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964 cam grind in 2.7

Anyone have a 964 cam grind in there 2.7 with carbs. Like to know how it performs.

Old 05-25-2016, 11:01 AM
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Used it a 3.0. Was very happy. 20/21 come highly recommended.
Old 05-25-2016, 11:19 AM
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What were the gains M? Did you keep the old springs or replace with new?
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Old 05-25-2016, 12:20 PM
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The 964 cam will likely require more static compression to do well in the 2.7 compared to the 20/21 the 20/21 should do fine at stock compression ratio. So if you do NOT plan to alter compression I vote for the 20/21.

Do your homework on dynamic compression and how camshaft changes can really lower dynamic compression. This is a very common mistake made by many who just assemble engines.
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1984 911 Carrera Cab M491 (Factory Wide Body)
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Old 05-25-2016, 12:43 PM
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My 3.0 Euro SC has 964 cams, SSIs and our CDI+ with a custom ignition map. The peak HP is only up by 10HP but it's all about that torque....

Here's the plot (green line is a standard Euro SC)

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Old 05-25-2016, 01:24 PM
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Nice
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'85 Carrera Targa
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Old 05-25-2016, 01:27 PM
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Cheers! Forgot to say, standard pistons too.
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Old 05-25-2016, 01:46 PM
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Here's a great read on static compression and cam selection.
Dynamic CR
Just reading the 'Why it matters:' 3rd section clearly shows the pit fall of why cams should never just be changed in a given motor. Changing the cam in that engine with disregard to static compression will completely defeat the reason for putting in the longer duration cam in the first place!

I point this out because the 20/21 and the 964 cam vary greatly on intake valve close event. These cams should never just be interchanged in any motor without considerations to the static compression.
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Last edited by scarceller; 05-26-2016 at 06:06 AM..
Old 05-26-2016, 05:56 AM
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Here is what my 3.2SS did with 964 cams...agreed that the torque available down low is tremendous.



204 ft/lbs from ~3700~4800 RPM at the wheels, 193 HP peak at the wheels.

This was on a Mustang Dyno, 4R CIS intake manifold and B&B Headers and Muffler.
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Old 05-26-2016, 06:20 AM
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Very good low end torque!
At what compression?

For comparison, here's a recent 84 3.2L all stock except DC20 cams and Custom exhaust, I just helped tune:

These 2 motors differ greatly! Your has tons of low end torque, real nice for the street. While this one has tons of hi-end torque. HP numbers often mean very little. These 2 motors in the same car are totally different.

You motor comes on cam at 3500-5000RPMs while the one I just did comes on cam at 5000-6000RPMs.

Quote:
Originally Posted by '76 911S 3.0 View Post
Here is what my 3.2SS did with 964 cams...agreed that the torque available down low is tremendous.

204 ft/lbs from ~3700~4800 RPM at the wheels, 193 HP peak at the wheels.

This was on a Mustang Dyno, 4R CIS intake manifold and B&B Headers and Muffler.
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Old 05-26-2016, 06:29 AM
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Quote:
Originally Posted by scarceller View Post
Very good low end torque!
At what compression?

For comparison, here's a recent 84 3.2L all stock except DC20 cams and Custom exhaust, I just helped tune:

These 2 motors differ greatly! Your has tons of low end torque, real nice for the street. While this one has tons of hi-end torque. HP numbers often mean very little. These 2 motors in the same car are totally different.

You motor comes on cam at 3500-5000RPMs while the one I just did comes on cam at 5000-6000RPMs.
Thanks Sal! I am using JE 9.5:1 pistons in this engine, single plug. I am currently in the process of converting to an AEM Infinity with a 3.2 intake manifold so hopefully I can pick up some more up top!

The car is a blast to drive on the street, very usable power band.
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1976 911S Signature Edition - 3.2SSt (JE 98mm 9.5:1 pistons, 964 Cams, ARP Rod Bolts, Big Port SC Heads, 3.2 Carrera Manifold, ID725's, B&B Headers, TS HyperGate45 Gen V, TS RacePort, BW S360, AEM Infinity 506, E85)
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Old 05-26-2016, 06:45 AM
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Quote:
Originally Posted by scarceller View Post
The 964 cam will likely require more static compression to do well in the 2.7 compared to the 20/21 the 20/21 should do fine at stock compression ratio. So if you do NOT plan to alter compression I vote for the 20/21.

Do your homework on dynamic compression and how camshaft changes can really lower dynamic compression. This is a very common mistake made by many who just assemble engines.
+1
it all has to do with the closing time of the intake.
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Old 05-26-2016, 06:50 AM
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As a guideline for dynamic compression (DCR)
Single plug 7.0:1 to 7.5:1 DCR is safe on street 91 octane fuel.
Dual plug 7.5:1 to 8.0:1 DCR is safe.

On good quality 93 octane twin plug can run at about 8.3:1 to 8.5:1 DCR if everything is done correctly and intake temps controlled and compensated for properly.

