Turbo's and carbs - how do they work?

[_Iain_]

Am aware of the basics of how a carb works & a turbo but interested in how the two work together.

Obviously the float bowl would need to be pressurised - but where from? surely connecting to the overflows a shit idea as you no longer have an overflow and connecting pressurised air to the drain hole would surely bubble up & interfere with jets?

How does one run an overflow port without blowing fuel everywhere as soon as you hit boost? Is it done away with entirely or whats to replace it? some kind of boost sensitive valve that doesn't open unless zero boost?

Jetting - Is there a formula to work out roughly where you need to start?

Plenum chamber - why? could it be done with one 90 deg hose, three T pieces & some ally joining pipe or does it have to be a specific volume?

Turbo oil feed - is there a max pressure? would a restrictor be needed?

Turbo oil drain - provided it's above engine oil level and runs downwards & is a significantly large enough bore this would also work fine?

How is a "safe" level of boost determined?

What about ignition timing on a low boost setup? Would this still need altering & how without the costs of megajolt?
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Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[cb1rocket]

You need to see Chris's turbo topic in show and tell !
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[Ariel Badger]

Superchargers are easier to set up.
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[Ariel Badger]

Superchargers are easier to set up.
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[orac]

safe boost level is determined by engine parts, if the piston, bores bolts etc tec ar all good for 15psi, but the head gasket is gone by the time you get to 8psi then there your answer.

plnum chamber from my understand is due to the fact that if you give it a hand full there will not be enough air in the pipe to sustain the engine, it kinda like a reserve if air which is then replished as the motor winds up.

oil feed, that depends on the turbo, the drain would have to run into wht ever you are using to pump it, are you using shared engine and turbo oil? dont forget turbo will dump a shed load of extra heat into that oil, so an extra oil cooler for a seperate oil loop is normally the best way to go.

again, i dont fully understand but ignition will normally be variable and it more important to be accurate with higher boosts.

carb presurising is beyound my currect understanding, however i have heard that putting the entire thing in a seal box and then presurising the box with the turbo is way to resolve the issue... not really thought about it to be honest
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[Pete.]

You don't pressurise the float bowls via the overflow - you do it via the carb bowl breathers. Turn carbs over, remove bowl and you'll see the breather hole. They vent into the top of the bowl chamber.

Carbs are pressurised by a pitot tube. This is just a piece of pipe that pokes into the airflow in the pipe between the turbo and plenum.

Jetting - leave it standard. More pressure equals more fuel.

Plenum is just a mixing-pot to distribute air evenly across the cylinders. It's not so much a reservoir of air - more of a damper.

Oil feed - turbo manufacturers specify an oil pressure at the turbo usually. Think plain-bearing often is 35-40psi. Put a gauge on the feed line after the restrictor to set the size, I use an old carb jet.

Safe level of boost is determined by remembering how much you were using last time it detonated.

Ignition timing - pff I'd leave it stock and see what happens. Loads of stock-timed bikes out there.


My best advice if you're thinking of turbocharging your bike - get the turbo high up on the engine. High as possible, then move it up a bit. It's most important.

Don't go mad on the header and up-pipe tube sizes. For a 600 you only need headers of about 30-35mm ID, up-pipe about 40mm and very often smaller works a lot better than bigger. You DON'T need stainless for headers, mild steel is perfectly acceptable just that it goes rusty. It's also less likely to crack. For a budget up-pipe radiator hose is perfectly good.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[P.]

Assuming if its FI, you'll need a way of remapping?

[_Iain_]

Paddy, you need one of theese if you're doing it the pikey way and a fully mappable ECU if the "proper" way. At least thats what i remember from building the civic - we packed it off in the end for a proper ecu & setup. Made a respectable 180bhp at the wheels from a D14 engine for all of three months before it shit the bottom end.

https://www.ebay.co.uk/itm/RISING-RATE-FUEL-PRESSURE-REGULATOR-KIT-ADJUSTABLE-/180464897392

Basicly have been looking at rear turbo setups on cars. Seem to work just fine. Looking at my bike if i can mount a turbo instead of a can it'd put the drain higher than the oil filler cap & theres adaptors to fit breather hoses onto them anyway, so could drain directly into the oil filler cap & feed off that pressurised 8mm bolt on the head that everyone runs top end oiling kits off. Its not an ideal set up for maximum power, but for simplicity & cost purposes it seems ideal - and easily swapped between bikes.

Pete, could i do away with the pitot tubes & run a nipple off the plenum to pressurise the whole lot?
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[P.]

They do a bolt on SC They make a funny noise and provide 180hp to the rear wheel.



Dear Santa...

[_Iain_]

For the TL?!?

Link please.
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[P.]

Don't have link Seen one on a TL on TLPlanet, various others have bought one. Looking at a fairly large sum though..

[Pete.]

[_Iain_]

[Pete.]

Pitot size makes almost no odds, it's not flowing anything. The position in the up-pipe is what matters. The up-pipe diameter has a much bigger effect than pitot size. I recall one guy who built a system that ran like a dog until he fitted a smaller up-pipe and it was transformed into a nice responsive bike. Bigger isn't always better.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[lihp]

The trick to turbo exhaust systems and installations that work well is more about gas velocity rather than volume
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[Pete.]

And that velocity is achieved by releasing heat energy in a confined space. As the exhaust gases exit the port they must expand into the exhaust and give up a large amount of energy whilst doing it which is spent driving the turbine fan. It's basically free power as it would otherwise just escape out the tailcan.
If you put the turbo further downstream the gases have already expanded into the exhaust and there is far less energy to drive the turbine - the initial expansion carries the most benefit.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Shaft]

For all the reasons Pete has already explained, I can't see what the advantage is of running a remote turbo.

It might be slightly less of an issue on a bike, due to the shorter distance involved, but on a car, surely you must have to use massive boost pressure to get anything like the efficiency of a conventionally mounted turbo.

The point of forced induction is to improve the performance of an engine of a given size (originally to save fuel) by optimising the use of otherwise wasted energy; the further you put your turbocharger from the optimum position, the more energy you waste, so it's kinda self defeating.
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