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People keep saying the SC give more low end and the C2 more top end.

I suspect this has more to do with how people are timing them when they set up there motors.

SC can be timed to make peak HP at any where from 5500 (most do this) to 6000rpm or so.

The C2 cams having more lift I am guessing can not be advanced as much with out worrying about clearance. The C2's make peak at about 6100rpm I understand of timed to stock N/A specs.

I think the SC dose have a bit higher effective compression so that might be part of it.

------

Also, as to the Groupe B cam, I thought is was more of a high rpm cam. I suspect is can be timed that way but it seems the Group cams made peak HP at 5500 unless that was miss leading info.

They also said they made about 360hp at 1 - 1.3 bar.

.9 bar on a prepped 930 motor of such a build can make 390-400hp.

Take it to 1.3 bar and 450+ hp could be possible with fire rings, inter-cooler, cams, zork, and 1.3 bar if they could use a larger turbo and or open up the intake ports a bit.

If anyone has more info on the actual Group B builds I would love to see it. Might be fun to build a vintage/DE car along the same specs. Especially if it has a boost knob between the seats.
Old 01-30-2010, 01:17 PM
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Quote:
Originally Posted by 911st View Post
People keep saying the SC give more low end and the C2 more top end.

I suspect this has more to do with how people are timing them when they set up there motors.

SC can be timed to make peak HP at any where from 5500 (most do this) to 6000rpm or so.

The C2 cams having more lift I am guessing can not be advanced as much with out worrying about clearance. The C2's make peak at about 6100rpm I understand of timed to stock N/A specs.

I think the SC dose have a bit higher effective compression so that might be part of it.

------

Also, as to the Group B cam, I thought is was more of a high rpm cam. I suspect is can be timed that way but it seems the Group cams made peak HP at 5500 unless that was miss leading info.

They also said they made about 360hp at 1 - 1.3 bar.

.9 bar on a prepped 930 motor of such a build can make 390-400hp.

Take it to 1.3 bar and 450+ hp could be possible with fire rings, inter-cooler, cams, zork, and 1.3 bar if they could use a larger turbo and or open up the intake ports a bit.

If anyone has more info on the actual Group B builds I would love to see it. Might be fun to build a vintage/DE car along the same specs. Especially if it has a boost knob between the seats.
This car has group B cams

I have heard from others the motors were tested open exhaust at what boost level I do not know but maxium set up overall I would assume. . So now after the US restrictions, who knows. We just had the turbo out for oil seals to Bob @ Durabilt turbo rebuilders Chicago. They usually have a 1 day turn around however he said the turbo rebuild parts took a week to get as the Turbo was a race hybred and was similar to the much later KKK 7200s inside. Anyway I do not know what that has to do with the HP output other than he said it was well suited for the motor spec, by it's internal condition.img]http://forums.pelicanparts.com/uploads16/DSC000821264891087.jpg[/img]
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Old 01-30-2010, 01:44 PM
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Quote:
Originally Posted by 911st View Post
People keep saying the SC give more low end and the C2 more top end.

I suspect this has more to do with how people are timing them when they set up there motors.

SC can be timed to make peak HP at any where from 5500 (most do this) to 6000rpm or so.

The C2 cams having more lift I am guessing can not be advanced as much with out worrying about clearance. The C2's make peak at about 6100rpm I understand of timed to stock N/A specs.

I think the SC dose have a bit higher effective compression so that might be part of it.

------

Also, as to the Groupe B cam, I thought is was more of a high rpm cam. I suspect is can be timed that way but it seems the Group cams made peak HP at 5500 unless that was miss leading info.

They also said they made about 360hp at 1 - 1.3 bar.

.9 bar on a prepped 930 motor of such a build can make 390-400hp.

Take it to 1.3 bar and 450+ hp could be possible with fire rings, inter-cooler, cams, zork, and 1.3 bar if they could use a larger turbo and or open up the intake ports a bit.

If anyone has more info on the actual Group B builds I would love to see it. Might be fun to build a vintage/DE car along the same specs. Especially if it has a boost knob between the seats.
OOps here is that photo

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Old 01-30-2010, 01:52 PM
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Quote:
Originally Posted by 911st View Post
People keep saying the SC give more low end and the C2 more top end.
I think the SC dose have a bit higher effective compression so that might be part of it.
This is not possible.
The cam with the best low rpm response is the stock cam that has no overlap. Any cam in a turbo motor that has overlap will cause reversion, which impacts efficiency at low rpm.
The SC cam enhances power in the mid range. The 964 is best mid to top. Both do not function as well as the stock cams at low rpm.
Cams cannot affect compression since they are closed during compression.
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Old 01-30-2010, 02:50 PM
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Quote:
Originally Posted by 911nut View Post
Cams cannot affect compression since they are closed during compression.
Not true, you have two types of compression, geometric which is the ratio of the the volume of the cylinder at BDC vs the volume at TDC. Then you have effective compression which is when the intake valve closes just past BDC and only the remaining volume gets compressed.

