Dyno'd the SC yesterday

rpiper · 10-08-2003, 07:36 AM

Just wondering what the approximate "loss" from the crank to the wheels would be on a 915 equipped 911. 20%? 15%? The dynojet came back with 194.3 at the wheels. 80 degree day.
Thanks!

dd74 · 10-08-2003, 07:40 AM

15% drivetrain loss. 194 at the wheels is pretty healthy for an SC. Is it a 3-liter? What modifications did you do to it?

Rot 911 · 10-08-2003, 07:42 AM

That's interesting. I thought a stock 78SC only put out 180hp.

rpiper · 10-08-2003, 07:48 AM

It's been rebuilt by FlatSix here in Bloomington with a few mods, namely the 9.8:1 Euro P/Cs. It has 964 cams and SSIs as well. I'm using an OEM style 2 in 1 out muffler but may switch to a Bursch for a little more bark. The Bursch also made a little more horsepower, but it was on a cooler day so that could be enough to raise the HP numbers. It's just a great engine. Very tractable. Fires right up, idles beautifully, and makes good power.

Noel · 10-08-2003, 07:48 AM

Mine dynoed at 168 at the wheels or 197 at the crank using 15% about four years ago. (80 SC).

Noel

dd74 · 10-08-2003, 07:52 AM

Quote:

Originally posted by rpiper
It's been rebuilt by FlatSix here in Bloomington with a few mods, namely the 9.8:1 Euro P/Cs. It has 964 cams and SSIs as well. I'm using an OEM style 2 in 1 out muffler but may switch to a Bursch for a little more bark. The Bursch also made a little more horsepower, but it was on a cooler day so that could be enough to raise the HP numbers. It's just a great engine. Very tractable. Fires right up, idles beautifully, and makes good power.

Do you still have CIS?

rpiper · 10-08-2003, 08:03 AM

Yes. It's the original '78 case and heads (78 and 79s had larger ports and lower CR than the 80-83 cars) and new 9.8:1 Euro spec (from the 81-83 Euro SCs) P/Cs. It makes a great combination. I thought about Webers and some hotter cams (964s are about the hottest that can be used w/CIS) but the CIS is just so easy to deal with that I decided to keep it.

1fastredsc · 10-08-2003, 08:32 AM

, dude, your pulling like 228 at the flywheel, that's pretty damn good. That's a 48hp increase at the fly.

rpiper · 10-08-2003, 08:40 AM

It's a lot of fun. Just changed to a 7:31 R&P with ZF limited slip too. It really goes. I have a few more exterior/interior details to work out and then I'll post some pics.

dd74 · 10-08-2003, 09:05 AM

Good work.

Look forward to the photos.

rdane · rdane's Garage

The stock SC is supposed to be 180 at the crank! If it didn't make that at the factory the engine would be rebuilt before being installed in a car is my understanding.

194 at the wheel is very good but it is almost exactly where you would expect to be with the mods you have done to you engine. Add the normal 15% makes it 228 at the crank which is a very nice SC.

Almost 50 hp difference!

Sounds like a great car, congrads!

Denis54 · 10-08-2003, 03:00 PM

I have several theories that I would like to see validated regarding SC HP increase.

My understanding is that a stock SC produces 172 SAE HP which equals 180 DIN HP. DIN is the method used in Germany to measure HP. SAE is the method used in NA. We should thus refer to 172 HP. Can anyone validate if I am right or wrong?

rpiper, if your engine produces 228 HP at the crank, that represents a 56 HP increase. I would guess the increase comes from the following modifications:

20 from SSI and muffler

10 from 964 cams

26 from increased compression. I understand the rule of thunb is 10% increase for each point increase in compression. You increased from 8.5 to 9.8. That would equal a 13% increase. 13% X (172+20+10) = 26 HP.

Are my estimated gains realistic?

rpiper, can you run your engine on 91 octane gas?

Noel, has your engine been modified?

Denis54 · 10-08-2003, 06:43 PM

I searched through a lot of documents I saved to my hard drive and found the following comment from Wayne:

"roughly speaking, you get about a 10 percent power increase per compression point increase"

Increasing comression from 8.5 to 9.5 on a 78-79 SC would thus result in approximately 10% more power.

In that same article he also says that:

"964 (a.k.a. 911 C2 and C4, ’89-’94) camshafts are compatible with CIS injection, but produce about 10 more horsepower and a more peaky power curve"

The article I refer to is a Pelican Guest Technical Article and its title is "Extracting Power from CIS 911s"

Denis54 · 10-08-2003, 08:18 PM

From the above dyno charts, it seems that Tom Tweed's and David Dorian's cars seem to have similar specifications and produce approximately 165 HP

The main difference between rdane's engine and the other 2 seems to be the 20/21 cams. rdane's engine produces 180 HP.

Could it be that that the 20/21 cams produce the extra 15 HP?

dd74 · 10-08-2003, 08:35 PM

20/21 cams have, according to some, produced a large range of horsepower ratings. I've heard anything from 10 to 40 hp. A lot depends as well on what heads one is running. If early heads (78-79), the hp will be (much) higher than on an '83 because the ports on an '83 are 34 mm; on 78-79 the port sizes are 36 mm. Conversely, however, an '83 will probably out torque an earlier engine, making it better for the all-important city driving and auto X-ing.

