Technical SBC 350 Getting Hot on Highway

Under full throttle, no vacuum, at RPM, you're probably at 32-36degrees mechanical advance.
Get it up to 65 on the highway and back off the throttle (it really only takes about 30-40hp to maintain cruising on level ground). So now you're at higher RPM and high vacuum while cruising with cylinders that are only getting a small air/fuel charge, lotta space between the molecules, and less time to burn it.

Thats why the factory's vacuum advance adds a bunch of timing to get it up to around 50degrees advance, otherwise more burning fuel goes out the exhaust, wasting power, polluting, and adding a TON of heat to the water jackets around the exhaust port and valves.

-rick

 

That's hilarious, because there is tons of bad advice in all those posts you wrote.

 

welll good luck with that and thanks...great post,.... I've never really checked to see how much advance at 3000 with vac adv hooked up... I know it spikes, didn't think it was that much though..

personally,... I just check the plugs to see where the timing is at, and if it's tooo much

 

Corn fuel kinda messes up plug reading, correct?

 

so quote one.... hope you catch something...

 

I've had this almost exact setup twice Come into my shop for the same problem. Once on an impala and once on a chevelle. Both customers thought the latest and greatest fan shroud combo would be the best thing for them and in the end, wasted their money. Ended up putting a stock 1966 or 67 shroud on both cars, which is plastic and covers the entire radiator and a 7 blade fan with a severe duty fan clutch and cured it all. One with a 500 inch big block. As for the timing, I set my neck anywhere from 12 to 16°. Initial with the vacuum advance ported. Just my experience and opinions.

 

I had issues with my BBC powered Falcon gasser like this. Had the exact same shroud and it cooled fine at idle or slower speeds, but get on the highway and it ran over temp immediately! The way the shroud is made it restricts flow from being too close to the core, and blocking off flow outside of the fans.
I removed the shroud and after cutting the side mounts off and used aluminum sheet metal to space it off the radiator another 1.5" and closing in gaps at top and bottom, it ran cool at highway speeds. Just getting it away from the core allowed the fans to pull air through the corners of the core also.

 

I've put my fan speed meter on many of those fans and they were quiet, but all done @ 20 mph, that means at 60 mph they were blocking most the air

 

The Judge runs cool in 100 degree Texas ambient in traffic or on the highway with A/C and transmission heat exchanger in front. 383 stroker. Believe what you want.

 

You spewed at least 7 posts worth and are the self-proclaimed expert, I've got better things to do than waste my time on that. The irony is hilarious, though.

 

LOL.... heres why they started putting the flaps....
shroud sellman to engineer.." the shrouds are causing peoples cars to over heat and they want there money back"
engineer" ah crap!!!!, I put an order for 5000 of them to my china fab shop.....better give them a calll....

china fab rep.. "not to worry,,, we put extra holes with flap"

 

See there....we agree,,,,

 

Worked on plenty of OE fan set ups with flaps

just saying

 

With today’s fuel blend engine heat will always be a problem for vehicles made to run richer on leaded fuels. With correct sizing of radiators, water pump speeds, adding fan shrouds, and multi blade fans most engines can be made to perform as designed but care needs to be taken with each part with no electric fans.
I fought overheating of a stock engine in a stock engine bay for 5-6 years to get the cooling correct and we had owner these cars in the mid 50’s new and never ever saw a cooling issue.
Looking back it’s only the fuel blend has changed….good luck.

 

and the flap were added why???? my guess is they were making the cars over heat so they added them...

so let me retract,... I now know nothing about any thing

 

None of my old rides have a shroud.
No cooling issues but 210-215 isn’t too hot either

 

Fuel blend, usage (longer and faster highway driving, more time stuck in traffic, etc.), and weather conditions...

 

No need to tell me good luck with it. I'm just stating how and why the factory used the vacuum advance in about half a billion vehicles. Others on this thread also mentioned the need for 45 to well over 50 degrees of timing at light throttle high rpm cruise. They seem to get it. No one's trying to turn over an engine with 50 degrees, lol.

-rick

 

Chevrolet doesn’t provide a specific “max” timing value for small-block Chevy engines, as it can vary based on factors like cylinder heads, compression ratio, camshaft, and distributor advance curve. However, here are some general guidelines:

1. Base Timing (Initial Timing): Depending on your setup, the base timing (initial timing) for a street high-performance small-block Chevy typically falls in the 12- to 18-degree Before Top Dead Center (BTDC) range1. Starting with 12 degrees of initial advance is a good rule of thumb2.
   
