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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Greetings – this site is such a benefit to 3rd gen owners and has helped in numerous ways throughout the past. Thank you for all the assistance in the past and any that might be provided in the future.
I have a 1984 Z28 with a carbureted and computer-controlled L69 305; manual T5 and 3.73 posi rear. After 95,000 mi it is time to rebuild the engine. Most of the internals for a rebuild are straightforward, but the selection of a camshaft is proving to be quite a challenge. Note: the car must stay a 305 for compliance purposes. This car has to pass emissions.
Primary concerns are that the cam provide at least the performance the original L69 cam gave if not better, while not freaking out the computer or ruining drivability. I have read here that a lumpy idle for a 305 is not such a good thing, maybe a little rumble but not a lump like a full-out 350 or bigger sbc with a big cam.I want a fairly smooth idle, good vacuum for the brakes, and solid torque / low end jump for stoplight to stoplight performance.
The original L69 cam wasn’t bad for its day; to the best of my research the specs are:.202 I / .206 E @ 0.50 - adv dur at .294 I & E - max lift .403 I / .415 E with LSA 114.5.If this is incorrect, any corrections would be appreciated. As this cam is no longer available from GM, I am considering aftermarket replacements. I know it is best to avoid over-camming the small bore 305, and that is the challenge.
First I looked at the Edelbrock 2102 grind; .204I/.214E @ 0.50; adv dur.278/288 - .420I/.442E lift with LSA 112.This was not deemed a computer-friendly cam and I am concerned it will screw the ECU and might be too much for the 305 by ruining drivability and killing vacuum.
Second I looked at the Lunati grind 10120100LK; .204I/.214E dur @ 0.50 - adv. dur at .270I/.280E - lift .420I/.443E with LSA 112. Contrasting reports indicate this may or may not be computer compatible; it is a bit smaller than the 2102 grind but might still be too big. It might be good, but I just don’t know.
Finally I looked at the Comp Cams computer-controlled cam grind # 12-388-4. This is deemed a computer-friendly cam that should not aggravate the ECU, but I am wondering if this will actually be smaller or weaker than the original L69 cam. I don’t want to step the car down; I do want to maximize whatever potential the L69 setup has available. This cam has specs .206I/.212E dur @ 0.50 - .252I/.260E adv dur - .425I/.440E lift and 112 LSA.
I am totally lost as to what cam is the magic touch; I really don’t want to waste the time, labor, and money rebuilding this engine only to botch it with the wrong cam choice. Again, the car must remain a 305 so I have to get this right. I have searched through the forums but not found a definitive answer. Any help from the veterans here is much, much appreciated.
First of all - why do you believe it needs a rebuild at 95k miles? This would not be typical in my experience unless abuse or neglect was involved.
Second - yes the carb has a computer, but that is not what they mean when they speak of computer control with respect to cams. They are talking about EFI, and specifically what the cam does to intake manifold airflow and how this affects air flow sensors. With a CC carb, you don't have the same sensors so it really doesn't apply to you. You can use a normal cam grind without concern of confusing the carb computer.
Comp has a Dual Energy 255 that is 50 states legal and CARB certified for 87 and older. Similar but slightly better specs to your stock cam, good idle, broad power band, etc:
GD, great explanation. I will add that the ECM only controls idle and part throttle.
Beyond that it's in open loop mode and the engine relies on the jetting and calibrations of the carb itself.
Read - you can mess with this system and still pass emissions!
The Crane cams CompuCam 114132 is another choice also: https://www.summitracing.com/parts/crn-114132
First I looked at the Edelbrock 2102 grind; .204I/.214E @ 0.50; adv dur.278/288 - .420I/.442E lift with LSA 112.This was not deemed a computer-friendly cam and I am concerned it will screw the ECU and might be too much for the 305 by ruining drivability and killing vacuum.
Second I looked at the Lunati grind 10120100LK; .204I/.214E dur @ 0.50 - adv. dur at .270I/.280E - lift .420I/.443E with LSA 112. Contrasting reports indicate this may or may not be computer compatible; it is a bit smaller than the 2102 grind but might still be too big. It might be good, but I just don’t know.
