Hey guys I've been scratching my head over a few things for a little while and haven't been able to figure things out to my satisfaction. Its probably not the best place for small block help, but I figured I'd try here first.


I recently installed a 350 out of another Jag to replace my 305 and have been struggling with it for a week or two. I replaced a bunch of gaskets while it was on the stand. Before pulling it I tested compression to around 115 all around, solid oil pressure, and perhaps low vacuum at 10 in-hg. The low vacuum didn't alarm me since I was reusing a carb base gasket and assumed I had a small leak.


A bit of info on the 350 in question. 4 bolt main, 60 over. It has a mild unknown cam, Wieand 8004 dual plane intake, 2" rams horn manifolds, and a rebuilt Carter AFB. Fresh double roller timing kit. I installed a new cap and rotor but kept the wires. My car was converted using a John's Cars kit (for better or worse).


Issue 1: For the life of me I can't get 12v off the key switch to power the dizzy. I have been running jumpered for test purposes but this really is a hassle and not an option for a long term solution. The wiring diagram indicates a white wire powering the stock dizzy. Its no where to be found. I was expecting a nice two prong molded plug with the JC kit, could it be a cheesy wire crimped slotted female connection? If so, thats crap.

Issue 2: No matter what I do with the the timing or carb settings, I can't get over 11 in-Hg. Traditionally this should indicate a valve timing issue (which I hope isnt the case). There was an offset woodruff key in the crank for the lower timing gear which I left in in place when I changed the gear. An offset key shouldn't be more than 2-6 degrees of timing change though. I guessed it was there for a reason so I left it.

Tested for vacuum leaks and everything looked good. Another thing, I'm at 5000 above sea level so I should make less vacuum...but only 10-ish? That seems low.



I'm not sure where to go with these two issues. I'm getting frustrated with the world of SBC's, so simple yet so many damn options! I'm afraid I might know where to go on the vacuum issue, which will be no fun at all. Its alot easier working on that stuff when the engine is out. Oh well. Any input or advice is always appreciated.

 

110 PSI is way too low. I get about 195psi on my SBC 400 with 10.5:1 with an agressive cam. My stock LT1 with stock cam produces 220psi during a compression test.

10 inches of vacuum is also way too low. A typical mild cam will make 15 to 18 inches. There is a huge diffrence between 10 and 15 inches of vacuum.

So you've got issues. Whats the history of this motor? It could be simple. Check the rocker arms. If they are not adjusted properly when the lifters pump up the valves will hang open which will offer up low compression and low vacuum. Also sounds like a valve timing issue.... I'd set the valve timing back to stock. Make sure the round dots on both the small and large timing gears are aligned when piston 1 is at TDC.

 

Maybe you can find what left of the white wire at the bulkhead pass-thru connector. It's roughly under the battery as I recall


Cheers
DD

 

I used a Johnscar kit when I installed the LT1 and 4L60E in my car. It was quite complete. However, I used an after market harness for th engine. It included ignition wires for the coil and tach.

My car does not use a conventional distributor, but a device known as an Optilite. An amazing device but cursed by some.

Now, in your car, you are changing a conventional 305 to a conventional 350. What did you do with the wire that provided 12v to the distributor on the 305? Use it in the same manner. All you need is switch to coil in crank and run!!

The switch to coil wire on the original Jaguar harness will do just fine for a distributed SBC!! So, John may not have seen the need to provide a different one!!

As to HG's, me thinks that cam is not as mild as you think! Is your guage trustworthy?

I am also a tad suspicious of the offset key. Why?

Me thinks the only way to check out the cam is with a degree wheel. But, what can the PO tell you as to the real ID of the cam, iskendarian 404, Crane 45, etc.

And, some folks marketed some outlaw cams with odd timing!!

I'd consider going to a known good stock cam. Used OK, but beware of flat lobes or some that are going flat.

An "RV grind" cam is a good choice as these cars need torque early on, they are heavy.

Don't give up on that SBC, they are remarkable.

 

110-120 were the readings which should work out to around 8.5:1 compression ratio. It has large 76cc chamber heads with flat top pistons. Since all the readings were close, I wasn't concerned with it too much.

Yea its way too low and I have no reason to believe its inaccurate. I was expecting around 15 in hg, 10 is bad.

I have very little info on the motor other than what I have been able to figure out. The car was owned by an elderly lady. Strangely, there was a two barrel carb with an adapter installed on the aluminum intake. Could someone have made the valve timing late for economy reasons? It's a bit pokey right now and I'd rather emphasize performance than gas sipping.

I adjusted rockers using the "Jiggle the rod" method. Once jiggle was gone, I tightened 1/4 turn. From what I was able to gather, this is the most reliable method for setting lash. Tomorrow I'll take a look at them again and see if things still look okay. Timing was set on both round dots, I didn't use the retard/advance option on the gear set I installed. Could it be possible I installed them on the TDC of the exhaust stroke?



Alright, I'll take a gander at the bulkhead and see if I'm getting a switched 12v.

I'm not giving up on the SBC yet, its just been time consuming learning all this for the first time. Take a head gasket for example. I'm used to an OEM option and a 2-3 aftermarket choices. On an SBC, there are hundreds and each has it's proper application. Luckily, things are generally cheap and there are more experienced folks than me to help.

Thanks for the input thus far guys!

 

Something is not right...a compression ratio calculator shows a 350 with 76cc heads with a head gasket thinkness of .025 and 8cc assumed for the valve reliefs yields a compression ratio of 9:1. At 9 to 1 you should have 160 to 170 PSI. Even at 8:1 compression you would have about 145 to 160 PSI. All this assumes a mild cam. To be sure get the casting # off heads and block. On the heads it's cast into the material between the rockers. The block numbers can be found on a pad at the front passenger side at the base of the head.

If you're dot to dot on the cam gears then you may want to better identify the cam. Maybe it's more aggressive than you think. Figuring out duration is difficult when the cam in the motor but you can easily get the cam lift. The lift will suggest if the cam is aggressive or not. I doubt someone put an aggressive cam with 76cc stock heads and a 2 barrel. When the engine is running and the PCV valve plugged do you get excessive blow by?

Your valve adjustment procedure seems ok but you need to loosen the all the rockers, wait for the lifters to extend for 15 min or so before you tighten until the push rod spins by hand with some drag. Then 1/4 to 3/4 of a turn on the rocker arm nut is ok. As a test you could just back off a turn and run the engine loose and see what happens.

You can answer all these questions with a leak down tester. You pressurize the cyl with 120 PSI and see where the air goes. If it goes out the crank case you've got worn rings, out the intake or exhaust you've got warn valves. You can even figure out the actual cam timing with a leak down tester.

For economy you would want the valve to close early or retard the timing and that would generally yield higher compression and higher vacuum.

So true about the head gaskets on a chevy. There are hundreds....marine, with steam holes, and with out, MLS, copper, pre-crushed, non brinelling and so many different thicknesses and bore sizes of them all.