Increasing performance of 1978sc!

[crashmy911]

i' would like to increase the performance of my sc. At the moment it has 964cams 8000rpms valve springs and pre 74 exhaust. How can I get this car to pull better from low rpms and put me back in my seat? Also when I rebuilt the engine it has mahle pistons and cylinders so what would my compression be with this engine?

[Vipergrün]

Have you tried advancing your timing and richening the fuel mixture? It would be wise to know your CR, though, so you don't have detonation issues...

-B

[crashmy911]

timming is set at 35 degrees at 6000 rpms per John Walkers advise. She runs good but not alot of low end torque.

[crashmy911]

Mixture is set at 3.5% can this be set alittle bit richer?

[crashmy911]

Will going to carbs really make that much of a difference. the car is just a car used for fun.

[Lothar]

I don't believe that the 964 cams are known for low end torque. They would have moved the torque curve more toward the top end.

[crashmy911]

Once engine is reved up it pulls nicely but you have to have the rpms up all the time or there is nothing.

[dd74]

Originally posted by crashmy911
Will going to carbs really make that much of a difference. the car is just a car used for fun.

Depends. Carbs (Webers) react best to more radical cams than 964s and different pistons than what sounds like CIS pistons that you've put in your engine. To really make use of carbs - not that you can't now - but to their highest ability, you need to tear apart your motor and put new pistons in, not to mentione open up the heads some, and maybe modify the fuel pump.

If you're wishing for more low-end torque, you may as well go back to SC cams. I have an '83 SC engine with '74 heat exchangers, and it has good torque from as low as 2,500.

If you want a more radical cam than the 964, go with the WebCam 20/21. You might get power up to 7,000 RPM with the 20/21, and since you have 8,000 RPM valve springs, well...

[crashmy911]

So what do I need to do to have a really radical engine go to higher commpression more radical cams and carbs. Should I go to dual plugs also. What kind of difference will I see and will I have to fudge with it all the time to get it to run right. Or is it a set and go thing?

[dd74]

You need to get "Porsche 911 Engines," authored by the Mojo Jo-Jo of this forum. He has a very nice section on different flavors of modified 911 engines. Then, you need to decide which types of mods you like (webers, supercharging, turbo, short-stroking, etc.), then pose many questions to the board. Get oodles of money together, but before you spend, make sure you do not already have enough power. To do this, you should take your car to your nearest race track and make an honest assessment if your current setup is enough for you.

[nostatic]

buy a Mustang.

[PSRacing]

Good advice, you need to know how you want to use your car, how much power you want, and how much you want to spend.

I have had very good results with SC’s by using SSI heat exchanges dull outlet, Dansk Sport Muffler w/ dull inlet and 4” outlet, Porting and Polishing heads, Polishing intake runners, Enlarge throttle body, Ignition timing @ 35 degrees @ 6000 RPM then if I have detonation I back off the timing until it is gone.

You already have the better F.I. w/ large intake runners. I would do the bolt on items before tearing your engine down again, to save expense and incase you find the power that you are searching for.

Doug

[fintstone]

I have a Supertec built '78 engine with webcam 20/21 cams, SSIs, ported heads (39 intake, 38 exhaust) and 9.3:1 compression JE pistons. It accelerates very well throughout the rpm range, but my car is probably quite a bit lighter than yours. Less weight is often easier than more hp. Gearing/tire size also makes a big difference.
If your rebuild used the mahle pistons/cylinders that were stock for '78, your compression is 8.5:1 . Stock port size for '78 is 39 intake, 35 exhaust. If you know who built your engine, call and ask them for a copy of the build sheet.

[chuckw951]

"put me back in my seat"

Could be a tall order!

I'm running a 1982 SC motor with 9.3 to 1 compression, 40mm PMO carbs and SSI exhaust. The motor also has the HPX ignition with allows you to change the ignition curve easily. I'm running stock pistons and cams so I'm not getting the most from the carbs. If I were to go for more power I would change the pistons and cams and maybe open up the intake ports. I suppose I could twin plug and run more compression. Or add larger P&Cs to make a short stroke 3.2. I'm not sure when 46mm carbs are needed on a modified 3.0-3.2. I know when I built my motor 40mm carbs were recommended. But all of these things get expensive quick, and in my case I'm committed to using carbs as I made that big purchase.

I think you have a couple of options, and as others have stated, it depends on what you would like to do with the car.

If the motor was rebuilt with stock 78-79 P&Cs you could be running a 8.5 to 1 compressions ratio. In 1980 porsche bumped up the compression ratio to 9.3 to 1 (but for some reason used small intake runners and intake ports). But who knows and beyond opening up the motor I'm not sure how you can tell. Perhaps consult with the shop that did the motor? Perhaps the cylinders have part numbers that you could read and cross reference?

There are a number of threads on the 911 engine rebuilding forum (and this forum) about modifying a 3.0 for more power.

Couple of ideas:
1. Give up on motor modifications and focus on the suspension or making the car lighter.
2. Build a 3.2 short stroke motor by adding bigger P&Cs.
3. Carbs, cams, heads, pistons (and perhaps twin plug, even higher compression)
4. EFI instead of carbs with the mods in #3
5. 3.2 or 3.6 swap
6. Sell the car and buy something faster like a 930 or install your motor into a light early 911.
7. supercharge

My friend Jim is running a supercharger on his 79 SC. Lots of low end power.