Those 2 cams are ABSOLUTELY IDENTICAL IN EVERY WAY. The only reason they "look" different is because the advertised duration is specified at a different lift. They are also identical to the Summit 1102 https://www.summitracing.com/parts/sum-1102 for about half the price, one from A-Motion, one from Melling, and one from VIRTUALLY EVERY OTHER maker/seller of generic copies of copied generic cams over the last 45 or 50 yrs. I can't remember who came out with it first: it was one of a series of 4, that were aimed at engines in the 300, 350, 400, & 450 CID neighborhoods. That's the 300 CID one. Was very popular initially in 283s. While it's an "OK" cam for a 305, and a very slight step up from the stock L69 grind, it's not "competitive" in any sense of the word. It will cause no trouble with the carb ECM.
To give you some idea, I left the computer-controlled system that came on my L69 in the car when I put a 400 in it with a Comp 282 solid cam. It was a hassle at first getting it to idle right but apart from that, it was within the range the ECM and the rest of the system could cope with. The car passed TN emissions at the time (late 80s / early 90s... basically, new car specs, at the time), including the sniffer test.
The Comp XE256 and XE262 are well and widely known to be EXCELLENT choices for the L69. I would recommend the 256 if you're in California, the 262 if anywhere else.
Why are you "rebuilding" it? What exactly will this "rebuild" consist of? Why do you think it "must" remain a 305?
I agree with Sofa - why keep it a 305? Even in CA there is NO WAY for them to tell you have a 350 in it. They aren't going to care anyway as long as it passes the sniffer and all the equipment is in place. Just get a mild crate 350 and call it done. Rebuilding a 305 is really pointless and WILL cost the same as putting in a 350. Probably more than a respectable crate engine. Will take a lot less time also.
And you STILL haven't said WHY you think it needs to be rebuilt? 95k is LOW miles for an L69. What does it do/not do that leads you to this conclusion? You are here for THE BEST HELP right? We can give you that if you let us.
I do appreciate all the feedback GD, and I did submit a detailed response but it has not been posted; I figure it is because I am new and any post more than a sentence or two must be approved by a Moderator before going on the thread. I'll try again.
Firstly, thank you for responding and providing some very solid insight. As to the rebuild, I do apologize but I dropped a digit from my post in haste, mileage at 195K not 95; the engine does still run and was not neglected nor abused severely. It did have some compression loss upon cylinder testing and smokes a bit at startup, which I assume is valve seals. With the heads coming off for a valve job, it seemed prudent to just pull it and have fresh rings and bearings installed, a new oil pump, and a cam/timing chain as well. The engine has served well since 1984 and I was second owner as of 1990. Never been rebuilt, not even a valve job.
Thanks to all for the cam recommendations and the information related to how the carbed system operates with regard to cam change. I did know the system drops ECM control when off idle, but I assumed the wrong cam would trigger CEL if it varied beyond what the ECM was programmed to handle. Thank you Sofa for the illumination in this matter - if it could accommodate a 400 and not throw a fit then I am obviously in error with my assumption. I know a custom chip can be burned but would rather avoid brain surgery if possible. As to remaining a 305, a good part of that is budgetary constraints. I will look into the particulars as to other power plant options and the requirements involved.
I am looking at the Dual Energy cam as another option, but it is good to know that the cams mentioned will not confound the ECM.
Thanks again to all who replied. The info is appreciated.
Well if you are keeping the 305 then just do the valve job, toss in a new set of rings (don't hone it), and do the cam and new timing set. Don't worry about the oil pump and don't hone it or change the mains/rods unless they are damaged. And if they are STOP. Just get a 350 at that point. The proper machine work to bring that back (correctly) is way outside the cost of a crate motor.
Sound advice and the insight is appreciated. I will let the teardown guide the decision and determine if a rebuild is feasible. I am looking at the alternate option more closely. Much food for thought and a new perspective on the whole situation.
It's not really possible to "burn chips" for that ECM. At least, even if you could reverse-engineer the firmware, it's not really practical. It uses an old MC6805 series 8-bit chip with about 128 bytes of RAM and possibly 2k of ROM (might have only been 1k, can't recall which step in the product line it was). It's very simple and crude, and doesn't really do all that much. Not at all like EFI. And even at that, there's enough mechanical adjustment in the carb, that it's largely unnecessary anyway. Ignition timing is a different matter, but you can make a MAJOR improvement over stock by just twiddling the dist body to find the point at which it runs the best, making a note of what that setting is, and restoring it to near stock temporarily for the alternate-year ritual.
