[track73]

I would try some Rhodes lifters.

[PontiacHO]

Run thru the valve adjustment first just for eliminating the valves too tight on one side. Run a compression check again on that weak side. If that doesn’t reveal anything (and it probably won’t) you’re on your way to removing the heads anyway.

[se428bandit]

Are you using the 2bbl throttle bracket? I use one on my 1970 Lemans and it was getting but 1/2 throttle, just enough to crack the back barrels on my Q-jet. I didn't read through all the comments but what gear and stall are you running. My Ventura with the stock convertor would run 9.80s in the 1/8, changing it to a tight 10 inch convertor picked up to a 9.24 with a 3.23 gear with a 8.4 comp 350, 068 cam adv 4 degrees, stock 4 bbl intake and a Q-jet.

[HWYSTR455]

Originally Posted by 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 .

I drove that car on the Power Tour, and when going over some mountains it was overheating. The Holley crew stopped and we jetted it up by 4 sizes to control it, but once I came out of the elevation it was pig rich.

I juggled jets in that car well before going on the Power Tour, and no matter what I did it was never 'right'. Even the Holley guys made comments and suggested going to the 770.

It may not have been due to CFM, but the Holley guys recommending the 770 made me think it was.

My 1/2" fuel line thread was based on that car, so delivery was not an issue, for sure.

It had #5 69 heads on it that were ported.

The tbi setup allowed me to tune it all out, wasn't going to waste time with elaborate tuning of an off the shelf 'budget' VS Holley.



.

[steve25]

Oh I see .
Your comment just seemed odd to me because I know you know better.

[PontiacHO]

Oh I see .
Your comment just seemed odd to me because I know you know better.

If that is for me then maybe you can educate me….

If the lifter preload is adjusted too tight it will cause poor performance and possibly less compression due to valve not seating as it should. I’m sure the op has an adjustable valvetrain with aftermarket heads.

[HWYSTR455]

I honestly believe there was some type of casting defect or whatever, and there were known problems with the Avenger carbs at the time, specifically the 670s.

I went thru all the passages poking them w safety wire, but never really found a smoking gun.

I had an 870 on my LeMans, and that ran very well.

I suspect if I would have stuck with diags of the 670 I could have got it running right, but I had spent so much time on it already I was done. It just shouldn't have required that much effort IMO.



.

[steve25]

No, I was referring to HWYSTR455 with his misfit Avenger carb.

[PontiacHO]

10-4 Steve. Thanks for helping all of us here with these Pontiacs.

[chiphead]

Originally Posted by ericwoo

[*]Kaufmann KRE 65 cc D-port heads- they are supposed to be milled down further to get compression around 10.1-10.5 but I never confirmed it was actually done. Valves are 2.00/1.66
.

In light of the compression results, this is what the kids of today would call super-sus, bruh.

65CC chamber would give about 9.75CR. A 58 CC chamber would give 10.56. Assuming a 30 over 350 with .015" deck height. 3/4 point of compression difference would yield approx those pumping numbers.

Do not pass go, do not waste time on a leakdown, pull both heads and CC the chambers. A leakdown may help confirm condition of bottom end, but I don't think it's the root cause of what's going on here. It would appear that one head got milled and one didn't. Where did these heads come from?

[ericwoo]

Originally Posted by chiphead

Do not pass go, do not waste time on a leakdown, pull both heads and CC the chambers. A leakdown may help confirm condition of bottom end, but I don't think it's the root cause of what's going on here. It would appear that one head got milled and one didn't. Where did these heads come from?

Originally Posted by PontiacHO

Run thru the valve adjustment first just for eliminating the valves too tight on one side. Run a compression check again on that weak side. If that doesn’t reveal anything (and it probably won’t) you’re on your way to removing the heads anyway.

Originally Posted by 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.
.

Ok this is what I found out with the leak down test. Air is coming out of the valve cover breather on the Driver side but not the Passenger side. From what I am reading, that would be worn piston rings, correct?

