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Engine building advice needed

I purchased a 79' 911 SC last year and have fallen in love with it. I am getting ready to modify the drive train and even though I have been building cars and motorcycles for many years I am not familiar with the strengths and weaknesses of the 3.0 engine, 915 trans-axle and half shafts.

Please don't mistake the following comment as attitude, but I am not looking to be told to do a search for information (as I already have numerous times), or to be given opinions from people who haven't modified these cars. What I really need is to hear from people that have gone out and broken parts, or can share experience they have been directly involved in.

I have already upgraded the suspension, brakes, tires and wheels, so now it's time to get the drive train up to speed. I am planning to rebuild a 3.0 and add 930 type headers with a single Garrett GT series turbo along with a stock 930 inter-cooler. I plan to add a Bitz EFI kit, an MSD ignition with boost retard, forged pistons, ARP rod bolts and ARP head studs. I intend to keep the stock 915 trans-axle and I have a Sachs Power Clutch kit along with a light weight fly wheel that should be adequate to handle the torque.

I have been unable to get any definitive information as to whether the stock crankshaft, connecting rods and crankcase are adequate. I also need to address any oiling concerns, although my car has a large oil cooler in front of the passenger front tire that I can duct additional air too. I am also considering o-ringing, porting and dual plugging the heads, but I don't think it is necessary.

Any experience sharing you are willing to offer would be greatly appreciated.

Thanks for your time,
Chris
Old 10-25-2009, 07:56 PM
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Chris, I suggest getting Wayne's book he goes into some mods pretty extensively.. Also you may want to also post the same questions over on the engine re-build area.
Are you planning on keeping it as a 3.0?
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Old 10-25-2009, 08:42 PM
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Rods will be fine (as long as you don't rev too high)
915 probably will not feel fine after a while. You might consider billet side plate and/or steel bearing carrier.
MSII is probably better deal than MSI. Then you can get rid of dizzy, use EDIS and have both timing and fuel in one box.
You will need custom intercooler as matching stock SC runners with 930 intercooler might be non-trivial.
GT turbo is a good choice. You will need to either mount it high and drain oil into chain cover or install 930 oil pump. Again, non-trivial.
Depending on boost and engine version, you will need new pistons as well (CR-wise).
SC brakes are on the margin even with stock engine so you might consider bigger items if you want to do more than street driving.

It might be cheaper to sell your SC engine and purchase Carrera engine to begin with so you don't have to re-invent injector rails etc.
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Last edited by beepbeep; 10-26-2009 at 05:43 AM..
Old 10-25-2009, 11:57 PM
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As far as answering your question on crankcase strength.
The 3.0 SC engine used the identical block as for the 3.3 turbos. The rods and rod bolts are actually stronger than the turbo and later Carrera rod bolts which were downsized. You should be able to rev safely to over 7000rpm as long as valve springs are updated.
The pistons you mentioned are forged replacements, stockers are cast, good choice but make sure C/R is down to 7.5 to 1 or so for detonation protection.
You will need a modified intake manifold to add intercooling and FI injectors....you already know this probably. Probably easier to start with a 3.2 Carrera manifold unit as mentioned above.
You are gonna need alot of oil cooling so get a front mount cooler that mounts below front bumper. Everything else will not get enuff airflow to cool properly.
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Old 10-26-2009, 05:29 AM
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Mine is a 3.0 bottom with 3.2 heads, intake, and throttle body and K27S turbo on GSF header/heat exchangers. I think the 3.2 heads (or port your SC heads to match) combined with a 3.2 intake are the preferred route to EFI turbo unless you want custom injector blocks and go with a 930 intake. Major modifications of the stock 930 intercooler or piping would be required unless using the 930 intake. I don't know how applicable the tbitz EFI kit would be here as it is based on the NA CIS manifold of the SC. You may be better off going with an MS-II unit and adding electronic distributorless ignition for total control such as I did with EDIS.
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Old 10-26-2009, 06:38 AM
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Quote:
Originally Posted by 9dreizig View Post
Chris, I suggest getting Wayne's book he goes into some mods pretty extensively.. Also you may want to also post the same questions over on the engine re-build area.
Are you planning on keeping it as a 3.0?
Yes, I am planning on reusing the cylinders and keeping it as a 3.0. What is the title of Wayne's book?
Thanks
Old 10-27-2009, 06:48 AM
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Quote:
Originally Posted by beepbeep View Post
Rods will be fine (as long as you don't rev too high)
915 probably will not feel fine after a while. You might consider billet side plate and/or steel bearing carrier.
MSII is probably better deal than MSI. Then you can get rid of dizzy, use EDIS and have both timing and fuel in one box.
You will need custom intercooler as matching stock SC runners with 930 intercooler might be non-trivial.
GT turbo is a good choice. You will need to either mount it high and drain oil into chain cover or install 930 oil pump. Again, non-trivial.
Depending on boost and engine version, you will need new pistons as well (CR-wise).
SC brakes are on the margin even with stock engine so you might consider bigger items if you want to do more than street driving.

