Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

[Dennis K.]

Hi Guys,

I recently drove my L76 (30-30 cam) 1965 Coupe to the NCRS National Convention in San Diego. While there I ran into Duke Williams who graciously helped me to better understand the specifics of the 30-30 cam and to improve the performance of my engine and eliminate/reduce detonation. Duke suggested that I start a new post on the forum so that anyone else running a 30-30 cam might benefit from our experimentation and “tweaking” on the motor and setup. So here it is… I hope it may prove to be informational or helpful to others who are running the 30-30 cam in their car. First – a BIG THANK YOU to Duke Williams for all of his insight and assistance. Thank you Duke! Now - the background…

My Car Setup:

• 1965 Coupe with L76 Engine Option, close ratio 4-speed, and 3.70 Rear-end.
• “Blueprinted” 30-30 Cam installed (this cam was blueprinted by CRANE Cams’ lead cam grinder – CRANE was the OEM manufacturer for GM’s 30-30 cams from mid to late 60s).
• Actual compression = 11:1. This is the actual compression on the engine
• Engine bored .030” over; engine was machined and zero decked. All rotating assembly balanced. Each valve spring was tested/shimmed appropriately to ensure proper lift.
• Rocker Arms – running theoretical 1.5:1 ratio rocker arms (but with roller tips).
• Stock Holley 4-barrel carburetor (List 2818). (I have experimented with Jets – please read below, but currently run 77s in the secondaries and 70s in the primaries)
• Heads – I am running the later hi performance small block heads with the larger valves. For clarity, these are not the stock “fuelie” double hump heads. I am running the heads that GM installed on later Comaros and Corvettes with high performance cams. They have bolt holes on the front of the valve head and larger intake + exhaust valves. I have done some mild porting/bowl/blend work to match the heads to the block.
• Stock distributor with Mallory ignition (replaced the points with Mallory photo-optic unit). I am running a NAPA replacement vacuum advance can (model B28). The distributor and vacuum can was “dialed-in” on a distributor machine so that it is exactly as per GM spec for the car
  
• Compression is approx. 155 - 160 ft/lbs. on each cylinder.
• Valve lash set at .025” (tight) when engine is cold.
• I run 10w-40 Royal Purple synthetic motor oil.
• I typically run approx. 2.5 gallons of Sunoco Purple (110 octane leaded race fuel) per tank. The remaining 17.5 gallons in each tank is a “top-tier” 91 POM octane fuel from Shell or Chevron.

The NCRS Run:

1. San Diego to Santa Clarita (the base of the Grape Vine on I-5)
   
2. Santa Clarita to Los Banos (the heart of the CA Central Valley near Fresno)

c. Los Banos to SF Bay Area

Summary:
I am happy with the engine’s reduced detonation – and am grateful to Duke for his time and assistance. I believe that the reduced detonation to be the result of the tighter .025” valve lash. I think that I will continue to run 2.5 gallons of 110 octane race fuel in each tank. I may experiment with reducing the primary jets back down to 69s or 67s – and put a sniffer on the car to truly assess the carb mixture. I am still somewhat concerned about the increased engine temp and tendency to stall. I am looking into potential remedies like blocking off the cross over ports or even changing the fuel pump to try to remedy the stall situation. I may also play with the valve lash (changing it between .023 - .027) just to see how this affects overall engine performance and temperatures… Please let me know if you have any advice, thoughts, or observations in your own engines. I hope that my story helps others who are running 30-30 cams in their small blocks.

Thanks again Duke!

Cheers,
Dennis Kurimai
Member 33979

[Joe C.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

If you're using a stock Holley, List 2818, you should know that the stock jets are 65/76. I see no need for you to be running such big jets with your current build. If the engine is still lean, and still detonates with the tight lash (tantamount to bleeding compression at low engine speeds, and increasing duration), despite the doping with race fuel, then I'd look into the possibility of a carburetor problem.

I'd start by checking for the proper 6.5 power valve and ensuring that your floats are adjusted properly. Tie the heat riser wide open, and seal ALL gaps between the fan shroud and radiator with weatherstripping. Install a supplemental radiator seal kit used for SBC with air conditioning. You are probably using AC R45 plugs, correct?

