Cam shaft Opinion Please

[Ed R.]

I am having my 66 327/300 rebuilt and the builder recommended a Comp Cam EX262H cam. The specs are as follows:

Camshaft Specification Table

Part Number 12-238-2
Engine 1955-1998 Chevrolet
262ci-400ci
8cyl.
Grind Number CS XE262H-10

Description

Intake Exhaust
Valve Adjustment 0 0
Gross Valve Lift 0.462 0.469
Duration At 0.006 Tappet Lift 262 270

Valve Timing At 0.006
Open Close
Intake 25 57
Exhaust 69 21

These Specs Are For The Cam Installed At 106 Intake CL

Intake Exhaust
Duration At 0.05 218 224
Lobe Lift 0.308 0.313
Lobe Separation 110

Recommended Valve Springs 981-16

I am looking for a little performance enhancement and still run on pump gas. Does this cam seem like a good fit?

[Pete Whelan]

Re: Cam shaft Opinion Please

Ed,
You should see around 12-15 lb-ft additional torque and about 10 more peak HP with this camshaft and the factory intake and exhaust, based on simulation results. I can't vouch for the idle quality but it should be relatively smooth. You shouldn't have any problems running on pump gas provided that your actual static compression ratio is 9.5:1 or less. Use their recommended valve springs. This camshaft looks like a good fit to me.

Good luck.

Pete

[Duke W.]

Re: Cam shaft Opinion Please

Idle quality and low end torque will be considerably poorer because of the much higher overlap. A better improvement in power can be had by working the heads without degradation of idle quality and low end torque.

Most aftermarket cams have too much overlap. High overlap and the OE exhaust manifolds/system do not get along. Even some of the OE SHP cams have too much overlap, but they have less than aftermarket cams with similar duration.

Overlap can be effective at improving torque/power in the upper half of the rev range, but headers and open exhaust are needed to fully exploit high overlap. If you have the OE manifolds and mufflers, excess overlap can reduce output across the entire rev range.

Duke

[Byron Martin]

Re: Cam shaft Opinion Please

I have your exact setup. '65 327/300 all stock except the Comp-cams XE262H. The 262 has a very smooth idle and will idle smooth at 600 rpms with the A/C on. Vaccum is 16.5 inches at idle. I bought the "K-kit" which comes with the recommended springs, retainers, lifters and timing gear set. I'm pretty happy with it. But if I was to do it again, I would have gone with the XE268H as the 262 is pretty mild. Good luck, Byron

[Ed R.]

Re: Cam shaft Opinion Please

Byron, thanks for the feed back. Do you, as Duke states, notice a loss of low-end performance. I don't intent to drive this car hard but, occasionally put my foot in it and go through the gears. I'm beginning to agree with Duke and just do some head work and stick with the OE cam. I am running 3.36 rear end, AC, 4-speed, stock intake, and stock exhaust so I don't want to sacrifice any low-end performance.

Is there any other combination out there?

[Ed R.]

Re: Cam shaft Opinion Please

Thanks again Duke. You're beginning to convince me to stay with the OE cam. As for head work, I'm assuming a 3-angle valve job, pocket porting is what you are talking about.

[Duke W.]

Re: Cam shaft Opinion Please

Yes, matching the head and manifold ports is also worthwhile as is relieving the combustion chamber overhang, especially on the exhaust sied. You could consider doing the basic pocket porting/port matching/relieving yourself if you are patient and study available information like David Vizard's books on SB heads, but leave the three angle valve job to a good pro. Use (minimum) seat widths of .040" on the inlet side and .060" on the exhaust.

The above rework will improve the top end power by about 7-8 percent, and it should pull strong all the way to 5500, while maintaining the docile idle and stump pulling low end torque characteristics of the 300 HP engine.

The OE deck height in conjunction with OE replacement pistons and a composition head gasket should yield a true CR of about 9.5:1, which is okay for premium unleaded fuel.

As with any engine restoration, you should measure the piston to deck clearance for each cylinder BEFORE the pistons/rods are removed. This will tell you if the decks are parallel to the crankshaft and give you the information you need to calculate the compression ratio with the selected pistons and head gasket.

