Denis54

I want to modify my dead stock, low miles 79 SC engine for more power. I love my car but would like more power. I do not mind spending some money on it as I will probably keep it for the rest of my life.What do you think of the following mods?

SSI with sport muffler. HP: +20 Cost: $1400

20/21 cams. HP: +15, Cost:$1100

9.5 piston. HP: +20, Cost: $1500. My car has 8.5 to 1 pistons

Tensioners upgrade. Cost: $800

Pop-up valve. Cost: $50

This should bring me to approximately 225-230 HP. I think my car would be much nicer with this much power.

Do you think this is a realistic upgrade path? Are my estimated HP and costs numbers right? Any other mod I should be thinking of. As I said at the begining of my post, my car is currently exactly as it came from the factory.

I am the original owner of the car and the modifications will be performed by a local highly reputed shop.

Bill Gregory

Dennis,

You'll get some opinions on this. My two cents: The pop-off valve should be done ASAP. This isn't expensive, and can save you a bundle if your airbox blows up. The general consensus is that upgrading your tensioners is a good thing to do also, but not as pressing perhaps as the pop-off valve.

In terms of the other upgrades, I'd guess you don't have to be concerned with emissions inspections. The SSI upgrade is a nice one, but it removes the catalytic converter.

If you want more power on the SC engine, I'd suggest you upgrade to 3.2 pistons and cylinders. Bruce Anderson discusses this upgrade (Max Mortiz 3.2 P&C's) in his "911 Performance Handbook". This allows the rest of your CIS system to remain intact, unless you are thinking of converting to Webers. You may know you need to watch your cams on a 3.0 engine, as CIS isn't very allowing. Doesn't say you can't upgrade, it's just that there are some injection system limitations.

The other thing to consider is when you increase the horsepower, you should consider your brakes and suspension. If you were to go to 230 hp, at a minimum, I'd upgrade to Carrera (84-89) brakes, and some might recommend larger brakes. You may find you want to also upgrade your torsion bars a few mm. and consider Bilstein shocks. Of course you can go crazy with engine, brakes, and suspension, but it doesn't sound like you want to do that. As a guide, take a look at what Porsche did to brakes and suspension as it raised the HP on the production 911's

Another option you have, is to sell your engine and buy a 3.2 or 3.6 engine. Of course you have a known quantity today to build on.

jlkline

When I went from a 3.0 to 3.2 keeping my CIS, I changed the crank and rods as well.

My original upgrade thought was crank and rods only, but I had to go with the Carrera P/C's as well due to the differeces in the small ends of the rods.

I also put a cat pipe on.

The car runs great, and I'm very happy with a 3.2 in my light car.

Steve Weiner-Rennsport Systems

Hi Dennis:

As Bill said, you'll get a bunch of opinions on what you are proposing and everything really depends upon your budget.

If I may, I'd add my 2 cents worth here and comment on what you are thinking about, and offer some of my own, based upon experience,...

1) Aside from any smog issues, this one is very cost effective and highly recommended. Don't go "cheap" on the muffler; its VERY important.

2) Cams will help, but nowhere near that HP figure. Due to changes in the shape of the torque curve, it feels like more than it is. I like the 964 cams, myself.

3) If you buy pistons and cylinders, get the 3.2 (98mm) set. I cannot comment on what JKline was told, but there are different 98mm sets; one for the SC engine and its 22mm wristpins and one for the Carrera engine. You do NOT need to buy anything else and the displacement & compression increase will really make a big difference.

4) The Carrera Tensioner upgrade is an excellent idea and well worth the money. Its a durability /reliability issue. Be sure to use the later wide idlers when you do this as that was the root cause of the tensioner problems.

5) Pop-off valve is a no-brainer and will help keep you from walking,... Do this one before anything else.

Remember, with all these mods the engine will be making more power and thus heat,.......upgrade that oil cooler and get some air ducted into it.
The other issue is that the these CIS cars run very lean and with the compression increase, you will need to tweak the idle mixture and control pressures to get more fuel into it.

Hands-down, the best thing you can do to increase the acceleration of the car is to install a close-ratio gearset. Nothing you can practically do to these motors even comes close to what close-ratio gears do. Its like adding 50 HP to the car.

There is no question that the installation of a 3.6 litre engine would eclipse anything you can do to your 3.0, but its a quantum leap in costs to do it right.

Lastly, upgrade the suspension and brakes as this is an integral part of the overall performance equation. Larger torsion bars, better shocks, adjustable swaybars and better brakes are not budget busters and are a must when starting a program of performance enhancements.

My apologies for being so long-winded but hopefully this advice will help save you some money and get you the biggest bang-for-the-buck.

jlkline

Steve,

I think the difference in my situation was that I started with the purchase of the Carrera crank and rods for my upgrade, which it turned out didn't match my existing 3.0 wristpins diameters. I opted to proceed with the new crank and rods anyway, and used a set of Carrera P/C's to accommdate the 3.2 rod wristpin diameter.

Just curious though, am I making more HP and torque than just going to 3.2 pistons with the whole set up as described above, or did I shell out an extra thousand bucks just for fun?

Steve Weiner-Rennsport Systems

JKline:

Ahhhh, now I understand what you did....