I would NOT TOUCH a 305 short block in any manner way shape form or fashion. Not rings, not pistons, not bearings, nothing. MAYBE an oil pump while changing the pan gasket but probably not even that. If the pan gasket doesn't leak, and the motor is still in the chassis, I wouldn't even touch that. But if it appears to need any short block work of any kind, I'd suggest you just get a cheeeep "crate" 350 and put your freshly reworked 416 heads on it. The inspection station doesn't look up casting #s unless they get suspicious for some other reason. Remember, they're lazy too, and get paid by the hour, they're not going to go out of their way without already suspecting that they need to. If everything that's supposed to be there is there and it all appears to be working (all hoses & wires are hooked up), everything that's not bone-stock has a CARB EO # on it, and the measured emissions are within limits, they'll just take your money and send you on your way.
I'd strongly suggest NOT running stock valve springs or any of that hardware with an aggressive aftermarket cam of ANY sort. For that matter, even on a stock cam, better springs can make a noticeable improvement at higher RPMs. Use Comp 981 springs and their retainers and keepers; leave off the oil splash shields and "rotators"; use Vortec "positive" type valve guide seals; and shim the springs carefully to 1.700" installed height. Don't depend on some corner parts store type of machine shop to set all that up for you. That's all stuff you can do yourself with a minimal investment in specialty tools.
I used a Summit K1103 with an LG4 and it ran good with the quadrajet setup until I saved up and changed to a Holley DP. Did have a bit of lope though so K1102 may be a better choice for you.
The CCC goes into WOT mode under full acceleration - the master control solenoid rises and strikes the rich stop (it’s adjustable by the way) that’s under the air horn , letting the primary rods go full rich. Timing goes to the low vacuum or WOT timing table as well. As previously indicated It’s in closed loop not just at idle but under partial throttle and cruising speeds. So you do need to pick a cam that pulls good vacuum to keep carb adjustments as simple as possible unless you’re willing to learn enough about them to tune what you can yourself.
As Sofa said, boxed “chips” do nothing more than bump timing a bit and maybe delay the lock up on the converter - you can tune these carbs and bump up the initial timing to run just as well without a "chip". I also can support what he said about how these carbs can be tuned to run on larger engines with pretty healthy cams. The largest and most HP engine I tuned one on was a 10.8:1 406 with a 239/249-110 solid flat tappet but it was a little tricky for me to dial in and I had tuned on 20 or more CCCs before hand.
Back in the day when I was installing cams in the L69s, my favorite, while keeping the stock stall (around 2000 rpm), was a high efficiency Lunati, 255/265 - 205/215 on a 112 spread. Next favorite was a custom grind 252/260 - 206/212 on a 110 spread with the Comp 260/260 - 212/212 on a 110 eventually being about as large as I liked to install - to keep carb adjustments rather simple.
One of the worst running with the stock converter and a little hard to tune was the Crane 272/284 - 216/228 on a 112 spread. I installed a couple Alliance cams back then, which were the same cam as the Summit 204/214 and 214/224 – 112s. The 204/214 idled rougher and never ran as quick as the 205/215 – 112 Lunati and I could say the same for their 214/224 cam compared to the largest cam I ended up installing, the 260/260 - 212/212 - 110 Comp.
The last cam I recommended and tuned on in a L69 just a few years back was the 254/262 – 210/218 - 111 Comp 4x4 (which is similar to those others have recommended). It idled about the same and was as crisp as the old high efficiency 205/215 Lunati I liked so much, but it pulled harder than the old 260 (212/212) Comp. It required minimal carb adjustments – idle mixture screws, air bleed, and idle speed (filed tang on the butterfly flaps and adjusted the spring tension and the throttle blade linkage for full throttle opening – most all do not open up all the way) http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=95&sb=2
I'll also DITTO Sofa on getting new springs. Plus, go ahead and get a decent timing chain while you're at it - the heavy duty Cloyes at $25 is hard to beat for the money. However, $10 more will get you a really nice multi-keyway, made in USA chain from Summit. https://www.summitracing.com/parts/s...0r-9/overview/
The CCC goes into WOT mode under full acceleration - the master control solenoid rises and strikes the rich stop (it’s adjustable by the way) that’s under the air horn , letting the primary rods go full rich. Timing goes to the low vacuum or WOT timing table as well. As previously indicated It’s in closed loop not just at idle but under partial throttle and cruising speeds. So you do need to pick a cam that pulls good vacuum to keep carb adjustments as simple as possible unless you’re willing to learn enough about them to tune what you can yourself.
