Help with cam ID on my 70 LS-5

[Donald A.]

Hello all;

Finally got some paperwork from the lady I bought my car from a year ago.

In the stack of stuff was a rebuild sheet from S&K Engine Specialists of Topeka KS (anyone heard of these people?)

It shows that in 1989 my Original LS-5 was rebuilt by a Don Crockett and that he used the following cam. 30005.

http://schneidercams.com/LSP5Hbbchydraulic.aspx

Can anyone comment regarding how this cam differs from the OEM ???

Particular interested if this can does not make a good idle because my engine idles rough and I've not been able to fix this.

Thanks

[Don H.]

Re: Help with cam ID on my 70 LS-5

Don
I don't know anything about that cam, that build, or that company. But I am impressed that you have a paper trail on the rebuild. That is great info to have and I am envious. Good luck
dh

[Joe L.]

Re: Help with cam ID on my 70 LS-5

Hello all;

Finally got some paperwork from the lady I bought my car from a year ago.

In the stack of stuff was a rebuild sheet from S&K Engine Specialists of Topeka KS (anyone heard of these people?)

It shows that in 1989 my Original LS-5 was rebuilt by a Don Crockett and that he used the following cam. 30005.

http://schneidercams.com/LSP5Hbbchydraulic.aspx

Can anyone comment regarding how this cam differs from the OEM ???

Particular interested if this can does not make a good idle because my engine idles rough and I've not been able to fix this.

Thanks

Don-------


This is really not all that wild of a cam. I would think the idle would have some "lope", but I don't think it should be a rough idle.

This is not a cam that, personally, I would use. But, I think it should be OK for you.

[Donald A.]

Re: Help with cam ID on my 70 LS-5

Joe

thanks for the reply.

A lot to ask but would you mind expounding on the differences in this cam and the OEM cam. I've no experience with another LS-5 with correct cam but wonder about the characteristics of what I have now and what you think the difference would be.

Thanks for for sharing your knowledge and helping me learn more about the car/cam I have

regards

don

[Gene M.]

Re: Help with cam ID on my 70 LS-5

Don
LS5 is #3883986 268/274 duration hydraulic
214/218 @ .050 .461/.480 115 LS

[Duke W.]

Re: Help with cam ID on my 70 LS-5

As you can see from comparing specs, the aftermarket cam has the same inlet duration, 6 degrees more exhaust duration, but a narrower LSA. This means it has about twice the effective overlap as the OE cam, which will reduce low end torque and result in a rougher idle while not having much effect either way on top end power. Also, the greater lift on similar duration means it probably requires stiffer than OE valve springs, which increses valve train loading and may reduce durability.

The OE cam is very good, and I recommend it for all hydraulic lifter big block rebuilds. It's a little milder than the L-79 cam, but hotter than the base small block cam. The OE cam idles fairly smooth at 600 in neutral at about 15" manifold vacuum.

My guess is that the aftermarket cam would need to be set in the range 750-850 to get acceptable idle quality and manifold vacuum would be about 12".

The nice thing about the OE cam is the stump pulling torque that allows a tall gear while easily spinning the tires in first gear, and massaging the heads gets you SHP type top end power without loss of the massive low end torque.

It's unfortunate that many owners get talked into a "cam upgrade" by engine shops, but what they end up with is downgraded performance in the lower end of the rev range where you spend 99.99 percent of your driving time and often reduced durability.

Duke

[Donald A.]

Re: Help with cam ID on my 70 LS-5

Thanks Duke for that information.

If I was to entertain a cam swap back to OE what would that entail and I would not want to pull the engine.

[Duke W.]

Re: Help with cam ID on my 70 LS-5

The camshaft/lifter are Sealed Power (Federal Mogul manufactured) CS1093M/HT817.

To change the cam without removing the engine the radiator will have to come out, the inlet manifold, distributor, and valve covers removed along with the water pump, torsion damper, and timing cover.

There should be more information in the CSM.

If the timing chain set needs to be replaced, use the Sealed Power truck roller chain set.

Duke

[Donald A.]

