L99 tech help needed - Chevy Impala SS Forum
 
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post #1 of 7 (permalink) Old 09-11-2001, 06:37 AM
ghost
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Does anyone know the max gross cam lift for the L99 engine? If not, any good sources of information where I can find the answer?

Thanks. :^)
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post #2 of 7 (permalink) Old 09-11-2001, 08:08 PM
kdrolt
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The L99 uses the same cam as the B/D car LT1.

So that means .418" lift at the intake valve and .430" lift at the exhaust valve, as taken through the stock cam and stock 1.5-ratio rockers. The cam lope sep angle is 111.5 deg, and the duration at 0.050" lift is 191 deg intake and 196 deg exhaust.
HTH.
post #3 of 7 (permalink) Old 09-12-2001, 05:02 AM
ghost
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Thanks, Ken.

Yeah, I have that info, and have even talked to the guys at GMPP about if the LT1 "Hot" cam would work in my L99 (they say yes), but I still don't know if the max lift is limited more than the LT1 (or less) due to the different heads, piston-top shape, etc.

For that matter, I don't know what the max gross lift is for the LT1 either.

 
post #4 of 7 (permalink) Old 09-13-2001, 05:17 AM
kdrolt
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If I understand you correctly, what you actually want is the maximum allowable lift at the valve in an L99, allowing for clearance between the valve(s) and the piston(s). Right?

That's not really what you've been asking.

The only sure way to get this answer is to pull one of the heads, and put some clay into a chamber, and then replace the head, and rotate it manually at the crank bolt with a breaker bar. Remove the head and measure the thickness of the deformed clay.

The other option is to call Joe Prince Racing and ask him. I think he's taken apart a number of L99 heads, and if you had access to one, you could measure the combustion chamber directly to see what amount of valve lift would cause the valve to cut into the plane of the head gasket --- that would be the point where you run risk of making valve-to-piston contact. I don't know what the depth of the valve reliefs are in the stock pistons so you'd be best not to rely on them.

That said, there are many people running around with the ZZ3/ZZ4 cam, as well as the LT4 HOT cam, and 1.6 rockers. The lift is around 0.525" I think, and that's almost 0.10" more lift than the stock L99 cam's lift measured at the exhaust valve.

I think you could add a hotter cam to your L99, but the ZZ3/ZZ4 or the LT4 HOT cam may be too much. They WILL make great power but the car will be a slug a low speeds. You might be better off using an F/Ycar LT1 cam and use 1.6 rockers. The lift will be around 0.480" max, you'll gain approx 15-20 hp from the cam alone, and you will not lose much torque at part-throttle low-speeds.

You will need new valve springs no matter what you choose, and if you do go with a high-lift cam you have to make sure you don't bind the valve springs. i.e. make sure that there is at least a gap between the spring coils at max lift. - Ken
post #5 of 7 (permalink) Old 09-15-2001, 10:27 PM
ghost
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Thanks Ken, for another good post. You're a wealth of information. [img]smile.gif[/img]

The cam swap is something I'm considering once I eliminate the next choke point in my air flow -- the stock exhaust manifolds. Geez, from what I've read here and about, adding headers is quite an ordeal, more or less, depending upon what brand you get. My problems would be the same as those with LT1s. One thing's for sure though, I'm getting the ceramic coating.

I'd mentioned the LT4 Hot cam to someone more knowledgeable than myself, and he countered with the ZZ3 idea. I understand about coil bind and will get the appropriate parts to go along with whatever cam I eventually select. Oh, and the 1.6 rockers. I know the Crane Gold rockers work with our cars, but what about anything else? Anybody use those light Crower rockers?

After the cam, the head work will begin. Maybe I'll do both at the same time, if I can scunge a pair of L99 heads to work on in the meantime. I can't afford any downtime with the car, it's my only ride.

Anybody know any good sources for porting info? Books, online, anything? I'm patient and careful, I'd like to try it myself on some donor heads. Just gotta avoid too much cross-sectional area for my little engine.
post #6 of 7 (permalink) Old 09-16-2001, 09:53 AM
kdrolt
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<BLOCKQUOTE>quote:</font><HR> The cam swap is something I'm considering once I eliminate the next choke point in my air flow -- the stock exhaust manifolds.<HR></BLOCKQUOTE>

I remember reading an exchange on the stock manifolds; one person said that the L99 manifolds were the same (identical) as the LT1 manifolds, while someone else said they were different.

I will add that IF they are the same, that you won't lose much flow by keeping them (at least for now) becauase they aren't that bad (the stock LT1 makes approx 280 fwhp and 350+ fw ftlbs torque with only aftermarket mufflers and a CAI) and you engine needs less big-air breathing than the LT1 due to the smaller displacement.

I'd suggest the cheap approach first: get a takeoff stock N10 dual exhaust from any LT1 sedan 94-96 and install it with aftermarket mufflers, and using the LT1 dual cats and downpipes.

<BLOCKQUOTE>quote:</font><HR> Geez, from what I've read here and about, adding headers is quite an ordeal, more or less, depending upon what brand you get. My problems would be the same as those with LT1s. One thing's for sure though, I'm getting the ceramic coating.<HR></BLOCKQUOTE>

I agree with what you said - but I still advocate using an LT1 factory dual setup with aftermarket mufflers for now. It's cheap, it's a complete bolt-on stem-to-stern with factory parts. It may provide you with plenty of exhaust breathing that you don't need the expensive aftermarket coated headers.