Thank you BadSS - more great insight. I have heard that the Quadrajets can be 'swept up' - something to do with drilling out the fuel passages and increasing the potential dwell range by manipulating those controls. My experience has been limited to just getting the dwell to 30 deg. and setting idle speed/mixture to best idle. All I have is a dwell meter and a vacuum gauge - any other equipment I should look to get for tuning these carbs? Learning the dynamics of how the carb operates in action is appealing. At this point I would defer to someone with the experience to do it right, especially on an initial tune. Definitely the advanced class. I'm working to get there. Thanks again!
It's not really possible to "burn chips" for that ECM. At least, even if you could reverse-engineer the firmware, it's not really practical. It uses an old MC6805 series 8-bit chip with about 128 bytes of RAM and possibly 2k of ROM (might have only been 1k, can't recall which step in the product line it was). It's very simple and crude, and doesn't really do all that much. Not at all like EFI. And even at that, there's enough mechanical adjustment in the carb, that it's largely unnecessary anyway. Ignition timing is a different matter, but you can make a MAJOR improvement over stock by just twiddling the dist body to find the point at which it runs the best, making a note of what that setting is, and restoring it to near stock temporarily for the alternate-year ritual.
I would NOT TOUCH a 305 short block in any manner way shape form or fashion. Not rings, not pistons, not bearings, nothing. MAYBE an oil pump while changing the pan gasket but probably not even that. If the pan gasket doesn't leak, and the motor is still in the chassis, I wouldn't even touch that. But if it appears to need any short block work of any kind, I'd suggest you just get a cheeeep "crate" 350 and put your freshly reworked 416 heads on it. The inspection station doesn't look up casting #s unless they get suspicious for some other reason. Remember, they're lazy too, and get paid by the hour, they're not going to go out of their way without already suspecting that they need to. If everything that's supposed to be there is there and it all appears to be working (all hoses & wires are hooked up), everything that's not bone-stock has a CARB EO # on it, and the measured emissions are within limits, they'll just take your money and send you on your way.
I'd strongly suggest NOT running stock valve springs or any of that hardware with an aggressive aftermarket cam of ANY sort. For that matter, even on a stock cam, better springs can make a noticeable improvement at higher RPMs. Use Comp 981 springs and their retainers and keepers; leave off the oil splash shields and "rotators"; use Vortec "positive" type valve guide seals; and shim the springs carefully to 1.700" installed height. Don't depend on some corner parts store type of machine shop to set all that up for you. That's all stuff you can do yourself with a minimal investment in specialty tools.
Thank you Soda for the education - the advanced technical aspects of engine dynamics and rebuilding is beyond my limited mechanical experience and I am grateful for the information. This is all helping greatly and I appreciate it.
Perhaps my terminology is inaccurate; I thought aftermarket chips were available for the PROM that offered enhanced fuel/spark tables beyond what the original provided. Hypertech comes to mind. But as you point out, that is likely not necessary given the original provides what is needed in a carbed scenario and further tweaking is possible through the mechanical side of things. It seems that far more radical mods would have to be imposed to necessitate changing the PROM.
The alternate power plant option is intriguing; what concerns me more than the alternate year ritual is the growing trend for random checkpoints, the automotive equivalent of a roadside proctology exam. Wonder what the consequences would be if they found what they were looking for.
I have the 981 Comp springs down in my notes; thanks for the tips. With the 416 castings enhanced through valve upgrades to 1.94 int and 1.5 exh, some mild porting to clean them up, and the improved valvetrain components, the heads should be flow better than when they were new. I didn’t know you could drop those 305 heads on to a 350, but the 58cc chambers should provide a nice bump to the CR. Would the smaller bore combustion chambers of the heads coincide to the bigger cylinder bore of the 350 block? Would it pose no problem?