Duke

[Pete Whelan]

Re: Cam shaft Opinion Please

Not in this particular instance. I've modeled this cam versus the OEM cam and it improves torque through 5000 RPM. While many aftermarket camshafts have significanly more overlap than the OEM, the XE262H does not. It has approximately 3 degrees LESS overlap than the OEM cam. The XE262H cam lobes provide higher acceleration, which opens the valves more quickly than the OEM's. These factors are contributors to the torque improvement across the entire operating range. Peak torque occurs in the vicinity of 3000 rpm and peak HP occurs near 5000 rpm.

In this case, the XE262H is an improvement over the OEM cam.

I am running a similar camshaft from Crane (HMV260-2) in my '66 327/300 and can vouch for the improvement in torque from off idle through 5000 rpm.

Pete

[Pete Whelan]

Re: Cam shaft Opinion Please

Ed,
As I mentioned in one of my earlier posts, I am running a Crane HMV260-2 in a '66 327/300 with the original intake and exhaust. I have also pocket ported my cylinder heads. This engine pulls 20 inches of vacuum at idle and is very smooth. My car has a wide ratio Muncie and a 3.08:1 axle ratio. I know of another individual with '67 327/300 running the same combination and we both love it. You won't be sacrificing any low end torque with the Comp Cams XE262H or the Crane HMV260-2 camshaft.

Pete

[Byron Martin]

Re: Cam shaft Opinion Please

Ed, My engine is bone stock except for the XE262H camshaft, original intake, carb, exhaust manifolds, untouched heads, 4-speed w/ 3.36 gears. I am running stock style under-car exhaust. The low-end power is fine and it pulls strong till about 5500.
Byron

[Ed R.]

Re: Cam shaft Opinion Please

Byron, this is exactly what I plan to run. With this cam are there different specs for timing, dwell, or distributor mods required? Are you using the same vacuum can?

[Ed R.]

Re: Cam shaft Opinion Please

Thanks to everyone that helped me with this. Ya gotta love this place.

[Duke W.]

Re: Cam shaft Opinion Please

According to the Comp Cams catalog the EX262H has a "noticeable idle". It looks a lot closer to a L-79 cam than a 300 HP cam, but has nearly double the effective overlap of the L-79 cam.

I ran the numbers through Engine Analyser on a 40 over SHP 327 with 10.5:1 CR and nicely reworked 461s. This engine model was developed for a SHP 327 with LT-1 cam, and in SAE gross trim correlates well to actual SAE gross dyno test data. For this exercise I simulated SAE net, which includes a clutch fan, exhaust system, and SAE correction conditions, which is what count's when it's installed in the chassis.

Cam specs, 050 duration, centerlines, LCA, lobe lifts as follows. I've listed the 300 HP cam specs to illustrate the comparison of the the basic specs for each.

XE 262H 218/224, 106/114, 110, .308/.313
L-79.... 221/221, 110/118, 114, .298/.298
300HP....195/202, 108/116, 112, .260/..273

EA computes 6.2 sq-in-deg of overlap for the EX262H versus 3.8 for the L-79 - almost twice as much.

The predicted torque and power curves with the XE262 are below the L-79 across the entire rev range from about two to five percent. The biggest difference is at the top end with the L-79 cam peaking at 6000. The EX 262H peaks at 5500.

With this much overlap - considerably more than any OE SHP cam including even the 30-30 I don't see how this cam could pull 16-20" of manifold vacuum at 600 RPM, which is why I wonder if apples and oranges are being compared here.

Duke

[Byron Martin]

A pictures worth 1,000 words

Duke and Ed,
First, let me say that I read all the corvette forums frequently and I value Duke's opinion. Duke knows his stuff.
However, I can assure you that my engine is completely stock, with the exception of the camshaft. It has been in my family for 35 years and I know its history well. It will idle at 6-700 rpms and maintain 16 inches of vacuum. It idles nearly as smooth as the original cam and has plenty of power down low.
I took this picture just for Duke.