It might be cheaper to sell your SC engine and purchase Carrera engine to begin with so you don't have to re-invent injector rails etc.

What would you recommend as a reasonable rev limit?

If I were to sell my SC engine and purchase a Carrera engine, would the injection be the only benefit and are you knowledgeable as to the value of both engines?

I appreciate the input, it's helpful.

Chris
Old 10-27-2009, 06:54 AM
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Quote:
Originally Posted by fredmeister View Post
As far as answering your question on crankcase strength.
The 3.0 SC engine used the identical block as for the 3.3 turbos. The rods and rod bolts are actually stronger than the turbo and later Carrera rod bolts which were downsized. You should be able to rev safely to over 7000rpm as long as valve springs are updated.
The pistons you mentioned are forged replacements, stockers are cast, good choice but make sure C/R is down to 7.5 to 1 or so for detonation protection.
You will need a modified intake manifold to add intercooling and FI injectors....you already know this probably. Probably easier to start with a 3.2 Carrera manifold unit as mentioned above.
You are gonna need alot of oil cooling so get a front mount cooler that mounts below front bumper. Everything else will not get enough airflow to cool properly.
I assume your reference to valve spring replacement is to use a stiffer spring and properly shimming them.
Does the Carerra manifold set up bolt up to my engine, or can it be modified (as I own a machine shop)?
I assume most people add the front oil cooler and retain the wheel well cooler?

Thanks
Old 10-27-2009, 07:06 AM
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My two cents:

A well developed 3.0T with a 915 could give many 3.3 Turbos fits.

As it is 10% smaller, by running 10% higher boost or moving the power band up 10% should alow you to match a 3.3T's power.

As you are using a 915, using RPM's is a better approach.

On top of that a 3.0 is well suited to extend the RPM range and with the right valve train (cams, springs & retainers) can go up to around 7500rpm without issue. As most 3.3's are done by 6500rpm, 7200rpm would for a 3.0 would put you on equal footing.

Further, most 3.3T's make there peak HP near 6000rpm. This would put your goal to make peak HP at around 6600rpm. This mostly comes from the cam as long as the ports are not to small. Your SC cams are good turbo cams. You might try timing them to the 1977 euro 3.0 specs. Most go the other way and time there SC cams for low end. Alternatly, you could look in to a custom cam that would match your goals. Kind of a moderan turbo Grupe B cam.

To put this another way. A 3.3 that makes 330 ft/lb of TQ at 6000rpm will make 380hp. A 3.0 that makes 300 ft/lb at 6600 will also make 380hp.

Your 915 will limit you to about 300 to 325 ft/lb of TQ. You might want to talk to Kenedy Enginering about what you are doing and if they can make you a disk that has springs of the right strength to help reduce the pounding load on your transmission. This is what Porsche did with the 944 Turbo S.

HP comes with boost. Pre-boost drivability and spool comes with compression. EFI reduces drag on the turbo and it spools faster. EFI also alows for closer to ideal AFR's and timing that also increases response. Most report that around 8/1 CR drivability seems to be imporved.

Proven boost to compression combonations are: 7/1 CR w 1 bar boost, 8/1 CR w .8 bar, and 8.5 should be good with about .7 boost.