All this has broadened my perspective; much food for thought. I have some serious reading to do - this site is a treasure trove of information. Thanks to all who ventured some help.
The last year of the L69 was 88. That is now 31 car model yrs ago. 6 yrs past "antique" already. This somewhat limits the market for "stock upgrade" parts like that; since all 5 of the people who still own cars that such a thing would apply to, have either already bought them or never will due to long-term lack of interest, potential mfrs respond by doing absolutely nothing.
The computer in the L69 is incredibly crude. Think back to what your cell phone looked like in 1980, or the computer you were surfing the web with then. The computer in your car is no different.
Never seen a roadside exam where they would check casting #s. That would be amazingly impractical at best. Check for presence of a cat, yes; Check Engine light, yes; sniffer even, maybe. But... imagine the database you'd have to have access to, to contain every casting # of every casting for every year of every kind of car; and what a PITA it would be to actually find and view the # in a roadside traffic-stop situation. Now, I know that just because you're not paranoid, does not mean that they're not all out to get you; but that idea does strike me as bordering on paranoia. (I hope the listening chip the FBI & CIA implanted in my brain didn't just transmit that thought back to the black helicopters... excuze me while I renew my tinfoil hat lining)
When I lived out there I had 186 (69-70 high-perf 350) head castings on my car. However my whole L69 control system was intact, the cat was there, the car blew clean on the dyno, every non-stock piece had its CARB EO # (except the Edelbrock TES I had on it at the time... had to print out the list from Edelbrock's web site and take it with me). It sailed right on through. Nobody even looked, even though the double humps were right out there in the open for anybody to see. Might even have been identifiable in the video feed available to the CARB Big Brother dept that watches the shops. Block casting #s are MUCH harder than that to just spot while in a hot, running, driving down the road car.
Yes the 305 heads will bolt right up to a 350 block, no problem. The heads don't have "bore" so that's not an issue.
I had a 305 Vortec with a Lunati HE 268 flat tappet cam in a 1999 Tahoe I built fpr my brothers daily driver. 218/218 @ .050, .457/.457" lift, 110 lsa. It was a cheap engine refresh that I used to replace a 350 with a broken crank. Only reason I used that cam is I had it and the stock roller cam had a few lifters that had been locking up and had worn it noticeably across the ramps. Ran for 40K without an issue. Smoked the 4L60E in that truck.
Only reason I pulled the 305 out is to put a GM420 HP Marine cammed 8.1L and matching 4L80E in its place.
The little 305 ran for 6 months on a stock 350 PCM. Only thing I did at the time was drill a slightly larger hole in the throttle plate to bypass more air so that the IAC would work properly with the slightly lower vacuum. It would make about 14 in/hg in gear with the stock torque converter. Eventually I ditched the stock manifolds for 1 5/8" primary long tubes, ditched the tiny 1 7/8" exhaust tubing between the manifolds and the muffler with 2.25" pipe and swapped the stock cats out for 2.25" thunderbolt high flows. Someone had already swapped on a magnaflow muffler when we bought it. I also put a 4.3 S10 converter and tuned the PCM.
https://youtu.be/mqs1Q1eabek
This was one of the few times that truck saw WOT. Merging onto a tollway in a 75 mph zone on a short uphill ramp. Not the fastest with the heavy 20" wheels and P305/50R20 tires and 3.42 gear but also quicker than the video would make you think. 50 mph on the speedo was roughly 60 mph due to the OEM rear differential being a 3.73 ratio and the OEM tires being about 2.5" shorter. What it lacked in sheer torque it returned in fuel mileage. 1,700 rpm @ 70 mph would get 20-22 mpg highway.
https://youtu.be/3G5Vr_bcIaA
With all the stock 350 stuff on it except muffler it was making about 270-280 HP at the flywheel at 5,200-5,500 rpm based off the fuel injector duty cycle and flow rate. The stock 350s move about 200-210 gms/sec of airflow. The cammed 305 was moving 240-250 gms/sec.
... Use Comp 981 springs and their retainers and keepers; leave off the oil splash shields and "rotators"; use Vortec "positive" type valve guide seals; and shim the springs carefully to 1.700" installed height....
