[Jay S]

You will go crazy with a stock 600 vac looking for power making engine changes. Out of the box they are only jetted for about 275 HP. That is the power level that has worked best for us with those carbs.

[steve25]

So you did a cranking compression test with all the other plugs in?

If so then now you have to do that test again or make a leak down test before you say that removing the heads is needed.

Be sure to kill the power to the HEI before making these test.

[Holeshot71]

Once you get the compression sorted you should definitely get that cam advanced. The 60916 needs to be advanced most likely 4 deg to a 108 intake centerline for best performance.

[Dragncar]

This engine, its kinda like he has different thickness head gaskets on each bank or something. The difference is strange.
600 Holley I would not waste my time with it.
A 3310 750 could be made to work well. At least you could tune it and the secondaries could be set up to come in as needed and not bog.
Or a real Holley 650 DP would be sweet too. I think I have one that somebody overtightened a base bolt with a thick gasket and snapped the ear off. Needs a new baseplate.
You do not see them a lot anymore. But, back when all us kids Hot Rodded everything we drove (the good ole days !) All the young guys with their 350s in their Camero's wanted one.

[PunchT37]

Originally Posted by Dragncar

This engine, its kinda like he has different thickness head gaskets on each bank or something. The difference is strange.
600 Holley I would not waste my time with it.
A 3310 750 could be made to work well. At least you could tune it and the secondaries could be set up to come in as needed and not bog.
Or a real Holley 650 DP would be sweet too. I think I have one that somebody overtightened a base bolt with a thick gasket and snapped the ear off. Needs a new baseplate.
You do not see them a lot anymore. But, back when all us kids Hot Rodded everything we drove (the good ole days !) All the young guys with their 350s in their Camero's wanted one.

Yep. A buddy of mine has a’68 dart with a 340. 230/236 cam. I have tried 3 Holley carbs on it. 650 dp, 700dp and 3310. It likes and starts better the best with the 650. It’s a Dodge, but…

[steve25]

Call me nuts, but I fail to see correlation as to how a certain size / cfm carb will start an engine better cold then another size carb if there both set up right .

[PunchT37]

Originally Posted by steve25

Call me nuts, but I fail to see correlation as to how a certain size / cfm carb will start an engine better cold then another size carb if there both set up right .

You’re not. These were out of the box. The 650 had the best factory idle circuit for this motor.

[Dragncar]

Originally Posted by PunchT37

You’re not. These were out of the box. The 650 had the best factory idle circuit for this motor.

340 is a pretty small engine with a short stroke. Its going to move air faster though a smaller venturi like the 650 DP has.

[HWYSTR455]

I can attest to the smaller carbs having better idle and off-idle drivability. Cold warm-up too.

On my Olds 350, the 670 avenger was great, but it flattened out around 45-4800 RPM.

I switched to a 770 and it pulled past 6000, but idle and drivability suffered.

There was really no in-between, and with the 670, as I would go into higher altitudes, it would lean out and overheat.

So I switched to a Holley Terminator throttle body setup. Problem solved. I'm sure timing control had some to do with it too.



.

[ericwoo]

Originally Posted by steve25

So you did a cranking compression test with all the other plugs in?

If so then now you have to do that test again or make a leak down test before you say that removing the heads is needed.

Be sure to kill the power to the HEI before making these test.

Originally Posted by Jay S

At very least you need to do it again before make any conclusions.

I had a Pontiac that the factory deck machining height was off .018” between banks.

So I adjusted the valves again just to get the hydraulic lifters to zero lash, then tightened 3/4 turn. Then tested the compression a 2nd time with the below. Took all the spark plugs out and the engine warm. Overall, the readings seems to be similar +/- 5 psi. (not sure how precise my old gauge is)

Driver side head
# 1: 155 psi
# 3: 160 psi
# 5: 155 psi
# 7: 158 psi


Passenger side head
# 2: 195 psi
# 4: 194 psi
# 5: 200 psi
# 8: 187 psi

I am ordering a leak down tester to see if there is leakage in that driver side head. Hopefully I should get that complete early next week.

The next thing I realized, is the pushrods are indeed a little too short. See the test I did in the attached photos

Passenger Side


Driver Side

[steve25]

So your saying your 350 Olds fitted with a 670 cfm avenger flattend out above 4800 due to lack of CFM / being too small for that motor?

I would like to refer you to a dyno test done on a factory Tripower built up 421 that made 475 hp, yet still made 350 hp up at 5500 running on just its center 2BBl !!

A gotta say for sure you had something going on with that 350 Olds that was cutting into power above 4500 ( like jetting ) but it sure was not CFM.

The poorer idle of that 770 was likely due to the idle air bleeds needing to be changed I would say .

[steve25]

Why bother shelling out money for a leak down tester?
Your to the point now of having to pull both heads to find out what’s going on at least in my mind.

