Comp cams

Keep in mind that if these lobes are highly loaded in a typical SBC application, they'll be even more so in the six because the little 1-3/4" cam journals will dictate a smaller base circle.

Keep in mind that if these lobes are highly loaded in a typical SBC application, they'll be even more so in the six because the little 1-3/4" cam journals will dictate a smaller base circle.

Can you hear a snapped camshaft already John?
I thought the big pushrods wouldn't be hard, and I figured the fancy lobe would hopefully take care of itself. I've got good rockers on 7/16 studs, but I haven't thought about the integrity of the cam itself or the gears I suppose. Which family of lobe do you think is as far I should go?

Maybe I should go 6302 and 6303?

I don't know about a snapped shaft but I do know that these lobes end up with a pretty sharpish nose. But really I'm just guessing so it'd be good to hear from someone with long-term experience with these lobes on the little Holden cores. You could go with something not quite so aggressive like a 6302 and I don't think you'd lose much power. On the exhaust side in particular you don't need a lot of area and lift so long as the duration is sufficient, so you could use something like a 6237 there. Even Comp's milder stuff is quite aggressive compared to the local products - the last one I bought was an XE profile for a street car and it has shorter seat timing and more area than many of the "generic" local competition lobes.

"extra oiling advised"

Hi,

What do comp mean by extra oiling advised? They list that on quite a few of their lobe families. EDM/Cool Face Lifters? Lifter bore groove?

Cheers.

Hi,

What do comp mean by extra oiling advised? They list that on quite a few of their lobe families. EDM/Cool Face Lifters? Lifter bore groove?

Cheers.

Yes, anything that will provide additional oil to the lobe and lifter face, so that would include anything from EDM'd lifters to a full NASCAR style flooded cam tunnel...

I imagine that the lifter bore groove would (I'm guessing that's what your calling "a full NASCAR style flooded cam tunnel") supply a lot more oil then the EDM'd lifter. Any one tried grooving the lifter bore (for cam lubrication) in a 202? Should be relatively easy/straight forward to do, but I am curious how much oil pressure is lost.

Cheers.

Edited by Ned Loh, 14 November 2012 - 08:52 AM.

Nascar engines have the camshaft fully enclosed in a sort of a tube or tunnel so that the entire shaft is at least partially submerged in oil all the time - kind of an extreme example of what’s needed to make a flat tappet cam survive with high spring pressures for 500 miles at 9000rpm. For a more "normal" application you'd probably just go with EDM'd lifters and/or slotted lifter bores. Comp (and others) will sell you the broaching tool.

Just keep in mind that there'll be diminishing returns with increasingly "savage" lobe profiles, so that with the most aggressive lobes you might get only a percent or two more power in exchange for a massive increase in the "iffiness" of survival. And that all these .842" lobes would have been originally designed for an SBC with bigger journals than our 202s. In other words I'd use some caution in selecting profiles with acceleration rates that are right on the bleeding edge for .842" lifters...

I ended up with a 6302 in 6303 ex 110lsa +1adv

Ah NASCAR, you wouldn't do it that way if you had a choice, but limit rules and throw enough time and money at it...anything is possible.

oldjohnno, do you think the bleed off from the slotted lifter bores will be an issue in our little 202?

I ended up with a 6302 in 6303 ex 110lsa +1adv

Good luck with it. I reckon it will meet your aim of 6000rpm (1st post in this thread) no drama. Make 100% sure it is dialled in right (I still reckopn there was more in your old combo). Let us know how you go.

What lifters are you going to run with it?

What lifters are you going to run with it?

I don't know? I don't know much about lifters. I'm not sure what's in it now, they just came in a box with the cam I bought when I put the engine together. What do I need to be looking out for?

Generally, buy the lifters from the cam grinder unless there is a good reason to buy elsewhere (eg. You want to run a cool face lifter but cam company don't sell them). Suggest contact cam company and get their recommendation.

I ended up with a 6302 in 6303 ex 110lsa +1adv

Maybe think about installing it a bit more advanced (say 4 or 5 degrees), especially if you don't have time to test different settings. Normally the performance will still be OK if it's a couple of degrees advanced beyond the optimum, whereas if it's on the retarded side of the it the performance can drop off pretty quickly.

oldjohnno, do you think the bleed off from the slotted lifter bores will be an issue in our little 202?

You'll definitely notice a drop in oil pressure at lower rpms. Depending on what you're doing with it this may or may not matter (you don't need much pressure at all at low rpms and loads) but if it's going to see much low speed work it would pay to use a bigger pump.

Maybe think about installing it a bit more advanced (say 4 or 5 degrees), especially if you don't have time to test different settings. Normally the performance will still be OK if it's a couple of degrees advanced beyond the optimum, whereas if it's on the retarded side of the it the performance can drop off pretty quickly.