That raises another question I was wondering about. Can you mix and match components from different makers? Could I use the Comp 981 springs with an Edelbrock cam and Summit lifters? Is it best to use all components for the rebuild from a single maker, or is it OK to use a combination from different mfgrs??
Except the Summit cams are made in China.
Lunati has decent prices on cams (and offers same specs as Edelbrock). I have a Lunati cam in a smallblock Ford with Comp Cams lifters, valve springs, rocker arms, and timing chain.
My Firebird has a Comp cam...
Except the Summit cams are made in China.
Lunati has decent prices on cams (and offers same specs as Edelbrock). I have a Lunati cam in a smallblock Ford with Comp Cams lifters, valve springs, rocker arms, and timing chain.
My Firebird has a Comp cam...
The Summit cams are not made in China. They are made by the either Mellings or Federal Mogul/Sealed Power and boxed in a Summit box.
I have had both a Comp and Crower roller cam fail. The lobes literally started coming apart. Cast core JUNK. Went with a billet Comp toller this time. I guess time will tell how it holds up this time around.
I would not discredit the quality of a part just because it is chinese. The quality of some chinese stuff rivals anyone else including US built stuff. In fact in some cases the chinese stuff is better.
That being said my chinese cast and machined Assault Racing heads were beautiful and run great. My only complaint is they did not drill the face for the gasket locating tabs on a Vortec intake gasket. I decided not to use the factory style plastic/rubber gasket as they only last a few years and went with a traditional style paper gasket anyway. Other than that the machine work, fit and quality was very good.
I did not read though all these posts. But back in the mid 80s I did a lot of development on the L69 engine for showroom stock racing. These numbers was all with exhaust manifolds. The stock cam retarded 6 degrees worked best for racing. and would run at 260HP. I tested a comp 260 and 268 and a Lunati 270. also tried 1.6 rockers on the stock cam, they did not make anymore power compared to the oem retarded cam. The GM L82 Camshaft 222 450 460 114 installed at 114. Was the only camshaft with the exhaust manifolds that made the engine come to life on the top end. Lost 25ft lbs down low, but made 285 peak HP. Ran Very strong in the car with 373 and 5 speed. Hope this helps.
Now, I know that just because you're not paranoid, does not mean that they're not all out to get you; but that idea does strike me as bordering on paranoia. (I hope the listening chip the FBI & CIA implanted in my brain didn't just transmit that thought back to the black helicopters... excuse me while I renew my tinfoil hat lining).
"THEY" implant the chip when you get a colonoscopy on the way out!
The Summit cams are not made in China. They are made by the either Mellings or Federal Mogul/Sealed Power and boxed in a Summit box.
I have had both a Comp and Crower roller cam fail. The lobes literally started coming apart. Cast core JUNK. Went with a billet Comp toller this time. I guess time will tell how it holds up this time around.
I would not discredit the quality of a part just because it is chinese. The quality of some chinese stuff rivals anyone else including US built stuff. In fact in some cases the chinese stuff is better.
That being said my chinese cast and machined Assault Racing heads were beautiful and run great. My only complaint is they did not drill the face for the gasket locating tabs on a Vortec intake gasket. I decided not to use the factory style plastic/rubber gasket as they only last a few years and went with a traditional style paper gasket anyway. Other than that the machine work, fit and quality was very good.
I'm pretty sure the Summit cams are made in China. You are correct though that not everything made in China is garbage...
We have run Summit cams in more than 8 r 10 builds. 0 problems.
That's cool. I have a co-worker who is also running a Summit cam (Edelbrock specs - 204/214, 112 LSA, 107 ICL) in a 305 in his '84 Chevy pickup with no problems...
Edelbrock merely buys the same generic cam from any of a handful of companies that grind it, boxes it up, and charges twice as much for it as Summit does. "Edelbrock" has NOTHING WHATSOEVER to do with the "specs" of that cam.
Edelbrock merely buys the same generic cam from any of a handful of companies that grind it, boxes it up, and charges twice as much for it as Summit does. "Edelbrock" has NOTHING WHATSOEVER to do with the "specs" of that cam.
I know, I just meant that if someone were interested in an Edelbrock cam, they can get the same exact grind for less money from other brands...
09-19-2018, 09:04 PM
