Witt

Engine mechanics are not my strongpoint, let alone valvetrains. (I like too toon teh soffwarez) I'm not real sure what common OEM boosted specs are for cams. I can believe no overlap just for durability/drivabilty issues.
If I'm correct you can get an idea of the lobe profile by comparing the difference between adv. duration and duration @ .050" lift. Closer the numbers, the quicker the ramp, correct me if I'm wrong.

Not bashing the jbp cams in anyway, but for the money, I can get a cam that better suits my application. I have other reasons too, but I don't want to turn the thread into a brand comparison.

I think I finally made a decision on the grind I want after debating between the blower grind, the LSJ 300hp book grind, and the stage 3 grind. I'm leaning towards the 252/262 blower one, hopefully by Monday, they'll be purchased as I already bought a set of 10-1Diamond pistons, neutral balance shafts, Supertech valve springs, head gasket and studs. The cams are my keystone at this point. Comp kept telling me they weren't getting any emails about my stock cam specs all week until today, so hopefully I make progress come monday.

Halfcent

Okay, well there is where you and I would make a strong team. I know everything about the internal mechanics and nothin' about tuning. Well, not nothin', but not as much as I know about the mechanics.

Witt

Cool, maybe you can answer this for me. I found a different calculator online that figures out overlap based on duration and lobe seperation angles. On the different Comp cams, they come out to anywhere between 20 and 40 degrees of overlap depending on the grind. Is there any posted information or anyway to figure out what the limit is as far as overlap and piston-valve clearance goes. Their stage 3 street/strip cam has the greatest amount of duration and overlap, but are we sure the valves stay clear of the piston at that point? That thought kinda makes me nervous.

Halfcent

You are rightfully nervous. The Ecotec has almost no room left in the combustion chamber at TDC. Unfortunately, knowing the amount of overlap will not tell you the amount of valve-to-piston clearance. They are independant variables.

There should be a published spec showing what the maximum allowable valve lift at TDC for the stock piston specifically is. I don't have the factory manual, but that's where you would look.

The L61 has a flat top piston with Zero deck height at TDC. With the dome shape of the head, that would mean you have about 2 mm of space for the valve to be open. I believe Diamond makes a valve relief piston that maintains the stock 10-1 compression ratio. With the reliefs, you now can have a larger amount of lift at TDC. So you can see, its very piston specific.

On a totally separate note, overlap is a function of aspiration. A normally aspirated engine will usually have more overlap, a forced induction will have less. Reason being the forced induction would cause the intake charge to be pushed right out the open exhaust valve, resulting in loss.

But on the Ecotec, they are a bit weird. The LSJs actually have 3 degrees MORE overlap then the L61. I have always believed that's why they run so "rich", because a lot of the gas is just being dumped out the exhaust and never actually burned. So, in fact, the combustion chamber mixture is leaner then your O2 wideband is reading. Which is why people are burning up pistons running at 12.0. The chamber is probably much higher then that. HOWEVER, this is just my educated opinion.

Witt

I looked everywhere in the factory manuals and nothing is listed.

Even worse than zero deck height travel is positive travel. That 300hp LSJ book says we actually have positive travel and when they CCed the combustion chamber they had to drop the piston to zero deck height. Compare some pics of the pistons at TDC and check out the valve location on the bottom of the head. I can't see how any overlap or even using adjustable cam gears would allow the valves to clear at TDC with stock pistons.

The same book uses 262/262 adv duration at 109 lobe separation angle which puts the overlap at 44 degrees, much higher than the blower grind from comp I'm purchasing(31 degrees overlap). I bought the same pistons used in that book, so thats the only assurance I have that this will work.

Halfcent

Let me look at that again. I busy today, might be Monday.

Halfcent

Okay, I've done a lot of reading. The clearance is dependant on two very obvious factors. The piston, and the cam. We are talking here about the use of aftermarket pistons and cams. I am fairly confident that you are not going to have a problem based on the fact that we haven't heard any stories about people jamming up new cams. The combination of cam AND pistons does make a possibility of interference fits.

You would have to do clearance measurements during the build phase to gaurantee tolerances. Build your bottom end and measure deck height as described in the LSJ build. I don't know what pistons you are using, but if you have the diamond ones with the valve reliefs, I'll bet your fine.

Witt

Well, its all a moot point now. Talked to Comp for the final time today, they said the hex keyway difference from the intake blank to exhuast blank is 11 degrees in difference. In other words, the alignment of the hex drive in the intake blank is not at the same angle from the centerline of what the exhaust blank should be.

It's still a mystery to Comp how GM got a set made for their 300hp LSJ book. Comp is saying they absolutely did not manufacture those.

I guess I'm just going to hold out for Crane, Crower(blah), or someone else to come along with a set of cams.

zinner

Probably explains why JPB was having issues with the CMP sync code being set on there initial set of LSJ cams. I bet they used intake blank and didn't know it was 11 degrees off ..

Also probably explains why they need to regrind stock cams for there cams.

I love how GM builds a tuner engine but you can't get cams for it without a ridiculous amount of work and research.

WSFrazier

WTH, I need and want cams for my build. Well maybe not need, but want.

Matty

So as of this moment JBP is the only place that offers cams?