   
2. Total Timing: The total timing (including both initial and mechanical advance) should be around 34 to 36 degrees BTDC at full centrifugal advance, measured at the crankshaft. Aim for this range at 2,800-3,000 rpm with the vacuum advance hooked up3.

Remember that individual engine combinations may require adjustments, so always check your specific setup and consult with experts if needed.
sooo... total timing is all in with the vac advance hooked up... and that should fall in the 32 to 36 range... total

you only disconnect the vac for idle timing...all in timing means all in...but should one question the total timing all you have to do is read the plug strap....

 

You need to re-read your own Number 2. Total timing is initial advance set by twisting the distributor, plus mechanical advance using the centrifugal weights should be around 34 to 36. You got that first part correct. UNHOOKED VACUUM IS ONLY INITIAL PLUS MECHANICAL..... because the vacuum is UNHOOKED.

Your part in Red about aiming for 34-36 with it hooked up means that when you have the throttle pinned you'd NEVER see 34 to 36 degrees.

But then how much is the vacuum going to add to that 34-36 when it's hooked up? Oh, about 12 to 16ish... giving you around 50ish on the highway at light throttle cruise! And yes on many distributors it's adjustable with an allen wrench inside the nipple, just check for the hex shape on the vacuum pod.....

-rick

 

I don't know about all that Chinese arithmetic, I know for fac this... you have to hook up the vac adv. to get total... then you either have to have a degree wheel balancer... or back to zero timing light.... yeah, i've read before that people claim they are running over 50 degrees timing doing some special adding.... but fact is when I hooked their motor up to my timing light it was 35 degrees all in... 50 degrees timing will burn the strap of the plug or hole in the piston...thats it doesn't detonate its self to death.... but being we are gentlemen... I will apologize if you can prove the running 50 plus degree's timing and you do the same when you find out i'm right...

 

Sorry bub, maybe these articles explain vacuum advance better than i can. Most people who understand vacuum advance know the average traditional american V8 will max out from 40-55degrees of total timing possible at light throttle cruise:

Timing Is Everything: How To Set Ignition Timing (motortrend.com)
Total timing requirements are dependent upon many variables. A typical street engine with a compression ratio of 9.0:1 runs very well with around 36 degrees of timing (initial plus mechanical) for a rough total of 15-55 degrees of timing at light throttle when vacuum advance is employed. If the engine detonates or pings under WOT, reduce the timing. If it surges or pings at part throttle, reduce the amount of vacuum advance.

Experimentation with timing can help performance, driveability, and mileage by customizing the ignition curve to your particular application. Don't be afraid to make changes.

How Initial, Mechanical, and Vacuum Advance Work Together to Make Power (onallcylinders.com)
At part throttle initial, vacuum, and mechanical advance are all added together. Here is an example: Let’s start with 10 degrees of initial timing at idle. We add 18 degrees of mechanical advance at 2,400 RPM for a total of 28 degrees of advance. Now let’s add 12 degrees of vacuum advance with engine vacuum at 16 inHg. This would create a total ignition advance of 40 degrees of timing at that specific point.

-rick

 

is it ok to say you are total wrong???? and I can explain....

 

I read the initial post a bit ago, first thing that jumped out at me was “2 degrees initial”. Next was 14/16? With advance plugged in.
As I read through the thread, I see others must have re-read the initial post and suggest (properly) set initial to 8-10-whatever it likes, VA disconnected, or with VA disconnected set total mechanical to where it’s happy, the proceed with which vacuum port you want, ported or manifold.
But yes, check the fluid in the MC

 

with timing, you never get it all,,, with low rpms you get higher vac advance and no mechanical... with high rpms you get all the mech. and no vac...theres a time on the dyno @ lets say 1800 rpms... now you have both mech, and vac, kicking in plus the base.... but the only number you can use is the base, plus the percent that each other is doing and you might see a spike to 40 degrees but a such a low rpm it's fine.... I'll invite anyone to prove me wrong by setting their timing all in at 51 degrees and doing a pull on a dyno and see what happens...

 

Vac advance is just a crutch to get you from base(easy to start) to full advance and is not needed to drag race where your only concern is total timing, the last ting you need is for the vac advance to go hay wire

 

initial plus mech,,, is total... you loose the vac number when theres no vac....