Joshy

granted i have no expirience in this area, but though i would make my imput.

I would have thought that the bigger BW turbo would be fine as your using a Close ratio box and the engine will always be running between 4500 and 8000.

Combine that with your VCT and high compression and i dont think drivability would suffer much?

just my 2 pence..

JOSH

SiZT

That's down to pressure drop in the boost pipes, intercooler and inlet manifold.


Will, have you got an idea of the exhaust manifold and system you're going to use?

Big Will_

Will be approaching a few places to get quotes on 4mm thick wall stainless manifold. I'll be getting it done as an equal length twin scroll setup too.

Exhaust system wise I'll probably go for a 3 - 3.5" system - need to do some CFD testing on it to see what works best...

SiZT

Tbh, if it's solely (sp?) as a track car I would choose the bigger turbo.

J1mbo

iTrader: (1)

I imagine that was their aim yes, will has beaten me to it, I was going to say about high comp low boost jsed with honda, I also imagine most of the engine tuners would not measurenthe back pressure, most don't lol

Also smaller capacity 1.6 to the 2.0 really

Big Will_

Jim,

You see much difference in downpipe size to backpressure?

Chip

iTrader: (3)

Most people dont measure it because its relatively difficult to do and normally its obvious if its an issue without actually needing to measure it.
In an ideal world though, we'd all measure everything possible, but time and money constraints mean most of us tuning engines compromise somewhere along the way.

small cubes and big revs are definately happy with the GT turbos yeah

J1mbo

iTrader: (1)

Will, yes the best we have found on the big power ybs are off the turbo straight to four inch,then come back down if nessecary,

It's easy I thought chip, drill, tap and a fitting with opposite fitting and pipe,

I can imagine it being difficult in car but for us on the dyno it's dead easy

Chip

iTrader: (3)

Then you need something to monitor it with compared to the map sensor to plot the differences, not trivial if you are on L8 etc

Although you could just run a pair of manual gauges and do the comparison yourself of course.

Need to be careful with heat soak up the pipe over long periods too obviously as its a bit warmer than normal for a map sensor or gauge.

J1mbo

iTrader: (1)

We have a manual gauge when testing and either write down the results of kee an eye on them making sure they're acceptable

Chip

iTrader: (3)

For most people, once its in the car and mapped etc, the problem is if you dont like the results much, its a bit late to do anything about it realistically.

Depends what you are trying to do, most of us arent really pushing the boudnaries of tuning anyway, if you are building 500bhp YB there really isnt a need for it particuarly.

Big Will_

Jim, when you've run GT3076Rs on the dyno and seen the high back pressure - have you seen any noticeable effects on the volumetric efficiency i.e leaning out the fuel map to suit the lesser volume of air entering the engine?

Chip

iTrader: (3)

Big back pressure is more of an issue on low CR too dont forget, as it has less cylinder pressure to push against the back pressure with to evacuate the cylinder still, so results in more spent charge remaining in the engine.

So only take a great deal of notice of jimbos results if they are from similar CR engines.

Big Will_

Fully agreed mate, just curious to see if it was anywhere near as clear and apparent as the interweb scare mongers make it out to be

"You can't have any turbine backpressure or your VE will drop 20% etc."

-beefy-

iTrader: (6)

quality thread



personally , id just put a t34 on it ,


by the time you actually finish the course/ car


time attack wont be running


come on fella , i want to see it our there !!

dojj

iTrader: (3)

from my understanding of your dilema so far:

if you want to keep the turbo spinning up at full speed then i would assume you'd need to get one that would be able to exhaust/vent off the most amount of gas at 8000 rpm

but, from my understanding of the compressor map thing that stu wrote about some time back, you need to keep it spun up at 6000 rpm as well

so the next thing would be to find out how much air your head will flow at those rpms and match a turbo for that

do i win a prize or have i got it totally and utterly wrong

also, one thing i'm still yet to fully understand, is there a big variation of flow between a n/a engine and a boosted engine and is this something your 40 degree's of vvt would help solve or hinder as you don't really need vvt if you are only going to be mashing the pedal at the top end

Chip

iTrader: (3)

Dojj, seeing as you ask you win a prize for stating a completely trivial and obvious point that isnt much to do with the thread I guess, but you said nothing at all useful.
It was kind if two people were discussing the intracies of a pile driver, and someone replied and said "as I understand it wrestling is based in a ring with ropes around it" its correct, but not really useful.

