MsVetteMan

I have tweaked out all of my tweaking.......none left. I have taken this new motor from one extreme to another as far as timing and carb setup are concerned........

Background....'81, new crate, 357/391atfly, .......Running an Edelbrock 411, 750cfm carb, hooker headers, true dual exhaust, basic mufflers, no cat, no computer..........

Every since I capped the exhaust back up....weak.......now that has nothing to do with the high engine temps.......but she doesn't feel the same as the open headers, not even close.

The hot running: Timing set at 16* she can't run on the highway at more than 60 mph without climbing towards 220, when I back it down......Now set at 12*, I can run 80 mph and never reach 200*. Of course at 12*, it's pretty slugish compared to running at 16*.....

She is the most responsive and runs the best at between 16 and 18*, but the temps will rocket!!

Another thought: My MSD distrib. has rubbed a lot of blue shavings off the rotor? and some red off the cover.....could this be a factor?

No dyno shop here, and the locals that I know about, don't know chit about carb motors........

Any thoughts?

oregonsharkman

Sorry for all the bad luck ms If you keep on dialing it in, you are going to eventually hit a sweet spot and live happily ever after (the sweet spot refers to the beer buzz not so much the vette)....my 76 is sittin in the garage with no tranny and no motor..cracked block on my $6000 crate stroker and bad synchros on my 4-speed...oh yeah i have over $18000 in my $6000 76 and it's in the shape I just described................however with the right tweaking my new 500hp motor (built by ME ONLY) will rock I AM SURE OF IT-------so don't give up the faith and dream of cruisin down the road in your bad
A$$ Corvette....

Perfomer

What vacuum are you pulling at idle? The edelbrock carb is very senstive you may have to put in stronger idle circuit springs . The running hot and bad after you capped the exhaust may be caused by a collapsed inner wall on the pipes . Do you have the same volume of exhaust from both sides.? When the last motor went south you could have collapsed the pipe with water from the motor hitting a cool exhaust pipe . You will not be able to see this from the out side only feel the difference in exhaust flow volume.

SIXFOOTER

OK, here are my thoughts. First off, advanced timong does not cause the heat, retarded timing does.
Second, 220 is not all that hot, but having that said. Cooling basics, Air dam in place, in shape? Air in the system? Are you sure? Keep in mind, the gauge sensor is mounted in the head (where heat is generated) and the harder you run (faster) the more heat you generate, the engind will run hotter the faster you go. As long as it does not get much above 220 your ok.
Next, Exhaust, Are your mufflers stock? they are more restrictive than 2 1/2 magnaflo's and the like so yes you will notice some power loss from open headers.
my .02

rcread

Where does your initial timing fall when you set your total timing to 36 degrees?

BarryK

MsVetteMan
start back at the basics and take it one step at a time.

first, you NEED to find out why your rotor and/or cap is getting shaved inside the distributor. Yes, that could be a problem!
once you find out why it's happening fix it and if needed replace the rotor and cap with new ones if they are damaged. These are not expensive parts but there are good ones and bad ones - get the correct MSD replacement units.

Next, I think 16*-18* initial timing is too high. You shouldn't need to be above about 12* initial.
What is your mechanical advance giving uoi (amount of degrees) and what's your total timing level (inital plus advance)
how much advance is your vacuum can giving you?
If tyou can't answer all these questions immediately than you are trying to time and tune the car blindly.

1. First, make sure the vacuum hose is disconnected from the vacuum can and plugged.
2. remove the cap and distributor and wrap a rubber band around the weights so you know the mechanical advance it's going to come in as you set initial timing.
3. replace the rotor and cap
4. Than set inital to 12* at your proper idle level (with the vacuum can disconnected you may have to temporily bump up the idle if it's too low
5. remove the rubber band off the weights and replace the rotor and cap again
6. double check the timing at idle and see if it's still ar 12* or if the mechanical is coming in too early. if it's above 12* at idle your mechanical advance is coming in and you need to change out the springs to a looser spring to it doesn't come in so soon. once you are sure your timing is still at only 12* at idle than you can continue
7. increas the speed of the motor and check timing to see what total timing is and when it's all in.
you should be somewhere between 34*-36* total timing and it should be all in by approx 2500rpms. With the stock springs in the distibutor chances are it may not be all in till around 4000rpm's so again you need to play with the springs and try different ones to bring the timing in sooner. Make sure you do NOT exceed 38* total timing MAXIMUM and 36* is better.
8. once you are set with the correct initial timing and the correct total timing take the plug out of the vacuum line and reconnect it to the can and once again check your time and see what the new total timing plus vacuum advance is. Make sure it doesn't exceed 52*.