Here is a pic:

[rdane]

At the moment it has 964cams 8000rpms valve springs and pre 74 exhaust. How can I get this car to pull better from low rpms and put me back in my seat? Also when I rebuilt the engine it has mahle pistons and cylinders so what would my compression be with this engine?

Cams, exhaust and muffler is pretty much it for cheap power in a CIS 3.0. Torque is even more expensive. High compression pistons or a big bore is the next step up in price. You have the best heads for power (78/79), the worst for torque. The later SC and the the 3.2 Carrera were all redesigned 3.0s to specifically give you even more torque.

Bottom line? More torque lower in the rev range on a 3.0 isn't going to happen.

964 and 20/21 cam will be hitting the torque curve flat at 4000 and drop off again by 5200/5000 max. Peak HP will be between 6300 and 6700 and dropping off sharply at 6700 or earlier.

There is nothing left in an SC engine to use the HD valve springs with. (althought their is some protection on a over rev or misshift) Your (and mine as well) engine is "all done" at 6500rpm.
I have a couple of dozen dynos on different CIS 3.0s that say the same thing.

SC-964-20/21 Cams and CIS are the limitations.

The answer to low end torque is more displacemnent. My 3.4 CIS has more torque now @ 2500rpm than my 3.0 had at peak. My peak torque rivals the 3.6 engines in performance for comparable cars.

The 3.0 was 168rwt @ 5500rpm and now it is 175rwt @ a lowly 2500rpm. (that is not a misprint) It means 2nd gear starts are now about what 1st was!

A recently dynoed 964 3.6 with exhaust and a performance chip was 216.3 max torque at the wheels..

My 3.0 to 3.4 CIS conversion is now 213.3 max torque. It hits 210 at 3800rpm and stays to 5200rpm.

More torque really means you want a bigger engine. None of them are cheap, 3.4/3.5/3.6.

My base engine was a '79 3.0 now a 3.4 CIS. 20/21 cam, SSI and a sport muffler and 9.8:1 single plug. Most recent Dynojet dyno @ 260 hp and 250 ft/lb of torque calculated with a 15% loss.

This is the first dyno at 1000 miles
219 rwhp=258 crank @ 6100rpm with a 15% loss
213 rwt= 251 crank @ 4100 with a 15% loss

[cvfncrew]

Put your car on a DIET.

[Don Dosmann]

I have a 78' SC with 964 cams, ssi's with Super traps, and 9.5:1 JE's. When I built this engine I noticed all the low end torque was gone, because of the 964 cams, but it really came on stong above 4K. Because of being rearended and the engine catching fire, I had to rebuild the engine induction system and electrical systems. I decided to build a Mega-Squirt EFI system (that has been well documented elsewhere on this board). The Mega-Squirt system works well, all the low end torque is back and than some. The torque is flat from idle to redline, though the engine is running a little on the rich side. I mostly track this car and dropped my lap times at Elkhart Lake from 2:55 down to 2:43 this passed July. It's fun passing 944 turbo's out of corner 14 and out pulling them down the front straight. I built my own system and have about $750 in the whole system. A really good bang for the buck.
Don

[rdane]

Dropping weight and/or lower gears /gearing will change your perception of the car and change its performance. Neither of those changes will give you more low end torque from a 3.0.

For a quick glance @ some 3.0 dyno numbers look here.
http://quelle911.com/phpBB2/viewforum.php?f=6&sid=ebc1ee9ad05409f3808993800a7f49d2

Not a natually aspirated CIS 3.0 car out there that actually "pulls" past 65/6700 or has anything (>150lb.) below 3000 for torque. Trust the dyno numbers and not your butt.

Engine management systems like Electromotive/Motec/ Megasquirt will add to the low end torque but it won't be much.

Single plug 3.0 9.:1 compression cars with a performance cam and SSIs will typically give you 195 hp at the wheels and 175# of torque.

Same 3.0 engine with the factory CIS 8.5:1 pistons same a performance cam and SSIs will be 180/5hp and the same 175#s of Torque.

Here is a '79 CIS SC with SSIs, a 2/2 Dansk and a 20/21 web cam
and 190,00 miles on the unopened engine.

[rdane]

I agree Noah, but you still have to keep the revs @ 3.5K or better to do that in a 3.0.

I "own" my share of 3.6s in all flavors 4K is the magic number in my car but 3K will work just fine as well. You just have to hold on till 7K. The last 500 rpm to 7K is just good measure for the next shift. It isn't makeing more power no matter how much faster it goes. And it does go.

But them today I got a good lesson on what a 2.2 S engine is capable of, driven with some skill. He was running 6 to 7000rpm all morning! Sounded awesome! It was also very quick.
.

[crashmy911]

You are the reason I went with the modifications that I have made to this car. I had broken studs and had to do something and cams and valve springs were two areas that where cheap to do. After doing this the car is fun and fast butI would just like to make faster and perform better lower in the rpm range. Hell to pull away from suv's and mini vans in this thing you have to really run it. Don't get me wrong either it is still a fast car I just wish you could get some level of performance with out hammering it.