With regards to your question, yes there is a big difference in flow between an N/A and turbo engine, and cams need to vary quite a lot between the two due to the way that they act during overlap in particular.

SiZT

I can't see it being that much of an issue with the VVT (dependant on manifold design). As I said, it would be the bigger turbo for me as your not really after low down spool.

turbotoaster

well to establish EMP and whats expected you need to look at a few things.

How your exhaust ports are done, ie can the gas easily get to the manifold.

Then the manifold tubing diameter, is it wide enough to minimise restriction yet still keep the flow high enough to offset boost threshold.

then you move onto exhaust wheel and turbine housing.

I personally try and aim for 1:1 ratio for EMP:IMP as my type of petrol engine suffers very heavily with exhaust gas reversion and the larger the port the worse effect it has.

i know the engine works in a different way but my engine is 9.0:1 compression ratio and we are typically limited to 15-18psi of boost due to auto-ignition issues.

I would strongly advise you first make sure you exhaust manifold is divided(if you can also run twin wastegates its prefered, if not try and keep the wastegate collector a little further away from the runners....yes this can sometimes a small boost spike with fast on/off transiant response but piston engines are pretty resiliant to that as long as your not to aggressive on your timing.


Also are you thinking of making a t4 or t3 manifold, ill assume t4 as thats the most sensible choice.....as you know rear turbine wheels work by applying a restriction to the exhaust gas(by way of turbine housing) to blow the 'speeded up' exhaust gas over the wheel.............this should be the one and ONLY restriction in a turbocharged exhaust system, anything else and your costing yourself VE

you have mentioned the gt35, remember garrett dont actually produce a gt35 t4 turbo......what they actually did was get a t3 turbine housing and fitted a t4 flange, for example the 1.06 t4 housing is actually more like a t4 0.84 housing so be careful on your choice.


overall since your engine is more of a 'revver' than typical 4 pot lumps i would allow a later boost threshold for the benefits of lower EMP

one thing to heavily consider in a higher compression engine is aux injection, what are you planning on running.

ive been in contact with glen at time attack and you can run a water/meth mix(your choice of %) which will increase the boost and timing allowed........though they wont check the % so you can probably run 100% either way to be fair.

For reference, the 15-18psi limit i mentioned earlier, with meth being sprayed, that rises to 25-27psi, virtually elimates knock(unless you go mental with IGN) and lowers EGTs......which is great, but then you dont want to go to low as effecting spool(850c seems to be a nice number to show your leaning on the engine)

ill of course progress to talk about downpipe diameter vs predicted exhaust gas flow and turbine housing size after a few more people have added there thoughts

J1mbo

iTrader: (1)

Tbh the old boy does the mapping side I normally just check the fuelling is acceptable along with back pressure on these engines, as it's difficult to do it all by yourself, I could have a look at the fuel map and see I suppose!

I'll have to ask him the question!

Rick

Not sure I agree with that. Low compression with big boost and lots of advance results in very high cylinder pressures.

Rick

Chip

iTrader: (3)

Read what I wrote again mate.

I was saying pressure to evacuate the cylinder with, ie at the end of the exhaust stroke, that is dictated just by the amount of gas in there and the amount of space it has at the end of the exhaust stroke

TimC

iTrader: (1)

Will I know this topic is about exhust pressure, but surely one of the elements of consideration is what sore of revs the engine will see after every gear change or the likely hood of what the lowest revs you'll expect to see during cornering.

Will they not help you choose what turbo to choose to suit the power band required?

Big Will_

Realistically i'm only looking at dropping around 2000-2500rpm in each gear, joys of having 6 of them and a funky final drive

Even on the bigger turbo I don't think it'd be a big issue as instant response would effectively allow me to do rolling burnouts everywhere

There is a part of me that thinks i'll just get the 7670 and then if I ever want more out of it, its available!

Joshy

agreed