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Piston Compression
- Thread starter jmayled
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Hi Jon,
The 74 & on, had quite a bit lower compression ratio than the 71's, about 7.5 to 1 I believe. This would lower the pressure noticeably. The 71's were about 8.5 to 1. In between years, they were about 7.75 to 1.
Depending on altitude & cranking speed, 110 to 120 is not too bad, but not like new. I would expect around 125 to 130 from a tight engine at Michigan altitude. The 71 & earlier engines would likely show 150 as you suggest.
Maybe someone else can give an opinion.
D
The 74 & on, had quite a bit lower compression ratio than the 71's, about 7.5 to 1 I believe. This would lower the pressure noticeably. The 71's were about 8.5 to 1. In between years, they were about 7.75 to 1.
Depending on altitude & cranking speed, 110 to 120 is not too bad, but not like new. I would expect around 125 to 130 from a tight engine at Michigan altitude. The 71 & earlier engines would likely show 150 as you suggest.
Maybe someone else can give an opinion.
D
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...and did you test with a warmed-up engine, plugs out, throttles open, how quickly the readings came up to the max. value on each cylinder, etc., etc.? Most importantly, I agree that the relatively consistent readings for all six is a good thing.
John_Mc
Jedi Knight
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I think this would be a good time for me to show off my ignorance with the following question:
What is the difference (ie advantages/disadvantages)between the higher and lower compression engines? Is it horsepower, performance, gas mileage? Is there any need to use a higher octane fuel on the higher compression TR6 engines? Why did they go progressively lower? Is the answer to all of this "42"?
What is the difference (ie advantages/disadvantages)between the higher and lower compression engines? Is it horsepower, performance, gas mileage? Is there any need to use a higher octane fuel on the higher compression TR6 engines? Why did they go progressively lower? Is the answer to all of this "42"?
OP
jmayled
Freshman Member
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Good Evening All,
Thank you for your feedback. I'll run the tests again after the car is sufficiently warmed up to see if the results differ. Based on Dave's response however I'm comfortable knowing that the later TR's did in fact have lower pressue.
Will post the measurements this weekend - Thanks again.
Thank you for your feedback. I'll run the tests again after the car is sufficiently warmed up to see if the results differ. Based on Dave's response however I'm comfortable knowing that the later TR's did in fact have lower pressue.
Will post the measurements this weekend - Thanks again.
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[ QUOTE ]
Is it horsepower, performance, gas mileage? Is there any need to use a higher octane fuel on the higher compression TR6 engines? Why did they go progressively lower?
[/ QUOTE ]
Higher compression will give more horsepower, gas mileage, & performance. You might need higher octane fuel.
I believe the 1971 was 8.5 to 1, 72 & 73 - 7.75 to 1, 74 & newer - 7.5 to 1. As they became more emissions aware, they lowered the compression ratio to reduce Nitric Oxide emissions which are produced by high combustion temperatures. A similar result could be obtained by using exhaust gas recirculation, which was a better method & sometimes done.
D
Is it horsepower, performance, gas mileage? Is there any need to use a higher octane fuel on the higher compression TR6 engines? Why did they go progressively lower?
[/ QUOTE ]
Higher compression will give more horsepower, gas mileage, & performance. You might need higher octane fuel.
I believe the 1971 was 8.5 to 1, 72 & 73 - 7.75 to 1, 74 & newer - 7.5 to 1. As they became more emissions aware, they lowered the compression ratio to reduce Nitric Oxide emissions which are produced by high combustion temperatures. A similar result could be obtained by using exhaust gas recirculation, which was a better method & sometimes done.
D