A while back, I do remember seeing surface rust on steel components when I took off the valve cover. I was thinking a little bit of water must have seeped through the valve cover gasket when I degreased the engine compartment. I wonder if surface rust developed on the piston rings and cylinder, ruining it. However, I do not remember the engine producing much more power before washing the engine either.

I will never understand the engineering of Pontiacs poor valve cover design with the 4 bolts. I always had issues with sealing them to prevent oil coming out.

Originally Posted by tom s

Are both heads 6500?Tom

Yes, I just confirmed both sides say 6500

[Green Elephant]

Lots of good suggestions by others. In my mind the compression difference from bank to bank is a big red flag. Particularly with all the cylinders being so close to each other on each bank.
I think I saw Jay S mention something about an improperly milled deck height. I’ve seen this before, machine shops do make mistakes. Unless you checked it on assembly, I would check the deck height on both sides when/if you pull the heads. Even if the block wasn’t milled by the machine shop, I would check it anyhow. It’s very easy to do with the heads off and will verify if there is a problem.
Pistons will need to be at absolute TDC to check. Piston tops will also need to be clean (no carbon) and you’ll need to measure at the center of the piston to eliminate any piston rock in the bore. Any good machinist friend should have a depth micrometer, you can also use a caliper but it’s very easy to tilt those at an angle and get an improper reading.
It could be the cylinder head chambers too, as others have suggested. CC’ing the head chamber should tell you that.

[Schurkey]

Originally Posted by ericwoo

Ok this is what I found out with the leak down test. Air is coming out of the valve cover breather on the Driver side but not the Passenger side. From what I am reading, that would be worn piston rings, correct?

Maybe. I don't understand why one side of the engine would have blowby pressure but the other side doesn't. However, "air coming out the valve cover" could be TOTALLY NORMAL. Kinda depends on the volume of blowby--there's always going to be some.

What are the gauges on the leakdown tester showing? Do you have a Master Orifice to provide some feedback on what is acceptable? If not, you need to test some known-good cylinders of about the same bore diameter.

You don't have "breathers" on BOTH valve covers...right? Is there a properly-functioning PCV system on this engine?

Originally Posted by ericwoo

A while back, I do remember seeing surface rust on steel components when I took off the valve cover. I was thinking a little bit of water must have seeped through the valve cover gasket when I degreased the engine compartment. I wonder if surface rust developed on the piston rings and cylinder, ruining it. However, I do not remember the engine producing much more power before washing the engine either.

One of the main byproducts of combustion is water vapor. Blowby puts that water vapor into the crankcase.

If the engine is running, there's no "surface rust" on the cylinder walls.

Originally Posted by ericwoo

I will never understand the engineering of Pontiacs poor valve cover design with the 4 bolts. I always had issues with sealing them to prevent oil coming out.

Bolts cost money. So do drilled and tapped holes. You want GM big-shots to give up their bonuses so you don't have oil leaks?

[steve25]

So let me get this straight!

Any cylinder you leak down test on the low reading bank of cylinders will produce air being heard coming up out of the crankcase with the valve cover off?

If this is truly the case then each cylinder in that bank could have busted rings and or Pistons.

Once again as I and many others have posted a few times, its high time to pull that head!

Busted rings and broken ring grooves in the Pistons will leave scratchs and even grooves on the cylinder walls

[Formulas]

Originally Posted by steve25

So let me get this straight!

Any cylinder you leak down test on the low reading bank of cylinders will produce air being heard coming up out of the crankcase with the valve cover off?

If this is truly the case then each cylinder in that bank could have busted rings and or Pistons.

Once again as I and many others have posted a few times, its high time to pull that head!