DO NOT fiddle with the lash. Leave it right where it is. If you remember, this is where I told you to put it when you put up the first thread asking for help.

[George J.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

Dennis,
I, too, noticed a slight increase in temp when tightneing up the valve clearances to 0.022". Even though there was a fairly large increase on the temp gauge, by measuring with the IR gun it was only a few degrees. I drove the car last week in 90+ weather, stop and go, and it never was much over 200F, even though it was showing at the hash mark half way between straight up and full right. I can not hear any detonation, I'm running Shell 93 octane, 38 degrees wot timing, the roller tip rockers, like you, and 10.2 to 10.3 compression ration (measured), fuel injection, non-dated wires, 1100 to 1200 idle, etc.
One question, are you running the ignition shielding? I could never get a good idle with that on. Keep trying. If mine runs ok, so should yours. I do get a slight misfire, or hesitation, at part throttle cruise at 1800 rpms, but I probably shouldn't be running it that low, anyway. It just translates to 40mph and that is the speed on the road I most cruise on.

George

[Timothy B.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

I agree with post #2, there is no reason why you should need large primary jets in your carburetor. The 65-76 works good for the small block.

You may try to tune you power enrichment (power valve) to open at a higher vacuum reading as this will enrich the A/F ratio sooner when the engine is put under load. Take a vacuum gauge and check cruise vacuum and get a Holley power valve with a opening point 1-2" lower than the cruise vacuum.

Is the metering block the correct part # for the 2828 holley. When you replace the P/V check the power valve channel restriction to see the size of the holes. The size should be approx 50% of the diameter of the main jet. Example, with a 65 (.065) main jet the PVCR should be approx .033, on my 3810 Holley it's .039 so it's a little rich for what ever reason but better rich than lean.

[Duke W.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

The tighter lash, in addition to ensuring that the valves are picked up and set down at clearance ramp velocity, result in a slightly later closing inlet valve, which may bleed off enough compression to quell minor part throttle detonation.

Most California gasoline has 10 percent ethanol, which means the fuel has about 3.7 percent oxygen by mass. This can result in lean surge in some applications, so increasing main jet diameter by about 2 percent, which is about one size will usually help this situation.

Fuel percolation due to the lower mid range boiling characteristics of E10 gasoline is a problem for many, and the solution is to cool down the fuel lines and carburetor. Blocking the heat riser will certainly help, but it might also cause some warm-up driveabililty problems like start off stumble, which will be worst with the big cams.

With a 15 psi cap and a 50-50 mix of glycol/water the boiling temperature is about 265F, so running at 200-210 in hot weather is not a big problem.

I don't recall looking at your radiator, Dennis. Is it a "316" OE type aluminum radiator or something else? Also modern replacement fan clutches are set up to engage at higher temperature for later emission controlled cars with 195 stats, so they can cause hotter running in traffic than the original fan clutch that was set up for a 180 stat.

Glad to hear you are making some progress, Dennis. A closer look at your radiator and fan might help get the temps down, but 200-210 in hot weather won't cause any problems. Also, compare the gage temperature with an IR gun on the outlet nipple and the upper radiator hose. Some modern replacement temp senders are known to be inaccurate.

I recall a drive from Phoneix to LA back in August '67. It was well over 100 degrees and going faster - like about 100 MPH with the windows open - seemed to help keep me cool, but the temp gage rose to about half way between the center mark of 180 and the high mark, 240, so I suppose it was running about 210. Back then there was little I-10 freeway. Most of the trip was two lane road with very little traffic.

A month later I drove to Vegas, and Nevada had no daytime speed limit back then, so I cruised the 40 miles from the border to the strip at 130. I don't recall the engine temperature climbing during that jaunt as the outside temperature was cooler than the Phoenix trip, which was the only time I ever recall that my SWC ran hotter than 180.