For example, the stock 930 cam specs are:
Intake 214 degrees @ 0.040" with a 110 degree centerline
Exhaust 202 degrees @ 0.040" with a 106 degree centerline

Starting at valve overlap at TDC the intake valve would close at 110 + 214/2 = 217 degrees, if BDC is 180 degrees from TDC, that puts the intake valve closing 37 degrees after BDC, into the compression stroke, or 143 degrees before TDC. You will not be getting a full stroke of compression.

If you use a 964 cam with intake duration of 246, lobe center of 113, the intake valve closes at 113 + 246/2 = 236 degrees, or 56 degrees after BDC, 124 degrees before TDC, leaving even less volume to compress.

The 964 cam will have less effective cylinder pressure than the stock turbo cam.
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Old 01-30-2010, 07:31 PM
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Originally Posted by WinRice View Post
Not true, you have two types of compression, geometric which is the ratio of the the volume of the cylinder at BDC vs the volume at TDC. Then you have effective compression which is when the intake valve closes just past BDC and only the remaining volume gets compressed.
Ok, that makes sense.
Sounds like another reason to bump the static compression ratio. This is recommended for n/a engines when running cams with a lot of overlap too.
Maybe it's better to leave the stock cams in place and switch to a more efficient turbo like a Garrett GT35.
Thoughts?
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Old 01-31-2010, 05:18 AM
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You guys are on to some cool stuf.

I have long suspected the stock cam is the best 'pre-boost onset' cam for making HP. Mostly because it creats the longest compression stroke of the bunch.

However, many report the SC cam improves low end with its lower 'effective compression' stroke.

I am wondering why the SC is reported as such an improvement?

I know that if the exhaust system is not up graded the SC will inhibit low end per Bruce Anderson's book noting the restrictive stock early US headers much be improved on.

I am wondering if it is in our deffenition of what low end is?

For most it is probably boost onset that is low end. In my thinking it is the off idle normally asperated part.

Cold it be the SC cam has somthing about it that brings boost onset in earlyer or when it dose come into boost onset it dose it better?

I am wanting to believe it is because it gets more air in the motor but more significantly with the exhaust valve opening earlier less heat is converted to TQ and more goes to the turbine to spin it up faster.

That is my guess.

Anyone know why the SC is seen to improve low end over the stock cam?
Old 01-31-2010, 07:07 AM
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Adding a point to compression in the 7/1 to 8/1 range inproves normaly asperated HP about 4-5%.

However, with this we have to give up about 3.7 psi of boost or about .25 bar. Going from a net of 1.8 to 2.05 bar is about 14% more HP potential.

That is say4- 5% more pre boost HP chasing say 10-14% plus on boost HP assuming the motor can operate efficiently with the increase in boost.
Old 01-31-2010, 07:23 AM
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Quote:
Originally Posted by 911nut View Post
This is recommended for n/a engines when running cams with a lot of overlap too.
Maybe it's better to leave the stock cams in place and switch to a more efficient turbo like a Garrett GT35.
Thoughts?
Exactly!

When designing a new engine, the engine builder starts with the heads and the cam, matching the cam profile to the flow of the heads. Once that is nailed down, the pistons are chosen that give the proper effective compression ratio, or effective cylinder pressure. Then the intake and exhaust are matched up for the proper flow rates.

Maybe someone can elaborate on the group B turbo, but that's what they did with the cams is optimize the duration as far as the valve train geometry would allow, while maintaining the same lift. This allows more flow, and a would allow a higher flow turbo.
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Old 01-31-2010, 07:59 AM
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Originally Posted by 911st View Post
I am wondering if it is in our deffenition of what low end is?
That's the million dollar question!

Everyone's definition of low-end is different, and the stock 930 cams are probably matched well to the stock 32mm intake ports and the 3ldz turbo. Probably a good compromise package for emissions, street durability and liability due to the power in an 'unstable' car.

I've always wondered if Porsche designed the engine around the restrictive cat and muffler they had to use for US emissions? Keeping the power level around the flow mandated by exhaust? All I know, is when I bolt on the stock cat and muffler on my setup, it's completely gutless.

Once you change one component, the others should follow for a balanced package. If you compared a stock 930 with a better muffler, to a SC cam/K27/muffler setup, the stock setup would probably build more torque off idle, but be quickly offset by the smooth build up of power for the SC/K27 setup.

