roller camshaft opinions please.

[Terry F.]

Re: The whole point of a roller cam

Thanks for telling me that. I didn't realize that head flow was so much a part of the equation. Thanks, Terry

[Clem Z.]

so they can use syn oil for a factory fill

and get better mileage on the CAFE test

[Duke W.]

Re: more grunt, no loss in HP @ high RPM

The trouble with that 660HP is that it's SAE gross achieved on a lab dyno with open exhaust. Put that engine in a car with an exhaust system and it's a whole different story.

I took my EA model of LS7, which is right on the money, and added overlap with long tube race headers. Predicted SAE net power with the vehicle exhaust system increased only marginally with a BIG drop in low end torque. With open exhaust, top end power jumped a good 15 percent, but there was still a loss of low end torque.

The OE gearing yields 1500-1800 revs at typical freeway cruise speed, but the loss of torque in this rev range is so great that sixth may not be a useable gear, and the combination of higher cruise revs and overlap is going to turn what is a fairly economical car into a gas hog, not to mention the fact that idle quality and emission performance goes to hell.

There was a lot of hype about long tube headers and big cams on the Corvette Forum, but it was usually accompanied by "tuning". And, of course, they stated the dyno pulls at 2500-3000, so you couldn't see the loss of low end torque in the sixth gear highway cruise rev range.

Then Jim Hall looked at the spark and fuel tables and found that they were very conservative, so a few otherwise OE engines were "tuned" with more aggressive spark tables and leaner WOT A/F ratio, and they made about the same power increase as the header and big cam engines. And you can bet they didn't loose any low end torque in the process. If anything the changes fattened up the torque bandwidth.

Duke

[Duke W.]

Re: so they can use syn oil for a factory fill

The move to "roller everthing" in the engine is probably also motivated by the desire to remove ZDDP from the oil to support longer emission warranties.

Duke

[Clem Z.]

Re: more grunt, no loss in HP @ high RPM

the people that spend $8000 for the upgrade are not looking for MPG. they also change the cats,reprogram the computer with a chassis dyno and change the exhaust system. i will let you know what the rear wheel HP is after jan. when we take one up to have it done.

[Terry F.]

Re: The whole point of a roller cam

I am going to guess about why the switch to roller cams....Here goes. I think it is multi-factorial. 1) Something to brag about having. 2) Engines designed to run higher RPM's. 3) Higher valve spring pressure to tackle the lift velocity at the higher RPM's. 4) Lobe design that partially needed the mechanical advantages of a roller design for longevity.

That is the best I can doooooo.

I really appreciate all the responces. My goal on rebuilding my engine is to make it run very well and be very well balanced. I think I will take the time to measure the deck clearances and adjust head gaskets as needed to get the compression ratio where Duke recommended and also match each side of the engine. I will probably use TRW pistons, chrome rings, factory grind cam, roller rockers, nice valve job, roller timing chain, new connecting rod bolts, check the rods, balance the flywheel, check the harmonic balance or have it rebuilt.

Any other suggestions would be great. Who's bearings should I use these days? Thanks for all the information, Terry

[Terry F.]

Re: so they can use syn oil for a factory fill

I bet you are right. Emissions and and removal of ZDDP. Terry

[Michael H.]

Re: The whole point of a roller cam

As you know, if there was actually enough friction at the lifter/lobe to cause any substantial drag, the lobe and lifter would quickly grind itself away, so we know that this isn't the case. A constant high volume flow of oil prevents damage and wear.

Here's the story. One of the reasons why mfg's have switched to rollers is because they require a LOT less lubrication. What's that got to do with it? Well, more lubrication means that the oil pump has to work a lot harder and this is consuming energy. (HP and fuel) Believe it or not, most of this is a result of the EPA regs on fuel mileage. This is one of the reasons why newer cars have/require less oil pressure.

If we reduce the oil pressure/volume, the amount of energy lost in driving the oil pump is less, but we eventually get to a point where the reduced amount of oil isn't enough to properly lubricate the lifter. Rollers cure this problem.

There's an incredible amount of energy lost in any engine that produces 60-70 lbs of oil pressure at 2500+ RPM. That's why engineering wanted to reduce this pressure and volume requirement. Lifters and rocker arm oiling was consuming a large part of the volume so efforts were made to reduce this requirement.

In racing engines, some builders are actually switching to roller cam bearings for this same reason. There's no HP gain from reduced friction but there is gain in not having to pump as much oil to these bearings.

Internal engine oil requirements and leaks are responsible for a lot of energy loss. Another example would be the oil that leaks by the distributor lower housing. Some new distributors for comp now have "O" ring grooves to seal the housing to the block to prevent these leaks.

If folks don't thinkk the oil pump consumes a lot of energy, think again. In a drag race motor, the distributor drive gear can be completely worn out in 50 passes. (thus, the invention of the bronze driven gear) I've never known the actual numbers on this but I'm sure it would be interesting to learn just how much HP is required to drive an oil pump at 7000 engine RPM with 40W or 50W racing oil.

[Duke W.]

Re: The whole point of a roller cam

Forget the roller rocker arms - waste of money and they reduce valvetrain limiting speed because they are heavier than OE rockers. If your existing valvetrain parts show no signs of excess wear they can be reused, but buy new OE equivalent valvesprings, cam, and lifters. Get a copy of "How to Hot Rod Your Big Block Chevy" and the Chevrolet Power Manual and learn about head modifications. If you can't do the work yourself, find a pro who understands this (might not be easy).