Re: Help with cam ID on my 70 LS-5

Thanks Duke!!

For entertainment sake here is the original build sheet from 1989. I think prices have gone up and you will also note the "9.5 to 1" note at the top.

Any thoughts on this overall?

regards

Don

[Duke W.]

Re: Help with cam ID on my 70 LS-5

It's good that you still have that work order. Usually such documentation never makes it to subsequent owners. The rebuild was typical for the era, and unfortunately often, today - a high overlap cam with "lowered" compression and machining operations that were likely not required. My basic philosophy is do not remove metal unless absolutely necessary and the need is easily determined with simple measurements that don't take much time. High valve overlap and low compression is the absolute worst combination for a road engine where you want good low end torque and decent fuel economy, and nothing is gained at the top end. In fact, often top end power is lost.

Grinding the crank and align boring the mains was likely unnecessary, but most shops just do it rather than taking the simple measurements to see if those operations are necessary.

The same applies to resizing rods, and if they are resized you increase deck clearance a few thou, which reduces CR a tenth or so. Way back when I recommended Magafluxing rods, which requires the bolts to be removed, so resizing is required. And I usually recommended higher stremgth bolts. Nowadays these operations cost about the same a a new set of Eagle SIR rods, so one is better off just buying and installling the new rods and using the old ones as paperweights.

I can't ID the pistons, but they are probably "speced" at 9.5:1, but when combined with a thick head gasket and the increased deck clearance, I bet if we took the engine apart and made all the measurement to compute CR it would be closer to 9 than 9.5. You can measure head gasket thickness with feeler gages at the corners of the head-block interface. The OE gasket was a .028" thick steel shim type.

It also looks like the block was decked, which is rarely necessary and wipes out the engine ID and VIN derivative data.

The lifters are the Sealed Power parts I mentioned, and it looks like the timing set is the "truck set" (roller chain) I recommend.

There is no indication that anything was done to the heads. Could that work be a different shop of different work order?

Though the rods were not Magaflux inspected, one used rod was was used in the rebuild. It could be that one was damaged and could not be repaired via resizing or other means.

So I see about $230 in likely unnecessary machining operations that would have been much better spend massaging the heads, which back then would have probably cost and additional $300 over and above a standard valve job.

Hopefully some guys can learn from this.

Duke

[Donald A.]

Re: Help with cam ID on my 70 LS-5

Thanks for that analysis Duke!

Regarding the decking I got very lucky in two ways. 1. The decking did not totally erase the engine build date and type. 2. Since this car was built on the first day of production (Jan 5th) the VIN was on the alt location with is down by the oil filter on the block! So I can still verify that this was the born with engine.

On the CR, I guess I won't worry about running anything higher that 91 octane.

Based on how this was done I think I will just drive the wheels off and enjoy it. maybe someday I would pull it and got back 100% stock. maybe when I decide to do a frame off soup to nuts on the entire car.

Regards

[Duke W.]

Re: Help with cam ID on my 70 LS-5

Your OE centrifugal curve is short (start @ 1085, 22 deg. @ 3200), so you should run initial timing at about 16-18. Also if you have not converted the ported vacuum advance to full time, do so, and you will probably need the 8" B28 VAC to meet the Two-Inch Rule.

The engine will probably tolerate lighter springs to get full advance in earler, and the idle will be a little smoother with the approx. 32 degrees total idle advance.

The result should be better low end torque, better fuel economy, and more top end power if you are currently running no more than 12 initial.

Ideally, I'd grind out the advance slot to achieve 24-28 total centrifugal, in as soon as possible, with initial timing set to achieve 38-40 deg. total WOT advance.

Duke

[Joe L.]

Re: Help with cam ID on my 70 LS-5

As you can see from comparing specs, the aftermarket cam has the same inlet duration, 6 degrees more exhaust duration, but a narrower LSA. This means it has about twice the effective overlap as the OE cam, which will reduce low end torque and result in a rougher idle while not having much effect either way on top end power. Also, the greater lift on similar duration means it probably requires stiffer than OE valve springs, which increses valve train loading and may reduce durability.

