Say to the stock cam in my L03. Also, I remember once someone posted on here that it would yield a 16 hp increase. Couldn't find the post though, was a long time ago. Can someone verify that? Also, with the stock cam, would I bennifit more from 1.6 on the exaust and 1.5 on intake, or 1.6 all around. Thanks.

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1989 Firebird Formula L03
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Stock with Functional Formula Cowl Induction, Centerforce Clutch, KYB GR2 struts and GAJ shocks, 89k on the clock and running smooth.

 

The increase in horsepower comes from increasing the lift that your cam already has. The amount of horsepower increase will depend on what cam is in the car right now. I have heard people say they have noticed a difference from doing this, but I have also heard people say that they didnt really get much out of it. Also make sure that your heads dont require any reworking to accept the 1.6 ratio rockers. Some people told me they had to make the slots for the pushrods a little bit longer. I have not done this job, but I wouldnt expect a major gain. You would probably be much happier with changing the cam (if yours is stock). Hope this helps.
peace

 

How bout this? Take whatever lift number you want to convert (the standard is to give them for 1.5 rockers, right?), divide that number by 1.5, and then multiply the new number by 1.6. This should give you the lift number with 1.6 rockers. I don't know the specs for your cam though. Somebody correct me if I'm wrong, but this seems to make sense to me.

 

MikeS is correct. The 16hp you are refering to is probably due to the fact of going from standard rockers to rollers, freeing up friction loss hp.

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Rob
'86 TA 305 TPI
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Going from stamped steel rocker to roller rockers alone will increase HP due to the reduced friction. If you had 1.5 rollers and went to 1.6 rollers you would only gain about 5 HP. Some people actually lose HP because the cam is better suited for 1.5 rockers.

A typical 1.5 to 1.6 rocker swap gives around .030 extra lift but it varies a few thousands depending on the cam lobe lift.



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That sounds like some good info. Let try that. From the tech data section I see that my cam has 350 lift on the intake and 384 on exaust.

350/1.5 = 233.3 | 233*1.6 = 373.3

384/1.5 = 256.0 | 256*1.6 = 409.6

So you guys think that with an increase of 25.6 lift on the exaust and 23.3 on the intake will only yield a 5 hp gain. That doesn't seem right to me. Correct me if I did this wrong.

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1989 Firebird Formula L03
Black with 5-Speed
Stock with Functional Formula Cowl Induction, Centerforce Clutch, KYB GR2 struts and GAJ shocks, 89k on the clock and running smooth.

 

It will only yield 5 hp if you took off the stamped steel 1.5 rockers and put on stamped steel 1.6 rockers. All you've done is increased the lift. You've done nothing to duration, valve overlap or lobe seperation angle. You could get a cam with that same lift but different values for the rest of the numbers and get 50 HP increase.

1.6 rockers are just a poor mans cam swap. The only time they are really needed is when you start getting into very large cams. Instead of getting a cam with .700 lift with 1.5 rockers you only need a cam with .656 lift then put the 1.6 rockers on it to get the .700.

 

Actually increasing rocker ratio DOES increase duration since seat timing is reduced. To get the higher lift the valve must open and close quicker, and since duration is commonly measured at .050" lift, it will happen sooner.

 

Maybe someone could plug it into desktop dyno or something and find out? Just a thought. 5 hp just doesn't seem right for the increase in lift.

 

SC,

The Crane rollers I have used advertise UP TO a 16 HP gain. As stated earlier, much of the gain is likely from a reduction in friction at both the valve tip and fulcrum. Some of the gain probably can be attributed to the stiffer rocker providing a lot more accurate ratio and lifts. The rest is probably from the 6% lift increase and slight increse in effective duration (at 0.075" valve lifts).

I'm almost certain Crane used the worst case stamped rockers and cam profile to make their comparison, so they could advertise the biggest numbers for power gains. I would expect less than the 16 HP in most installations, but 5 HP does sound a little bit below what should happen with your cam. Just make certain the springs can take the extra lift without binding.

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Later,
Vader
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"Let the bodies hit the floor!"
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So theres not much out there that would cause or possess someone to venture into the 1.7 would there be?

 

I ran it through Desktop Dyno 2000 two days ago and it provided only a 4hp increase. Just not worth it in my book

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_ _ _ _ _ __ _ _ _ _ _
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Thanks guys. I think it's 1.5 rollers for me then. Just got to figure out how I'm ever going to put in a new cam. Thanks again.

