65tripleblack

The engine harness splits before it reaches the battery with part of it heading down to the starter. I broke into the downward heading branch of the harness up high, right after the split and installed a spade connector onto the purple wire going to the solenoid. I leave that spade connector exposed all the time but you can tape it back into the harness if it bothers you and un-tape it every time you need the remote switch. Jump the purple solenoid wire that you broke into to the positive battery terminal with the battery cutoff switch (if you have one) closed.

Since there is some pushback on the lash as I expected, then you deserve to know why GM changed the lash setting from 25 to 30. The short answer is that the 346 was simply TOO MUCH cam for a street engine, so they had to tame it (viz.: "de-tune", or "emasculate") by widening the lash. Widening the lash in effect decreases the valve lift as well as decreasing the duration which also decreases the overlap.

GM was forced to do this because the fuel injected engine wouldn't run with .025/.025 lash..............the cam wouldn't develop enough vacuum at idle to enable the Rochester unit to function.

I suggest lashing them at .026/.026 which is a good compromise. Frankly, I have tried all settings and I think .023/.023 is too tight and driveability does suffer at that setting. I would idle it @ 850-900, which always worked best for me. That cam sounds nice but frankly, it is an antique and EXTREMELY inefficient. I would never build an engine for myself and use that cam. You can boost torque very effectively by increasing the static timing from the recommended 10 degrees. There is so much wasted compression at low engine speeds as a result of the very lazy valve action, that I have been able to increase the static timing from 10* to almost 20* without detonation. The effect on throttle response is dramatic. Give it as much static as it will take, and listen for detonation! If you hear any, back off 2 degrees at a time until it goes away. IMPORTANT......IF YOU DO THIS THEN YOU WILL HAVE TO LIMIT WOT SPARK ADVANCE BY THE SAME NUMBER OF DEGREES THAT YOU ADVANCED THE STATIC FROM FACTORY SPEC. THE ENGINE OPERATES BEST WITH BETWEEN 37 AND 40 DEGREES TOTAL TIMING WITH THE VACUUM ADVANCE DISCONNECTED AND PLUGGED.

Critter1

In one paragraph, you're saying that the 346 cam has too much duration.
In another paragraph, you're saying the lash should be set even tighter than the recommended .030"!

Just exactly what do you think setting a tighter lash does? Make up your mind!

I know this to be true. 98% of all 64-65 Corvette owners are a lot better off sticking to the recommended .030" lash setting. Maybe 99%.

If an owner wants his 64-65 365 HP to SOUND a lot more powerful, but be hopelessly slower on the street with stock exhaust system, then your recommended setting will deliver those results.

65tripleblack

Ya know, yer reading comprehension is lousy.
Try readin' it a few more times.
Don't worry, yer a pretty fart smeller so you should get it.......eventually.

gsholz

I have done a few valves using EOIC. Unless I'm doing something wrong, it turns out my valves were way too tight, between .006 and 0.010. The lash probably was not set during the last 10 years. But would it tighten up that much?

Frankie the Fink

Highly doubtful - sounds like to me somebody set them for the "tighter" "weekend racer" specs of the Duntov 097 cam not the 30/30...

gsholz

Well, I fired her up and she sounds fine. More mechanical but not diesel like. Exhaust note has changed too. I'll have to take her for a spin once the darn rain stops.

Thanks for all the help

65tripleblack

In your first post you stated that the engine can idle @ 550 RPM. A 30-30 cam will not idle at 550 RPM and with the lash set THAT tight it won't idle at 800 either. How long have you had this car? It sounds to me like you don't have the 346 cam. It could very well be the 097 installed. What is your vacuum @ 850-900 RPM?

gsholz

I had the car for 5 months. It is supposedly numbers matching, 1964 L76 365 hp, 97,000 miles, one repaint in factory color in the early 90s, NCRS Topflight award in '94. Little use since then. Still looks very nice and original.

So far I have not found anything to contradict that it has the original engine. I'm also not aware of any rebuilds at least since late '80s. No records from before that.

But could someone have swapped in a different cam at some point, maybe. But my guess is one would not do it and go through the effort to get a Top Flight award. The engine does seem to really wake up around 4500 rpm which fits an L76.

Is there any way to check short of taking the intake off?

I'll get the vacuum reading tomorrow.

jerrybramlett

Over the past ten years I've made hundreds of Dynojet chassis dynamometer pulls from 2,500 to 6,000 rpm with 30-30 cams in various fuel injected, 327-powered ~3,000 pound Corvettes. These runs have been made at sea level using stock exhaust systems, 1/8" domed pistons, 35 psi air in the rear tires, 3.70 or 4.11 rears, fourth gear only, ~180 degree water temperatures, and VP 110 racing gas.

