600-1800rpm and the BE5D TT spools to 1bar+ by 1400rpm.

Looking at the above points I personally disagree with Sultan/Mike and concur with MercuryFree/Rob

[gotasuby]

It knocks slot easier at lower rpm due to faster burn compared to rpm. When it knocks its also alot more violent. Also particularly with v7 on but at lower rpm the cam and crank angle sensors read less voltage so make it harder for ecu to get exact position. Link have known about this issue for ages.

[Wiretap]

 gotasuby said:

It knocks slot easier at lower rpm due to faster burn compared to rpm. When it knocks its also alot more violent. Also particularly with v7 on but at lower rpm the cam and crank angle sensors read less voltage so make it harder for ecu to get exact position. Link have known about this issue for ages.

I disagree with this statement. Knock is not a premature burn completion. However MBT does certainly shift to a more retarded timing at lower RPMs.

Some light reading to clarify my point: What is knock vs pre-ignition? http://en.wikipedia.org/wiki/Engine_knocking

[gotasuby]

Well headphones get he'll noisy if I don't keep timing low down low.

And I disagree with you. If I pull timing it will not knock anymore so it's not pre ignition as it would still do it as it ignites without spark plug. Knock is where the flame front is not stable and create more than 1 flame front that collides.

[Wiretap]

 gotasuby said:

Well headphones get he'll noisy if I don't keep timing low down low.

And I disagree with you. If I pull timing it will not knock anymore so it's not pre ignition as it would still do it as it ignites without spark plug. Knock is where the flame front is not stable and create more than 1 flame front that collides.

While it's not pre-ignition, it's ignition before MBT, your burn is completing before the crank reaches 16* ATDC, so it may aswell be pre-ignition. This will create the same rattle as knock, and it'll still come through the headphones, but at a different frequency (a knock sensor with appropriate filter will not register provided your timing isn't toooo absurd)

[gotasuby]

 Wiretap']

[quote name='gotasuby said:

Well headphones get he'll noisy if I don't keep timing low down low.

And I disagree with you. If I pull timing it will not knock anymore so it's not pre ignition as it would still do it as it ignites without spark plug. Knock is where the flame front is not stable and create more than 1 flame front that collides.

/quote]

While it's not pre-ignition, it's ignition before MBT, your burn is completing before the crank reaches 16* ATDC, so it may aswell be pre-ignition. This will create the same rattle as knock, and it'll still come through the headphones, but at a different frequency (a knock sensor with appropriate filter will not register provided your timing isn't toooo absurd)

You say it's not pre ignition but then turn around and say it is? Here is a quote from your source you supplied.

Pre-ignition (or preignition) in a spark-ignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events

Not pre ignition. It knocks less at high rpm because air mixes and swirls more and has less chance of knocking. That's a fact. Also stayed in your supplied source.

I also don't see the need to have 30psi before 3000 so held boost at 13psi till 3000 then up to 27-33 depending on fuel type used.

[Wiretap]

 gotasuby']

[quote name='gotasuby said:

Well headphones get he'll noisy if I don't keep timing low down low.

And I disagree with you. If I pull timing it will not knock anymore so it's not pre ignition as it would still do it as it ignites without spark plug. Knock is where the flame front is not stable and create more than 1 flame front that collides.

/quote]

While it's not pre-ignition, it's ignition before MBT, your burn is completing before the crank reaches 16* ATDC, so it may aswell be pre-ignition. This will create the same rattle as knock, and it'll still come through the headphones, but at a different frequency (a knock sensor with appropriate filter will not register provided your timing isn't toooo absurd)

You say it's not pre ignition but then turn around and say it is? Here is a quote from your source you supplied.

Pre-ignition (or preignition) in a spark-ignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events

Not pre ignition. It knocks less at high rpm because air mixes and swirls more and has less chance of knocking. That's a fact. Also stayed in your supplied source.

I also don't see the need to have 30psi before 3000 so held boost at 13psi till 3000 then up to 27-33 depending on fuel type used.

I said it's not, but with regards to its effects may aswell be, that is very different from saying it is. In any case, it seems you don't want to hear what I have to say so I will say no more

[vorigan]

 evowrx said:

how do you make 25psi @ 2500rpm?

+1

wont explain the effects more interested how this came about

[gotasuby]

Hx35 with 16cm exhaust housing. 2.5l forged block, ported and machined heads for 2.5 block. Avcs, twin scroll exhaust manifold and fmic.

[vorigan]

 gotasuby said:

Hx35 with 16cm exhaust housing. 2.5l forged block, ported and machined heads for 2.5 block. Avcs, twin scroll exhaust manifold and fmic.

depending what spec hx35 i think that's a bloody awesome effort if it did go bang change a few things internally and tune it a different way and you'll be onto a winner setup.

i think people need to think outside the square a bit more.

[gotasuby]

Yea the setup is going in a gc8 now so will see what we can get out of it. It is the 7 blade hx35 with 54mm inducer compressor and 60mm turbine exducer.

[vorigan]

 gotasuby said:

Yea the setup is going in a gc8 now so will see what we can get out of it. It is the 7 blade hx35 with 54mm inducer compressor and 60mm turbine exducer.

unfortunately with holset i need the 353...... or whatever number is on it to let you know what it can do.

top effort dude

[gotasuby]

3539343

[vorigan]

 gotasuby said:

3539343

ive lost my borgwarner cd but from mem its off a cummins 6bt but ill borrow another and let you know

[Wiretap]

 vorigan']

[quote name='gotasuby said:

3539343

/quote]

ive lost my borgwarner cd but from mem its off a cummins 6bt but ill borrow another and let you know

Google agrees with this. Jesus these things are cheap compared to VFs...

[vorigan]

 Wiretap']

[quote name='gotasuby said:

3539343

/quote]

ive lost my borgwarner cd but from mem its off a cummins 6bt but ill borrow another and let you know

Google agrees with this. Jesus these things are cheap compared to VFs...

i have no reason to lie and yes they can be

[Wiretap]

 vorigan']

[quote name='gotasuby said:

3539343

/quote]

ive lost my borgwarner cd but from mem its off a cummins 6bt but ill borrow another and let you know

Google agrees with this. Jesus these things are cheap compared to VFs...

i have no reason to lie and yes they can be

You were unsure, I wasn't suggesting you might lie. I was saving you the trouble of digging up a CD tomorrow

[vorigan]

 gotasuby said:

3539343

the turbo has no hp rating with on the cd but the comp wheel number is 3599649 and that covers many applications, by measuring the pressure angles and tip heights combined with the 60mm exducer turbine it should support 550hp sorry thats the best info i can find.