A well built normaly asperated 3.0 with SC cams and carbs should make around 200-220 normaly asperated HP. With 1 bar boost it should make up to 400-440hp, with .8 bar it should make around 360 to 400, .7 bar should be about 340 to 375. Cams that move the rpm's up 10% should approach 10% more HP than these numbers. Do note that these might be ideals and effecencies will fall off to some degree.

You will need to check if you have cylinders that can be re-used. Also, you should up grade your rod bolts and head studs.

JE makes good Turbo pistons if you want to lower compression. You should be able to use your 8.5/CR cast pistons also and might even be able to shim them or have the small end of the rod offset bushed and get near 8/1. The JE's are around $1k and will stand up to the heat of a turbo motor better.

It would be a shame to use a stock Inter-cooler. Go with a 3.2 Carrera manfold. You can prety much use an off the shelf IC with this and it dose not have to cost much but will offer a lot better performance.

Good luck.

Last edited by 911st; 10-27-2009 at 08:04 AM..
Old 10-27-2009, 07:59 AM
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Originally Posted by 911st View Post
My two cents:

A well developed 3.0T with a 915 could give many 3.3 Turbos fits.

As it is 10% smaller, by running 10% higher boost or moving the power band up 10% should alow you to match a 3.3T's power.

As you are using a 915, using RPM's is a better approach.

On top of that a 3.0 is well suited to extend the RPM range and with the right valve train (cams, springs & retainers) can go up to around 7500rpm without issue. As most 3.3's are done by 6500rpm, 7200rpm would for a 3.0 would put you on equal footing.

Further, most 3.3T's make there peak HP near 6000rpm. This would put your goal to make peak HP at around 6600rpm. This mostly comes from the cam as long as the ports are not to small. Your SC cams are good turbo cams. You might try timing them to the 1977 euro 3.0 specs. Most go the other way and time there SC cams for low end. Alternatly, you could look in to a custom cam that would match your goals. Kind of a moderan turbo Grupe B cam.

To put this another way. A 3.3 that makes 330 ft/lb of TQ at 6000rpm will make 380hp. A 3.0 that makes 300 ft/lb at 6600 will also make 380hp.

Your 915 will limit you to about 300 to 325 ft/lb of TQ. You might want to talk to Kenedy Enginering about what you are doing and if they can make you a disk that has springs of the right strength to help reduce the pounding load on your transmission. This is what Porsche did with the 944 Turbo S.

HP comes with boost. Pre-boost drivability and spool comes with compression. EFI reduces drag on the turbo and it spools faster. EFI also alows for closer to ideal AFR's and timing that also increases response. Most report that around 8/1 CR drivability seems to be imporved.

Proven boost to compression combonations are: 7/1 CR w 1 bar boost, 8/1 CR w .8 bar, and 8.5 should be good with about .7 boost.

A well built normaly asperated 3.0 with SC cams and carbs should make around 200-220 normaly asperated HP. With 1 bar boost it should make up to 400-440hp, with .8 bar it should make around 360 to 400, .7 bar should be about 340 to 375. Cams that move the rpm's up 10% should approach 10% more HP than these numbers. Do note that these might be ideals and effecencies will fall off to some degree.

You will need to check if you have cylinders that can be re-used. Also, you should up grade your rod bolts and head studs.

JE makes good Turbo pistons if you want to lower compression. You should be able to use your 8.5/CR cast pistons also and might even be able to shim them or have the small end of the rod offset bushed and get near 8/1. The JE's are around $1k and will stand up to the heat of a turbo motor better.

It would be a shame to use a stock Inter-cooler. Go with a 3.2 Carrera manfold. You can prety much use an off the shelf IC with this and it dose not have to cost much but will offer a lot better performance.

Good luck.
The new Sachs disk I have does have the spring loaded hub to reduce the shock loads and is rated for about 350 ft lbs of torque. I have previously read that the 915 is good for up to 400 ft lbs, do you know what the weak link is in the 915?

The aspect of moving the power up in the RPM range works for me as I am not trying to make a dragster and have no intentions of focusing on 0 to 60 times.

