Help me pick a cam

[K30Blazer]

Looking to get a new cam. Little background on my truck. Used to be a daily driver, but now is just a fun vehicle that I drive on weekends etc. I am looking to get a new cam to replace my factory one, but don't want to sacrifice tons of fuel efficiency.

I am not sure what the stock duration on the cam is, but I think it is around a 256. I am looking at going to a 266 or 268. I know this will bring me more torque and low end power, which is what I am looking for, but how will this affect my driveability. The Crane website reccomends this cam for all around. Is this accurate?

What about gear drive? I know my timing chain is worn (160k miles on it) and will be replacing it when I do the cam, but I am considering doing a gear drive as they seem a much better solution to the chain drive. Any cons?

Thanks

 

[tavis]

Moving from 256 to 268 adv dur is actually going to in most cases decrease your low rpm torque. It may make more torque ... but it will be at a higher rpm. i.e. It will move your power band up in RPM. I would personally look at a comp XTREME 4X4 cam kit either the X4254H (254/262 adv and 212/218 @.05) or the X4262H (262/270 adv and 218/[email protected]) for a mild upgrade in a carburated K5 with a 350. I would need some info on intended usage before i could make a more exact recommendation. Also you didn't tell us what year/type of engine, carberated/fuel injected, tranny and rear gear ratio is in question. The newer 350s are a roller from the factory ... as opposed to the older 305s and 350s which are standard hyd flat tappet.

Hope this helps.

T.

 

[K30Blazer]

sorry,

350 with TBI. 3.42 in the rear. Running 25's. Gears maybe getting changed.

TH350 Transmission. I believe. Not sure on that though, could be the 700 R4. I do have overdrive if that makes a difference.

I am looking for a cam that gives me more mid range power (2000-4000 RPM) and the truck will be used for street, moderate mud and trails.

 

[tavis]

I would suggest Comp cams X4258HR part# 08-409-8
Cam Style: Hydraulic roller tappet
Basic Operating RPM Range: 1,000-5,000 RPM
Intake Duration 050 inch Lift: 206
Exhaust Duration 050 inch Lift: 210
Duration at 050 inch Lift: 206 int./210 exh.
Advertised Intake Duration: 258
Advertised Exhaust Duration: 262
Advertised Duration: 258 int./262 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.458
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.458
Valve Lift with Factory Rocker Arm Ratio: 0.458 int./0.458 exh. lift
Lobe Separation (degrees): 111

The largest i would go is Comp cams X4260HR part# 08-409-8
Cam Style: Hydraulic roller tappet
Basic Operating RPM Range: 1,200-5,200 RPM
Intake Duration 050 inch Lift: 210
Exhaust Duration 050 inch Lift: 214
Duration at 050 inch Lift: 210 int./214 exh.
Advertised Intake Duration: 260
Advertised Exhaust Duration: 264
Advertised Duration: 260 int./264 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.474
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.474
Valve Lift with Factory Rocker Arm Ratio: 0.474 int./0.474 exh. lift
Lobe Separation (degrees): 111

Anything much larger than this on a stock motor will get you into trouble. You have to start upgrading your converter, valve train, gears, performace chip and induction etc......

I assume you meant 35s

If you have overdrive it will be a 700R4.

Hope this helps. If you don't like compcams i can make you a recommendation from a different cam line.

T.

 

[K30Blazer]

Really appreciate your help. This board is a breath of fresh air. Everyone is totally helpful and willing to work through my newbie questions.

In regards to the cam. The one my mechanic had recommended was the Crane 266/266. It is described as smooth idle, daily usage, fuel economy, 2200 - 2700 cruise RPM.

I am doing new heavy duty heads on my 350 as the current heads are shot. They are GM heavy duty truck heads?

What else should I be concerned about with the cam stressing?

Any suggestions on the gear drive. Good idea, bad idea?

 

[beater_k20]

with 3.42s and 35s, before i even thought about pulling a valvecover, i'd swap those gears out. you'll see WAY more results than the cam change you're talking about, because your specs really arent changing that much. your truck will be much happier with 4.10s or 4.56s

 

[SUBFAN]

I agree on the gears....

It would be unwise to assume your block will automatically accept a roller cam. Some of the blocks need machined for this upgrade. Some of them need the spider set up.

I don't think I would drop a roller cam in without at least changing valve springs too....

 

[K30Blazer]

what is the gear change going to do for my freeway RPM? Right now I run about 1900 at 70 which is really great for the mileage. By going to a 4.10 or 4.56 I would jack that up a lot right?