Peak horsepower has usually been 250 - 260 at the rear wheels. The highest horsepower I've seen is 265. The hp peak is always reached at about 5,700 rpm. The air/fuel ratio on the strongest pulls was ~13.1 to one. I've never dyno-tested the tighter valve lash settings recommended on the internet because of the unreliable idle and off-idle bogging it causes with FI on the street.

I use .030" (or more) lash straight across because that gives a steady 11" - 12" of manifold vacuum at 850 rpm. I set the distributors to have 36 degrees of total advance at high rpm under full throttle. Using 34 or 38 degrees of total advance reduced peak power by ~5 hp in back-to-back pulls.

Some aftermarket cam grinders sell "30-30" cams that they consider "upgraded designs". These require even more than .030" lash in order to eliminate the off-idle bog with FI.

I realize I'm leaving myself open to trash talk by even mentioning the results of my dyno pulls, but that's okay. I'm just too old to care. Go ahead and tell me about all of your better results with tighter lash settings. No computer simulations or seat-of-the-pants readings, please.

Critter1

Good info. Thanks.

I'm sure there will be a few comments real soon.

MikeM

No trash talk here but I'd love to see results on a chassis dyno with a stock FI 375 engine and open exhaust headers. Don't care if they're cheap ones or the high dollar tuned ones.

SWCDuke

What type to dyno? Was the RW data observed or corrected. If corrected what correction type was used. SAE? STP?...

Without full data context it can't be compared with other data. The default should be a Dynojet inertia dyno and SAE correction.

Duke

gsholz

I took the car out after adjusting the valves. Wow. It is like a different engine. I thought it was running fine before, but this is a different ballgame. Pulls well, revs nicely, kicks in above 4000 rpm. Sounds good. I really like it.

Came back and checked the vacuum after adjusting the idle mixture. Well, first surprise was that the connection on the 2818 that goes to the distributor vacuum can is for ported vacuum, producing 0 inches HG at idle.

I switched the gauge over to the brake booster and found 17 inches HG. Obviously not a 30-30 cam. I wonder what I have. It really liked the valve adjustment (I set them at .026").

jerrybramlett

Duke, please post up your 30-30 cam dyno results before we jump down into the weeds and wallow around.

Jerry

SWCDuke

Thirty over '65 L-76, all OE equivalent other than massaged heads, 10.5:1 measured CR, 38 deg. total WOT advance, VS677 OE replacement valve springs shimmed to .090-.100" coil bind clearance at full lift, valve clearance .023", 290 SAE corrected RWHP @ 6500, 270 lb-ft @ 4500 on a Dynojet 248... about 10 HP rolloff at 7200, and a big drop at 7250, which was probably the point of incipient valve float.

Massaged heads typically increase top end power by ten percent and raise the torque and power peaks by at least 500 revs.

So can you answer my questions now?

Duke

jerrybramlett

The Dynojet I rent was bought from Dobeck back in the nineties. It was one of the first in Mobile and looks like a 248, but I've never noticed a model number on it. The correction factor I use is STD (or STP as you call it). Because I'm at sea level and normally test in the early morning when it's 60 - 80 degrees, the correction factor is seldom significant. Tire pressure, placement on the drums, hood position, and rear end ratio make more of a difference than humidity, temperature, and atmospheric pressure for me.

Your numbers are impressive for a stock exhaust system.

Jerry

wmf62

Jerry
some people 'know' what they're talking about, and some people 'think' they know what they're talking about..

I've tried the 'tight valves' thing and regretted it; a BIG loss in drivability...

Bill

MikeM

Sometimes in the pursuit of excellence in engineering, you lay a goose egg.

Wonder if anyone has a dyno graph of "average" torque from 1500 through 6000+ rpm using the valve lash settings as specified in the service manual vs the theoretical?

My '69 Z 28 would turn the tires halfway through low gear when set where the service manual says. Way before there was an internet, somebody told me the "real" spec was .'025 and to set the valves there. I tried it and almost would stall the engine taking off at high rpm. It'd turn the tires about a round and that was it.

wmf62

yep, and some are 'goose eggs'; just remember, there are people that graduate Summa *** Laude and some that are lucky to just graduate....

Bill

MikeM

Nothing to brag about here. I'm just your ordinary deplorable.