One of the problems I am trying to understand is why these parts are so rediculously priced. I can spec out a custom set of pistone and rings from Wiseco for less money then any existing off the shelf sets. I can also make cylinders from scratch for less then buying a set. Are you aware of any sources of parts that aren't ridiculously priced?

I have considered seeing if a few people on Pelican want to team up to spec out cylinders and pistons and then I could put them through my engineering department for CAD prints and programing and produce the cylinders on one of my (unfortunatelly) idle CNC mills and buy the pistons directly from Wiseco at a good cost and then split the cost with anyone involved.

Does that sound appealling to anyone?

I hope this doesn't violate any forum rules.

Chris
Old 10-27-2009, 08:29 AM
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I have a decent amount of experience using a 915 behind a 930 engine.
325 ft/lb of torque is about all they can live with. Not just tolerate but live with. Mine has been in place for 10 years. Yes myself and others I work with have busted many so know the limits.
The weak points are the side plate, R&P retain plate and 2nd gear. Those areas can be beefed, but of course no drag racing.
I can shoot you some info on exhaust systems and mods as well if you like.
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Old 10-27-2009, 08:42 AM
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There are relative values.

As to cylinders, they are probably best if forged and need special plating unless you want to sleeve them. Then matching the piston and the cylinder thermal expansion rates so that the piston dose not bind or slap takes some work and that they do not expand and pull the head studs out.

I suspect one of the best value ways to build a tubo motor would be to sell your motor and buy a solid 3.2 Carrera motor for about $5k. Get a 84-86 or an 89. They come with the good cylinders. It already has the EFI plumbing and manifold all in place. They have a great turbo cam and the heads are already ported and matched to the manifold. Just an easy way to begin. The AFM can be sold off. The heat exchangers are good and a factory 930 J pipe can but purchased used for $100 so most of you plumbing is done.

Then just go through it with new up grade rod bolts, rings and valve guides. May not even need to split the case though it is better to do so. Can have the tops cut off the pistons for 8/1 or get J&E's for $1000.

Aftermarket inter-cooler cores can be purchased on the cheap if you have the skills to make and weld your tanks or a complete off the shelf IC can be used and elbowed into the throttle body.

Some have run more through the 915 but I trust people that know more than me that 300-325 is about the limit. Do a search on 915 transmission titles in the 930 section there is lots of info I believe. I know I asked this in one thread myself. Things can be done. Rear tire size, car weight, open v LSD are probably a few of the variables. The side plate is another. The main shaft, size of the gears are others. Porsche also heat treated there first couple of gears in the 944 Turbo S and the 996TT with the optionally larger motors. Limiting boost with some type of active boost management in first and or second might help.
Old 10-27-2009, 08:56 AM
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ps Could just sell the SC and buy a high milage 87-94 911 like I am concidering so you get the G-50 transmission and all the other plumping goodies.
Old 10-27-2009, 08:58 AM
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My opinion... If you want to enjoy a turbocharged 911 rather than work on it all the time and spend ridiculous amounts of money on aftermarket parts that are not engineered to work together like the factory parts and will have little to no reliability over the long run... then sell your SC and buy an origonal 930.

It is already engineered to go fast and last and they're relatively cheap these days and they will be worth alot more in the future in origonal form than any modified SC or Carrera.
Old 10-27-2009, 09:26 AM
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Originally Posted by jfairman View Post
my opinion... If you want to enjoy a turbocharged 911 rather than work on it all the time and spend ridiculous amounts of money on aftermarket parts that are not engineered to work together like the factory parts and will have little to no reliability over the long run... Then sell your sc and buy an origonal 930.

It is already engineered to go fast and last and they're relatively cheap these days and they will be worth alot more in the future in origonal form than any modified sc or carrera.
+1+1+1!!!
Old 10-27-2009, 04:40 PM
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Originally Posted by chris.lovell View Post
What would you recommend as a reasonable rev limit?

If I were to sell my SC engine and purchase a Carrera engine, would the injection be the only benefit and are you knowledgeable as to the value of both engines?

