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Thermal efficiency vs CR request
 Madrid, Madrid, Spain
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1974 MG MGB GT "El Cherada"
1978 MG MGB Racecar "El 81 De Carrera" 1995 Honda Civic "Beasty Boy (Race Car)" 1999 BMW Z3 Coupe "BATMOBILE" |
Any of you have some table/graphic about Thermal efficiency vs Compression Ratio for an MGB engine? And the Volumetric Efficiency at full throttle vs RPM?
During the last days I've been having some discussions with a Dastsun 510 vintage driver about the amount of power that an MGB engine can deliver with a CR lower than 12.0:1
The Datsun guy states that such an engine can not deliver more than 125 HP at the flywheel, not even theorically!
This guy has affected my MG ego and I need some information as a resource for making a new argument.
Thanks in advance.
Edited 1 time(s). Last edit at 2014-11-23 01:34 PM by JuancarlosMGB.
During the last days I've been having some discussions with a Dastsun 510 vintage driver about the amount of power that an MGB engine can deliver with a CR lower than 12.0:1
The Datsun guy states that such an engine can not deliver more than 125 HP at the flywheel, not even theorically!
This guy has affected my MG ego and I need some information as a resource for making a new argument.
Thanks in advance.
Edited 1 time(s). Last edit at 2014-11-23 01:34 PM by JuancarlosMGB.
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Madrid, Madrid, Spain
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1974 MG MGB GT "El Cherada"
1978 MG MGB Racecar "El 81 De Carrera" 1995 Honda Civic "Beasty Boy (Race Car)" 1999 BMW Z3 Coupe "BATMOBILE" |
In reply to # 2857309 by RedLine
Kind of reminds me of a local dyno operator (and I use the term loosely) and Honda lover who told my son that a small block
Chevy engine could never put out over 400 hp, but he could get 1000 from a 4 banger Civic!
Kind of reminds me of a local dyno operator (and I use the term loosely) and Honda lover who told my son that a small block
Chevy engine could never put out over 400 hp, but he could get 1000 from a 4 banger Civic!
Honda civics...I don't dislike those cars....only dislike the drivers
(only a joke)
In honor of the truth, I must accept his full prep L18, with its overhead camshaft, it's a more efficient engine than a B series one; but that doesn't mean I won't be able to beat him next year
Edited 2 time(s). Last edit at 2014-11-24 05:15 AM by JuancarlosMGB.
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Madrid, Madrid, Spain
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1974 MG MGB GT "El Cherada"
1978 MG MGB Racecar "El 81 De Carrera" 1995 Honda Civic "Beasty Boy (Race Car)" 1999 BMW Z3 Coupe "BATMOBILE" |
Steve, thanks a lot for that link! Thtere are terrific calculators there; but those calculators are using average thermal efficiencies. In the case of our beloved B series engines, for instance, for a given RPM, air flow and gas rate, it's possible to get different power outputs deppending on the Compression Ratio. The higher the CR, the higher the thermal efficiency and the higher the power output. But never mind, I'd better work on my car; will improve my driving skills and will do my best to beat those Datsun 510 next year without enagaging in silly discussions
I am pretty sure I've already surpassed those 125 HP but I need to go to the dyno. I will tell you when I have some data.
Edited 1 time(s). Last edit at 2014-11-24 11:43 AM by JuancarlosMGB.
I am pretty sure I've already surpassed those 125 HP but I need to go to the dyno. I will tell you when I have some data.
Edited 1 time(s). Last edit at 2014-11-24 11:43 AM by JuancarlosMGB.
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Madrid, Madrid, Spain
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1974 MG MGB GT "El Cherada"
1978 MG MGB Racecar "El 81 De Carrera" 1995 Honda Civic "Beasty Boy (Race Car)" 1999 BMW Z3 Coupe "BATMOBILE" |
Steve, thanks a lot for that link. The table which relates CR with power gains is just awesome! That's the kind of information I was looking for. Even when they are aproximate values, it's a very valuable information prior to make a decition about my engine. (I won't show this table to the Datsun guy because this information validates his statement, at least, if we only take into account the CR changes and we forgot about other factors like hot camshafts and other stuffs 
)
About my engine, you remember right, I was having problems with detonation and destroyed an almost new set of flat top pistons. I had to rebuild the engine but people from this forum gave me a lot of information and advices. I adressed the problema by limiting the distributor centrifugal advance and by using av gas.
My actual CR is 11.25:1 and I wouldn't dare to bump it to 15:1; but I think I could manage 12.5:1.
Edited 1 time(s). Last edit at 2014-11-24 07:20 PM by JuancarlosMGB.
)
About my engine, you remember right, I was having problems with detonation and destroyed an almost new set of flat top pistons. I had to rebuild the engine but people from this forum gave me a lot of information and advices. I adressed the problema by limiting the distributor centrifugal advance and by using av gas.
My actual CR is 11.25:1 and I wouldn't dare to bump it to 15:1; but I think I could manage 12.5:1.
