Poor Performance When Hot

[55 Tony]

I did, which is why I'm wondering what is your A/F ratio when the power goes up, or down?

If I get the street tires on tomorrow I'll let you know. I know when fully warmed up it hovers *around* 14.7 at light throttle, cruising the highway, pretty much all the time until I open the secondaries. My gauge is small and I don't have the comfort level trying to read it at the track, especially where it is now. I'll have to move it again in front of the tac so I can see it better during WOT.

[chasracer]

Ahh, so there is an Ignore List with this board - just the thing for the situation.

[55 Tony]

Ahh, so there is an Ignore List with this board - just the thing for the situation.

Ahh, great news! I found it and I'm all set.

[markm]

Sorry Tony but I afraid I could drain your tank and fix at least half if not all of your problem
.

[55 Tony]

I saw two things today, maybe 3. I checked the timing when it was cold and it was at 16° advanced where I thought it was, but I have what looks like a random misfire but I don't really hear it in the exhaust. I used 2 different lights. The one light is a dial back so I tried a few other cylinders and adjusted the dial to where I could see it, and the misfire was on other cylinders as well as #1. But I really didn't hear a misfire, is it normal to jump around a little bit or is that a definite problem?

I went for a drive and I didn't think it really ran that well from the start, maybe it warmed up enough from checking the timing? Ran it on the highway then parked with it in gear and running, the temp didn't go above 195F. Normally that is when I get the hottest readings, well except for shutting it down.

Back home when everything under the hood was hot as hell I checked the timing again. Whoa, it was 18 advanced. So I backed it down to 16. I'm guessing when cold the MSD is retarding it 2 degrees and when hot it goes to normal, but like I said, I'm guessing. I didn't get a chance to try it again.

One more thing I don't know if it's a problem, but I tried fast idle and at 1500rpm the mechanical advance already has it advanced to 28°. Is that too much too soon?

[55 Tony]

Sorry Tony but I afraid I could drain your tank and fix at least half if not all of your problem
.

I don't think the local track has any fuel, but I'd be willing to try it if I can get some somewhere.

[55 Tony]

I did, which is why I'm wondering what is your A/F ratio when the power goes up, or down? Everything I have runs best at 190 degrees plus.

Oh, I forgot to put that in my other post. At WOT it varies from 11:1 to 12:1, so I guess from the links to the charts I posted that should be good right?
OK, got to get some paying work done...

[solidsguy]

I don't know if or how much it helped, but I've heard from more than one person how they used to put bags of ice on the intake manifold for as long as possible before the race or next race. And I don't know if they help any, but they still sell fuel chillers at Summit. A container with a coil that the fuel goes through and filled with ice/ice water. These days I think it's more of a retro thing.

They used to ice the intake (besides just cooling the engine overall) in an attempt to get as cool of a charge as possible. The theory was good, but I'm not sure if it made much difference since the A-F mix went through the ports so fast. Also, when the fuel mix comes out of the bottom of the carb it cools things anyway. If you ever run a tunnel-ram you can watch the outside of the top piece of the intake actually start to ice up after running for awhile.

Another thing is that the days I remember seeing them use ice was long before the days of air-gap intakes. The normal engine heat would heat up the regular intake runners quite alot, so they would pack ice bags on there to cool them back down.

This brings up the question whether or not you have the intake gaskets with the heat crossover block-offs? They can make quite a difference in runner heat.

The cool can things were bunk in my opinion also. A phenolic spacer helps just as much at keeping the carb cool.

I like your air feed setup. What piece is that at the filler panel? It looks a little cone shaped.

[55 Tony]

If someone made an air gap for a spreadbore BBC, I'd have it! Yes I have both crossovers completely blocked and a 1" phenolic spacer. The spacer was needed way back before I rebuilt the motor, the carb would boil over quite often and flood the crap out of it. I think I blocked the crossovers at the same time. Had it apart a few times and always keep them blocked.. With as much problems I have with heat, I still get people telling me to either drill a hole in the crossover plates, or remove one. No, it ain't happening. At one time I had some pretty bad wiring and the ignition cut out then on again, it backfired so hard that it blew out the cheap thin aluminum crossover pieces that came with the gasket! Now they are stainless steel.

The air inlet is from Spectre or whatever their name is. It's 6 or so inches at the front and goes down to 4". Hard to keep shiny since it's aluminum. It does look cool for sure.

[chasracer]

On those crossover ports, we used to take heavy duty aluminum foil and make balls of it about the size of the crossover passage and just keep filling it and cramming them in until we couldn't put anymore in there. The stainless steel plates are probably a better idea. On the timing movement, what you are seeing is not uncommon on Chevy engines, rare that any of them with stock type distributors and timing chains are dead steady. Besides a touch of slop in the chain with use, there is also the torsional twist of the cam. Sort of like a spring, it will twist a bit and then unload, then twist again. Unless it's bouncing around a larger number of degrees, I think it's okay. What MSD unit are you using, a 2 degree deal sounds funny, most of their built in retard units pull the timing back 10-20 degrees for starting. And are you saying you have 16 degrees initial timing and then all in at 28 degrees or are we adding that together for a 44 degree total? And I take it that you are reading this off of a degreed balancer. Dial-back timing lights are notorious for being off and using them with a MSD can be even worse.