Hot Rods High exhaust temps on my new 283

Hi All,
I acquired a 1960 283 that was supposed to be rebuilt, bored to 4" (301ci), no paperwork. I tore it down, and re-assembled everything checking clearances, etc. Everything seemed to check out. It has 1959 Power-Pak heads that were rebuilt as well, flat top pistons, really mild cam. For induction I bought a tri-power setup from Speedway that uses their new Stromberg 97's with a primary carb and 2 secondary carbs. I set it all up on my test stand with just the center primary carb and block off plates on the end carb holes, the idea being keeping it simple for initial fire and cam break-in. All went well, but I noticed 2 plug wires were starting to burn near the headers. I got the cam broke-in, initial timing is 14 degrees advance, replaced the burnt plug wires. Using a HF infared temperature gun on each header tube near the head I am averaging about 650-700F. After warming up the 350 in my driver (mild carb motor with uncoated block hugger headers) the header tubes are about 350F.

What might cause this? My initial thought were: lean fuel mixture, retarded timing, or vacuum leak. I checked for vacuum leaks and found no signs, timing is at 14 advance (I checked the timing tab during assembly and it is correct). The carb is small, but apparently lot's of guys run them without problems. Seems odd I would need to jet it up. It has the factory supplied .045 jets and the largest they sell is .050. Fuel pressure is recommended 3psi. Vacuum is 14.5lbs at idle.

Any ideas? I appreciate any and all advice!

Steve

 

what is the timing "all in", at higher RPM? Maybe the advance isn't working like you want it to work

 

Did you verify TDC and check to your timing mark? I mean with a piston stop. Most times I’ve seen overly hot exhaust temps it was retarded timing.

 

Not sure of the total advance, however the dist. was taken out of another daily driven car that at some point in the past I had set the total advance and made sure the advance was working. After setting the initial timing the idle rpm raised slightly upon attaching the advance hose.

 

While assembling the shortblock and #1 was at TDC I temporarily put the timing cover on with a few bolts and slid the balancer on just enough to see it read TDC. And my experience as well has been retarded timing causing hot headers. The engine sounds good and all, but I'm hesitant to install it in my car with expensive coated headers and ruin them. And the plug wires are still close to melting.

 

Compression makes heat. What is the compression ratio of each engine?
Fresh rebuild will be hotter than a worn motor as well.

 

What do the plugs look like? Are they brown at all,or bone white ? If white your way to lean.

 

If there's no apparent vacuum leak on the 'surface' (spray carb cleaner over intake ports at manifold parting line) there MAY be a vacuum leak from in the valley.
Read: Two wires.
Are both exhaust manifolds heating up? Is it just in one place?

Stromberg 97s run jets in the 49-52 range, as I recall. .050" jets should be in the middle...

 

Hi egt is usually fuel burning in the headers,advance the timing and see what it dies,don't worry about the numbers,see if the exhaust temps go down .Because is worked fine in another motor means nothing.

 

I’m guessing you meant 14.5 inches of vacuum? That’s not much for a “ really mild cam”, have you tried adjusting the timing for best vacuum?

 

A

Good question - and I was wondering about that. The heads are 1959 date code Power-Paks. Doesn't appear they are milled much, if at all. Intake bolts lined up fine. Flat top pistons with 4" bore. Not sure what the stock 1959/60 compression ratio was on a 283. Maybe someone else knows? I am running Non-ethenal premium gas.

 

Sometimes the obvious needs to be pointed out to me! Hench my posting here. I haven't pulled the plugs. I will do that tomorrow and report back. Thanks!

 

I sprayed carb cleaner around the manifold edges, carb base, and block-off plates on end carb mount locations. No change of RPM.

Both headers are heating up with the center two slightly higher as would be expected.

Speedway says the carbs come with .045 jets, and the largest replacements they sell are .050. I know a lot of the new strombergs end up on flatheads and other small displacement engines - maybe why they come with fairly small jets. Maybe go to their largest jet?

 

Good point. If I can advance it to the point of cooling things down, and it still starts easily, how far can you safely go without causing other problems?

 

Inches, Pounds, Ounces Yes. Inches. I tried adjusting the mixture screws on the carb for best vacuum, but not the timing. I don't know that I've ever done that. Can you explain further?

I say mild cam because it was in it when I got the engine. It idles pretty well. The cam says Camonics on it and a number. I think that is an old company out of business. The cam and lifters were new however.

 

do you have a dial type timing light, so you can check the timing when it's past the marks on the timing tab?

 

With a vacuum gauge hooked up to manifold, adjust timing to achieve the highest reading then back off an inch of vac and tighten the distributor bolt.

