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ivanhoew
278 posts
110 months
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Evoluzione said: Thanks for your answer, I understand where you are coming from. Have you done much work on your huge flow bench yet? how on earth do you know about that top secret development ?? ;-)
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Evoluzione
869 posts
112 months
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ivanhoew said: How on earth do you know about that top secret development ?? ;-) Oh I think I read about it somewhere. 
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Evoluzione
869 posts
112 months
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spitfire4v8 said: A rear mounted turbo is an option we've considered. As it is it will be going in the passenger footwell as that's conveniently adjacent where the manifolds finish in the engine bay.
The weaknesses are long spindly crank, weak rods, weak pistons, weak head gasket .. etc etc .. basically to do it properly will cost a fortune .. but the car is very competitive already but we're giving away 60bhp to the fast cars at the end of the straights.
All I need is 50-60bhp at the top end of the rev range, we don't need it anywhere else as the car is fine elsewhere already .. it's only on the long straights where we're having the problems .. hence a specific set of requests for our particular car. I'd like the whole project to come in at under 2k if possible. Is chemical supercharging allowed? I think a rear mounted turbo sounds like it could meet your needs, a small one at the front could be over-spinning by the time you need it to be working.
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stevieturbo
8,363 posts
116 months
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spitfire4v8 said: A rear mounted turbo is an option we've considered. As it is it will be going in the passenger footwell as that's conveniently adjacent where the manifolds finish in the engine bay.
The weaknesses are long spindly crank, weak rods, weak pistons, weak head gasket .. etc etc .. basically to do it properly will cost a fortune .. but the car is very competitive already but we're giving away 60bhp to the fast cars at the end of the straights.
All I need is 50-60bhp at the top end of the rev range, we don't need it anywhere else as the car is fine elsewhere already .. it's only on the long straights where we're having the problems .. hence a specific set of requests for our particular car. I'd like the whole project to come in at under 2k if possible. If the rods can handle rpm's, then they can handle boost. Likewise for the crank. Pistons, a lot will depend on design and ring placement. Power is less relevant. And you have to remember, especially in a track car. Throttle response is everything. Building a laggy system is just going to give soggy throttle response. Is that what you want ? It would be more sensible to build a setup capable of making 4psi relatively early in the power range that you use, and just maintaining that throughout, or perhaps a little more boost as required. The wider spread of power will make it a much faster car and should still retain decent throttle response at the higher rpm's Comparing what you want to a centrifugal build ignores one aspect. A CF blower will still offer instant throttle response. The turbo will not, and a deliberately laggy turbo will just be horrific.
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Max_Torque
4,812 posts
86 months
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Jeez, guys, get it together! This thread is 10/10 for totally misleading and wrong information! Things like "diesels need more air to make power than gasoline engines" or the er, merits, of "using diesel turbo's on gasolines" etc etc ;-(
And, you really need to understand the shape of a boosted engines cylinder pressure curve when compared to an unboosted one in order to estimate the extra mechanical loading present (hint1: just because you boost your engine, doesn't mean that Pmax is actually higher than the N/A engines Pmax). On top of that, generally it is the thermal loads that are the issue, rather than the pure mechanical ones, and if you want more power, then you WILL get a higher thermal loading. Finally, understand the implication of a normal pneumatic wastegate actuator system with respect to both the minimum boost line and the maximum one (particularly at high engine speeds) (hint2: think about the forces acting on the wastegate valve)
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Evoluzione
869 posts
112 months
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stevieturbo said: If the rods can handle rpm's, then they can handle boost. Likewise for the crank.
Pistons, a lot will depend on design and ring placement. Power is less relevant.
And you have to remember, especially in a track car. Throttle response is everything. Building a laggy system is just going to give soggy throttle response. Is that what you want ?
It would be more sensible to build a setup capable of making 4psi relatively early in the power range that you use, and just maintaining that throughout, or perhaps a little more boost as required. The wider spread of power will make it a much faster car and should still retain decent throttle response at the higher rpm's
Comparing what you want to a centrifugal build ignores one aspect. A CF blower will still offer instant throttle response. The turbo will not, and a deliberately laggy turbo will just be horrific. Remember he said he's adding the turbo to an unchanged N/A engine so there won't be any change in throttle response - just more power.
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Evoluzione
869 posts
112 months
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Max_Torque said: Jeez, guys, get it together! This thread is 10/10 for totally misleading and wrong information! Things like "diesels need more air to make power than gasoline engines" or the er, merits, of "using diesel turbo's on gasolines" etc etc ;-(
And, you really need to understand the shape of a boosted engines cylinder pressure curve when compared to an unboosted one in order to estimate the extra mechanical loading present (hint1: just because you boost your engine, doesn't mean that Pmax is actually higher than the N/A engines Pmax). On top of that, generally it is the thermal loads that are the issue, rather than the pure mechanical ones, and if you want more power, then you WILL get a higher thermal loading. Finally, understand the implication of a normal pneumatic wastegate actuator system with respect to both the minimum boost line and the maximum one (particularly at high engine speeds) (hint2: think about the forces acting on the wastegate valve) Then please educate us. (no sarcasm intended!).
