2.7 vs 3.0 torque
05-19-2007, 12:56 PM
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2.7 vs 3.0 torque
I am still looking for a 911 as my project car.
I have narrowed it down to the 74-77s and 78-83 SCs.
I am leaning towards the 74-77s as I want PMO carbs and as little add ons to the electrical/mechanical to keep it simple.
I really like the low end torque on the SCs. Can the 2.7 be built to give more low end torque ?
Jonny A.
87 BMW 635 csi highly modified
looking for a 911
I have narrowed it down to the 74-77s and 78-83 SCs.
I am leaning towards the 74-77s as I want PMO carbs and as little add ons to the electrical/mechanical to keep it simple.
I really like the low end torque on the SCs. Can the 2.7 be built to give more low end torque ?
Jonny A.
87 BMW 635 csi highly modified
looking for a 911
05-19-2007, 01:37 PM
#2
Burning Brakes
My '77 2.7 has plenty of torque with an MSD and SSi headers. I prefer the '77 because they are the last of the narrow bodies and the first year with full galvanized treatment against rust.
However, the magnesium crankcase is a weak point in the 2.7 engine. By now, any decent running 2.7 has probably been properly sorted and the heat generating stock exhaust should be gone, but you can add more hp toys and parts to 3.0 and later engines.
I find myself thinking about getting a 3.2 engine and setting my 2.7 aside until the time comes to put the car back into original configuration for sale or leisurely driving in my old age.
However, the magnesium crankcase is a weak point in the 2.7 engine. By now, any decent running 2.7 has probably been properly sorted and the heat generating stock exhaust should be gone, but you can add more hp toys and parts to 3.0 and later engines.
I find myself thinking about getting a 3.2 engine and setting my 2.7 aside until the time comes to put the car back into original configuration for sale or leisurely driving in my old age.
05-21-2007, 02:31 PM
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I really like the low end torque on the SCs. Can the 2.7 be built to give more low end torque ?
The answer to your question is no, low speed torque is a function of displacement and the SC has 11% more. Your desire for carbs conflicts with your low speed torque idea. If you want the most torque in the rpm range the engine spends the most time in ( 2-4K), look at what the factory did. The later SC has small ports and runners for this very reason. The 82-83 SC's had the best over the road torque of the models you at looking at and a much better version of CIS.
Paul
The answer to your question is no, low speed torque is a function of displacement and the SC has 11% more. Your desire for carbs conflicts with your low speed torque idea. If you want the most torque in the rpm range the engine spends the most time in ( 2-4K), look at what the factory did. The later SC has small ports and runners for this very reason. The 82-83 SC's had the best over the road torque of the models you at looking at and a much better version of CIS.
Paul
05-21-2007, 03:00 PM
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Originally Posted by psalt
I really like the low end torque on the SCs. Can the 2.7 be built to give more low end torque ?
The answer to your question is no, low speed torque is a function of displacement and the SC has 11% more.
The answer to your question is no, low speed torque is a function of displacement and the SC has 11% more.
High compression twin-plug 2.7 with MFI can have significantly more torque than SC...
05-21-2007, 03:53 PM
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High compression twin-plug 2.7 with MFI can have significantly more torque than SC...
Not low speed torque. Look at the numbers for identical engines. A one point increase of compression is around a 4% increase. A 12:1 compression 2.7 would not have the same low speed torque as a 9.3:1 SC. MFI would have the opposite effect of raising the torque curve higher than the small port, long runner CIS engine. The length of intake runner to throttle plate is directly related to the torque peak of the engine. You can raise the torque peak rpm and hp, but you cannot raise the low speed torque by shortening the intake length. About the only way a 2.7 will have higher low speed torque than an identical 3.0 is with positive manifold pressure.
Not low speed torque. Look at the numbers for identical engines. A one point increase of compression is around a 4% increase. A 12:1 compression 2.7 would not have the same low speed torque as a 9.3:1 SC. MFI would have the opposite effect of raising the torque curve higher than the small port, long runner CIS engine. The length of intake runner to throttle plate is directly related to the torque peak of the engine. You can raise the torque peak rpm and hp, but you cannot raise the low speed torque by shortening the intake length. About the only way a 2.7 will have higher low speed torque than an identical 3.0 is with positive manifold pressure.
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05-21-2007, 04:14 PM
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Originally Posted by psalt
Not low speed torque. Look at the numbers for identical engines. A one point increase of compression is around a 4% increase. A 12:1 compression 2.7 would not have the same low speed torque as a 9.3:1 SC.
By your math, a hot 2.7 would have more low-speed torque (and much more peak torque) than an SC with 8.5:1 compression...
05-21-2007, 04:36 PM
#9
Drifting
A properly built 2.7 can run very strong. Real advantage of the SC's is much stronger case and better heads and rear flares. You can build almost any charesteristic you want into most Porsche motors. If torque is what you are after it's hard to beat cubic inches. I have a 3.3 a 3.5 and a 3.6, they all pull like a train.
Phil
Phil
