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 Post subject: turbo peak pressures?
PostPosted: Wed Feb 23, 2011 10:13 pm 
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whats the highest peak pressures in a petrol turbo? can it exceed turbo diesels? even at 30 psi boost?


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PostPosted: Wed Feb 23, 2011 10:20 pm 
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depends on how well built the bottem and top ends are... compression, fuel octane, etc...
kind of a general question with myriad answers


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PostPosted: Wed Feb 23, 2011 10:36 pm 
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98 gt wrote:
depends on how well built the bottem and top ends are... compression, fuel octane, etc...
kind of a general question with myriad answers


well im trying to find the right bottom and top end. maybe a diesel block from the smallest diesel engine i can find is good enough? i can have custom heads built to fit.


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PostPosted: Wed Feb 23, 2011 11:04 pm 
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I think a better question would be, "what are the highest peak power figures?" A lot of folks like to say stuff like, "the stock bottom end can only handle 7 psi" which is largely complete rubbish. They should say, "the stock bottom end can only support about 250 HP".

To answer your question though, I've seen boost pressures as high as 65 PSI in a petrol engine before. The sky is really the limit but the final number is going to depend on a ton of other stuff.

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PostPosted: Wed Feb 23, 2011 11:33 pm 
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Boost is directly related to restriction of air flow. What are you really trying to do? Find an engine that will put out a certaing amount of torque or HP? If you're just looking for the highest boost level, any engine, any turbo on it, just restrict the output of the turbo and whamo! the boost goes up and you get to brag.

How much air flow the head can handle is a better measure of an engine's capability, not boost it can take.

Tom

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PostPosted: Thu Feb 24, 2011 2:18 am 
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The voice of reason
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If you can afford custom built heads but have no idea whether to use a diesel block or not, pay someone to build a motor for you.

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PostPosted: Thu Feb 24, 2011 3:16 am 
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horizenjob wrote:
If you can afford custom built heads but have no idea whether to use a diesel block or not, pay someone to build a motor for you.


i can modify casting patterns and molds and have somebody cast the head and i can machine the casting myself. and stock parts for the rest. except the crankcase.

a whole block is way out of my capability. and asking an engineer is way out of budget. and the engineer wants royalties! so that means i have to do a little research on my own.

ok i found out that highly turbocharged engines can reach 3000 psi. thats all i need. i dont know how strong existing blocks are but ill just go ahead and weld myself a heavy little steel crankcase and use separate cylinder barrels.

im targeting the highest available continuous power that can be extracted from an engine that weighs no more than 95 kg. it needs to take chassis loads. its going into my planes too.


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PostPosted: Thu Feb 24, 2011 10:20 am 
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flat4 wrote:
...im targeting the highest available continuous power that can be extracted from an engine that weighs no more than 95 kg.

The key factors that's been left out is: for how long and at what cost?

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PostPosted: Thu Feb 24, 2011 10:34 am 
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KB58 wrote:
flat4 wrote:
...im targeting the highest available continuous power that can be extracted from an engine that weighs no more than 95 kg.

The key factors that's been left out is: for how long and at what cost?


how long? 1000 hours. i know vw engines converted for aircraft use can do 70-90 hp continous for twice that long...

cost? ideally just plugs, oil, timing belt and gasoline.

mild steel is 2 times stronger than cast iron and 10 times the fatigue life.


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PostPosted: Thu Feb 24, 2011 12:21 pm 
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Moved this thread to the "In theory it could work" section.

I think building your own engines is an interesting topic, but I don't see much applicability to us Locosters. It's hard to find light and physically small engines that are best suited to us. If you can keep the topic towards that direction perhaps it's a plus for us. I don't want this to become a huge useless thread though that doesn't pan out with anything useful, maybe not even educational.

Airplane engines are quite good at what they do. Trying to match them really raises the ante, with the downside of getting yourself hurt when they go wrong.

If you want a light engine remember to keep that in mind and not be distracted by solutions that provide high horsepower for displacement - they may turn out to be different things.

It becomes frustratingly difficult when your goals are different then the general industries, many parts are sort of what you want but not exactly and hard to use the way want to...

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PostPosted: Thu Feb 24, 2011 9:19 pm 
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horizenjob wrote:
Moved this thread to the "In theory it could work" section.

I think building your own engines is an interesting topic, but I don't see much applicability to us Locosters. It's hard to find light and physically small engines that are best suited to us. If you can keep the topic towards that direction perhaps it's a plus for us. I don't want this to become a huge useless thread though that doesn't pan out with anything useful, maybe not even educational.

Airplane engines are quite good at what they do. Trying to match them really raises the ante, with the downside of getting yourself hurt when they go wrong.

If you want a light engine remember to keep that in mind and not be distracted by solutions that provide high horsepower for displacement - they may turn out to be different things.

It becomes frustratingly difficult when your goals are different then the general industries, many parts are sort of what you want but not exactly and hard to use the way want to...


fair enough

it has to be light. otherwise whats the point? i can just get a straight 6 from a truck and slap a turbo on it. but im just going to end up building parts for it anyway.

based on my experience developing an aftermarket cylinder head for volkswagens i realize that there is a big market for modular engine componenets that homebuilders can mix and match. the volkswagen afterparts market is a good example but the prices are just outrageous. and some have dubious engineering. like the racing heads with pathetic cooling fin area and those tiny valve stems. since im both an airplane and car builder i can see that nice sweet spot that covers the needs of both.

it doesnt take much really. there is an ocean of stock parts out there that can be used. its just a few pieces that needs to be made. for an inline 4 it all boils down to crankcase and cylinder heads. and maybe foil air bearings for the turbo.

a flat 6, my main target is harder. there are no diesel flat sixes. and a porsche crank just wont do. so that means a custom crank if i want big journals and thick webs. not much engineering to be done here too. lots of examples around.


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PostPosted: Thu Feb 24, 2011 9:34 pm 
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you could get a euro spec subaru flat 6 diesel...


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PostPosted: Thu Feb 24, 2011 10:03 pm 
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98 gt wrote:
you could get a euro spec subaru flat 6 diesel...


i have checked it out. very nice variable geometry turbo.

its about 2 times heavier than my target. and it cant be a structural member. its a nice engine but i dont know where to buy the engines though and i have to practically buy a running second hand car so i can get the engine.


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PostPosted: Fri Feb 25, 2011 1:29 am 
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Wait.

Let me get this straight.

You aren't an engineer, you aren't willing to pay an engineer.

But you want to build your own turbo engine from scratch that is under 95kg and can be a stressed member that can last 1000 hours?

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PostPosted: Fri Feb 25, 2011 1:41 am 
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I think that's where the "in theory..." part comes in.

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