[Project'68]

After a bunch of research, some testing, and hours on the phone with a buddy who has experience building race engines, its time to make some changes.

Dual carbs out, holley 750 in. I also need to retard the cam timing because my cranking cylinder pressure is 210 PSI

 

[Project'68]

Time to tear it down

Got it pulled apart and set the cam back 4 degrees

Got the intake ready for a splash of paint

Also updating the color on the timing cover. Originally was painted a different yellow from when I started the build. Now in neon yellow powder.

Going back together

 

[Project'68]

So I got this beast running again, but during the install of the manifold it was super tight to get the bolts started. The last manifold was like this as well, so I ignored the issue (bad idea).

Then after a lap around the block I found this on the valve cover vent.

The manifold not fitting properly made the intake gaskets not seal at all (both coolant and oil). The heads have been decked enough that the manifold needs to be machined to match. So I machined it! I took .025" off of each side, and now it sets in place perfectly. Unfortunately one of the bolt holes in the head is clearly ready to strip. Hoping it is not an issue since it is tight, but not super tight. If it leaks again I may try to get a helicoil in there with the manifold still in place (its a blind hole, so it wont put metal chips in to the engine).

 

[xxdabroxx]

Is that a precision mathews mill?

 

[Project'68]

Is that a precision mathews mill?

Haha I see Matthews retails the same machine. This one came from Bolton. I wouldnt use precision to describe it. I would have set this up in the CNC mill but the part is too big for that machine. I used a dial indicator to sweep it in and it was about .001" over the 20" in X, and about .0003" in Y. Close enough.

 

[Project'68]

Got the Holley 750 set in place and have been putting some miles on it. Finally got all the oil leaks under control, but still a question on if the intake manifold gasket is leaking. Just need to keep an eye on it and put more time on it.

 

[Project'68]

Working to mount the Innovate MTX-L AFR gauge. Im making a small mounting plate from this sheet of carbon and it will fill the empty slot in the dash console (where HVAC controls would go).

 

[Project'68]

I finished the AFR gauge install. What is that ugly switch you say? That would be my reverse lights...

 

[Project'68]

Ive been messing around a bit with tuning the new Holley carb and putting some more miles on the car. Since this 383 is 11:1 compression ratio, detonation has been an issue. Ive upped the octane to 100 + some octane booster, and its better, but still just doesnt seem right. AFR is off a bit (rich at idle, bit lean under power) but something still is just not right. I swapped in some hotter plugs and gapped them pretty small, and it ran GREAT for about 20 miles. Pulled the plugs and they are super oil slicked.

Looking in the exhaust port, I can see a bunch of oil getting by the valve guides. Im guessing the intake is just as bad if not worse. These heads have been an issue (too small so it drives the compression up) so im thinking im going to get some larger displacement heads to get the static and dynamic compression in to the right area. Ill probably get some Dart iron heads because ultimately I plan to build a new engine for the car. I just want to be able to drive it and work on suspension before Im ready for a new build.

Also, if anyone can tell me why the valve stem right there is shiny and all the others (except 1) are covered in soot im interested. Im guessing the whole thing is just a big leaky ******* but Im not really sure.

 

[xxdabroxx]

The oil issue could be contributing to your ping too.

 

[kimmer71]

Hmmm. 🤔

are you running any crankcase ventilation/pcv? If so, you could be pulling oil into the intake from that? Coolant is staying put?

 

[Project'68]

Hmmm. 🤔

are you running any crankcase ventilation/pcv? If so, you could be pulling oil into the intake from that? Coolant is staying put?

I originally only had a breather (no PCV) and was getting oil leaks around the valve covers. The oil slick issue on the plugs was still present.

I added a PCV and the oil leak issue went away, but didnt change the plugs at all. Coolant is OK. I am also questioning the intake manifold gaskets as I had to mill the intake down to fit properly. I think, though, that all these things combined means these heads are just a bit sketchy.

Going to start tearing it down today and will look for issues along the way.

Also to clarify the valve stem issue, pretty much every exhaust valve has varying degrees of the pictured build up.

 

[Project'68]

I got some more go look fast parts.

If youre thinking about purchasing fiberglass parts from Unlimited Products....dont.

 

[kimmer71]

I can’t think of how you would test for an isolated leak on an intake runner to valley but It seems like it’s ingesting oil or oil vapor through the Entire induction system due to the plugs. Is it possible that it could be the rings? Usually when you see an engine burning oil you think valve seals or rings right? Does it smoke badly when it’s running? It seems like that one odd valve stem is trying to tell us something but I can’t make sense of it. The only thing I could think to suggest is that cylinder is not firing but you would have known if that was happening because it would have been shaking the car and sounding horrible I would think. That picture you took was through the exhaust port on the head right?

 

[kimmer71]

that picture might make me think the valve seal is leaking oil down into the exhaust port then coking when it finds the heat?