Edited 1 time(s). Last edit at 2014-11-24 07:20 PM by JuancarlosMGB.
 La Center, WA, USA
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1941 Ford N-Series
1958 MG MGA 1500 Coupe "Rosie" 1970 MG MGB GT "Pat's GT" 1971 MG MGB "Gifted To Me" & more |
Nov 24, 2014 11:23 PM
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 Joined 15 years ago
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"... the amount of power that an MGB engine can deliver with a CR lower than 12.0:1 The Datsun guy states that such an engine can not deliver more than 125 HP at the flywheel, not even theoretically."
Granted that our Huffaker SCCA MGB E/P engine was 15:1 +, we put lots of GT-3/GT-4 510 Datsun's on the trailer. 160hp @ 6750rpm delivers a lot of yank.
Be safe out there.
Kenny
Granted that our Huffaker SCCA MGB E/P engine was 15:1 +, we put lots of GT-3/GT-4 510 Datsun's on the trailer. 160hp @ 6750rpm delivers a lot of yank.
Be safe out there.
Kenny
Attachments:
Huffaker dyno Snyder MGB EP.png 206.6 KB
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Madrid, Madrid, Spain
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1974 MG MGB GT "El Cherada"
1978 MG MGB Racecar "El 81 De Carrera" 1995 Honda Civic "Beasty Boy (Race Car)" 1999 BMW Z3 Coupe "BATMOBILE" |
Kenny, one million thanks! That table has real life data and the gasoline mass flow is included, so it's possible to calculate the thermal efficiency (for a 15.0:1 engine). I could extrapolate some data and see how I can improve my engine. And the most important thing: I will show this table to the Datsun guy 
Therm Eff = (Power output) / (Gasoline energy rate) = HP x (2545 BTU per HP per Hour) / (fuel flow pounds per hour x 19,000 BTU per pound)
Thermal Eff = 0.1339 x HP / Fuel flow
I've got a maximun efficiency of 29% for your engine, which is impressive, even for today standards for moder engines! I am attaching a table with the data.
Edited 1 time(s). Last edit at 2014-11-25 06:36 AM by JuancarlosMGB.
Therm Eff = (Power output) / (Gasoline energy rate) = HP x (2545 BTU per HP per Hour) / (fuel flow pounds per hour x 19,000 BTU per pound)
Thermal Eff = 0.1339 x HP / Fuel flow
I've got a maximun efficiency of 29% for your engine, which is impressive, even for today standards for moder engines! I am attaching a table with the data.
Edited 1 time(s). Last edit at 2014-11-25 06:36 AM by JuancarlosMGB.
Attachments:
Huffaker Thermal Efficiency.png 98.8 KB
 Philly 'burbs, PA, USA
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Nov 26, 2014 01:13 PM
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Madrid, Madrid, Spain
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1974 MG MGB GT "El Cherada"
1978 MG MGB Racecar "El 81 De Carrera" 1995 Honda Civic "Beasty Boy (Race Car)" 1999 BMW Z3 Coupe "BATMOBILE" |
In reply to # 2859496 by dickmoritz
It's not just all about compression ratio. I'm running 12.75:1, and you can make plenty of hp at that rate of squeeze...
Dick
It's not just all about compression ratio. I'm running 12.75:1, and you can make plenty of hp at that rate of squeeze...
Dick
That sounds like music to my ears
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Here is the VE table from my car.
My research and experience with my car seems to confirm that 120 hp is about as much as you likely get from a road car suitable for long, trouble free road trips.
Beyond that the exhaust port bend is so tight that eddies stall flow. If a head were made with a higher outlet or one that pointed more upward things would be different. Super charging and turbos force more through but peak power generally does not go up that much with gasoline, without going closer to full race motors. Mid range torque improvements can be huge with boost, compression and/or head work.
I went with a sequential fuel injection and the car runs very well at all altitudes and on long trips. I really put more into the motor then I should have. Swapping to a very modern motor would be a very good choice. Current swaps trend to motors that are dated.
Here is a look at my engine
My research and experience with my car seems to confirm that 120 hp is about as much as you likely get from a road car suitable for long, trouble free road trips.
Beyond that the exhaust port bend is so tight that eddies stall flow. If a head were made with a higher outlet or one that pointed more upward things would be different. Super charging and turbos force more through but peak power generally does not go up that much with gasoline, without going closer to full race motors. Mid range torque improvements can be huge with boost, compression and/or head work.
I went with a sequential fuel injection and the car runs very well at all altitudes and on long trips. I really put more into the motor then I should have. Swapping to a very modern motor would be a very good choice. Current swaps trend to motors that are dated.
Here is a look at my engine
Attachments:
VE-table.jpg 65.9 KB
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Madrid, Madrid, Spain
Sign in to contact
1974 MG MGB GT "El Cherada"
1978 MG MGB Racecar "El 81 De Carrera" 1995 Honda Civic "Beasty Boy (Race Car)" 1999 BMW Z3 Coupe "BATMOBILE" |
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