Technical Timing with Dual Quads - HELP!!!!

ahhh, i thought he was using a different word for "compression".

 

Edelbrock did not make a C26 for Vortec heads.

The C26 fits pre 1986 heads, and 1986-1995 heads, if you re-drill the center four manifold to head holes.

 

I think it’s called a 5426. At least the one I have is.



Clean up on aisle six please.

 

I can only go by what he said, which was C26.

It says C26 under the Edelbrock script.

 

It's a C26 with the endurashine finish. Don't mind my cat getting in the way.

 

I agree. I cannot get the detonation issues into the scenario.

I do suspect that there may be an under-carburetor sealing issue, as has been previously mentioned.

 

Ok.

Those are not Vortec heads. They are 1992-1995 Corvette heads, or GM Performance heads (plus aftermarket ones).

The Vortec (L31) head was produced from 1996-2001.

 

Indeed, I stand corrected in that regard.

 

It does not help that GM used the Vortec "double-quench" combustion chamber many years earlier in the Vortec 4300 V6 (the successor to the 4.3l 90º V6, which was 75% of a 350).

When the 5.0/5.7 nomenclature came along in 1986, people later ***umed that they were Vortec.

Until 1995, SBC heads were plan old wedge chambers.

1995 and earlier wedge on the left. 1996 and later Vortec on the right:


They were a 5-year truck head, all OEM in Iron.

After that, GM threw the name on anything and everything.

 

If you have those spacers under the carburetors, with gaskets on either side, then you should not have a sealing issue.

 

You haven't said how the distributor is set up.

Mechanical advance only, mechanical and vacuum both, if with vacuum advance hooked up, is it to ported or manifold vacuum?

If the vacuum advance was hooked to a vacuum source and timing checked, that's not initial base timing.

We generally setup Chevy V8s with around 15 degrees initial and 36-38 degrees total as a starting point.
Then go from there. Some engines will be only mechanical advance, some with both and some with mechanical and either ported or manifold vacuum. It all depends on what the engine likes.

Its not uncommon for engines to idle at 40-50 degrees or even more with vacuum advance hooked to manifold vacuum. The initial still needs to be in the 15 degree range or so to start easily.

If the engine speeds up at idle with advancing the timing, without changing anything else, that is telling you that it is burning fuel more efficiently at idle, there is no other reason for the RPM to increase.
This is why many engines will idle more smoothly with a vacuum advance hooked to manifold vacuum.
Some will ping in mid range or under a load, then you need to try an adjustable vacuum advance canister.

A couple words of caution with using a screw in piston stop:

They will bend if hit too hard while turning the engine over by hand, while finding true TDC, so be gentile.

Not sure on a small block, but on a big block, you must remove the rocker arms on intake and exhaust of that cylinder, or you can bend a valve.

I have done that twice while degreeing a cam on two different BBC engines, with the engines on the stand.
I loosened up the piston stop after finding true TDC, so the engine would turn over to degree the cam and forgot to remove it while adjusting the valves. I even told the guy that was working with me on the second one, "don't let me forget to remove that ******* piston stop" and he forgot and so did I.
Had to remove the heads on both engines to replace the bent valve.

Ditch the stamped timing tag and get an adjustable pointer, they are not that expensive and you can position it perfect and can see the degree marks on the balancer easier.

Bill

 

I always set my base timing with the vacuum advance disconnected and the ports plugged.

I'd have to go back and verify which vacuum port I had the advance hooked up to. I'm fairly sure I used full manifold vacuum since this is a non-EGR equipped application, but I'll have to go back and look.

 

In your picture of the engine compartment are your valves adjusted ? I noticed #2 cyl intake valve rocker arm stud/nut isnt at the same adjusted level as the others . Just an observation same with #8 exhaust .

 

I've adjusted them. This picture was just to show the intake on the engine. That was one of the first things that I wanted to rule out, that I had a valve too tight that was bleeding off up into the intake causing my idle issues. But the compression test would indicate even compression in all cylinders.

 

Hey @swade41 , you got anything to say about this issue?

 

Have you tried timing by vacuum gauge or ear, and then check with a light to verify your setting.

 

If it wasn't for new stuff breaking down ,I would have never had a job.

 

A**** other things to check, remove the carbs & Look Up Thru them & be SURE the secondarys on BOTH are COMPLETELY CLOSED with the throttle lever in the idle position. A secondary air leak @ idle will drive you Nutz! And it's Pemanent!

 

I put in my two cents, I'll just sit back and watch everyone thump their chest, argue and fight like always on who is right and who is wrong.
I'll also sit here knowing all my 2x4 cars run great without any issues.

 

Hell I guess I missed your post brother

 

Looks like I may need to change avatars then lol

 

No please don't LOL

 

Lol my fault, I had seen what you said about fuel pressure, leave Marilyn alone

 

one of the coolest avatars for sure

 

Marilyn stays... Everyone else can get bent!

 

This, i would try a straight linkage

 

i could have sworn i read about a 4x2 setup with progressive linkage, one carb acted as 4 primaries, the other as 4 secondaries. i havent found anything about it since and dont know what to look for.

 

Straight linkage may work fine, but I can tell you for sure that progressive also works just fine. If anyone is having problems with dual quads, it's not due to using progressive linkage.

 

I was considering going to a solid linkage for the simple fact of keeping the fuel fresh in the front carb. Like I mentioned, this is not a hot rod application where this car is going to see lots of full throttle action. In reality, the only reason I'm going with the dual quads is because they look cool and if I'm going to put a SBC that everyone likes to **** on in place of a 394 Olds, I might as well make my life miserable making it run to even it out.

The nice thing about the Edelbrock linkage is that I can slide the stops and set screws to adjust it into a solid linkage.

 

Totally depends on the intake manifold, some intakes will not provide equal fuel distribution from front to rear and they need both carbs working front and rear to prevent cylinders going lean.