Really? I was thinking along the lines of too advanced now, it's only that changing cam timing is a big job and I thought I'd upgrade camshaft seeing as I have to pull it apart anyway. I did some reading that indicated that advanced cam will give me stronger bottom end and less top which is what's happening to my engine. It pulls like a 14 year old boy till 4500 then struggles till it hits what feels like a soft rev limiter at 52-300.

You'll definitely notice a drop in oil pressure at lower rpms. Depending on what you're doing with it this may or may not matter (you don't need much pressure at all at low rpms and loads) but if it's going to see much low speed work it would pay to use a bigger pump.

Appreciate your thoughts. I'm going to give this a try (after Christmas).

Really? I was thinking along the lines of too advanced now, it's only that changing cam timing is a big job and I thought I'd upgrade camshaft seeing as I have to pull it apart anyway. I did some reading that indicated that advanced cam will give me stronger bottom end and less top which is what's happening to my engine. It pulls like a 14 year old boy till 4500 then struggles till it hits what feels like a soft rev limiter at 52-300.

What cam is in it now? If everything else is ok even [email protected]" should get you to around 6000.

It's 243@50 (+2 degrees)
Ex 82-42
In 46-78
.326 lobe lift
108lsa
.86 lift@tdc on intake

It's 243@50 (+2 degrees)
Ex 82-42
In 46-78
.326 lobe lift
108lsa
.86 lift@tdc on intake

Thats an older design fairly slow acting cam,an equivalent from camtech has 23deg less intake adv duration for 244 @ 50 ,.346 lobe lift, and is completely reliable with cool face lifters and castrol or penrite oil.

Really? I was thinking along the lines of too advanced now, it's only that changing cam timing is a big job and I thought I'd upgrade camshaft seeing as I have to pull it apart anyway. I did some reading that indicated that advanced cam will give me stronger bottom end and less top which is what's happening to my engine. It pulls like a 14 year old boy till 4500 then struggles till it hits what feels like a soft rev limiter at 52-300.

The vast majority of cams run best when they are advanced a few degrees from "split overlap". You could argue that 4 or 5 degrees should be the baseline or reference point instead of the customary 50:50 point. If a cam lacks top end at 4 deg adv I'd take that as a sign that it needs more duration, not less advance.

Even with your old-style cam profile, it should have been peaking well into the 5000's, it appears that you may have other issues besides a lack of cam.

The vast majority of cams run best when they are advanced a few degrees from "split overlap". You could argue that 4 or 5 degrees should be the baseline or reference point instead of the customary 50:50 point. If a cam lacks top end at 4 deg adv I'd take that as a sign that it needs more duration, not less advance.

Even with your old-style cam profile, it should have been peaking well into the 5000's, it appears that you may have other issues besides a lack of cam.

The vast majority of cams run best when they are advanced a few degrees from "split overlap". You could argue that 4 or 5 degrees should be the baseline or reference point instead of the customary 50:50 point. If a cam lacks top end at 4 deg adv I'd take that as a sign that it needs more duration, not less advance.

Even with your old-style cam profile, it should have been peaking well into the 5000's, it appears that you may have other issues besides a lack of cam.

Let's not forget the engine is under pretty big load at these revs. It's like driving a car in top gear and towing a caravan trying to get to 6000, so it's not toooo bad the way it is now. I realise its power is down being 212hp but i was warned by others that that dyno doesnt like spitting out big numbers so just use it for tuning not bragging rights (my friends super sedan chev made 590hp on that dyno where everyone else is apparently making 720 and no noticable difference on the track)and through its acceleration and handling we have manged a few first place trophies last season, but my top end speed is down on the competition
I've tried everything now from Dyno tuning, changing carbies, manifolds, valve springs, it's just the cam left so that's where I'm aiming my focus at the moment.
Earlier on in this thread I put up my engine Dyno results and it shows peak torque at 4600 and I think that's what I need to lift up the rev range.
I'm a little confused as to how I dial this cam in now. I'm a novice engine builder at best and in the past have just set the cam in at the lift at tdc that written on my cam card. I can borrow a degree wheel and work it out i suppose, but any tips?

Let's not forget the engine is under pretty big load at these revs. It's like driving a car in top gear and towing a caravan trying to get to 6000, so it's not toooo bad the way it is now. I realise its power is down being 212hp but i was warned by others that that dyno doesnt like spitting out big numbers so just use it for tuning not bragging rights (my friends super sedan chev made 590hp on that dyno where everyone else is apparently making 720 and no noticable difference on the track)and through its acceleration and handling we have manged a few first place trophies last season, but my top end speed is down on the competition
I've tried everything now from Dyno tuning, changing carbies, manifolds, valve springs, it's just the cam left so that's where I'm aiming my focus at the moment.
Earlier on in this thread I put up my engine Dyno results and it shows peak torque at 4600 and I think that's what I need to lift up the rev range.
I'm a little confused as to how I dial this cam in now. I'm a novice engine builder at best and in the past have just set the cam in at the lift at tdc that written on my cam card. I can borrow a degree wheel and work it out i suppose, but any tips?