It's all perception.
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Old 01-31-2010, 08:35 AM
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The secret is to maximize the charge in the cylinder. There are a million combinations to do this. Also, at low RPM, I suspect a 930 has about the same CR as a VW 1300 engine. Efficiency is a function of CR, with the caveat of maximized charge.
I suspect SC cams decrease the parasitic losses in the induction system, and thus increase the efficiency at low to mid in the 930 powerplant. I also suspect that when not making boost, the compressor wheel is just a restriction in the path of the air going to the cylinders.
I run DC-20 cams, but I have a turbo SC engine, with static CR of 8.5, and boost limit at 5.8 PSI.
I also firmly believe that the factory considered possible warranty issues with the 930, and made it rather tame for production.
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Old 01-31-2010, 08:37 AM
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Again, the Group B cam is a cam of artificial restraints. For Group B racing Porsche was not allowed to exceed the lift of the stock cam.

There may have been other restrictions like stock internal, stock gear ratios or something else.

A 3.3 with stock rods and oiling will not live past 6700rpm for long.

A 3.3 that makes big peak HP at 7k is not going to work well with the stock wide ratio transmission.

With a low lift Group B cam might have come some possible side advantages like less stress on the valve train and also higher initial port vorticity for improved air fuel mixing but those are probably just side benefits and not of prime confederations.

However with a limitation on lift, I suspect that there was only so far Porsche could stench duration without trade offs in other areas. At some point with a long duration and limited lift the ramps would have to be so low an increase in duration is not going to add much. Alternately they could have tried to make kind of a flat top lobe but that might have taken them to to much duration or even added different stress to the valve train.

I have little doubt that if we move the TQ & HP peak up 1500rpm from 5500 with matched cams, ports, turbo, exhaust..., a 930 could make 25% more power. However, if we can not match the transmission ratios to it, we will may not achieve much improvement in average HP per gear and might end up slower in places that could cost us dearly on the track like out of a corner.


A 930 is a study in limitations and comprises while still having so, so much potential.

Last edited by 911st; 01-31-2010 at 01:25 PM..
Old 01-31-2010, 01:18 PM
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Stop the presses!

Tony,

This is so cool!

It is so easy to skip over and miss good things in some of these threads.

There is a very good chance this is very, very close to the Group B build!

I bet that HP is at 1.3 bar.


I am dying to learn more about the turbo and see a picture of such an intercooler and exhaust.

They also note a special exhaust with 'waste gates" plural.

Wow, wow, wow!

That HP is right what I was coming up with. 400hp at .9 bar is a well accepted data point. Thus, (400/1.9) x 2.3 = 484hp potential if efficiency did not suffer at higher boost.

Quote:
Originally Posted by voitureltd View Post
This car has group B cams

I have heard from others the motors were tested open exhaust at what boost level I do not know but maxium set up overall I would assume. . So now after the US restrictions, who knows. We just had the turbo out for oil seals to Bob @ Durabilt turbo rebuilders Chicago. They usually have a 1 day turn around however he said the turbo rebuild parts took a week to get as the Turbo was a race hybred and was similar to the much later KKK 7200s inside. Anyway I do not know what that has to do with the HP output other than he said it was well suited for the motor spec, by it's internal condition.img]http://forums.pelicanparts.com/uploads16/DSC000821264891087.jpg[/img]

More GroupB info here:http://www.qv500.com/porsche911scp7.php


Last edited by 911st; 01-31-2010 at 02:43 PM..
Old 01-31-2010, 02:38 PM
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Since this started in California......

First, for what it is worth, the Gruppe B cams won't pass California emission testing, unless you know how to apply a combination of special tricks. I went through all this stuff almost 20 years ago when I was building my first special 930.

Second, errr Kremer built quite a few cars, yes. The brothers were also great salesmen. Please, just because it is in writing, don't believe everything stated. For a start... the secs on that car.. WOW.. great, isn't it? Now.. .look again.. They changed a lot of things and make some nice performance claims. I will ask one simple question and you can have a ball trying to figure out how it would be possible... Look at the claimed 0-60 and TOP speed.. and note how they increased acceleration by swapping R&P. So, what is WRONG with these figures, unless they built a "miracle" engine?


Last, over the years Ruf made a lot of performance gains with intense engineering and backed them up on the Autobahn. His firm did a LOT with ..among other things.. cams. His Gruppe B cams really work. There is amazing attention to detail on how they made their cams. Things like how they angle the ramps all make a difference to performance and few if another cam grinders seem to pay attention to this. Back when I was building my first big time 930 I aquired a new set of his cams and reluctantly had to resell them out of state to an enthusiast who didn't have to deal with the strict California smog testing. They simply wouldn't pass with the other technology we had available at that time. I have remained a big fan.