 

I'll back up Stephen on this one in that switching from 1.5 to 1.6 DOES NOT increase duration. Duration is measured at .050" lift, true, but for comparing other manufacturer's cams with competitors. This is because different manufacturer's measure advertised duration at different point (ie: most typical are lash point (.000" lift), or .006" lift) This does not change the true duration, which is at the lash point or .000" lift. What you are trying to say is that the lobe ramp profile is changed to a steeper one, that IS correct. But duration is the same.

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George P. Lara
1984 Z28
2001 SS #0391
SCCA, SCFB, SC3GFB

 

In other words, George, you're saying that the valve reaches the 0.075" lift point sooner, and stays there (or above) later than with a 1.5:1 ratio rocker arm. To my way of thinking, you are saying that the effective duration of the valve opening at 0.075" lifts (where most reputable manufacturers advertise their specs) is increased, while the actual duration of the cam profile is not changed. I'm not trying to put words in your mouth, but that's what I've been saying all along - the effective duration (at the valve, where it counts) is increased slightly. Certainly the change is minimal, but there is an increase nonetheless.

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Later,
Vader
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[This message has been edited by Vader (edited August 10, 2001).]

 

I think we get into this hair-splitting type of argument fairly often.... somebody should put it into the FAQ.

If you actually calculate the effect of the increased ratio on the valve motion, you'll find that for most typical street cams, that change increases the duration by less than 3°. So, does the duration increase? Definitely yes. Is it significant? I doubt it. That tiny change in duration at .050" is completely swamped by the increase in lift, and by the improved consistency from one valve to another, especially if you change from sheet-metal "pretend" rockers to real ones.

To answer the original question, there's no way you'll get 16 HP out of that change. That's an almost 10% increase in the motor's output, in exchange for a 6% change in peak lift. That's patently bogus on the face of it. You might see 3 or 4 HP, maybe, if you changed from decent 1.5 rockers to identical 1.6s. Going from stock garbage to quality 1.6s, you might see 7 HP tops, and I doubt it would be even that much. There are too many other limiting factors (in order of importance: exhaust, exhaust, and exhaust; then the heads) to get a very big result from such a small change.

The L03 cam is so miniscule with such puny little pimples for lobes that you could put 1.8 ratio rockers on there and not exceed the lift limits of the heads themselves. If I was going to go to the trouble of changing half the rockers, I believe I'd do them all. I certainly wouldn't leave sheet metal ones on half of the valves.

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ICON Motorsports

 

Hey RB83L69,

Wasn't the whole "thought" of using 1.5/int. 1.6/ex. mainly used on single pattern cams to compensate for GMs crappy exhaust port sizes & designs? But now that cam companies make dual pattern cams, doesn't that eliminate the "need" for the use of different ratio rockers? Like was said earlier, by using the grind of the cam to increase the lift of the ex. valve (rather than the rocker arm), then they can add 10deg+ to the duration also.

And wouldn't using 1.6 rockers increase stress on the cam lobes? I mean you are moving the pushrod closer to the fulcrum, right? That would mean more pressure on the pushrods & lifters, which would add more pressure on the lobes, right? Then that would also add more deflection to the pushrods, which would decrease valvetrain symmetry and accuracy.

It just seems like they are a "crutch" for a bad cam choice, and a bad crutch at that. But I guess you said that already, huh?

AJ

 

AJ: You are correct on all 3 counts.

But with a stock cam like his specific one, the exhaust lobe is already bigger than the intake lobe. And in that cam, both lobes are equally pitiful, and so maximum benefit comes from improving both of them.

Yes, now that dual-pattern aftermarket cams are the norm, it's not as likely that using different ratio rockers would be as useful. In fact I've never had a motor where it actually ran better with 1.5 rockers anywhere than it did with 1.6s, though I've heard of such a thing, especially with racing heads. It's highly unlikely that any kind of stock head would ever flow well enough on the intake side that it wouldn't benefit from higher ratio rockers.

Of course if you bump up the rocker ratio you increase cam loading, by more than the "ratio of the ratios". Because in addition to increasing the amount if mechanical advantage the valve spring has on the push rod, you also depress it farther, which produces higher pressure. Stock valve springs are made of few turns of thick wire, and as such, have a spring rate that is not linear: their rate (lbs pre inch) is low at low deflection, then increases radically as deflection increases. So with a large cam, you could destroy the cam/lifter surface with bigger rockers. But with teh "peanut" cam he's got, I doubt it's a problem. Even with the 1.6s his final theoretical lift will only be about .425" IIRC the cam specs.