Much has been said about Noah's engine, which is not exactly a phenonmenon when one considers this: he has a Carrera 3.0 engine, which is a much different beast than an SC engine.

I don't know if it is a "better" engine, because out of the box, I do believe the SC engine is more robust. But his engine did come up in conversation a week ago, and simply put, for the equivalent mods done on an SC engine, they might not come close to Noah's. Remember; if there is one difference to the Carrera 3.0 engine, it's the crank, which is lighter, and from a 2.7 - any other differences I'm not aware of.

20/21s are extremely attractive. Yet, if one is to go that far, they might as well tear down the entire engine. And if they do that, get a 74.4 mm crank, 98 mm pistons, honed-heads and ditch (yes, really - ditch) the CIS, because with the crank and pistons, you'll want to run at least an S cam, and for an S cam, you'll need Webers or an equivalent EFI.

With all that, you'll have a high-cammed 3.4 with excellent induction, torque (because it's a 3.4) and horsepower of at least 250, probably more.

Of course, YMMV, particularly if you go with a 3.6.

rdane · rdane's Garage

The big difference on the 3 dynos is the difference in exhaust systems. Each would seem to be a little better than the other as the HP goes up.

The cam is where the 10hp comes from on my engine I suspect. 164, 168 and 182 on the dynos I posted but the cam isn't worth more than 10hp in a CIS system from what I have seen. ( I have the early '79 heads)

Early stock exhaust, SSIs and 3 different mufflers. The cam is accumlative to the exhaust mods I am told.

Noah's mods done on an SC show similar HP figures or close enough as Bobby's was 194 and Noah's 203. Add the high compression P&Cs and I would expect my 182 to jump the obligatory 10/13% and hit around 195/205 hp duplicating Bobby's and Noah's results.

Pretty easy to change cams when the engine is out of the car btw.

I have been reassured a set of PMO carbs will add another 20/25hp (not the 10/15 max I was thinking) and a huge jump in throtte response to this equation.

The more data we can collect on SC mods, the more we can afix a hypothetical HP gain to each. Be nice to see more info documented on hot rodding SCs. Seems like the cars have lasted so well, many were reluctant to do any changes until the cars began wearing out. I am right at 200K myself with good leak down and compression across the board. Adding new P&Cs at the moment would seem to be a waste of money. Carbs on the other hand might be really fun! I might try them with the 20/21 cam for a bit and see how that works out.

dd74 · 10-08-2003, 09:22 PM

But not all SC engines are the same. As I said, Noah's engine varies from an SC engine in at least the crank, so that's one variable to consider. I hope he chimes in on this with his opinion and a copy of his dyno sheet - quite an impressive achievement.

Ed Bighi's engine seems freakishly strong for stock. I'm figuring something has to be up with the fuel distributor, but I've heard fuel distributors mean nothing in horsepower ratings. Hmmm...

All I know of his engine is he races it regularly. What does that mean? Dunno, other than the engines respond to being driven hard. Maybe he has less carbon in his than anyone else's, LOL...

Or maybe he simply got a very well-built version.

rdane · rdane's Garage

Quote:

Originally posted by dd74
Yet, if one is to go that far, they might as well tear down the entire engine. And if they do that, get a 74.4 mm crank, 98 mm pistons, honed-heads and ditch (yes, really - ditch) the CIS, because with the crank and pistons, you'll want to run at least an S cam, and for an S cam, you'll need Webers or an equivalent EFI.
[/B]

Good follow through on the S cams and crank. Problem that I see with that....which is what most of the motor builders suggest.....is that the crank adds $2500 in parts to the rebuild alone. I saw a quote for 12K$, by Wayne I think, for any flat 6 rebuild. New high performance parts not included. Add 3K for P&Cs with a $2500 to $3500 crank and you might as well jump to the extra coin and do a newer, factory 3.6 transplant. 18K verses 20/22K!

I have been able to add an exhaust sysyem, then cams months later when I needed to pull the engine to fix some oil leaks. If new P&Cs can happen on a top end rebuild that would be great. Throw carbs in there any time (as needed ) and you have some nice options to build a fairly stout SC motor that can be easily budgeted for without taking out a second morgage.

More
SC engine upgrade questions...ones with hotrod SC's please respond...

okay what is the word on the displacement increase for 3.0 SC

dd74 · 10-08-2003, 09:44 PM

The funny thing about this thread is it proves the point that there is more than one way to skin a 911 engine as, up to a point, the cost of modifying a Porsche puts one in the next fiscal bracket where a second option can be to consider a larger stock engine.

Modifying a 3.0 into a healthy 220-230 horsepower can as well get one a true 3.2 that only needs a chip and exhaust to better that 230 by 10 hp. The cost of modifying a 3.2 to 270 or so, will get you into a 3.6 worth about 280.

It's mathematics even an English major can understand...

Or conversely, one has to really love their current engine to spend an equivalent amount of money that will get them very close to a newer and larger engine.

Interesting...

stealthn · 10-08-2003, 09:50 PM

MAN THIS IS GOOD STUFF!!!!

My nipples could cut glass

Never have so few, spent so much, to get not enough, yet had so much; enjoyment on an SC engine.....

25 years and still pull'n strong.