Keep the boost up.
JR
Old 01-31-2010, 02:52 PM
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oops....

Just noted Paul B's post. Sorry Paul, wouldn't have stated as posted had I spotted your post first. Nice to see that someone on this side of the pond IS aware and working to get the cams right. I am not sure I agree that the 964 cam is the absolute best [but I will claim to have been the first independent here to use them in my built 930.] I also need to say that I use these in my present 930. .. But there is better stuff out there if I ever decide I want to drop a lot of money..again.. on this old beast. Frankly, I am pretty much tapped out on pouring more $$ into it when I have difficultly using much of it's potential as it is. Still, it is nice to know there is more available.

You can sometimes get hints about alternatives and how they work in some of the Factory information. It is increasingly difficult to get this info tho. I used to subscribe to Christophorus just for the once in a while detailed technical article with information you would find nowhere else. The publication is now pretty much fluff. Porsche Engineering makes some information available online but is oriented to people subscribing to their very expensive website. You will sometimes find great info in Race Car Engineering magazine, as well as buried in interviews in Excellence and Porsche Panorama. I have found amazing tidbits in these places.

Enough.
JR
Old 01-31-2010, 03:02 PM
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Welcom JR.

Quote:
Originally Posted by alwaysflat6s View Post
... I will ask one simple question and you can have a ball trying to figure out how it would be possible... Look at the claimed 0-60 and TOP speed.. and note how they increased acceleration by swapping R&P. So, what is WRONG with these figures...

Keep the boost up.
JR
This caught my eye to.

I wonder what RPM this would have to be at with a stock 4th, the low R&P, and probably almost 26" tall tires?

Thx for the info on smog 'g a G/B cam. Please tell us your tricks?

Seems the Group B has 18 deg of overlap v none for a 930, 4 deg for an SC, and 8 deg for a C2.

As noted, not good when trying to pass smog. J. Woods told me once the C2 normal is about it for passing Ca. smog on a 930.

I thought Dwight at Vision Motor Sports (ex Andial) was the first C2 cam guy?

Not much new as to CIS 930 tuning. Just looking for clues now that this is more of a vintage thing.

The best.
Old 01-31-2010, 04:15 PM
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[

Second, errr Kremer built quite a few cars, yes. The brothers were also great salesmen. Please, just because it is in writing, don't believe everything stated. For a start... the secs on that car.. WOW.. great, isn't it? Now.. .look again.. They changed a lot of things and make some nice performance claims. I will ask one simple question and you can have a ball trying to figure out how it would be possible... Look at the claimed 0-60 and TOP speed.. and note how they increased acceleration by swapping R&P. So, what is WRONG with these figures, unless they built a "miracle" engine?





Keep the boost up.
JR[/QUOTE]


It does seem Manfred wanted it both ways. The car might do 192 if it had the stock 3.7 and still had the 480 FWHP as tested w/open exhaust. With the 4.10 gears ( as it left Kremer ) around 160MPH is more realistic, with the emissions and exhaust system installed to pass, it is probably more like 350 RWHP @ a safe 1.0 bar, by my estimate, when I compare its grunt with another I just had on the dyno. However I have had it around Road America at 1.3 bar with 110 gas which makes it noticabily quicker. It is pretty quick thru the gears for a street build in 1984 trim with the lighter body and shorter final drive.
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Old 01-31-2010, 05:14 PM
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My biggest wonder about the Kremer's, RUF, and factory Group B is how they handled the CIS fueling and AFR's at 1.3 bar?

350whp is within the fuel deliver capacity with maybe a little lower control pressure.

However, 1.3 bar would put it over the edge quickly.

RUR, Kremer, and the factory (Group B) had some tricks up there sleeve and it was more than lower control pressure and mildly bumped system pressure.

RUF has some type of what looks like a fuel pressure reg on it. Never figured that one out unless it was to lower control pressure some way at higher boost levels or to protect some of the early WUR's from rupture (a known issue).

I am sorry but I truly have to believe it would include the profile of the metering cone (as seems to be done on the 3.6T) to work at such air flow numbers.

I love this stuff a little to much.
Old 01-31-2010, 07:01 PM
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Agreed, there must have been performance enhanced differences available in the CIS developement over the production 930 systems considering they were into making more performance to target that sort of buyer, not the the average person that walked into a Porsche showroom.
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Old 02-01-2010, 05:49 AM
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