I'll also add one more thing. Several years ago there was some discussion on the NAISSO digest about people on the east coast that had modded their intake manifold by adding extra interior volume to the plenum (that part that is directly under the home plate). The reason for this was to enhance cylinder filling, by reducing the sharp turns in the manifold that the air has to travel within, as well as to provide a better straight-shot into each manifold runner.

Those manifold mods are exactly what you would want to do to an L99 engine, because they will help boost engine torque. Finally, get onto any GM Perf Parts website (Scoggin Dickey is one) and look carefully at the pictures of the GMPP 350 Ramjet crate motor. Look closely at the intake manifold. It looks just like an L99/LT1/LT4 intake except that it is raised up with a larger volume inside it. That motor makes 400+ ftlbs using a camshaft that is milder than any of the F/Ycars LT1 or LT4 cams, as well as 350 hp.

If you know anyone handy with welding aluminum, that would be my suggestion -- to increase the volume of the plenum in the intake manifold, by making it taller. It will still fit under the hood (because you've removed the home plate) and it leaves the lower part of the manifold ALONE.


<BLOCKQUOTE>quote:</font><HR> I'd mentioned the LT4 Hot cam to someone more knowledgeable than myself, and he countered with the ZZ3 idea.<HR></BLOCKQUOTE>

If I were you, I'd choose an F/Y LT1 or LT4 (non HOT) stock type cam; but if you really want more power at the expense of part-throttle low-speed torque, then the ZZ3 is a better choice than the LT4 HOT cam.

<BLOCKQUOTE>quote:</font><HR>..... Oh, and the 1.6 rockers. I know the Crane Gold rockers work with our cars, but what about anything else? Anybody use those light Crower rockers?<HR></BLOCKQUOTE>

There are many people using roller-tip rockers, as well as full rollers, in bth 1.5 and 1.6 ratio. There are also 1.6 stamped steel self-aligning replacement rockers made by Sealed Power/Federal Mogul (the OEM rocker supplier to GM). Scoggin Dickey has the set of 16 listed at $65 using pn R1023R. The roller tip and full roller rockers have less friction but in terms of power you won't see much difference among them over the stamped ones until you are above 4000+ rpm.

<BLOCKQUOTE>quote:</font><HR> After the cam, the head work will begin. Maybe I'll do both at the same time, if I can scunge a pair of L99 heads to work on in the meantime. ..... Anybody know any good sources for porting info? Books, online, anything?<HR></BLOCKQUOTE>

The Chev Cylinder head porting book by David Vizard. The exact title escapes me, but the author's name is correct. It's around $16, and your best bet.

Post a new thread on the engine perf section, to get a discussion of the intake manifold going. A neighbor of mine has one on his car now, but he hasn't tested it properly on the track yet. He says he can feel a difference but he/I both know that people won't believe SOTP until they see it in a timeslip.

Getting a set of L99 heads to port is a great idea. - Ken
post #7 of 7 (permalink) Old 09-16-2001, 07:56 PM
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<BLOCKQUOTE>quote:</font><HR>I'd suggest the cheap approach first: get a takeoff stock N10 dual exhaust from any LT1 sedan 94-96 and install it with aftermarket mufflers, and using the LT1 dual cats and downpipes.<HR></BLOCKQUOTE>

One of the first things I did with the car back in '97 was put on a full Dynomax Ultraflow cat-back system. Since the L99 has dual cats anyway, I just ordered the one for the SS and it bolted right up. Just needed to add a hanger in the driver's side rear corner. It probably flows even better now than before since I've deleted the rear resonators that came with the cat-back and now have them exiting behind the rear tires.

<BLOCKQUOTE>quote:</font><HR>Finally, get onto any GM Perf Parts website (Scoggin Dickey is one) and look carefully at the pictures of the GMPP 350 Ramjet crate motor. Look closely at the intake manifold. It looks just like an L99/LT1/LT4 intake except that it is raised up with a larger volume inside it.<HR></BLOCKQUOTE>

Yeah, I have a GMPP account and have looked at the crate engines they offer, though until now I hadn't noticed your observation about the RamJet intake plenum. That's an interesting approach, and one that I handn't considered. Thanks for pointing that out. [img]smile.gif[/img]

<BLOCKQUOTE>quote:</font><HR>If I were you, I'd choose an F/Y LT1 or LT4 (non HOT) stock type cam; but if you really want more power at the expense of part-throttle low-speed torque, then the ZZ3 is a better choice than the LT4 HOT cam.<HR></BLOCKQUOTE>

Since I already have enough torque to the rear wheels to make the áss end go sideways from launch, I may consider a slight reduction in torque off the line an improvement in overall performance. I like the torque now but if I can launch better without having to feather the throttle as much, it may improve overall quarter time, whatever that is (Still waiting to borrow the G-Tech that my friend now has). I'm interested in your thoughts on this.

<BLOCKQUOTE>quote:</font><HR>There are also 1.6 stamped steel self-aligning replacement rockers made by Sealed Power/Federal Mogul (the OEM rocker supplier to GM). Scoggin Dickey has the set of 16 listed at $65 using pn R1023R.<HR></BLOCKQUOTE>

Hmmm...another option. I believe the stock springs will just work with the 1.6's, but at this point, with my car now 7 years old and as hard as I drive it, I should probably get something different in there. Weak springs will more than negate the added ratio. Maybe I can use these stamped rockers until I go full-boogie with the valvetrain. Thanks for the heads-up on that plus the book recommendation.
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