Have the crankshaft and connecting rods Magnaflux inspected. If the rods pass, install higher quality bolts/nuts, have them resized, and reuse them. (Shotpeening is a good idea, too.) Have the entire crankstrain balanced, and pay careful attention to achieving a reasonable target compression ratio range. Start by taking all the required measurements and getting the specs you need to compute the CR of the engine as it is now. Did it detonate? If not you can assemble it with the same CR. If it does detonate, adjust the CR down a quarter to half point with suitable piston and head gasket selection.

There's nothing wrong with an OE replacement silent chain set. Buy name brand parts like Sealed Power (Federal Mogul) or other brand names from F-M and Dana.

The completed engine will have the same idle characteristics, fuel economy, and low end torque, but about 10 percent more top end power with less rolloff beyond the peak and 500 more useable revs, which will extend the useable rev range to the valvetrain limiting speed - somewhere around 6000 revs.

Don't use chrome rings. They haven't been used since the sixties. Use an OE replacement moly faced ring set.

Duke

[Michael H.]

Re: so they can use syn oil for a factory fill

Yup, thanks Clem. I forgot about the 5Wsomething synthetic oil. That too was part of the reduced energy loss and mileage increase.

[Clem Z.]

duke you assume that everyone drives like you

using top gear to keep the engine at the lowest possible revs and never wanting to down shift. i take this from the fact i belive you have a 3.08 or some tall rear gear in your 63 SWC when all the rest of us ordered ours with 4.11 or 4.56. the tall factory gears in these newer corvettes are to get by the gas guzzler tax and emissions that i belive are checked in parts per mile.. the owners who change cams,headers etc change the stock 3.42 rear gears to 3.90 or even 4.11. with the double overdrive in these 6 speeds it does not hurt the MPG that much. the new ZO-6 will pull 26 MPG average but of it drops to 20 or 22 MPG and you have a 100 more HP it sound like a good trade off to me. a lot of corvette owners like to run her thru the gears and when she comes on like a freight train at 3000/3500 RPM it puts a smile on your face. everyone does not like the same thing or ugly women would never get married.

[Duke W.]

Re: The whole point of a roller cam

That's why I discourage guys from buying "high volume oil pumps" (and "high flow water pumps", too) and not increasing oil pressure beyond the OE level.

It takes a lot of power to pump oil at several GPM and coolant at a couple of dozen GPM.

Like you, I've never seen any data on oil or coolant pump power consumption, but I can say that a good SHP 327 that makes about 325 net/275 RWHP is consuming about 150 HP internally in the engine in the upper ten percent of the rev range, and this does NOT include drivetrain loss - just friction and parasitic loss INSIDE the engine, and I'd guess that the fluid flow power is a good 20-25 percent of this amount, or at least 30 HP.

One of the great unrecognized sources of power improvement is reducing internal friction and parasitic power loss, and you can bet that F1, IRL, Champcar, and NASCAR engine desigers work this to the max, but a lot of backyard hotrodders install aftermarket parts (like high volume/flow oil and coolant pumps) that actually INCREASE parasitic power loss.

You only need enough oil and coolant flow to keep the engine lubricated and running within an acceptable temperature range. Any more just reduces power available at the flywheel. Many OE water pumps are designed to provide high coolant flow at idle to ensure good coolant flow through the heater core for cold weather heating. This means they flow more than necessary at high revs, so if anything, a street engine for a mild climate should have a LOW FLOW coolant pump.

Duke

[Duke W.]

Re: duke you assume that everyone drives like you

Yeah, I ordered my SHP SWC with a 3.08, because I wanted high speed cruising ability and top speed. If I need maximum power at cruise speed I downshift to second gear, and that gets me to a little over 100 MPH.

One of the great benefits of modern cars are their tall cruise gears, which yield excellent fuel economy and low noise. On a long road trip short gearing just makes a car unpleansant, noisy, and fuel hungry, and in urban freeway traffic all you can do most of the time is go with the flow. As long as a car has reasonable top gear response to manuever in freeway traffic, that's all you need, but a downshift once in a while doesn't hurt. I like to shift, anyway, so it gives me an excuse.

A lot of vintage Corvette guys are replacing short gears with tall gears for the more relaxed highway cruise manners.

Headers and a big cam won't really improve top end power that much - in the car with an exhaust system, but will kill low end torque big time.

One of the ways to make the top end feel stronger is to kill the bottom end, but the top end just feels stronger because the bottom end is weaker. I see that a lot, and it's one reason why I keep harping about starting dyno pulls at 1500 or less.

Duke

[Duke W.]

Re: more grunt, no loss in HP @ high RPM

Start the pull from 1500 or less, okay?

When I tested my Cosworth Vega a couple of years ago with the reindexed cams (reduced the effective overlap about 75 percent) I had the pulls done from 1000-7000. The 80 percent torque bandwidth started at 1900 and the top was beyond 7000, but extrapolating the curves indicated the top was about 7200.
With the OE cam indexing the 80 percent bandwidth starts at about 2800, which is why in OE trim they were such dogs on the street - lots of overlap (to kill NOx) and about 12 psi exhaust backpressure at the top end. What a disaster, but it was an easy fix with no internal engine modifications. The trick was to understand the cause of the problem, which was high exhaust backpressure and too much overlap.

Duke

[Clem Z.]

that is why drag racers use electric water pumps

and the NASCAR restrictor plate engines run 0W-5 oil in quailifing and back down the oil pressure in the dry sump oil pumps. i have seen several cars lose engine when backing the oil pressure down too far. when you prime a engine using a a HD 1/2" electric drill and the engine come up on full oil pressure it can pull the drill out of your hands if you do not have a firm grip. we used to grind every other fin off of the water pump impellers and used different size pulleys to slow down the water pump on race engines.