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sc cams in a turbo

i am i the the process of rebuilding a 76 row turbo motor
nothing crazy just an upgraded new k27 turbo with the raptor mod and a high flow ss exhaust carrera tensioners and a few factory case modifications pretty much the rest will be stock. just looking to have a fun responsive street car . i have question regarding cams i have a very nice set of 3.0l sc cams and the original turbo cams . is there a benefit in running the sc cams in lue of the turbo cams will they provide a little more low end torque and help even out the the lower rpm responsiveness ?? is there a downside to using the sc cams ?

Regards Ned


Last edited by gorskined; 01-07-2020 at 08:27 AM..
Old 01-07-2020, 08:10 AM
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Crotchety Old Bastard
 
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There is no down side to SC cams. They make a HUGE difference in off-boost driveability.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 01-07-2020, 11:19 AM
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Quote:
Originally Posted by RarlyL8 View Post
There is no down side to SC cams. They make a HUGE difference in off-boost driveability.
just plug and play or will i need to change/ adjust anything else?
Old 01-08-2020, 04:26 AM
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The SC cams will need the drive provision for the turbo oil pump. On the '76 3.0L engine this is simply a pin and not a boss as used in the later 3.3L engine which also drives the air pump. Other than that it is plug and play. Timing of the cams is personal preference based on how much torque you want to dial in at lower RPM. Cams need to follow and complement the build and turbo power band. With the mods you list SC cams have a great complementary grind. Should you go further with mods or wish to push the build more towards HP with less emphasis on low end torque other grinds become a better choice. It gets really involved, this is a simplistic answer to your question.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-08-2020, 06:02 AM
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Thanks for the info .. going to stick with the factory grind and play with the timing when i cross that bridge .

Regards Ned


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Originally Posted by RarlyL8 View Post
The SC cams will need the drive provision for the turbo oil pump. On the '76 3.0L engine this is simply a pin and not a boss as used in the later 3.3L engine which also drives the air pump. Other than that it is plug and play. Timing of the cams is personal preference based on how much torque you want to dial in at lower RPM. Cams need to follow and complement the build and turbo power band. With the mods you list SC cams have a great complementary grind. Should you go further with mods or wish to push the build more towards HP with less emphasis on low end torque other grinds become a better choice. It gets really involved, this is a simplistic answer to your question.
Old 01-08-2020, 07:01 AM
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Quote:
Originally Posted by gorskined View Post
Thanks for the info .. going to stick with the factory grind and play with the timing when i cross that bridge .
This seems incompatible with you wanting a "fun responsive street car".

The 3.0 is even more of a slug off-boost than the 3.3, which stock is infamously bad until it makes some boost.

Lame cam profile (think it's the same), even lower compression (6.5:1 static, vs 7:1 for the 3.3) and less cubic displacement will not make for "responsive".

SC cams in a 3.3 with everything else stock RoW won't fix all the problems, but it at least responds faster off-boost, thus building boost quicker. And also makes ~10% more at the top.
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Old 01-08-2020, 01:35 PM
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I would do the cams now.

I am
I found a used set to put in.
those along with a modified 7200 should bring in the boost before 3k!!!!
if I get another 1K RPM of boost, that would be awesome.

put some JE pistons in to raise the compression
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Old 01-09-2020, 04:02 AM
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If you like low end and mid-range set them at 2.0 mm.
Old 01-09-2020, 05:36 AM
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Also worth bearing in mind the effect cam profile/overlap has on dynamic compression; I won't pretend to know how to start to do the math, but John Dougherty said:

Quote:
Originally Posted by camgrinder View Post
I can calculate a dynamic compression ratio based on the rod length, stroke length, cylinder bore diameter, static compression ratio and intake valve closing point. For example,
Stock 930 3.3 turbo with 7-1 compression and stock cam = 6.12-1 dynamic compression ratio.
Swapping to an SC profile cam lowers the dynamic compression to 5.55-1. Going further and swapping to a 964 profile reduces the dynamic compression to 5.19-1.
Off boost the power will be down with the 964 profile. But on boost you will see a jump in HP. Now if you bump the static compression up to 8-1, the dynamic compression will also jump, up to 5.89-1. This new dynamic C/R is slightly lower than the original turbo engine.
in this thread 8.0/8.5 CR for 930 ???

So the more radical the cam, the more boost you can run. I figured >99% of my street driving is off-boost - so kept SC cams and 8:1 for my 3.4 Motec conversion. I like the way it drives.

CIS 3.3 930 with 8:1 and SC cams drives like a sports car with a big old, torquey, willing engine - until it spools. How I imagine an SC with a big bore kit would feel. You can drive this around all day off-boost and it doesn't feel like a hardship.