To often I see build specs with hot cams resulting in DCRs well below 7.5:1 or even below 7.0:1 doing this simply compromises the potential for the motor!

I have concrete test cases showing these results.
Here's a 3.4L twin plugged, very expensive build that made this very mistake.
Red lines are the initial results with DC21 cams
Blue is after just a cam change to DC43 longer duration cams.


Only thing changed were the cams! The goal was to reshape torque curve so it carried out more torque higher in the RPM range. The DC43 cam certainly has a different looking torque curve and got the job done but a huge price was paid across the board with a torque drop of 15ftlbs! Why? simply because the DC43 lowered the DCR way to much! To fix this is very expensive as it requires new pistons and a total tear down! Get this stuff wrong and your domed for failure!

You won't find much info like this published because pro-builders don't want you to know! But even showing you this it's still very difficult to get the correct and fully optimized as it requires engine to be assembled measured and then disassembled. Great builders go to a lot of time and expense to get this correct. This motor correctly fixed with the DC43 cams would easily break 250 wheel horse! This mistake likely cost that motor 30HP at the wheels, easily.

Enjoy
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Last edited by scarceller; 05-26-2016 at 07:12 AM..
Old 05-26-2016, 07:07 AM
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Really want to understand the importance of DCR get this book:
http://www.amazon.com/Tuning-Engine-Definitive-Performance-Economy/dp/1859606202
Read the cam chapter!

Written by David Vizard a master engine builder with 40+ years experience!
Known to be one of the best analytical engine builders of all time, simply because he measure and records all results. This in-site allowed him to discover what works and what does not. Then he wrote several books, the best I've seen.

Here's a video of one of his formal class sessions, video is old but material is great. Video is 2 hours long but you will not stop watching once you start!
https://www.youtube.com/watch?v=ow5cGV7bXCw
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Old 05-26-2016, 07:22 AM
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Quote:
Originally Posted by scarceller View Post
Here's a great read on static compression and cam selection.
Dynamic CR
Just reading the 'Why it matters:' 3rd section clearly shows the pit fall of why cams should never just be changed in a given motor. Changing the cam in that engine with disregard to static compression will completely defeat the reason for putting in the longer duration cam in the first place!

I point this out because the 20/21 and the 964 cam vary greatly on intake valve close event. These cams should never just be interchanged in any motor without considerations to the static compression.
All good info.

So, since we are talking 911s here, can we talk about some numbers?

To get the desired DCR, 8.2 to 1, when would the intake valve be closing with a SCR of 9.5 to 1 in a 3,0L? I'm guessing ~50 deg ABDC?

How do you get the valve timing numbers for aftermarket cams? They are not published, that I can find.

If this has been discussed, what is the link?

Thanks,
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Old 05-26-2016, 08:24 AM
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I hear the 964 works well in the 3.0, the SC grind works similarly well in the 2.7
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Old 05-26-2016, 08:59 AM
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Gordon,

The very best way to find intake close point is to actually test for it in the given engine. The same exact cam in a different motor can vary on it's close and open events. The best builders assemble the motor up to find EXACT cam points, they do not trust specs!

With that said the 964 closes the intake to the seat at about 75deg ABDC
The 3.2 cam around 68deg ABDC
The 20/21 at 62deg ABDC

Of those 3 the 20/21 will have the most DCR in the same given motor. This is one reason the 20/21 cam does well in the stock lower compression setup but it (it has high DCR) does not mean it's the best cam for that motor. The 20/21 is very similar to the stock 3.2 cam but higher lift and closes intake sooner. The 20/21 cam simply is clever in that it increases DCR, I believe Webcam designed it for that very purpose! In my opinion it's sort of a cheater cam that does well in stock configurations.

To properly calculate DCR you MUST find the seat close location then accurately measure the distance from the piston at that point to TDC. You really don't want to estimate this, you want to measure it in the engine's given configuration. It's time consuming because you need to put the motor together to find the seat close point and write down that deg # ABDC then remove the heads put the piston at that same location and measure distance piston has left to travel to TDC. Not easy and requires time.

Quote:
Originally Posted by Trackrash View Post
All good info.

So, since we are talking 911s here, can we talk about some numbers?

To get the desired DCR, 8.2 to 1, when would the intake valve be closing with a SCR of 9.5 to 1 in a 3,0L? I'm guessing ~50 deg ABDC?

How do you get the valve timing numbers for aftermarket cams? They are not published, that I can find.

If this has been discussed, what is the link?

Thanks,
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1984 911 Carrera Cab M491 (Factory Wide Body)
1975 911S Targa (SOLD)
1964 356SC (SOLD)
1987 Ford Mustang LX 5.0 Convertible

Last edited by scarceller; 05-26-2016 at 09:45 AM..
Old 05-26-2016, 09:42 AM
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I would avoid cam grinds if you can and get the real thing!

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Old 05-26-2016, 11:04 AM
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