C/3 engine upgrade

[Ed P.]

I have a 71 350/270hp that I would like to increase performance on. I have searched the archives and agree on the 3863151 327/350 hp camshaft, My question is what would you suggest for cylinder head upgrades or aftermarket head replacement. This is a driver not a show car. Thanks

ED

[Joe L.]

Re: C/3 engine upgrade

Ed-----

The problem is that your 270 hp "bottom end" was not designed to support the kind of RPM that the "151" cam produces its maximum power at. You could use the "151" cam, though, as long as you're careful about "winding it out".

A better choice for driveability and "power you can use" would be a modern, dual profile, retrofit hydraulic roller camshaft. These are available from most of the cam manufacturers. I'd use one with about 270 degrees "advertised" intake duration and, certainly, no more than this. In my opinion, the Federal-Mogul/Speed-Pro CS-1070R is about right. This cam will produce greater power and torque in the "below 5500 rpm" range that your bottom end was designed for.

Using this camshaft, or one like it from the other cam grinders, your stock cylinder heads should work just fine. If you want to improve on it, I'd go with a set of Edelbrock Performer cylinder heads for your application.

[Clem Z.]

Re: C/3 engine upgrade

if you have a auto trans a "looser" converter will give you a better SOP feeling when you jump on the loud pedal.

[Patrick H.]

Re: C/3 engine upgrade

I've got the same car and motor.

In 1996 I rebuilt the motor. I changed to SpeedPro hypereutectic pistons with two valve reliefs (not 4), used a Comp Cams 265 DEH hydraulic camshaft, and had some mild work done on the heads. I also swapped to Manley Street Series stainless steel valves. Some tweaking of the Quadrajet, as well as a reproduction open element air cleaner (like a 1970 350/350) with a K&N air filter. Of course, the bottom end is more or less the same as stock except for ARP rod bolts.

Right now the car is quite a bit faster than it used to be. I have an unrestored 1972 that also has the base motor, and I can tell you that my mildly modified 71 will beat it any day.

The only thing I'd consider doing differently would be using the camshaft Joe mentions. It's not cheap, though.

Patrick

[Joe L.]

Re: C/3 engine upgrade

Patrick-----

The camshaft, itself, is not too bad in price-----about twice what flat tappet cams cost. The problem is that you usually need lifters with a retrofit hydraulic roller camshaft. The lifters are the problem. They ARE expensive! But, they're worth it, too.

[Patrick H.]

Re: C/3 engine upgrade

Joe,

Yes, I was referring to them as the Kit that Crane sells. The cam plus lifters is about 4x the price of a standard hydraulic cam kit. Ouch.

Patrick

[Clem Z.]

speed cost money how fast do you want to go??? *NM*

[Ed P.]

Re: C/3 engine upgrade

I should have given more info. The car is an automatic and I am looking for more low end torque and power,I am not concerened about top end high rpm.
zero to eighty Thanks Ed

[Patrick H.]

Re: C/3 engine upgrade

Swap your rear end gears from a 3.08 to a 3.70 or 4.11

It's the fastest way to get what you're after. Of course, you won't be able to go faster than 65, but...

Or, set your original engine aside, and find a drop-in 383 stroker motor.

On my motor, carb tuning and distributor work did as much for low end grunt as anything. The package as a whole, though, works quite well and has much more SOTP feel than stock.

Patrick

[Bill E.]

Re: C/3 engine upgrade

Ed:

I have a 1974 automatic with mild engine and exhaust upgrades and a shift kit. The shift kit really changes the driving experience from stock 74's, especially coming off the line. A medium heavy foot will chirp the tires from 1st to 2nd if that sort of thing turns your crank. A heavy foot will make you popular at the tire store.

Bill

[Mike Cobine]

Re: C/3 engine upgrade

While you are looking for more low end torque, don't use that as your basis in buying a cam. This is because most who will give you advice will give you good advice for the wrong car.

Typically, people advise cams for low end torque that end up with an operating range of 1000 rpm to 3500 rpm. (good RV cam - lots of torque) This sounds great, the power is in a nice low range. HOWEVER, your automatic in forced shifting (passing gear) won't shift until around 4000 or 4500 rpm or more.

So you get an engine that runs out of steam at 3500 and you still have 500 or 1000 rpm to climb before the transmission will upshift while your foot is in it. So you are stuck in second, and can't get any faster until it shifts which it won't, and it won't shift until you take your foot out of it, which now means you slow down. (Ever try letting off the gas when passing and a car is coming?)

This is most noticable in any high load situation - towing a trailer, running uphill, passing, etc.

In most driving, you may never notice it, but if you are passing uphill sometime, you may just find yourself hanging out in the wrong lane with not enough to get around.

Remember that the torque convertor negates almost anything under 1500 and often under 2000 RPM so have your cam operating range start in between there for best results. A good range for a cam is 2000 - 4500 RPM for an automatic.

I think you'd like the 350/350 or L82 cam quite well. I liked it a lot in my Suburban.

If you had a stick, it would be all different.

[Duke W.]

Re: C/3 engine upgrade

If you're looking for more low end torque you DO NOT want to install a SHP type cam. These cams will shift the torque curve up the rev scale. Stick with the stock cam.

On good way to improve the bottom end it to quicken the centrifugal advance curve. Get it in as quicky as possible without detonation. Production curves are typically conservative and your engine is also mapped for emission control, which further compromises performance.

You want the total of initial plus full centrifugal to be in the range of 36-38 degrees. A vacuum can with 16 degrees at 12-16" should also be installed and run from full manifold vacuum, so there is full vacuum advance at idle, and the total idle timing - the sum of initial plus full vacuum advance should be in the range of 20-25 degrees.

Don't have the specs for you engine, but they are in your service manual and are probably quite different from what I recommend. As a rule, the spark advance map can be improved by backdating it to an antecedent engine from the pre-emission era, which is your case would be the 327/300.

Duke

[Patrick H.]

Re: C/3 engine upgrade

Duke,

As you know, I actually had another distributor made for my 71 car using the 65 SHP curve. My CEC items are disconnected. I'd have to agree with you that it made a big difference.

For my untouched 72, I actually have two sets of advance springs. One exactly mirrors the original setup, and one provides for more advance as with the factory TCS setup there is no vacuum to the distributor in gears 1 through 3. You CAN tell the difference between the sets of springs!

I don't think he'd like an SHP or the 351 cam with an automatic. With a 4 speed it would be a whole different story.

Patrick