On the vacuum line to the vacuum advance can, make sure it's hooked up to a full manifold vacuum source, not a timed source. Usually you can tell by where the port is on the carb. if it's on the baseplate it should be as full vacuum source. if it's above the butterflys it's a timied vacuum source. If needed you proably have a plug on the intake manifold you could get a fitting for and use that as a full mamifold vacuum source also.
You can check the vacuum for full or timed but having the car at idle, pull the hose off the vacuum can on the distributor and put your finder over the hose. if you feel vacuum at idle it's a full source, if you don't have vacuum at idle it's a timed source.

your probably running hot because your timing is off. Usually timing that is retarded to much causes higher temps, but running too adavanced can also cause higher temps as you mentioned you already discovered anyway.

Once the timing is dialed in, get a vacuum gauge and hook it up to a full vacuum port on the carb. adjust your mixture at idle so that you get the highest steady vacuum reading. make only small changes at a time on the mixture adjustment and watch the vacuum gauge carefully as you do it. after each small adjustement let the carb settle down for about 20-30 seconds as you watch the vacuum gauge before proceeding. keep adjusting until you get the highest STEADY vacuum reading.

DR.Jay

I know you are getting fed up with this motor so I will try to hopefully throw a new Idea out. I know you have been dealing with trying to adjust the ignition timing, but have you checked the valve timing? Engine cooling is accomplished by transfering heat from the intake & exhaust valves to the heads where thermal energy is absorbed by the coolant which is then pumped to the radiator and transfered to air.
The reason I bring this up is that some performance timing chain and gear sets are adjustable. With these sets you can advance or retard the cam timing a few degrees by turning an adjusting bolt on the cam gear. There are also timing sets that have 3 different holes in the cam gear too allow for changes in cam timing. The three holes are for 4* advanced-TDC-4*retarded. The other possibility is that the timing chain is off a tooth.
If Marshall installed one of these performance timing chain sets it could be why you are having performance, and cooling problems at the same time.

Dr. Jay

MsVetteMan

Good thoughts guys....thanks for the replys. This is a weird deal......

Failed to mention that I can't seem to pull over 4200 rpm.....Now I'm still breakin' the motor in, so I haven't "floored" it yet, but very close!! The automatic seems to shift really early. Of course the more retarded the timing is, the worst the shift is.......

Stock tranny and rear end....

She has plenty of torque as I can preload the brake a little, and sit and burn rubber all day long..........

Just some more info for y'all to think about.......

Oh.........sweet cruisin' at 70mph, even with the 3spd auto........(set at 12*)

MsVetteMan

16* to 18* depending upon what day it is.......

MsVetteMan

I'm close to being with ya!! Still have the original block and parts in the garage.

694speed350

with a presurised system 220 should be ok but with saying that i would check for air in the cooling system. crank the engine with the pressure cap off let it warm up when the fluid starts curclating keep adding antifreeze/water mix untill its at the top then put the cap back on.

BarryK

that's not a lot of mechanical advance (18*-20*)
you should be more around 24* or so. you need to play with the mechanical advance to get more in. That will allow you to lower to the initial timing down to where it should be at around 12* and still give you a total timing of 36*

MsVetteMan

Once again, good thoughts. Going to replace the existings muff's and pipes (2nd time) shortly. Oh........was running open headers when the first crate went south.........so the pipes should be fine.

MsVetteMan

With a 160* t'sat and water wetter like product? Again.....does not come over 200 at 60mph when timing is low at around 12*, but will start climbing if timing set higher.....?? Not gonna see how much over 220* she will go in this case........

MsVetteMan

So how do you do that? Bushings on the distrib.? Springs aren't going to change anything but the advance curve....which is also a cluster fruck....

MsVetteMan

Dr. Jay.......got know idea of what you speak.....but, Marshall did dyno this engine at 391hp, 410 torque, before it left. I'm running the same setup (carb, distrib.), but they were using a different bushing on the distributor, that I am.

big_G

Sixfooter asked about the factory air-dam. Do you have one installed? It is required for highway driving .

MsVetteMan

NO..........but I have built up a damn on top of the rad.......but, what difference would that make at 60mph, vrs 70 mph when the temps start climbing.........or at 50 mph when set at a higher timing? As I said, I can run highway speeds (as fast as 85) all day set at between 10 and 12*............that's what's confusing.

sperkins

I agree with Barry to start over, but I have one other thought. A 160* T-stat doesn't allow the coolant to stay in the radiator long enough to give up all the heat possible. Basically, the coolant just keeps flowing and never really stays in the radiator long enough to cool down and the thermostat just can't keep up (especially with the ponies your making - we're not talking about a rice burner here). Some guys think that even taking the T-stat out completely will make it run cooler, but it doesn't, it just keeps heating up. I would definately install a 195* T-stat and then do what Barry says.
Hang in there man. We've all had nightmares like this before and soon enough, you'll be saying "Remember when that dayum motor ran so friggin hot that....."

SIXFOOTER

Air Dam is the bottom piece in front of the rad, Directs air from under the bumper to the rad. Makes a Huge difference. Most of the get dammaged, pushed up from parking curbs. Even a little out of shape will cut air flow down.