Duke

[Dennis K.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

Hi Joe,

First of all - THANK YOU too! I forgot to mention in my post that you had offered some sage advice early on via the discussion boards. As for your analysis - I agree. My fooling around with the jets was an experiment during the trip which I am likely to revert back to (e.g. I was running 65/76 before the trip and will likely go back to these this weekend.). Power valve is a 6.5 (and I have run a test to confirm it is working properly) and the carb is the the Holley 2818. Floats are adjusted properly (according to the Holley tune-up guide for the 4150 carb - I *believe* that this is the Holley model for our List 2818 carbs - agree?) I too believe that your original suggestion on the valve is responsible for eliminating my detonation. I will leave it at .025". However, I believe that new heat is an unintended consequence of the tighter lash. I will tie the heat riser wide open and see what happens. As for the lean condition - I am starting to wonder if my "visual" analysis on the lean condition is inaccurate (e.g. I visually saw a "whiter" color around my exhaust pipes and my spark plugs were not the cocoa brown I expected - so I interpreted this as the car running lean... when in fact maybe it was not lean and this is just a trait of running leaded fuel).

Thanks again,
Dennis

[Dennis K.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

Hi George,

I do run the ignition shielding but have not witnessed the problem you have. I am running .025" lash as suggested by Joe and Duke. My detonation is mostly gone now... just heat is the issue for me. Gonna take out the IR gun and see what the REAL temp is vs. my car's gauge this weekend. Car ran hot on my way home in 95 degree temp... but it did not detonate (for the most part). My compression is an ACTUAL 11:1 (not theoretical). The engine block was machined this way (zero decked and compression calculated with the gasket under specific torque). I would prefer to run a lower idle (900 RPM) if I could... but based on what I am witnessing and recommendations from others... will likely keep it at the current 1100RPM.

Thx again,
Dennis

[Dennis K.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

Hi Duke,

I am running the stock radiator and fan (with clutch). Fan and clutch are functioning properly. I am running a 180 thermostat. I will wire open the heat riser valve as Joe indicated and see what happens. Also will be interesting to see what the IR gun reads this weekend vs. the car's gauge (which was rebuilt a few years back so it may be inaccurate as you suggested). I will also put the jets back to normal this weekend. All in good fun and experimentation...

Cheers,
Dennis

[Michael H.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

I still can't understand why anyone would want to adjust valve lash at anything less than the original recommended .030" for the GM 3849346 30-30 cam. Yes, I heard all the reasons but if someone that recommends much closer lash obviously never actually owned a car with the 30-30 cam in it. They run like a tipped over out house at .023".
I know I will now hear all the fancy numbers and reasons why .023" is best but I've owned/driven/raced too many cars with the 30-30 cam over the decades to buy that nonsense.

Dinky dyno table top computers with cam programs are not engines.

I bought a brand new 64 with a 365 HP and my engine ALWAYS idled properly at around 800 RPM. So did all the other cars I've owned over the next 40 years with that cam. Why is it suddenly necessary to have to set the idle at 1100 RPM? Or increase jet size? Or any of the other fancy trick of the week mod's.

That engine should run properly with the correct carburetor jetting. If it doesn't, something else is wrong.

[Dennis K.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

Hi Mike,

Thanks for the feedback. I can appreciate your perspective and experience - in the 60s these cars ran fine on the stock setup and the gas you could get at the pump (which I believe was 100-102 octane - albeit this rating was not R+M/2... suggesting that the octane was probably closer to 95-97 (?) under today's R+M/2 rating method)... So - "what is different today? Why shouldn't the car run perfectly with stock setup?" The only thing I can point to is gas. That is the ONLY thing that is different between yesterday and today. Admittedly, in my specific case - my engine is not "stock" - it is a blueprinted engine with "better heads" and a few extra tweaks (non of which in my opinion should affect its ability to run the same way the engine was setup in the mid 60s)... all of this was detailed in my post above... but for some reason my engine detonates. My efforts to identify the source of this detonation has been detailed in other posts.