As you (and others) know, there are 2 ways to achieve the 3.2 litre displacement:

1) Short stroke: 98mm 70.4mm

2) Long stroke: 95mm 74.4mm

Each configuration has its own "flavor; that is, both engine sizes have different torque and RPM characteristics. This not to say that one is better than the other, they are simply different and a person may prefer the way one performs over the other.

Now,..whether you wasted the money spent on the 74.4mm crank and rods is not for me to say but, if you were here I would have simply suggested the big bore kit without spending the $$$ for the other hardware.

Normally speaking, whenever an engine is rebuilt the P/C's are replaced, not the crank and rods so we usually do the short-stroke version as mentioned above. For folks with a bigger budget, one can combine these (98mm X 74.4mm) for a 3.4 which REALLY rocks. A 3.4 with 964 cams, appropriately modified heads, and twin-ignition, is quite the piece,...

Jeff Curtis

Dennis, the Webcam 20/21 idea works great, so will a 964 grind, I had the 20/21 and a friend of mine has the 964 grind...both of us seemed happy.

As for Steve's suggestion for shorter gears or a 7:31 R&P - I did the R&P and MY GOD!

...loved it!

Just get it done right, pay someone to set your pinion depth and backlash with FACTORY tools.

Steve Weiner-Rennsport Systems

Hi:

Just a giant-sized Caveat Emptor here about using a 7:31 R&P with any 3.2 or larger,........not a good idea.

They do not hold up well, even if setup by the very best transmission folks in the world.

scupper

Question for Steve - - -
You mentioned installing a close ratio gear set. Does this affect 5th gear too, or just say 2, 3 and 4? In other words, is it possible or feasbible to run a close ratio gear set and retain the 5th gear original ratio for crusing on the Interstates?

Steve Weiner-Rennsport Systems

[quote]Originally posted by scupper:
<strong>Question for Steve - - -
You mentioned installing a close ratio gear set. Does this affect 5th gear too, or just say 2, 3 and 4? In other words, is it possible or feasbible to run a close ratio gear set and retain the 5th gear original ratio for crusing on the Interstates?</strong><hr></blockquote>

Scupper:

Indeed, you may have almost any setup you want. The choices are up to you.

Normally, we change 2nd through 5th gears, as 1st gear is very expensive. The gear ratios are determined by factoring rear tire size, engine RPM range, and desired top speed/cruising speed.

Some folks elect to retain the stock 5th gear for freeway work and change 2nd-3rd-4th for much improved acceleration. One just needs to be prudent and not create a big RPM jump from 4th-to-5th.

Everything is always a compromise and this type of thing is no exeception.

Denis54

Thanks all for the answers received so far.

Emission controls do not apply around here.

Handling is not an issue. I am happy with the handling of my car. I will not track my car, nor drive it very hard.

Brakes are excellent and are more than enough for my type of driving.

Same thing for oil cooling I do not intend to drive hard for long periods of time.

I am afraid the 3.2 P/Cs at $3,700 are too expensive for the potential HP increase.

The 7:31 R&P could be a good idea. I did that on a Corvette many, many years ago. The result was spectacular. I would guess going from a 8:31 to a 7:31 R&P would be like adding approximately 14% more power. Am I right?

Could I buy only the 7 teeth gear to replace my 8 teeth one and keep my 31 teeth gear (sorry, but I do not remember which one is the ring and which one is the pinion). How much would the gear(s) cost? How much for installation?

Are my other HP and cost estimations OK?

CamB

Shop around a little - I paid quite a lot less than that for a set of 98mm p&c (Mahle 10.3:1 ones). That way you don't have to use your old cylinders.

Jeff Curtis

Dennis, I had the 7tooth pinion gear...and from what I understand, according to Jim Patrick Motorsports...there were 8tooth pinion gears made with more teeth on the ring gear, of course - that still equaled a 7:31 ratio.

This provided more pinion tooth to ring gear contact thus being able to handle more HP.

JackOlsen

Before you do anything (well, anything except the pop-off valve), I'd talk to as many 3.0 owners as you can who have done the same thing. Post on here and on Pelican. Building up your stock engine can jeopardize the reliability and integrity of the engine, and (in my opinion), you're not going to get to 230 hp without spending buckets of money.

Also try to talk to some people who have swapped in 3.2 or 3.6 liter engines.

And finally, try and get some rides in cars with the two different approaches. This is definitely not something you want to jump into without a lot of information. It can get phenomenally expensive, and phenomenally time-consuming, with ultimately disappointing results.

My guess -- with the goals that you're stating -- is that a 3.6 swap would be the most cost-effective way to go. You don't need low displacement for any classification rules, and you're not planning on extensive mods to the brakes or suspension, which is fine (in my opinion) for street driving. You're going to feel the torque a 3.6 provides in ways a built 3.0 or 3.2 could never approach (at least, for the same money).

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=1&t=004330" target="_blank">Read this thread. too.</a>

Gordo

Ever consider Nitros Oxide? Lots of bang for the buck and only when you want/need it.

Don't know what kind of kits are made for the 911SC but I should think you could find something/someone to strap one on.

For my money, that's where I would look.

Gordo