Engine situation

[Dominique Williams]

Hi everybody, just wanted to get peoples opinion on a situation so my friend did the timing on my engine i have a 440rb engine with factory estreet aluminum heads and a comp cam that’s 206 at 50 with a 750 summit carb if i said that wrong please forgive me he plugged the carb ports as well as the distributor port and set the overall timing to 38 I drove it home from work and it responded actually really well and was a smooth drive but after getting home and doing research im seeing alot of people with various opinions saying you don’t need to use it while others say its a must among checking boards outside of this site it’s said that overall timing should be between 32-36 for my engine and that I should give it wot to listen for a pinging sound to see if the timing needs to be brought down im here for any advice that will help I want it to get as much power as possible but I also don’t want to (detonate) my engine either my friend told me to drive it this weekend and if their are any problems to bring it back on Monday and he’ll hook the vacuum back up but he’s said he hasn’t used his in year and hasn’t had any problems

 

[furious70]

Usually vacuum advance will give you better mpg and cooler operating temps. There is no reason to run it unhooked. You're a little better off with aluminum heads.

 

[CBODY67]

Sounds like a pretty nice combination you have there. What is the compression ratio that you ended up with the Edelbrock aluminum heads?

The 38 degrees total advance (mechanical) is about right, BUT if the fuel (93 pump octane Premium) causes it to ping at WOT, then you'll need to back things back a few degrees. If the ping is at part-throttle, then adjust the vacuum advance for a bit less advance in the vacuum advance "can". An Allen wrench of the size that will just fit through the nipple should do it. Once you get the Allen wrench engaged with the adjusting screw inside, turn it about 1/2 turn ccw and re-check for pinging.

So there are two "pinging/clattering" areas. One is at WOT and higher rpm (like just before the 1-2 and 2-3 upshifts) and the other at cruise/highway speeds (55-70mph, for example) when going up hills or accelerating at part-throttle without a downshift. If the engine has anything more than about 9.5 to 1 compression ratio, then unleaded Premium fuel will be needed, usually. The vacuum advance needs to be operational (from a ported vacuum port on the carburetor) for best fuel economy.

Many times, the factory distributor + base timing specs for 440s ended up with a total in the 34-36 degrees area, but 38 can be used if you have good enough fuel to not ping/clatter (as mentioned above).

Hope this might help,
CBODY67

 

[Dominique Williams]

Sounds like a pretty nice combination you have there. What is the compression ratio that you ended up with the Edelbrock aluminum heads?

The 38 degrees total advance (mechanical) is about right, BUT if the fuel (93 pump octane Premium) causes it to ping at WOT, then you'll need to back things back a few degrees. If the ping is at part-throttle, then adjust the vacuum advance for a bit less advance in the vacuum advance "can". An Allen wrench of the size that will just fit through the nipple should do it. Once you get the Allen wrench engaged with the adjusting screw inside, turn it about 1/2 turn ccw and re-check for pinging.

So there are two "pinging/clattering" areas. One is at WOT and higher rpm (like just before the 1-2 and 2-3 upshifts) and the other at cruise/highway speeds (55-70mph, for example) when going up hills or accelerating at part-throttle without a downshift. If the engine has anything more than about 9.5 to 1 compression ratio, then unleaded Premium fuel will be needed, usually. The vacuum advance needs to be operational (from a ported vacuum port on the carburetor) for best fuel economy.

Many times, the factory distributor + base timing specs for 440s ended up with a total in the 34-36 degrees area, but 38 can be used if you have good enough fuel to not ping/clatter (as mentioned above).

Hope this might help,
CBODY67

He didn’t tell me the compression ratio on the heads I’ll ask tomorrow and right now im running 91

 

[Davea Lux]

If it runs nice the way it is, leave it alone. There are a lot of different ways to set up the timing. Not knowing the comp ratio, carb jetting and the mechanical advance curve, you will be shooting in the dark to improve the performance. If a pro shop did the setup, it should be good.

Dave

 

[Dominique Williams]

Sounds like a pretty nice combination you have there. What is the compression ratio that you ended up with the Edelbrock aluminum heads?