Ok firstly ,can you let us know the procedure you used to dial the cam in.

Let's not forget the engine is under pretty big load at these revs. It's like driving a car in top gear and towing a caravan trying to get to 6000, so it's not toooo bad the way it is now. I realise its power is down being 212hp but i was warned by others that that dyno doesnt like spitting out big numbers so just use it for tuning not bragging rights (my friends super sedan chev made 590hp on that dyno where everyone else is apparently making 720 and no noticable difference on the track)and through its acceleration and handling we have manged a few first place trophies last season, but my top end speed is down on the competition

The numbers are actually pretty reasonable. The maximum achievable top speed will occur at the same rpms as maximum engine hp. So using our analogy of a car pulling a caravan up a slope we'd try to gear it so that the engine could just reach the peak hp rpms. I don't know anything about boats or props so I'm probably talking out of my arse but if your boat was a car you'd say it was overgeared. No doubt you've already tried different props; what did you find using a bit less prop?

...I'm a little confused as to how I dial this cam in now. I'm a novice engine builder at best and in the past have just set the cam in at the lift at tdc that written on my cam card. I can borrow a degree wheel and work it out i suppose, but any tips?

There are several ways to dial in a cam, I'll outline one way below. But before everyone jumps in and replies that there are simpler methods (eg. the lift at TDC method) I'll explain why I'm showing this one. One reason is that as well as getting the cam positioned properly it'll also confirm that you actually got what you ordered. Another is that you don't have to work out where the lobe centrelines are, and this can get messy when you are working with assymetrical lobes like many of the Comp lobes.

First, install the cam in the block and fit lifters to number one cylinder. Don't use any lube on the lobes but make sure the lifters move freely in the bores. I'll assume you also have pistons and rods fitted, at least to number one.

Next, fit a degree wheel to the crank snout and some sort of pointer with a sharp point so you can get an accurate reading.

The next step is to set the wheel so that it is accurately aligned with TDC of number one piston. For an initial setup just eyeball TDC and set your degree wheel at TDC.

Now rotate the crank to move the piston down and set up a positive piston stop over the top of the cylinder. A piece of flat steel bolted down using two head bolt holes diagonally is the usual setup. You'll have to tack something to the middle of the strip to stop the piston around 1/2" or 1" from TDC.

Turn the crank until the piston is up against the stop. Note the degree wheel reading. Now turn it back the other way until it is against the stop again. Compare the reading with the first one and adjust the wheel until you get the same reading when you turn the crank either way. Double and triple check it then remove the piston stop.

Now let's take a look at the cam card. Here's an example with a couple of things highlighted.



The bit with the shaky red circle around it shows that the cam is ground with lobe centrelines of 108deg, and has the keyway positioned so that when installed it will (or at least should) be advanced 2 degrees.

The bit with the blue line around it says that the timing figures above it are with an intake centreline of 106 degrees, or in other words 2 degrees advanced. So if 2 degrees advance is what we want we just need to check that the cam actually matches the card.

Set up a dial indicator on the intake lifter, you may need to extend it with a piece of rod. Rotate the engine so the lifter is on the base circle and zero the indicator. Turn the crank either way to double check is at its lowest point and adjust if necessary.

Turn the crank until the lifter starts to rise and stop when the indicator show 0.050". Check the degree wheel reading, in our example it should be on 16 BTDC. If it is all is good. But let's say it's on 12 degrees BTDC, that would indicate it is 4 degrees retarded from where we want it and we would need to adjust our gears or keys to get it there.

Or let's say that while the cam was ground 2 degrees advanced, we actually want to run it 4 degrees advanced. In that case we just need to adjust it another 2 degrees so that the wheel shows 18deg BTDC at 0.050" tappet lift.

Assuming everything is where you want it now, you can also go ahead and check all the other events ie. intake closing, exhaust opening and exhaust closing. This will confirm that the cam is indeed what you ordered. Keep in mind that if you have advanced or retarded the cam to a different setting to that on the cam card all these readings will be advanced or retarded by the same amount. For example, if we gave the cam on the card above an additional 2 degrees advance then we should get intake close at 46 abdc, EXO at 54 bbdc and EXC at 10 atdc (all these at 0.050" lift).

I know this sounds a bit involved but it probably takes as long to explain as what it does to actually do. Keep notes as you go, once you've done it a few times it'll be second nature. The worst part is fitting and removing the gears to make the adjustments.