So in answer to your question - I decided to tighten the lash to .025" because I was getting detonation at .030" and I had tired just about everything else. I consider all of the jet/spring changes I did just "noise"... and just experimental. The real change that reduced the detonation problem for me was the change in valve lash. If there is something "wrong" with my engine... I have yet to find it... and I have been looking for some time in all the places you would look for problems. You can read my prior posts. As for the engine running poorly with the valve lash at .025" vs. 030" (where I had it set prior to these changes)... I am not witnessing the drastic difference you are speaking of. My engine runs like a raped ape right now.... but then again I am not driving it on a track, so how do I know what I have potentially lost by setting the lash at .025"? The only way to validate your assertion would be for me to do back-to-back dyno runs (before and after a valve lash change). Conceptually - I understand how a tighter lash should reduce my power on the top end... but wouldn't it enhance torque on the low end for this cam? Given the type of driving I am doing in the car (e.g. street - not track)... I am having a hard time telling the difference before (.03" lash) and after (.025" lash).

I'm here to learn, have fun with my car, and help/meet others who want to do the same. I have no ego here. In fact - I would LOVE to find a way to run my car on straight 91 POM pump gas... without it detonating... and having it perform like a 30-30 cam engine should. I am starting to believe that with my unique engine that this might not be possible. As for now - my current setup is the best compromise I have come up with to date (2.5 gallons of 110 octane leaded race fuel... and a tighter lash at .025").

Cheers,
Dennis

[Timothy B.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

Dennis,

IMO, the tighter valve lash will make the motor run better up top and the .030 will allow more low end.

What's the idle vacuum at 900rpm? Give some thought to the power valve opening point as this will help that ping when the engine goes under load going up hills. All this will do is allow a richer A/F ratio sooner as the vacuum drops, the factory power valves are set to open at 6.5" so you may be able to use a 8.5 or 9.5" opening power valve. Just make sure the valve does not open when the motor is at cruise vacuum.

If the engine still detonates under load try to reduce the ignition timing, with 11-1 compression you may not need the timing to come in as quick.

[Joe C.]

Re: Tuning my L76 (30-30 Cam) 65 Coupe with Duke Williams

In response to post #6: "Floats are adjusted properly (according to the Holley tune-up guide for the 4150 carb - I *believe* that this is the Holley model for our List 2818 carbs - agree?)". Yes, the 2818 is a model 4500. The model 4500 has a secondary metering block, while the 4600 as used in 1966 and later SBC, have a secondary metering plate.

In response to post #10: "Conceptually - I understand how a tighter lash should reduce my power on the top end... but wouldn't it enhance torque on the low end for this cam? Given the type of driving I am doing in the car (e.g. street - not track)... I am having a hard time telling the difference before (.03" lash) and after (.025" lash)." Timothy is correct in that tighter lash will increase the engine's high speed output (horsepower), at the expense of bottom/midrange torque. The reason for this is that tighter lash increases the cam's duration and lift, and consequently, its overlap, which will lower idle vacuum. The net result of this is that the cam becomes "bigger", loses some low speed cylinder pressure but more than makes up for it in increased high speed cylinder pressure.

In response to some who believe that the 30-30 cam should be lashed at .030/.030...................this has been hashed and rehashed here, ad nauseum. The "short answer" is that the original design spec on that cam called for lash to be set at .025/.025, but the lash was increased later on, as a "band-aid", to address customer complaints of erratic idle with fuel injected cars, which are extremely sensitive to idle vacuum.

I have considerable experience with the 30-30 cam. Here, I must disagree with Tim about choice of power valve. Your engine most likely cruises at about 14-15 in-hg on a dead level surface and steady speed. Calling for a PV that cuts in at 2 in-hg below this, or 12 in-hg is not right. There's no reason to change out PV, and this only masks a problem elsewhere. I'd leave it at 6.5 if I were you. The only reason that bigger jets might be called for, is if you drive your car at high altitudes. I don't know whether or not you mentioned this before. If you do, then going from 65/76 to 67/78 would be helpful, while leaving the PV at 6.5.

Your engine, if properly set up at .025/.025 lash, should idle at 900 RPM and develop about 8 in-hg vacuum at that speed. There should be no reason, if everything is adjusted right, for you to be idling at 1100 RPM with a carburetor.

The motor should not be detonating, at all. You can probably rule out carbon in the chambers if the motor was rebuilt within the last 10 years or so. I'd check the timing, carefully, with either a dial-back timing light, or, better still, with a Mr.Gasket degree tape fastened to your harmonic damper.