The OE cam is very good, and I recommend it for all hydraulic lifter big block rebuilds. It's a little milder than the L-79 cam, but hotter than the base small block cam. The OE cam idles fairly smooth at 600 in neutral at about 15" manifold vacuum.

My guess is that the aftermarket cam would need to be set in the range 750-850 to get acceptable idle quality and manifold vacuum would be about 12".

The nice thing about the OE cam is the stump pulling torque that allows a tall gear while easily spinning the tires in first gear, and massaging the heads gets you SHP type top end power without loss of the massive low end torque.

It's unfortunate that many owners get talked into a "cam upgrade" by engine shops, but what they end up with is downgraded performance in the lower end of the rev range where you spend 99.99 percent of your driving time and often reduced durability.

Duke

Duke------


I generally agree. However, I really don't think this cam should cause a rough idle. Of course, "rough idle" is all in the "eyes of the beholder". As I mentioned, I would expect this cam to cause the engine to have a moderate lope. But, I would not expect a rough (by my standards) idle with a "rumpety-rump" sound and high idle speed requirement. I would expect the 750-850 RPM you mention which is not all that much greater than the stock cam.

I also agree that the stock LS-5 cam is a great street cam, probably the best that GM ever came up with for a street big block of the 60's and 70's. However, as I've mentioned many times before, I've been a "hydraulic roller cam guy" now for a long time. I think that flat tappet hydraulics are obsolete and passe and one can do a lot better with a modern hydraulic roller cam.

[Mark E.]

Re: Help with cam ID on my 70 LS-5

Another data point: My 1970 LS5 was rebuilt (really just overhauled- same pistons, rods, crank, valves) years ago by the PO, and although I wasn't given any documentation, I was told a Crane cam with specs virtually identical to the OE high-lift hydraulic cam was installed. It idles smoothly with 16-17" hg vacuum at 750 RPM.

I'm not a cam expert, but as Joe suggests, if I did replace it I would research a modern hydraulic roller. I've read that a roller provides significantly more HP, torque, efficiency and reliability, with no downside other than maybe cost. It's perhaps one of the few mods that really works and is invisible during judging.

Does anyone have experience with a roller cam upgrade they can share? Does this require any special machining on the block?

[Duke W.]

Re: Help with cam ID on my 70 LS-5

Another data point: My 1970 LS5 was rebuilt (really just overhauled- same pistons, rods, crank, valves) years ago by the PO, and although I wasn't given any documentation, I was told a Crane cam with specs virtually identical to the OE high-lift hydraulic cam was installed. It idles smoothly with 16-17" hg vacuum at 750 RPM.

I've read that a roller provides significantly more HP, torque, efficiency and reliability, with no downside other than maybe cost. It's perhaps one of the few mods that really works and is invisible during judging.

Power is ultimately limited by the heads, not the cam. Converting to a roller can cost several hundred dollars over and above the cost of using a flat tappet cam.

My advise is to use an OE cam and put the "roller money" into head massaging. Head massaging will not effect idle behavior or low end torque with the OE cam, but increases top end power by 10-15 percent, adds 500-1000 revs to the top of the useable power bandwidth, and is truely invisible.

Rollers might make more peak power, but their rev range is often limited due to the heavy valve lifters and aggressive dynamics. What makes for good WOT maximum acceleration is high average power delivered over the top 30 percent of the rev range, not peak power.

Also, most aftermarket rollers have more than OE valve overlap, which will cause different idle behavior and hurt low end torque. I don't know what you mean by "efficiency", but better fuel economy is unlikely, especially if the roller has more effective overlap than the OE cam

IMO any roller cam installation is a R & D project, but most guys don't realize that. There are lots of horror stories about roller installations that were improperly done by engine shops leading to rapid failure, so I would certainly not say they are more reliable. OE cams and valvetrain components are proven in hundreds of billions of miles over the decades. As long as you use OE equivalent components (with the exception of known weak parts like small bearing SB connecting rods and first design big block valve springs) from high quality manufacturers and the engine is assembled properly, reliability of vintage Corvette engines will be equal or better than their first life.


Duke