NoRemorse

I'm going to vomit at the reality of that statement...

sunfirejoe

iTrader: (1)

level zero motorsports might be offerering some, im in the talks with them right now

Matty

No kidding. Sad state of affairs.



That's good news. The more options the better.

sunfirejoe

iTrader: (1)

anyone interested, please pm me, i got a hook up hes willing to work, his webpage is not up to date, and id hate to get busted for adverstising cuz thats all i seem to do on this site(yes im still pissy) but if ur interested pm ill hook ya up with a contact, and just make sure u say JoeyB sent yah

Witt

Level Zero also regrinds using Colt Cams.

If I could get lash caps to preload the lash adjusters, I would think about using regrinds, but thats way too much money considering Crane regrinds cams for 50 bucks a cam. Maybe I'll get a hold of them.

WSFrazier

I am going to get Comp Cams. No reason why GM and Rice can get them. Me starring at mine tonight made me want new ones. Stock FTL.

Witt

So out of this thread, I've talked to two people personally that have had Comp cams custom made without issue, both over 400whp, who state the blanks are identical. I've had one GM engineer state the same, I've reviewed cad drawings of the cams as they are sent to the contractor to be produced which show no difference, however, no matter how I state it to Comp, they seem to find an excuse on why it won't work. They just sent me an email a few minutes ago basically saying I'm retarded for trying to make a 4 cylinder fast, when their own company doesn't know the difference between a 2.0 and 2.2 liter engine when they publish their catalog. Add on top of that they somehow claimed that a cam sensor could be internally placed into a steel billet cam (rofl), then saying flanges are different sizes when the drawings I was currently looking at stated the opposite, then when I PROVED that the blanks are identical they claimed to have lost my email. Only when I pestered them on a twice daily basis did they find their next excuse about cam angles, which I have found out, is now totally false.

Any idea on why a major cam company seems to want to shun an entire market segment? I guess I'm also supposed to believe that GM lied to us when they stated in their 300HP lsj book that comp manufactured the cams. Unbelievable.

player_1

the JBP cam really is'nt as bad as you might think. the Tri flow regrinds are done with Colt Cams.
and the gains for the LSJ are definatly there.
as far a dyno's go, here you go.



I've run a year with this cams and no problem except for the fact that It was the prototype, so my cam sensor is out of place. but it's only a light.

if you look at the dyno you can clearly see it makes far more then the 2.4L cam. I suspect because it was more geared to a forced induction type motor. which is why he showed so little gains.

I must also mention about the dyno sheet. you can see that the cam build more boost, and the boost by pass vavle kicks in and bleads all my boost. on a stock car the cam made 15psi.

to bad I didn't think about the by-pass mod when I was on the dyno. then you could have really seen the gains.

NoRemorse

Cam building more boost? .... yea, not possible unless it LOSES power.

A cam that provides more power means it flows more, which means LESS boost, and MORE power....

player_1

take a look at the dyno and tell me I lost power.

you'll see that I lost some low end, until about 2800RPM then it just kept building.

say what you want but that chart doesn't lie and my eye's werent lieing when I say the needle on the boost gauge go to 100Kpa (~15psi) then drop to 85Kpa(~12.5psi) at 5700RPM, and that is untuned, stock car.

I wish I had done the by-pass mod when I was on the dyno, because I know it makes more power. if you interperlate the chart you'd see I gained about 12hp peak. assuming that it continued to flow more the stock cam to redline. (vary safe and likely assumption.)

we'll learn just how far the cam will continue to make power after I get tuned next week.
I also know this. me with everything stock except the cams, I was faster then a stock cobalt with the Fugita intake.
that to should tell you what kind of power it makes.

NoRemorse

I didn't say you didnt make an improvement, I am just saying you did NOT increase BOOST AND POWER with a cam. It does not work that way. In this case, I am saying you read the gauge wrong.

Halfcent

That is not necessarily true. A cam specifically for forced induction may result in slightly higher boost pressures. Forced induction cams favor less valve overlap. So the intake will open a bit later then normally aspirated cams would. Hence, close later as well. The idea is to use the boost to fill the combustion chamber as opposed to inertial vacuum flow. The piston will actually move up on the compression stroke a little further, resulting in a opposing forces (the piston compression VS the blower compression while the intake valve is still open). So it is possible that his boost did rise.

player_1

and that is the exact differance between a NA Cam and a Turbo/Supercharger Cam.

which is why putting this cam actually hurts your gains (hence the 2.4L making only 2HP)
the overlap favoring the intake actually negated the grind.
thank god for adjustable cam gears so you can fix this issue

socalsilverRL

overlap also helps engine cooling, allowing intake air to pass through and cool the exhaust valves.

the main reason there is no overlap in a FI cam grind is for TURBOS...on a turbo, you want to avoid REVERSION, when exhaust flow is hindered too much by the T/C and starts to flow back into the cyl. With a positive displacement S/C you dont have to worry about reversion, as there is nothing to create backflow, and the positive displacement S/C will overpower any backflow (Reversion) into the engine.

Im not saying you want more overlap, but overlap on a S/C'd car isnt such a bad thing, as it would be on a t/c'd car...

P.S. and i have a set of blank cams, NIB...im too afraid to open the box, ar ethe GMPP blanks the same length?