Strap on a better turbo etc as well, and it's a different ball game. Given enough load on the dyno, my K27/HF made 6 psi @ 2400 RPM. In contrast to the 3DLZ (which hit like a hammer to the chest and wouldn't be completely spooled until 3300, 3500 in lower gears - 5 speed), boost onset is linear and progressive - hard to tell exactly when it starts, boost just comes in as you rev. More throttle/load, it just comes in faster/harder.
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Old 01-09-2020, 05:52 AM
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I would seriously reconsider keeping the stock cams, siting everything that has been said. The change in driveability with SC cams is significant. Porsche used this grind in their SE 330HP engines which had awesome street manners. The 3.0L early 930 engine is even more lacking in off-boost power than the 3.3L engine and would really benefit from the torque bump. We put a set in Phil's (now yellow) '76 930 during the restoration, ask him how he likes the cams.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Last edited by RarlyL8; 01-09-2020 at 06:16 AM..
Old 01-09-2020, 06:13 AM
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Quote:
Originally Posted by RarlyL8 View Post
, siting everything that has been said. The change in driveability with SC cams is significant. Porsche used this grind in their SE 330HP engines which had awesome street manners. The 3.0L early 930 engine is even more lacking in off-boost power than the 3.3L engine and would really benefit from the torque bump. We put a set in Phil's (now yellow) '76 930 during the restoration, ask him how he likes the cams.
. i was in a rush and wasn't clear in my response i was referring to the last part of your post when you mentioned custom grinds..i assumed you meant regrinding the sc cam to achieve a different outcome .. i do plan on using the stock sc cams
thanks for the advice i really appreciate the help
Regards Ned

Last edited by gorskined; 01-09-2020 at 10:05 AM..
Old 01-09-2020, 09:40 AM
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Quote:
Originally Posted by spuggy View Post
This seems incompatible with you wanting a "fun responsive street car".

The 3.0 is even more of a slug off-boost than the 3.3, which stock is infamously bad until it makes some boost.



Lame cam profile (think it's the same), even lower compression (6.5:1 static, vs 7:1 for the 3.3) and less cubic displacement will not make for "responsive".

SC cams in a 3.3 with everything else stock RoW won't fix all the problems, but it at least responds faster off-boost, thus building boost quicker. And also makes ~10% more at the top.
Spuggy... I know it's not a 300hp+ plus car but considering my fun driver now is a 55hp pre a 1955 Porsche 356 continental cab .. this turbo should scratch the itch. Just fine

Last edited by gorskined; 01-09-2020 at 10:25 AM..
Old 01-09-2020, 10:22 AM
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I run SC cams in mine. No issues and plenty of power from 3-5500 until it runs out of push. On our roads it's easy to keep the motor humming at 3000 in 3rd pretty much all day ready to pass that line of 3 or 4 cars at once. Roll out
Old 01-09-2020, 02:32 PM
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I think a big part of the fun about our cars is the hard acceleration when boost hits. The cars with sc cams have power that is too linear. Some had efi, all had upgraded turbos so i was really surprised that i didnt care for them.

Could just be the cars i tried but every 930 ive driven with sc cams was faster and easier to drive but also way more boring-er.
Old 01-11-2020, 06:23 AM
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Cams

Here it is very important to understand the complexity of the correct way to go.

You always have to focus the peripheric situation around a cam choose:

Inlet plenum
Intercooler
Turbo
Exhaust
Etc.

Also very important is the static compression ratio and the dynamics defined by the cam.

A good cam fitting into a concept will open up the engine making it a much more happy system !

Always hold in mind: there are na cams used in turbo engines and dedicated turbo cams.

Very often NA cams are used because they are available and cheap - but they are compromising the result also.

Not saying the sc cam is a bad cam but you need to know what you’re doing.

Since the 3,0 l turbo engines are very low in compression ratio they will react on the lift in TDC quite sensitive - so my proposal would be a 964 cam where we see lower TDC lift rates because these cams are more connected to emission laws.

With this cam you will have a better off boost and over all performance.

If you are going for the better you will buy a turbo cam.

Best reg.

Dirk
Old 01-11-2020, 08:52 AM
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While I have zero experience with SC cams into a 930 I can offer perspective why NA grinds have been successful in other applications.

When I hear people ask about cams the biggest piece of missing info is turbine inlet pressure. It’s critical to know the boost to TIP ratio. With that information decisions about overlap and lobe separation angles can be better made. Modern turbos have a lot less back pressure than earlier turbos. Some achieve 1:1 balance. NA OEM cams work pretty well in these applications. It was not unusual (non Porsche) to see 3:1 in older OEM cars.

Even though NA cams work better than stock there’s room for improvements via the custom route. Opening the exhaust valve earlier than NA would helps turbo spool. The upside far outweighs the downside here. OEM cam designs are also centered around smog limits. With more freedom to choose optimized profiles comes great returns. This all seems cheap to me for around $1k when considering the rest of the build costs.

I would also advise caution when using the HP gained as a metric. This can be misleading. The positive personality change can be difficult to quantify but it’s something I hear over and over again. I’ve heard the term “happy engine” used in the past. As I’ve grown older I’ve come to appreciate what that really means. That has become the target of all my street build now.
Old 01-13-2020, 05:39 AM
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"most torque under the curve" is what I want for a street car.
Old 01-13-2020, 10:58 AM
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Typical relatively economic formula to improve drivability (max torque under the curve) is tuned headers, SC cams, and improving the timing profile/curve. Next step would be to go to engine management / EFI and custom cams. A quick linear spooling turbo then blurs the line between on and off boost.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 01-14-2020, 06:15 AM
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For those that want an upgraded cam, but love the sensation when the boost hits, you can always go with a Gruppe B cam grind. Still has the lightswitch power delivery, but will rev out more and have more power than stock.
Old 01-14-2020, 10:22 AM
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Can anyone expand more (Edelweiss?) on the turbo specific cams? I've heard them mentioned several times but have not really see nor heard anything about them compared to the typical SC or 964 cam upgrades. Is there not much gain with a CIS engine using a turbo specific cam? How about a mildly modified engine with bolt on mods (ie. headers, turbo, adjustable WUR)
Thanks, Frank

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Old 01-15-2020, 08:23 AM
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