The 38 degrees total advance (mechanical) is about right, BUT if the fuel (93 pump octane Premium) causes it to ping at WOT, then you'll need to back things back a few degrees. If the ping is at part-throttle, then adjust the vacuum advance for a bit less advance in the vacuum advance "can". An Allen wrench of the size that will just fit through the nipple should do it. Once you get the Allen wrench engaged with the adjusting screw inside, turn it about 1/2 turn ccw and re-check for pinging.

So there are two "pinging/clattering" areas. One is at WOT and higher rpm (like just before the 1-2 and 2-3 upshifts) and the other at cruise/highway speeds (55-70mph, for example) when going up hills or accelerating at part-throttle without a downshift. If the engine has anything more than about 9.5 to 1 compression ratio, then unleaded Premium fuel will be needed, usually. The vacuum advance needs to be operational (from a ported vacuum port on the carburetor) for best fuel economy.

Many times, the factory distributor + base timing specs for 440s ended up with a total in the 34-36 degrees area, but 38 can be used if you have good enough fuel to not ping/clatter (as mentioned above).

Hope this might help,
CBODY67

He said “Both vacuum ports at the carb were full vacuum so they were adding vacuum advance at idle which isnt needed at idle. I plugged those. I also plugged the vacuum advance at the distributor just because. I set the initial timing at 12 degrees, full centrifugal advance at 38 degrees”

 

[CBODY67]

What Summit carb? What hot base idle speed?

If it's an AFB or AVS, only ONE of the front ports should be manifold vacuum at idle, with the other one being ported vacuum, other than the PCV port in the middle. The ported vacuum port CAN have a small bit of vacuum there at idle, but as it takes about 9" vacuum to actuate the vacuum advance, not a big deal. But more than that is.

 

[Dominique Williams]

What Summit carb? What hot base idle speed?

If it's an AFB or AVS, only ONE of the front ports should be manifold vacuum at idle, with the other one being ported vacuum, other than the PCV port in the middle. The ported vacuum port CAN have a small bit of vacuum there at idle, but as it takes about 9" vacuum to actuate the vacuum advance, not a big deal. But more than that is.

P/N SUM-M08750VS (electric choke) I might switch back to a edlebrock so much simpler

 

[mopar440]

I believe aluminum heads can take more timing if I've heard right, they run cooler

 

[CBODY67]

When I did the 355 for my '77 Camaro, I put the OEM '86 Corvette aluminum heads on it, with matching OEM-style pistons, which should have made about 9.5CR. I'd susptected that with the thermal issues of aluminum heads, I might be able to downgrade to 91 or 87 pump octane fuel. NOT THE CASE. Still had to use 93 pump octane super unleaded with the same timing I'd used in the prior 305 with the OEM iron heads. One benefit was that the heater worked much sooner in cold weather. One issue to deal with was the lack of a heat crossover passage in the heads, so the intake manifold warmed with the heat from the heads and the oil hitting the bottom of it (not applicable on a B/RB Chrysler V-8). The Holley 4175 has an electric choke, though.

Just my experiences,
CBODY67

 

[CBODY67]

P/N SUM-M08750VS (electric choke) I might switch back to a edlebrock so much simpler

Go into www.summitracing.com and put your carb number into the search window at the top of the page. Then click on the carb number on the page that comes up.

In the "Overview" section for the carb description, there is an icon for "Instructions", with 4 different files and one file for "Specifications". Look and DOWNLOAD ALL OF THEM for future reference. In one of the files, there is an image which details the vacuum take-offs on the front of the carb. One is termed "gold" and is noted as "Timed" spark advance to distributor (i.e., "ported vacuum"). It is on the rh (passenger) side of the larger pcv take-off, near the corner of the carb base.

I hadn't really paid any attention to their branded carbs, but that's a pretty nice carb. A combination of lots of Holley features in an earlier Ford-type (as in 1960s Ford 4bbl architecture, which Holley brought back in the middle 1980s or so, but was not accepted very well compared to their normal 4150/4160-family 4bbls), but this one is in aluminum with annular-discharge primary venturis. Lots of good features! Only thing I see is that the power valves actuate at 9.5' of vacuum, which might be very close to what the vacuum is at idle, in gear. So check that to see what it is on your engine. Might need to get closer to the more normal (for Holley) 5.5" vacuum power valves on their other 4bbl carbs? IF they are two-stage, then no problems, as if it's like their 4160s, the first stage does not do much and the second stage comes in about 5.5" vacuum.

Take care,
CBODY67