I am getting new heads, will the valve springs be up to the task with the new head?

 

[beater_k20]

what is the gear change going to do for my freeway RPM? Right now I run about 1900 at 70 which is really great for the mileage. By going to a 4.10 or 4.56 I would jack that up a lot right?

I am getting new heads, will the valve springs be up to the task with the new head?

sure, its great for milage, but its hell on your trans. what is "really great" milage? 12? 13? swapping to 4.10s you'd be somewhere in the neighborhood of 2000-2100 rpms in OD with the TCC locked. your engine and trans will apprectiate this SO much more. the engine will be more into its powerband, and the trans will be doing a lot less work to turn those 35s, so you'll actually have more power available to put to the ground, rather than using it just to get the tires rolling. i would guess you may actually see a milage increase.

 

[tavis]

Really appreciate your help. This board is a breath of fresh air. Everyone is totally helpful and willing to work through my newbie questions.

In regards to the cam. The one my mechanic had recommended was the Crane 266/266. It is described as smooth idle, daily usage, fuel economy, 2200 - 2700 cruise RPM.

I am doing new heavy duty heads on my 350 as the current heads are shot. They are GM heavy duty truck heads?

What else should I be concerned about with the cam stressing?

Any suggestions on the gear drive. Good idea, bad idea?

I agree with the others on the gear change. Unless you drive VERY fast overdrive is probobly useless for you currently with the 3.42s. I did a quick calc. With your current gear ratio you are doing 1600rpm at 70mph. A switch to 4.10s will net you 1900rpm at 70mph. A switch to 4.56 will net you 2100rpm at 70mph. As mentioned before ... your engine will like that rpm much better as it will be into its powerband. Moving 5000-6000lbs down the highway is alot of work for a small block so running the engine in its torque powerband will probobly net you a few MPG. It will also be much more enjoyable to drive.

I would be careful on the crane cam recommendation. That cam is for a regular old style small block(2pc rear main seal). You have a late-model 1pc rear main engine with fuel injection that comes with a factory roller camshaft . The crane 266 will not fit your engine.

Also although the X4260HR cam i recommended have less advertised duration the .05 numbers are equal on the intake side and longer on the exhaust. This is to help with the less than optimal exhaust flow on a stock engine. Also both cams i recommended have more lift ... this will give you more flow at the same duration. I strongly recommend a dual pattern camshaft for your configuration. The crane 266 is a single pattern cam.

If you are looking at rebuilding/replacing your heads i would highly recommend taking a look at swapping to a set of vortec heads(heads off of a 96 or newer truck). You can also purchase them from summit/jegs or your local GM dealership. You will also require a GMPP TBI intake manifold (PN 12496821) and provistions for moving the EGR. GM recommends using the '96 exhaust manifold (PN 12557828), EGR pipe (PN 10220275), and EGR valve (PN 17052693). You could grab some/all of these pieces at your local bone yard as well.

I think for the most part gear drives are a waste of money. If you want the gear whine of a supercharger .... buy a supercharger I would just install a quality double roller like a comp or a crower.

Hope this helps.

T.

 

[tavis]

I agree on the gears....

It would be unwise to assume your block will automatically accept a roller cam. Some of the blocks need machined for this upgrade. Some of them need the spider set up.

I don't think I would drop a roller cam in without at least changing valve springs too....

The engine in question is a late-model 1pc rear main block. These engines come with a roller camshaft from the factory.... in fact you have to "retrofit" a standard hyd lifter in these engines.

T.

 

[HarryH3]

The engine in question is a late-model 1pc rear main block. These engines come with a roller camshaft from the factory.... in fact you have to "retrofit" a standard hyd lifter in these engines.

T.

Not until the '96 Vortec V8's... Truck V8's didn't get the roller cam before then, even though the block is made for it. Meanwhile, my '90 4.3 V6 came with a roller cam from the factory. What was GM thinking???

 

[beater_k20]

while some 87-95 truck blocks were roller ready, not all were. as for "retrofitting" them with flat tappet cams, that information is incorrect. a standard flat tappet cam will drop right in. the lifter bores are a little taller on the roller cam engines, but the oil holes line up perfectly with a flat tappet. i compared a '79 350 to a '96 Vortec 350.

 

[SUBFAN]

Gear drive = bad idea....The knock sensor will not appreciate all that racket in there and screw with your timing all the time....