I appreciate the input, it's helpful.

Chris
With SC cams and turbo, you will probably make peak torque around 4000 RPM and peak HP around 6000 RPM. With 5-speed gearbox, I see no reason to rev past 6500RPM.

Regarding SC vs. Carrera engine, you will get injector rails and Carrera intake "free" if you chose Carrera engine. Carrera has identical crank and rods as 930 engine, so that's a non issue...(SC actually has even beefier rod bolts than 930/Carrera but as long as you keep rev limit under 6500 RPM, no worries).

Main issue is 915. It doesn't like torque and it will twist. Thus you must go for revs in order to transmit lot's of power trough it.

When I rethink all this, a complete G50 Carrera would be even better object to start with (money-wise). After you've reinforced your 915, found a Carrera intake etc. you would (arguably) spend as more money than if you were to sell your SC and buy a G50 Carrera and still have a dodgy old 915.

Regarding selling and buying 930, that will work too but 4-speed gearbox, CIS and narrow intake ports make it somewhat hard to tune.
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Old 10-28-2009, 12:02 AM
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I appreciate the input from everyone and would welcome more.
Now I need to back up and re-think my direction. I don't have much interest in selling the SC I love the car and bought it right after the previous owner spent the money to do a complete ground up restoration. The work involved doesn't bother me in fact I love these kind of projects, but the Carrera engine and G50 are appealing and at a minimum it sounds like I need to look into the engine. I currently have 2 complete 79' SC engines, one has about 20,000 miles on it after a complete rebuild to euro specs with all the approriate upgrades and the other is a good running original engine with about 100,000 miles and no known upgrades. Can anyone give me an idea on what these engines are worth in todays market? I would also like to now what my nice rebuilt 915 is worth and what I would have to spend for a G50?

I am very appreciative for all the great input I have gotten from everyone, it has probably saved me a lot of head aches and time.

Thanks,
Chris
Old 10-28-2009, 03:59 PM
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i used a 79 SC 3.0 engine for my build they make great little turbo engines.
I used a 930 cis intake from a 86 euro 930 matched the SC intake ports, Supertec head studs, ARP rod bolts, 930 oil pump, racing valve springs, twin plugged the heads, 91-3.3 turbo pistons and Cylinders, used the SC heads and cams, used the stock SC rods with offset wrist pin modification for stroke. MSD ignition and twinplug distributor made from my SC distributor by Supertec. K-27 7200 turbo. 1030 CFM intercooler and 46 Tial wastegate and Tial BOV.1bar boost. Kennedy stage 2 228mm pressure plate unable to hold the power in 5th gear.

Makes a 3.12 displacement engine similar to the 935 IMSA engines.
Engine spins up freely and very quick, loves to run up the RPM's without running out of breath.
If your not trying to build the biggest badest engine on the planet then your SC engine is a good
place to start from and you can easily make 400hp + out of it.
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Old 10-28-2009, 06:16 PM
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Quote:
Originally Posted by chris.lovell View Post
I assume your reference to valve spring replacement is to use a stiffer spring and properly shimming them.
Does the Carerra manifold set up bolt up to my engine, or can it be modified (as I own a machine shop)?
I assume most people add the front oil cooler and retain the wheel well cooler?

Thanks
Yes stiffer springs, shimmed to preload, lightened retainers.
The Carrera manifold should bolt up I assume, not 100% sure about how well it matches the ports on the SC heads. Earlier 78-79 SC used larger intake manifold runners so I assume heads/ports were changed to match the smaller runners on later years.
Oil cooling, I went thru the whole excercise of upgrading the trombone cooler to the later Carrera cooler with fan in the fender and found that it was not enuff cooling for the turbo under heavy loads, as at a DE event. The real solution is a front center mount cooler....plumbed inline with fender cooler is best. Now I never see more than 220 degrees on a hot 85 degree track day after 25 minutes running.
You know that a g50 box conversion is not trivial in a SC. You may wanna think about starting with a real turbo and gain the suspension, brakes, and tranny improvements that come with it.
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Old 10-29-2009, 05:08 AM
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