A cam has a limit to how tall the lobes can be, namely they can't be any taller than the radius of the cam journal or you wouldn't be able to install it. So, to get a "bigger" cam, what is actually done, is the back side of the lobe is made smaller, since lift = the difference between the tip and the back of the lobe. That's also why you have to lengthen push rods when you increase lobe lift, and why you can "regrind" a "little" cam and make it "bigger" to some extent. But, the smaller you make a cam's diameter, the less strength it has. So there's also a downward limit on the lift you can get from a particular cam blank. Therefore a limit to the lobe lift a particular blank can support. To go above that, rockers are the easiest way.

Another argument in favor of higher ratio rockers in some applications, is that the geometry of the lobe/lifter interface creates a tradeoff between maximum lift rate or ramp steepness, and lobe/lifter lifetime. Rockers give you a way to achieve higher lift without exceeding that limit. But of course with roller systems that's not an issue at all, so it's a whole lot easier to use more cam and less rocker in those applications if you want to.

Cam design and selection has to be one of the most complex areas of building (not just "rebuilding" or "assembling") an engine. Granted, for most near-stock engines in well-characterized applications there's not much difference, but once you get outside of thattype of situation, it's a pretty big world out there. I don't see the factory's choice of a 1.5 nominal ratio for the SBC as any kind of a gold standard for how all should be built; but rather as something to be understood before just arbitrarily changing it.

Now my fingers are tired.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Thank you.

I was aware of the fact that the cam lobes could not be larger than the bearings, but I never thought of the fact that the cam would lose strength. Overlooked the obvious.

I was also aware of the fact that you need to worry about retainer/guide clearance and push rod length when using more lift, but I never thought of the spring pressure being raised. Again, overlooking the obvious. Thanks.

Just one more Q if you don't mind. I gotta a 350/4 bolt out of a C1500 that I'm building (on a budget of course) for my C-maro. I'm using a Hyd. (non-roller) cam and was planning on using the stock push rods from that engine. The cam I'm using is .442/.465, 214/224 @.050", 112 LSA. Can I get away with using stock springs (new ones of course) as far as seat pressure goes? And can I use stock length push rods with that little lift? The reason I ask about the springs is the retainer issue on GM heads. You know, the height diff. and rotator on the ex. valve.

Thanks again,
AJ

[This message has been edited by AJ_92RS (edited August 11, 2001).]

 

IMHO even new stock springs are borderline at that much lift. If I was going to spend money at all, I'd get something better. At that level you don't have to go wild, but you should step up to a performance spring (and retainers). That's getting to the point where the spring pressure at peak lift reaches levels that shorten cam & lifter lifetimes.

The rotators are useless. Get rid of them.

Stock length pushrods should be OK.

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"So many Mustangs, so little time..."
ICON Motorsports

 

I almost quoted the entire text of RB's esxplanation of valve train dynamics, but thought I'd spare everyone....

Once again, RB has demonstrated his thorough understanding of the system. Effective duration must increase, even if it is not a significant amount.

All I wanted to reiterate was that the 1.5:1 "standard" is really not a "standard" at all. GM regularly uses rocker ratios up to 1.72:1 on vastly inferior engines. The SBC case can support a cam adequately to endure a lot more ratio and valve train pressure than that, and roller lifter valve trains make the job even that much easier. The weenie little 151CID "Iron Duke" four-holer used 1.71:1 rockers from the factory, and most of those were with flat tappet cams. The valve trains on those engines usually survived well beyond the life of the crank and rods. It was probably done because of the small case bores for the camshaft, and doesn't hurt a thing.

Many LS1 engines are getting 1.7:1 rockers by the millions, and most of us don't see that as a weakness. A lot of those 302 Fords in SVO cars used 1.7:1 rockers without problems, and we all know that small block Ford heads aren't the greatest thing since sliced bread.

BBC engines have used 1.6:1 and 1.72:1 rockers for millions of miles, and we don't hear about chronic valve train problems with them. Early Pontiac Ram Air 400 engines came with 1.6:1 and flat tappets from the factory as well.

You can buy rockers with up to 1.8:1 ratios from Crane and Comp Cams any day of the week. As long as you have screwed studs, piston clearance, and the correct springs, it isn't a big deal at all. If you've got a roller cam and weenie lifts, I don't know why you wouldn't anyway as long as you changed springs and studs at the same time.

Just my input.

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Later,
Vader
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"Let the bodies hit the floor!"
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