 

[Project'68]

I can’t think of how you would test for an isolated leak on an intake runner to valley but It seems like it’s ingesting oil or oil vapor through the Entire induction system due to the plugs. Is it possible that it could be the rings? Usually when you see an engine burning oil you think valve seals or rings right? Does it smoke badly when it’s running? It seems like that one odd valve stem is trying to tell us something but I can’t make sense of it. The only thing I could think to suggest is that cylinder is not firing but you would have known if that was happening because it would have been shaking the car and sounding horrible I would think. That picture you took was through the exhaust port on the head right?

It has new rings, but that doesnt mean that they areant leaking. It smokes on start up after sitting for a while, which makes me think valve stem seals (oil leaks in as it sits and burns on start). I have not noticed it smoking during running.

Also, thats not an odd valve stem. Most of them look like that. And you are correct, that is a picture through the exhaust port.

A new set of plugs ran GREAT until they got oil fouled. Engine ran super smooth, power delivery was super smooth also. I guess an important detail is that every plug is oil fouled, not just that one cylinder. I do have one cylinder which looks cleaner than the rest, but not great.

I have the valve cover off, pulled 2 rockers and guide plate, and got under the intake manifold with my small inspection mirror. I cant see anything that would suggest an oil leak in to the intake manifold, but its pretty hard to tell. It would be a lot better to use a borescope from the other side so I could look at the top of the valve.

Also, when I pulled the carb, there is oil sitting inside the intake manifold. That seems really odd to me, like it would be coming from the PCV. If that was the case, then when I was running it with no PCV I should not have seen oil fouled plugs. I think.

 

[kimmer71]

I agree. If the valve seals are really bad, when you ran it without the pcv, the added pressure in the valve covers would probably increase the oil leaking through the valve seals? If oil were leaking down through the intake seals too, it could eat oil that way? Are the heads new or used? Have you done any work to them? You could do a compression test and leakdown test to get an idea of ring and valve seat condition. It wouldn’t be too horrible to replace the valve seals while you have the compressed air on the cylinder either. The other thing you might try is a catch can in the pcv system. At least you would know how much oil is moving through that system.

 

[Project'68]

I agree. If the valve seals are really bad, when you ran it without the pcv, the added pressure in the valve covers would probably increase the oil leaking through the valve seals? If oil were leaking down through the intake seals too, it could eat oil that way? Are the heads new or used? Have you done any work to them? You could do a compression test and leakdown test to get an idea of ring and valve seat condition. It wouldn’t be too horrible to replace the valve seals while you have the compressed air on the cylinder either. The other thing you might try is a catch can in the pcv system. At least you would know how much oil is moving through that system.

These heads came with the engine when I bought the car. There are a few issues here:

1. I didnt do the calculations and research to understand the dynamic compression ration and what that really meant. This engine is 11:1 static and really wants like 104 octane (which I cant provide unless I pay 9 bucks a gallon for 100 and then add octane booster).
2. I should have at least replaced the valve stem seals
3. The manifold doesnt fit properly. I think the heads have been surfaced enough that the bolt pattern is dropped pretty low in the valley. So this oil issue could also be coming from the manifold gasket.

I had the heads bead blasted and surfaced when I rebuilt the engine.

I will likely add a catch can anyway. I was purchasing parts to do that but didnt have the PCV as part of the system, so Ill likely make that change and put something together.

I am looking at some Dart cast iron 76cc heads which with a thicker head gasket should give me 9:1 static and 7.85:1 dynamic. Right now the goal is to get back on the road for the least amount of cost while I work on suspension and other parts of the car. Down the road Ive always planned on building another engine, and hopefully get it right vs re-using someone else's poorly planned build.

 

[Project'68]

I havent been putting much time in to the Nova lately, work has gotten busy again.

Since I last posted, I pulled heads off and changed the valve stem seals and valve springs. The seals were pretty crispy and some were busted. It seems like there would be an oil leak through them. I now have positive stop seals installed.

I also found this awesome valve spring, so I have all new comp springs in there.

Everything is going back together with new head gaskets, new cam, new seals, etc.

So regarding the compression issue, basically Ive changed the cam to something much more aggressive which will bleed off some compression. The cranking compression is now 175psi instead of 215. If I can get the plug to stay clean, I should be golden. Still sketched out by the manifold gaskets, but we will see how it goes.

 

[Project'68]

Before I put the heads back on, I had to helicoil some of the manifold holes in one head. This was from ramming the old manifold down in to place. The new manifold fits properly after milling the faces down a bit. Next time ill just slot the manifold holes instead of milling the faces.

I made this jig block to get the hole for the helicoil tap straight. I inherited a small mill from work so I was able to get the hole in the jig block square. I use the bolt to center it, then clamp it a drill. Worked really well.