 

Hydrocarbons can lead to high exhaust temp as can a slew of other stuff so have you sniffed the exhaust with an analyzer .
Exhaust gases in the port are about 1875 F and I said gases . Other things your cam controls temp by how long it dangles open and whenever I first break in an engine I do it with a single carb unit . Personally I think you may be tripping on it cause your cam is different than the other motor . Take it into consideration and don't loose sleep over it yet . Get a single carb setup for testing purposes and sniff the pipe and put that temp gun away for now . Use other forms of troubleshooting devices

 

I do have a dial back timing light. Great tool to use.

 

Thanks for the explanation. I had not heard of that method. Never stop learning!!

 

Good advice. Thanks. Sometimes I think this was all easier 50 years ago when my friends and I just bolted s^*t together, not knowing enough to be worried. And things often went surprisingly well! Now I know just enough to over-think everything.

 

You might want to check what the timing is, with vacuum disconnected. Rev the engine up to 3000-4000 rpm, make sure it stops advancing, and note what the timing is at that point. It should be around 34 degrees. If not, you can safely advance the timing more.

 

Yup, done that before . I was breaking in a cam on a 327 with my just purchased Jet Hot Coated headers. I had the timing retarded enough to ruin the coating. What a pain to pull off and send them back to be recoated.

 

Adjust timing with vacuum advance plugged to best vacuum then hook up vacuum advance and test it.

 

^^^ yes! forgot to mention that the vac advance needs to be disconnected, overlooked that step mostly cause that’s the port I use when I connect vac gauge

 

put it on a dyno and have air fuel ratio confirmed. You will have an answer in minutes (or you can cross a few things off the list)

 

Try it with a single carb intake and a known good carburetor. Whenever you run multiple carburetors it's best to get the engine dialed in with a single carburetor, single carburetor intake.
This eliminates chasing your tail. At least the fuel side will be crossed off the list if the problem persists.

 

Thanks for your (AND EVERYONE ELSE'S) thoughtful responses. I probably am tripping a bit here. As for the single carb idea, which I totally get, I was trying to accomplish that by running only the single center carb and blocking off the end ones for the initial fire-up. Since the end carbs are secondary carbs with no idle circuits I didn't think it would affect my initial tuning and I could fine tune things at a later point when I install the end carbs and progressive linkage

 

Your plan makes sense and I admit I'm a detailed type but the more parts the more mind farts as to where and what's happening . I think as a baby I must have started with the rattle then much later the wind up mobile lol
But for on the real I got two engine projects right now and Roseville Carl's advice on this to me is a single two barrel carb well you have older throttle plates and throttle rods and the possibility of air slipping through . You know people say they rebuild parts but what is a rebuild to them and were all the parts available for a true and complete factory rebuild . I show you what I'm working on today well it's a later WCFB I am restoring it not a complete rebuild cause at the moment I cannot get any throttle plates or rod bushings so after this first engine is running I'm going to machine my own throttle assemblies for these carbs . Yes it's ok but is air going to leak thru ? Yes . And how much ? I don't know until I install it . You can see I cleaned it up the best one can without causing a gap and yes I'm installing new idle jets . Will it make it I don't know so I don't want to burn new valves or rinse my new rings so do you see your break in period is crucial so this happens so many times you just gotta cut out all the problems first . We are not really doing catalogue you tube builds you and I are doing fun old fashioned engine builds so we need a cushion of safety . The more throttle plates the more leaks may occur or do you have the intake blocking plates ? Use those instead of pulling the manifold and you can also use starting fluid spray around a little not much as you got a baby engine so use the Valvoline it's got valve protection the cheaper ones don't lube the valves really slams them into the seat. So just spray around the manifold and carb throttle assembly as your cupping the air horn . If RPMs go up alot you got vacuum leaks . Look at the photo and you see damage severity unknown so I use the two barrel for break in ( 200 low rpm hours ) then your rings are seated as are valves in their seats and ready for a try at the big time . The patience and anticipation is part of the thrill ya ? And that's what car stereos are for ! Cruising around the block for 200 hours but we used to cut loose at 200-500 miles it's just grueling ya know

 

UPDATE - Based on the advice given, and my own thoughts, here's where it stands. I eventually landed on 16 degrees advanced initial timing with it advancing to 32 degrees @ 3200 rpm. No vacuum leaks detected, still about 14-15 inches vacuum @ idle. Plugs look very slightly white (could be my imagination) so may jet the center primary carb up a bit, but FWIW, the exhaust headers at the ports are between 650-700 degrees, so maybe that is what this combo is gonna run. The plug wires aren't melting anymore so that's good. The coated headers are supposed to be good to 1300 degrees so I should be safe from discoloring them. I took it off the test stand and am getting ready to put it in my Model A. Probably will be a few weeks til I am ready to fire it.