Busted rings and broken ring grooves in the Pistons will leave scratchs and even grooves on the cylinder walls

They also smoke like a forest fire, no mention of smoke being an issue yet.

pressurizing cylinders with shop air with a novice ear and inaccurate tester means relatively nothing, air will escape you will hear it in a healthy engine, .. what matters is an accurate percentage reading then if that is to high you then care if its valves or rings by the audible

[Stan Weiss]

If the problem is rings, What are the odds that 4 out of 8 cylinders have ring problems, and all 4 of those cylinders are in the same bank?

Stan

[Green Elephant]

Hey ericwoo, not to pile on with too much information, but if it was me, this would be my plan of attack. Pull the engine, remove heads, have someone cc the chambers, check deck height as suggested below, check compressed head gasket thickness and p/n. Somewhere in there I think you’ll find the culprit for the bank to bank compression disparity.
While the engine is out you can re-degree and advance the cam as others have suggested, or go with a different cam based upon the whole combination, (still degree it in though, it’s not as difficult as it sounds and you’ll be learning something new and getting a better understanding of your engine while you do it). Re-degreeing your cam will also wake up any potential missing power.
It’s up to you but I would also pull the pistons and rods and check everything over to see if the rings and cylinder finish are sound. Check the rod bearings as well and see what they are telling you.
I know, it sucks going backwards, but the outcome should be far better if you take all the advice from everyone here and apply it to the final product.
If you haven’t switched it out already, I would also go with a Q-jet rebuilt by Cliff Ruggles or one rebuilt with his suggestions. If I remember correctly the Performer RPM is a spreadbore manifold, so a Q-jet would be a better option IMO.
Dial in the timing, make sure you have no vacuum leaks and enjoy the results.
With 3:55 gearing your Firebird should run pretty good. I think Pontiac produced a 326 HO Firebird in 67 that put out 320 hp and I’m sure those were pretty spunky rides. Best wishes.

[chiphead]

Originally Posted by Stan Weiss

If the problem is rings, What are the odds that 4 out of 8 cylinders have ring problems, and all 4 of those cylinders are in the same bank?

Stan

Keep in mind all 4 on each side are consistent. One side is 150-160 and the other side is 185-200 PSI. Usually when you have a damaged cylinder or gasket, two adjacent cylinders are really low and the others are much higher. A damaged set of rings shows high leakdown and compression numbers in that hole only. The other cylinders are usually consistent and higher. Even a nitrous type failure only kills a hole or two unless it throws parts into the grandstands.

Having one side consistently at 150 and the other side at 190 is not cylinder sealing, usually. Its always possible something went through one side of a motor or the drunk uncle built one side, but that's a weird one-off.

I still say confirm the leakdown then pull the heads.

[Stan Weiss]

Originally Posted by ericwoo

So here are the numbers. Oddly the cylinders on the passenger side were similar and the cylinders on the driver size were similar but the 2 heads were drastically different.

Driver side head

• # 1: 160 psi
• # 3: 165 psi
• # 5: 160 psi
• # 7: 163 psi

Passenger side head

• # 2: 192 psi
• # 4: 188 psi
• # 5: 190 psi
• # 8: 185 psi

I take it this a street engine and wants to run on pump gas. Looking at the Passenger side cranking compression numbers. Why would I want to advance the cam?

Stan

[Green Elephant]

Originally Posted by Stan Weiss

I take it this a street engine and wants to run on pump gas. Looking at the Passenger side cranking compression numbers. Why would I want to advance the cam?

Stan

Good question Stan, I was basing that off of a post by someone earlier who said that Cliff R almost always advances Crower cams. I didn’t intend that it would be mandatory, but I guess I could have been more clear on that.
Either way I would degree the cam instead of just lining up the timing marks.
I would assume that the cranking compression on that side is due to the 65cc chambers and the decks possibly being machined. Indeed, that is a bit high for a pump gas engine.
Depending on what was discovered, the 65cc heads can be machined by Kauffman to have a larger chamber, but that would all need to be planned out before re-assembly.