Even if you did a leak down tester and it pointed to valve leakage, then you’re still yanking that head at that point anyway.

You lower compression on that bank is so even that I can’t see it being due to rings, so that leaves the head as the cause.

[ericwoo]

Originally Posted by steve25

Why bother shelling out money for a leak down tester?
Your to the point now of having to pull both heads to find out what’s going on at least in my mind.

Even if you did a leak down tester and it pointed to valve leakage, then you’re still yanking that head at that point anyway.

You lower compression on that bank is so even that I can’t see it being due to rings, so that leaves the head as the cause.

Good point, but wont the leak down tester show me if its leaking out of the head gasket vs the valves so I know what to fix when removed? I've never used a leak down tester- just looking into stuff I read online.

If it's a valve leak, is that most likely the valve stems that need to be replaced?

[Joe-Touring]

Originally Posted by ericwoo

Good point, but wont the leak down tester show me if its leaking out of the head gasket vs the valves so I know what to fix when removed? I've never used a leak down tester- just looking into stuff I read online.

If it's a valve leak, is that most likely the valve stems that need to be replaced?

Does your compression tester have a quick disconnect on it between the hose and gauge? A lot of the comp tester hoses have what’s essentially an air compressor fitting on the end.

All you’d have to do is screw your comp tester hose into the head, and hook up your air compressor hose to it. Then you can listen to the intake/exhaust manifolds to see if you can hear air rushing out

[johnta1]

The next thing I realized, is the pushrods are indeed a little too short. See the test I did in the attached photos

Do a test with the driver's side head rockers. Back them off 1/2 turn and see what the compression test shows for that side?

[Schurkey]

Originally Posted by ericwoo

I am ordering a leak down tester to see if there is leakage in that driver side head. Hopefully I should get that complete early next week.

There's a hundred companies selling leakdown testers for automotive use, and NONE of them are trustworthy...until you've either confirmed them with a Master Orifice, or you've tested known-good cylinders of the same approximate bore diameter as what you have. If you test enough engines, with enough different bore sizes, you can have a good idea of how your leakdown tester works--but the Master Orifice is WAY faster.

There are no "industry standards" or legislation/regulation of automotive leakdown testers. They build whatever they want, and depending on how they're built, they can give WILDLY different results on the same cylinder.

However, the FAA has standards for AIRCRAFT piston-engine leakdown testers, and the ones suitable for 5" bores and smaller aircraft engines are also suitable for automotive engines.

Even better, Continental/Teledyne came up with the "Master Orifice", a calibrated leak that is the equivalent to the MAXIMUM leakage allowable in their engines. You'd plug a leakdown tester into a Master Orifice, note the reading. Then if the engine has less leakage than the Master Orifice, it's considered "good". My standards are higher than that, so I only allow about 2/3 the leakage of the C/T Master Orifice, and only then if it's past the rings--not past the valves, or into the cooling system.

I bought an aircraft-spec leakdown tester with a built-in Master Orifice a dozen years ago. Very recommended. It normally ships with an 18mm cylinder adapter, they'll supply a 14mm automotive adapter on request...or buy several sizes and be able to do motorcycles and old Fords and Mopars.

https://www.aircraft-tool.com/detail?id=2EM

Originally Posted by ericwoo

The next thing I realized, is the pushrods are indeed a little too short. See the test I did in the attached photos

Passenger Side


Driver Side

The first witness mark isn't readable, the second one is not bad, but wider than optimum. Adjust the pushrod length to minimize the sweep (narrowest pattern) even if it's somewhat off-center on the valve tip.

[Schurkey]

Pumping compressed air into the cylinders without a leakdown tester is ABSOLUTELY FINE for testing valves, head gaskets, and looking for cracked castings. Because the only acceptable result is ZERO leakage past the valves, into an adjoining cylinder, or into the cooling system.

Evaluating leakage past the rings requires gauges to measure the leakage. There will always be "some" leakage past the rings. The crankcase/lifter valley/valve covers are gigantic echo-chambers, small leaks can "sound" like big leaks, big leaks may--or may not--sound all that huge.

I would NOT loosen or remove the rockers--at least at first. If you have no leakage past the valves, you're set. Assess the leakage past the rings, into the cooling system and adjacent cylinders, and move on. If you do have leakage past the valve(s), then you can loosen the rocker(s) on that cylinder, which may or may not confirm that the lifter preload was set too tight.

If you loosen the rockers first, you'll never know that the lifter preload was/wasn't correct.

[tom s]

Are both heads 6500?Tom

[steve25]

As you disassemble on that bad side here's what you can look for.

Pull the Intake and look into each Intake port, if the bad compression side looks blacker and soot coated then the good bank then you have leaky Intake valve seats and that head then may needa valve job done and or have the valves trued up along with a valve job done.

[ta man]

Are both heads part number 6500?