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spitfire4v8
Original Poster
1,306 posts
50 months
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Max_Torque said: Jeez, guys, get it together! This thread is 10/10 for totally misleading and wrong information! Things like "diesels need more air to make power than gasoline engines" or the er, merits, of "using diesel turbo's on gasolines" etc etc ;-(
And, you really need to understand the shape of a boosted engines cylinder pressure curve when compared to an unboosted one in order to estimate the extra mechanical loading present (hint1: just because you boost your engine, doesn't mean that Pmax is actually higher than the N/A engines Pmax). On top of that, generally it is the thermal loads that are the issue, rather than the pure mechanical ones, and if you want more power, then you WILL get a higher thermal loading. Finally, understand the implication of a normal pneumatic wastegate actuator system with respect to both the minimum boost line and the maximum one (particularly at high engine speeds) (hint2: think about the forces acting on the wastegate valve) The weak rods and crank mean we can't go pushing the revs any higher, so more naturally aspirated hp is going to be tough to find. I see the upper-rev turbo idea as making our life, and the engine's life, easier. What flaws do you see other than thermal ?
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scarble
1,784 posts
26 months
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Max Torque said: (hint1: just because you boost your engine, doesn't mean that Pmax is actually higher than the N/A engines Pmax) Surely that's only if you change the CR? If you put more air (and fuel) in, compress it the same amount and make it go bang.. it goes bang more? Evoluzione said: Remember he said he's adding the turbo to an unchanged N/A engine so there won't be any change in throttle response - just more power. The turbo is a new piece of geometry in the intake path so it will change throttle response.
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Boosted LS1
13,450 posts
129 months
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Peak cylinder pressure will probably be higher then n/a for a nanosecond but average pressures, all though higher then n/a will be lower then peak n/a so should be acceptable. They'll just be highish for longer and make a lot of torque in the process. Throttle response will be great fun when on boost 
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scarble
1,784 posts
26 months
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Boosted LS1 said: Peak cylinder pressure will probably be higher then n/a for a nanosecond but average pressures, all though higher then n/a will be lower then peak n/a so should be acceptable. They'll just be highish for longer and make a lot of torque in the process. Throttle response will be great fun when on boost I thought about arguing but with a name like that.. 
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Evoluzione
869 posts
112 months
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scarble said: The turbo is a new piece of geometry in the intake path so it will change throttle response. My answers range from 'No it shouldn't' to 'If so, barely discernible' What's your theory?
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scarble
1,784 posts
26 months
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Just what is throttle response?
There is not, to my knowledge, an official definition of throttle response but I would suggest that in simple terms it is a measure of how much torque the engine produces (which is dependant on temperature, pressure and density of air available to the engine) varies with torque request (i.e. throttle position).
When you're (a) off boost or (b) engine air requirements exceed compressor delivery capabilities the compressor wheel, housing and associate twists, turns and extensions to the intake path will be a restriction, meaning less air available to the engine. When the turbo is on boost, more air is available to the engine.
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stevieturbo
8,363 posts
116 months
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scarble said: Just what is throttle response?
There is not, to my knowledge, an official definition of throttle response but I would suggest that in simple terms it is a measure of how much torque the engine produces (which is dependant on temperature, pressure and density of air available to the engine) varies with torque request (i.e. throttle position).
When you're (a) off boost or (b) engine air requirements exceed compressor delivery capabilities the compressor wheel, housing and associate twists, turns and extensions to the intake path will be a restriction, meaning less air available to the engine. When the turbo is on boost, more air is available to the engine. Certainly nothing like what you have described. Throttle response is very easy. If you push the pedal down, you expect instant full power delivery relative to the throttle angle. If it is not instant, it has poor throttle response. Turbo engines never achieve this. Some are quite acceptable though, some can be pretty bad.
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scarble
1,784 posts
26 months
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stevieturbo said: If you push the pedal down, you expect instant full power delivery relative to the throttle angle.
If it is not instant, it has poor throttle response. Yes, exactly what I said only even simpler.
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chuntington101
4,042 posts
105 months
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eliot
5,321 posts
123 months
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ivanhoew said: your right it is often said on forums that diesel turbo's are not to be used in a petrol ,perhaps by people that have not actually done it .personally i have never found a problem .i have a diesel t25 on the bike ,and a diesel holset hc3 on the tvr v8.they have been running for over 10 years with no probs . I was told by Giles @ turbo technics personally (i.e. not internet rumor) that running a turbo designed for a diesel engine would cause the turbine to "mushroom" i.e. warp with the elevated temperatures seen on petrol engines. Not saying it cant be done because i have read about it beeing done plenty of times - such as you say. When i was searching for a turbo i found that the turbines were disproportiantely sized to the compressors - and as steve says you do need something of a 7-10L engine.
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